Tracer-diffusion of 44Ti in TiAl single crystal

Tracer diffusion of 44Ti in TiAl has been investigated using single crystal samples in the temperature range from 1133 to 1307 K by the ion-beam sputter technique. The tracer diffusion coefficient of 44Ti has been measured in the directions parallel to [001] axis and perpendicular to [001] axis and has been found to be anisotropic; the diffusivity in the direction parallel to the [001] axis is an order of magnitude lower than that perpendicular to the [001] axis. The diffusion coefficient is expressed as DTi*(⊥)=7.66−7.42+2.36×10−4 exp(−(311±35/kJ mol−1)/RT) m2 s−1 (perpendicular to [001] axis), DTi*(//)=2.38−2.12+1.93×10−2 exp(−(370±22/kJ mol−1)/RT) m2 s−1 (parallel to [001] axis). The cause of the anisotropy of the diffusion coefficient has been considered in view of the defect structure and the correlation of the jump vectors of successive vacancy jumps.