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.