Mechanistic fatigue in Ni-based superalloy single crystals: A study of crack paths and growth rates

Abstract

The mechanistic basis of microstructurally short crack paths and growth rates is investigated in Ni-based superalloy single crystals using Crystal Plasticity (CP) and eXtended Finite Element (XFEM) analyses of experimental edge-cracked samples over a range of crystal orientations. Crack paths are determined to be those along crystallographic slip systems within which the slip is highest. Crack growth rates are determined by the crack tip critical stored energy density. Experimental observations of tortuous crack paths and their dependence on crystal orientation are reasonably well captured by the mechanistic model. Key features of alternating and straight crack paths are reproduced. The experimentally measured crack growth rates as a function of crystal orientation are also captured by the mechanistic model and controlled by the crack tip critical stored energy density which was found to be 385 Jm−2 in the Ni-based superalloy single crystals analysed. A new methodology for determination of critical stored energy density and mechanistic quantification of short crack growth rates is presented.