The Effect of Long-Term Thermal Exposure on the Microstructure and Stress Rupture Property of a Directionally Solidified Ni-Based Superalloy

Microstructural degradation and microstructure-property relationship during long-term thermal exposure in a directionally solidified Ni-based superalloy are systematically studied. The coarsening kinetics of gamma' precipitation conforms well to the LSW model during the long-term thermal exposure. The detailed time dependence of MC decomposition during the long-term thermal exposure is revealed. Grain boundary coarsening was mainly facilitated by gamma' and M23C6 precipitates coarsening in GBs region, and the GB coarsening kinetics conforms well to the JMAK theory. During different stages of the thermal exposure, dominant factors for the decrease of stress-rupture lifetime vary due to the evolution of multiple microstructures (gamma' coarsening, MC decomposition, and grain boundary coarsening).