FEM ANALYSIS OF THERMAL STRESSES IN THERMAL BARRIER COATINGS

Abstract

Thermal barrier coatings are generally used to increase the life and efficiency of the high temperature application components such as turbine blades, engine parts, etc. Thermal barrier coatings system consists of two layers on the substrate: ■ Bond coat (NiCrA1Y) to provide oxidation resistance at high temperatures. ■ yttria stabilized zirconia (YSZ) ceramic layer is used as top coat for thermally insulating, the system. Due to the thermal cyclic loading (heating and cooling) and thermal expansion mismatch between the top coat and bond coat thermal stresses are produced. These thermal stresses play a crucial role in determining the life of the thermal barrier coatings. To enhance the life of these thermal barrier coatings it is necessary to have detailed thermal analysis. In the current study, TRANSIENT THERMAL ANALYSIS is carried out to fmd the temperature and thermal stress distribution in the coating. Finite element method based software; ANSYS 10.0 has been used for the analysis. This analysis is carried out on the following three different types of thermal barrier coatings systems, developed by plasma spray process and compared to fmd out the optimal life of the coatings. (i) Traditional (ii) Nano-structured and (iii) Functionally graded thermal barrier coating systems. Based on the present study, it is observed that the stresses (Sx) within the nanostructured YSZ ceramic layer and functionally graded YSZ ceramic layer in the axial direction are 48% and 14%, respectively of the values observed for the traditional YSZ coatings. The stress (Sy) in the y -direction at the vicinity of the interface between the TOO and the YSZ topcoat at the edge of the sample for nanostructured YSZ is about 70% and for functionally -grade is about 19% that of the traditional YSZ. Thus functionally graded coatings will give better life compared to nanostructured and traditional thermal barrier coatings.