Diffusion behavior and mechanical properties of Cu/Ni coating on TC4 alloy

Diffusion process during heat treatment can be successfully employed to connect dissimilar metals. In order to get interconnected plating structure with a good biological performance on TC4 alloy, the most widely used titanium alloy, the surface of TC4 alloys were modified by deposition of Ni and Cu layers, and heat treatment was performed to increase the diffusivity at the interface. In this paper, the elements diffusion behaviors of Cu/Ni and Ni/Ti at the interfaces of Cu/Ni/Ti were investigated. A diffusion model was developed to reveal the diffusion coefficients and diffusion activation energies based on the Fick's law and Arrhenius-type equation. The adhesion strength and hardness of the coatings were also measured to evaluate the influence of diffusion behavior on mechanical properties. It was found that the diffusion behavior was significantly influenced by heat treatment temperature. The diffusion coefficient increased with the increase of heat treatment temperature, especially above 700 °C. The difference in the diffusion activation energies can be attributed to the difference in contact area and defect density caused by different coating processing technologies. In addition, the improvement of adhesion strength and hardness were mainly due to the solution strengthening and intermetallic compounds (IMCs) in the coating.