Microstructural Parameters Controlling High-Temperature Creep Life of the Nickel-Base Single-Crystal Superalloy MC2

The influence of both topologically close-packed (TCP) phase precipitation and pores on the creep life of a single-crystal superalloy has been studied at 1323 K (1050 °C)/160 MPa. Despite very reproducible primary and secondary creep stages, the creep life is scattered for this specific condition where a very steep tertiary creep stage is observed, corresponding to a highly localized failure process. Image processing was performed after failure to determine the stereological parameters characterizing pores and TCP-phase particles. It was determined that pores are major determinants of creep life under these temperature and stress conditions. It was also observed that the average surface area or the density of pores is not sufficient to explain creep life variability. A homogenization method including modified γ/γ′ microstructure area surrounding pores and TCP-phase particles was developed and correlated to creep life. It is shown that the greater the extent of the modified microstructure, the lower the creep life. Moreover, a better understanding of the TCP-phase role in controlling the creep life was obtained: TCP-phase particles modified the local stress field and disturbed the local γ/γ′ microstructure. They enhance the generation of vacancies and subsequent nucleation and growth of pores.