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

Abstract

The binary interdiffusion coefficients D∼(Ti–Fe) in β Ti–Fe alloy and D∼(Ti–Al) in β Ti–Al alloy, Fe impurity diffusion coefficients DFe(Ti–Al)∗ in β Ti–Al alloys, and ternary interdiffusion coefficients D∼AlAlTi, D∼FeFeTi, D∼AlFeTi and D∼FeAlTi in Ti-rich β Ti–Al–Fe alloys were determined at 1423K 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 DFe(Ti–Al)∗ values in β Ti–Al alloys steeply decrease with Al concentration up to 7at.%Al and become almost constant over about 7at.%Al. In the ternary β Ti–Al–Fe alloys, the D∼AlAlTi, D∼FeFeTi, D∼AlFeTi and D∼FeAlTi values are positive, and the D∼FeFeTi and D∼FeAlTi values are larger than the D∼AlAlTi and D∼AlFeTi ones, respectively. They show the complicated dependence on concentrations of Al and Fe elements. The positive ratios of D∼FeAlTi/D∼FeFeTi and D∼AlFeTi/D∼AlAlTi indicate that the repulsive interactions exist between Al and Fe atoms in the ternary alloys, but the negative ratios of converted interdiffusion coefficients D∼FeTiAl/D∼FeFeAl 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.