Thermal shock resistance and bonding strength of tri-layer Yb2SiO5/mullite/Si coating on SiCf/SiC composites

A Yb2SiO5/mullite/Si tri-layer environmental-barrier-coating (EBC) were coated on SiCf/SiC substrates via Air Plasma Spraying (APS). The thermal cycle tests (TCT) were conducted under thermal corrosive condition of vapor-oxygen (50 vol% H2O and 50 vol% O-2) with thermal shock from 1200 degrees C to 200 degrees C. Microstructures, weight loss and bonding strength of the samples were systemically investigated after 101, 396, 606 and 700 TCT cycles respectively. The results show that the corner of the tri-layer coating peel off from the sample with weight loss of 1.3% after 700 TCT cycles. The bonding strength between substrate and tri-layer coatings gradually decreases to 6.79 MPa (approximately 55.2% of virgin specimens) after 700 cycles due to thermal shock induced cracks distributed horizontally within Si layers and between Si layer and outer layers.