Abstract 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.

中文翻译：

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低温下高应变率变形双峰结构 Fe22Co22Ni20Cr22Mn14 合金中纳米孪晶的研究

摘要 冷轧 Fe22Co22Ni20Cr22Mn14 高熵合金（变形率为 70%），并分别在两个温度（1100 和 800 °C）下退火，在具有平均晶粒尺寸的大晶粒 (LG) 样品中产生双峰晶粒尺寸分布45.9 ± 20.0 μm 和平均晶粒尺寸为 4.3 ± 3.0 μm 的小晶粒 (SG) 样品。在三个低温（-50、-100 和-150 °C）下，高速变形（~9 × 103 s-1）在分裂式霍普金森压力棒（SHPB）系统上进行，以研究变形的微观结构演变双峰结构样品中的纳米孪晶。在低温下高速变形后，LG 样品的机械性能优于 SG 样品。值得注意的是，在-150°C的高速变形下，LG 结构实现了~3.3 GPa 的优异机械强度和~31.9% 的良好延展性。大量层状退火纳米孪晶预先存在于 LG 样品的粗晶粒中，促进了有效的细化强化。高分辨率透射电子显微镜 (HR-TEM) 清楚地表明，由高速变形引起的变形纳米孪晶进一步细化了 LG 样品粗晶粒中预先存在的退火纳米孪晶，大概为高速变形提供了先进的机械可持续性低温。建议微米级和纳米级退火孪晶首先出现在粗晶基体中，增强了初始加工硬化；随后变形纳米孪晶在预先存在的退火纳米孪晶和基体的窄条中形成，