Low cycle fatigue behavior of inconel 718 at 298 K and 823 K

Fournier, D.; Pineau, A.

doi:10.1007/bf02667395

Cited by 296 publications

(128 citation statements)

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“…Partly this is due to the experimental difficulties of observing short cracks at high temperature. For a variety of superalloys, high temperature crack initiation has been observed at slip bands [16,17], inclusions [18], pre-cracked carbide particles [19] and preferentially oxidised carbides [20][21][22][23]. In some superalloys, primary carbides have script-like morphologies, which react to form oxide intrusions from which fatigue cracks can grow.…”

Section: Introductionmentioning

confidence: 99%

Short crack initiation and growth at 600°C in notched specimens of Inconel718

Connolley¹,

Reed²,

Starink³

2003

Materials Science and Engineering: A

115

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The natural initiation and growth of short cracks in Inconel ® 718 U-notch specimens has been studied at 600 o C in air. U notches were introduced through broaching, and hardness traces and optical microscopy on cross sections through the U notch broaching showed that the broaching process had introduced a deformed, work hardened layer. Fatigue tests were conducted under load control using a 1-1-1-1 trapezoidal waveform, on specimens with as-broached and polished U-notches. Multi-site crack initiation occurred in the notch root. Many of the cracks initiated at bulge-like features formed by volume expansion of oxidising (Nb,Ti)C particles. In unstressed samples, oxidation of (Nb,Ti)C particles occurred readily, producing characteristic surface eruptions. Scanning electron microscopy on metallographic sections revealed some sub-surface (Nb,Ti)C oxidation and localised matrix deformation around oxidised particles. A mechanism for crack initiation by carbide expansion during oxidation is discussed. Surface short crack growth rates in the notch root of polished specimens were measured using an acetate replica technique. Observed short crack growth rates were approximately constant across a wide range of crack lengths. However, there was a transition to rapid, accelerating crack growth once cracks reached several hundred microns in length. This rapid propagation in the latter stages of the fatigue life was assisted by crack coalescence. Polishing the U-notch to remove broaching marks resulted in a pronounced increase in fatigue life. IntroductionNickel-base superalloys like Inconel ® 718 (IN718) are used extensively for turbine discs and other components in industrial and aerospace gas turbines. Since turbine discs are safety-critical components, considerable effort is expended in determining their safe operating life. The lifing procedure adopted must enable the reliable prediction of the safe life of the disc, without being overly conservative. Once engines are in service, regular inspection of the engines and refinements of lifing models may enable life-extension programs to be considered. In the traditional predicted safe life philosophy, the life is declared based on laboratory specimen and component testing. In recent years a damage-tolerant approach to lifing has been adopted, in which it is accepted that components contain defects or inhomogeneities from which cracks can initiate. Assuming an initial flaw size c o , the fatigue life is determined as the number of cycles required to propagate the crack to some critical size c c . The initial size c o can be based on the maximum defect size present in the material, or on the minimum defect size detectable by nondestructive testing (NDT) [1]. Selection of c c is based on knowledge of the fracture toughness of the material, the limit load, the maximum allowable strain or maximum permitted compliance change for a particular component. Damage-tolerant lifing requires accurate information on fatigue crack initiation and growth rates. Fatigue lives are determi...

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Section: Introductionmentioning

confidence: 99%

Short crack initiation and growth at 600°C in notched specimens of Inconel718

Connolley¹,

Reed²,

Starink³

2003

Materials Science and Engineering: A

115

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“…This alloy is widely used and has been thoroughly studied: we focus here on observations carried out at Ecole des Mines de Paris [1][2][3] on Snecma material.…”

Section: Crack Initiation and Propagation Mechanisms In Da 718mentioning

confidence: 99%

“…[1,3,[8][9][10]). The effect of grain size reduction ,assumed to be beneficial on fatigue lives, was more particularly studied for conventional and DA 718 alloys (see e.g.…”

Section: Fatigue Crack Initiation Sitesmentioning

confidence: 99%

“…The effect of grain size reduction ,assumed to be beneficial on fatigue lives, was more particularly studied for conventional and DA 718 alloys (see e.g. [1,2,10]). These studies confirmed that the reduction in grain size produces a significant increase in fatigue life, as shown in Figure 1, where the material is tested at 350°C and a frequency of 1Hz under strain controlled conditions (Rε t =ε min /ε max =0) [10,3].…”

Section: Fatigue Crack Initiation Sitesmentioning

confidence: 99%

“…This produced a significant decrease in LCF life, as observed in Figure 1. Detailed studies [1] showed that in the case of crack initiation on particles, initiation can occur on sub-surface particles instead of surfaces particles; the competition between surface and sub-ε min ε max ε σ surface sites can be attributed not only to effects of crack propagation rates and thresholds in short cracks (see e.g. [12]), but also to the probabilistic nature of second phase particle presence and crack initiation on particles.…”

Section: Fatigue Crack Initiation Sitesmentioning

confidence: 99%

See 2 more Smart Citations

Probabilistic Life of DA718 for Aircraft Engine Disks

Deyber¹,

Alexandre²,

Vaissaud³

et al. 2005

Superalloys 718, 625, 706 and Various Derivatives (2005)

Self Cite

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The micro-mechanisms of crack initiation and propagation identified for DA 718, as well as the competition between initiation site types and locations, cannot be accurately accounted for by current certified methods used to establish aircraft engine disks life,essentially phenomenological.Once identified, these micro-mechanisms have been modelized by mesoscopic models using very few parameters and depending strongly on material mechanical behavior. LCF data scatter was mainly attributed to probabilistic nature of particle presence in a given volume, and probability of fracture at the first LCF cycle.In order to describe these effects and develop a model able to account for LCF scatter by the only means of physical mechanisms description, a global macroscopic and probabilistic model has been proposed. This model can be used as a post-processing routine of a finite element analysis.Confrontation of the global probabilistic model to experimental data gathered on notched samples gives good results, and the proposed method shows more realistic than the standard one on the cases exposed. Contrary to the standard method, it allows in addition to determine the predominant initiation site as a function of loading, material behavior and microstructure inherited from forging process, giving way to possible material and forging route optimisation at the design stage, to fulfill given structural life objectives.

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Effect of the LCF Loading Cycle Characteristics on the Fatigue Life of Inconel 718 at High Temperature

Taina¹,

Pasqualon²,

Velay³

et al. 2010

Superalloy 718 and Derivatives

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A series of both stresscontrolled and straincontrolled low cycle fatigue tests were conducted on alloy Inconel 718 to investigate the impact of various parameters on the behaviour of the material. Namely, focus was placed on the influence of major parameters such as the cycle frequency, the strain/stress rate, the holding time at various stress levels, the stress relaxation and the fatigue stress ratio. A detailed characterisation of the fatigueinduced rupture surfaces was performed to analyse the role of the alloy microstructure on the mode of crack propagation. In order to account for the time dependent effect of the mechanical response of the alloy, the PortevinLe Châtelier effect and the oxidation behaviour of the material are discussed. Results are analysed, in terms of MansonCoffin plots, to discriminate the relative impact of the various tested parameters on the stress/strain response and the fatigue life of the material.

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Low cycle fatigue behavior of inconel 718 at 298 K and 823 K

Cited by 296 publications

References 10 publications

Short crack initiation and growth at 600°C in notched specimens of Inconel718

Short crack initiation and growth at 600°C in notched specimens of Inconel718

Probabilistic Life of DA718 for Aircraft Engine Disks

Effect of the LCF Loading Cycle Characteristics on the Fatigue Life of Inconel 718 at High Temperature

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