Crystallization Kinetics and Phase Transformation Mechanisms in Cu56Zr44 Glassy Alloy

Journal Reference

Metallurgical and Materials Transactions A, 2015, Volume 46, Issue 8, pp 3356-3364.

Ilkay Kalay¹ , Matthew J. Kramer^2,3, Ralph E. Napolitano^2,3

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1. Department of Materials Science and Engineering, Cankaya University, 06790, Ankara, Turkey
2. Department of Materials Science and Engineering, Iowa State University, Ames, IA, 50011, USA
3. Materials Sciences and Engineering, Ames Laboratory, U.S. Department of Energy, Ames, IA, 50011, USA

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Abstract

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.

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