Finite element analysis of the effectiveness of interlayers in reducing thermal residual stresses in diamond films

The residual stresses resulting from cooling of diamond thin films deposited at elevated temperature have been investigated using finite element analysis. Interlayers of various properties and thicknesses between the diamond and substrate have been simulated to determine the potential for residual stress reduction. Interlayer materials of WC, Si₃N₄ and TiC with tungsten and WC-6%Co substrates were modeled. Multiple interlayer systems composed of Si₃N₄, Si and WC, with Si₃N₄ next to the diamond and WC next to the WC-6%Co substrate, were also modeled to determine if residual stress advantages could be obtained by a simplified gradient material approach. These studies were supplemented by parametric studies to determine the effects of interlayer thickness, elasticity, plasticity and thermal expansion coefficients. Although thermal expansivity is the most significant property in elastic interlayers, the yield strength is most critical in plastic interlayers.