Examination of Fracture Process and Environmental Resistance of Ceramic Matrix Composites (SiC/SiC)

In Japan, the development of a 1700°C-class gas turbine utilizing combustion of methane (LNG) and oxygen was carried out as a national project. A ceramic matrix composite (CMC (SiC/SiC)) was focused as one of candidate materials for hot-gas-path parts, and its development and evaluation were conducted. In order to examine a relationship between bending strength and fracture process, 3-point bending tests were carried out, and they were interrupted halfway to observe the fracture of the specinen. While the CMC showed elastic behavior in a load-displacement curve, a crack was initiated in the tensile side of the specimen. It was clarified that the elastic behavior of CMC was different from that of metals. In order to protect the CMC from receission under combustion gas flow, Y 2 SiO 5 was selected as a candidate material for an environmental barrier coating (EBC). Y 2 SiO 3 specimen, which was by prepared by sintering, and Y 2 SiO 5 -coated specimen, in which Y 2 SiO 5 was coated on CMC substrate, were prepared. Combustion gas exposure tests were performed by means of these specimens (gas temperature 1200∼1500°C, a gas pressure of 0.3 MPa, a flow velocity of 150ms/, exposure time of 5∼40hours). The utilizaon of Y 2 SiO 5 for the EBC improves the environmental resistance of the CMC. However, taking long-term use in an in-service gas turbine into consideration, the development of new materials with more resistance to recession is necessary.