Simultaneous Optimization of Machining Parameters for Dimensional Instability Control in Aero Gas Turbine Components Made of Inconel 718 Alloy

Subhas, B. K.; Bhat, Ramaraja; Ramachandra, K.; Balakrishna, H. K.

doi:10.1115/1.1287591

Cited by 27 publications

(9 citation statements)

References 3 publications

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“…Moreover, because of residual stress distribution generated by machining operations combined with those stresses generated by previous manufacturing process, dimensional instability (distortion) can occur after machining. Subhas et al (2000aSubhas et al ( , 2000b found the Inconel 718 more prone to dimensional instability than the titanium alloys, although the latter has a lower modulus of elasticity. According to them, this phenomenon was not noticed in other nickel-based alloys and may be due to the presence of γ ″ phase.…”

Section: Nickel-based Alloysmentioning

confidence: 99%

A review of surface integrity in machining and its impact on functional performance and life of machined products

M’Saoubi¹,

Outeiro²,

Chandrasekaran³

et al. 2008

IJSM

235

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This paper presents an overview of the past research on Surface Integrity (SI) studies in the context of machined components from a range of work materials including stainless steels, Ni and Ti alloys, hardened steels for dies and moulds, bearings and automotive applications. Typical surface alterations such as phase transformations, microhardness and residual stress are discussed and correlated with the functional performance of the machined products. A summary of past and current modelling efforts is then presented along with projections for developing predictive models for SI and means for enhancing product sustainability in terms of its functional performance.

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Section: Nickel-based Alloysmentioning

confidence: 99%

A review of surface integrity in machining and its impact on functional performance and life of machined products

M’Saoubi¹,

Outeiro²,

Chandrasekaran³

et al. 2008

IJSM

235

View full text Add to dashboard Cite

show abstract

“…This phenomenon brings problems in structural assembly, as it destroys the structural integrity. Inconel 718 has revealed the dimensional instability after machining, and it is more prone to dimensional changes in comparison with both titanium alloys and mild steels [79,80].…”

Section: Residual Stressesmentioning

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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“…This phenomenon brings problems in structural assembly, as it destroys the structural integrity. Inconel 718 has revealed dimensional instability after machining, and it is more prone to dimensional changes in comparison with either titanium alloy or mild steel [67,68].…”

Section: Residual Stressesmentioning

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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Simultaneous Optimization of Machining Parameters for Dimensional Instability Control in Aero Gas Turbine Components Made of Inconel 718 Alloy

Cited by 27 publications

References 3 publications

A review of surface integrity in machining and its impact on functional performance and life of machined products

A review of surface integrity in machining and its impact on functional performance and life of machined products

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

Surface Integrity of Broached Inconel 718 and Influence of Thermal Exposure

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