Diffusion of Si in Ti₃Al intermetallic compound

The diffusivity of Si in Ti₃Al with six compositions of 24.5at%Al to 34.7at%Al was invesitigated by using the diffusion couples (Ti ₃Al/Ti₃Al-X; X=0.5at%Si) at 1248-1423K. The diffusion coefficients of Si, D_Si'S, were smaller than those of Ti and Al by a factor of 1/20 at most. The D_Si'S slightly depended on Al concentration. The activation energies of Si diffusion, Q_Si'S, were in the range of 450-550kJ/mol, and they tended to decreace with increasing Al concentration. From the comparison of the Q's evaluated for various diffusion mechanisms and the experimantal Q_Si'S it was indicated that Si atoms preferably substitute for Al-site in Ti₃Al with D0₁₉-type ordered structure, and the Si diffusion is dominated by the sublattice antisite diffusion (SAD) mechanism in which Si atoms diffuse via Ti-sublattice in the form of antistructure-like atoms as well as the Al diffusion.