Ultrafine-grained and Heterostructured Materials (UFGH XII): Microstructure, Mechanisms & Property I
Sponsored by: TMS: Shaping and Forming Committee
Program Organizers: Penghui Cao, University of California, Irvine; Xiaoxu Huang, Chongqing University; Enrique Lavernia, Texas A&M University; 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

Tuesday 8:00 AM
March 1, 2022
Room: 262A
Location: Anaheim Convention Center

Session Chair: Yuntian Zhu, City University of Hong Kong; Xiaolei Wu, Institute of Mechanics, Chinese Academy; Hao Zhou, Nanjing University of Science and Technology

8:00 AM  
Strain Hardening and Ductility by Grain Refinement-induced Plasticity in Multi-level Hetero-structured Brass: Xiaolei Wu1; 1Chinese Academy of Sciences
    Grain refinement in metals has dual effects of strengthening and strain hardening, but it seldom occurs during tensile deformation. Here we report a dynamic grain refinement induced plasticity and strain hardening during tensile deformation in a Cu-30% Zn (wt percent) alloy processed by cold rolling followed by recrystallization annealing. The initial heterogeneous tri-modal grain structure was designed on purpose from high to low including micrometer-, ultrafine-, and nano-grains. To be specific, nano-grains are mostly corner twins located at grain boundaries and triple junctions of ultrafine-grains. Upon tensile straining, the successive generation of corner twins which later evolves into nano-grains causes the dynamically reinforced grain refinement-induced plasticity (GRIP) effect to produce a superior strength and ductility synergy especially at the high strength level, making an inversed strength-and-ductility banana relationship.

8:20 AM  
Ultra-high Strength and Ductility of a Multiple Component Alloy with a Heterogeneous Microstructure of Grains and Precipitates: Weitong Wang1; Shengyun Yuan1; Yong Zhang1; 1Nanjing University of Science and Technology
    In the present study, a heterogeneous microstructure characterized by a mixture of nano-grains and ultrafine-grains embedded with γ’ precipitates is fabricated by cold rolling a coarse-grained Ni-Co-Cr alloy and subsequent thermal annealing. The sample with heterogeneous microstructure exhibits simultaneously higher strength and larger uniform elongation compared with the original alloy without cold rolling. Electron backscatter diffraction, transmission electron microscopy, energy dispersive X-Ray spectroscopy, and atom probe tomography are performed to investigate the microstructural evolution of the heterogeneous structure tensile loaded to various strains, with an emphasis on the evolution of defects around the interface between nano-grains and ultrafine-grains. With a thorough comparison with the original coarse-grained sample on the deformation mechanisms, the effect of the complexity of the heterogenous microstructure on the evolution of dislocation density and deformation mechanism is illustrated, which serves to reveal the mechanisms responsible the work hardening and ductility.

8:40 AM  
Microstructural Evolution and Tensile Properties of Nano-crystalline Twinning Induced Plasticity Steel Produced by High-pressure Torsion: Gyeonghyeon Jang1; Jae Nam Kim1; Hakhyeon Lee1; Taekyung Lee2; Nariman Enikeev3; Marina Abramova3; Ruslan Z Valiev3; Hyoung Seop Kim1; Chong Soo Lee1; 1Pohang University of Science & Technology; 2Pusan National University; 3Ufa State Aviation Technical University
    In this study, microstructural evolution and tensile properties of nanocrystalline (NC) twinning induced plasticity steel (TWIP) steel were investigated. Increasing high-pressure torsion revolutions resulted in the grain refinement: after 10 revolutions, the initial fine (10 μm) and coarse (100 μm) grained materials were refined to the average grain sizes of 21 and 51 nm, respectively. Tensile strength was increased with decreasing grain size. However, the initial fine grained material exhibited the inverse Hall-Petch effect in the regime of nano-size grain; the maximal grain refinement after 10 revolutions resulted in the reduction of the tensile strength by 350 MPa as compared to the state achieved by 5 revolutions. TEM observation on the finest (21 nm) grained specimen showed that the softening was closely associated with the absence of deformation twins and the formation of numerous stacking faults.