Influence of Both γ′ Distribution and Grain Size on the Tensile Properties of UDIMET 720Li At Room Temperature

Vaunois, Jean‐Roch; Cormier, Jonathan; Villechaise, Patrick; Devaux, Alexandre; Flageolet, Benjamin

doi:10.1002/9781118495223.ch14

Cited by 16 publications

(23 citation statements)

References 15 publications

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“…The resolution of the micrographs was adapted so that the smallest dimension of the δ-phase was defined by at least five pixels. The δ-phase fraction and morphology were images processed using Fiji® software with a similar algorithm as the one developed at Institut Pprime [26].…”

Section: Microstructural Characterization Methodsmentioning

confidence: 99%

Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

Texier

Cormier

Villechaise

et al. 2016

Materials Science and Engineering: A

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105

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Fatigue crack initiation in the direct aged version of the nickel-based superalloy Inconel 718 has been investigated at room temperature in the low stress/very high cycle regime via ultrasonic fatigue testing. Three different microstructures have been examined at the same strain amplitude in order to understand the influence of non-metallic inclusions (NMIs), i.e. carbides, carbonitrides and nitrides, and Σ3 twin boundary density on lifetime and failure mode. A slight refinement in grain structure and a higher Σ3 twin boundary density is associated with substantial reductions in lifetime. Decreasing Σ3 twin boundary density for fine grain microstructures results in a change in crack initiation mechanism from strain localization within grains at the high end of the grain size distribution to cracking of NMIs. To study the early stages of crack initiation and growth, specimens with pre-cracked NMIs were also tested in order to examine the role of the surrounding grain structure. Pre-cracked NMIs mainly result in macroscopic failure initiation at NMIs independent of the wrought microstructure. However, pre-loading specimens within the plastic domain highlighted the competition in crack initiation mode between cracked-NMIs and favorably oriented twin boundaries. Crack arrest from most of the pre-cracked NMIs demonstrates that surrounding grain structure (grain orientation, local plasticity and roughness in the vicinity of crack tip due to pre-straining) play a key role in the fatigue life of components stressed in the nominal elastic regime.

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Section: Microstructural Characterization Methodsmentioning

confidence: 99%

Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

Texier

Cormier

Villechaise

et al. 2016

Materials Science and Engineering: A

Self Cite

105

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“…Additionnal SEM observations to characterize the evolution of the δ phase during this heattreatment have been performed using a JEOL JSM 7000F field emission gun SEM and a backscattered electron imaging mode. Image processing techniques developed in the laboratory using the Visilog software [28] permit to perform a stereological analysis of the δ phase. The Gaussian averages of the length, width and equivalent diameters of the δ particles before and after the heat treatment are summarized in Table 2.…”

Section: Effect Of the Heat Treatment On The Microstructurementioning

confidence: 99%

Influence of residual stresses on the fatigue crack growth from surface anomalies in a nickel-based superalloy

Doremus

Cormier

Villechaise

et al. 2015

Materials Science and Engineering: A

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“…1c, average grain size = 456 µm, range = [45 µm -1900 µm]) and a homogenous intragranular γ' precipitation built with secondary (cooling) particles whose average size is 69 nm (Fig. 1f) and fine tertiary particles whose average size is close to 10 nm [17]. A very small content of primary γ' particles (0.7%) remains after such a ST.…”

Section: Methodsmentioning

confidence: 99%

“…A very small content of primary γ' particles (0.7%) remains after such a ST. This microstructure will be mentioned in the following of the article as the "HS-homogenous" microstructure since very high 0.2% yield stress (YS) are obtained with such a supersolvus heat treated alloy (YS ~ 1090 MPa) [17]. Moreover, this microstructure presents very little strain hardening during tensile testing [17].…”

Section: Methodsmentioning

confidence: 99%

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Mechanical Behavior and Damage Processes of Udimet 720Li: Influence of Localized Plasticity at Grain Boundaries

Villechaise¹,

Cormier²,

Billot³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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The creep-fatigue properties at 700°C of cast and wrought Udimet 720Li superalloy have been investigated. As expected, the introduction of a dwell time as low as 1s at maximum stress induces a creep-fatigue life debit compared to pure fatigue conditions. It is demonstrated that the mechanical behavior (plastic strain rate, ductility) is greatly affected by the grain size and precipitation distribution. Moreover, the creep-fatigue life seems to be hardly affected by the alloy microstructure, due to the development of localized damage. Whatever the environmental conditions (i.e. in air or under vacuum), failure has been identified to be intergranular.To get a better understanding of the contribution from grain boundaries to the first stage of plasticity and damage development, in-situ tensile tests were performed in a scanning electron microscope (SEM). In a first step to get a full understanding of the role of grain boundaries in controlling the mechanical properties and alloy durability, we first paid attention to the contribution of the local grain crystallography to the plasticity heterogeneity near grain boundaries. This was performed at room temperature where, compared to creepfatigue loading at 700°C, the role of viscoplasticity can be neglected. First evidences of slip activity were shown to depend only on the local Schmid factor and not on the grain size. In addition, these experiments were performed using samples with a homogeneous grain size and a homogeneous intragranular γ' particles distribution. By using the recently developed electron backscattered diffraction (EBSD) pattern cross-correlation technique, it has been shown that critical grain configurations exist, which lead to the activation of micro-volumes (~ 1-2 µm 3 at maximum) where intense plastic activity develop near grain boundaries. These volumes nucleate at grain boundaries separating two grains having a slip activity contrast: they develop in the grain less favorably oriented for slip, ahead of slip bands which had developed in the grain with easier slip. It is observed that the very first stages of development of intense plasticity micro-volumes are quite insensitive to a contrast in Schmid factors between neighboring grains. The local von Mises stress magnitude in these volumes can be as large as several GPa, sufficient enough to develop micro-cracking.

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Influence of Both γ′ Distribution and Grain Size on the Tensile Properties of UDIMET 720Li At Room Temperature

Cited by 16 publications

References 15 publications

Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

Influence of residual stresses on the fatigue crack growth from surface anomalies in a nickel-based superalloy

Mechanical Behavior and Damage Processes of Udimet 720Li: Influence of Localized Plasticity at Grain Boundaries

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