Coarsening kinetics of lamellar and equiaxed microstructures of eutectic Au–20Sn during the annealing

Abstract

Abstracts: In this study, the microstructural evolution and coarsening kinetics of lamellar and equiaxed microstructures of eutectic Au–20Sn alloy during the annealing at 160–220 °C were systematically investigated. The lamellae and near-equiaxed grains coarsened strongly depending on the annealing temperature and holding time. Specifically, a higher annealing temperature effectively accelerated the coarsening process. Quantitative evaluations of lamellar and near-equiaxed coarsening kinetics of eutectic Au–20Sn alloy were performed respectively. The coarsening mechanisms for these two microstructures of eutectic Au–20Sn alloy were also discussed. During the annealing, the lamellar coarsening kinetics of eutectic Au–20Sn was described as λ2-λ02 = KLt with the characteristic activation energy Q about 116.64 kJ mol−1. The lamellar coarsening behavior was dominantly controlled by the fault migration and annihilation aroused from the interfacial diffusion of Sn atoms. The near-equiaxed grain coarsening followed the Lifshitz-Slyosov-Wagner theory rn-r0n = KMLSWt with temporal exponent n = 4 at 180 °C and n = 5 at 220 °C, respectively. The near-equiaxed grain coarsening was controlled by grain-boundary diffusion. This study provided a microstructural evolution law for eutectic Au–20Sn alloy, and it further offers a theoretical basis for the deformation processing during the thermal processes.

Keywords

• Eutectic alloy
• Annealing
• Thermal instability
• Coarsening kinetics
• Diffusion