INTERFACE CHARACTERIZATION OF CHEMICALLY VAPOR-DEPOSITED DIAMOND ON TITANIUM AND TI-6AL-4V

Continuous 1-mum-thick diamond films have been grown by chemical vapor deposition (CVD) at approximately 900-degrees-C on pure titanium and on a Ti alloy, Ti-6Al-4V. The diamond film exhibits good adhesion to t he substrates in spite of the presence of approximately 7 GPa of in-pl ane residual stress which arises from the large differences in thermal expansion coefficients between diamond and titanium. The interface be tween the CVD diamond film and the substrate was exposed by deforming the substrate, thereby removing parts of the diamond film, under both ultrahigh vacuum and ambient conditions. After fracture, both the subs trate and diamond film sides of the interface were characterized by a combination of x-ray photoelectron spectroscopy (XPS), scanning Auger microscopy, secondary electron microscopy, and Raman microprobe spectr oscopy. The substrate fracture surface is inhomogeneous, containing so me areas of diamond and amorphous carbon. XPS analysis revealed that c arbon and. oxygen are present on the substrate fracture surface. Micro n-size areas of Ti were also found on the diamond fracture surface. Ra man spectroscopy of the substrate fracture surfaces found evidence for the presence of amorphous, nonstoichiometric titanium oxides; no evid ence of crystalline TiC or stoichiometric TiO2 was seen. Analysis of t he XPS core level structure of the Ti and C spectra confirmed the pres ence of titanium carbide; little evidence of metallic titanium was see n in the interfacial region. Differences in the structure of the subst rate fracture surface between titanium and the Ti alloy were also seen . The interface at the diamond/Ti-6Al-6V alloy was more heavily oxidiz ed than the diamond/titanium interface. Depth profiling studies also r evealed a thicker oxygen-containing surface layer on the alloy fractur e surface. The presence of diamond and Ti compounds on both sides of t he exposed interfaces indicates that the fracture did not occur discre tely at the diamond/reaction layer interface. From these findings we p ropose a model of the failure region of the highly adherent diamond/ti tanium system.