Splat cooling and metastable phases

Abstract

It was first shown in 1960 that rapid quenching of certain alloys from the melt could form completely extended solid solutions, new metastable crystalline phases, and amorphous solid phases. These effects were attributable to the high cooling rates (>or approximately=105 K s-1) from the melt achieved by new techniques of rapidly spreading a few milligrams of liquid alloy into a thin layer in close contact with a good heat conductor (splat cooling). A comprehensive review of developments to data which have resulted from the application of this technique in laboratories throughout the world is presented. It includes an analysis of the range of methods now available for quenching the melt and of present understanding of how they form and quench specimens. The structural features observed as-quenched are then discussed under the divisions of microstructure and extended solid solubility, and of formation of both metastable crystalline and amorphous solid phases. A survey of the response of the as-quenched microstructure to annealing then precedes treatment of the properties and applications of splat-cooled alloys. It is concluded that splat cooling is being established in ever widening fields of study as a tool for controlling structure and properties, and that further applications can be anticipated.