Creep Crack Growth Behaviour of Alloy 718

Liu, C.D.; Yan, Han; Yan, Maode; Chaturvedi, M.C.

doi:10.7449/1991/superalloys_1991_537_548

Cited by 13 publications

(10 citation statements)

References 13 publications

(13 reference statements)

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“…In general, crack growth caused by creep is attributed to diffusion behaviour, which is presented as the movements of vacancies [12,13]. Under the creep situation, a constant applied loading leads to stress concentration at the triple points which are formed by the three adjacent grains ( Figure 3).…”

Section: Established Principles In the Literaturementioning

confidence: 99%

“…This, on the one hand, results in plastic deformation (crack opening) at the crack tip; on the other hand, it gives a more favourable situation for diffusion. (f) Diffusion creep [12,13] provides a mechanism that leads to grain elongation and then further crack opening. In addition, since atoms diffuse from a high-to a low-concentration region, more vacancies are generated and converged at the crack tip, where highly localised stress is presented, which provides a more favourable situation for creep damage.…”

Section: Established Principles In the Literaturementioning

confidence: 99%

“…Specifically, on the one hand, a crack may traverse (or grow along) the grain boundary, where the weakest atomic bonds are present. This may be attributed to stress concentration at the grain boundary, since the existence of the stress gradient results in the convergence of vacancies [12,13], and in particular, the vacancies at the grain boundary provide favourable conditions for diffusion creep [10,50]. In this case, the crack along the grain boundary gradually accumulates, and then reaches the next triple point, where the opportunity for re-direction is provided.…”

Section: Crack Propagationmentioning

confidence: 99%

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Crack Propagation Mechanisms for Creep Fatigue: A Consolidated Explanation of Fundamental Behaviours from Initiation to Failure

Liú

Pons

2018

Metals

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Background-Creep-fatigue damage is generally identified as the combined effect of fatigue and creep. This behaviour is macroscopically described by crack growth, wherein fatigue and creep follow different principles. Need-Although the literature contains many studies that explore the crack-growth path, there is a lack of clear models to link these disparate findings and to explain the possible mechanisms at a grain-based level for crack growth from crack initiation, through the steady stage (this is particularly challenging), ending in structural failure. Method-Finite element (FE) methods were used to provide a quantitative validation of the grain-size effect and the failure principles for fatigue and creep. Thereafter, a microstructural conceptual framework for the three stages of crack growth was developed by integrating existing crack-growth microstructural observations for fatigue and creep. Specifically, the crack propagation is based on existing mechanisms of plastic blunting and diffusion creep. Results-Fatigue and creep effects are treated separately due to their different damage principles. The possible grain-boundary behaviours, such as the mismatch behaviour at grain boundary due to creep deformation, are included. The framework illustrates the possible situations for crack propagation at a grain-based level, particularly the situation in which the crack encounters the grain boundary. Originality-The framework is consistent with the various creep and fatigue microstructure observations in the literature, but goes further by integrating these together into a logically consistent framework that describes the overall failure process at the microstructural level.

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Section: Established Principles In the Literaturementioning

confidence: 99%

Section: Established Principles In the Literaturementioning

confidence: 99%

Section: Crack Propagationmentioning

confidence: 99%

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Crack Propagation Mechanisms for Creep Fatigue: A Consolidated Explanation of Fundamental Behaviours from Initiation to Failure

Liú

Pons

2018

Metals

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“…As reported in the literature, coarse grain size superalloys usually exhibit lower creep crack growth rates (Floreen, 1983). For example, an inverse relation between CCGRs and grain size has been reported for Alloy 718 at 650°C (Liu et al 1991). Stronger grain-size dependence is predicted by the model for materials with a continuous grain boundary precipitate network that may result from overaging or extended service exposure.…”

Section: Creep-brittle Casesmentioning

confidence: 55%

Life Prediction of Gas Turbine Materials

Wu¹

2010

Gas Turbines

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“…The results presented in Table III The K th values for various oxide formations are predicted as a function of yield strength using the oxide properties and transformation strains listed in Table III and an oxide layer of 0.25 lm, which was estimated based on micrographs of crack-tip oxide layers reported in the literature. [28] The computed K th values for an oxide layer of 0.25 lm are compared against experimental data [2,28,[41][42][43][44][45][76][77][78][79][80][81][82][83] for Ni-base superalloys in Figure 5. The experimental K th data include those of powder metallurgy (PM) and wrought alloys, which all exhibit oxidation-induced time-dependent crack growth.…”

Section: Model Applicationsmentioning

confidence: 99%

Time-Dependent Crack Growth Thresholds of Ni-Base Superalloys

Chan

2014

Metall Mater Trans A

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A micromechanical model has been developed for predicting the time-dependent crack growth threshold and its variability by considering oxide formation or cavity formation ahead of an elastic crack subjected to a sustained load at a stress intensity factor, K, at elevated temperatures in air. It is demonstrated that stress relaxation associated with a volume-expansion process such as the formation of creep cavities or oxides with a positive transformation strain can induce residual stresses at the tip of the elastic crack. The near-tip residual stresses must be overcome by the external load, thereby instigating a growth threshold, K th , for the onset of time-dependent crack growth. This micromechanical framework provides the basis for developing appropriate predictive models for the time-dependent crack growth thresholds associated with several damage processes, including (1) oxidation-assisted intergranular crack growth, (2) K-controlled creep crack growth along an intergranular path, and (3) stress corrosion cracking. The micromechanical threshold models have been utilized to predict the time-dependent crack growth thresholds of a variety of Ni-base superalloys. The material parameters that contribute to the variability of the time-dependent crack growth thresholds have been identified and related to variations of mixed oxides or creep cavities formed near the crack tip. A size scale effect is also predicted for the transformation toughening phenomenon, which is largest at or below K th but diminishes at increasing K levels above the threshold. Finally, the micromechanical models are utilized to identify means for suppressing time-dependent crack growth in Ni-base alloys.

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Creep Crack Growth Behaviour of Alloy 718

Cited by 13 publications

References 13 publications

Crack Propagation Mechanisms for Creep Fatigue: A Consolidated Explanation of Fundamental Behaviours from Initiation to Failure

Crack Propagation Mechanisms for Creep Fatigue: A Consolidated Explanation of Fundamental Behaviours from Initiation to Failure

Life Prediction of Gas Turbine Materials

Time-Dependent Crack Growth Thresholds of Ni-Base Superalloys

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