Microstructural evolution and mechanical properties of a new Ni-based heat-resistant alloy during aging at 750 °C

Microstructural evolution and mechanical properties of a new candidate Ni-based heat-resistant alloy for advanced ultra-supercritical (A-USC) steam turbine rotors were investigated during aging at 750 °C up to 10000 h. The evolutions of γ′ particles inside austenitic grain and M₂₃ C₆ carbides along grain boundaries were characterized according to their morphologies, distributions, and growth kinetics. Mean radius of the γ′ spherical particles grew from 20.3 to 90.0 nm after aging for 10000 h, and the corresponding coarsening behavior was conformed to the law of Lifschitz-Slyosovd-Wagner (LSW). The weight fraction of γ′ particles slightly increased from 10.0 to 12.0 wt. % after aging of long duration at 750 °C. The Cr-rich M₂₃C₆ carbides discontinuously precipitated along grain boundaries, while other detrimental phases were not formed during the aging treatment, and hence the strength of grain boundary was enhanced by these discontinuously distributed carbides. The critical size of γ′ had a direct influence on the maximum hardness of this alloy. Moreover, this alloy presented a good impact toughness for the safety after long time aging at high temperature.