In-situ tensile testing of crystalline diamond coatings using Raman spectroscopy

In the present work, the fracture behaviour of crystalline diamond thin films on titanium substrate has been studied under uniaxial in-situ tensile loading in Micro-Raman spectroscopy. Thin crystalline diamond films were deposited onto thin titanium foils using a hot filament chemical vapour deposition technique. The in-situ investigations in Raman spectroscope indicated that the internal stresses, which were compressive at the beginning, can be reduced by the application of tensile load. At higher strain values, when internal stresses were of tensile nature, cracks were formed in the coating with reduced crack spacing at higher strains and also the tensile stress stayed constant during cracking. Cross-section analyses, across tensile cracks, with a focused ion beam microscopy showed that the crack starts from the surface of the coating, then propagates into the interlayer, stops at the surface of the metallic substrate and opens up on further straining without delamination. This cracking behaviour indicates a good adhesion of the coating to the substrate.