Plasma-assisted chemical vapor deposition process for depositing smooth diamond coatings on titanium alloys at moderate temperature

摘要

A simple process has been perfected to deposit smooth fine-grained diamond coatings at 600deg C on titanium alloys or titanium-coated surfaces. It consists of a two-step microwave plasma-assisted chemical vapor deposition (PACVD) procedure including first the deposition of a sacrificial sp~2-carbon containing layer from a methane-rich CH_4-H_2 mixture and then the diamond growth from a CO_2-CH_4 inlet mixture. Scanning electron microscopy, X-ray diffraction, visible and UV Raman spectroscopy show that the coatings are smooth and mainly composed of crystalline diamond with a fine-grained morphology. The results are compared with the results obtained with classical rough polycrystalline coatings deposited from 8percent CO-H_2. Optical emission spectroscopy reveals important differences between the plasma species produced for the deposition of these smooth coatings and the plasma species produced for the deposition of both polycrystalline coatings from 1percent CH_4-H_2 or 8percent CO-H_2 mixture and nanocrystalline films from Ar-CH_4(-H_2).