Comparison of thermal stresses developed in Al2O3-SG, ZrO2-(12% Si+Al) andZrO2-SG thermal barrier coating systems with NiAl, NiCrAlY and NiCoCrAlY interlayer materials subjected to thermal loading

Surface preparation techniques such as plasma spraying? physical vapour dep osition and chemical vapour deposition have been used to make convenient ma terial combinations for use in high- technology applications. High-temperat ure coatings are used for two main functions, either to protect a base meta l 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 co atings. In this investigation, thermal and structural finite element analysis has b een employed to analyse the level of stresses developed in Al2O3-spherical cast iron (SG), ZrO2-(12% Si + Al) and ZrO2-SG coatings subjected to therma l loading. Coatings with a coating-to-substrate thickness ratio of 1/10 wer e modelled. ZrO2-SG coatings with an NiAl, NiCrAlY or NiCoCrAlY interlayer, and with different combinations of these interlayer materials, were also m odelled. Nominal and shear stresses at the critical interface regions (film /interlayer/substrate) were obtained and compared. The results showed that the ZrO2-SG coatings have a higher thermal shock resistance than the Al2O3- SG and ZrO2-(12% Si + Al) coating systems. Furthermore, the interlayer thic kness and material combinations have a significant influence on the level o f thermal stresses developed. It is also concluded that the finite element technique can be used to optimise the design and processing of ceramic coat ings. (C) 1999 Elsevier Science S.A. All rights reserved.