Dynamic shock response of high-entropy alloy with elemental anomaly distribution

Abstract

Elemental inhomogeneities formed during the actual preparation or heat treatment of high entropy alloys (HEAs) have a profound effect on the mechanical properties of HEAs. In this work, molecular dynamics (MD) was used to simulate the plastic response of CoCrFeNiMn HEAs with Mn element as the concentration fluctuation variable under shock loading. The results show that the unique physical shock properties, including shock wave propagation, dislocation evolution, defect collapse, and energy dissipation, are related to the anomaly arrangement of Mn elements. Compared to the uniform distribution of Mn elements, the gradient distribution of Mn leads to lattice mismatch between heterogeneous tissues, increasing the energy barriers of the dislocation mediated slip and reducing the probability of generating disordered atoms (from 27.9 to 11.5%), which results in anomalous shock strength in the Hugoniot elastic limit (HEL) (from 69.1 Gpa to about 72.9 Gpa). As the main product of shock energy conversion, energy dissipation is subjected to the complex interaction between the shock compression and the reflection unloading, and the gradient distribution of Mn element can significantly reduce the efficiency of shock energy conversion due to dislocation activity and crystal phase changes caused by lattice mismatch. Finally, when defective structures are introduced, the gradient dislocation nucleation and energy conversion fluctuations of the microstructure were observed during shock loading. This work can provide a new perspective for further understanding the influence of solid solutions with non-uniform element distribution on the plastic deformation mechanism of high entropy alloys subjected to extreme dynamic shock.