Diffusion Coefficients and Phase Equilibria of the Cu-Zn Binary System Studied Using Diffusion Couples
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Diffusion Coefficients and Phase Equilibria of the Cu-Zn Binary System Studied Using Diffusion Couples Christopher M. Eastman Jr1,2 • Qiaofu Zhang1,3 • Ji-Cheng Zhao1,4
Submitted: 11 May 2020 / in revised form: 22 July 2020 Ó ASM International 2020
Abstract The diffusion behavior and phase equilibria in the Cu-Zn binary system were investigated using solid– solid and solid–liquid diffusion couples. Heat treatments at temperatures ranging from 100 to 750 °C were performed and the samples were examined using optical microscopy, energy dispersive x-ray spectroscopy, and electron probe microanalysis to identify the phases and to obtain composition profiles. Solubility limits of both solid solution and intermetallic phases were then evaluated, and a forwardsimulation analysis (FSA) was applied to extract interdiffusion coefficients. The composition profiles from Hoxha et al. were also re-analyzed using FSA to obtain more reliable diffusion coefficient data without the assumption of constant diffusion coefficients for the intermetallic phases. A comprehensive assessment of the interdiffusion coefficients in three intermetallic phases of the Cu-Zn system was performed based on the results from the current study as well as those in the literature. Activation energies and Arrhenius pre-factors were evaluated for each phase as a function of composition. The fitted equations based on the comprehensive assessment have the capabilities of computing the interdiffusion coefficients of each of the phases at a given composition and temperature. Suggested modifications to the Cu-Zn binary phase diagram were & Ji-Cheng Zhao [email protected] 1
Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210
2
TimkenSteel Corporation, Canton, OH 44706
3
QuesTek Innovations LLC, 1820 Ridge Avenue, Evanston, IL 60201
4
Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742
presented based on the new experimental information gathered from the present study. A clear explanation is provided for the puzzling low Zn concentrations often observed in the Cu-rich fcc phase of Cu-Zn diffusion couples in comparison with the expected high solubility values based on the equilibrium Cu-Zn phase diagram. Keywords Cu-Zn diffusion couples interdiffusion coefficients phase diagram
1 Introduction Zinc is one of the most widely used alloying elements in Cu alloys, thus diffusion coefficients in both the solid solution and intermetallic phases in the Cu-Zn system and the Cu-Zn binary phase diagram are essential for understanding the kinetics and phase stability of Cu alloys. Even though several research groups have studied this important binary system over the years,[1–16] there are still discrepancies and lack of systematic data for the diffusion coefficients of various phases. The aim of this study is to develop a more comprehensive picture of the diffusion behavior in the Cu-Zn system by performing diffusion experiments across a wide range of temperatures and by assessi
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