Thin film thermocouples for advanced ceramic gas turbine engines

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Thin film temperature sensors were developed for both the rotating and non-rotating components of ceramic-based gas turbine engines. These type-S thin film thermocouples were fabricated on hot isostatically pressed Si3N4 substrates (Norton-TRW NT154), whose surfaces were altered to maximize adhesion. Annealing cycles and sputtered oxide interlayers were utilized in the fabrication to prevent blistering of the metallic thin films and enhance adhesion. Completed sensors were tested at temperatures up to 1300°C, with a variety of temperature gradients applied along the length of the test bars. Both oxidizing and inert gas atmospheres were used to investigate environmental effects on sensor performance. Sensor tests performed in oxidizing atmospheres resulted in the formation of volatile platinum and rhodium oxides, which caused significant drift and ultimate failure. Sensor tests performed in inert gas environments had drift rates 5-10 times lower than those observed in oxidizing atmospheres. Therefore, sputtered oxide overcoats were employed to minimize adverse reactions between the sensor elements and the atmosphere, the results of which will be discussed in terms of sensor performance. © 1994.

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Surface and Coatings Technology