Microstructural evolution and property degradation of a novel low-cost third-generation nickel-based single crystal superalloy during long-term thermal exposure

This study investigates the microstructural stability and creep properties of a third-generation nickel-based single-crystal superalloy after thermal exposure at 1120 °C. The LSW model and TIDC model were adopted to calculate the coarsening rates, respectively. As thermal exposure duration increases, a little quantity of TCP precipitates at 1000h, displaying rod-like and blocky morphologies. TCP are rich in W, Re, Mo and Cr, and are surrounded by the γ′ phase. Creep tests performed at 1120 °C/137 MPa demonstrate a substantial reduction in the creep life of the superalloy following 1000h of thermal exposure. This is mainly attributed to the weakening of the solid solution strengthening effect of the γ′ phase and the precipitation of harmful TCP phases. At 1000h of thermal exposure, the width of the γ matrix channels increases significantly, thereby significantly reducing the Orowan resistance to dislocation motion in the matrix. At the initial stage of creep, dislocations are more prone to bow out within the γ matrix channels, leading to a notably higher initial creep rate in the thermally exposed superalloy. Meanwhile, thermal exposure causes the originally stable interfacial dislocation network to fragment and degrade, making it difficult to effectively impede dislocation shearing and climbing. Upon entering the tertiary creep stage, a large number of superdislocations are able to shear into the interior of the γ′ precipitates, directly accelerating the creep failure process of the superalloy.