Comparison of the thermal stresses developed in diamond and advanced ceramic coating systems under thermal loading

Surface preparation techniques such as plasma spraying, physical vapour deposition and chemical vapour deposition have been used to make convenient material combinations for the use in high-technology requirements. High-temperature coating are used for two main functions. Either to protect a base metal against corrosion or erosion, or to minimise wear. A third function is to reduce the temperature of the base metal in the case of thermal barrier coatings. In this investigation, thermal and structural finite element analysis has been employed to analyse the level of stresses developed in coatings subjected to thermal loading. Diamond, Si3N4, Al2O3 and TiC coating systems were modelled. Coatings with NiAl interlayer material were also modelled. Nominal and shear stresses at the critical interface regions (film/interlayer/substrate)were obtained and compared. The results showed that the level of the thermal stresses is influenced by coating material, coating thickness, interlayer material thickness and the mismatch of the thermal and mechanical properties between coating and substrate materials. It is also concluded that the finite element technique can be used to optimise the design and processing of diamond and ceramic coatings. (C) 2000 Elsevier Science Ltd. All rights reserved.