Precipitate Redistribution during Creep of Alloy 617

Schlegel, Scott; Hopkins, Sharla; Young, Evan; Cole, James I.; Lillo, T.M.; Frary, Megan

doi:10.1007/s11661-009-0027-7

Cited by 46 publications

(8 citation statements)

References 26 publications

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“…It has been shown that carbides will redistribute by migrating from grain boundaries of high resolved compressive stress, those parallel to the applied load, to the grain boundaries of high resolved tensile and shear stress, those perpendicular and at forty-five degrees to the applied load (Schlegel, 2009). It has been further shown that voids form along the grain boundaries of high resolved tensile and shear stress, frequently accompanied by a high population of carbides (Lillo et al, 2009).…”

Section: Discussionmentioning

confidence: 99%

Predicting Creep in Alloy 617 Pressurized Tubes Using Uniaxial Bar Test Data

Croteau¹,

Bateman²,

Bhetwal

et al. 2014

IJURCA

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This work has undergone a double-blind review by a minimum of two faculty members from institutions of higher learning from around the world. The faculty reviewers have expertise in disciplines closely related to those represented by this work. If possible, the work was also reviewed by undergraduates in collaboration with the faculty reviewers. AbstractAlloy 617, a nickel-based alloy, is a leading candidate for application in next-generation nuclear plants (NGNPs). Creep, a thermally activated, time-dependent deformation process impacts the lifetime and failure of heat exchangers used at the very high operating temperatures and pressures of such plants. Current methods of testing creep are generally limited to bar specimens in uniaxial tension. In an attempt to correlate uniaxial to multiaxial creep behavior a method to test creep in a pressurized tube was developed. Test specimens were pressurized with argon up to 3.5 MPa, and heated to 950°C. Creep rates were measured as strain rates by tracking diametric changes with time. Parallel experimental and modeling efforts were used to characterize creep behavior in the pressurized tubes. The aim of this research was to use the existing body of knowledge concerning creep in Alloy 617 to develop a model to accurately predict creep in tubular components. Towards this end, a constitutive model was developed and computer simulations undertaken which were ultimately verified experimentally.

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Section: Discussionmentioning

confidence: 99%

Predicting Creep in Alloy 617 Pressurized Tubes Using Uniaxial Bar Test Data

Croteau¹,

Bateman²,

Bhetwal

et al. 2014

IJURCA

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show abstract

“…EDS is an analytical technique widely used for the element analysis and chemical composition quantification of a material [133]. When combined with EBSD, it can be used to identify the precipitates formed in alloys [11,134].…”

Section: Surface Integrity Characterization 731 Scanning Electron Mmentioning

confidence: 99%

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

Chen¹

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Gas turbines are widely used in e.g., power generation, and aero-industries. Due to global warming, the demand for more efficient gas turbines has increased. A way to achieve this is by increasing the operating temperature of gas turbines. Therefore, nickel-based superalloys have been developed to withstand these extreme temperatures and loads, especially in the hot sections.Today, the way of operating land-based gas turbines is changing. Instead of running for long periods of time, the operation is becoming more flexible, with everincreasing cyclic loads and number of start and stop cycles. To handle the increased stress and cycles, component resistance to fatigue failure needs to be improved.Surface integrity is critical to fatigue performance, since fatigue cracks are normally initiated at surfaces. Nickel-based superalloys are difficult-to-machine materials, primarily due to their high strength, high tendency for work-hardening, and low thermal conductivity. The machining process changes the surface integrity of the alloys which can result in worse fatigue resistance.The work presented in this Ph.D. thesis was conducted in collaboration with Siemens Industrial Turbomachinery AB in Finspång, Sweden. Surface integrity changes which are induced during machining and their effects on fatigue performance have been studied on alloy Inconel 718. Inconel 718 is a widely-used nickel-based superalloy for high temperature applications in modern gas turbines.Broaching, milling, and wire electrical discharge machining, related to component manufacturing in turbo machinery industries, were included in this study. Surface irregularity and defects induced by machining provide preferential sites for fatigue crack initiation which influence the fatigue performance of the alloy. If compressive residual stresses are induced during machining, they benefit the fatigue life by retarding fatigue crack initiation away from surface regions. Shot peening was performed on machined Inconel 718, by which high compressive residual stresses are deliberately induced. It results in increased fatigue performance. The high iv temperatures in gas turbines generally deteriorate the surface integrity. For instance, recrystallization often occurs in the highly plastically-deformed surface layer. Microstructural degradation, in a form of α-Cr precipitates, have also been observed in the deformed surface and sub-surface microstructure when subjected to thermal exposure. Oxidation at elevated temperatures was found to degrade the surface integrity and thereby also the fatigue performance. Fatigue cracks are preferably initiated at oxidized surface carbides, if thermal exposure has been made prior to the test, and a reduced fatigue life is often obtained. It is even worse when high temperatures relax the beneficial compressive residual stresses induced by shotpeening and thereby lowering the fatigue resistance. This increases the interest for research regarding how to optimize the shot peening process in order to enhance the thermal stability o...

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“…EDS is an analytical technique for the element analysis or chemical composition characterization of a sample [79]. When combined with EBSD, it can be used to identify the precipitates formed in alloys [80].…”

Section: Scanning Electron Microscopy (Sem)mentioning

confidence: 99%

Surface Integrity of Broached Inconel 718 and Influence of Thermal Exposure

Chen¹

2014

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Inconel 718 is a nickel-based superalloy that is extensively used as a disc material in gas turbine engines. The service life of gas turbine discs is normally governed by the modes of material degradation and fatigue failure since they work mostly at high temperatures and are subjected to cyclic mechanical loadings. Fatigue failures often start with the initiation of cracks at the surface and the precise details of the failure process significantly depend on the surface conditions. In turbine disc production, one of the last manufacturing steps is to broach root fixings, commonly of fir-tree design, for blade mounting. It has always been a challenge when machining Inconel 718 due to its high strength retention at elevated temperatures, rapid work hardening, as well as low thermal conductivity. This usually leads to rapid tool wear, and consequently shorter tool life, and at the end to the deterioration of the surface integrity of the machined components.

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Precipitate Redistribution during Creep of Alloy 617

Cited by 46 publications

References 26 publications

Predicting Creep in Alloy 617 Pressurized Tubes Using Uniaxial Bar Test Data

Predicting Creep in Alloy 617 Pressurized Tubes Using Uniaxial Bar Test Data

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

Surface Integrity of Broached Inconel 718 and Influence of Thermal Exposure

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