Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy René N4: Part II. Low cycle fatigue behavior

Gabb, Timothy P.; Gayda, John; Miner, R. V.

doi:10.1007/bf02643956

Cited by 122 publications

(58 citation statements)

References 8 publications

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“…The motivation behind these studies has been the high temperature application of precipitation hardened nickel-base superalloys in modern gas turbine aero-engines for their superior thermal, fatigue and creep properties compared to conventional cast alloys by removal of grain boundaries. The cyclic deformation behavior and low-cycle fatigue (LCF) failure of γ precipitation-hardened nickel base superalloys is strongly influenced by temperature [6][7][8][9][10] , frequency [5,[11][12][13] , strain rate [10] , crystallographic orientation [14,15] and environment [16] etc.…”

Section: Introductionmentioning

confidence: 99%

Temperature Effect on Low-Cycle Fatigue Behavior of Nickel-Based Single Crystalline Superalloy

Shi

et al. 2008

Acta Mech. Solida Sin.

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The low-cycle fatigue (LCF) behavior of a nickel-based single crystal superalloy with [001] orientation was studied at an intermediate temperature of T0 • C and a higher temperature of T0 + 250 • C under a constant low strain rate of 10 −3 s −1 in ambient atmosphere. The superalloy exhibited cyclic tension-compression asymmetry which is dependent on the temperature and applied strain amplitude. Analysis on the fracture surfaces showed that the surface and subsurface casting micropores were the major crack initiation sites. Interior Ta-rich carbides were frequently observed in all specimens. Two distinct types of fracture were suggested by fractogaphy. One type was characterized by Mode-I cracking with a microscopically rough surface at T0 + 250 • C. Whereas the other type at lower temperature T0 • C favored either one or several of the octahedral {111} planes, in contrast to the normal Mode-I growth mode typically observed at low loading frequencies (several Hz). The failure mechanisms for two cracking modes are shearing of γ precipitates together with the matrix at T0 • C and cracking confined in the matrix and the γ/γ interface at T0 + 250 • C.KEY WORDS low cycle fatigue, single crystal, nickel-based superalloy

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Section: Introductionmentioning

confidence: 99%

Temperature Effect on Low-Cycle Fatigue Behavior of Nickel-Based Single Crystalline Superalloy

Shi

et al. 2008

Acta Mech. Solida Sin.

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“…Due to the anisotropic behaviour of single-crystal materials, the crystal orientation in which the material is loaded will influence the fatigue life (during strain-controlled fatigue) and orientations with a low stiffness are superior, see for example [39,67,68]. However, according to both Dalal et al [67] and Miner et al [39], it seems that the influence of the crystal orientation disappears when inelastic strains are considered instead of total strains.…”

Section: Isothermal Fatiguementioning

confidence: 87%

“…However, according to both Dalal et al [67] and Miner et al [39], it seems that the influence of the crystal orientation disappears when inelastic strains are considered instead of total strains. As in the case of TMF, dwell times influence the life time during LCF and results indicate that this is detrimental to the LCF life [68].…”

Section: Isothermal Fatiguementioning

confidence: 99%

“…This difference in yielding behaviour is also further discussed in more detail in Paper II in this thesis. Gabb and Miner carried out extensive work into the orientation dependence of the mechanical properties of the singlecrystal superalloy René N4 [35,39,40]. At RT, the yield strength of the 001 direction was 889 MPa, while it was 830 MPa for the 011 direction.…”

Section: Yielding Behaviourmentioning

confidence: 99%

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On Thermomechanical Fatigue of Single-Crystal Superalloys

Segersäll¹

2014

Linköping Studies in Science and Technology. Dissertations

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Thesis cover: Design by Maria J. SegersällPrinted by: LiU-Tryck, Linköping, Sweden, 2014 ISBN 978-91-7519-211-6 ISSN 0345-7524 Distributed by: Division of Engineering Materials, Department of Management and Engineering Linköping University SE-58183, Linköping, Sweden © 2014 Mikael SegersällThis document was prepared with L A T E X, October 17, 2014 AbstractThanks to their excellent mechanical and chemical properties at temperatures up to 1000°C, nickel-based superalloys are used in critical components in high-temperature applications such as gas turbines and aero engines. One of the most critical components in a gas turbine is the turbine blade, and to improve the creep and fatigue properties of this component, it is sometimes cast in single-crystal form rather than in the more conventional polycrystalline form. Gas turbines are most commonly used for power generation and the turbine efficiency is highly dependent on the performance of the superalloys.Today, many gas turbines are used as a complement for renewable energy sources, for example when the wind is not blowing or when the sun is not shining, which means that the turbine runs differently compared to earlier, when it ran for longer time periods with a lower number of start-ups and shutdowns. This new way of running the turbine, with an increased number of start-ups and shut-downs, results in new conditions for critical components, and one way to simulate these conditions is to perform thermomechanical fatigue (TMF) testing in the laboratory. During TMF, both mechanical strain and temperature are cycled at the same time, and one fatigue cycle corresponds to the conditions experienced by the turbine blade during one start-up and shut-down of the turbine engine.In the work leading to this PhD thesis, TMF testing of single-crystal superalloys was first performed in the laboratory and this was then followed microstructure investigations to study the occurring deformation and damage mechanisms. Specimens with different crystallographic directions have been tested in order to investigate the anisotropic behaviour shown by these materials. Results show a significant orientation dependence during TMF in which specimens with a low elastic stiffness perform better. However, it is also shown that specimens with a higher number of active slip systems perform better during TMF compared to specimens with less active slip sysiii tems. This is because a higher number of active slip systems results in a more widespread deformation and seems to be beneficial for the TMF life. Further, microscopy shows that the deformation during TMF is localised to several deformation bands and that different deformation and damage mechanisms prevail according to in which crystal orientation the material is loaded. Deformation twinning is shown to be a major deformation mechanism during TMF and the interception of twins seems to trigger recrystallization. This is certainly negative for the mechanical properties of single-crystal superalloys since no grain boundary strengthening elemen...

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“…Much effort has been invested in understanding the creep [2][3][4][5][6][7][8][9] and fatigue [10][11][12][13][14][15] responses of Ni-base superalloys. However, understanding the effects of thermomechanical fatigue (TMF) on the life of Ni-base superalloys is paramount because the deformation and damage mechanisms observed in creep and fatigue typically do not directly transfer to the behavior of Ni-base superalloys under TMF loadings [16,17].…”

Section: Introductionmentioning

confidence: 99%

Parameters influencing thermomechanical fatigue of a directionally-solidified Ni-base superalloy

Kirka

Brindley

Neu

et al. 2015

International Journal of Fatigue

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Thermomechanical fatigue (TMF) is a low cycle fatigue process in which material life is correlated to the mechanical strain amplitude. However, it is well known that several other factors influence this life. This paper examines several of these parameters and their influence on life using experiments conducted on a second generation directionally-solidified (DS) Ni-base superalloy. The parameters considered include the influence of the temperature extremums (T max of either 750 or 950 • C and T min of either 100 or 500 • C), strain ratio (R ), the strain-temperature phasing (in-phase (IP) and out-of-phase (OP)), the influence of dwells at the high temperature end of the cycle resulting in a creep-fatigue (CF) interaction, and material anisotropy associated with the grain growth direction (longitudinal versus transverse). Results suggest that the phasing has a primary role in controlling the mechanism of degradation. IP TMF is dominated by crack formation in volumes surrounding debonded carbides for both continuously cycling (CC) and CF at 950 and 750 • C, while OP TMF is dominated by surface oxidation and repetitive cracking of the oxide that reforms at the crack tip at 950 • C. Decreasing the T max to 750 • C the environmental and creep effects are reduced resulting in virtually pure fatigue exposure under OP conditions. With decreasing T min from 500 • C to 100 • C was observed an increase in inelastic strain amplitude and 1 corresponding decrease in life. Variations in R were found to have no significant influence on life or stabilized stress behavior. TMF loading in the transverse orientation resulted in life reductions over the longitudinal orientation due to cracks propagating in a transgranular manner. Lastly, only in material exposed to CF with a T max of 950 • C rafting of the γ precipitates was observed.

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Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy René N4: Part II. Low cycle fatigue behavior

Cited by 122 publications

References 8 publications

Temperature Effect on Low-Cycle Fatigue Behavior of Nickel-Based Single Crystalline Superalloy

Temperature Effect on Low-Cycle Fatigue Behavior of Nickel-Based Single Crystalline Superalloy

On Thermomechanical Fatigue of Single-Crystal Superalloys

Parameters influencing thermomechanical fatigue of a directionally-solidified Ni-base superalloy

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