Glass-Forming Ability and Early Crystallization Kinetics of Novel Cu-Zr-Al-Co Bulk Metallic Glasses

In recent years, CuZr-based bulk metallic glass (BMG) composites ductilized by a shape memory B2 CuZr phase have attracted great attention owing to their outstanding mechanical properties. However, the B2 CuZr phase for most CuZr-based glass-forming compositions is only stable at very high temperatures, leading to the uncontrollable formation of B2 crystals during quenching. In this work, by introducing Co (i.e., 4, 5, and 6 at. %) and 10 at. % Al into CuZr-based alloys, the relatively good glass-forming ability (GFA) of CuZr-based alloys still can be achieved. Meanwhile, the B2 phase can be successfully stabilized to lower temperatures than the final temperatures of crystallization upon heating CuZr-based BMGs. Unlike previous reported CuZr-based BMGs, the primary crystallization products upon heating are mainly B2 CuZr crystals but not CuZr2 and Cu10Zr7 crystals. Furthermore, the primary precipitates during solidification are still dominated by B2 crystals, whose percolation threshold is detected to lie between 10 +/- 2 vol. % and 31 +/- 2 vol. %. The crystallization kinetics underlying the precipitation of B2 crystals was also investigated. Our results show that the present glass-forming composites are promising candidates for the fabrication of ductile CuZr-based BMG composites.