Role of Lattice Resistance in the Shock Dynamics of Fcc-Structured High Entropy Alloy

The shock response of high entropy alloys (HEAs) would be important for their performance under extreme conditions. However, it is still difficult to obtain the shock response data at the atomic scale over the wide range of loading conditions. Here, the shock compression response of fcc-structured modeled HEAs and pure metals with different degrees of lattice resistance and stacking fault energy has been studied using the molecular dynamics simulations in the terms of the Hugoniot stress, atomic structure, and dislocation density. The results show that the HEA with low lattice resistance exhibits a significantly low shock compression strength in comparison with pure metal. In contrast to pure metal, Shockley partial dislocations and stacking faults with high density were found in HEA with low lattice resistance. Interestingly, during the shock wave propagation in HEA with high lattice resistance to dislocation glide, the crystalline to amorphous phase transformation has been observed to occur behind the shock front. The high lattice resistance slows down the movement of dislocations in HEA, and then promotes the amorphization process. This trend gives an effective toughening mechanism in shock loading of HEAs. In addition, the microstructure-based physical model suggests the obvious effect of lattice resistance on the working hardening of the HEAs after shock compression. It indicates that the lattice resistance of intrinsic chemically disordered structures dominates the rate of dislocation generation and the shock compression strength. The current study provides an important atomic insight for understanding the dynamic mechanical behaviors of HEAs.