The pressure dependence of the diffusivity of transition elements (table 23) was studied by using the radio-tracer method, with serial sectioning by microtome. The radio-isotopes were implanted so as to avoid problems with oxide hold-up and with the low solubility of transition elements. Diffusion annealing was then carried out in a high-pressure cell at Ar pressures of up to 0.8GPa. The activation volumes for diffusion were determined by isothermal annealing. It was recalled that the activation volumes of non-transition elements were close to one atomic volume, and were not very different from the activation volume for self-diffusion. On the other hand, the transition elements had diffusion activation volumes of between 2.7 and 1.67 atomic volumes. They were also characterized by high activation enthalpies and pre-exponential factors. The results were explained in terms of differences, in vacancy-solute interaction, between transition and non-transition solutes. The results could be described by:

D (m2/s) = 1.93 x 10-2 exp[-168.4(kJ/mol)/RT]

G.Rummel, T.Zumkley, M.Eggersmann, K.Freitag, H.Mehrer: Zeitschrift für Metallkunde, 1995, 86[2], 131-40

Table 23

Diffusivity of 57Co in Al under Hydrostatic Pressure