Interdiffusion in Co-Based Co–Al–W Ternary Alloys at Elevated Temperatures

Abstract

L1₂-type Co₃(Al,W) compound is a very important phase in Co-based high temperature materials. This study investigated the interdiffusions of Co-based Co–Al–W ternary alloys at 1423, 1473 and 1523 K. Two types of diffusion couples were employed to estimate four diffusivity matrix coefficients (, , and ). A modified ternary Boltzmann-Matano method was employed for the evaluation of interdiffusion coefficients. The estimated cross-interdiffusion coefficients ( and ) had opposite signs at 1523 K which is not contradictory to but rather consistent with the Onsager’s reciprocity theorem. The second derivative of the Gibbs free energy with respect to the Al concentration, (), may have a sign opposite to that of W concentration, (). Experimental results revealed that the effect of W on the Al diffusion flux is greater than that of Al on the diffusion flux of W by about one order of magnitude.