superdislocation mobility with different character angles in Ni3Al

Abstract

The glide of <110>/{111} superdislocations in Ni3Al becomes prevalent in tertiary creep and take a dominant role in influencing the creep resistance of Ni-based single crystal superalloys at the tertiary stage. Here we carried out atomistic simulations to investigate the mobility law of screw, 30° mixed, 60° mixed and edge <110> superdislocations in Ni3Al. Based on the Peierls-Nabarro model, we found that the distance of the dissociated anti-phase boundary (APB) and complex stacking fault (CSF) of <110> superdislocations increases with increasing the character angle (from screw to edge), keeping a good accordance with the analysis by anisotropic elastic theory. We further study the motion of the superdislocations at temperatures ranging from 300 K to 1000 K. The dislocation mobility is distinct to its character angle, i.e., the edge-like (30° and 90°) superdislocations have a higher speed than the screw-like (0° and 60°) superdislocations. For all types of superdislocations, the drag coefficient increases linearly with increasing temperature in the phonon-drag regime, while behaves to be independent on temperature in the asymptotic regime. Finally, we explored the origin of mobility disparity between the edge-like and screw-like superdislocations in terms of energy landscape for the dislocation glide. We observed that the two 1/2<110> dissociated superpartials move coordinately in edge-like superdislocations with no variation of APB ribbon width. However, the motion of two superpartials are uncorrelated in screw-like superdislocations with the expansion and reduction of APB, resulting in a relatively higher Peierls barrier. Our present work could help to understand the creep failure in Ni-based single crystal superalloys.