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

摘要

The binary interdiffusion coefficients D_(Ti-Fe) in p Ti-Fe alloy and D_(Ti-Al) in β Ti-Al alloy, Fe impurity diffusion coefficients D*_(Fe(Ti-Al)) in β Ti-Al alloys, and ternary interdiffusion coefficients D_(AlAl)~(Ti), D_(FeFe)~(Ti), D_(AlFe)~(Ti) and D_(FeAl)~(Ti) in Ti-rich β 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_(Ti-Al) values increase with Al concentration, and the D_(Ti-Fe) values show almost no concentration dependence. The D_(Fe(Ti-Al))values in p 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 β Ti-Al-Fe alloys, the D_(AlAl)~(Ti), D_(FeFe)~(Ti), D_(AlFe)~(Ti) and D_(FeAl)~(Ti)values are positive, and the D_(FeFe)~(Ti) and D_(FeAl)~(Ti) values are larger than the D_(AlAl)~(Ti) and D_(AlFe)~(Ti) ones, respectively. They show the complicated dependence on concentrations of Al and Fe elements. The positive ratios of D_(FeAl)~(Ti)/DD_(FeFe)~(Ti), and D_(AlFe)~(Ti)/D_(AlAl)~(Ti) indicate that the repulsive interactions exist between Al and Fe atoms in the ternary alloys, but the negative ratios of converted interdiffusion coefficients D_(FeTi)~(Al)/DD_(FeFe)~(Al) 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 β Ti-Al-Fe alloys.