Differential effects of Fe, Ti and Fe + Ti addition on the discontinuous precipitation and properties of cu-Ni-Sn alloys

Abstract

Controlling discontinuous precipitation is crucial for improving the microstructure and mechanical properties of Cu-Ni-Sn alloys. Through the utilization of various characterization techniques such as transmission electron microscopy, scanning electron microscopy, optical microscopy, and mechanical testing, we have successfully demonstrated that the introduction of either Ti or a combination of Fe and Ti elements effectively inhibits the formation of discontinuous precipitation. Notably, the combined addition of Fe and Ti elements showcases superior suppression of the discontinuous precipitation structure. Consequently, we have developed a novel alloy, namely Cu-15Ni-7.5Sn-0.5Fe-0.5Ti, which exhibits remarkable resistance to over-aging. Our analysis indicates that the mechanism of inhibiting discontinuous precipitation is multifaceted. The main effect is believed to be the reduction in nucleation sites and the pinning effect of the D024-Ni3Ti phase on grain boundaries, resulting in a significant decrease in the nucleation rate and growth of the DP reaction. The secondary impact may be due to the distribution of D024-Ni3Ti phase at grain boundaries, which leads to a decrease in grain boundary energy. Meanwhile, the formation of D019-Ni3Sn phase reduces the chemical driving force required for DP growth.