Microstructure Evolution During Solidification of Cu–Zr–Ti Alloy Forming B2 Phase Particles Embedded in a Glassy Matrix

Abstract

Microstructural evolution during injection casting Cu50Zr50−xTix (x = 0–8) alloys has been investigated using X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Cubic CuZr(Ti) B2 phase is competing against the glass transition during solidification for all the alloys and the primary B2 phase has transformed into the martensitic phase for x < 6 alloys during cooling after solidification. The formation of spherical morphology and spatially inhomogeneous distribution of B2 phase in a glassy matrix can be rationalized in terms of reduced interface kinetics of solid/liquid interface and polymorphic nature of the primary solidification taking place without solute partition. The partial replacement of Zr with Ti improves not only glass forming ability but also suppresses the martensitic transformation of B2 phase, enabling the fabrication of BMG composites consisted of the B2 phase embedded in a CuZr(Ti) glass matrix. However, due to local cooling rate change during solidification, development of non-uniform microstructure in the BMG composites seems to be inevitable, which may be an obstacle in future application of the BMG composites.