Interdiffusion in CMSX-4 Related Ni-Base Alloy System at a Supersolvus Temperature

Interdiffusion in Ni-base superalloy CMSX-4 and alloys related to CMSX-4 was investigated at the temperature 1288 °C, which is 8 °C above the γ’-solvus temperature of this superalloy, 1280 °C. This temperature is of a special interest because it is a temperature of hot isostatic pressing applied to CMSX-4 and modeling of this process needs verified diffusion data for this specific temperature. Various diffusion couples were assembled from the investigated alloys, annealed at 1288 °C and studied by electron probe microanalysis. So far as the annealing temperature was higher than the γ’-solvus temperature of CMSX-4 and other investigated alloys have no strengthening γ’-phase, interdiffusion occurred in the fcc solid solutions of nickel. It was found that in the case when the γ’-forming and γ-stabilizing elements diffuse in the same direction (towards nickel) the diffusion rate accelerates, but when they diffuse in the opposite directions (counter diffusion) it slows down. Such an interdiffusion behavior is in agreement with the results predicted with diffusion simulation software Dictra.