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Thermodynamic Study of Co-Cr and C-Co-Cr Systems
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

An experimental investigation of the binary system Co-Cr and the ternary system C-Co-Cr has been carried out in the present thesis. The experimental strategy adopted for the binary system was to measure the thermodynamic activities of Cr, the molar heat capacity as function of time, the phase transformation temperatures with corresponding enthalpies, the Curie transition temperature as well as melting temperatures with corresponding enthalpies. In the ternary system the strategy was to determine the solubility of Co in the Cr7C3 phase as well as the C and Cr contents in the Co rich (fcc) binder phase. The experimental results were compared with atomistic simulations of the solubility of Co in the Cr7C3 phase.

Solid state galvanic cell measurements were conducted with both ZrO2-7.5 mol % CaO and CaF2 as the solid electrolyte. In view of possible errors in the measurements with ZrO2-7.5 mol % CaO, as a result of electronic contributions to the conduction of the solid electrolyte, new measurements were conducted with CaF2 as the solid electrolyte. The results indicated that the measured EMF values showed trends which were contrary to the thermodynamic behaviour expected from phase diagram considerations. It was concluded that further detailed experimentation was necessary in order to throw more light on the thermodynamic behaviour of the Co-Cr system.

Two different series of DSC measurements were conducted, i.e. one in an atmosphere of pure hydrogen and another in pure argon. In the first investigation, conducted in an atmosphere of pure hydrogen in the temperature interval 318-1660 K, evidence was obtained for the existence of a phase transformation around 900 K in the compositional range 20.7-67.1 wt.% Cr. No indications of such a phase transformation had earlier been seen. In the second investigation, conducted in an atmosphere of pure argon in the temperature interval 298-1823 K, special attention was given to alloys in the Co rich corner of the phase diagram, i.e. 0-10 wt.% Cr. This investigation verified earlier findings of a phase transformations around 900 K in the compositional range 20.7-67.4 wt.% Cr. The magnetic transition temperatures for alloys low in Cr content were also obtained. With the use of the DTA technique the melting temperatures with corresponding enthalpy values for alloys in the compositional range 0.9-7.7 wt.% Cr were obtained.

The three-phase triangle fcc+Cr7C3+graphite was investigated at 1373 K, 1423 K and 1473 K. The obtained results showed that the solubility of cobalt in the Cr7C3 phase was significantly higher than previously predicted by thermodynamic calculations.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 110 p.
Keyword [en]
Cobalt, chromium, carbon, experimental thermodynamics, , solid state galvanic cell technique, differential scanning examination
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-418ISBN: 91-7178-125-0 (print)OAI: oai:DiVA.org:kth-418DiVA: diva2:11104
Public defence
2005-09-23, K2, teknikringen28, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100930Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2010-09-30Bibliographically approved
List of papers
1. Thermodynamic investigation of Co-Cr alloys, I: Galvanic cell Measurements of Chromium Activities using ZrO2-CaO solid electrolyte
Open this publication in new window or tab >>Thermodynamic investigation of Co-Cr alloys, I: Galvanic cell Measurements of Chromium Activities using ZrO2-CaO solid electrolyte
2005 (English)Report (Other academic)
Publisher
19 p.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-6399 (URN)KTH/MSE--05/74 (ISRN)
Note

QC 20100930

Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2017-02-23Bibliographically approved
2. Thermodynamic investigation of the Co-Cr system by the solid state galvanic cell technique involving CaF2 solid electrolyte
Open this publication in new window or tab >>Thermodynamic investigation of the Co-Cr system by the solid state galvanic cell technique involving CaF2 solid electrolyte
2005 (English)Report (Other academic)
Publisher
17 p.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-6400 (URN)KTH/MSE--05/74 (ISRN)
Note
QC 20100930Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2010-09-30Bibliographically approved
3. Thermodynamic investigation of Co-Cr alloys. II.: Heat capacity measurements in the temperature interval 318-1660 K
Open this publication in new window or tab >>Thermodynamic investigation of Co-Cr alloys. II.: Heat capacity measurements in the temperature interval 318-1660 K
2003 (English)In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 32, no 5, 233-240 p.Article in journal (Refereed) Published
Abstract [en]

The thermodynamic properties of several Co-Cr alloys have been determined in the temperature interval 318-1660 K using differential scanning calorimetric (DSC) technique. The compositional range of the alloys investigated extended from 10 to 90 wt% Cr. Heat capacity equations, C-p (J/mol K) = A + B . T (K), were derived in the temperature interval of interest to fit the experimental data. The experimental Cp values are compared with those from the Neumann-Kopp rule. The phase transformations observed in the present measurements are discussed in the light of the phase diagram <LF>information available in the literature for the Co-Cr binary system.

Keyword
chromium, cobalt, differential scanning calorimetric (DSC) technique, experimental data, experimental thermodynamics
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-6401 (URN)10.1034/j.1600-0692.2003.00646.x (DOI)000185253200002 ()
Note
QC 20100930Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2017-12-14Bibliographically approved
4. Thermodynamic investigation of Co-Cr alloys, III: Thermo-analytical measurements using DSC and DTA techniques
Open this publication in new window or tab >>Thermodynamic investigation of Co-Cr alloys, III: Thermo-analytical measurements using DSC and DTA techniques
2006 (English)In: INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, ISSN 1862-5282, Vol. 97, no 11, 1533-1538 p.Article in journal (Refereed) Published
Abstract [en]

Several Co-Cr alloys have been investigated by Differential Scanning Calorimetry (DSC) as well as by Differential Thermal Analysis (DTA) in the temperature range 2981823 K. The compositional range investigated was from 0 to 87 wt.% Cr with special attention given to alloys with low Cr contents, i.e. 0 to 10 wt.% Cr. From the DSC measurements molar heat capacity values, phase transformation temperatures, enthalpies of transformation and Curie transition temperatures were derived. From the DTA measurements, the melting temperatures and melting enthalpies were evaluated. The trends obtained were compared with the results for pure Co as well as the proposed phase diagram reported in literature.

Keyword
differential scanning calorimetry, differential thermal analysis, Co-Cr, experimental thermodynamics
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-6402 (URN)000242436700008 ()2-s2.0-33751401404 (Scopus ID)
Note
Uppdaterad från submitted till published: 20100930. QC 20100930Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2010-09-30Bibliographically approved
5. Thermodynamic investigation of C-Co-Cr alloys: The M7-C3-fcc-graphite equilibrium in the Temperature Interval 1373-1473 K
Open this publication in new window or tab >>Thermodynamic investigation of C-Co-Cr alloys: The M7-C3-fcc-graphite equilibrium in the Temperature Interval 1373-1473 K
Show others...
2005 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940Article in journal (Other academic) Submitted
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-6403 (URN)
Note

QS 20120316

Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2017-12-14Bibliographically approved
6. Solubility of Co in Cr7c3-Ab initio studies and experimental verification
Open this publication in new window or tab >>Solubility of Co in Cr7c3-Ab initio studies and experimental verification
2006 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 54, no 8, 1491-1495 p.Article in journal (Refereed) Published
Abstract [en]

Experimental determination of the cobalt solubility in the three-phase triangle face-centered cubic + Cr7C3 + graphite have been carried out. In the present work these results are compared with atomistic calculations of the solubility of Co in Cr7C3 phase based on ab initio cohesive energies and lattice inversion method. Comparisons are also made with the literature data reported earlier [Koster W, Sperner F. Arch Eisenhuttenwesen 1955;26:555; Thompson ER, Lemkey FD, Metall Trans 1970-1:2799; Sabin PR, Watts DJ. Metall Trans 1971;2:1260; Sahm PR, Lorenz M, Hugi W, Fruhauf V. Mettal Trans 19723:1022; Tuma H, Lobl K. Kovove Mater 1971;9:221; Fritscher K. Thermochim Acta 1979;29:357].

Keyword
thermodynamics, quenching, electron probe microanalysis (EPMA), atomistic simulations (ab-initio calculations)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-6404 (URN)10.1016/j.scriptamat.2005.12.057 (DOI)000235588800010 ()2-s2.0-32544454474 (Scopus ID)
Note
Uppdaterad från submitted till published: 20100930. QC 20100930Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2017-12-14Bibliographically approved

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