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

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 of epsilon-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 of e-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.