Comparison of thermal stresses developed in Al2O3-SG, ZrO2-(12% Si+Al) and ZrO2-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 deposition and chemical vapour deposition have been used to make convenient material combinations for use in high- technology applications. High-temperature coatings 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 Al2O3-spherical cast iron (SG), ZrO2-(12% Si + Al) and ZrO2-SG coatings subjected to thermal loading. Coatings with a coating-to-substrate thickness ratio of 1/10 were modelled. ZrO2-SG coatings with an NiAl, NiCrAlY or NiCoCrAlY interlayer, and with different combinations of these interlayer materials, were also modelled. 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 thickness and material combinations have a significant influence on the level of thermal stresses developed. It is also concluded that the finite element technique can be used to optimise the design and processing of ceramic coatings. (C) 1999 Elsevier Science S.A. All rights reserved.