X-ray diffraction analysis of residual stresses in smooth fined-grain diamond coatings deposited on TA6V alloys

A mechanical and micro structural characterization has been done in diamond coating deposited on TA6V titanium alloys using X-ray diffraction. The CVD deposition process used allows elaborating layers at moderated temperature (600 °C). Varying the precursor gas composition, the purity level (sp3), the morphology (columnar or fine grains) and the roughness of the polycrystalline layers may be changed. Stress measurements indicate that diamond layer is under huge compression (3-6 GPa) as well as the intermediate TiC1 - x layer but with a lower stress magnitude (< 1 GPa) whatever the deposition parameters. A good agreement is found between X-ray and Raman diamond stress values except for the low purity layers where the Raman values are lower than the X-ray ones. This discrepancy is certainly related to the elastic modulus softening evidenced by Brillouin scattering and nanoindentation which has not been taken into account for the X-ray evaluation. Furthermore, a <110> fiber texture has been observed in thick columnar grain coatings and also in low purity fine grain coatings; the texture intensity is weaker for this last coating morphology.