Embedded thermocouples for CMC engine components

Nickel-based super alloys have been the mainstay for gas turbine components comprising the hot section. However, due to their superior thermomechanical properties, SiC-SiC ceramic matrix composites (CMC) are replacing nickel-based superalloy components. This requires that the CMC components be instrumented to determine structural integrity. Traditional wire thermocouples report reliable data but are not suited for the conditions in the gas turbine engine since they affect gas flow and vibrational modes during operation. Thin-film thermocouples provide a true surface temperature measurement but there are reliability issues with thin-film thermocouples such as selective oxidation, dewetting, and metallurgical changes as well as small diffusional distances. Sensors utilizing the bulk semiconducting properties of SiC in the CMC have been developed. High purity sputtered platinum is coupled with SiC in the base CMC to form a new class of thermocouples which produced thermoelectric powers of 250uV/°K at ~1000°C. These thermocouples are able to survive high temperature by using sputtered diffusion barrier coatings. Performance of this new class of thermocouples will be presented and the potential for embedded thermocouples for advanced CMC will be discussed.