Structure and stress evaluation of diamond films deposited on Ti-6Al-4V alloy at low temperature using CH4/O2/H2 and CO/H2 gas mixtures

Low temperature diamond deposition on metal substrates is motivated by the need to reduce thermal stress so that the film adhesion is satisfactory. Although the use of oxygen-containing gas mixtures have been shown to extend the temperature range for which diamond can grow as well as to improve film quality, most studies have focused on the use of silicon as substrates and have neglected technologically important metallic systems. To this end, microwave plasma chemical vapor deposition (MPCVD) was used to grow diamond films on Ti-6Al-4V alloy at low temperature (615 to 780 C) using CH4/O-2/H-2 and CO/H-2 gas mixtures. In-situ pyrometric interferometry (ISPI) shows that as the oxygen concentration increases, the onset time for diamond nucleation and subsequent film surface roughness increases while the average growth rate decreases. Micro-Raman spectroscopy shows improved film quality and suggests a trend toward increasing in-plane compressive stress with increasing oxygen concentration. Glancing-angle xray diffraction (XRD) was complimentary to the Raman data and indicates the presence of a TiC interfacial layer thickness which decreases with increasing oxygen concentration. We found that the CO/H-2 mixture resulted in poorly adhered "white soot" films with low diamond content whereas the CH4/O-2/H-2 mixture yielded well adhered high quality diamond films.