Formation of voids and dislocation loops in near-stoichiometric nial by aging at 700° to 900°c, and some effects on alloy properties

Abstract

Dislocation loops and voids form spontaneously in stoichiometric NiAl annealed between 700° to 900°C. The former probably are formed by a punching mechanism from impurity particles, and the latter are frequently seen to have nucleated on particles. However, it is possible that both loops and voids are nucleated by vacancy/impurity complexes. Some of the loops act as dislocation sources during plastic deformation so that, for example, NiAl annealed at 700° to 900°C is softer and has greater ductility at room temperature, or has poorer creep resistance at higher temperatures, than material annealed at 1300°C. It is probable that small precipitate particles, possibly carbides and/or aluminum oxide form at 700° to 900°C but are in solution at higher temperatures. Their effect on mechanical properties is a form of precipitation softening.