GLASS FORMATION IN MECHANICALLY ALLOYED Fe-BASED SYSTEMS

Rapid solidification processing of metallic melts has been traditionally employed to synthesize metallic glasses in several alloy systems. However, in recent years, solid-state processing methods, and more specifically, mechanical alloying, have become popular methods to synthesize glassy phases in metallic alloy systems. Although a large number of criteria have been developed to identify alloy compositions that can be solidified into the glassy state, very few attempts have been made to predict the glass-forming ability by solid-state processing methods. To evaluate if some clear criteria could be developed to predict glass formation by solid-state processing methods and to understand the mechanism of glass formation, mechanical alloying of powder blends was conducted on several Fe-based alloy systems. Three different aspects of glass formation are specifically discussed in this paper. One is the development of a criterion for identifying glass-forming systems from phase diagram features, the second is the process of mechanical crystallization (formation of a crystalline phase on continued milling of the amorphous powders obtained by mechanical alloying), and the third is the novel phenomenon of lattice contraction during amorphization. It was shown that the conditions under which a glassy phase is formed by mechanical alloying are different from the solidification methods.