Glass forming ability and a novel method for evaluating the thermoplastic formability of ZrxTi65-xBe27.5Cu7.5 alloys

Abstract

Zr-Ti-based bulk metallic glass (BMG), in particular Be-Cu-bearing BMG (Vitreloy), displays an outstanding combination of characteristics, i.e. while showing good glass forming ability (GFA) it exhibits low glass transition temperature (Tg) and a relatively wide supercooled liquid region (SCLR, ΔT), facilitating their thermoplastic formability, which is critical for BMG applications. In the present work, the effect of composition on the GFA and thermoplastic formability in ZrxTi65-xBe27.5Cu7.5 BMG alloys are investigated in the range x = 20, 25, 30, 35, 40, 45, 50 at%. Results show that GFA is optimal in the composition range from 30 to 45 Zr at%. In addition, the optimal composition range for thermoplastic formability is consistent with that for GFA. Furthermore, 3-mm diameter BMG rods with the aspect ratio 2:1 are compressed in the SCLR at temperatures T = 643 K and T = Tg + ΔT/2, by applying a constant load of 8 kN, and the thermoplastic formability is evaluated measuring the final diameters d1 and dg-ΔT, respectively. The larger measured dg-ΔT values in the optimal composition range indicates that the ideal temperature for the thermoplastic formability is given by T = Tg + ΔT/2.