Understanding the yield behaviour of L12-ordered alloys

Nickel superalloys exhibit a remarkable characteristic. Their yield stress that required to cause the onset of plastic deformation increases with temperature. This typically occurs up to a temperature of around 800 degrees C. This effect is thought to originate from the precipitates of the microstructure, which have an L1(2)-ordered crystal structure. A number of other L1(2)-based alloys exhibit similar yield properties. It is generally accepted that this is caused by the exhaustion of dislocations by cross-slip from {111} glide planes to {010} planes on which they are sessile. However, the underlying mechanisms that control this cross-slipping process are yet to be fully understood, with little consistency between empirical results and theory. A critical review of the various theories surrounding nickel superalloys is offered.