Investigation of nanotwins in the bimodal-structured Fe22Co22Ni20Cr22Mn14 alloy subjected to high-strain-rate deformation at cryogenic temperatures

Tsai Fu Chung, Pin Jung Chen, Cheng Ling Tai, Po Han Chiu, Yo Shiuan Lin, Chien Nan Hsiao, Chih Yuan Chen, Shing Hoa Wang, Jien Wei Yeh, Woei Shyan Lee, Chin Lung Kuo, Jer Ren Yang

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Cold-rolling Fe22Co22Ni20Cr22Mn14 high entropy alloy (with a deformation of 70%), and annealing it at two temperatures (1100 and 800 °C) respectively created a bimodal grain size distribution in large-grain (LG) samples having an average grain size of 45.9 ± 20.0 μm and in small-grain (SG) samples having an average grain size of 4.3 ± 3.0 μm. Under three cryogenic temperatures (−50, −100, and −150 °C), high-speed deformation (~9 × 103 s−1) was conducted on a split Hopkinson pressure bar (SHPB) system to investigate the microstructural evolution of deformation nanotwins in the bimodal-structured samples. Subjected to high-speed deformation at decreasing cryogenic temperatures, the mechanical behaviors of LG samples were superior to those of SG samples. Notably, under high-speed deformation at −150 °C, LG structures achieved excellent mechanical strength of ~3.3 GPa with good ductility of ~31.9%. Profuse lamellar annealing nanotwins, which pre-existed in the coarse grains of LG samples, promoted efficient refinement strengthening. High-resolution transmission electron microscopy (HR-TEM) clearly revealed that the deformation nanotwins induced by high-speed deformation further refined the pre-existing annealing nanotwins in the coarse grains of LG samples, presumably providing advanced mechanical sustainability for high-speed deformation at cryogenic temperatures. It is suggested that the micrometer-scaled and nanometer-scaled annealing twins appear first in the matrices of coarse grains, enhancing the initial work-hardening; subsequently the deformation nanotwins form in pre-existing annealing nanotwins and narrow strips of the matrix, effectively providing the dynamic grain refinement and the work hardening capacity.

Original languageEnglish
Article number110667
JournalMaterials Characterization
Publication statusPublished - 2020 Dec

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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