Mechanical alloying of highly processable glassy alloys

Glasses are generally produced from the undercooled liquid state by rapid quenching methods or quasi-statically at slow cooling by the effective control of heterogeneous nucleation sites. For metallic systems the latter method recently has led to the development of multicomponent metallic glasses with large glass forming ability and a wide supercooled liquid region before crystallization. Large-scale bulk samples of such alloys can be produced by conventional casting techniques. Alternatively, glass formation can be achieved by solid-state processing without passing through the liquid state. This crystal-to-glass transition is observed when a sufficiently high energy level is reached and kinetic conditions prevent the establishment of equilibrium. Hence, mechanical alloying as a special form of solid-state reaction technique and subsequent consolidation of the resulting powders above the glass transition temperature can be used to prepare bulk metallic glasses via the powder metallurgy route. The glass formation and the thermal stability of mechanically alloyed glassy alloys are compared with data for melt quenched samples showing that basically the same glassy state can be reached approaching it from the liquid or the solid state. Special emphasis is given to the glass forming ranges achievable by the different techniques and to the influence of impurities. Results for consolidated bulk samples are presented and compared with data for cast bulk specimens.