Self-diffusion of cobalt in B2 type intermetallic compound CoAl

The self-diffusion coefficient of 57Co in B2 type intermetallic compound CoAl at the concentrations of 42, 46, 50 and 52 at.% Al has been determined in the temperature range between 1250 and 1630 K by use of the serial radio-frequency sputter-microsectioning technique. The diffusion coefficient of cobalt, DCo*, decreases with increase in Al concentration from the Co-rich composition to the stoichiometry, while DCo* in Al-rich Co-52 at.% Al alloy is almost equal to that at the stoichiometry. At higher temperature region above 0.8 Tm (Tm: melting temperature of alloys), DCo* deviates upward largely from the Arrhenius line, suggesting that the diffusion mechanism changes with increasing temperature from the monovacancy to the divacancy mechanism.