Decorrelated movements of Shockley partial dislocations in the γ-phase channels of nickel-based superalloys at intermediate temperature

Raujol, S.; Benyoucef, Mustafa; Locq, Didier; Caron, Pierre; Pettinari, F.; Clément, N.; Coujou, A.

doi:10.1080/14786430500254685

Cited by 33 publications

(20 citation statements)

References 17 publications

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“…The narrow channel widths, between the secondary γ′ precipitates, appear to promote dislocation dissociation. Raujol et al have reported similar observations after creep deformation of disk alloy NR3 at 650MPa and 700ºC [15]. Phase field dislocation dynamics simulations that support this hypothesis are discussed further in a following section.…”

Section: Discussion Of Experimental Resultsmentioning

confidence: 57%

Deformation Mechanisms in Ni-Base Disk Superalloys at Higher Temperatures

Kovařík¹,

Chen²,

Wang³

et al. 2008

Superalloys 2008 (Eleventh International Symposium)

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This paper presents results from a research initiative aimed at investigating high temperature creep deformation mechanisms in Ni-base superalloys through a combination of creep experiments, TEM deformation mechanism characterization, and state of the art modeling techniques. The effect of microstructure on dictating creep rate controlling deformation mechanisms was revealed for specimens with a bimodal γ′ size distribution that possessed different secondary γ′ size, tertiary γ′ volume fraction, and γ channel width spacing. It was found that the less creep resistant microstructure was the one with a greater secondary γ′ size, wider γ channel width, and higher volume fraction of tertiary γ′. Deformation in this microstructure commences by way of a/2<110> dislocations concentrated in the γ matrix at lower strains, which then transition to a SISF precipitate shearing mode at larger strains. The more creep resistant microstructure possessed a finer γ channel width spacing, which promoted a/2<110> dislocation dissociation into a/6<112> Shockley partials at lower strains and microtwinning at higher strains. Dislocation precipitate interaction was further explored using microscopic phase field modeling, which was able to capture key microstructural aspects that can favor dislocation dissociation and decorrelation since this appears to be a precursor to the microtwinning deformation mode. New viable diffusion pathways associated with the reordering processes in microtwinning have been explored at the atomistic level. All of the above activities have shed light onto the complex nature of creep deformation mechanisms at higher temperatures.

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Section: Discussion Of Experimental Resultsmentioning

confidence: 57%

Deformation Mechanisms in Ni-Base Disk Superalloys at Higher Temperatures

Kovařík¹,

Chen²,

Wang³

et al. 2008

Superalloys 2008 (Eleventh International Symposium)

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“…(Refer to Figure 4b). The process by which these dislocations dissociate into Shockley partial dislocations have previously studied in polycrystalline Ni-based superalloys through in-situ and post mortem TEM characterization where it was determined that a narrow γ channel width (distance between γ′ precipitates) promotes the dislocation dissociation process [19]. Figure 4.…”

Section: Resultsmentioning

confidence: 99%

“…Additionally, there are extra twin reflections that are present, which provides direct evidence that these highly planar faulted structures are microtwins. The appearance of microtwins during creep in Ni-based superalloys have been reported in both polycrystalline disk and single crystal blade alloys [17][18][19][20][21]. One of the earliest experimental evidence of microtwinning in a γ′ strengthened Ni-base Superalloy was reported by Guimier and Strudel in Waspaloy deformed above 500ºC [20].…”

Section: Resultsmentioning

confidence: 99%

A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus®

Unocic¹,

Daehn²,

Unocic³

et al. 2010

7th International Symposium on Superalloy 718 and Derivatives (2010)

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A preliminary study on the evolution of creep deformation substructure in Ni-base superalloy Allvac 718Plus has been performed. Specimens crept at 620 MPa and at temperatures ranging from 690-732ºC were examined utilizing diffraction contrast TEM characterization techniques.Creep was interrupted at 1-2.5% strain in order to study the deformation substructure following a limited amount of deformation. The dominant deformation modes at each of the test temperatures were highly planar in nature and involved shearing of the matrix and ′ precipitates on {111} glide planes. In addition, paired a/2<110> dislocations were evident which suggest an antiphase boundary shearing mechanism. Creep induced microtwinning was also observed at the highest creep temperature which was created by identical a/6<112> Shockley partial dislocations that shear the matrix and ′ precipitates on consecutive close packed {111} glide planes. IntroductionNi-based superalloys are predominately utilized in aircraft and land-based industrial gas turbine engines where they excel in the retention of mechanical properties during service at elevated temperatures. In order to improve both engine performance and efficiency significant emphasis has been placed on developing alloys that can operate at higher temperatures without significant loss in structural integrity. In the conventional 718 alloy, the upper bound service temperature is limited to ∼650º, which is governed primarily by microstructural instability through coarsening of the prime strengthening DO 22 structured Ni 3 Nb-based γ′′ precipitate phase followed by its transformation to the equilibrium orthorhombic Ni 3 Nb δ-phase [1][2][3][4][5][6]. With this in mind, Allvac 718Plus was developed with the specific goal of increasing the temperature capability by ∼55ºC while maintaining the excellent workability and weldability characteristics of 718 [7][8]. The alloy chemistry was modified such that the Fe content was reduced while the W, Co and Al/Ti ratio was increased. This combination of changes enables the precipitation of ordered L1 2 structured (Ni 3 Al,Ti) based γ′ precipitates that are coherently embedded in a solid solution γ matrix [9][10]. It is expected that the alteration of the prime-strengthening constituent from γ′′ to γ′ will have a significant effect on the thermal stability of this alloy as well as the high temperature mechanical properties.In Ni-based superalloys where γ′ is the prime-strengthening phase, a rich variety of deformation modes have been reported [11][12][13][14][15][16][17][18]. The precipitates themselves are unique in that during deformation, the γ′ precipitates impart resistance to plastic deformation since they act as effective γ γ γ γ 7th International Symposium on Superalloy 718 and Derivatives Edited by:

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“…278decorrelation process. This uncoupled motion of partial dislocations has been enlightened in this material and exists also in other polycrystalline Ni-based superalloys as well as in monocrystalline Ni-based superalloys [4,9]. It is a matter of importance as it is at the origin of a frequent shearing process.…”

Section: Tem Observationsmentioning

confidence: 99%

“…Dissociated dislocations constrained to move through channels present different types of behaviour. Two different mechanisms involving partial dislocations have been studied in previous papers: the dislocations have been precisely characterized and the local stress corresponding to the observed dislocation configurations have been evaluated [3,4]. This paper is aimed to give a more general analysis of the condition for each mechanism to occur using a combination of dislocation dynamics simulations, analytical calculations and experimental observations.…”

Section: Introductionmentioning

confidence: 99%

Decorrelated Dislocation Movement in the γ-Matrix Channels of a Ni-Based Superalloy: Experiment and Dislocation Dynamics Simulation

Pettinari‐Sturmel

Douin

Locq³

et al. 2011

AMR

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Abstract. The mechanical behavior of the polycrystalline NR3 Ni-based superalloy has been investigated at the microscopic scale. The elementary deformation mechanisms have been analyzed using transmission electron microscope observations as well as in situ straining experiments. Under low stress and relatively low strain rate conditions, a large variety of shearing micromechanisms has been observed depending on the local microstructure and the local effective stress. The influence of the smallest precipitates on the creep behavior has been enlightened: they induce narrow channels which act as obstacle for the movement of the dislocations. In the case of the narrowest channel, the deformation can operate by the propagation of Shockley dislocations or else, by the only propagation of the leading partial resulting from the partial dislocation decorrelation. The occurrence of the observed micromechanisms has been quantitatively analyzed using a nodal dislocation dynamics simulation.

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Decorrelated movements of Shockley partial dislocations in the γ-phase channels of nickel-based superalloys at intermediate temperature

Cited by 33 publications

References 17 publications

Deformation Mechanisms in Ni-Base Disk Superalloys at Higher Temperatures

Deformation Mechanisms in Ni-Base Disk Superalloys at Higher Temperatures

A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus®

Decorrelated Dislocation Movement in the γ-Matrix Channels of a Ni-Based Superalloy: Experiment and Dislocation Dynamics Simulation

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Decorrelated movements of Shockley partial dislocations in the γ-phase channels of nickel-based superalloys at intermediate temperature

Cited by 33 publications

References 17 publications

Deformation Mechanisms in Ni-Base Disk Superalloys at Higher Temperatures

Deformation Mechanisms in Ni-Base Disk Superalloys at Higher Temperatures

A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus&reg;

Decorrelated Dislocation Movement in the γ-Matrix Channels of a Ni-Based Superalloy: Experiment and Dislocation Dynamics Simulation

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A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus®