Deformation Mechanisms, Microstructure Evolution, and Mechanical Properties of Nanoscale Materials: Deformation Mechanisms I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Niaz Abdolrahim, University of Rochester; Matthew Daly, University of Illinois-Chicago; Hesam Askari, University Of Rochester; Eugen Rabkin, Technion; Jeff Wheeler, Femtotools Ag; Wendy Gu, Stanford University
Monday 8:30 AM
March 20, 2023
Room: Aqua 300AB
Location: Hilton
Session Chair: Timothy Rupert, University of California, Irvine; Christoph Kirchlechner, KIT
8:30 AM Invited
The Role of Amorphous Shear Bands in Deformation of Crystalline Materials: Izabela Szlufarska1; 1University of Wisconsin-Madison
Amorphous shear bands (a-SBs) are known to form in crystalline materials subjected to high strain rates or in the presence of severe plastic deformation. Formation of a-SBs is typically followed by cavitation and fracture and therefore a-SB have been considered detrimental to mechanical performance. We have recently found that a-SBs can form in crystalline materials without pre-existing damage and at low strain rates. We also found that a-SBs do not have to lead to cavitation and fracture, but instead can be drivers of plasticity in the absence of dislocations. Using a combination of molecular simulations and small-scale mechanical testing we identified properties of materials that support formation of a-SBs and we proposed criteria for when a-SBs will increase fracture toughness instead of leading to cavitation. Our findings provide insights into improvements of fracture toughness of nominally brittle materials.
9:00 AM
Submicron Intermetallic Particle Heterogeneity Controls Shear Localization in High-strength Nanostructured Al Alloys: Tianjiao Lei1; Esther Hessong1; Jungho Shin2; Daniel Gianola2; Timothy Rupert1; 1University of California Irvine; 2University of California Santa Barbara
The mechanical behavior of nanocrystalline Al alloys, Al-Mg-Y and Al-Fe-Y, was investigated with in-situ micropillar compression testing. Both systems exhibited yield strengths higher than 600 MPa, due to grain boundary segregation, amorphous complexions, nanorod precipitates, and intermetallic particles. However, some micropillars plastically softened through shear banding. Post-mortem transmission electron microscopy investigation revealed that intermetallic-free deformation pathways were responsible for this failure. Further characterization showed significant grain growth and the same grain orientation within the shear band, pointing to grain boundary mechanisms for plastic flow, specifically grain rotation and/or grain boundary migration. The presence of intermetallic particles made it difficult for both matrix and intermetallic grains to rotate into the same orientation, due to the different lattice parameters and slip systems. Therefore, we conclude that a uniform distribution of intermetallics with an average spacing less than the percolation length of shear localization can effectively prevent the maturation of shear bands.
9:20 AM
Rejuvenation of Plasticity via Deformation Graining in Submicron Magnesium: Boyu Liu1; Zhen Zhang2; Fei Liu1; Bin Li3; Zhiwei Shan1; 1Xi'an Jiaotong University; 2Hefei University of Technology; 3University of Nevada, Reno
Magnesium, the lightest structural metal, usually exhibits limited ambient plasticity when compressed along its crystallographic c-axis (the “hard” orientation of magnesium). Here we report large plasticity in c-axis compression of submicron magnesium single crystal achieved by a dual-stage deformation. We show that when the plastic flow gradually strain-hardens the magnesium crystal to gigapascal level, at which point dislocation mediated plasticity is nearly exhausted, the sample instantly pancakes without fracture, accompanying a conversion of the initial single crystal into multiple grains that roughly share a common rotation axis. Atomic-scale characterization, crystallographic analyses and molecular dynamics simulations indicate that the new grains can form via transformation of pyramidal to basal planes. We categorize this grain formation as “deformation graining”. The formation of new grains rejuvenates massive dislocation slip and deformation twinning to enable large plastic strains.
9:40 AM
The Heterogeneous Nature of Mechanically Accelerated Grain Growth: Elton Chen1; Brad Boyce1; Remi Dingreville1; 1Sandia National Laboratories
Atomistic simulations are used to study the process of heterogeneous thermal-mechanical grain growth in Pt nanowire. Systems are thermally relaxed at the temperature of 400K and 600K in combination with tension and equivalent shear fatigues of 0.6%, 0.8% and 1.0% across 50 cycles over 5ns. In order to extract general grain growth trends, analysis is performed for the top 10 largest grains. At 400K both mechanical fatigue modes accelerate grain growth, however the effects are heterogeneous to each grain. At 600K, tension fatigue disproportionally affects a different set of grains, while shear fatigue consistently de-accelerates grain growth in a few grains. No direct correlation can be observed between relative grain growth rate and grain size; largest grain is not always the fastest growing nor especially benefit from mechanical acceleration. Only abnormal grain growth mechanism observed is the abrupt rotation of smaller neighboring grain of similar orientation.
10:00 AM Break
10:20 AM Invited
Thermal Stability and Mechanical Behavior in Segregation-Engineered
Nanocrystalline Ternary Al Alloys: Jungho Shin1; Fulin Wang2; Glenn Balbus3; Tianjiao Lei4; William Cunningham1; Ravit Silverstein1; Timothy Rupert4; Daniel Gianola1; 1University of California-Santa Barbara; 2Shanghai Jiao Tong University; 3Air Force Research Laboratory; 4University of California Irvine
The deliberate use of solute enrichment at grain boundaries, otherwise known as segregation engineering, is a promising approach to tailor the properties of interface dominated materials such as nanocrystalline alloys. The ensuing chemical and structural evolution at grain boundaries can give rise to thermal stability and excellent mechanical properties, but the interplay between enrichment, phase decomposition, grain growth, and mechanical behavior exists in a vast composition and processing space. In this study, a combinatorial synthesis and rapid characterization approach was applied to segregation-engineered nanocrystalline Al-X-Z (X=Ni, Fe, Mg, Z=Y, Ce) alloys to assess the evolution of microstructure and resulting mechanical behavior as functions of alloying content and annealing conditions. In addition to the identification of alloys and processing conditions that give rise to exceptional thermal stability, strength retention, and homogeneous plastic flow, we construct combined thermal stability and deformation mechanism maps that demarcate several important regimes of behavior.
10:50 AM
Deformation Behavior and Microstructural Characterization of Pure Mg Deformed by Nanoindentation: Yi-Cheng Lai1; Yuwei Zhang1; George Pharr1; Kelvin Xie1; 1Texas A&M University
Dislocations and twinning play important roles in the deformation of Mg. However, there are few detailed microstructural observations to identify deformation mechanisms beneath the indented surface at the dislocation level. In this work, we employed TEM and precession electron diffraction to reveal the dislocation characteristics (e.g., types and distribution) at two indentation depths in two grains of Mg with different orientations. After indentation, well-defined plastic zones are observed, the size of which is discussed and correlated to the indentation depth and crystal orientation. The new knowledge generated in this work enables us to advance our understanding of the indentation size effect and the mechanisms of plastic deformation in Mg.
11:10 AM Invited
Dislocation Twin Boundary Interactions: Slip Transfer and Dislocation Nucleation: Christoph Kirchlechner1; 1Karlsruhe Institute of Technology
Nanotwinned materials are known for their high strength and ductility. In this work we will use introduce micro pillar compression as well as spherical nanoindentation experiments to highlight two aspects of the strength of microstructures with twin boundaries: (i) In the first part of the talk the interaction of dislocations with single and multiple coherent Sigma 3 twin boundaries in copper will be shown. Aspect as slip compatibility, slip transfer mechanisms and their quantitative impact on strength will be discussed.(ii) In the second part of the talk, the important role of pre-existing defects at twin boundaries for dislocation nucleation and the effect of stacking fault energy on dislocation emission from imperfections at the twin boundary will be discussed.