Thermodynamics and kinetics of discontinuous precipitation in Cu–9Ni–xSn alloy

Abstract

In this work, the hardness during aging, the, morphology and the thermodynamics and growth kinetics of discontinuous precipitation (DP) in Cu–9Ni–xSn alloy were investigated by mechanical testing, metallographic optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that Cu–9Ni–xSn alloy overages faster with increasing Sn content and aging temperature. Also, thermodynamic analysis shows that the γ-DO3 phase precipitates more easily with increasing Sn content. The growth kinetics of DP were described by using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. The diffusion activation energy (Q) values of DP in Cu–9Ni–xSn (x = 3,4,6) alloy are calculated to be 45.5 kJ/mol, 54.6 kJ/mol, and 97.7 kJ/mol, respectively, indicating that the DP reaction was controlled by grain boundary diffusion. The thermodynamics and growth kinetics analyses of DP support the concept that the diffusion of Cu–9Ni–xSn alloy becomes easier with increasing Sn content. Moreover, the results show that the aging temperature and Sn content greatly affect the Interlamellar spacing of DP in Cu–9Ni–xSn alloy.