Evaluation of microstructural degradation and its corresponding creep property in integral cast turbine rotor made of K424 alloy

Abstract

Abstract This study establishes the relationship between the microstructural degradation and temperature distribution of an integral cast turbine rotor made of K424 alloy, based on a selection of quantitative characterization parameters. The influence of the thermal exposure at a very high temperature on the creep property of the turbine rotor was also analyzed by isothermal and non-isothermal creep tests. The results indicated that the turbine rotor experienced overheating exposure during engine test, where the upper locations on the blades of turbine rotor were exposed to the highest temperature (about 1080\u202f°C). The 1080\u202f°C temperature jump during the non-isothermal creep had significant influence on the creep property of the turbine rotor. Extensive amount of dislocations cut through the γ′ precipitates and impinged on the grain boundaries to form dislocation tangles upon the high temperature jumps due to the relatively lower γ′ volume fraction. Stress concentration induced by the accumulation of dislocations was responsible for the initiation of cracks along grain boundaries. This study will be helpful for providing guidelines for alloy design aimed at improving the creep resistance of superalloy during non-isothermal creep with the introduction of overheating exposure, and thus enhance the service safety of turbine engine components.