Variation of Thermo-Mechanical Properties of Air-Plasma Sprayed Thermal Barrier Coatings by Calcium-Magnesium-Aluminosilicate (CMAS) Infiltration

Abstract

Thermal Barrier Coating (TBC) protects structural components from high temperature environment of gas turbines. The TBC consists of ceramic top coat and metallic bond coat, deteriorate by the high temperature operating condition. Calcium-Magnesium-Aluminosilicate (CMAS) infiltration into the top coat is also one of degradation process for TBCs. Damage mechanism associated with the CMAS are significant in the novel turbine system, which operates at higher temperatures than the melting point of the CMAS. In this study, thermal deformation measurements between 300°C and 900°C on the CMAS infiltrated air plasma sprayed (APS) TBC topcoat specimens were conducted. Inflection point on a thermal strain curve for the CMAS infiltrated top coat specimen was observed around 700°C. The temperature corresponds to the glass transition temperature of CMAS grass. About 10 % decrease in linear expansion coefficient of the CMAS infiltrated top coat was also observed. These results indicated that the thermo-mechanical properties of CMAS infiltrated top coat were influenced by that of the CMAS, and such properties may play an important role to develop a thermal stress and failure mechanism of TBCs.