In order to clarify the role which was played by thermal defects in diffusion in metallic glasses, measurements were made of the temperature and pressure dependences of the diffusion of Ni (a probe for Co) in relaxed and non-relaxed amorphous alloys (table 29, figure 25). This was done by means of tracer techniques and secondary-ion mass spectroscopy. In the case of the relaxed state, the results could be described by:

D (m2/s) = 2.4 x 10-6 exp[-1.65(eV)/kT]

The pressure dependence yielded an activation volume which was equal to 66% of the average atomic volume of the alloy. This value was similar to the activation volumes found for crystalline materials, and indicated that diffusion occurred via thermally generated defects. Unlike the monovacancies in crystals these defects appeared, on the basis of published isotope-effect measurements, to be spread out. A comparison with published data also showed that the activation volume, and hence the diffusion mechanism, in the metallic glass depended upon the structure and composition; even for a given component. The activation volume in the as-quenched state was found to be equal to 93% of the average atomic volume of the alloy.

Structural Effects on Diffusion in Metallic Glasses - the Pressure Dependence of Ni Diffusion in As-Quenched and Relaxed Co42Zr58. P.Klugkist, K.Rätzke, F.Faupel, P.Troche, P.Fielitz, V.Naundorf: Philosophical Magazine Letters, 1999, 79[10], 827-36

Figure 25

Diffusivity of 57Co and Ni in Zr58Ni42

(open circles: Ni in as-quenched samples, closed circles: Ni in relaxed samples,

square: 57Co in relaxed sample)

Table 29

Diffusivity of Ni in Zr58Co42 Glass