Ultrafine-grained and Heterostructured Materials (UFGH XII): Poster Session 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 5:30 PM
February 28, 2022
Room: Exhibit Hall C
Location: Anaheim Convention Center


H-25: Microstructure Evolution Kinetics and Strengthening Mechanisms of the Partially Recrystallized High Entropy Alloys: Feng He1; Zhongsheng Yang1; Zhijun Wang1; 1State Key Laboratory of Solidification Processing
    Recrystallization has been a major method to induce heterogeneous grain structure for improving the strength-ductility combination of single phase high entropy alloys (HEAs). However, the recrystallization kinetics of single phase HEAs, which are the guideline for controlling the recrystallization behavior, are still lack of attention. How the partially recrystallized structure affects the mechanical response also remains less explored. Here, we uncovered the recrystallization behaviors of typical Ni-Co-Cr-Fe HEAs. NiCoCrFe and Ni2CoCrFe exhibit almost similar recrystallization activation energy around 230 kJ·mol-1, but distinctively different recrystallization kinetics. Such difference in recrystallization behavior results in distinct mesoscale structures, leading to different mechanical resonpse.

H-26: New Strategies for the Control, Study, and Scale-up of Surface Nanocrystallization: Samuel Scott1; Mark Atwater1; 1Liberty University
    Despite their strength-ductility benefits, heterogeneously nanostructured materials are difficult to manufacture and implement at industrial scale. To realize their benefits in a processing-friendly manner, surface mechanical attrition treatment (SMAT) can be used to produce surface nanocrystallization on bulk parts through repeated impacts leading to cumulative deformation and microstructural refinement. This results in a gradient of grain size for improved strength and fatigue resistance. In most SMAT approaches, the randomness of surface treatment prevents the direct, quantitative study and control of individual impacts needed to directly connect processing variables with surface geometry and nanoscale grain development. This project utilizes surface impact with controlled energy and position to study the fundamentals of impact-induced microstructural phenomena in samples with both single impact sites and precisely patterned impact arrays. These methods provide new approaches to research heterogeneous materials and are directly scalable for industrial implementation. Both aspects and preliminary findings will be discussed.

H-27: Structural Evolution during Nanostructuring of Additive-manufactured 316L Stainless Steel by High-pressure Torsion: Isshu Lee1; Jae-Kyung Han1; Xiaojing Liu2; Yulia Kuzminova3; Stanislav Evlashin3; Klaus-Dieter Liss2; Megumi Kawasaki1; 1Oregon State University; 2Guangdong Technion - Israel Institute of Technology; 3Skolkovo Institute of Science and Technology
    This study investigates the significance of post-printing nanostructuring on structural evolution in an additive-manufactured 316L stainless steel through high-pressure torsion (HPT) at 6 GPa. A limited formation of an ε-martensite phase is observed in the nanostructured austenitic steel with an average grain size of 60 nm after 8-15 HPT turns. X-ray diffraction reveals significant structural changes by decreasing crystallite sizes and increasing micro-strains and lattice parameters even after 1/2 HPT turn. Significant strain gradients exist between the close-packed planes and out-of-close-packed-planes in the nanostructured steel, while such strain gradient was not observed in the as-printed sample. These drastic changes in structure are attributed to severe lattice distortion by the excess of dislocations and defects introduced during nanostructuring.