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

A simple process has been perfected to deposit smooth fine-grained diamond coatings at 600 degreesC 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)-ca rbon containing layer from a methane-rich CH4-H-2 mixture and then the diam ond growth from a CO2-CH4 inlet mixture. Scanning electron microscopy, X-ra y diffraction, visible and UV Raman spectroscopy show that the coatings are smooth and mainly composed of crystalline diamond with a fine-grained morp hology. The results are compared with the results obtained with classical r ough polycrystalline coatings deposited from 8% CO-H-2. Optical emission sp ectroscopy reveals important differences between the plasma species produce d for the deposition of these smooth coatings and the plasma species produc ed for the deposition of both polycrystalline coatings from 1% CH4-H-2 or 8 % CO-H-2 mixture and nanocrystalline films from Ar-CH4(-H-2). (C) 2000 Else vier Science B.V. All rights reserved.