Thermal Instability and Crystallization Characteristics of Amorphous Metal-Metalloid System

Annealing effects on structure of several amorphous metal-metalloid systems (Pd-Si, Fe-P-C, Fe-Si-B, Co-Si-B and Ni-Si-B) were examined by electron microscopy, X-ray analysis and further by measurements of internal friction, electrical resistivity, specific gravity, microhardness and fracture strain. In T-T-T diagrams, distinct differences in transformation sequence were observed above and below the critical temperature. Above this temperature, crystallization proceeds through two metastable phases and finally to the stable phase by nucleation and growth mechanisms. Below this temperature, however, progressive aging gradually changes the structure through two stages ; the initial stage is due to some degree of ordering in atomic arrangements in the as-quenched state and the subsequent stage due to transformation from amorphous to single phase with the same structure as the metallic element. A remarkable decrease in fracture strain of Fe-P-C alloys occurs after aging treatments at the incipient stage. This phenomenon is not a general character of all amorphous alloys