FeMnCoCrNi高熵合金双晶微柱变形机制的分子动力学模拟

Molecular Dynamic Simulations of Deformation Mechanisms for FeMnCoCrNi High-Entropy Alloy Bicrystal Micropillars

为了揭示高熵合金中晶界对塑性变形机制的影响,利用分子动力学模拟方法研究了具有不同初始取向组合的等主元FeMnCoCrNi高熵合金双晶在单轴拉伸变形中的力学性能与变形系统演化,并揭示了晶界与拉伸方向的位向关系对高熵合金力学行为的影响。结果表明,对研究的所有双晶模型而言,位错优先在晶界处形核并向两侧的晶粒内滑移。在变形过程中,晶界发生了不同程度的宽化和弯曲。当晶界与拉伸方向垂直时,颈缩易于在晶界处发生,这导致双晶的流变应力随外加载荷增大而降低。而当晶界平行于拉伸方向时,在整个塑性变形过程中模型保持1 GPa以上的流变应力。相对于其他双晶而言,[111]与[110]取向组合的双晶流变应力波动幅度最大,同时呈现出最强的加工硬化能力。其中应力的下降归因于大量的位错发生了滑移,而高的硬化能力则是由较多的ε-马氏体、层错以及孪晶形成所致。此外,还对比了FeMnCoCrNi、FeCuCoCrNi和纯Cu 3种材料的变形行为。与Cu相比,FeMnCoCrNi和FeCuCoCrNi高熵合金中的晶格畸变使晶界更加粗糙,这使得外加载荷作用下位错易于形核,且层错能较低的FeMnCoCrNi中形成的ε-马氏体最多。

High-entropy alloys(HEAs)have attracted considerable research attention in the material field because of their outstanding mechanical properties.For metallic materials,grain boundary plays a crucial role in the mechanical behavior and plastic deformation mechanisms.To show the effect of grain boundary on deformation mechanisms in HEAs,the mechanical behavior and evolution of deformation systems in the equiatomic FeMnCoCrNi HEA bicrystals with various orientation combinations during uniaxial tension are investigated using molecular dynamic simulations,and the effect of the orientation relationship between the grain boundary and tensile direction on mechanical behavior is demonstrated.The findings reveal that for all models studied,dislocations nucleate preferentially at the grain boundary and slip into the grains on both sides.Grain boundaries are widened and curved during deformation.Necking tends to occur at the grain boundary when the grain boundary is perpendicular to the tensile direction,which decreases flow stress with increasing loading.For the model with a grain boundary parallel to the deformation direction,the model's flow stress remains at a level above 1 GPa during the whole plastic deformation.The bicrystal with a combination of[111]and[110]orientations shows the most significant fluctuation of flow stress and the highest work hardening ability compared with other models.The decrease in stress with deformation is due to the slip of numerous dislocations,while the high strain hardening ability is caused by the formation ofε-martensite,stacking faults,and twins.Furthermore,the deformation behavior of FeMnCoCrNi,FeCuCoCrNi HEAs,and pure Cu are compared.Compared with Cu,the larger lattice distortion in FeMnCoCrNi and FeCuCoCrNi HEAs makes the grain boundaries coarser,which makes dislocations easy to nucleate under loading,and the formation ofε-martensite is the most outstanding in FeMnCoCrNi HEA with a lower stacking fault energy.The results of this study can guide the design of microstructures and orientations in high-performance HEAs with micron-and nanoscaled grains.