Effect of Sintering on Microstructure and Mechanical Properties of Air Plasma Sprayed 7 wt Y2O3 Stabilized ZrO2

Abstract

Air plasma sprayed (APS) 7 wt.% Y2O3 stabilized ZrO2 (7YSZ) coating is conventionally used for thermal insulations (in form of thermal barrier coating, TBC) in various hotter sections of land-based gas turbine engines and aero-engines. Due to the use of 7YSZ as TBC, the maximum temperature of gases in the turbine engines could be extended to 1300-1400 0C from 1100-1150 0C; this has led to significant increase in the thermal efficiency of the gas turbine engines. Furthermore, nowadays these coatings are also being explored to be used as heat insulator in the combustion chamber of diesel engines, which work at relatively lower temperatures (e.g., lt 900 0C). Here also, the YSZ coated diesel engines (called as low heat rejection, LHR, engines) has shown improved thermal efficiency. APS YSZ coating which is used as a thermal barrier coating (TBC) has 15-25 % of microcracks and porosity in the as-deposited condition, which is purposefully engineered to reduce the thermal conductivity and elastic modulus of the coating. However, the YSZ coatings are exposed to high temperatures during the service, which results in evolution of their microstructure, wherein the microcracks and porosity slowly start to reduce. The reduction in microcracks and porosity not only leads to an increase in the thermal conductivity of the coating, but also significantly affects (deleteriously) its mechanical properties, such as elastic modulus, hysteresis loss, etc. In practice, degradation in the mechanical properties over extended period of high temperature exposure becomes one of the main reasons of the coating failure. Several studies have focused on understanding the effects of exposure to very high temperatures (e.g., gt 1000-1100 0C) on the elastic modulus, hysteresis loss, fracture resistance, microstructure and relevant structure-property relationships. However, there are very few studies discussing the effect of low temperature (e.g., and#61603; 1000 0C) exposure on the microstructure evolution and mechanical response of APS YSZ coatings and,...