In Situ High-Temperature Tensile Fracture Mechanism of PS-PVD EBCs

Environmental barrier coatings (EBCs) are increasingly being used in the high-temperature sections of gas turbines because of their protective effects on SiC fiber-reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) when subjected to high-temperature water oxygen corrosion. The objective of this study was to investigate the failure behavior of EBCs prepared on SiCf/SiC CMC matrix materials under coupled high-temperature and load conditions. A plasma spray-physical vapor deposition (PS-PVD) method was used to prepare Si/3Al2O3·2SiO2/Yb2SiO5 EBC composite coatings on the surface of SiCf/SiC ceramic matrix composites. In situ scanning electron microscopy was used to study the evolutionary behavior of the coating surface cracks at different temperatures and the failure and fracture mechanism of the coating/substrate when held at 766 °C and subjected to different loading conditions. The results show that no significant crack extension occurred on the coating surface as the temperature of the coated specimen increased from room temperature to 766 °C in the absence of an applied tensile load, indicating that the effect of a single temperature factor on the failure of the specimen was negligible. However, under coupled high-temperature and load conditions, the specimens fractured at a load of 340 N when subjected to 766 °C, indicating that the coated sample is more likely to fail when subjected to high-temperature and tensile loading. The step-like fracture exhibits features consistent with the coating fracture and spalling caused by surface cracks extending from the coating surface to the interior. The spalling, large crack formation and step-like shape of the fracture in the coating and the substrate indicate that cracks were generated between the coating and the substrate under the coupled high-temperature and load conditions. The generation and extension of cracks in both parts eventually led to full specimen rupture.