Diffusion Research in BCC Ti-Al-Zr Ternary Alloys

Abstract

Diffusion behavior in the BCC Ti-Al-Zr ternary alloys was experimentally investigated at 1273 K (1000 °C) and 1473 K (1200 °C) by means of the diffusion-couple technique. Upon the Whittle-Green and generalized Hall methods, the inter- and impurity diffusion coefficients were respectively extracted from the composition profiles acquired by the electron microprobe analysis (EPMA) and subsequently represented by the error function expansion. The extracted main interdiffusion coefficient $\tilde{D}_{\text{AlAl}}^{\text{Ti}}$ increases with increasing the content of either Al or Zr, and the increase is appearing more considerably at the higher temperature. However, $\tilde{D}_{\text{ZrZr}}^{\text{Ti}}$ was noticed to decrease with the increase of Al and Zr contents at 1273 K (1000 °C) while there is an upward trend at 1473 K (1200 °C). The impurity diffusion coefficients of Al in Ti-Zr binary alloys, $D_{{{\text{Al}}\left( {\text{Ti - Zr}} \right)}}^{*}$, and of Zr in Ti-Al binary alloys, $D_{{{\text{Zr}}\left( {\text{Ti - Al}} \right)}}^{*}$, increase with increasing the Zr and Al contents respectively. A comparison of average main interdiffusion coefficient $\overline{{\tilde{D}_{\text{XX}}^{\text{Ti}} }}$ made among ten Ti-Al-X ternary systems suggests that the Zr diffusion is most comparable to Cr and could operate via a vacancy-controlled mechanism.