Damage analysis of CVI SiCf/SiCm ceramic matrix composites under thermal shock

The low density, high strength, and excellent high-temperature resistance of ceramic matrix composites (CMCs) determine their significant application value in the extreme environments of advanced aero-engines. In this paper, the thermal shock performance and internal damage evolution of CMCs materials are investigated by Xray computed tomography (XCT), infrared thermal imaging and acoustic emission (AE) non-destructive testing technologies. The results show that the silicon carbide (SiC) sealing coating on the chemical vapor infiltration - ceramic matrix ccomposites (CVI-CMCs) substrate is severely oxidized and peels off during the cyclic thermal shock process, resulting in exposure and damage to the fiber-reinforced phase and matrix phase. The k-means clustering results of the damage modes of CMCs materials during the thermal shock cycle test can be classified to four damage modes: fiber fracture (280-360 kHz), fiber/matrix crack propagation (225-270 kHz), interlayer spalling (125-165 kHz) and interface debonding or slipping between the fiber and matrix (80-115 kHz). Environmental barrier coatings (EBCs) can enhance the thermal shock resistance of CMC materials. After 900 thermal shock cycles, the peeling area of CVI-CMCs substrate coated with the EBCs is only 15 %, significantly lower than the 25 % observed in uncoated CVI-CMC substrate.