Grain Boundary and Intragranular Deformations during High Temperature Creep of a PM Nickel-Based Superalloy

Soula, Aurélie; Renollet, Y.; Boivin, Denis; Pouchou, Jean-Louis; Locq, Didier; Caron, Pierre; Bréchet, Y.

doi:10.7449/2008/superalloys_2008_387_394

Cited by 10 publications

(11 citation statements)

References 14 publications

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“…Digital image correlation [5][6][7][8][9] is a technique often used at larger scales to investigate how strain localizes around part geometric features, such as cracks, holes, and notches. Recently, this technique has been applied at increasingly smaller scales; i.e., in-situ scanning electron microscope (SEM) [10][11][12][13][14] and atomic force microscope [15][16][17][18] studies are now on the order of the underlying microstructural features. For example, Sutton et al [10,11] used SEM imaging with digital image correlation (DIC) to validate the experimental strain measurement capability over a large range of magnifications.…”

Section: Introductionmentioning

confidence: 99%

Microstructure-Dependent Local Strain Behavior in Polycrystals through In-Situ Scanning Electron Microscope Tensile Experiments

Tschopp

Bartha

Porter

et al. 2009

Metall Mater Trans A

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Digital image correlation of laser-ablated platinum nanoparticles on the surface of a polycrystalline metal (nickel-based superalloy Rene´88DT) was used to obtain the local strain behavior from an in-situ scanning electron microscope tensile experiment at room temperature. By fusing this information with crystallographic orientations from electron backscatter diffraction (EBSD), a subsequent analysis shows that the average maximum shear strain tends to increase with increasing Schmid factor. Additionally, the range of the extreme values for the maximum shear strain also increases closer to the grain boundary, signifying that grain boundaries and triple junctions accumulate plasticity at strains just beyond yield in polycrystalline Rene´88DT. In-situ experiments illuminating microstructure-property relationships of this ilk may be important for understanding damage nucleation in polycrystalline metals at high temperatures.

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Section: Introductionmentioning

confidence: 99%

Microstructure-Dependent Local Strain Behavior in Polycrystals through In-Situ Scanning Electron Microscope Tensile Experiments

Tschopp

Bartha

Porter

et al. 2009

Metall Mater Trans A

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“…Soula et. al utilized the standard deviation in the strain maps as an indicator of the degree of heterogeneity in the strain fields [23]. The average and standard deviation in the axial strain fields of the standard and serrated materials are very similar, 1.48 + 0.69% and 1.6 + 0.62% strain respectively.…”

Section: Dic Analysismentioning

confidence: 99%

Characterization of Strain Accommodation at Grain Boundaries of Nickel-based Superalloys

Carter¹,

Zhou²,

Sosa³

et al. 2012

Superalloys 2012 (Twelfth International Symposium)

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Elevated temperature in-situ experiments, local crystallographic mapping and digital image correlation techniques have been used to gain insight into strain localization near grain boundaries in polycrystalline René-104. Samples were heat treated to create either smooth (standard) or serrated grain boundaries. Deformation experiments concluded that strain tended to localize at triple points and special boundaries in the standard microstructure, while strain had a less-pronounced correlation in the serrated microstructure. Both materials exhibited grain boundary sliding (GBS), but the standard microstructure proved to be more susceptible. Site-specific extraction of TEM foils indicated that boundaries that exhibited strain localization experienced activation of multiple slip systems, while boundaries showing GBS showed activation of only a single slip system. Based on m′ analysis, slip transmission was expected to be difficult in boundaries that exhibited strain localization while boundaries that showed sliding allowed for easy slip transmission. A volume containing a boundary that exhibited GBS was analyzed to assess boundary surface topography and indicated that the boundary was macroscopically planer with local deviations that were on the order of the secondary γ′ size.

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“…Very few studies have been devoted to the understanding of the contribution of grain boundaries and local crystallography to the alloys durability [9,11,12]. As example, it was recently demonstrated that there is a pronounced contribution of grain boundaries to the creep deformation of NR6 superalloy [12].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2012

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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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Grain Boundary and Intragranular Deformations during High Temperature Creep of a PM Nickel-Based Superalloy

Cited by 10 publications

References 14 publications

Microstructure-Dependent Local Strain Behavior in Polycrystals through In-Situ Scanning Electron Microscope Tensile Experiments

Microstructure-Dependent Local Strain Behavior in Polycrystals through In-Situ Scanning Electron Microscope Tensile Experiments

Characterization of Strain Accommodation at Grain Boundaries of Nickel-based Superalloys

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

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