Ternary diffusion and thermodynamic interaction in the β solid solutions of Ti-Al-Fe alloys at 1423 K

The binary interdiffusion coefficients (D) over tilde ((Ti-Fe)) in beta Ti-Fe alloy and (D) over tilde ((Ti-Al)) in beta Ti-Al alloy, Fe impurity diffusion coefficients D-Fe(Ti-Al)(*) in beta Ti-Al alloys, and ternary interdiffusion coefficients (D) over tilde (Ti)((AlAl)), (D) over tilde (Ti)((FeFe)), (D) over tilde (Ti)((AlFe)) and (D) over tilde (Ti)((FeAl)) in Ti-rich beta Ti-Al-Fe alloys were determined at 1423 K using binary and ternary diffusion couples by ordinary and extended Matano methods and Hall's one. The (D) over tilde ((Ti-Al)) values increase with Al concentration, and the (D) over tilde ((Ti-Fe)) values show almost no concentration dependence. The D-Fe(Ti-Al)(*) values in beta Ti-Al alloys steeply decrease with Al concentration up to 7 at.%Al and become almost constant over about 7 at.%Al. In the ternary beta Ti-Al-Fe alloys, the (D) over tilde (Ti)((AlAl)), (D) over tilde (Ti)((FeFe)), (D) over tilde (Ti)((AlFe)) and (D) over tilde (Ti)((FeAl)) values are positive, and the (D) over tilde (Ti)((FeFe)) and (D) over tilde (Ti)((FeAl)) values are larger than the (D) over tilde (Ti)((AlAl)) and (D) over tilde (Ti)((AlFe)) ones, respectively. They show the complicated dependence on concentrations of Al and Fe elements. The positive ratios of (D) over tilde (Ti)((FeAl))/(D) over tilde (Ti)((FeFe)), and (D) over tilde (Ti)((AlFe))/(D) over tilde (Ti)((AlAl)), indicate that the repulsive interactions exist between Al and Fe atoms in the ternary alloys, but the negative ratios of converted interdiffusion coefficients (D) over tilde (Al)((FeTi))/(D) over tilde (Al)((FeFe)) show the attractive interactions between Ti and Al and between Ti and Fe atoms in this alloy. These diffusion coefficients and data suggest that Al diffusion occur by vacancy diffusion mechanisms and Fe diffusion takes place by some kind of interstitial diffusion mechanism in beta Ti-Al-Fe alloys. (C) 2012 Elsevier B.V. All rights reserved.