Enhancement of high temperature oxidation resistance and spallation resistance of SiC-self-healing thermal barrier coatings

Abstract

Abstract Thermal barrier coatings (TBCs) are extensively used to protect metallic blades in gas-turbine engines where the operating conditions include an aggressive environment at high temperatures. The most important factor controlling TBC durability is the growth of a thermally grown oxide (TGO) layer which is formed during high temperature oxidation. To improve the oxidation resistance of conventional TBC, the SiC-self-healing coating, named the SAZ coating, was prepared by air plasma spray (APS) technique on the top of the classic bilayer TBC (YSZ TBC), which consist of the bond coating (BC) and the YSZ coating. Cracks allow SiC particles locating on the crack outside surface to react with the oxygen in the atmosphere at the temperature above 720 °C resulting in healing. As oxidation progress, the crack surfaces are covered with the formed oxide. Finally, the space between the crack surfaces is completely or incompletely filled with the formed oxide. The sealing effect enhanced the oxygen diffusion resistance of SAZ coatings, therefore the partial pressure of oxygen at the BC-YSZ interface of SAZ TBC samples would be lower than of YSZ TBC samples. The oxidation and spallation resistance of the SAZ TBC samples will be enhanced because the growth rate of TGO is slower due to the low partial pressure of oxygen. The high temperature cyclic oxidation tests performed at 1127 °C was carried out to investigate the oxidation and spallation resistance of the SAZ TBC. The results demonstrated that the mass gain of SAZ TBC samples, which was related to oxidation resistance, was 63.29% of YSZ TBC samples, and the mass loss of SAZ TBC samples, which was related to spallation resistance, was 56.08% of YSZ TBC samples.