High‐Temperature Creep Behavior and Damage Mechanism of an Advanced Powder Metallurgy Ni‐Based Superalloy

The creep behavior of a novel powder metallurgy (PM) Ni‐based superalloy is investigated at temperatures ranging from 760 to 815 °C and stress levels in the 480–620 MPa. The steady‐state creep rate, strain to rupture, and rupture time are analyzed based on the Monkman–Grant relation (MGR) and the modified MGR (MMGR). The creep damage factor is redefined by the analysis of Monkman–Grant ductility (MGD). A general relationship between the time reaching MGD and creep life is established. The sharply accelerated creep stage is proposed and the MMGR of the transient creep parameters in this stage is established. The nucleation, growth, and connection of grain‐boundary creep cavities dominate the creep damage of the alloy. The stress concentration caused by the accumulation of dislocations at grain boundaries and σ‐phase interfaces and the grain‐boundary slipping are the main reasons for the nucleation of grain‐boundary cavities. The coupling effect of the temperature and the stress aggravates the damage of grain boundary and the degradation of microstructure.