Oxidation induced intergranular cracking and Portevin–Le Chatelier effect in nickel base superalloy 718

Fournier, Lionel; Delafosse, David; Magnin, T.

doi:10.1016/s0921-5093(01)01224-2

Cited by 81 publications

(50 citation statements)

References 16 publications

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“…An unambiguous characterization will require specific equipments in order to follow, at high temperature, the local strains along nearly the whole specimen quasi-instantaneously. Figure 5 together with the results obtained previously by Fournier et al [13]. Rupture paths observed by SEM show systematically that above 450°C the fracture is transgranular ductile when PLC triggers off whereas an intergranular brittle mode of fracture is observed in the other cases.…”

Section: Characterization Of Plc Typessupporting

confidence: 82%

“…This experimental fact is so systematic that a border can be drawn which separates both smooth from serrated plastic flow and intergranular fracture from transgranular ductile. : data from Fournier [13] It is worth mentioning here that when the testing mechanical conditions are located in the left part of the map, any thermo-mechanical modification that initiates PLC instabilities will stop the intergranular damaging process. Complementary mechanical tests were performed and are still in progress to verify this last point.…”

Section: Characterization Of Plc Typesmentioning

confidence: 99%

“…An interesting way to study this particular point can be found in the scientific field dealing with oxidation assisted intergranular cracking (OAIC) because, in most of the cases, this damaging process requires to operate an intergranular oxidation process together with a high level of intergranular internal stresses. Fournier et al [13] have clearly shown that the occurrence of PLC instabilities in alloy 718 during slow strain rate tests at 400°C stops immediately the intergranular crack propagation. The aims of the present paper are firstly, to bring new experimental results completing at higher temperature the work undertaken by Fournier et al and then, to evaluate the interactions between crack initiation and localization of plastic instabilities.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Portevin-Le Chatelier Effect on Rupture Mode of Alloy 718 Specimens

Garat¹,

Cloue²,

Viguier³

et al. 2005

Superalloys 718, 625, 706 and Various Derivatives (2005)

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A set of tensile tests has been carried out under air environment in the temperature range [450°C-700°C] in order to characterize the interactions between oxidation assisted intergranular cracking and Portevin -Le Chatelier effect. It is shown that the occurrence of jerky flow stops the intergranular damaging mechanism. The construction of a Dynamic strain aging-Intergranular fracture-PLC instabilities map is then proposed. The surprising relation between crack initiation disappearance and PLC instabilities of type C in the temperature range explored is discussed. Finally the assumption of the occurrence of such phenomenon at the tip of a propagating crack is addressed. IntroductionJerky flow also known as Portevin-Le Chatelier effect has been first shown on Al-Cu alloys [1] and, afterwards, has been studied intensively in other dilute metallic alloys especially in steels, aluminium and nickel based alloys [2][3][4][5]. Physical processes involved in this type of flow instability as well as the associated localization of the deformation have been modeled and simulated [6][7][8]. Recent improvements of measuring techniques for deformation fields [9] offer the possibility to check those simulations under several aspects (localization, spatial coupling between bands, bands width). Nevertheless, a few studies are dealing with the role of grain boundaries on PLC plastic instabilities [10][11][12] and consequently, there is a lack of knowledge on the effect of this phenomenon on the evolution of intergranular internal stresses. An interesting way to study this particular point can be found in the scientific field dealing with oxidation assisted intergranular cracking (OAIC) because, in most of the cases, this damaging process requires to operate an intergranular oxidation process together with a high level of intergranular internal stresses. Fournier et al [13] have clearly shown that the occurrence of PLC instabilities in alloy 718 during slow strain rate tests at 400°C stops immediately the intergranular crack propagation. The aims of the present paper are firstly, to bring new experimental results completing at higher temperature the work undertaken by Fournier et al and then, to evaluate the interactions between crack initiation and localization of plastic instabilities. As strain rate controlled tensile tests have been carried out on thin strip, both crack initiation and propagation sensitivity to dynamic strain aging (DSA) have been investigated. Materials and Experimental ProcedureThe material used in this study was obtained through a double melting process: vacuum induction melting plus vacuum arc remelting. The nominal composition of the alloy is given in Table 1. The cast ingot was hot and cold rolled down to a thickness of 1 mm, followed by a solution annealing heat treatment at 1000°C for one hour ended by air quenching.

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Section: Characterization Of Plc Typessupporting

confidence: 82%

Section: Characterization Of Plc Typesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influence of Portevin-Le Chatelier Effect on Rupture Mode of Alloy 718 Specimens

Garat¹,

Cloue²,

Viguier³

et al. 2005

Superalloys 718, 625, 706 and Various Derivatives (2005)

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“…The intergranular cracking observed could either be purely mechanical or due to the small amount of oxygen present in the environment. It has been shown that PLC can modify the propagation of a crack when SCC occurs [Fournier 2001]. A creep mechanism could also be involved.…”

Section: Mechanical Behavior Of Austenitic Alloys In Argonmentioning

confidence: 99%

Feasibility Study of Supercritical Light Water Cooled Reactors for Electric Power Production, Progress Report for Work Through September 2003, 2nd Annual/8th Quarterly Report

MacDonald¹

2003

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“…During a study on the effect of oxidation on mechanical behavior of alloy 718, Fournier et al [7] shown that the occurrence of Portevin-Le Chatelier (PLC) effect during tensile test systematically resulted in an absence of brittle area on the fracture surface of the samples. By contrast, for higher testing temperatures, when the stress-strain curves are smooth, intergranular cracking areas are always observed on the fracture surface.…”

Section: Introductionmentioning

confidence: 99%

Studying the influence of substitutional elements on mechanical behavior of Alloy 718

Max

Juán

Nó

et al. 2014

MATEC Web of Conferences

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Abstract. In nickel-based superalloys, substitutional solute species have a strong impact on in service mechanical properties as well as on oxidation and corrosion resistances. In alloy 718, recent studies carried out by tensile tests highlighted the fact that refractory solute species are able to interact strongly with mobile dislocations during plastic deformation, generating dynamic strain ageing, and, in wide ranges of tests temperatures and strain rates, Portevin-Le Chatelier effect. The precise nature of the substitutional element responsible for such a dynamic interaction is still subject to debate. We addressed this question by means of mechanical spectroscopy studies of alloy 718 and various related alloys corresponding to monitored changes in the chemical composition. Only a single internal friction relaxation peak has been observed for all the studied alloys. By analyzing the damping behavior of these alloys at different imposed solicitation frequencies by sweeping a large temperatures range, the activation energies of the relaxation process and the type of mechanism involved have been determined. The process is a "Zener relaxation" in the alloys, i.e. a substitutional atoms dipole reorientation under applied stress. The results tend to prove that Niobium is not involved in the relaxation process whereas Molybdenum content seems to play an important role in the relaxation intensity.

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Oxidation induced intergranular cracking and Portevin–Le Chatelier effect in nickel base superalloy 718

Cited by 81 publications

References 16 publications

Influence of Portevin-Le Chatelier Effect on Rupture Mode of Alloy 718 Specimens

Influence of Portevin-Le Chatelier Effect on Rupture Mode of Alloy 718 Specimens

Feasibility Study of Supercritical Light Water Cooled Reactors for Electric Power Production, Progress Report for Work Through September 2003, 2nd Annual/8th Quarterly Report

Studying the influence of substitutional elements on mechanical behavior of Alloy 718

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