Dilute alloys which contained up to 0.56wt%Ta were prepared. Diffusion couples between these alloys, and pure Fe, were prepared by spot-welding. After vacuum annealing, the diffusion profiles were determined by using

electron probe microanalysis. The diffusion rate of Ta in austenite was about 6 times higher than that for the self-diffusion of Fe. In ferrite, the diffusion of Ta required a higher activation energy than did other transition metals. The diffusivity of Ta in austenite (0.54%Ta alloy), at between 1147 and 1347C, was described by:

D (mm2/s) = 6.72 x 103 exp[-319000/RT]

The diffusivity of Ta in ferrite (0.54%Ta alloy), at between 826 and 894C, was described by:

D (mm2/s) = 2.75 x 106 exp[-324000/RT]

Q.A.Shaikh: Materials Science and Technology, 1990, 6[12], 1177-80