Synthesis of Bulk Metallic Glasses
Metallic glasses have been produced by rapidly solidifying metallic melts at cooling rates of about 106 K s−1. This early excitement of being able to produce the normally crystalline metals in a glassy state, and their excellent mechanical, chemical, and magnetic properties, led to the development of a variety of techniques to obtain metallic glasses in different sizes and shapes (ribbons, wires, powders, etc.). Some of these techniques have been described in some earlier publications (see, e.g., Refs. [1-4]). But, the commercial requirements of large-size sheets for different applications resulted in the development of the planar ¡ow casting method, wherein rapidly solidied sheets of at least 30 cm in width could be produced. The quest for bulk glassy alloys for industrial applications eventually culminated in the discovery of bulk metallic glasses (BMGs). BMGs have been produced at relatively slow solidication rates of about 103 K s−1 or less. But, before describing the different techniques to synthesize BMGs, let us brie¡y look at the requirements for rapid solidication processing (RSP) and the important techniques used to produce rapidly solidied ribbons. This assumes relevance here because a lot of researchers in theeld of BMGs still use the melt-spinning technique to produce ribbons and study their properties and crystallization behavior before proceeding to investigate the synthesis and characterization of BMGs.