Dynamic recrystallisation and microstructural evolution in Ni 3 Al

Abstract

The mechanical behaviour and microstructural evolution during high temperature compression were investigated in pure nickel and boron doped Ni₃Al. Flow behaviour and microstructural development indicate the occurrence of dynamic recrystallisation. In Ni₃Al the recrystallised microstructure is a typical ‘necklace’ structure at low deformation temperatures, but a uniformly recrystallised structure at high deformation temperatures. Pure nickel revealed a uniform structure at all temperatures. The dislocation arrangement of the deformed structure in Ni₃Al showed a tendency to cell formation, although dislocation free cells were seldom observed. Locally, the formation of ordered dislocation networks was evident. The nuclei of dynamically recrystallised grains were always found at or close to prior grain boundaries, but the dislocation arrangement suggests that nucleation does not necessarily occur by bulging of grain boundaries. The relationships between flow behaviour, recrystallisation kinetics, and grain size have been analysed according to standard concepts and reveal substantial differences between nickel and Ni₃Al. The results indicate that there may be a transition from dislocation glide to superplastic flow at high temperatures.

MST/1282