Measurements were made of the tracer diffusivity in amorphous samples which had been prepared by melt-spinning in a vacuum. The diffusivity in as-quenched material was enhanced by the presence of quasi-vacancies. That is, excess free volume. During annealing, the quasi-vacancies were removed and the diffusivity tended to a constant value which depended only upon the temperature. The tracer self-diffusion of 57Co, at temperatures ranging from 513 to 693K, in relaxed amorphous material (table 35) could be described by:

D (m2/s) = 8.03 x 10-7 exp[-147(kJ/mol)/RT]

The tracer self-diffusion of 195Au, at temperatures ranging from 633 to 684K (table 36), could be described by:

D (m2/s) = 0.79 exp[-274(kJ/mol)/RT]

Appreciable atomic motion at temperatures where solid-state amorphization reactions occurred was restricted to Co diffusion. This suggested that diffusion-limited growth of an amorphous phase could take place without nucleation of the more stable intermetallic compounds. The activation enthalpy for crystallization (335kJ/mol) was much higher than that for Co diffusion.

W.Dörner, H.Mehrer: Physical Review B, 1991, 44[1], 101-14

Table 35

Diffusion of 57Co in Annealed Amorphous Co89Zr11

Table 36

Diffusion of 195Au in Annealed Amorphous Co89Zr11