Influence of the corrosion resistance and high temperature oxidation resistance of Cu-15Ni-8Sn alloy with Co or P additions

The influence of trace additions of Co or P elements on the corrosion resistance and high-temperature oxidation resistance of Cu-15Ni-8Sn alloy was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical testing methods. The results indicate that adding of trace amounts of Co enhances the corrosion resistance of the Cu-15Ni-8Sn alloy in 3.5% NaCl solution. In contrast, adding P deteriorates the alloy's corrosion resistance. This phenomenon is closely related to the formation of second phases at grain boundaries. During the corrosion process, these second phases act as cathodes for galvanic corrosion, participating in the anodic dissolution of the alloy matrix, leading to localized corrosion. The exacerbation of localized corrosion also results in the detachment of second phases, further exacerbating corrosion. Additionally, during prolonged oxidation at 500 ℃, the weight gain of the three alloy compositions follows a parabolic trend. The addition of trace Co does not affect the oxidation resistance of Cu-15Ni-8Sn, whereas the addition of trace P deteriorates the oxidation resistance of the alloy. This is attributed to the low adhesion strength of the oxide products formed in Cu-15Ni-8Sn-0.2P alloy, leading to the formation of voids, surface blistering, and cracking, thereby accelerating the oxidation behavior of the alloy.