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Khvan A.V.,RWTH Aachen | Khvan A.V.,Thermochemistry of Materials Scientific Research Center | Hallstedt B.,RWTH Aachen | Broeckmann C.,RWTH Aachen
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2014

The availability of recent data on Gibbs energies of Fe7C 3 and Fe23C6 based on ab initio calculations required the complete reassessment of the thermodynamic parameters in the Fe-Cr-C system. In order to perform the optimization process a detailed critical evaluation of the experimental literature data on the Fe-Cr-C system was made. The Calphad technique using a computerized optimization procedure (PARROT) was applied in the work. Thus, a new self-consistent thermodynamic description of the Fe-Cr-C system based on a detailed literature survey was obtained in the present work. The results are presented in a number of phase diagrams. © 2014 Elsevier Ltd.All rights reserved. Source


Schmetterer C.,Julich Research Center | Khvan A.,RWTH Aachen | Khvan A.,Thermochemistry of Materials Scientific Research Center | Jacob A.,Julich Research Center | And 2 more authors.
Journal of Phase Equilibria and Diffusion | Year: 2014

A new thermodynamic assessment of the binary Cr-Nb system was performed using the CALPHAD method based on a review of the available literature and ab initio calculations for the hypothetical end members of the C15 Laves phase. Recent experiments reported in the literature revealed that there is no C14 type high temperature phase in this system, which is in contrast to most of the literature. A thorough analysis of these reports, however, showed that the C14 phase has never been directly observed and that its presence had been derived from ternary phase diagram data, twinning of the C15 low temperature phase and erroneous interpretations of x-ray diffractograms. Due to the lack of clear evidence in favor of its existence, the C14 phase was not considered a thermodynamically stable compound in the present evaluation. © 2014 ASM International. Source


Syutkin E.A.,Thermochemistry of Materials Scientific Research Center | Jacob A.,Julich Research Center | Schmetterer C.,Julich Research Center | Schmetterer C.,Fraunhofer Institute for Environmental, Safety and Energy Technology | And 3 more authors.
Thermochimica Acta | Year: 2016

Standard enthalpies of formation, ΔfH, of the Laves-phases within their solid solutions along the Cr2Nb-Fe2Nb section were measured using drop solution calorimetry for the first time. The enthalpy values change linearly from -2.9 kJ mol-1 atom-1 for binary C15-Cr2Nb to -13.6 kJ mol-1 atom-1 for C14-Fe2Nb. The obtained values are compared with some earlier results on the binary compounds gathered mostly from ab initio calculations. © 2015 Elsevier B.V. All rights reserved. Source


Jacob A.,Julich Research Center | Jacob A.,Vienna University of Technology | Schmetterer C.,Julich Research Center | Khvan A.,Thermochemistry of Materials Scientific Research Center | And 3 more authors.
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2016

A liquidus projection and a thermodynamic assessment of the Cr-Fe-Nb ternary system are proposed for the first time. The construction of the liquidus projection was obtained through evaluation of the microstructure of as cast samples and high temperature DTA measurements of equilibrated samples. Thermodynamic modeling was then done via the Calphad method based on DFT calculation for the description of the energy behavior of the phases and experimental evidence. © 2016 Elsevier Ltd. All rights reserved. Source


Khvan A.V.,Thermochemistry of Materials Scientific Research Center | Dinsdale A.T.,Thermochemistry of Materials Scientific Research Center | Cheverikin V.V.,Thermochemistry of Materials Scientific Research Center | Kudashov D.,Engineering technology center | And 3 more authors.
Materials Science and Technology (United Kingdom) | Year: 2016

The influence of Mn and Cr on the formation of surface oxides and their entrapment during electric resistance welding of Si containing low carbon steels was studied using thermodynamic calculations and experimental investigation of the microstructure of the different oxide inclusions within welds on electric resistance welding-fabricated pipes. The process of oxidation during the welding process, its dependence on oxygen content, temperature of oxidation and the composition of ferrite within the parent steel were analysed. It was shown that the most important influence on the type of oxide inclusions formed during welding is the Mn/Si ratio, while Cr has an indirect influence via carbide formation, which increases the relative content of Mn in ferrite. © 2016 Institute of Materials, Minerals and Mining. Source

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