04/12/2024
Our collaborative paper "Neural Network Kinetics for Exploring Diffusion Multiplicity and Chemical Ordering in Compositionally Complex Materials" is published in Nature Communications.
This paper describes the development of a neural network kinetics scheme that can predict and simulate diffusion-induced chemical and structural evolution in complex concentrated alloys. The method is used to study the temperature-dependent local chemical ordering in a refractory NbMoTa alloy and reveal a critical temperature at which the B2 order reaches a maximum. See our Publications page for more info.
04/08/2024
Pulkit's paper "Strengthening from dislocation restructuring and local climb at platelet linear complexions in Al-Cu alloys" is published in Journal of Materials Science: Materials Theory.
This paper describes how platelet array linear complexions alter dislocation motion and result in a pronounced strengthening effect. A unique climb mechanism is observed, where the dislocation first relaxes up along the platelet, which greatly restricts subsequent dislocation motion. Climb down is therefore required at both the leading and trailing partial dislocations, with the dislocation line length where this climb occurs also appearing in the strength-scaling law formulated here. See our Publications page for more info.
02/07/2024
Our collaborative paper "Topology and evolution of dislocation structures mediated by glissile reactions in face-centered cubic metals" is published in Acta Materialia.
This paper describes dislocation configurations resulting from glissile reactions, using a combination of transmission electron microscopy, molecular dynamics, and discrete dislocation dynamics. The pathway and evolution of the glissile reaction was shown to depend on reaction node mobility, which itself depends on stacking fault energy. As these features are key for plastic deformation and strain hardening, this work opens new avenues for the development of constitutive theories of mechanical behavior. See our Publications page for more info.
01/05/2024
Doruk's paper "Enhanced radiation damage tolerance of amorphous interphase and grain boundary complexions in Cu-Ta" is published in JOM.
This paper demonstrates how amorphous interphase and grain boundary complexions, which are formed in situ during irradiation, resist further radiation damage in Cu-Ta. Thicker interfacial films are found to be more damage-tolerant because they alter the defect production rate due to differences in intrinsic displacement threshold energies during the collision cascade. Overall, the findings of this work highlight the importance of interfacial engineering in enhancing the properties of materials operating in radiation-prone environments and the promise of amorphous complexions as particularly radiation damage-tolerant microstructural features. See our Publications page for more info.
01/04/2024
Our collaborative paper "Vacancy diffusion barrier spectrum and diffusion correlation in multicomponent alloys" is published in Acta Materialia.
This paper describes neural network-based Monte Carlo simulations of vacancy diffusion in multicomponent Nb-Mo-Ta alloys across a broad temperature range. We find that the diffusion correlation factor and activation energy are not constant for these alloys, in contrast to pure metals. Vacancy diffusion rate was also found to drop noticeably in the presence of local chemical order in the NbMoTa
system, particularly for MoTa alloys with long-range B2 order. See our Publications page for more info.
01/02/2024
Our collaborative paper "Reversible Enhancement of Electronic Conduction caused by Phase Transformation and Interfacial Segregation in an Entropy Stabilized Oxide" is published in Advanced Functional Materials.
This paper describes a study of electrical transport in a rocksalt entropy stabilized oxide as a function of secondary phase content. Secondary phases were found to selectively grow inside the grains and at grain boundaries, enabling the tuning of electrical conductivity properties and mechanisms. Specifically, a shift from conduction by small polarons to Cu ions inside the grains was observed. See our Publications page for more info.
12/12/2023
Our collaborative paper "Compositional inhomogeneity and its effect on the hardness of nanostructured refractory high-entropy alloys" is published in Materials Characterization.
This paper describes transmission electron microscopy imaging, chemical analysis, and nano-hardness tests that are used to investigate compositional inhomogeneities in a series of sintered high-entropy nanoalloys and elucidate their effect on the material’s hardness. The compositional inhomogeneity is revealed to be temperature- and component-dependent. This work demonstrates that compositional inhomogeneity can be tuned by sintering temperature or alloying towards optimized microstructure and hardness. See our Publications page for more info.
10/22/2023
Our collaborative paper "High-throughput assessment of the microstructural stability of segregation-engineered nanocrystalline Al-Ni-Y alloys" is published in Materialia.
This paper describes a study where combinatorial synthesis is combined with high-throughput characterization techniques to explore microstructural transitions during annealing of a nanocrystalline ternary Al-base alloy containing a transition metal (TM=Ni) and rare earth dopant (RE=Y). This work demonstrates the benefits of co-segregation for enhancing mechanical hardness and delaying the onset of microstructural instability. See our Publications page for more info.
10/21/2023
Tianjiao's paper "Binary nanocrystalline alloys with strong glass forming interfacial regions: Complexion stability, segregation competition, and diffusion pathways" is published in Materials Characterization.
This paper elucidates the effect of dopant choice on the retention of amorphous complexions and the stabilization of grain size due to various forms of interfacial segregation in three binary nanocrystalline Al-rich systems: Al-Mg, Al-Ni, and Al-Y. This work demonstrates nanocrystalline stability via simple alloy formulations and fewer dopant elements, which further encourage the usage of bulk nanostructured materials. See our Publications page for more info.
10/12/2023
Divya's paper "Dislocation breakaway from nanoparticle array linear complexions: Plasticity mechanisms and strength scaling laws" is published in Materialia.
This paper describes how dislocation mechanics are altered by the presence of nanoparticle array linear complexions in a Ni-Al alloy. A combined bowing and progressive unpinning mechanism is uncovered, leading to the demonstration of a new strength scaling law that differs in keys ways from classical Orowan bowing. See our Publications page for more info.
09/21/2023
Our collaborative paper "Discovery of Ni activated sintering of MoNbTaW predicted by a computed grain boundary diagram" is published in Scripta Materialia.
This paper describes a study of how minor Ni dopant additions can result in activated sintering of MoNbTaW high-entropy alloys. A computed grain boundary diagram was created with thermodynamic analysis methods to forecast high temperature grain boundary disordering. See our Publications page for more info.
09/15/2023
Tim presents a seminar at Carnegie Mellon University.
Tim's talk was titled "Segregation-induced complexion transitions: Manipulating defects to improve the performance of nanostructured metals."
08/25/2023
Tim presents a seminar at North Carolina State University.
Tim's talk was titled "Segregation-induced complexion transitions: Manipulating defects to improve mechanical properties."
08/13/2023
Pulkit's paper "Local structural ordering determines the mechanical damage tolerance of amorphous grain boundary complexions" is published in Scripta Materialia.
This paper describes how patterns of structural short-range inside of amorphous complexions control mechanical damage nucleation from dislocation absorption, an important mechanism for nanocrystalline plasticity. A more disordered region far away from the dislocation absorption site is found to be beneficial, as collective deformation throughout the complexion can occur. See our Publications page for more info.
07/19/2023
Tim presents a seminar at Johns Hopkins University.
Tim's talk was titled "Manipulating defect structure and behavior through segregation-induced complexion transitions."
07/06/2023
TJR presents an invited talk at the THERMEC Conference in Vienna, Austria.
Tim's talk, titled "High Strength, Hierarchically Nanostructured Al Alloys through an Interfacial Nucleation Pathway," focused on using amorphous complexions to fabricate lightweight alloys with unique reinforcing phases and outstanding properties.
06/22/2023
Tim presents a seminar to scientists at the Army Research Laboratory.
Tim's talk was titled "Nanoscale templating of reinforcing phases with dislocation complexions."
06/21/2023
Our collaborative paper "Twin nucleation from disconnection-dense sites between stacking fault pairs in a random defect network" is published in Materialia.
This paper describes a simulation study of twin nucleation in Mg, using a model starting defect network that makes no assumptions about the types and densities of dislocations present. Disconnection dense sites between stacking faults were found to enable twin nucleation through a pure shuffle pathway. See our Publications page for more info.
03/24/2023
NMML has 12 presentations at TMS 2023 Annual Meeting in San Diego, CA.
Our group presented eight talks at the conference, with an additional three talks and one poster from collaborations. Tim's invited talks were titled "Tunable Short-range Order Within Amorphous Complexions and Its Connection to Damage Nucleation" and "Nanoscale Templating of Reinforcing Phases with Linear Complexions to Achieve Extreme Strength". Esther's talk was titled "Exploring the structure and chemistry contributions to interfacial segregation in NbMoTaW with high-throughput atomistic simulations." Doruk's talks were titled "Computer Vision Assisted Automated Grain Segmentation and High-Throughput Composition Analysis with Scanning Electron Transmission Microscopy" and "Structural Transitioning in Near Boundary Segregation Zones due to Chemical Ordering in NbMoTaW". Tianjiao's talks were titled "Diffusion Pathway of Dopant Elements in Grain Boundary Engineered Al Alloys" and "Submicron Intermetallic Particle Heterogeneity Controls Shear Localization in High-strength Nanostructured Al Alloys". Pulkit's talk was titled "Local Structural Ordering Affects the Toughening Ability of Amorphous Grain Boundary Complexions".
03/03/2023
Divya's paper "Linear complexions directly modify dislocation motion in face-centered cubic alloys" is published in Materials Science and Engineering A.
This paper describes the mechanics behind strengthening due to linear complexions, or unique phases stabilized by the presence of a dislocation, in face-centered cubic metals. Linear complexions impart higher resistance to the initiation and continuation of dislocation motion when compared to solid solution strengthening, with the exact strengthening level determined by the linear complexion type. See our Publications page for more info.
12/08/2022
Our collaborative paper "Strong and Ductile Refractory High-Entropy Alloys with Super Formability" is published in Acta Materialia.
This paper describes a set of refractory NbTaTi-based high entropy alloys which can be cold-rolled to a reduction of over 90% without requiring special surface treatment or annealing. A high-density of dislocations and deformation twins are found within the microstructure, enabling a homogeneous microstructure to form at lower annealing temperatures and times. These alloys retain their high strength at elevated temperatures and also exhibit ductility at cryogenic temperatures. See our Publications page for more info.
12/06/2022
Pulkit's paper "Grain incompatibility determines the local structure of amorphous grain boundary complexions" is published in Acta Materialia.
This paper describes the structural short-range inside of amorphous complexions and the dependence of this feature on the confining crystals on each side. Asymmetry in the structure of the transition regions is found to not just be controlled by the nearest crystal, but instead the entire grain-film-grain system must be considered. The incompatability between grains is found to be the key to understanding this behavior and is quantified using the concept of grain boundary strain. See our Publications page for more info.
11/25/2022
Ian's paper "Influence of chemistry and structure on interfacial segregation in NbMoTaW with high-throughput atomistic simulations" is published in Journal of Applied Physics.
This paper describes high-throughput atomistic modeling of grain boundaries in a complex concentrated alloy, where hundreds of bicrystals in both low-energy and metastable states were used to access over 130,000 interfacial sites. While Nb is the primary segregant, other interesting events were observed due to local structural and chemical driving forces. For example, incomplete depletion of Ta in low-angle boundaries resulted from chemical pinning associated with chemical short-range ordering. See our Publications page for more info.
11/22/2022
Doruk's paper "Chemical order transitions within extended interfacial segregation zones in NbMoTaW" is published in Journal of Applied Physics.
This paper describes atomistic modeling of grain boundary segregation in a NbMoTaW refractory complex concentrated alloy. Our results reveal extended near-boundary segregation zones that are much larger than traditional segregation regions, which also exhibit chemical patterning that bridges the interfacial and grain interior regions. Furthermore, structural transitions pertaining to an A2-to-B2 transformation are observed within these extended segregation zones. See our Publications page for more info.
10/24/2022
Tim presents a seminar at Texas A&M University.
Tim's talk was titled "Segregation-induced complexion transitions: Manipulating defects to improve the performance of nanostructured materials."
09/07/2022
Tianjiao's paper "Intermetallic particle heterogeneity controls shear localization in high-strength nanostructured Al alloys" is published in Acta Materialia.
This paper describes the mechanical behavior of nanocrystalline Al-Mg-Y and Al-Ni-Y, both reinforced by hierarchical microstructures. A uniform distribution of intermetallic particles with an average spacing less than the percolation length needed for shear localization was found to effectively prevent the maturation of shear bands, offering a design strategy for high-strength nanocrystalline Al alloys with both high strength and stable plastic flow. See our Publications page for more info.
08/23/2022
Our collaborative paper "Optimizing Thermal Stability and Mechanical Behavior in Segregation-Engineered Nanocrystalline Al-Ni-Ce Alloys: a Combinatorial Study" is published in Journal of Materials Research.
This paper describes the combinatorial synthesis and rapid characterization of segregation-engineered nanocrystalline Al-Ni-Ce alloys. In addition to the identification of alloys and processing
conditions that give rise to exceptional thermal stability, strength retention, and homogeneous
plastic flow, combined thermal stability and deformation mechanism maps that
demarcate several important regimes of behavior are constructed. See our Publications page for more info.
05/23/2022
Our collaborative paper "Damage tolerance in additively manufactured ceramic architected materials" is published in Journal of the European Ceramic Society.
This paper reports on ceramic micro-architected materials fabricated using
direct ink writing (DIW) of an alumina nanoparticle-loaded ink, followed by a sintering process. After characterizing the rheology of the ink and extracting optimal processing
parameters, the microstructure of the sintered structures is investigated to assess
composition, density, grain size and defect population. Our research group led nanoindentation experiments to probe the properties of the fully dense and woodpile structures. See our Publications page for more info.
05/14/2022
Our collaborative paper "Processing-Dependent Stabilization of a Dissimilar Rare-Earth Boride in High-Entropy (Ti0.2Zr0.2Hf0.2Ta0.2Er0.2)B2 with Enhanced Hardness and Grain Boundary Segregation" is published in Journal of the European Ceramic Society.
This paper demonstrates that 20% of the rare-earth element Er can be stabilized in a high-entropy transitional metal boride, despite the dissimilar chemical properties and lattice parameters. Notably the Er addition leads to improved hardness. Our research group led transmission electron microscopy experiments showing that the Er segregates to the grain boundary regions. See our Publications page for more info.
04/15/2022
Tim presents an invited seminar at the Arizona State University.
Tim's talk was titled "Segregation-induced complexion transitions: Manipulating interfaces to improve the performance of nanocrystalline metals."
03/29/2022
Tim is elected a Fellow of ASM International.
The honor of Fellow represents recognition of distinguished contributions in the field of materials science and engineering, and develops a broadly based forum for technical and professional leaders to serve as advisors to the Society. Tim's citation reads: "For significant contributions in understanding of structure-property relations of nano-crystalline metals and alloys, addressing the limitations of the material class, and enabling the widespread usage of these advanced materials." He will receive his ASM Fellow Award at IMAT’22 in New Orleans, LA.
03/04/2022
NMML presents seven talks at TMS 2022 Annual Meeting in Anaheim, CA.
Our research group was heavily represented at TMS, with four talks from NMML group members and an additional three from collaborations at the conference. Tim's invited talks were titled "In situ nanoscale mechanical testing to isolate the effect of grain boundary complexions" [link] and "Disordered interfacial features as local equilibrium states capable of modifying nanocrystalline metals" [link]. Ian's talk was titled "Exploring the structure and chemistry contributions to interfacial segregation in NbMoTaW with high-throughput atomistic simulations." Doruk's talk was titled "Machine Learning-Assisted Prediction of Interfacial Segregation in a Refractory Multi-Principal Element Alloy."
01/04/2022
Tianjiao's paper "Growth and structural transitions of core-shell nanorods in nanocrystalline Al-Ni-Y" is published in Scripta Materialia.
This paper reports on the evolution of core-shell nanorods inside of a bulk nanocrystalline Al-Ni-Y alloy during annealing. While some nanorods are initially structurally disordered, annealing leads to a transition to an ordered core structure. The shell composition also changes from Y-rich to Ni-rich with longer annealing treatments. See our Publications page for more info.
12/10/2021
Our collaborative paper "Amorphous intergranular film effect on the texture and structural evolution during cold-rolling of nanocrystalline Ni-Zr alloys" is published in Metallurgical and Materials Transactions A.
This paper reports on the role of amorphous complexions during cold rolling deformation, a process of great practical importance for the processing and fabrication of nanostructured materials. We find that the presence of amorphous intergranular films reduces grain rotation and grain boundary migration during rolling. The amorphous complexions also aid in confinement of dislocations near the surface of the specimens and annihilation of defects in the center grains, thus generating a harder surface and a softer core. See our Publications page for more info.
12/02/2021
Charlette's paper "Room Multi-principal element grain boundaries: Stabilizing nanocrystalline grains with thick amorphous complexions" is published in Journal of Materials Research.
This paper reports on grain size stability enabled by amorphous complexions, specifically as it relates to the compositional complexity of the grain boundary region. We show that adding more elements to the grain boundary region results in thicker amorphous complexions and a very stable nanocrystalline grain size, even after extreme annealing conditions. See our Publications page for more info.
10/28/2021
Tim presents an invited talk at the Université de Lille - TimeMan Seminar Series.
Tim's talk was titled "Using a typically brittle structure to toughen nanocrystalline metals."
10/25/2021
Our collaborative paper "Visualization and Validation of Twin Nucleation and Early-stage Growth in Magnesium" is published in Nature Communications.
This paper reports on in situ transmission electron microscopy deformation experiments of specially designed nanoscale samples. These experiments allowed the team to isolate the nucleation and growth of a high density of pyramidal dislocations in a localized region, from which nanometer-wide twin seeds form and then coalesce into a twin embryo several nanometers wide. Atomistic simulations reveal that a stress-induced dissociation reaction of the dislocations causes the atoms to locally shuffle into the precise arrangement corresponding to a twin. See our Publications page for more info.
10/25/2021
Our collaborative paper "Room Temperature Deformation-induced Solute Segregation and its Impact on Twin Boundary Mobility in a Mg-Y Alloy" is published in Scripta Materialia.
This paper reports on room temperature, deformation-induced solute segregation in a Mg-Y alloy. Periodic segregation of Y-rich columns and nanoscale clusters were observed with high-resolution transmission electron microscopy. Our group modeled these features to understand the segregation mechanism, and also to uncover a pinning effect on boundary migration that leads to mobility anisotropy. See our Publications page for more info.
10/18/2021
Tim presents an invited talk at the 2021 MS&T Conference.
Tim's talk was titled "Microstructure-within-a-microstructure: Understanding critical structural variations within grain boundary networks."
10/12/2021
Megan's paper "Emergence of near-boundary segregation zones in face-centered cubic multi-principal element alloys" is published in Physical Review Materials.
This paper reports on grain boundary segregation in two face-centered cubic multi-principal element alloys, one with quaternary composition and another a quinary alloy. We observe unexpected enrichment of Fe in the near-boundary zones, signalling the existence of a structurally-distinct region of reduced atomic volume. See our Publications page for more info.
10/07/2021
Tianjiao's paper "Bulk nanocrystalline Al alloys with hierarchical reinforcement structures via grain boundary segregation and complexion formation" is published in Acta Materialia.
This paper reports on three different fully dense bulk nanocrystalline Al alloys (Al-Mg-Y, Al-Fe-Y, and Al-Ni-Y) with small grain sizes that were successfully fabricated using a simple powder metallurgy approach. Full densification of the samples were connected directly to the onset of amorphous complexion formation, and a hierarchical microstructure containing boundary complexions, core-shell nanorods, and intermetallic precipitates was observed. See our Publications page for more info.
09/23/2021
Tim presents an invited talk at the Collaborative Research Centre SFB1394 Workshop on Defect Phases.
Tim's talk was titled "Defects-by-design: Tailoring material behavior with grain boundary and dislocation complexions."
09/15/2021
Tim presents an invited talk at the IMAT 2021 Conference.
Tim's talk was titled "Creating nanoalloys that actually prefer extreme environments using amorphous interfacial complexions."
09/13/2021
Our collaborative paper "Microstructure, mechanical properties, and ionic conductivity of a solid-state electrolyte prepared using binderless laser powder bed fusion" is published in Journal of Materials Research.
This paper reports on a solid-state electrolyte fabricated using binderless laser powder bed fusion. Laser-based additive manufacturing offers a potential path to single-step fabrication, versus the typical glass-ceramic processing route that requires multiple processing steps. Our group measured the Young's modulus and hardness of these materials with nanoindentation techniques. See our Publications page for more info.
07/26/2021
Pulkit's paper "Segregation competition and complexion coexistence within a polycrystalline grain boundary network" is published in Acta Materialia.
This paper reports on the complex nature of segregation and complexion transitions within a polycrystalline grain boundary network using atomistic modeling. We find that multiple complexion types can coexist, in this case either ordered grain boundaries or amorphous complexions, and that each type can have their own distinct chemical composition distributions with skew-normal character. See our Publications page for more info.
05/26/2021
Jenna's paper "Amorphous complexions alter the tensile failure of nanocrystalline Cu-Zr" is published in Materialia.
This paper reports on the tensile failure of nanocrystalline Cu-Zr alloys, with identical grain structures and chemistries but different grain boundary complexions. We find that the inclusion of amorphous complexions can dramatically change the failure mode of nanocrystalline materials, and increase the ductility of the materials. See our Publications page for more info.
05/13/2021
Tim is promoted to the rank of Professor, effective July 1, 2021.
Tim has been promoted to the rank of Professor (sometimes referred to as "Full Professor"), effective July 1, 2021, in the Department of Materials Science and Engineering. Tim is excited to continue working with the students and postdocs in the group to tackle the toughest and most impactful questions in metallurgy and materials science!
05/13/2021
Our collaborative paper "Bulk Rare Earth High-Entropy Hexaborides" is published in Journal of the European Ceramic Society.
This paper reports on CaB6-typed cubic rare earth high-entropy hexaborides that were successfully fabricated into dense bulk pellets. The sintered pellets were determined to be single-phase without any detectable oxides or other secondary phases, with homogenous elemental distributions at both themicro and nanoscale. Our group measured the Young's modulus and hardness of these materials with nanoindentation techniques. See our Publications page for more info.
05/04/2021
Our collaborative paper "Disordered interfaces enable high temperature thermal stability and strength in a nanocrystalline aluminum alloy" is published in Acta Materialia.
This paper reports on the stabilization of nanocrystalline Al-rich alloys using co-segregation of Ni an Ce. These dopants cause amorphous intergranular films which separate sub-10 nm grains. In addition to high thermal stability, notable elevated temperature strength is reported. See our Publications page for more info.
04/02/2021
Our collaborative paper "Synergic grain boundary segregation and precipitation in W- and W-Mo-containing high-entropy borides" is published in Journal of the European Ceramic Society.
This paper reports on the segregation of W and Mo to the grain boundary regions in high entropy borides. This segregation leads to precipitates along the grain boundary which are coherent and have a cube-on-cube orientation relationship
with the matrix. Our group, led by Tianjiao, showed that these grain boundary phenomena have a hardening effect on the materials. See our Publications page for more info.
03/16/2021
Pulkit presents a talk at TMS 2021 Annual Meeting (Virtual).
Pulkit's talk was titled "Interfacial Segregation and Segregation-induced Transitions in a Polycrystalline Grain Boundary Network" and was well-received by the audience.
03/09/2021
Congratulations to Megan McCarthy for a successful Ph.D. defense.
Megan successfully defending her thesis, which was titled "Faceted Ʃ11 Grain Boundaries: Unique Migration Mechanisms and the Effects of Alloying." Congrats Megan!
01/12/2021
Charlette's paper "Critical cooling rates for amorphous-to-ordered complexion transitions in Cu-rich nanocrystalline alloys" is published in Acta Materialia.
This paper reports on the stability of amorphous complexions, measured as the ability to resist a transition back to ordered structure during quenching experiments, in binary and ternary Cu-rich nanocrystalline alloys. Gradients in sample cooling within a bulk piece are used to show that ternary alloys have much more stable amorphous complexions, with the critical cooling rate necessary to avoid complexion transitions in the Cu-Zr-Hf alloy found to be at least three orders of magnitude slower than that for the Cu-Zr alloy. See our Publications page for more info.
01/08/2021
Tianjiao's paper "In situ mechanical testing of an Al matrix composite to investigate compressive plasticity and failure on multiple length scales" is published in Journal of Materials Science.
This paper reports on the compressive plasticity and failure of an Al-matrix composite on multiple length scales, from strain localization through a complex microstructure to the debonding of individual microparticles from the matrix. The matrix-particle interface is ruled out as a possible weak point, and instead shear localization is identified as the mechanism that can drive interface debonding. See our Publications page for more info.
12/07/2020
Vlad's paper "Interdependent linear complexion structure and dislocation mechanics in Fe-Ni" is published in Crystals.
This paper reports on how linear complexions alter the fundamental mechanisms responsible for dislocation motion in an Fe-rich alloy. Even though the nanoscale precipitates are not in the slip plane, the dislocation must bow to overcome the local restriction. In addition, the crystal structure of the complexion depends on the location of the dislocation, demonstrating an interdependence between dislocation mechanics and complexion structure that is unique. See our Publications page for more info.
12/04/2020
Zhifeng's paper "Dislocation-induced Y segregation at basal-prismatic interfaces in Mg" is published in Computational Materials Science.
This paper reports on the structure of basal-prismatic boundaries in Mg, as well as the segregation of Y dopants to these defects. Short coherent interfaces and long semi-coherent interfaces containing disconnections and dislocations are found to be more energetically stable than disordered interfaces. In addition, Y is observed to prefer the sites associated with interfacial dislocations due to the local hydrostatic stresses at these features. See our Publications page for more info.
12/04/2020
Tim presents an invited talk and participates in a live panel at the 2020 MRS Virtual Spring/Fall Meeting.
Tim's talk was titled "Controlling the structure of interfaces and dislocations to directly alter mechanical response." It was followed by a live Q&A session and then a panel discussion focused on the important opportunities in the structural materials field.
11/20/2020
Our collaborative paper titled "Accommodation and formation of {-1012} twins in Mg-Y alloys" is published in Acta Materialia.
This paper describes a transmission electron microscopy study of tensile twins that terminate inside of a grain in a deformed Mg-Y alloy. These observations indicate that both basal <a> and <c + a> matrix glide
were involved in accommodating the plastic stresses developed in the vicinity
of terminating twins. See our Publications page for more info.
11/19/2020
Megan's paper "Alloying induces directionally-dependent mobility and alters migration mechanisms of faceted grain boundaries" is published in Scripta Materialia.
This paper reports on how alloying of faceted grain boundaries can cause faster migration in one direction over the other. Segregation to the higer energy facets alters a slip plane shuffling migration mechanism that can only be activated in one direction. See our Publications page for more info.
10/22/2020
Megan's paper "Shuffling mode competition leads to directionally-anisotropic mobility of faceted Ʃ11 boundaries in face centered cubic metals" is published in Physical Review Materials.
This paper reports on grain boundary mobility that varies significantly in different directions for certain faceted boundaries, a result that is unexpected based on traditional thinking. Migration of the faceted boundaries is accomplished through transformation events at facet nodes and incommensurate boundary plane facets, which are termed shuffling modes, with the emergence of a disordered shuffling mode responsible for reducing or removing any anisotropy in migration behavior. See our Publications page for more info.
10/08/2020
Yang's paper "Embracing the chaos: Alloying adds stochasticity to twin embryo growth" is published in Physical Review Letters.
This paper reports on high-throughput simulations of the effect of alloying on the early growth stages of twin embryos. We find that the embryos in the Mg-Al alloys undergo a stochastic incubation stage where multiple twin variant selection can occur, in contrast to the deterministic behavior observed for pure Mg. See our Publications page for more info.
09/26/2020
Congratulations to Megan McCarthy for being awarded a Rose Hills Foundation Science & Engineering Fellowship.
This fellowship is intended to recognize and reward the most meritorious graduate students who are pursuing a Ph.D. or Master’s degree in the life or natural sciences, or engineering. Awardees have demonstrated academic excellence and accomplishments, financial need, and leadership qualities consistent with the mission of the Rose Hills Foundation, which is to represent, develop, and support our future leaders. Congrats Megan!
08/17/2020
Congratulations to Yang Hu for a successful Ph.D. defense.
Yang successfully defending her thesis, which was titled "Probing solute-grain boundary interactions in alloys." Congrats Yang!
08/05/2020
Congratulations to Charlette Grigorian McDevitt for a successful Ph.D. defense.
Charlette successfully defending her thesis, which was titled "Enhanced Stability of Nanocrystalline Metals with Amorphous Grain Boundary Complexions via Compositional Manipulation." Congrats Charlette!
07/22/2020
Our collaborative paper titled "Influence and Comparison of Contamination Partitioning on Nanocrystalline Stability in Sputter Deposited and Ball Milled Cu-Zr Alloys" is published in Journal of Materials Science.
This paper describes dopant distributions and second phase content in Cu-Zr nanocrystalline alloys fabricated by ball milling and sputter deposition. Complementary precession electron diffraction and atom probe tomography are used to measure the chemical variations within these two materials to provide an understanding of the contribution of processing route. See our Publications page for more info.
05/18/2020
Our collaborative paper titled "Revealing the deformation mechanisms for room-temperature compressive superplasticity in nanocrystalline magnesium" is published in Materialia.
This paper describes how grain boundary mediated deformation and basal dislocation slip can combine to give large superplastic strains in nanocrystalline Mg. Compressive strains larger than 120% were observed, and were accompanied by grain boundary migration. See our Publications page for more info.
05/08/2020
Our collaborative paper titled "Toughening Magnesium with Gradient Twin Meshes" is published in Acta Materialia.
This paper describes how surface ball milling can be used to create gradients in grain size, orientation, and twin mesh density near a surface in Mg. The modified structure results in increased tensile strength and ductility compared to untreated samples. See our Publications page for more info.
04/16/2020
Megan's paper "Emergence of directionally-anisotropic mobility in a faceted Ʃ11 <110> tilt grain boundary in Cu" is published in Modelling and Simulation in Materials Science and Engineering.
This paper reports on the discovery of a new phenomenon concerning the migration of faceted interfaces: Mobility that depends on the direction of motion. This behavior is related to the unique structure of faceted interfaces, which leads to directionally-anisotropic properties, but is also material-dependent. See our Publications page for more info.
04/06/2020
Yang's paper "Disconnection-mediated twin embryo growth in Mg" is published in Acta Materialia.
This paper investigates the early stages of twin embryo growth, using atomistic simulations to show the importance of disconnection motion on twinning. We then use these findings to build a phenomenological model that agrees well with experimental observations in the literature. See our Publications page for more info.
02/26/2020
NMML presents eleven talks at TMS 2020 Annual Meeting in San Diego, CA.
Our research group was heavily represented at TMS, with seven talks from NMML group members and an additional four from collaborations at the conference. Tim's invited talks were titled "Moving Closer to Equilibrium but Maintaining the Defects (and the Properties)" and "Making Strong, Tough, Thermally-stable, and Radiation Tolerant Nanocrystalline Materials in Bulk Form." Tim also presented Olivia's talk titled "Probing the Deformation Mechanisms of Al-Matrix Composites with Small-Scale Mechanical Testing." Vlad's talk was titled "Linear Complexion Formation and their Effect on the Strength of Metallic Alloys." Megan's talk was titled "Anisotropic Mobility of Faceted Σ11 <110> Tilt FCC Grain Boundaries and the Effect of Subsequent Doping." Yang's talk was titled "Manipulating Twin Morphology in Mg Alloys by Varying Solute Concentration." Charlette's talk was titled "Thick Amorphous Complexions Enabled by Compositional and Thermal Manipulation."
02/03/2020
Jen's paper "Solid-state dewetting instability in thermally-stable nanocrystalline binary alloys" is published in Materialia.
This paper investigates how selective alloying can result in solid state dewetting, a process that can serve as another instability in addition to grain growth. This paper teaches us that a balance must be struck between grain size stabilization and stabilization of the thin film structure when adding dopants. See our Publications page for more info.
01/05/2020
Tim presents two talks at the International Conference on Plasticity, Damage, and Fracture in Riviera Maya, Mexico.
Tim's talks were titled "The thermodynamics and kinetics of defect-driven complexion formation" and "Optimizing the mechanical behavior of metals with grain boundary and dislocation complexions." They focused on our efforts to design the structure of dislocations and grain boundaries using the concept of segregation-induced complexion transitions, as well as uncovered interesting effects on mechanical behavior.
12/30/2019
Jen's paper "Amorphous intergranular films mitigate radiation damage in nanocrystalline Cu-Zr" is published in Acta Materialia.
This paper investigates how amorphous grain boundary complexions can alter the radiation tolerance of nanocrystalline metals. A sample with ordered boundaries was compared to another with amorphous intergranular films, using both in situ TEM and ex situ ion irradiation experiments. We found a notable decrease in the amount of stored defects after adding the amorphous complexions, demonstrating that these features are strong defect sinks. See our Publications page for more info.
11/29/2019
Vlad's paper "Prediction of a wide variety of linear complexions in face centered cubic alloys" is published in Acta Materialia.
This paper investigates how nanoscale phases can form along dislocation lines in FCC alloys, highlighting multiple new types of linear complexions. We demonstrate that segregation to the elevated stress region near a line defect can result in the precipitation of a nanoscale phase that is confined to that location. We find that partial dislocations in FCC alloys provide a consistent template for linear complexions and that alloy choice determines the structure of the resultant complexion. See our Publications page for more info.
10/07/2019
NMML's efforts to create tough nanocrystalline metals in bulk form are profiled on the UCI Engineering webpage.
An article profiling the success of our Army Research Office grant appears on the UCI Engineering website. The full story details the importance of the research and can be found here [link].
09/30/2019
NMML presents four talks at MS&T 2019 in Portland, OR.
Our research group took MS&T by storm, with four talks in the first day of the conference. Tim's invited talk was titled "Coupled Experimental and Computational Studies of Amorphous Grain Boundary Complexions." Vlad's talk was titled "Discovery of a Wide Variety of Linear Complexions in Metallic Alloys." Megan's talk was titled "Anisotropic Mobility of Faceted Σ11 <110> Tilt Grain Boundaries in Face Centered Cubic Metals." Yang's talk was titled "Growth of Twin Embryos by Disconnection Propagation in Mg: Molecular Dynamics and Phenomenological Modeling."
09/16/2019
Tim presents an invited talk at Dislocations 2019 in Haifa, Israel.
Tim's talk was titled "Linear complexion formation driven by local stress concentrations near dislocations" and focused on nanoscale complexion transitions near line defects called dislocations.
08/22/2019
Tim presents an invited talk at the USACM Workshop on Nanoscale Materials in Philadelphia, PA.
Tim's talk was titled "Probing nanoscale complexion transformations with computational techniques that complement experiments" and focused on using atomistic modeling techniques to complement experiments when studying complexions.
08/19/2019
Charlette's paper "Thick amorphous complexion formation and extreme thermal stability in ternary nanocrystalline Cu-Zr-Hf alloys" is published in Acta Materialia.
This paper investigates how compositional complexity at the grain boundary can affect the formation of amorphous intergranular films. We demonstrate that the usage of a ternary alloy can lead to noticeably thicker amorphous intergranular complexions, a finding that will allow us to improve the toughness of nanostructured materials. We also find that these alloy are extreme stable against grain growth, maintaining a small nanocrystalline grain size even after 2 weeks at 98% of their melting temperature. See our Publications page for more info.
08/13/2019
Our collaborative paper titled "Heavy Ion Irradiation Effects on GaN/AlGaN High Electron Mobility Transistor Failure at Off-state" is published in Microelectronics Reliability.
This paper describes in situ TEM ion irradiation experiments on high-electron mobility transistors. Heavy ions were found to create a number of defects, which then acted as charge traps and lowered the breakdown voltage. See our Publications page for more info.
07/09/2019
Tim presents an invited talk at the Gordon Research Conference on Physical Metallurgy in Manchester, NH.
Tim's talk was titled "Segregation-Induced Complexion Transitions: New Opportunities for Materials Design" and focused on the groups work to design grain boundary and dislocation structure to access outstanding properties.
07/01/2019
Olivia's paper "Amorphous Intergranular Films Enable the Creation of Bulk Nanocrystalline Cu-Zr with Full Density" is published in Advanced Engineering Materials.
This paper investigates the consolidation of nanocrystalline powders into bulk pieces, with a specific focus on understanding how amorphous complexions affect the trade-off between densification and grain growth. Prior work has either produced fine-grained but porous pieces or dense pieces with large grains. In this study, we demonstrate a rapid increase in sample density once amorphous intergranular films are formed, which allows for an optimal combination of small grains (~55 nm) and full density (>99.8%). These interfacial features will be the key to producing bulk nanocrystalline materials with high strength and appreciable toughness. See our Publications page for more info.
05/24/2019
Congratulations to Jennifer Schuler for a successful Ph.D. defense.
Jen successfully defending her thesis, which was titled "Amorphous Intergranular Film Design Criteria and Application as Damage Tolerant Features." Congrats Jen!
05/13/2019
NMML's paper on linear complexion thermodynamics is profiled on the UCI Engineering webpage.
An article profiling a recent Physical Review Letters paper by Vlad and Tim appears on the UCI Engineering website. The full story details the importance of the research and can be found here [link].
05/01/2019
Our collaborative paper titled "Twinning Formation from a Twin Boundary in Mg during In-situ Nanomechanical Testing" is published in Materials Science and Engineering A.
This paper describes in situ TEM deformation experiments of twin boundary nucleation and propagation in single crystal Mg. These experiments captured an important intermediate state, where smaller twin emryos coalesce into a larger embryo before moving into the crystal. See our Publications page for more info.
03/12/2019
NMML presents four talks at the TMS Annual Meeting in San Antonio, TX.
Olivia presented a talk with the title "Fabrication of bulk nanostructured materials with high toughness through simple powder processing" while Jen presented a talk with the title "Irradiation and Mechanical Behavior of Nanocrystalline Alloys with Amorphous Intergranular Films." Tim presented two invited talks, with titles of "Amorphous intergranular films for improved performance under irradiation" and "Tailoring mechanical behavior with one- and two-dimensional complexions."
03/07/2019
TJR presents a seminar at the University of California, Los Angeles.
Tim's talk, titled "Promoting beneficial complexion transitions: Tuning defect structure to make better materials," addressed the usage of complexions as toughening features in Cu-Zr, as well as the extension to all binary transition metal alloys and linear complexions. Dopants were used to decorate the defects and induce nanoscale phase transformations that improved performance.
02/27/2019
Vlad's paper "Linear complexions: Metastable phase formation and coexistence at dislocations" is published in Physical Review Letters.
This paper investigates the formation of nanoscale phases that are restricted to the region near dislocations, which have recently been named "linear complexions." While prior experimental work had shown evidence of a new phase with face centered cubic order along dislocation lines in Fe-rich alloys, our atomistic modeling study reveals that a metastable body centered cubic phase must first nucleate to serve as a precursor. A detailed thermodynamic treatment of the energetics associated with linear complexion nucleation is formulated, to help guide the further study of these important features. See our Publications page for more info.
02/26/2019
TJR presents a seminar at the University of Illinois in Urbana, IL.
Tim's talk, titled "Promoting beneficial complexion transitions: Tuning defect structure to make better materials," addressed the usage of complexions as toughening features in Cu-Zr, as well as the extension to all binary transition metal alloys and the consolidation of bulk materials. Dopants were used to decorate the defects and induce a nanoscale phase transformation that improved performance.
02/25/2019
Yang's paper on boundary segregation in ternary alloys is named the March finalist for the 2019 Cahn Prize.
The Robert W. Cahn Best Paper Prize recognizes a truly exceptional original research paper published in the Journal of Materials Science in a particular calendar year. Yang's paper, titled “Atomistic modeling of interfacial segregation and structural transitions in ternary alloys," describes the complex segregation phenomena that arise when multiple dopants are competing for segregation sites and also describes how complexion formation is affected.
01/22/2019
Jen's paper "In situ high-cycle fatigue reveals the importance of grain boundary structure in nanocrystalline Cu-Zr" is published in JOM.
This paper investigates the toughening mechanisms that resist fatigue crack propagation in nanocrystalline Cu-Zr. We use a combination of transmission electron microscopy and nanoindentation-based in situ fatigue testing to show that alloys with amorphous grain boundary films experience fatigue damage that is much more ductile in nature than their counterparts with ordered boundaries, where crack propagate in a brittle fashion. See our Publications page for more info.
01/14/2019
TJR presents a seminar at Dartmouth College in Hanover, NH.
Tim's talk in the Thayer School of Engineering, titled "Promoting beneficial complexion transitions: Tuning defect structure to make better materials," addressed the usage of complexions as toughening features, as well as the extension of this concept to line defects or dislocations. Dopants were used to decorate the defects and induce nanoscale phase transformations that improved performance.
12/16/2018
Zhifeng's paper "Combined effects of metallic dopants and nonmetal impurities on grain boundary energy and strength" is published in Acta Materialia.
This paper demonstrates the combined effects of metallic dopants and nonmetallic impurities on grain boundary energy and strength using first-principles calculations. The interplay between these two types of dopants is extremely important as we usually want to dope nanostructured metals with other metallic elements to improve their properties, but also accidentally incorporate impurities in real materials processing routes. See our Publications page for more info.
11/12/2018
Yang's paper "Atomistic modeling of interfacial segregation and structural transitions in ternary alloys" is published in Journal of Materials Science.
This paper shows how the multiple dopant species in ternary alloys can compete for segregation sites, as well as how complex grain boundary chemical composition affects the formation of amorphous intergranular films. We find that ternary compositions should be able to promote the formation of thicker disordered boundary films. See our Publications page for more info.
10/16/2018
TJR presents an invited talk at the Materials Science & Technology (MS&T) Conference in Columbus, OH.
Tim's talk, titled "Decorating defects with segregating dopants to tailor mechanical properties," focused on understanding how segregating dopants can induce complexion transformation at grain boundaries and dislocations.
10/11/2018
TJR presents two invited talks at the Society of Engineering Science (SES) Meeting in Madrid, Spain.
Tim's first talk, titled "Dislocation-assisted linear complexion formation in body-centered cubic and face-centered cubic alloys," was a keynote talk which described our new work on phase transitions near dislocation cores in a variety of metallic alloys. His second talk, titled "Controlled alteration of nanocrystalline grain boundary networks using cyclic plasticity at elevated temperatures," summarized our efforts to extend the concept of grain boundary engineering to nanocrystalline materials.
09/08/2018
Jason's paper "Concurrent transitions in wear rate and surface microstructure in nanocrystalline Ni-W" is published in Materialia.
This paper shows wear experiments on nanocrystalline Ni-W, where three different wear regimes were observed. We find that large, order-of-magnitude variations in wear rate are accompanied by different types of structural evolution near the contact surface. See our Publications page for more info.
08/24/2018
David's paper "Pronounced grain boundary network evolution in nanocrystalline Cu subjected to large cyclic strains" is published in Journal of Materials Research.
This paper describes the use of cyclic loading and elevated temperature to alter the grain boundary network in nanocrystalline Cu. We find large changes such as a 300% increase in the twin length fraction and use detailed analysis to conclude that the evolution is caused by stress-driven grain boundary migration. This paper will be included in the Early Career Scholars in Materials Science 2019 issue of JMR, where David will be recognized. See our Publications page for more info.
07/18/2018
TJR presents a talk at the International Conference on the Strength of Materials (ICSMA) in Columbus, OH.
Tim's talk, titled "Anisotropic Mobility of Faceted Grain Boundaries," focused on understanding how faceted grain boundaries are formed during cyclic plastic deformation and how these features then behave during grain boundary migration.
07/09/2018
TJR presents an invited talk at the THERMEC Conference in Paris, France.
Tim's talk, titled "Stabilization and toughening of nanocrystalline alloys through the incorporation of amorphous complexions," focused on finding new material systems that can sustain amorphous complexions as well as extending this concept to ternary alloys.
06/18/2018
Our collaborative paper with UCSB researchers titled "Femtosecond Laser Rejuvenation of Nanocrystalline Metals" is published in Acta Materialia.
This paper describes the discovery that grain boundaries can be "rejuvenated" by treatment with a femtosecond laser. This behavior is similar to prior observations made in glassy materials, with the connection being the common disordered structure that is characteristic of interfaces and amorphous materials. See our Publications page for more info.
05/17/2018
Jen and Olivia's paper "Amorphous complexions enable a new region of high temperature stability in nanocrystalline Ni-W" is published in Scripta Materialia.
This paper describes the finding that Ni-W films can sustain amorphous intergranular films at high temperatures, a hypothesis that came from our previous work on materials selection rules for complexion formation. We find that such films can enable a completely new type of grain size stability at high temperatures (roughly above ~1000 °C). See our Publications page for more info.
05/10/2018
Vlad's paper "Dislocation-assisted linear complexion formation driven by segregation" is published in Scripta Materialia.
This paper describes a computational study of linear complexion formation along edge dislocations in body-centered cubic Fe-Ni. Driven by Ni segregation, precipitation of the metastable B2-FeNi and stable L10-FeNi phases occurs along the compression side of edge dislocations. If the Ni segregation is not intense enough to ensure precipitate growth and coalescence along the dislocation lines, linear complexions in the form of stable nanoscale precipitate arrays are observed. See our Publications page for more info.
04/23/2018
TJR presents an invited talk at the International Conference on Metallurgical Coatings and Thin Films in San Diego, CA.
Tim's talk, titled "In situ mechanical testing of hierarchical and gradient nanostructures," focused on understanding the uniaxial failure of nanostructured materials with tailored grain boundary structures.
04/03/2018
TJR presents an invited talk at the University of Pennsylvania in Philadelphia, PA.
Tim's talk in the Materials Science and Engineering and Mechanical Engineering and Applied Mechanics departments, titled "Promoting Beneficial Grain Boundary Phase Transitions with Segregation Engineering," addressed the usage of grain boundary complexions as toughening features. Dopants were used to decorate the grain boundaries and induce nanoscale amorphous intergranular films, by encouraging a premelting transition at the boundary.
03/26/2018
Vlad's paper "Grain boundary complexions and the strength of nanocrystalline metals: Dislocation emission and propagation" is published in Acta Materialia.
This paper describes a computational study of the impact of different complexion types on dislocation nucleation and propagation. These two mechanisms are potential rate-limiting mechanisms for plasticity in nanocrystalline materials. We find that grain boundary doping and amorphous film formation make dislocation nucleation easier but propagation harder. The observed trends for propagation mirror experimental strength trends, suggesting that dislocation pinning and unpinning is most important for grain sizes of tens of nanometers. See our Publications page for more info.
03/20/2018
TJR presents an invited talk at UC Berkeley in Berkeley, CA.
Tim's talk in the Mechanical Engineering department, titled "Manipulating the Structure and Properties of Nanocrystalline Metals using Segregation Engineering," addressed the usage of grain boundary complexions as toughening features. Dopants were used to decorate the grain boundaries and induce nanoscale amorphous intergranular films, by encouraging a premelting transition at the boundary.
03/11/2018
Tim presents five invited talks at the TMS Annual Meeting in Phoenix, AZ.
Tim presented five invited talks, with titles of "Competing effects of nonmetal impurities and planned metallic dopants on grain boundary deformation," "Stabilization of nanocrystalline alloys through the incorporation of grain boundary complexions," "Small-scale mechanical testing of hierarchical nanostructured materials," "Modeling of complexion transitions at one- and two-dimensional defects," and "Surface structure transitions during sliding contact of nanostructured metals."
02/07/2018
Yang's paper "Identifying interatomic potentials for the accurate modeling of interfacial segregation and structural transitions" is published in Computational Materials Science.
This paper describes a study to uncover the types of interatomic potentials that can accurately model chemical segregation and structural transitions at interfaces. Such behavior is inherently a nanoscale phenomenon, making atomistic modeling very powerful, but unfortunately interatomic potentials must be fit to secondary physical properties. We find that the potentials that are able to recreate the correct behavior (in this case, matching experimental observations for Cu-Zr) accurately reproduce the enthalpy of mixing as well as the bond energies, providing a roadmap for the future exploration of interfacial phenomena with atomistic modeling. See our Publications page for more info.
02/01/2018
Tim hosts the "Controversies Colloquium 2018: Stability of Nanostructures" workshop at UCI.
This workshop brought together ~50 top scientists and engineers to discuss the thermal and mechanical stability of nanostructured materials. These materials contain a high density of grain boundaries, meaning that there is a large driving force for structural evolution. They also deform through unique deformation mechanisms. This workshop had an unconventional format, which focused on cultivating discussion and friendly arguments.
01/30/2018
Zhifeng's paper "Uncovering the influence of common nonmetal impurities on the stability and strength of a Σ5 (310) grain boundary in Cu" is published in Acta Materialia.
This paper describes how eight common nonmetal impurities affect the stability and mechanical behavior of grain boundaries in Cu. These impurities are important because they can be easily incorporated during processing (e.g., mechanically alloying for our Cu-Zr materials) or service. First-principles calculations using density functional theory (DFT) allow us to find the preferred segregation site for these impurities while also measuring grain boundary energy and mechanical strength. Tensile simulations are also used to provide additional insight into the grain boundary fracture process. See our Publications page for more info.
10/10/2017
Tim receives the Bradley Stoughton Award for Young Teachers from ASM International.
This award recognizes a teacher of materials science, materials enginering, design, and processing. Tim received the award for "dedication to teaching and mentoring of students in the fields of materials science and metallurgy, as well as organization of innovative outreach activities aimed at high school students."
08/20/2017
Jen's paper "Materials selection rules for amorphous complexion formation in binary metallic alloys" is published in Acta Materialia.
This paper describes a set of materials selection rules aimed at predicting the formation of amorphous complexions. We emphasize the segregation of dopants to the interfaces and the lowering of the formation energy for a glassy structure. To validate our predictions, we look at four Cu-rich alloys and one Ni-rich system. Finally, our materials selection rules are applied to a wide variety of transition metal alloys to make amorphous complexions widely available. See our Publications page for more info.
08/10/2017
Zhiliang's paper "Mechanisms of near-surface structural evolution in nanocrystalline materials during sliding contact" is published in Physical Review Materials.
This paper describes molecular dynamic simulations of sliding wear in nanostructured metals, with a focus on quantifying and tracking structural evolution near the contact surface. While the microstructure far away from the sliding contact remains unchanged, grain growth accompanied by partial dislocations and twin formation was observed near the contact surface, with more rapid coarsening promoted by higher applied normal loads. The coarsening process is balanced by the rate of material removal when the normal load is high enough. See our Publications page for more info.
05/18/2017
Tim is invited to participate in the National Academy of Engineering's 2017 US Frontiers of Engineering Symposium.
The Frontiers of Engineering program brings together through 2-1/2 day meetings a select group of emerging engineering leaders from industry, academe, and government labs to discuss pioneering technical work and leading edge research in various engineering fields and industry sectors. The goal of the meetings is to introduce these outstanding engineers (ages 30-45) to each other, and through this interaction facilitate collaboration in engineering, the transfer of new techniques and approaches across fields, and establishment of contacts among the next generation of engineering leaders. See the UCI Engineering link for more info.
05/16/2017
Tim is promoted to Associate Professor, effective July 1, 2017.
Tim has been promoted to Associate Professor, effective July 1, 2017, in the Department of Mechanical and Aerospace Engineering. This rank is a tenured position in the University of California system, allowing our group the freedom to continue to pursue high-risk, high-reward research topics.
04/24/2017
Simon's paper "Nanocrystalline Al-Mg with extreme strength due to grain boundary doping" is published in Materials Science and Engineering A.
This paper describes the creation of nanocrystalline Al-Mg alloys, with a focus on isolating the effect of grain boundary doping on strength. We find pronounced strengthening from Mg segregating to the grain boundaries, resulting in one of the strongest lightweight metals reported to date. See our Publications page for more info.
02/27/2017
Tim and Jen attend the TMS Annual Meeting in San Diego, CA.
Tim gave two invited talks titled "Collective deformation mechanisms and their effect on nanoscale interfacial networks" and "Complexion transitions in metals: Unique opportunities for mechanical behavior and materials processing." Jen presented a talk titled "Unambiguous Complexion Identification and Inspection in High Purity Binary Alloy Systems."
02/23/2017
TJR presents an invited talk at Caltech in Pasadena, CA.
Tim's talk, titled "Controlling Nanocrystalline Structure and Properties with Segregation Engineering," addressed the usage of grain boundary complexions as toughening features. Dopants were used to decorate the grain boundaries and induce nanoscale amorphous intergranular films, by encouraging a premelting transition at the boundary.
02/17/2017
David's paper "Formation and characterization of large twin related domains" is published in Acta Materialia.
This paper describes the formation of large clusters of twinned grains during recrystallization in grain boundary engineered Ni, as well as interesting correlations between the size of the twin related domains and other microstructural descriptors. See our Publications page for more info
01/25/2017
TJR is appointed to the Editorial Board of the journal Scientific Reports.
Scientific Reports is an online, open access journal from the publishers of Nature, with a focus on publishing primary research from all areas of the natural and clinical sciences.
01/21/2017
Zhiliang's paper "Spatial variation of short-range order in amorphous intergranular complexions" is published in Computational Materials Science.
This paper describes how local structural order varies throughout amorphous intergranular films, serving to highlight how constraints by the neighboring crystals influence the complexion itself. See our Publications page for more info
12/23/2016
Amir and TJR receive the 2017 TMS Structural Materials Division JOM Best Paper Award.
The award recognizes the most notable paper on structural materials that was published in the preceding year's JOM journal. This paper, titled "High-temperature stability and grain boundary complexion formation in a nanocrystalline Cu-Zr alloy," describes a nanocrystalline alloy with impressive thermal stability and a unique microstructure.
11/28/2016
TJR presents a talk at the Materials Research Society (MRS) Conference in Boston, MA.
Tim's talk, title "Restructuring of Nanoscale Grain Boundary Networks during Cycling," addressed how grain boundary structure canevolve under stress, combining experimental and computational techniques.
11/19/2016
Zhiliang's paper "Formation of ordered and disordered interfacial films in immiscible metal alloys" is published in Scripta Materialia.
This paper describes segregation-induced intergranular film formation in Cu-Zr and Cu-Nb alloys, with an eye for understanding how different alloys form different types of grain boundary films. See our Publications page for more info
10/26/2016
Tim and Jason attend the Materials Science & Technology (MS&T) conference in Salt Lake City, UT.
Tim's talk was titled "The mechanics and thermodynamics of interfacial complexions in transition metal alloys" while Jason gave a talk titled "Plasticity-induced Restructuring of Nanocrystalline grain Boundary Networks".
09/08/2016
TJR presents an invited talk at Sandia National Laboratory in Albuquerque, NM.
Tim's talk, titled "Using Interfacial Structure to Control the Properties of Nanocrystalline Metals," addressed attempts to control the thermal stability and ductility of nanocrystalline materials. Experiments and simulations of Cu-Zr alloys were presented, showing a dramatic improvement in performance.
09/01/2016
TJR presents an invited talk at the University of Southern California in Los Angeles, CA.
Tim's talk, titled "Promoting Beneficial Grain Boundary Phase Transitions with Segregation Engineering," addressed the usage of grain boundary complexions as toughening features. Dopants were used to decorate the grain boundaries and induce nanoscale amorphous intergranular films, by encouraging a premelting transition at the boundary.
08/14/2016
Jason's paper "Plasticity-induced restructuring of a nanocrystalline grain boundary network" is published in Acta Materialia.
This paper describes how cyclic plasticity serves to evolve the grain boundary network of nanocrystalline materials, pushing the system towards a lower energy state with more special boundaries. See our Publications page for more info
07/10/2016
Three from NMML attend the Gordon Research Conference on Structural Nanomaterials in Hong Kong.
Tim's talk was titled "Effect of Interfacial Doping and Complexion Formation on Nanocrystalline Mechanical Behavior" while Jen and Zhiliang presented posters detailing experimental observations of complexions in thin films and simulations of nanocrystalline wear, respectively.
05/08/2016
TJR's paper "The role of complexions in metallic nano-grain stability and deformation" is published in Current Opinion in Solid State & Materials Science.
This review paper describes how interfacial complexions can potentially optimize the mechanical properties of nanostructured materials while also improving the thermal stability of these materials. See our Publications page for more info.
04/21/2016
NMML receives a Young Investigator Program (YIP) grant from the Army Research Office.
The NMML has been chosen by the Army Research Office to receive a research grant through the Young Investigator Program. This grant will support a research project that aims to create bulk nanostructured alloys with optimized mechanical properties through the use of boundary complexions. [link]
04/13/2016
TJR is appointed to the Editorial Board of the journal Materials Science and Engineering A.
An editorial board member is expected to help maintain and improve journal standards by monitoring the editorial policy of the journal in terms of scope and the level and quality of papers published. Materials Science and Engineering A is an international journal for the publication of theoretical and experimental studies related to the load-bearing capacity of materials as influenced by their basic properties, processing history, microstructure and operating environment.
04/06/2016
Zhiliang's paper "Effect of grain boundary character on segregation-induced structural transitions" is published in Physical Review B.
This paper describes how the starting structure of a grain boundary affects segregation of alloying elements to the interface, as well as the transition between different complexion states. See our Publications page for more info.
02/18/2016
NMML's latest paper is profiled on the UCI Engineering webpage.
An article profiling a recent Nature Communications paper by Amir, Zhiliang, and Tim appears on the UCI Engineering website. The full story details the importance of the research and can be found here [link].
02/18/2016
Amir's paper "Manipulating the interfacial structure of nanomaterials to achieve a unique combination of strength and ductility" is published in Nature Communications.
This paper describes how grain boundary complexions can be used to access an unprecedented combination of strength and ductility in nanocrystalline Cu-Zr. See our Publications page for more info, as well as the story on the Engineering Website.
01/07/2016
TJR presents two invited talks at the International Symposium on Plasticity in Kona, HI.
Tim's talks, titled "Formation and Toughening Effects of Amorphous Interfacial Phases" and "Nanocrystalline Grain Boundary Engineering with Cyclic Plastic Deformation", detailed our separate efforts to ductilize nanocrystalline materials and understand the evolution of grain boundary networks during cyclic loading, respectively.
11/30/2015
TJR presents an invited talk at the Materials Research Society (MRS) Conference in Boston, MA.
Tim's talk, title "Tuning Grain Boundary Structure to Control the Mechanical Behavior of Nanostructured Metallic Alloys," addressed how grain boundary structure can influence the mechanical properties of nanocrystalline materials. Specifically, the talk focused on how structural order is an important variable for controlling failure, with disordered interfaces highlighted as useful features.
11/09/2015
David's paper "Grain boundary character distributions in nanocrystalline metals produced by different processing routes" is published in Metallurgical and Materials Transactions A.
This paper describes how the processing route used to make a nanocrystalline metal influences the grain boundary network. David shows that nearly identical grain boundary character distributions are found in materials made by various deposition methods, while the boundaries in materials made by severe plastic deformation are very different. See our Publications page for more info.
11/03/2015
TJR presents an invited talk at the University of Florida in Gainesville, FL.
Tim's talk, titled "Controlling Grain Boundary Structure and Properties with Segregation Engineering," addressed the long-standing issue of brittleness in nanocrystalline materials. Dopants were used to decorate the grain boundaries and induce nanoscale amorphous intergranular films. In effect, this doping encourages a premelting transition at the boundary.
10/07/2015
TJR presents an invited talk at the Materials Science and Technology (MS&T) Conference in Columbus, OH.
Tim's talk, title "Nanoscale Amorphous Intergranular Films: Mechanical Properties and Interfacial Thermodynamics," addressed how amorphous interfacial films form and then affect mechanical properties.
10/01/2015
TJR presents an invited talk at the 4th International Workshop on Interfaces at Bear Creek Mountain Resort.
Tim's talk, title "Using amorphous complexions to tailor the mechanical behavior of nanostructured metals," addressed how grain boundary state affects the failure of nanograined materials. Specifically, he described efforts to create tough yet strong nanocrystalline metal alloys through the addition of amorphous complexions.
09/24/2015
TJR presents an invited talk at the University of North Carolina at Charlotte in Charlotte, NC.
Tim's talk, titled "Characterizing and Modifying Grain Boundary Networks in Nanocrystalline Metals," addressed our recent work on bringing grain boundary engineering to nanoscale materials. A combination of transmission Kikuchi diffraction, bulge testing, and atomistic simulations was used to address evolution of the grain boundary network.
09/02/2015
Amir's paper "High-temperature stability and grain boundary complexion formation in a nanocrystalline Cu-Zr alloy" is published in JOM.
This paper describes a nanocrystalline alloy with impressive thermal stability, retaining a nanoscale grain structure after annealing for 1 week at 98% of the melting temperature. Amir shows that grain boundary complexions can provide thermodynamic stabilization while nanoscale ZrC particles provide kinetic stabilization. See our Publications page for more info.
08/17/2015
TJR presents a talk at the International Materials Research Congress in Cancun, Mexico.
Tim talked about how small-scale mechanical testing can be used to study plasticity and failure of nanostructured metals. Our work on using grain boundary disorder to toughen these materials was also discussed.
07/29/2015
Joseph's paper "Amorphous intergranular films act as ultra-efficient point defect sinks during collision cascades" is published in Scripta Materialia.
This paper describes how grain boundary structure is important for healing radiation damage. Joseph shows that amorphous intergranular films are much more efficient sinks for point defects than ordered grain boundaries. See our Publications page for more info.
07/22/2015
Congratulations to Amir Khalajhedayati for a successful Ph.D. defense.
Amir successfully defending his thesis, which was titled "Grain boundary structure and interfacial complexions for the creation of tough, stable nanostructured metals." Congrats Amir!
07/10/2015
Our paper "Modelling wrinkling interactions produced by patterned defects in metal thin films" is published in Extreme Mechanics Letters.
This paper describes how thin metal films with added stress concentrations wrinkle out-of-plane. This work was a collaborative effort between UC Irvine, University of Sydney, University of Pennsylvania, and Johns Hopkins University. See our Publications page for more info.
06/03/2015
Jason receives a Mazda Foundation Scholarship.
Jason was one of only two graduate students selected for a $10,000 scholarship from the Mazda Foundation. Congrats Jason! The full story can be found here [link].
05/12/2015
Jason receives the Hysitron Presentation Silver Medal Award for his talk at TMS.
Jason received the award for his outstanding presentation, where he discussed Mapping Grains and Interface Networks in Atomistic Simulations. Congrats Jason!
05/06/2015
NMML receives DOE Early Career Research Program award.
The NMML has been chosen by the Department of Energy to receive an Early Career award. The purpose of this program is to support the development of individual research programs of outstanding scientists early in their careers and to stimulate research careers in the areas supported by the DOE Office of Science. This grant will support a research project to understand how grain boundary structure can be controlled by locally and selectively adding other elements, with the idea of inducing planned grain boundary phases or “complexions” to create tougher materials. [link]
04/24/2015
Amir's paper "Disruption of Thermally-Stable Nanoscale Grain Structures by Strain Localization" is published in Scientific Reports.
This paper describes how even thermally stable alloy systems can undergo mechanically-driven structural evolution, provided that the deformation applied is extreme. Amir shows that stable nanocrystalline Ni-W coarsens inside of shear bands, where there are very large localized plastic strains, while it remains unchanged in areas where there has been homogeneous plasticity. See our Publications page for more info.
04/22/2015
TJR presents an invited lecture at Mackenzie Presbyterian University in São Paulo, Brazil.
Tim's talk, titled "Doping Nanocrystalline Metals to Improve Ductility and Toughness," addressed the long-standing issue of brittleness in nanocrystalline materials, using a combination of experimental and computational techniques. Dopants were used to decorate grain boundaries and induce amorphous intergranular films, which gave a toughening effect and improved thermal stability.
03/26/2015
NMML receives an NSF grant to perform research on wear damage transitions in nanostructured metallic alloys.
The NMML has been chosen by the National Science Foundation to receive a research grant. This grant will support a research project on transitions in surface structure and properties in nanostructured alloys, studied through a combination of atomistic simulations and wear experiments.
03/18/2015
Jason and Zhiliang present talks at TMS 2015 Annual Meeting in Orlando, FL.
Jason talked about how cyclic plastic deformation leads to structural evolution and a changing grain boundary character distribution in nanocrystalline materials, while Zhiliang showed amorphous intergranular films can act as toughening features in a microstructure. Congrats Jason and Zhiliang!
03/06/2015
TJR presents an invited talk at Boise State University in Boise, ID.
Tim's talk, titled "Controlling Grain Boundary Structure and Properties with Segregation Engineering," addressed the long-standing issue of brittleness in nanocrystalline materials. Dopants were used to decorate the grain boundaries and induce amorphous intergranular films.
02/06/2015
Zhiliang's paper "Amorphous intergranular films as toughening structural features" is published in Acta Materialia.
This paper describes how amorphous intergranular films, features with planned structural disorder, can act as toughening agents in materials. Zhiliang shows that dislocations can be easily absorbed so that crack nucleation is delayed, while also demonstrating that cracks then grow slowly in such films. See our Publications page for more info.
01/08/2015
TJR presents two invited talks at International Symposium on Plasticity in Montego Bay, Jamaica.
Tim's talks, titled "Connecting Computational and Experimental Tools for Tracking the Evolution of Nanostructured Materials" and "Cyclic Plasticity and Microstructural Modification in Nanocrystalline Thin Films", detailed our work to understand and control the evolution of grain structure and boundary networks during cyclic loading using a combination of simulations and experiments.
12/15/2014
Jason's paper "Quantitative tracking of grain structure evolution in a nanocrystalline metal during cyclic loading" is published in Modelling and Simulation in Materials Science and Engineering.
This paper describes simulations of structural evolution in nanocrystalline Al during cyclic deformation at different temperatures. In this paper, Jason uses his recent algorithm for tracking grains to quantify such behavior. See our Publications page for more info.
12/11/2014
TJR presents an invited talk at Penn State - Materials Science and Engineering in State College, PA.
Tim's talk, titled "Complexion Engineering in Nanostructured Materials," focused on the creation of tough nanostructured Cu-Zr using complexion engineering. Specially-designed amorphous intergranular films were added during processing to act as efficient dislocation sinks.
12/05/2014
Amir wins Second Place in the Science as Art competition at MRS Fall 2014 conference in Boston, MA.
Amir's photo, titled "Newton's Color Wheel," shows an SEM image of a pillar designed for microcompression testing viewed from the top. The pillar was made with an automated lathe milling technique using a Focused Ion Beam microscope. Congrats Amir! See the MRS Webpage for more info.
12/04/2014
Amir and David present talks at MRS Fall 2014 conference in Boston, MA.
Amir talked about his processing and characterization of super tough nanocrystalline Cu-Zr, while David showed that nanocrystalline metals can be grain boundary engineered for the first time. Congrats Amir and David!
11/19/2014
TJR is selected as a recipient of the 2015 TMS Young Leaders Professional Development Award.
Tim was selected to receive the Young Leaders Professional Development Award from the Structural Materials Division (SMD) of TMS, one of the major professional organizations for materials scientists. This award was created to enhance the professional development of dynamic young people from TMS’s five technical divisions. Tim will receive the award at the 2015 TMS conference in Orlando, FL.
11/04/2014
David's paper "Nanocrystalline grain boundary engineering: Increasing Σ3 boundary fraction in pure Ni using collective deformation physics" is published in Acta Materialia.
This paper focuses on understanding how nanocrystalline grain boundary networks evolve during cyclic deformation. In this paper, we report on the first observations of grain boundary engineering resulting from thermomechanical processing in nanocrystalline metals. See our Publications page for more info.
10/25/2014
TJR presents an invited talk at the International Conference for Young Researchers on Advanced Materials (ICYRAM) in Haikou, China.
Tim's talk, titled "Nanocrystalline Grain Boundary Networks and Their Evolution during Thermomechanical Cycling," detailed our work to understand and control the evolution of grain structure and boundary networks during cyclic loading. Our successful grain boundary engineering in nanocrystalline metals, the first of its kind, was highlighted.
10/15/2014
Zhiliang gives a talk at MS&T 2014 conference in Pittsburgh, PA.
Zhiliang's talk, titled "Damage Nucleation from Dislocation-Grain Boundary Interactions: Mechanisms and Toughening Strategies," discusses a computational study of crack nucleation at internal interfaces. Zhiliang's work is important for toughening nanocrystalline materials and improving fatigue life, and identifies amorphous intergranular films as promising structural features.
09/26/2014
TJR presents an invited talk at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, Germany.
Tim's talk, titled "Catastrophic Failure of Nanocrystalline Metals: Mechanisms and Novel Toughening Strategies," focused on understanding failure in nanomaterials while also highlighting ways to toughen these systems. Routes for the creation of tough nanostructured Cu-Zr were specifically described.
09/23/2014
TJR presents a keynote address at Materials Science Engineering (MSE) in Darmstadt, Germany.
Tim's talk, titled "Doping Nanocrystalline Alloys to Improve Strength and Toughness," focused on alloying interfaces to control grain boundary structure and fracture toughness. Routes for the creation of tough nanostructured materials were described.
07/04/2014
Zhiliang's paper "Damage nucleation from repeated dislocation absorption at a grain boundary" is published in Computational Materials Science.
This paper focuses on understanding how dislocation absorption leads to cracking and damage at grain boundaries. Such processes are important for stress corrosion cracking, fatigue failure, and fracture of nanocrystalline materials. See our Publications page for more info.
06/20/2014
TJR is selected as a Hellman Fellow.
Tim has been selected as a Hellman Fellow for 2014-2015. The Hellman Fellows Program aims to support the research of promising assistant professors who show capacity for great distinction in their chosen fields of endeavor. The program was created by a generous gift from Mr. F. Warren Hellman, a distinguished UC Berkeley alumnus and supporter of junior faculty. Hellman Fellows Awards provide recognition and flexible research funds for the recipient. Tim ’s project is titled “Enabling Generation IV Nuclear Reactors with Interface-Dominated Materials,” and will focus on the computer simulation of radiation damage at specially designed interfaces in materials.
05/22/2014
David is selected as a Lawrence Graduate Scholar.
David was selected to participate in the Lawrence Graduate Scholar Program (LGSP). Under the LGSP, Ph.D. candidate students from eligible campuses are granted appointments for up to four years to conduct research at the Lawrence Livermore National Laboratory (LLNL) while completing their thesis. These appointments are implemented through a close working partnership involving the student, the student’s academic thesis advisor and the Laboratory technical mentor. David's mentor at LLNL will be Dr. Mukul Kumar.
05/01/2014
TJR presents an invited talk at the International Conference on Metallurgical Coatings and Thin Films in San Diego, CA.
Tim's talk, titled "Mechanical and Tribological Behavior of Nanocrystalline Ni-W Coatings: Importance of Grain Size and Grain Boundary State," focused on understanding how the uniaxial failure and wear resistance of nanocrystalline metal coatings.
03/01/2014
TJR's paper "Solid solution strengthening and softening due to collective nanocrystalline deformation physics" is published in Scripta Materialia.
This paper focuses on understanding solid solution effects on strength in the finest nanocrystalline metals, where collective mechanisms dominate plasticity and traditional strengthening theories break down. Cu-Pb and Cu-Ni were used as model FCC alloys and these result show that elastic modulus changes are of the utmost importance. See our Publications page for more info.
02/17/2014
NMML presents four talks at TMS 2014 conference in San Diego, CA.
Tim gave two invited talks, outlining our work on nanocrystalline grain boundary engineering and doping grain boundaries to increase toughness. In addition, Amir talked about his experiments on shear localization in nanocrystalline Ni-W, while Jason introduced his algorithm for extracting quantitative microstructure data from atomistic simulations. Congrats Amir and Jason!
01/06/2014
TJR presents an invited talk at the International Symposium on Plasticity in Freeport, Bahamas.
Tim's talk, titled "Plasticity and failure of nanocrystalline alloys: the importance of grain boundary structure," focused on understanding how nanocrystalline grain boundary structure influences fracture and failure.
12/03/2013
TJR presents an invited talk at THERMEC 2013 conference in Las Vegas, NV.
Tim's talk, titled "The Influence of Grain Boundary Structure on Plastic Flow and Failure in Nanocrystalline Alloys," focused on understanding how grain boundary structure in nanocrystalline metals can be used to improve toughness. The work connected the experimental work that Amir is performing with atomistic simulations run by Zhiliang.
11/26/2013
Jason's paper "Tracking Microstructure of Crystalline Materials: A Post-Processing Algorithm for Atomistic Simulations" is published in JOM.
This paper introduces an algorithm for analyzing atomistic simulations of crystalline solids. The Grain Tracking Algorithm (GTA) provides a quantitative tool for identifying crystallites, their crystallographic orientation, and overall sample texture, while also tracking such features during a simulation. See our Publications page for more info.
10/25/2013
Amir's paper "Emergence of localized plasticity and failure through shear banding during microcompression of a nanocrystalline alloy" is published in Acta Materialia.
This paper focuses on understanding the uniaxial flow and failure of nanocrystalline metals using micocompression testing. Nanocrystalline Ni-W is used as a model system to explore the importance of the deformation physics at different grain sizes, as well as the effect of grain boundary relaxation. See our Publications page for more info.
09/05/2013
Amir Khalajhedayati passes PhD Qualifying Exam.
Amir has passed his qualifying exam and advanced to candidacy. Congratulations Amir!
08/06/2013
TJR presents a poster at the Third Annual Meeting for NSF BRIGE Principal Investigators in Arlington, VA.
Tim's poster, titled "Interfacial Defects and the Failure of Nanostructured Metals," focused on research and outreach activities centered on a study of failure in nanocrystalline alloys using cutting-edge experimental and computational materials science techniques. Tim's poster can be accessed here:
07/31/2013
TJR presents an invited talk at SES Annual Technical Meeting at Brown University in Providence, RI.
Tim's invited talk, titled "Shear Localization in Nanocrystalline Metals: A Combined Atomistic and Experimental Study," focused on understanding a type of catastrophic failure that has recently be observed in nanostructured materials. It was part of the symposium titled "From Atomistics to Reality: Spanning Scales in Simulations and Experiments."
07/01/2013
TJR's paper "Strain localization in a nanocrystalline metal: Atomistic mechanisms and the effect of testing conditions" is published in Journal of Applied Physics.
This paper focuses on understanding strain localization in nanocrystalline metals using molecular dynamics simulations. Nanocrystalline Ni is used as a model FCC system to explore the atomic mechanisms of localization, as well as probe the importance of testing conditions on such behavior. See our Publications page for more info.
03/04/2013
TJR presents a talk at TMS 2013 conference in San Antonio, TX.
Tim's talk, titled "The Evolution of Nanocrystalline Grain Boundary Networks under Mechanical Cycling," focused on understanding how interfacial networks in nanocrystalline metals change during deformation and was included in the symposium titled "Fatigue and Fracture of Thin Films and Nanomaterials." The work connected the experimental work that David is performing with atomistic simulations run by TJR.
02/27/2013
TJR is profiled on the UCI Engineering webpage.
An article profiling Tim and discussing his recent NSF CAREER award has been published on the UCI Henry Samueli School of Engineering (HSSoE) website. The full story can be found here [link].
02/13/2013
NMML receives NSF Faculty Early Career Development (CAREER) Award.
The NMML has been chosen by the National Science Foundation to receive a CAREER award. The CAREER program provides grants to young faculty with innovative research and educational programs. This grant will support a research project to understand the evolution of the grain boundary network during cyclic deformation, and to quantify how grain boundary network features influence the mechanical behavior of nanocrystalline materials. For more info please see [link].
02/01/2013
Mukul Kumar (LLNL) visits the MAE Department at UC Irvine.
Dr. Mukul Kumar from Lawrence Livermore National Laboratory (LLNL) was hosted by TJR for a visit to the MAE Department at UCI. Dr. Kumar is an expert in the fields of interfacial network analysis and grain boundary engineering. His talk, titled "Grain boundary networks: From consideration of the individual constituents to the collective response," detailed recent work to understand how the population of grain boundary types in a microstructure control the mechanical response of FCC metals and alloys
01/10/2013
TJR's paper "Abrasive wear response of nanocrystalline Ni-W alloys across the Hall-Petch breakdown" is accepted for publication in the journal Wear.
This paper describes the wear of nanocrystalline Ni-W alloys under Taber abrasion, an aggressive form of wear testing. The wear resistance of the finest grain size sample was found to be higher than would be predicted by hardness alone, which is traced to grain growth and grain boundary relaxation during testing. See our Publications page for more info.
11/27/2012
TJR presents an invited talk and poster at MRS Fall 2012 conference in Boston, MA.
Tim's talk, titled "Tribology of Nanocrystalline Ni-W: Evolving Structure and Properties," focused on understanding how grain growth and grain boundary relaxation influences the wear resistance of nanocrystalline alloys. Tim and Amir's poster was titled "The Influence of Atomic Grain Boundary Structure on Plastic Flow in Nanocrystalline Alloys" and examined how the relaxation of grain boundaries impacts failure. Both were included in the symposium titled "Mechanical Behavior of Metallic Nanostructured Materials."
10/18/2012
Vanessa Dang and Jason Panzarino join the Nanoscale Mechanics and Materials Lab (NMML).
Vanessa and Jason are Ph.D. students in Mechanical and Aerospace Engineering (MAE) at UCI, and their office will be located in 3115 Engineering Gateway.