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

Abstract

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 CuZr 2 and Cu 10 Zr 7 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.

On Long-Term Stability of Metallic Glasses

“…An open question is why no intermediate Cu-Zr intermetallic compounds are formed on the surface of Zr 50 Cu 50 and Cu 60 Zr 30 V 10 alloys in accordance with the Cu-Zr phase diagram but pure Cu? Although the glassy phase rather easily forms in the alloys containing as much as 70 at% Cu and more [46] formation of Cu 51 Zr 14 (hP65) phase with high thermal stability as well as Cu 9 Zr 2 (tP24) or Cu 8 Zr 3 (oP44) should be possible [47] at an intermediate state when the glassy phase becomes gradually diluted in Zr. A reasonable explanation is connected with difficulties in bypassing the energy barrier for nucleation of these phases at room temperature.…”

Martensitic Transformation and Plastic Deformation of TiCuNiZr-Based Bulk Metallic Glass Composites

“…The fracture morphologies (Figure 5f) show a number of vein-like and river-like patterns while some fine river-like patterns appear at the interface between the amorphous phase and the crystals, implying that the "blocking effect" [52] originating from the crystals has a large influence on the fracture mode. Generally speaking, by introducing ductile shape memory crystals into the glassy matrix, the ductility of BMG composites can be improved [20][21][22][23][24][25][26]. During the early stage of deformation, martensitic transformation occurs within B2 crystals in CuZr-based BMG composites [20][21][22][23][24][25][26].…”

“…Generally speaking, by introducing ductile shape memory crystals into the glassy matrix, the ductility of BMG composites can be improved [20][21][22][23][24][25][26]. During the early stage of deformation, martensitic transformation occurs within B2 crystals in CuZr-based BMG composites [20][21][22][23][24][25][26]. With increasingly applied stress, martensitic transformation becomes more prominent while a large amount of twins form easily within B2 crystals with a relatively lower stacking fault energy [53].…”

“…Based on the concept of transformation-induced plasticity (TRIP), CuZr-based BMG composites were developed by introducing the ductile, shape memory B2 CuZr phase into the glassy matrix [20][21][22][23][24][25][26]. Such BMG composites exhibit high strength and good plasticity together with obvious work-hardening under compressive and tensile loading conditions [20][21][22][23][24][25][26].…”

“…Based on the concept of transformation-induced plasticity (TRIP), CuZr-based BMG composites were developed by introducing the ductile, shape memory B2 CuZr phase into the glassy matrix [20][21][22][23][24][25][26]. Such BMG composites exhibit high strength and good plasticity together with obvious work-hardening under compressive and tensile loading conditions [20][21][22][23][24][25][26]. In order to promote the further development of such shape memory BMG composites, a lot of research has been devoted to applying this concept to other glass-forming compositions [27][28][29][30][31][32].…”