Prediction of crack growth in a nickel-based superalloy under fatigue-oxidation conditions

Abstract

• This is the author's version of a work that was accepted for publication in the journal Engineering Fracture Mechanics. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication.A definitive version was subsequently pub- AbstractPrediction of oxidation-assisted crack growth has been carried out for a nickel-based superalloy at elevated temperature based on finite element analyses of oxygen diffusion, coupled with viscoplastic deformation, near a fatigue crack tip. The material constitutive behaviour, implemented in the finite element code ABAQUS via a user-defined material subroutine (UMAT), was described by a unified viscoplastic model with non-linear kinematic and isotropic hardening rules. Diffusion of oxygen was assumed to be controlled by two parameters, the oxygen diffusivity and deformation-assisted oxygen mobility. Low frequencies and superimposed hold periods at peak loads significantly enhanced oxygen concentration near the crack tip. Evaluations of near-tip deformation and oxygen concentration were performed, which led to the construction of a failure envelop for crack growth based on the consideration of both oxygen concentration and accumulated inelastic strain near the crack tip. The failure envelop was then utilised to predict crack growth rates in a compact tension (CT) specimen under fatigue-oxidation conditions for selected loading ranges, frequencies and dwell periods. The predictions from the fatigue-oxidation failure envelop compared well with the experimental results for triangular and dwell loading waveforms, with marked improvements 2 achieved over those predicted from the viscoplastic model alone. The fatigue-oxidation predictions also agree well with the experimental results for slow-fast loading waveforms, but not for fast-slow waveforms where the effect of oxidation is much reduced.

A crystal plasticity study of cyclic constitutive behaviour, crack-tip deformation and crack-growth path for a polycrystalline nickel-based superalloy

“…and one cubic slip system (100) [0][1][2][3][4][5][6][7][8][9][10][11]. The 2D in-plane traces of these four slip systems are shown in Fig.15a, and the accumulated shear strain are plotted in Fig.15b for each slip system.…”

“…By changing the orientation of the crack-tip grain to that for grain 1' and 1'', as shown in the inverse pole figure in Fig.4, crack growth will then follow the trace for the octahedral slip system (-1-11) [-110] and the cubic slip system (111) [1][2][3][4][5][6][7][8][9][10], respectively, which happen to have the maximum amount of accumulated slip (see Fig.16). …”

“…It turns out that four slip systems appear to have the most notable amount of shear deformation accumulated in four cycles, which include three octahedral slip systems (111) [1][2][3][4][5][6][7][8][9][10], (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)[-101] and (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)[110]…”

“…Constitutive, fatigue and creep behaviour of RR1000 at high temperature have been systematically studied at Portsmouth, and the data and the models are already available for validation of the material for turbine discs [1][2][3][4][5][6][7][8][9].…”

High Temperature Fatigue Crack Growth in a Ni-based Superalloy : Modelling Including the Interaction of Dwell Times

“…Examples of such models can be found in e.g. [39][40][41][42][43][44]. These models can prove useful in the description of a dwell time cycle, as they will also in some cases include history effects.…”