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Fatigue Behaviour of an Additively Manufactured Ductile Gas Turbine Superalloy
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0001-8306-3987
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
2020 (English)In: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638, no 108, article id 102604Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing (AM) offers new possibilities in gas turbine technology by allowing for more complex geometries. However, the fatigue performance, including crack initiation and crack propagation of AM gas turbine material, is not fully known. In addition, AM materials shows anisotropic properties due to the columnar grain growth in the building direction during the AM process, which needs to be accounted for. Also, an AM component often solidifies with a cellular dendritic structure during the manufacturing process. In the present study, the bulk material of an AM adopted nickel-based superalloy based on Hastelloy X was subjected to low-cycle fatigue (LCF) loading at room temperature. The LCF tests were conducted in strain control on additively manufactured smooth bars,with two different build orientations (with an angle of 0° and 90° relative to the building platform). The LCF results showed that the major part of the fatigue life is spent in the crack initiation phase, namely 78% to 99% of the total fatigue life. Based on the experiments, a model to predict the crack initiation life was developed that takes the anisotropic material behaviour into account. The last part of the fatigue life, the crack propagation phase, was studied on a microstructural level, where initial fractography of the ruptured LCF specimens revealed that the dendritic structure was visible on the fracture surface. It was noted that the dendritic structure could easily be mistaken for regular striations although they represent a different fracture mechanism. The fracture surfaces were therefore cross sectioned and possible correlations between fracture surface characteristics and underlying microstructure were studied using electron backscatter diffraction and electron channelling contrast imaging. The outcome showed that the dendritic structure had some effect on the LCF crack propagation behaviour by interdendritic tearing, which was discussed.

Place, publisher, year, edition, pages
Elsevier, 2020. no 108, article id 102604
Keywords [en]
Additive manufacturing, fatigue, fractography, EBSD, crack initiation model
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:liu:diva-166081DOI: 10.1016/j.tafmec.2020.102604ISI: 000552039000037OAI: oai:DiVA.org:liu-166081DiVA, id: diva2:1436582
Note

Funding agencies:  Swedish Energy AgencySwedish Energy Agency; Siemens Industrial Turbomachinery AB through "Turbines for Future Energy Systems" [44112-1]

Available from: 2020-06-08 Created: 2020-06-08 Last updated: 2022-09-09Bibliographically approved
In thesis
1. Fatigue life prediction of additively manufactured ductile nickel-based superalloys: Constitutive and crack initiation modelling
Open this publication in new window or tab >>Fatigue life prediction of additively manufactured ductile nickel-based superalloys: Constitutive and crack initiation modelling
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation was produced at the Division of Solid Mechanics at Linköping University, and is the final result of a project that included mechanical testing and modelling of an additively manufactured ductile nickel-based superalloy.

The main objective of the work presented in this thesis was to investigate and model the cyclic behaviour and the fatigue life behaviour of an additively manufactured ductile nickel-based superalloy, with emphasis on modelling the stabilised material behaviour, by which fatigue life predictions can be based upon. The mechanical and fatigue behaviour of additively manufactured alloys have shown to often depend on how the components are manufactured in the 3D-printing machine, meaning that the material is anisotropic. This anisotropic effect is important to account for when predicting the life of components. Therefore, in this work models to predict the mechanical response and the fatigue life of such components have been established. Monotonic tensile tests, creep tests and cyclic fatigue tests at constant temperatures, as well as anisothermal cyclic tests, have been performed to investigate the mechanical and the fatigue behaviour of the material, where specimens built in different orientations have been used to also study the anisotropic behaviour of the material. With the tests as a basis, a constitutive model has progressively been developed and implemented in a finite element context that accounts for the anisotropic behaviour under both elastic and inelastic deformations. In addition, a fatigue crack initiation life model has been developed for the tested low-cycle fatigue and thermomechanical fatigue conditions, which account for both material anisotropy and temperature effects.

Abstract [sv]

Denna avhandling har producerats vid avdelningen för Mekanik och Hållfasthetslära vid Linköpings universitet, och är resultatet av ett projekt som omfattar mekanisk provning och modellering av en additivt tillverkad duktil nickelbaserad superlegering. Det huvudsakliga målet med arbetet som presenteras i denna avhandling har varit att studera och modellera det cykliska beteendet och utmattningsbeteendet hos en additivt tillverkad duktil nickelbaserad superlegering, med fokus på modellering av det stabiliserade materialbeteendet, utifrån vilket livslängdprediktering kan baseras på. Det mekaniska beteendet och utmattningsbeteendet hos additivt tillverkade material har visat sig ofta vara beroende hur komponenten är byggd i 3D-printern, vilket betyder att materialet är anisotropt. Det anisotropa beteendet är viktig att ta hänsyn till vid prediktering av utmattningslivslängd hos dessa komponenter. I detta arbete har därför modeller utvecklats för att prediktera det mekaniska beteendet och utmattningslivslängd för additivt tillverkade komponenter. För att sätta upp modellen har monotona dragprov, krypprov och cykliska utmattningsprov vid olika temperaturer, samt anisoterma cykliska utmattningsprov utförts, där provstavar byggda i olika riktningar har använts för att studera materialets anisotropi. Baserat på proven har en konstitutiv beskrivning av materialet progressivt utvecklats och implementerats i en finita element-kontext, där modellen tar hänsyn till det anisotropa materialbeteendet vid både elastiska och inelastiska deformationer. En modell för prediktering av sprickinitiering för de testade förhållandena har också utvecklats, vilken tar hänsyn till både anisotropi och temperatureffekter.

 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2022. p. 61
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2245
Keywords
Additive manufacturing, Low-cycle fatigue, Thermomechanical fatigue, Constitutive modelling, Anisotropy
National Category
Applied Mechanics
Identifiers
urn:nbn:se:liu:diva-188326 (URN)10.3384/9789179294199 (DOI)9789179294182 (ISBN)9789179294199 (ISBN)
Public defence
2022-10-14, C3, C Building, Campus Valla, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Note

Funding agencies: The Swedish Energy Agency, Siemens Energy AB

Available from: 2022-09-09 Created: 2022-09-09 Last updated: 2022-09-13Bibliographically approved

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Lindström, ThomasCalmunger, MattiasEriksson, RobertLeidermark, Daniel

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