A general micromechanics-based model for precipitate strengthening and fracture toughness in polycrystal high entropy alloys

Abstract

High-entropy alloys (HEAs) usually exhibit exceptional mechanical properties attributed to one of important core effects for serious lattice strain to impede dislocation motion compared to the traditional alloys. However, their roles on the quantitative measurement for precipitate strengthening and fracture toughness are lack using the existing physical model. Here, we propose a mechanistic modelling to study effect of heterogeneous strain caused by lattice distortion on the precipitate strengthening and fracture toughness in the HEAs, and then verify this role using atomic simulation. The results indicate that the lattice distortion and precipitate synergistically impede the grain boundary migration, increasing the strength. In the dilute alloy with a low lattice distortion, the grain boundary migration process is less sensitive to the precipitate size. The stress field generated by the lattice distortion relieves the stress concentration at the crack tip under external force. This in turn alleviates the accumulation of dislocations and reduces the probability of crack extension. Furthermore, the heterogeneous strain caused by lattice distortion counteracts some of the applied stress and raises the critical stress for crack extension, which enhances the plasticity and the critical stress intensity factor. The developed unified model would be applicable to high entropy ceramics in similar scenario.