The self-diffusion of the 58Co radiotracer in amorphous or isothermally crystallized samples was investigated by using ion-beam sputtering serial sectioning. It was found that the self-diffusivity in as-prepared melt-spun specimens decreased, with time, to a final value that was characteristic of the relaxed amorphous state. The effect of isothermal crystallization at 713 or 750K was studied, and the state of crystallization was monitored by means of transmission electron microscopy. The diffusivity at 663K first

decreased by 2 orders of magnitude during crystallization, according to a t-1 law, followed by a t-2/3 dependence. The crystallization enthalpy was deduced to be 2.8eV. The diffusion enthalpy increased from 1.8eV, in the relaxed amorphous state, to 2.2eV after crystallization for 100h at 750K. It was suggested that diffusion occurred via a direct diffusion mechanism in both the relaxed amorphous and nanocrystalline states.

J.Pavlovský, W.Ulfert, W.Frank: Materials Chemistry and Physics, 1994, 36[3-4], 383-8

Table 71

Diffusivity of 57Co in Co2Nb

 

Composition

Temperature (K)

Method

D (m2/s)

Co69Nb31

1523

sputtering

2.29 x 10-15

Co69Nb31

1473

sputtering

8.78 x 10-16

Co69Nb31

1423

grinding

4.18 x 10-16

Co69Nb31

1373

grinding

1.92 x 10-16

Co69Nb31

1323

grinding

8.18 x 10-17

Co69Nb31

1273

grinding

2.43 x 10-17

Co69Nb31

1223

grinding

6.29 x 10-18

Co69Nb31

1183

grinding

2.38 x 10-18

Co69Nb31

1143

grinding

1.10 x 10-18

Co71Nb29

1423

grinding

3.11 x 10-14

Co71Nb29

1373

grinding

7.11 x 10-15

Co71Nb29

1323

grinding

2.59 x 10-15

Co71Nb29

1273

grinding

5.96 x 10-16

Co71Nb29

1223

grinding

3.14 x 10-16

Co71Nb29

1183

grinding

2.10 x 10-16

Co71Nb29

1141

grinding

6.72 x 10-17