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 gamma', irregular shaped MC and discrete M23C6 after the long-term exposure. Harmful phases, such as phase and eta phase, were not observed. The amount of M23C6 increased with aging time at 700 degrees C while it decreased at 750 degrees C and 800 degrees C. During thermal exposure gamma' 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 degrees C, but it decreased gradually with increasing exposure time at 750 degrees 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. (C) 2014 Elsevier B.V. All rights reserved.