Interdiffusion in FCC Co-Al-Ti Ternary Alloys

Abstract

Interdiffusion in the FCC phase of the Co-Al-Ti ternary system was investigated at 1373 and 1473 K by analyzing diffusion-couples composed of appropriate pairs of terminal alloys. From the concentration profiles acquired by electron probe microanalysis and thereafter represented by error function expansion, the ternary interdiffusion coefficients were extracted by using the Whittle-Green method whereas the impurity coefficients, i.e. Al diffusion in the Co-Ti binary alloys and Ti in Co-Al, were determined by the generalized Hall method. For all concentrations, the ternary main interdiffusion coefficients $$\tilde{D}_{\text{AlAl}}^{\text{Co}}$$ , $$\tilde{D}_{\text{TiTi}}^{\text{Co}}$$ and the cross coefficients $$\tilde{D}_{\text{TiAl}}^{\text{Co}}$$ were found to increase with its own concentrations, whereas the cross term $$\tilde{D}_{\text{AlTi}}^{\text{Co}}$$ varies only slightly with Al. The values of the impurity diffusion coefficients D Al(Co-Ti) * and D Ti(Co-Al) * increase with increasing the Ti and Al concentrations respectively at 1373 K while they are less dependent on concentrations at 1473 K.