- Zhido Zheng

Diamond coatings are of interest for a wide range of applications due to the unique properties of crystalline diamond. Many applications require that the coating adhere strongly to metallic substrates which may have a large difference in thermal expansion coefficient with diamond.

The mechanistics of the interface for a coating-substrate system loaded by thermal expansion mismatch is modeled. Both continuous coatings and coatings containing a through-thickness hole surrounded by an annular delamination crack are examined.

The residual stresses in the diamond coatings are analysed using Raman microprobe spectroscopy and compared with the predictions of the analytical model. The adhesion of the diamond coatings on various substrates with and without an intermediate layer of TiC is evaluated by measuring the length of the delamination crack surrounding through-thickness holes in the coating and comaring with the relationship derived between crack length and strain energy release rate. The measured adherence on WC-Co substrates, as characterised by the critical strain energy release rate for growth of the delamination crack, was found to be significantly higher in the presence of the TiC intermediate layer developed during the course of this work.