Effects of Marker Size and Distribution on the Development of Kirkendall Voids, and Coefficients of Interdiffusion and Intrinsic Diffusion

Abstract

Development of Kirkendall voids, and determination of interdiffusion coefficients, marker plane movement and intrinsic diffusion coefficients were investigated as functions of marker size and distribution using Cu versus Ni solid-to-solid diffusion couples, annealed at 1000 °C for 48 h. The Al₂O₃ marker particles, varying in size, 1, 3, 5 and 9 μm, were dispersed in absolute ethanol, with concentration ranging from 0.67 to 33.33 mg/mL. To place the markers in diffusion couple, Ni was immersed in the Al₂O₃ dispersed ethanol, and removed to quickly dry under a lamp, leaving only the Al₂O₃ particle makers on the Ni surface. Optical microscopy was employed to document the distribution of Al₂O₃ particle markers on the Ni surface prior to the diffusion couple assembly. Field emission scanning electron microscopy equipped with x-ray energy dispersive spectroscopy was employed to examine the development of Kirkdendall voids and to determine the concentration profiles. The concentration profiles were analyzed to determine the interdiffusion and intrinsic diffusion coefficients via Boltzmann–Matano and Heumann methods, respectively. As the marker concentration (or cross-sectional area coverage) increased, the Kirkendall voids became more elongated and interconnected, leading to a gap within the interdiffusion zone. Better consistency in the magnitude and composition-dependence of interdiffusion and intrinsic diffusion coefficients were observed with smaller, 1- and 3-μm Al₂O₃ marker particles in general. For 5- and 9-μm Al₂O₃ marker particles, only the concentration of 0.67 mg/mL, corresponding to no more than 11% of cross-sectional area coverage was acceptable to yield consistent interdiffusion and intrinsic diffusion coefficients.