Molecular dynamics simulation of twin nucleation and growth in Ni-based superalloys

Micro-twinning is the major creep deformation mechanism in most Ni-based superalloys at temperatures above 700 degrees C. Nevertheless, many aspects of twin nucleation and growth remain unexplored. The Kolbe mechanism for micro-twinning is currently widely accepted in the community to explain these processes, based on post mortem TEM characterization and indirect theoretical estimations. However, this does not mean that other mechanisms cannot contribute to creep. Molecular dynamics (MD) simulations offer an alternative possibility to probe different creep mechanisms. In this work, we use MD simulations to demonstrate that a qualitatively different mechanism for nucleation and growth of twins can be competitive with the Kolbe mechanism in the intermediate temperature regime of 600 degrees C-800 degrees C. The proposed mechanism is closely related to the formation mechanism of super intrinsic stacking faults (SISFs) originally introduced by Condat and Decamps in 1987.