Investigation on the Tension-Compression Asymmetry of CoCrFeNiAl High-Entropy Alloy Under the Influence of Twinning Boundary Spacing

Molecular dynamics (MD) simulation was employed to test the tension and compression of CoCrFeNiAl high-entropy alloy (HEA) at a strain rate of 109 s-1 in order to examine the development mechanism of tension-compression asymmetry in the HEA as well as the mechanism of its own mechanical characteristics. Molecular dynamics study shows that there is a very obvious tension-compression asymmetry in HEA, and that the HEA in the compressed state has a higher flow stress than that in the stretched state. This phenomenon can be explained by the limitation of grain boundary sliding and the stimulation of dislocation nucleation. In the set simulation unit, when twinning boundary spacing (TBS) is 3.66 nm, the tension-compression asymmetry has a critical minimum. The interaction of the free surface and dislocation activity under different twinning boundary spacing can account for the observed terminations. This is due to the fact that, as the TBS gradually increases, the intragranular deformation mechanism of HEAs switches from partial dislocation nucleation and dislocation crossing and sliding along twin grain boundaries to partial dislocation nucleation and dislocation sliding parallel to the grain boundaries.