Cobalt diffusion during the initial stage of CVD diamond growth on cemented carbide – A molecular dynamics and experimental study

Systematical researches on cobalt diffusion during the initial stage of diamond growth on cemented carbide (WC) are conducted by combining molecular dynamics (MD) and experimental investigations. Simulation results and characterizations indicate that temperature, WC grain size, initial cobalt distribution (including cobalt content and Co-removal depth after acid treatment), diamond crystal orientation, and the grain composition of polycrystalline diamond significantly affect cobalt diffusion. It is proven that cobalt tends to diffuse along grain boundaries in both cemented carbide and diamond, and the intricate nature of grain boundaries in smaller grain sizes results in higher activation energy for cobalt diffusion. However, due to the strong interaction between cobalt and parallel double six-membered ring structures at grain boundaries, cobalt diffusion to the diamond surface is exceedingly challenging. The accumulation of cobalt at the interface between the diamond film and substrate leads to graphitization, which ultimately deteriorates the adhesion of the diamond film during prolonged deposition. In conclusion, the reduction of cobalt diffusion in chemical vapor deposition (CVD) processes can be achieved by employing cemented carbide with smaller grain sizes and lower initial cobalt content. Additionally, decreasing the growth temperature or increasing the Co-removal depth significantly inhibits cobalt diffusion to the diamond film.