A dislocation based criterion for the raft formation in nickel-based superalloys single crystals

Buffière, Jean Yves; Ignat, M.

doi:10.1016/0956-7151(94)00432-h

Cited by 139 publications

(51 citation statements)

References 22 publications

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“…The formation of the interface dislocations has been reported to be related with the relaxation of γ/γ coherency stresses [15]. Relieve of the lattice misfit can influence the change of chemical potential of atoms and thus provide the easy diffusion paths, enabling dissolution of γ channels and coalescence of γ cubes.…”

Section: Resultsmentioning

confidence: 99%

Analytical Electron Microscopy Studies of the CMSX-4 Single Crystal Superalloy Subjected to High Temperature Annealing

et al. 2017

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The aim of the present work is to investigate the development of the γ/γ microstructure and the changes in chemical composition of γ and γ phases during high temperature annealing of CMSX-4 superalloy at a temperature of 1100• C in the time range from 500 to 2500 h. The studies were performed by means of scanning electron microscopy and the modern scanning-transmission electron microscopy with Super-X EDS system of four SDD detectors. Results of scanning electron microscopy and scanning-transmission electron microscopy analyses have shown that the microstructure of CMSX-4 superalloy is unstable during ageing at high temperature and the coalescence of cuboidal γ precipitates was observed. Energy dispersive X-ray microanalysis revealed the distribution of particular alloying elements in the γ and γ phases and the differences in their concentration in the function of the annealing time.

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Section: Resultsmentioning

confidence: 99%

Analytical Electron Microscopy Studies of the CMSX-4 Single Crystal Superalloy Subjected to High Temperature Annealing

et al. 2017

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“…Rafting is a time-dependent high temperature (≈ 900°C) diffusion controlled process [7,45] and it is believed that the driving force of this phenomenon is to decrease the internal lattice misfit stresses [46,47]. A decrease of the overall γ/γ interfacial energy is attributed to both an elastic interaction between the internal stresses at the γ/γ interface, [48], and the interaction of dislocations relaxing the lattice misfit [49,50]. Generally, the rafting phenomenon is connected to creep deformation at elevated temperatures, see for example [8,33,[51][52][53][54][55].…”

Section: Raftingmentioning

confidence: 99%

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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“…The role of elastic driving force to form the raft structure in the primary creep stage has extensively been discussed [5][6][7][8][9]. From their previous works, it is known that an applied external stress and introductions of creep dislocations slightly modify the internal elastic fields in an early stage of the primary creep, and the elastic fields drive the initial cuboidal structure to the raft structure.…”

Section: Introductionmentioning

confidence: 99%

Effect of Elastic Driving Force on the Evolution of Microstructures in the Secondary Creep Stage

Tanaka

Hashimoto

Inoue

et al. 2011

AMR

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Abstract. The effect of elastic driving force on the microstructural change of superalloys in the secondary creep stage is evaluated by elastic energy calculations with the concept of effective eigen strain where both lattice mismatch and creep strain are taken into account The elastic energy calculations indicates that the elastic state in the secondary creep stage is totally different to that in the initial one where the lattice misfit between γ and γ' phases is over accommodated along the [100] and [010] directions by creep deformation in the γ phase. The excess creep dislocations for the over accommodation are required so as to develop an internal stress field to prevent further creep deformations. The planer raft structure with the plane normal oriented to the [001] direction is unstable in the over accommodated state. The γ/γ' lamellar interfaces will be inclined to make a wavy raft structure of which elastic energy is lower than the ideal 001 planer raft structure.

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A dislocation based criterion for the raft formation in nickel-based superalloys single crystals

Cited by 139 publications

References 22 publications

Analytical Electron Microscopy Studies of the CMSX-4 Single Crystal Superalloy Subjected to High Temperature Annealing

Analytical Electron Microscopy Studies of the CMSX-4 Single Crystal Superalloy Subjected to High Temperature Annealing

On Thermomechanical Fatigue of Single-Crystal Superalloys

Effect of Elastic Driving Force on the Evolution of Microstructures in the Secondary Creep Stage

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