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A thermodynamic assessment of the Co-V system
Swed. Institute for Metals Research.
KTH, Superseded Departments, Materials Science and Engineering.
2003 (English)In: Journal of phase equilibria (Print), ISSN 1054-9714, E-ISSN 1544-1032, Vol. 24, no 6, 495-503 p.Article in journal (Refereed) Published
Abstract [en]

A thermodynamic evaluation of the binary Co-V system has been done using experimental thermochemical and phase diagram data. A consistent thermodynamic description, using a Redlich-Kister model for solution phases and sublattice models for the intermetallics, was obtained, and it agreed well with the critically evaluated experimental data. The model for the solid phases accounts for the magnetic contribution to the Gibbs energy. The addition of a composition dependent magnetic term also led to the prediction of an fcc-Co miscibility gap. The model parameters have been determined using a computerized optimization technique. Several diagrams and tables concerning phase equilibria are presented.

Place, publisher, year, edition, pages
2003. Vol. 24, no 6, 495-503 p.
Keyword [en]
phase-equilibria, sigma phase, alloys, vanadium, cobalt, model
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-23062DOI: 10.1361/105497103772084534ISI: 000187667400002OAI: diva2:341760
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-09-29Bibliographically approved
In thesis
1. Phase equilibria and thermodynamic properties of high-alloy tool steels: theoretical and experimental approach
Open this publication in new window or tab >>Phase equilibria and thermodynamic properties of high-alloy tool steels: theoretical and experimental approach
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The recent development of tool steels and high-speed steels has led to a significant increase in alloy additions, such as Co, Cr, Mo, N, V, and W. Knowledge about the phase relations in these multicomponent alloys, that is, the relative stability between different carbides or the solubility of different elements in the carbides and in the matrix phase, is essential for understanding the behaviour of these alloys in heat treatments. This information is also the basis for improving the properties or designing new alloys by controlling the amount of alloying elements. Thermodynamic calculations together with a thermodynamic database is a very powerful and important tool for alloy development of new tool steels and high-speed steels. By thermodynamic calculations one can easily predict how different amounts of alloying elements influence on the stability of different phases. Phase fractions of the individual phases and the solubility of different elements in the phases can be predicted quickly. Thermodynamic calculations can also be used to find optimised processing temperatures, e.g. for different heat treatments. Combining thermodynamic calculations with kinetic modelling one can also predict the microstructure evolution in different processes such as solidification, dissolution heat treatments, carbide coarsening, and the important tempering step producing secondary carbides.

The quality of predictions based on thermodynamic calculations directly depends on the accuracy of the thermodynamic database used. In the present work new experimental phase equilibria information, both in model alloys containing few elements and in commercial alloys, has been determined and was used to evaluate and improve the thermodynamic description. This new experimental investigation was necessary because important information concerning the different carbide systems in tool steels and high-speed steels were lacking.

A new thermodynamic database for tool steels and high-speed steels, TOOL05, has been developed within this thesis. With the new database it is possible to calculate thermodynamic properties and phase equilibria with high accuracy and good reliability. Compared with the previous thermodynamic description the improvements are significant. In addition the composition range of different alloying elements, where reliable results are obtained with the new thermodynamic database, have been widened significantly.

As the available kinetic data did not always predict results in agreement with new experiments the database was modified in the present work. By coupling the new thermodynamic description with the new kinetic description accurate diffusion simulations can be performed for carbide coarsening, carbide dissolution and micro segregation during solidification.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 68 p.
thermodynamic modelling, thermodynamic calculations, tool steels, high-speed steels, CALPHAD
National Category
Other Materials Engineering
urn:nbn:se:kth:diva-453 (URN)91-7178-120-X (ISBN)
Public defence
2005-10-21, salongen, KTHB, Osquars backe 31, Stockholm, 10:00
QC 20100929Available from: 2005-10-18 Created: 2005-10-18 Last updated: 2010-09-29Bibliographically approved

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