In-situ electrical resistivity measurements for determining formation kinetics of gamma' phase in nickel-based wrought superalloys

Formation kinetics of γ′ (Ni₃Al) phase in Ni-based wrought superalloys were investigated using the indirect measurement method of electrical resistivity change during isothermal holding. It was found that formation of γ′ phase occurs in a very short time (as a function of temperature and alloying level) by a diffusion controlled nucleation mechanism. Al alone enhances the formation of γ′ nuclei in the alloy and enlarges their quantity. On the other hand, addition of Ti or Ta causes delay in nucleation. Any other alloying addition (e.g. Co or W) delays the primary stage of nucleation. Ta was found to be more substantial than Ti in increasing nucleation rate and volume fraction of the γ′ phase.