A comprehensive investigation of shock-induced deformation and spallation mechanisms in nanocrystalline CoCrNi medium-entropy alloys (MEAs) is conducted by large-scale molecular dynamics simulations, encompassing both gradient and homogeneous nanocrystalline structures. Under the shock velocity ranging from 0.2 km/s to 1 km/s, the effects of grain heterogeneity on shock wave propagation, spallation and defect evolution are examined. An inverse Hall–Petch relationship, where the Hugoniot elastic limit (HEL) increases with larger grain sizes is observed within the grain size range of 3 to 12 nm for homogeneous nanocrystalline samples. Compared to the localized strain distribution either within grain interior (GI) or at grain boundaries (GB) in homogeneous nanocrystalline structures, gradient-grained counterparts exhibit compatible deformation along shock direction, which coordinates the load partitioning between GB and GI. As a result, lower densities of dislocation and stacking fault are triggered within the GI, while shear localization is mitigated at GB, leading to higher spall strength observed in the gradient nanocrystalline MEA samples at the same shock velocity. The results shed light on the insights of deformation and spallation mechanisms in gradient-grained MEAs under dynamic loading, which may open up a new avenue for the design of advanced structural MEAs with high strength and toughness.

中文翻译：

---

梯度纳米晶CoCrNi中熵合金的冲击响应


通过大规模分子动力学模拟，对纳米晶 CoCrNi 中熵合金 (MEA) 中冲击引起的变形和散裂机制进行了全面研究，涵盖梯度和均质纳米晶结构。在0.2 km/s至1 km/s的冲击速度范围内，研究了颗粒不均匀性对冲击波传播、散裂和缺陷演化的影响。对于均质纳米晶样品，在 3 至 12 nm 的晶粒尺寸范围内观察到逆 Hall-Petch 关系，其中 Hugoniot 弹性极限 (HEL) 随着晶粒尺寸的增大而增加。与均匀纳米晶体结构中晶粒内部 (GI) 或晶界 (GB) 内的局部应变分布相比，梯度晶粒对应物表现出沿冲击方向的兼容变形，这协调了 GB 和 GI 之间的载荷分配。因此，在 GI 内触发较低密度的位错和堆垛层错，同时在 GB 处减轻剪切局部化，从而导致在相同冲击速度下在梯度纳米晶 MEA 样品中观察到更高的剥落强度。研究结果揭示了动态加载下梯度晶粒 MEA 的变形和散裂机制，这可能为高强度和韧性的先进结构 MEA 的设计开辟新途径。