Creep fatigue of a directionally solidified Ni-base superalloy - smooth and cylindrically notched specimens

Abstract

Turbine blade life modelling is complicated by the presence of notches, dwells, high temperatures, thermal cycles and temperature gradients. Furthermore, directionally so- lidified (DS) Ni-base superalloys are highly anisotropic. This work seeks to characterize the response of the DS Ni-base superalloy CM247LC subjected to isothermal low cycle fatigue at either 750 or 950 °C. This study considers the effects of strain rate, dwells at the maximum temperature, and stress concentrations. Experiments were conducted under uniaxial loading on smooth and cylindrically notched round-bar specimens in both longitudinal and transverse orientations. The location of the creep-fatigue crack is at the maximum Hill's effective stress in the notched specimens. In addition, the notch behaviour is discussed in light of finite element analysis using an anisotropic elastic-crystal viscoplastic material model.