Abstract The influence of annealing on the constitutive stress-strain response of nanocrystalline (nc) CoCrFeMnNi high-entropy alloy (HEA) was investigated through a series of nanoindentation experiments using five different three-sided pyramidal indenters. The nc HEA, produced by high-pressure torsion (HPT), was subjected to annealing at 450 °C for 1 and 10 h. Microstructural analysis using transmission electron microscopy (TEM) showed that three different nano-scale precipitates (NiMn-, FeCo-, and Co-rich phases) form in the primary single-phase matrix of nc HEA after annealing. The strain-dependent plastic flow response of nc HEA pre- and post-annealing was estimated using the indentation strain and constraint factor, revealing a significant strain softening in nc HEA, which becomes pronounced after annealing. TEM analysis of the deformed material underneath the indenter suggests that the plastic deformation aids in the dissolution of the annealing-induced intermetallic precipitates, which could be the mechanism for the pronounced softening. The dissolution mechanism was rationalized by the destabilization of precipitates during plastic deformation due to the increase in interface energy.

中文翻译：

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退火对纳米晶 CoCrFeMnNi 高熵合金塑性流动的影响：纳米力学分析

摘要 通过一系列使用五种不同三棱锥压头的纳米压痕实验研究了退火对纳米晶 (nc) CoCrFeMnNi 高熵合金 (HEA) 本构应力应变响应的影响。由高压扭转 (HPT) 生产的 nc HEA 在 450°C 下退火 1 小时和 10 小时。使用透射电子显微镜 (TEM) 进行的微观结构分析表明，退火后在 nc HEA 的主要单相基体中形成了三种不同的纳米级沉淀物（NiMn-、FeCo- 和 Co-rich 相）。使用压痕应变和约束因子估计 nc HEA 退火前和退火后的应变相关塑性流动响应，揭示了 nc HEA 中显着的应变软化，这在退火后变得明显。压头下方变形材料的 TEM 分析表明，塑性变形有助于退火诱导的金属间化合物析出物的溶解，这可能是显着软化的机制。由于界面能的增加，塑性变形过程中析出物的不稳定使溶解机制合理化。