Effects of alloy elements on microstructure and creep properties of fine-grained nickel-based superalloys at moderate temperatures

This study investigated the effects of alloy elements on the microstructure and mechanical properties of the TM-321 and Mar-M247 nickel-based superalloys using a fine-grain process. The results showed that the yield strength of the TM-321 superalloy was higher than that of the Mar-M247 superalloy at room and moderate temperatures, and the creep test found the life of the TM-321 superalloy 1.55 times longer than that of the Mar-M247 superalloy at 760 °C/724 MPa because of three major reasons. First, the TM-321 superalloy displayed a superior solid-solution strengthening effect than the Mar-M247 superalloy due to its higher content of solid-solution strengthening elements. Second, the higher content of Ta addition in the TM-321 superalloy, which can inhibit the γ′ phase from coagulating and growing at high temperatures during long exposure, helped decrease the γ′ phase size and enhance its thermal stability. Moreover, TM-321 possessed a larger number of primary γ′ and secondary γ′ phases exhibiting superior creep resistance because of the precipitation strengthening effect. Third, superior to that of the M23C6 carbides of the Mar-M247 superalloy, the thermal stability of the M6C type carbide of the TM-321 superalloy helped improve its mechanical properties.