Microstructure control and ductility in Ni3Al polycrystals

Equiaxed Ni3Al polycrystals at different impurity levels were prepared via isothermal forging and ductility at ambient temperature was measured in oxygen as a function of alloy composition and impurity content. Microstructures of single phase Ni3Al with stoichiometric and off-stoichiometric compositions were controlled by dynamic recrystallization occurring during isothermal forging. Dynamically recrystallized grain size increases with increasing deformation temperature and with decreasing strain rate. Grain boundary sliding takes place between dynamically recrystallized grains with a small grain size. Binary Ni3Al polycrystals exhibit appreciable ductilities even at the stoichiometric composition. Ductility is further increased by a deviation from the stoichiometric composition to the Ni-rich compositions. Ductilities of the Ni-rich Ni3Al polycrystals are increased by zone-refining starting material in UHV. It is concluded that polycrystalline Ni3Al is intrinsically ductile and its ductility is increased at Ni-rich compositions.