Anisotropic creep fracture mechanism and microstructural evolution in nickel-based single crystal specimen with a center film hole

Abstract

The influence of orientation on the creep rupture properties of nickel-based single crystal superalloy with a center film hole was carried out at 980 °C and 300 MPa. The mechanisms of creep rupture and microstructural evolution of the specimens were studied through macro- and micro-morphological observations and finite element analysis. The central film hole exhibited the creep-strengthening effect on the nickel-based single crystal plate specimens. The degree of strengthening was related to crystal orientations, and the most prominent effect was observed in the [011] orientation. The steady-state creep rate of the specimens with central film holes decreased in the order of [001] > [011] > [111], which was completely opposite of the specimens without central holes. The creep rupture mechanism occurred due to the growth and aggregation of micro-cracks and voids. The microstructural evolution in the strengthening phase γ’ of the specimens with central film holes was closely related to the local stress state. In the high-stress zone where fractures originated, the rafting directions of the [011] and [111] orientations formed a 50° angle with the loading axis, and that of the [001] orientation was perpendicular to the loading axis. The modified crystal plastic-damage model was employed to perform the analysis of stress and damage around the center hole. The simulation results concorded well with the experimentally observed fracture behaviors.