材料期刊网

We report bulk metallic glasses with critical diameter (D(c)) 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 Mg(61)Cu(28)Gd(11) and quaternary Mg(59.5)Cu(22.9)Ag(6.6)Gd(11) alloys was measured. In terms of the fragility parameter D(*), the Mg(59.5)Cu(22.9)Ag(6.6)Gd(11) 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. (c) 2007 American Institute of Physics.