Thermal behaviour of amorphous alloys of Ni with Zr, Hf and Pr near 40 at% Ni

Amorphous alloys of the type Zr 1-x Ni x , Hf 1-x Ni x and Pr 1-x Ni x were prepared by means of melt spinning. Their thermal behaviour was studied by means of X-ray diffraction, differential scanning calorimetry and electrical resistivity measurements. In several of the alloys of Zr and Hf near 40 at% Ni two strongly exothermic effects were observed in the DSC tracings. X-ray diffraction showed that only the heat effect occurring at the higher temperature is associated with crystallisation of the sample. The electrical resistivity shows features which correspond to the thermal events in the DSC tracing in that a marked drop can be identified with the crystallisation process. An increase in resistivity is observed to accompany the low-temperature heat effect. The origin of the first heat effect is discussed in terms of changes in the amorphous phase during heating. The activation energy for diffusion which controls the rate of the transformations, was determined in the above alloys by means of the Kissinger method. The results are compared with similar data obtained for a variety of other amorphous alloys. It is shown that the crystallisation temperatures are not simply proportional to the corresponding experimental values of the activation energy.