Tracer-diffusion of Ti-44 in TiAl single crystal

Tracer diffusion of Ti-44 in TiAl has been investigated using single crysta l samples in the temperature range from 1133 to 1307 K by the ion-beam sput ter technique. The tracer diffusion coefficient of 44Ti has been measured i n the directions parallel to [001] axis and perpendicular to [001] axis and has been found to be anisotropic; the diffusivity in the direction paralle l to the [001] axis is an order of magnitude lower than that perpendicular to the [001] axis. The diffusion coefficient is expressed as D-Ti*(perpendi cular to) = 7.66(-7.42)(+2.36) x 10(-4) exp(-(311 +/- 35/kJ mol(-1))/RT) m( 2) s(-1) (prrpendicular to [001] axis), D*(Ti)(//)= 2.38(-2.12)(+1.93) x 10 (-2) exp(-(370 +/- 22/kJ mol(-1))/RT) m(2) s(-1) (parallel to [001] axis). The cause of the anisotropy of the diffusion coefficient has been considere d in view of the defect structure and the correlation of the jump vectors o f successive vacancy jumps. (C) 2001 Elsevier Science B.V. All rights reser ved.