We report the hot deformation induced microstructure evolution and spheroidization in ultrafine lamellar CoCrFeNiNb_0.5 and CoCrFeNiTa_0.4 eutectic high entropy alloys (EHEAs) comprising of FCC solid solution and Co₂Ta-type Laves phase up to 1123 K (0.7T_m) under compression. The CoCrFeNiNb_0.5 EHEA retained high yield strength (${\sigma }_{\text{y}}$) of 1334–1820 MPa exhibiting fracture strain (${\epsilon }_{\text{f}}$) of 5.7–12.5% at room temperature (RT)-723 K and strain hardening up to 1932–2241 MPa. Whereas, CoCrFeNiTa_0.4 EHEA exhibited strain hardening with ${\sigma }_y$ = 1403–1847 MPa and ${\epsilon }_f$ = 11.1–15.6% for the same temperature range. A gradual decrease of ${\sigma }_y$ occurred at above 973 K exhibiting strain softening without failure even at ${\epsilon }_f$ > 50%. The Kocks-Mecking plot revealed the stage-III hardening followed by an inflection pointing to the onset of dynamic recrystallization at 1023 K and 973 K for Nb_0.5 and Ta_0.4, respectively. Whereas the flow softening occurred due to the flow localization, buckling, breakdown of the lamellar colonies, and spheroidization upon hot deformation. The microstructural coarsening and lamellar instabilities involve termination migration, cylinderization, edge spheroidization and boundary splitting. The superior specific yield strength of EHEAs has been observed up to 1023 K in dry laboratory conditions than that of other HEAs and high temperature alloys.

我们报告了由 FCC 固溶体和 Co ₂ Ta 型 Laves 相组成的超细片状 CoCrFeNiNb _0.5和 CoCrFeNiTa _0.4共晶高熵合金 (EHEA ) 在压缩下高达 1123 K (0.7 T _m )的热变形引起的微观结构演变和球化。CoCrFeNiNb _0.5 EHEA 保留了高屈服强度（${\sigma }_{\text{是的}}$) 的 1334–1820 MPa 表现出断裂应变 (${\epsilon }_{\text{F}}$) 在室温 (RT)-723 K 和应变硬化高达 1932-2241 MPa 时为 5.7–12.5%。而 CoCrFeNiTa _0.4 EHEA 表现出应变硬化${\sigma }_{\mathrm{是的}}$ = 1403–1847 兆帕和 ${\epsilon }_F$ = 11.1–15.6% 对于相同的温度范围。逐渐减少${\sigma }_{\mathrm{是的}}$ 发生在 973 K 以上，即使在 ${\epsilon }_F$> 50%。Kocks-Mecking 图揭示了阶段 III 硬化，随后出现拐点，表明 Nb _0.5和 Ta _0.4分别在 1023 K 和 973 K 发生动态再结晶。而流动软化是由于流动局部化、屈曲、层状菌落的破坏和热变形时的球化而发生的。微观结构粗化和层状不稳定性涉及终端迁移、圆柱化、边缘球化和边界分裂。与其他 HEA 和高温合金相比，在干燥的实验室条件下，已观察到 EHEA 的优越比屈服强度高达 1023 K。