A study was made of the atomic mechanism of the initiation of motion of a static twin plane under applied mechanical load in a model shape-memory material. By tracking the deformation under load and using linear stability analysis, it was found that the eigenvalues of the Hessian matrix provided an indicator of the initiation of motion of the twin plane. The initiation of motion was signalled by a linear instability and a drop in the lowest eigenvalue to zero as well as a sharp drop in higher eigenvalues. Additionally, by comparing with direct molecular dynamics, it was seen that the eigenmode associated with the zero eigenvalue accurately predicted the initial mode of motion. It was also found that the initial motion occurred via the formation of a stacking fault just ahead of the existing twin plane and that broadening of the stacking fault drove further transformation.

Linear Instability Signals the Initiation of Motion of a Twin Plane Under Load. C.T.Lu, K.Dayal: Philosophical Magazine Letters, 2011, 91[4], 264-71