Deposition of highly adhesive nanocrystalline diamond films on Ti substrates via diamond/SiC composite interlayers

Abstract

Diamond/SiC interlayer with intermediate thermal expansion coefficient is introduced for improving the adhesion of NCD films on Ti substrate. Herein, tetramethylsilane (TMS) gas is added to produce SiC phase, forming a diamond/SiC interlayer. The effect of TMS gas flow on the microstructural evolution of the interfacial layer and the film adhesion is systematically investigated. At TMS gas flow of 5 sccm, the NCD film shows an interlayer of about 15% SiC by phase area statistics in SEM image. This film exhibits the lowest residual compressive stress of 1.64 GPa and the optimum adhesion of about 28.2 ± 2 N against Ti substrate. Increasing TMS gas flow leads to the increase of SiC content and the grain refinement of diamond in the interlayers. It is found that Ti silicide and hydride with increased amount are formed in the Ti substrate at higher TMS gas flow. The presence of these Ti intermetallic compounds with larger thermal expansion coefficient results in the increased residual stress and poorer adhesion in the NCD films. On the basis of reduction of Ti intermetallic compounds, the addition of TMS gas flow at 5 sccm is crucial for the preparation of good-adhesion NCD films on Ti substrate.