Ultrafine-grained and Heterostructured Materials (UFGH XII): Fundamentals in Mechanical Behavior and Radiation Effects II
Sponsored by: TMS: Shaping and Forming Committee
Program Organizers: Penghui Cao, University of California, Irvine; Xiaoxu Huang, Chongqing University; Enrique Lavernia, University of California, Irvine; Xiaozhou Liao, University of Sydney; Lee Semiatin, MRL Materials Resources LLC; Nobuhiro Tsuji, Kyoto University; Caizhi Zhou, University of South Carolina; Yuntian Zhu, City University of Hong Kong

Monday 2:00 PM
February 28, 2022
Room: 262A
Location: Anaheim Convention Center

Session Chair: Khalid Hattar, Sandia National Laboratories; Michael Demkowicz, Texas A&M University; Brad Boyce, Sandia National Laboratories

2:00 PM  Invited
Helium in Metal Composites: Michael Demkowicz1; 1Texas A&M University
    The introduction of helium (He) into metal components is a major concern in nuclear energy applications. Metal composites open new avenues to mitigating He-induced damage, beyond those available in single-phase alloys. This talk will summarize experimental and modeling work on the behavior of He in a wide range of metal composites, focusing on the effects of composition, microstructure length scale and morphology, and interface character.

2:30 PM  Invited
Comparing the Thermal, Mechanical, and Radiation Stability of Nanocrystalline Platinum-gold: Khalid Hattar1; Alejandro Barrios Santos1; Emily Hopkins1; Christopher Barr1; James Nathaniel1; Elton Chen1; Chongze Hu1; Remi Dingreville1; Daniel Bufford1; David Adams1; Doug Medlin1; Fadi Abedljawad2; Brad Boyce1; 1Sandia National Laboratories; 2Clemson University
    Grain-size stability is essential to maintain the unique properties associated with ultrafine-grained and nanocrystalline metals. Binary alloying is a simple and effective means to drastically improve the grain-boundary stability. In this study, we explored and compared the thermal, mechanical, and ion irradiation stability of a model binary system, nanocrystalline platinum-gold. In-situ TEM annealing experiments showed that increasing alloy concentration results in less grain growth during heating. In-situ SEM fatigue experiments demonstrated that grain growth dominates failure mechanisms in pure Pt, while intergranular cracking governs Pt-Au alloy failures. In-situ and ex-situ heavy ion irradiation have shown extensive grain growth occurring in both systems, which can be attributed directly to the displacement damage. Analyzed with modeling results, these results suggest that it is extremely important to consider grain-boundary stability in the expected operating environment, as boundaries are not all equivalent. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

3:00 PM  Invited
Synergistic Thermal and Radiation Stability in Grain Boundary Doped Nanocrystalline Tungsten: William Cunningham1; Khalid Hattar2; Yuanyuan Zhu3; Danny Edwards4; Jason Trelewicz1; 1Stony Brook University; 2Sandia National Laboratories; 3University of Connecticut; 4Pacific Northwest National Laboratory
    Targeted doping of grain boundaries has a profound impact on thermal stability, but for nanocrystalline alloys to be advanced as radiation resistant materials, an understanding of its influence on damage tolerance and stability is needed. In this presentation, results from in situ heavy ion irradiation of a titanium doped nanocrystalline tungsten alloy are discussed with a focus on the coupling between defect accumulation and microstructural evolution. Relative to undoped tungsten, the alloy is shown to exhibit smaller defect loops and a delayed saturation dose, which is accompanied by a transient period of irradiation induced grain growth. Despite this modest coarsening, the grain structure remains decidedly nanocrystalline and plateaus at a much finer grain size than predicted for pure tungsten from a thermal spike grain growth model. Our results thus demonstrate that deliberate doping for enhanced thermal stability synergistically stabilizes the material against irradiation induced coarsening while limiting overall damage accumulation.

3:30 PM Break

3:50 PM  Invited
Amorphous Ceramic and Metallic Composites: Microstructure and Mechanical Properties: Jian Wang1; Binqiang Wei1; Wenqian Wu1; 1University of Nebraska-Lincoln
    Strength, plasticity and thermal stability that are highly desired for structural materials could be realized through optimizing microstructure and/or composition of materials. Crystalline materials are strengthened naturally through impeding the motion of dislocations which are generally achieved through manipulation of crystal imperfections. Tailoring the structural characters and properties of grain boundaries or reinforced units has been demonstrated to have positive effects on achieving the synergic combination of strength and plasticity. We synthesized NC Ni with the high crystallization temperature amorphous ceramic SiOC at the grain boundaries or embedded in Ni grains through magnetron co-sputtering techniques and following thermal treatments. Microstructure evolution and mechanical properties with thermal treatment, deformation temperature and strain rate have been systematically studied.

4:20 PM  Invited
Implications of Fatigue-crack Healing in Nanocrystalline Metals: Brad Boyce1; Christopher Barr1; Ta Duong1; Daniel Bufford1; Abhilash Molkeri1; Nathan Heckman1; David Adams1; Ankit Srivastava1; Khalid Hattar1; Michael Demkowicz1; 1Sandia National Laboratories
    In-situ TEM high-cycle fatigue experiments on electron transparent thin films of nanocrystalline Ni and Cu have revealed not only microstructural-sensitive crack propagation, but also unexpected microstructural-scale crack healing. Based on the experimental observations, atomistic modeling, and continuum-scale microstructural modeling, the mechanism appears to be crack flank cold welding facilitated by local compressive microstructural stresses and/or grain boundary migration. While these observations are specific to pure nanocrystalline metal thin films under a high-vacuum environment, there are potentially much broader ramifications. The existing observations can be used to help rationalize suppressed fatigue crack propagation rates in vacuum, subsurface, or under contact-inducing mixed-mode stresses; and even the precipitous decline in propagation rates near the fatigue threshold.

4:50 PM  Invited
A Perspective on Microstructural and Phase Evolution in Alloys during Extended Plastic Deformation: Pascal Bellon1; Robert Averback1; Fuzeng Ren2; Nirab Pant1; Yinon Ashkenazy3; 1University of Illinois at Urbana-Champaign; 2Southern University of Science and Technology; 3Hebrew University of Jerusalem
    Materials in service and during processing are often subjected to plastic deformation, resulting in grain refinement and forced chemical mixing. For multi-phase metallic alloys, simple geometric models and atomistic simulations suggest that there exist two distinctive regimes in these materials’ evolution during deformation. At low strains, evolutions are often dominated by the kinetic roughening of interfaces, which results from the superdiffusive transport of matter in sheared crystals. At high strains and at temperatures where thermal diffusion is sluggish, on the other hand, shearing-induced forced atomic mixing dominates these evolutions, resulting in significantly enhanced solubility. Distinguishing these two regimes is shown to provide a convenient framework for rationalizing and analyzing recent experiments and simulations on wear of layered structures in Cu-Au and Cu-Ag alloys in the low strain regime, and nonequilibrium phase co-existence and self-organization in highly immiscible or reactive alloy systems, such as Cu-Nb, in the high strain regime.

5:20 PM  
Microstructure Control in Metal Composites Processed by Equal Channel Angular Extrusion: Charles Borenstein1; Brady Butler2; James Paramore2; Robert Barber1; Zachary Levin3; Karl Hartwig1; Michael Demkowicz1; 1Texas A&M; 2US Army Research Laboratory; 3MS-16 Group, Los Alamos National Laboratory
    We investigated the microstructures achievable by equal channel angular extrusion (ECAE) of two-phase metal composites with face centered cubic (FCC) and body centered cubic (BCC) constituents, specifically tantalum and tungsten in copper-based matrices. Samples were prepared over a range of compositions by powder consolidation. A variety of extrusion sequences were explored using a novel ECAE tool capable of low speed, isothermal extrusions at up to 600C. The morphology and mechanical properties of the resulting microstructures were characterized. We will discuss the implications of our work for processing bulk multiphase composites with novel properties, with regards to potential processing parameters.