Crystallization Kinetics and Phase Transformation Mechanisms in Cu₅₆Zr₄₄ Glassy Alloy

The kinetics and phase selection mechanisms involved in the crystallization of an amorphous Cu-Zr alloy of eutectic composition (Cu₅₆Zr₄₄) were investigated using in situ high-energy X-ray diffraction (HEXRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) under isothermal and constant heating rate conditions. In situ HEXRD results for 10 K/min (10 °C/min) heating indicate that the amorphous alloy devitrifies into CuZr₂ and mainly Cu₁₀Zr₇ at the crystallization temperature of 725 K (452 °C). The sequence continues with the precipitation of CuZr (B2) at 1004 K (731 °C), where these three phases coexist until the decomposition of CuZr₂ is observed at 1030 K (757 °C). The two equilibrium phases Cu₁₀Zr₇ and CuZr (B2) remain present on further heating until melting at the eutectic temperature for the Cu₅₆Zr₄₄ alloy. TEM investigation of the isothermal [705 K (432 °C)] crystallization sequence reveals primary nucleation and growth of the Cu₁₀Zr₇ phase, where growth of the Cu₁₀Zr₇ crystals is initially planar with a transition to a cellular morphology, associated with partitioning of Zr at the growth front. Related cellular structures and composition profiles are quantified.