Abstract
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.
Highlights
Composites have been designed in an attempt to accomplish an optimal trade-off between strength and ductility in many classes of materials, which exhibit superior mechanical properties compared with either constituent material alone [1,2,3]
The as-cast samples were first annealed at the temperatures between Tg and the finish temperature (Tcryst-final ) of crystallization for (Cu0.5 Zr0.5 )90−x Al10 Cox (x = 4, 5, and 6 at. %) at a heating rate of 40 K/min and a cooling rate of 100 K/min, whose phases were characterized by an X-ray diffraction (XRD) device
In order to simultaneously improve the glass-forming ability (GFA) of CuZr-based alloys and keep the high thermal stability of the B2 CuZr phase, both 10 at. %
Summary
Composites have been designed in an attempt to accomplish an optimal trade-off between strength and ductility in many classes of materials, which exhibit superior mechanical properties compared with either constituent material alone [1,2,3]. Ductile crystals in BMG composites may serve as heterogeneous nucleation sites for the initiation of shear bands and act as attraction or pinning centers during shear band propagation. This leads to the formation of multiple shear bands in the glassy matrix and the enhancement of room-temperature ductility [16,17,18,19]. Shape memory B2 CuZr crystals were introduced into a glassy matrix as an alternative reinforcing phase because the B2 CuZr crystals usually show a pronounced work hardening during deformation due Metals 2016, 6, 225; doi:10.3390/met6090225 www.mdpi.com/journal/metals
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