Creep notch effect in DD6 Ni-based single crystal superalloy: Experimental and modeling studies

Abstract

Single-crystal turbine blades feature complex internal passages and surface cooling holes for forced convection air cooling, which introduce notches that may influence the blades' resistance to creep damage. This work studies the creep rupture behavior and notch effect of DD6 Ni-based single crystal superalloy through creep tests conducted in atmospheric air at 950 °C. Round bar specimens with varying notch features were examined, with stress concentration factors ranging from 1.0 to 5.0. The experimental results revealed a pronounced strengthening effect in the notched specimens, where creep rupture life was extended by 6–16 times compared to smoothed specimens, with the extension increasing as the stress concentration rose. A new creep damage model incorporated stress triaxiality factor was developed to predict the creep rupture life of the notched specimens, achieving a relative error within 20 % between simulation and experimental results. A competitive mechanism between maximum principal stress and stress triaxiality results in the creep notch strengthening effect, in which the stress facilitates the rupture but the stress triaxiality exerts an inhibition effect. As the stress concentration factor increases, the inhibition becomes increasingly dominant over the promotion and leads to longer creep rupture life.