The mechanism of creep in gamma prime precipitation-hardened nickel-base alloys at intermediate temperatures

Leverant, G. R.; Kear, B. H.

doi:10.1007/bf02811560

Cited by 226 publications

(79 citation statements)

References 4 publications

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“…The concept of reordering is a more precise description of the "atomic shuffles that were mentioned in the original work of Kear et al [4][5][6] in which the a 112 stacking fault ribbon structure was first introduced. Note that the extended nature of the ribbons in these samples precluded examination of each transition.…”

Section: Discussionmentioning

confidence: 99%

“…The structure of these dislocations and their role in viscous slip of superalloys was originally discussed by Kear et al [4,5]. TEM studies [3,6] have shown that the a 2 112 dislocations making up the a 112 ribbon are dissociated into partial dislocations enclosing a low energy superlattice intrinsic or extrinsic stacking fault (SISF and SESF respectively). According to these studies, the dissociation of a complete a 112 ribbon in the γ would take place according to the following scheme: It should be noted, that the a 112 dislocation is rarely observed passing through a single γ precipitate in its entirety.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

High-resolution electron microscopy of dislocation ribbons in a CMSX-4 superalloy single crystal

Vorontsov¹,

et al. 2012

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

High-resolution electron microscopy of dislocation ribbons in a CMSX-4 superalloy single crystal

Vorontsov¹,

et al. 2012

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“…During high temperature creep deformation, the γ′ precipitates play a vital role in restricting plastic deformation as high energy configurations such as antiphase domain boundaries (APB), complex stacking faults (CSF), superlattice intrinsic stacking faults (SISF), and superlattice extrinsic stacking faults (SESF) develop if the precipitates were to be sheared by a/2<110> type perfect matrix dislocations, a/3<112> super-Shockley partial dislocations, or a/6<112> Shockley partial dislocations. There have been many detailed post mortem TEM characterization studies describing the deformation mechanisms responsible for creating such defect structures and implications they may have on controlling creep deformation for several different Ni-base superalloys [1][2][3][4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

“…Examples of the different deformation mechanisms that have been observed during creep deformation are: (1) Orowan looping and shearing of γ' particles by coupled a/2<110> dislocations, (2) isolated faulting of the γ' particles, (3) thermally-activated microtwinning, (4) extended, continuous faulting of precipitates and matrix, and (5) dislocation climb by-pass at the highest temperatures. The preference for these mechanisms are dependent on factors such as alloy chemistry, the initial microstructure, stress, and temperature.…”

Section: Introductionmentioning

confidence: 99%

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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“…Linear relationships were observed between ln ( p ) and 1/T as well as ln ( c ) and 1/T. Activation energy for the tensile creep was 506kJ/mol which almost equivalents to that for Mar M200 (557kJ/mol [7] and 628kJ/mol [8]) and CMSX-3 (495kJ/mol [9]). They are generally accepted values for higher ' containing superalloys, although they are considerably large in comparison with that for selfdiffusion in nickel, about 270kJ/mol.…”

Section: Resultsmentioning

confidence: 77%

A Study on Bending Deformation Behavior of NI-Based DS and SC Superalloys

Tamaki¹,

Fujita²,

Okayama³

et al. 2004

Superalloys 2004 (Tenth International Symposium)

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IntroductionBending deformation behavior of Ni-based directionally solidified (DS) and single crystal (SC) superalloys was studied. For a DS superalloy, bending creep curves at 800, 850 and 900 O C were obtained. As a result, the stress exponents for the steady-state creep displacement rates of the bending creep were found to show the almost same values as those for the steady-state creep strain rates of the tensile creep. It was also confirmed that activation energy for the bending creep corresponded to that for the tensile creep within the temperature range of this study. It can be concluded from these results that the bending creep behavior of DS superalloys can be deduced from the simple tensile creep test data because the correspondence of the deformation mechanism between the bending and the tensile creep was proven.Uniaxial tensile deformations such as creep have been extensively characterized for Ni-based directionally solidified (DS) and single crystal (SC) superalloys. However, only few studies [1] [2] have been reported concerning bending deformation behavior of Nibased DS and SC superalloys. It can be considered as very important to characterize bending deformation behavior of Nibased superalloys used for gas turbine components because bending stresses are often observed in some critical portions of gas turbine blades and vanes. The representative example is the tip shroud [3]. The longer blades tend to be equipped with the tip shroud in order to effectively reduce gas leakage and increase high cycle fatigue margin on fundamental modes such as 1 st bending. The overhanging of the shroud causes a relatively high bending stress at the fillet which has become to be exposed to more severe circumstances due to the increase in gas-firing temperature of modern gas turbines. For reasons mentioned above, precise investigations of bending deformation behavior of Ni-based DS and SC superalloys have been required.For a SC superalloy, notable secondary orientation dependence of the steady-state creep displacement rates was observed at 750 O C/950MPa. The specimen, whose slip system caused the 45 Oshear-type slip, exhibited apparently faster creep displacement rate than the specimen, whose slip system caused the hinge-type deformation, even if their tensile/compressive directions were same. At 982 O C/294MPa, secondary orientation dependence of the creep displacement rates was not significant while [011] specimens showed higher creep resistance than [001] specimens. The microstructural observations after bending creep tests provided interesting results that one type of raft-like microstructure observed in the tension side of [011] specimens was also found in the compression side of [001] specimens and another type of raft-like microstructure observed in the compression side of the [011] specimens was also found in the tension side of the [001] specimens.

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The mechanism of creep in gamma prime precipitation-hardened nickel-base alloys at intermediate temperatures

Cited by 226 publications

References 4 publications

High-resolution electron microscopy of dislocation ribbons in a CMSX-4 superalloy single crystal

High-resolution electron microscopy of dislocation ribbons in a CMSX-4 superalloy single crystal

Deformation Mechanisms in Ni-Base Disk Superalloys at Higher Temperatures

A Study on Bending Deformation Behavior of NI-Based DS and SC Superalloys

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