Ultrafine-grained and Heterostructured Materials (UFGH XII): Fundamentals in Mechanical Behavior and Radiation Effects I
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 8:30 AM
February 28, 2022
Room: 262A
Location: Anaheim Convention Center

Session Chair: Ting Zhu, Georgia Institute of Technology.; Francesco Maresca, University of Groningen; Xialong Ma, Pacific Northwest National Laboratory

8:30 AM  Invited
Non-equilibrium Evolution of Metastable Grain Boundaries in Nanocrystals at Extreme Conditions: Zhitong Bai1; Yue Fan1; 1University of Michigan
    In ultrafine-grained materials and under non-equilibrium processing conditions, GBs are rarely in ground states and would instead present a multiplicity of microscopic metastable states, endowing the system with enhanced tunability. For example, recent experiments show nanocrystals can be rejuvenated by femtosecond laser and their hardness can be effectively controlled. However, a mechanistic understanding on metastable GBs’ evolution remains unclear. Here we investigate a variety of metastable GBs under fast driving conditions using atomistic simulations. Assisted with data-mining algorithm to analyze the annealing behavior of GBs at various conditions, we construct a high-fidelity energetic evolution map, showing that it can be divided into an ageing regime and a rejuvenating regime over the energy—temperature space. The ageing/rejuvenating stems from the energy imbalance during the interchanges between metastable states, and a kinetic equation is subsequently derived. The predicted energetic evolution and its implication on metastable GBs’ mechanical performance are consistent with experiments.

9:00 AM  Invited
NOW ON-DEMAND ONLY - Predicting the Transformation Strain that Controls Ductility and Toughness in Advanced Steels: Francesco Maresca1; Efthymios Polatidis2; Miroslav Smid2; Helena Van Swygenhoven2; William Curtin3; 1University of Groningen; 2PSI; 3EPFL
    Nanoscale metastable austenite can be essential for obtaining improved mechanical properties such as ductility, toughness and fatigue resistance of steels. Predicting the martensitic transformation is essential to assess TRIP and guide the design of better-performing alloys. Here, we combine HR-DIC, EBSD, neutron diffraction and TEM with a new, predictive theory of martensite crystallography to determine the full 3D transformation strain in situ (“shape deformation”) in a model Fe-20.2Ni-5.4Mn (wt%) alloy. By accounting for the contribution of the crystallographic slip, the crystallographic theory predicts within experimental accuracy the in-plane strain measurements at multiple regions and strain levels. This combined experimental-theoretical analysis reveals for the first time the full, 3D transformation strain, associated with the austenite-martensite transformation in Fe-Ni-Mn. The theory can then be used to predict new, tougher alloys. This strain is also a crucial input for micromechanics, crystal plasticity simulation of multi-phase steels and to assess their plasticity and toughness.

9:30 AM  Invited
NOW ON-DEMAND ONLY - On the Role of Gradients on Strengthening, Ductility, and Size Effects: Elias Aifantis1; 1Emeritus, Aristotle University, Thessaloniki 54124, GR; Emeritus, Michigan Technological University; Mercator Fellow, Friedrich – Alexander University, Erlangen – Nuremberg 90762, DE
     In recent years, various models of gradient elasticity, gradient plasticity and gradient dislocation dynamics have been advanced to model phenomena and experimental observations not captured by classical local theories for nearly homogeneous materials and configurations. A unifying procedure based on the introduction of the Laplacian and bi-Laplacian operators in classical continuum mechanics and metal physics theories is proposed herein. It is also shown that fractional/fractal and stochastic effects can be easily incorporated in the proposed methodology. Specific examples on nanograin heterogeneous materials and components are discussed and comparisons with related experiments are made. [References: E.C. Aifantis, Gradient Extension of Classical Material Models: From Nuclear & Condensed Matter Scales to Earth & Cosmological Scales, In: E. Ghavanloo et al (eds), Size-Dependent Continuum Mechanics Approaches, Springer Tracts in Mechanical Engineering, Springer, 417-452, 2021; E.C. Aifantis, Material mechanics & Hussein Zbib: A Tribute to his memory, J. Engng. Mater. Technol., accepted, 2021.]

10:00 AM Break

10:20 AM  
Deformation Mechanism of Ultrafine-grained FeCrAl Alloy – An In Situ Micropillar Compression Strain Rate Jump Study: Tianyi Sun1; Jaehun Cho1; Zhongxia Shang1; Tongjun Niu1; Jie Ding1; Dongyue Xie2; Jian Wang2; Haiyan Wang1; Xinghang Zhang1; 1Purdue University, School of Materials Engineering; 2University of Nebraska-Lincoln
    FeCrAl alloy is one of the promising candidates for cladding materials in advanced nuclear reactors. In this study, a model FeCrAl alloy, C35M, was processed by surface mechanical grinding treatment. In situ micropillar compression tests revealed high flow stresses exceeding 1.44 GPa of the UFG FeCrAl alloy, and excellent work hardening ability at room temperature. In situ micropillar compression strain rate jump tests probed the underlying deformation mechanisms of UFG FeCrAl alloys at intermediate temperatures (T ~ 0.23 Tm). The activation energy for the dominant deformation mechanism was estimated considering the presence of a threshold stress, which suggests a grain boundary-diffusion-controlled deformation mechanism.