Modelling the optimum grain size on the low cycle fatigue life of a Ni based superalloy in the presence of two possible crack initiation sites

Alexandre, Franck

doi:10.1016/j.scriptamat.2003.09.043

Cited by 143 publications

(82 citation statements)

References 9 publications

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“…[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]. These fatigue studies also revealed that for very low grain size (lower than 10µm) obtained by DA heat treatment the results of fatigue life measurements were largely scattered.…”

Section: Fatigue Crack Initiation Sitessupporting

confidence: 72%

“…At large grain sizes typical transgranular stage I crack initiation along intense slip bands was observed [3,11]. On the other hand, when the grain size was smaller than about 10µm, fatigue cracks were preferentially initiated at second phase particles, such as niobium carbides (NbC) or titanium nitrides (TiN) [3]. This produced a significant decrease in LCF life, as observed in Figure 1.…”

Section: Fatigue Crack Initiation Sitesmentioning

confidence: 99%

“…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%

“…In this range of grain size the shortest fatigue lives were systematically associated with a modification in the nature of fatigue crack initiation sites. At large grain sizes typical transgranular stage I crack initiation along intense slip bands was observed [3,11]. On the other hand, when the grain size was smaller than about 10µm, fatigue cracks were preferentially initiated at second phase particles, such as niobium carbides (NbC) or titanium nitrides (TiN) [3].…”

Section: Fatigue Crack Initiation Sitesmentioning

confidence: 99%

See 4 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)

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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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Section: Fatigue Crack Initiation Sitessupporting

confidence: 72%

Section: Fatigue Crack Initiation Sitesmentioning

confidence: 99%

“…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%

Section: Fatigue Crack Initiation Sitesmentioning

confidence: 99%

See 3 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)

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Characterization of Microstructures Containing Abnormal Grain Growth Zones in Alloy 718

Flageolet¹,

Dahan²,

Villechaise³

et al. 2010

Superalloy 718 and Derivatives

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A well known issue encountered by forgers transforming Alloy 718 consists in the appearance of coarse grain zones during the thermo-mechanical process. Although some industrial solutions have been implemented in order to get rid of this type of microstructural defect, the consequences of the presence of such coarse grained areas on the material's mechanical properties are of great interest.In this work, some zones that have undergone abnormal grain growth (AGG) have primarily been characterized from a microstructural point of view by means of both optical and EBSD observations. Special attention has been paid to grain orientation, grain boundaries and grain size distributions. In addition the effects of these microstructures on 350°C deformation controlled fatigue crack initiation mechanisms and the subsequent lifetime have been assessed as well as on 350°C tensile properties have also been evaluated.The results will be discussed with regard to microstructure/mechanical behavior relationships.

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Influence of γ′ Precipitate Size and Distribution on LCF Behavior of a PM Disk Superalloy

et al. 2012

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The influence of γ' precipitate distribution on tensile and low cycle fatigue (LCF) behaviors of a powder metallurgy (PM) disk superalloy was investigated at 450°C. Four γ' particle distributions were obtained through various cooling paths and/or aging treatments in coarse grain size superalloy N18. The mechanical tests show that the main influence of the intragranular microstructure concerns the 0.2% yield stress (0.2%YS) and the ultimate tensile stress. Wide variations of the 0.2%YS affect the mean stress under non symmetrical loading but have only little effect on fatigue life, the lower the 0.2%YS, the longer the fatigue life. The fatigue life of N18 at 450°C is independent of the intragranular microstructure as long as the mean stress effect is correctly taken into account. As expected with the coarse grain size N18, no crack initiation at pores or inclusions was observed.A precipitation model was coupled with a critical resolved shear stress calculation providing 0.2%YS value for a given heat treatment sequence. Finally, this computation procedure was implemented in a numerical modeling of the LCF life of a disk taking into account the heat treatment applied to its wrought preform.

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Modelling the optimum grain size on the low cycle fatigue life of a Ni based superalloy in the presence of two possible crack initiation sites

Cited by 143 publications

References 9 publications

Probabilistic Life of DA718 for Aircraft Engine Disks

Probabilistic Life of DA718 for Aircraft Engine Disks

Characterization of Microstructures Containing Abnormal Grain Growth Zones in Alloy 718

Influence of γ′ Precipitate Size and Distribution on LCF Behavior of a PM Disk Superalloy

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