Low cycle fatigue of a directionally solidified nickel-based superalloy: Testing, characterisation and modelling

Kashinga, Rudolph J.; Li, Zhao; Silberschmidt, Vadim V.; Farukh, Farukh; Barnard, Nicholas; Whittaker, Mark; Proprentner, Daniela; Shollock, Barbara A.; McColvin, G.

doi:10.1016/j.msea.2017.10.024

Cited by 21 publications

(17 citation statements)

References 31 publications

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“…The crystallographic orientation (see Figure 7) was generated by assuming a fibre texture in which all grains have a <100> direction oriented near the z axis-the perpendicular directions being quasi-randomly oriented. This texture corresponds to the typical texture obtained in DS FCC alloys [8,9,14]. The particular Euler angles (using the Bunge convention) used to generate the fibre texture are φ 1 = 20…”

Section: Numerical Set-upmentioning

confidence: 80%

“…Their microstructure is characterised by columnar grains, aligned with the principal-stress axis (-z- axis by convention), that grow in the preferred crystallographic orientation <001> [ 8 , 9 ], leading to considerable anisotropy when the loading changes from the solidification direction to the perpendicular one. Different approaches have been used to model the constitutive response of heterogeneous structures of this type, going from transversally isotropic viscoplastic models [ 10 , 11 ], through the use of self-consistent schemes [ 12 , 13 ], to the crystal-plasticity-finite-element method (CPFEM) [ 14 ]. Transversally isotropic models are of interest when the computational cost is an issue, i.e., simulating a full structural component, but present three main drawbacks: (1) the assumption of one plane of isotropy is not true for a small numbers of grains in the cross-section, (2) strain and stress-fields’ concentrations among grains are not replicated and (3) mechanical tests in at least three different directions are needed to fit the constants.…”

Section: Introductionmentioning

confidence: 99%

“…These disadvantages can be overcome by representing explicitly the oligocrystalline microstructure and with the use of CP, since it takes into account the main deformation mechanisms, the shape and orientation of each grain. In previous studies, CPFEM models have been used to investigate the fatigue behaviour of DS Ni-base alloys [ 14 ], the stress and strain fields close to a crack tip [ 15 ] or the strain-field localisation in oligocrystalline specimens with the aim of analysing fatigue-crack nucleation [ 16 ]. Focusing the attention on the dynamic loading—only a few studies can be found which model this regime.…”

Section: Introductionmentioning

confidence: 99%

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Crystal-Plasticity-Finite-Element Modeling of the Quasi-Static and Dynamic Response of a Directionally Solidified Nickel-Base Superalloy

et al. 2020

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The flow stress behaviour of a directionally solidified nickel-base superalloy, MAR-M247, is presented through the combination of experiments and crystal-plasticity simulations. The experimental campaign encompassed quasi-static and dynamic testing in the parallel and perpendicular orientation with respect to the columnar grains. The material showed low strain-rate sensitivity in all cases. Virtual samples were generated with DREAM3d and each grain orientation was established according to the DS nature of the alloy. The elasto-visco-plastic response of each crystal is given by phenomenological-base equations, considering the dislocation–dislocation interactions among different slip systems. The hardening-function constants and the strain-rate sensitivity parameter were fitted with the information from tests parallel to the grain-growth direction and the model was able to predict with accuracy the experimental response in the perpendicular direction, confirming the suitability of the model to be used as a tool for virtual testing. Simulations also revealed that in oligocrystalline structures of this type, the yield-strength value is controlled by the grains with higher Schmid factor, while this influence decreases when plastic strain increases. Moreover, the analysis of the micro-fields confirmed that grains perpendicular to the loading axis are prone to nucleate cavities since the stresses in these regions can be twice the external applied stress.

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Section: Numerical Set-upmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Crystal-Plasticity-Finite-Element Modeling of the Quasi-Static and Dynamic Response of a Directionally Solidified Nickel-Base Superalloy

et al. 2020

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“…It was found that the S-N data can be fitted by the Coffin-Manson equation under the LCF condition, and the model based on hysteresis loop energy can be predicted lifetime under TMF condition. Kashinga et al 29 investigated the effect of dwell time on the low cycle fatigue of a directionally-solidified Ni-based superalloy using both experimental and computational methods. It was shown that the misorientations between columnar grains resulted in heterogeneous deformation and localized stress concentrations, which became more severe when the loading direction was perpendicular to a solidification direction, showing the shorter lifetime observed.…”

Section: Introductionmentioning

confidence: 99%

Low cycle fatigue behavior and fracture mechanism of a directionally solidified CM247 LC superalloy

Salehnasab

poursaeidi

2020

Preprint

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In gas turbines, superalloys are exposed to thermal as well as mechanical cyclic loadings during start-up and shut down processes, which can accelerate the formation of fatigue failure mechanisms. In the present study, low cycle fatigue behavior and fracture mechanism of a directionally-solidified CM247 LC superalloy at two temperatures of 600°C and 800°C were investigated. For this purpose, strain-controlled low cycle fatigue tests were carried out at 600°C and 800°C, and constant total strain amplitudes of 0.4, 0.6, 0.8, and 1% were applied during the totally reversed loading ratio (R = -1). The Coffin-Manson model, based on plastic deformation and a model based on the hysteresis energy criterion is used to predict fatigue life and evaluate the low cycle fatigue behavior. SEM observations of the surface of the failed specimen showed similar LCF failure mechanisms in all the strain amplitudes and temperatures.

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“…8 It is worth noticing that the fundamental understanding of deformation of the alloy is intrinsically important in regulating damage mechanisms and accurately assessing CF life. So far, the creep elevated temperature low-cycle fatigue (LCF) and thermo mechanical fatigue (TMF) behaviours of the alloy TMF is basically thermo mechanical fatigue have been considerably explored 4,[8][9][10][11][12][13] ; however, CF interaction behaviour of this alloy is scarce and least explored. 14 Although few studies 14,15 have been directed to explore the CF behaviour of CM 247 DS LC alloy, our understanding of CF damage NOMENCLATURE: Δɛ/2 (%), Total strain amplitude; Δε p /2 (%), Plastic strain amplitude; ε f ′ (−), Fatigue ductility coefficient; c (−), Fatigue ductility exponent; G (MPa), Shear modulus of elasticity; τ OR (MPa), Orowan stress; b (nm), Burger vector; h (nm), Width of the γ-matrix channel; γ (nm), Gamma micromechanisms is far less than required.…”

Section: Introductionmentioning

confidence: 99%

Creep‐fatigue deformation micromechanisms of a directionally solidified nickel‐base superalloy at 850°C

Kumar

Sahu

Das

et al. 2019

Fatigue Fract Eng Mat Struct

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In the present exploration, it was attempted to understand the creep‐fatigue (CF) deformation micromechanisms of alloy CM 247 DS LC by conducting low‐cycle fatigue (LCF) and CF tests employing strain amplitude ranging from 0.6% to 1.0% at T = 850°C in the air and performing extensive electron microscopic examinations. The cyclic life of the alloy lessens for all CF tests conducted at 1 and 5 minute dwell time in comparison to LCF tests. Transmission electron microscopy (TEM) examinations confirmed that during CF tests substructure consists of dislocation loop, mixed dislocations, and γ' rafting, a typical creep deformation signature of nickel‐base superalloys, it also consists of features observed during fatigue deformation such as anti‐phase boundary (APB)‐coupled dislocations inside γ' precipitates and local tangles of dislocations. This confirms that the deformation of CF‐tested specimens is ascribed to the synergistic effect of both creep and fatigue. This fact was further verified by scanning electron microscopic (SEM) examinations.

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Low cycle fatigue of a directionally solidified nickel-based superalloy: Testing, characterisation and modelling

Cited by 21 publications

References 31 publications

Crystal-Plasticity-Finite-Element Modeling of the Quasi-Static and Dynamic Response of a Directionally Solidified Nickel-Base Superalloy

Crystal-Plasticity-Finite-Element Modeling of the Quasi-Static and Dynamic Response of a Directionally Solidified Nickel-Base Superalloy

Low cycle fatigue behavior and fracture mechanism of a directionally solidified CM247 LC superalloy

Creep‐fatigue deformation micromechanisms of a directionally solidified nickel‐base superalloy at 850°C

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