High glass-forming ability correlated with fragility of Mg–Cu(Ag)–Gd alloys

Abstract

We report bulk metallic glasses with critical diameter Dc in the 20–27 mm range over a relatively wide composition range in the Mg–Cu–Ag–Gd quaternary system. Such an extraordinary glass-forming ability is correlated with the relatively strong liquid behavior of these alloys in terms of Angell’s Science 267, 1924 1995 fragility concept. The relaxation time of the ternary Mg61Cu28Gd11 and quaternary Mg59.5Cu22.9Ag6.6Gd11 alloys was measured. In terms of the fragility parameter D*, the Mg59.5Cu22.9Ag6.6Gd11 alloy with a critical diameter of 27 mm under copper mold casting has a D * of 25, higher than all the bulk metallic glass–forming alloys reported so far. The implications of these findings are discussed. © 2007 American Institute of Physics. DOI: 10.1063/1.282175