Dsc study of surface induced crystallization in PdSi metallic glasses

Abstract

Differential scanning calorimetry, X-ray diffractometry and optical metallography were used to study the effect of surrounding atmosphere and sample preparation on the devitrification process in PdSi metallic glasses. The surface modification due to both oxidation and silicon out-diffusion increases the degree of surface crystallization. It is shown that the changed surface condition affects the overall crystallization process in Pd 77Si 23 glasses. For this composition, changing character of DSC traces and scatter in the apparent values of the crystallization parameters (e.g. crystallization temperature, activation energy for crystallization E a , Avrami coefficient n) were observed. It is shown that the lower-limit values of E a = 200 kJ/mol, n = 2.1 correspond to the surface induced crystallization, whereas the upper limit ones ( E a = 370 kJ/mol, n = 3.1) are characteristic of the bulk crystallization mechanism. The sample preparation for DSC measurements as well as experimental procedures leading to reproducible results are described. The eutectic Pd 85Si 15 glasses always crystallized in the bulk with E a = 295 kJ/mol, n = 3–4. These results were not affected by the surface condition.