Microstructural stability and mechanical properties of a newly developed Ni–Fe-base superalloy

Microstructural stability and mechanical properties of a newly developed Ni–Fe-base superalloy for advanced ultra-supercritical coal-fired power plant applications during long-term exposure at 700–800 °C for up to 10,000 h have been studied. The results showed that major precipitates in the alloy were spherical γ′, irregular shaped MC and discrete M23C6 after the long-term exposure. Harmful phases, such as σ phase and η phase, were not observed. The amount of M23C6 increased with aging time at 700 °C while it decreased at 750 °C and 800 °C. During thermal exposure γ′ coarsened with increasing the exposure time and temperature. The yield strength of the alloy increased at first and then decreased with the exposure time at 700 °C, but it decreased gradually with increasing exposure time at 750 °C and above. The ductility was higher for exposed alloys than that obtained in as-aged alloy. The changes in yield strength and ductility were rationalized with respect to the dominant deformation mechanisms of the alloys.