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Modelling Ti-6Al-4V microstructure by evolution laws implemented as finite element subroutines:: Application to TIG metal deposition
Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för industriell produktion.ORCID-id: 0000-0002-3687-7782
Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för industriell produktion.
2008 (Engelska)Ingår i: 8 th International Conference on Trends in welding research,: Pine Mountain, Georgia, June 2-6, 2008Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
Ort, förlag, år, upplaga, sidor
2008.
Nationell ämneskategori
Metallurgi och metalliska material
Forskningsämne
TEKNIK, Produktions- och materialteknik
Identifikatorer
URN: urn:nbn:se:hv:diva-2064OAI: oai:DiVA.org:hv-2064DiVA, id: diva2:281748
Tillgänglig från: 2009-12-17 Skapad: 2009-12-17 Senast uppdaterad: 2016-05-13Bibliografiskt granskad
Ingår i avhandling
1. Modelling microstructure evolution of weld deposited Ti-6Al-4V
Öppna denna publikation i ny flik eller fönster >>Modelling microstructure evolution of weld deposited Ti-6Al-4V
2008 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The microstructure and consequently the mechanical properties of titanium alloys are highly dependent on the temperature history endured by the material. The manufacturing process of metal deposition induces repetitive cooling and heating in the material determining a specific microstructure. The presented study is devoted to developing and implementing a microstructure model for Ti-6Al-4V intended to be coupled to a thermo- mechanical model of the metal deposition process.

Microstructural analysis of the metal deposited samples was first performed to understand the formed microstructure. A set of representative parameters for microstructure modelling were then selected as representative for the known impact of Ti-6Al-4V microstructure on mechanical properties. Evolution equations for these parameters were implemented for thermal finite element analysis of the process. Six representative state variables are modelled: the phase volume fraction of total alpha, beta, Widmanstätten alpha, grain boundary alpha, martensite alpha, and the alpha lath thickness. Heating, cooling and repeated re-heating involved in the process of metal deposition are taken into account in the model. The phase transformations were modelled based on a diffusionnal theory described by a Johnson-Mehl-Avrami formulation, as well as diffusionless transformations for the martensite alpha formation and the beta reformation during reheating. The Arrhenius equation is applied as a simplification to model temperature dependent alpha lath size calculation. Grain growth is not included in the present formulation, but would have to be added for capturing alpha lath coarsening during long term heat treatment.

The temperature history during robotised tungsten inert gas deposition welding is simulated together with the microstructure. The implementation of the model handles well the complex cyclic thermal loading from the metal deposition process. A particular banded structure observed in the metal deposited microstructure is partially explained using the proposed microstructure model. It is concluded that although qualitatively interesting results have been achieved, further calibration testing over a wider range of temperature histories must be performed to improve the transformation kinetic parameters for reliable quantitative predictions of the microstructure.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2008. s. 59
Serie
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757 ; 2008:47
Nyckelord
metal deposition, Ti-6Al-4V, microstructure modelling, titanium alloy, Finite Element Method, Johnson-Mehl-Avrami, RTMwD
Nationell ämneskategori
Materialteknik
Forskningsämne
TEKNIK, Produktions- och materialteknik
Identifikatorer
urn:nbn:se:hv:diva-2406 (URN)
Presentation
(Engelska)
Anmärkning
Corinne Charles ill. S. 1-28: sammanfattning, s. 31-59: 3 uppsatserTillgänglig från: 2010-04-29 Skapad: 2010-04-29 Senast uppdaterad: 2016-05-13Bibliografiskt granskad
2. Microstructure model for Ti-6Al-4V used in simulation of additive manufacturing
Öppna denna publikation i ny flik eller fönster >>Microstructure model for Ti-6Al-4V used in simulation of additive manufacturing
2016 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis is devoted to microstructure modelling of Ti-6Al-4V. The microstructure and the mechanical properties of titanium alloys are highly dependent on the temperature history experienced by the material. The developed microstructure model accounts for thermaldriving forces and is applicable for general temperature histories. It has been applied to study wire feed additive manufacturing processes that induce repetitive heating and cooling cycles.The microstructure model adopts internal state variables to represent the microstructure through microstructure constituents' fractions in finite element simulation. This makes it possible to apply the model efficiently for large computational models of general thermomechanical processes. The model is calibrated and validated versus literature data. It is applied to Gas Tungsten Arc Welding -also known as Tungsten Inert Gas welding-wire feed additive manufacturing process.Four quantities are calculated in the model: the volume fraction of phase, consisting of Widmanstätten, grain boundary, and martensite. The phase transformations during cooling are modelled based on diffusional theory described by a Johnson-Mehl-Avrami-Kolmogorov formulation, except for diffusionless martensite formation where the Koistinen-Marburger equation is used. A parabolic growth rate equation is used for the to transformation upon heating. An added variable, structure size indicator of Widmanstätten, has also been implemented and calibrated. It is written in a simple Arrhenius format.The microstructure model is applied to in finite element simulation of wire feed additive manufacturing. Finally, coupling with a physically based constitutive model enables a comprehensive and predictive model of the properties that evolve during processing.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå tekniska universitet, 2016. s. 159
Serie
Doctoral thesis / Luleå University of Technology, ISSN 1402-1544
Nyckelord
Titanium alloy, Ti-6Al-4V, Welding, Metal deposition, Additive manufacturing, Wire feed, Finite Element Method, Microstructure model, Johnson-Mehl-Avrami- Kolmogorov, Thermally driven
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsteknik
Identifikatorer
urn:nbn:se:hv:diva-9346 (URN)978-91-7583-579-2 (ISBN)978-91-7583-580-8 (ISBN)
Disputation
2016-05-24, E246, Luleå tekniska universitet, Luleå, 09:30 (Engelska)
Opponent
Handledare
Tillgänglig från: 2016-05-13 Skapad: 2016-05-13 Senast uppdaterad: 2016-05-13Bibliografiskt granskad

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