MORPHOLOGY OF γ' PRECIPITATES IN SECOND STAGE HIGH PRESSURE TURBINE BLADE OF SINGLE CRYSTAL NICKEL-BASED SUPERALLOY AFTER SERVICED

摘要

The morphology of the γ' precipitates in the single crystal nickel-based superalloy serviced as the second stage high pressure turbine blade of the aircraft engine was examined. The aim of this work was to estimate the temperature and the stress distribution, and the stress direction of the blade in service. The blade was cut into three parts parallel to (001) plane at 8, 40 and 64mm from the tip. These parts were named as the tip, middle and root parts. Furthermore, these three parts were cut into six parts parallel to {100} which were almost normal to the surface from the leading to the trailing edge at interval of 6mm. Microstructure observations by a FE-SEM were carried out on the thirty portions of each part parallel to (001) and {100} planes at the vicinity of the interface between the coating layer and the matrix in the suction and pressure sides. Most of the γ' precipitates contacted each other toward almost parallel to the surface at the vicinity of the interface in the blade. Especially, at the leading edge of the pressure side of the tip and middle parts, the rafted γ/γ' structures start to collapse. Consequently, the blade in service, at the leading edge of the pressure side of the tip and middle parts were exposed to the highest temperature and stress conditions. And the multi-axial compressive stresses parallel to the blade surface were expected to act on the blade in service.