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A thermodynamic re-assessment of Al-V toward an assessment of the ternary Al-Ti-V system
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.ORCID iD: 0000-0001-9010-525X
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.ORCID iD: 0000-0001-5031-919X
2015 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 51, 75-88 p.Article in journal (Refereed) Published
Abstract [en]

Titanium alloys are highly sought after due to their excellent mechanical properties. One of the most commonly used Ti alloys is Ti-6Al-4V, which contains 6% Al and 4% V by weight. Despite the popularity of this alloy, no thermodynamic description of the ternary Al-Ti-V system has been published in the open literature. In this work an assessment procedure of the ternary Al-Ti-V system was initiated based on the binary descriptions by Witusiewitcz et al. (J. Alloys Compds. 465 (2008) 64-77 [1]) for (Al-Ti), Gong et al. (Int. J. Mater. Res. 95 (2004) 978-986 [2]) for (Al-V) and Saunders (COST 507, 2 (1998) 297-298 [3]) for (Ti-V). When combining the three binary systems and looking at the extrapolated ternary isothermal sections, it was found that there was a very large miscibility gap in the bcc phase. The origin of this miscibility gap was mainly the Al-V system and therefore it was decided to reassess this system. The Al-V system was reassessed according to available experimental data along with the enthalpies of formation of all compounds as well as the enthalpies of mixing for all terminal phases obtained by first-principles calculations based on the density functional theory. For the Al8V5 phase there are two different sets of data for the enthalpies of formation. These two sets are investigated in this work and it is found that the set not used by Gong et al. in their assessment of the Al-V binary system gives better extrapolations. The final description produced improved extrapolated ternary isothermal sections.

Place, publisher, year, edition, pages
Elsevier, 2015. Vol. 51, 75-88 p.
National Category
Metallurgy and Metallic Materials
URN: urn:nbn:se:kth:diva-166246DOI: 10.1016/j.calphad.2015.07.002ISI: 000366790500009ScopusID: 2-s2.0-84940901655OAI: diva2:810043

Updated from "Manuscript" to "Article". QC 20151208. QC 20160121

Available from: 2015-05-06 Created: 2015-05-06 Last updated: 2016-02-10Bibliographically approved
In thesis
1. Thermodynamic investigation of systems related to TWIP steels
Open this publication in new window or tab >>Thermodynamic investigation of systems related to TWIP steels
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The world is facing serious challenges regarding environmental issues. Carbon dioxide levels increase every day. In an attempt to decrease carbon emissions the automotive industry searches for lighter, stronger materials. TWinning Induced Plasticity (TWIP) steels show an impressive combination of strength and ductility. The possibility of adding high amounts of aluminum that decreases the density while maintaining the mechanical properties makes this type of steel very interesting for use in automotive applications. The only thing keeping the TWIP steels from being used in the automotive industry is that the Yield Strength (YS) is too low. The TWIP steels usually have a YS around 400 MPa. For them to be useful in automotive applications YS around 600-700 MPa is necessary. One of the most promising ways of improving the YS is by precipitation hardening. This work has been performed within a European Research Fund for Coal and Steel (RFCS) project called Precipitation in High Manganese steels (PrecHiMn). As the name of the project suggests, the goal of this project has been to study the precipitation in TWIP steels. The precipitation hardening is achieved through the addition of carbide and carbonitride formers such as Nb, Ti and V. In order to build advanced models to simulate precipitation it is important to have a good understanding of the thermodynamics of systems related to TWIP steels.

The goal of this work has been to study the thermodynamic properties of systems related to TWIP steels, more specifically the system forming the matrix phases of TWIP steels. Therefore the Al-C-Fe-Mn system has been studied as well as the Al-Ti-V system. Complete thermodynamic descriptions that reproduce the experimental data well have been produced including descriptions of order-disorder transformations.

Abstract [sv]

Varlden star infor stora utmaningar nar det galler miljofragor. Koldioxidnivaerna okar varje dag. I ett forsok att minska koldioxidutslappen soker bilindustrinefter lattare och starkare material. TWinning Induced Plasticity (TWIP)stal uppvisar en imponerande kombination av hallfasthet och duktilitet. Mojlighetenatt tillsatta hoga halter av aluminium som minskar densiteten med bibehallnamekaniska egenskaper gor denna typ av stal mycket intressanta for anvandning ifordonstillampningar. Det enda som hindrar TWIP stal fran att anvandas inomfordonsindustrin ar att strackgransen ar for lag. TWIP stal har vanligtvis enstrackgrans runt 400 MPa. For att de ska vara anvandbara i biltillampningarkravs en strackrans omkring 600-700 MPa. Ett av de mest lovande satten attforbattra strackgransen ar genom utskiljningshardning. Detta arbete har utfortsinom en europeisk forskningsfond for kol och stal (RFCS) projekt kallat Precipitationin High Manganese steels (PrecHiMn). Som namnet pa projektetantyder, har malet med projektet varit att studera utskiljning i TWIP stal.Utskiljningshardning uppnas genom tillsats av karbid- och karbonitridbildaresasom Nb, Ti och V. For att bygga avancerade modeller for simulering av utskiljningar det viktigt att ha en god forstaelse for termodynamiken i systemrelaterade till TWIP stal.Malet med detta arbete har varit att studera de termodynamiska egenskapernahos system med anknytning till TWIP stal. Mer specikt har systemetsom bildar matrisfaserna i TWIP stal. Drfr har Al-C-Fe-Mn-systemet studeratsliksom Al-Ti-V-systemet. Fullstandiga termodynamiska beskrivningar somaterger experimentella data val har producerats inklusive beskrivningar av ordningsomvandlingar.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. v, 48 p.
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
urn:nbn:se:kth:diva-166224 (URN)978-91-7595-516-2 (ISBN)
Public defence
2015-05-22, B2, Brinellvägen 23, KTH, Stockholm, 10:00 (English)

QC 20150506

Available from: 2015-05-06 Created: 2015-05-05 Last updated: 2015-05-06Bibliographically approved

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