Examination of Ni-base superalloy diffusion couples containing multiphase regions

Four Ni-base superalloy diffusion couples with multiphase regions were studied. The diffusion couples contained single-phase (γ), two-phase (γ + MC carbide) and three-phase (γ + γ′ + MC carbide) regions. Measured average composition profiles were in good agreement with the diffusion simulation predictions. The measured and predicted γ′ phase fraction profiles showed similar trends; however, there were some discrepancies in the predicted position of the γ + γ′ + MC/γ + MC boundary. Phase fraction profiles and optical metallography were used to determine the type and direction of the moving phase region boundaries.