Doubling the Critical Size for Bulk Metallic Glass Formation in the Mg−Cu−Y Ternary System

Mg−Cu−Y alloys with optimal glass forming ability have been found at off-eutectic compositions. The critical size for bulk metallic glass formation at the pinpointed compositions more than doubles that of the previously discovered eutectic Mg65Cu25Y10 alloy, leading to fully glassy rods with near-centimeter diameters in the ternary system upon copper mold casting. The result is a striking demonstration of the strong composition dependence of the glass forming ability, as well as of the need to scrutinize off-eutectic compositions. The implications of the discovery are discussed.