Isothermal Oxidation and Thermal Shock Resistance of Thick and Porous LaMgAl11O19 Abradable Topcoat

Abstract

An exploration of the plasma-sprayed abradable sealing coatings (ASCs) of a thick and porous LaMgAl11O19 topcoat onto SiC/SiC ceramic matrix composites (CMCs) is detailed in this study. Interlayers comprising Si/Si + Yb2Si2O7/Yb2SiO5 environmental barrier coatings (EBCs) were strategically employed, considering their function in protecting the SiC/SiC CMCs from recession and mitigating thermal expansivity misfit. An isothermal oxidation test was conducted at 1300 °C and resulted in the formation of bubble and glassy melt on the side surface of the coated sample, while a significant reaction layer emerged at the Yb2SiO5/LaMgAl11O19 interface near the edge. The localized temperature rise caused by the exothermic oxidation of the SiC/SiC substrate was determined to be the underlying factor for bubble generation. The temperature-dependent viscosity of the melt contributed to various bubble characteristics, and due to the enrichment of Al ions, the glassy melt exacerbated the degradation of the Yb2SiO5 layer. After a thermal shock test at 1300 °C, the substrate on the uncoated backside of the sample experienced fracture, while the front coating remained intact. However, due to the presence of a through-coating crack, an internal crack network also developed within the substrate.