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

The binary interdiffusion coefficients D similar to (Ti - Fe) in [beta] Ti-Fe alloy and D similar to (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 similar to AlAl Ti , D similar to FeFe Ti , D similar to AlFe Ti and D similar to FeAl Ti 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 similar to (Ti - Al) values increase with Al concentration, and the D similar to (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 similar to AlAl Ti , D similar to FeFe Ti , D similar to AlFe Ti and D similar to FeAl Ti values are positive, and the D similar to FeFe Ti and D similar to FeAl Ti values are larger than the D similar to AlAl Ti and D similar to AlFe Ti ones, respectively. They show the complicated dependence on concentrations of Al and Fe elements. The positive ratios of D similar to FeAl Ti / D similar to FeFe Ti and D similar to AlFe Ti / D similar to 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 similar to FeTi Al / D similar to 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 [beta] Ti-Al-Fe alloys.