Interdiffusion within the β-phase region of the Ni-Co-Cr-Al quaternary system

Interdiffusion coefficients within the β-phase region of the nickel-cobalt-chromium-aluminum (Ni-Co-Cr-Al) quaternary system were estimated by square root diffusivity analysis. The obtained results indicated that the cross interdiffusion coefficients D_ij (i ≠ j, i, j = Al, Cr, Co) other than D_AlCo were less than the main interdiffusion coefficients D_ij (i = j), and that the values of D_Ali were greater than those of D_Cri and D_Coi. This finding suggests that the addition of chromium decreases the interdiffusion coefficients of aluminum and cobalt, but the addition of cobalt did not cause an obvious change in the interdiffusion coefficients of aluminum and chromium in the β-phase region. The different effects associated with the additions of chromium and cobalt were qualitatively discussed in light of the relationship between the thermodynamic properties of the system and Wagner's interaction parameter. The results revealed that the different effects could be ascribed to the stronger thermodynamic interactions between aluminum and cobalt compared to that between aluminum and chromium.