Early Stages of Solid-State Amorphization Reaction During Mechanical Alloying of a Multicomponent Zr-Powder Mixture

Abstract

The synthesis of amorphous alloys by non-equilibrium techniques such as rapid quenching or ball milling has become an active subject during the past decade. Recently, a new group of Zr-based multicomponent metallic alloys with large glass forming ability have been found and are characterized by an extended supercooled liquid region and a glass transition before crystallization. Due to their low critical cooling rates, these alloys also offer the possibility to produce bulk metallic glasses by mechanical alloying and subsequent warm consolidation of the obtained amorphous powders above the glass transition temperature. Although amorphous phase formation by ball milling of elemental or intermetallic powders was studied extensively on several binary alloys systems such as Zr combined with late transition metals, the driving forces and the mechanisms of amorphization are still the subject of many investigations and discussions. In this regard, in order to allow for a meaningful comparison of the thermal stability and compositional homogeneity of mechanical alloyed amorphous powders with that of metallic glasses of the same average composition prepared by rapid liquid quenching, it is essential to develop a clear understanding of the microstructural evolution and phase formation during ball milling. This issue is addressed in the present workmore » by showing detailed structural investigations on the early stages of phase formation during mechanical alloying of an elemental Zr{sub 60}Al{sub 10}Ni{sub 9}Cu{sub 18}Co{sub 3} powder mixture. The results reveal that formation of strongly supersaturated solid solutions and fast grain refinement are the prior steps before the onset of amorphization.« less