Corrosion Behavior of Cu/Ni Coatings on Ti-6Al-4V Alloy after Diffused Treatment

Abstract

To improve the low thermal conductivities and poor wear resistances of TC4 (Ti-6Al-4V) alloy, the most widely used titanium alloy, the surface of TC4 alloys is modified by electroplating deposition of Ni and Cu layers, and then heat-treated to increase the diffusivity at the interface. In this paper, the corrosion behavior of Cu/Ni coatings on TC4 alloy at different heat treatment processes was investigated in 3.5 wt% NaCl by the electrochemical analysis, and the microstructure and composition of corrosion products was carried out to reveal the corrosion resistance mechanism of Cu/Ni coatings. It was found that the corrosion resistance was significantly influenced by heat treatment temperature. With the increasing diffusion treatment temperature from 500 to 700 °C, the corrosion potential positively shifted from −330.87 to −201.14 mV, and the corrosion current density decreased from 4.02×10−3 to 0.514×10−3 mA/cm2. However, when heat treatment temperature increased to 800 °C, the corrosion potential negatively shifted to -207.21 mV, and the current density increased to 1.62×10−3 mA/cm2.The diffusion behavior of Ti, Ni and Cu elements occurred and small amounts of Ni and Ti elements appeared on the specimen surface under different heat treatment temperature. Especially heattreated at 700 °C, the smaller pore size, dense Cu2O film, and highly stable TiO and NiO oxide layer were formed, which dramatically enhanced the corrosion resistance of Cu/Ni coatings. Finally, a novel model of corrosion resistance was proposed based on the analysis mentioned above.