Influences of grain size, temperature, and strain rate on mechanical properties of Al0.3CoCrFeNi high–entropy alloys

Abstract

This study investigates the mechanical properties and deformation behaviours of Al0.3CoCrFeNi high-entropy alloys (HEA) under tension tests by using molecular dynamics (MD) simulations. The effect of different grain sizes (d), temperatures, and strain rates are examined. By varying the grain size from 4.0 nm to 20.0 nm, the shift from mechanical softening to strengthening was observed for the simulated samples. The result shows that the critical grain size of the inverse Hall – Petch and Hall – Petch regime is 12.0 nm. The average flow stress varies slightly increases from 3.02 to 3.19 GPa (5.3%) with the decrease of grain size from 20.0 to 12.0 nm in the Hall – Petch relation. While in the inverse Hall – Petch regime, the average flow stress significantly reduces from 3.19 to 2.7 GPa (15.3%) with grain size reducing from 12.0 to 4.0 nm. The migration of grain boundary (GB), and the rotation of grains are the dominant deformation mechanism in the inverse Hall – Petch regime. Meanwhile, in the Hall-Petch region, the dislocation activities are the main contribution to the deformation mechanism of polycrystalline. The GB plays as a barrier to hinder the dislocation propagation. Therefore, in the Hall - Petch regime, the fraction of GB increases as the grain size decreases, resulting in higher barrier densities for samples with small grain sizes and thereby causing the flow stress to increase. The result points out that Young's modulus of the HEA specimen increased with an increase of the average d. In addition, the result also shows that the ultimate stress, flow stress, and Young's modulus increase with rising the strain rate or decreasing the temperature.