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Thermodynamic investigations of transition metal systems containing coabon and nitrogen
KTH, Superseded Departments, Materials Science and Engineering.
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In view of the important applications of carbides and carbo-nitrides of transition metals in the heat-resistant and hard materials industries, the thermodynamic activities of Cr and Mn in the Cr-C, Fe-Cr-C, Mn-Ni-C and Mn-Ni-C-N systems have been studied in the present work by the use of the galvanic cell technique. CaF2single crystals were used as the solid electrolyte. The phase relationships in selected regions of the systems in question were investigated by the use of the equilibration technique. The phase compositions and microstructures of the alloys were analysed by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).

In the Cr-C system, the Gibbs energy of formation of Cr3C2 were obtained from ElectroMotive Force (EMF) measurements conducted in the temperature range 950-1150 K. The values of the enthalpy of formation of Cr3C2 were evaluated by the third-law method. The ground-state energy of the hypothetic end-member compound CrC3, in the bcc structure at 0 K, was calculated by use of the Ab-initio method. Based on the obtained results the Cr-C system was reassessed by use of the CALPHAD approach.

In the Fe-Cr-C system, 16 different alloys were quenched at 1223 K and their equilibrium phases identified by XRD. The experimental results show that the substitution of Cr by Fe in the (Cr,Fe)7C3 carbide changes the lattice parameters of the phase. A slight decrease of the lattice parameters with an increase in the Fe content was established. The lattice parameters of the γ-phase in the Fe-Cr solid solution did also show a decrease with an increase of the Fe content. The activities of chromium in Fe-Cr-C alloys were investigated in the temperature range 940-1155 K. The activity of chromium decreases with an increase in the Fe content when the ratio of C/(Cr+C) was constant. It was also established that the activity of chromium decreases with an increase of the carbon content when the iron content was constant. The experimental results obtained were compared with the data calculated by use of the Thermo-Calc software.

In the Mn-Ni-C system the phase relationships were investigated at 1073 K as well as at 1223 K. The experimental results obtained showed that the site fraction of Ni in the metallic sublattice of the carbides M23C6, M7C3 and M5C2 (M=Mn and Ni) was quite low (approximately 2~3 percent). The activities of manganese in Mn-Ni-C alloys were investigated in the temperature range 940-1165 K. The three-phase region γ/M7C3/graphite was partly constructed at 1073 K.

In the Mn-Ni-C-N system, nitrogen was introduced into Mn-Ni-C alloys by equilibrating with N2 gas. It was established that the solubility of nitrogen in the investigated alloys was effected by the carbon content, and that a (Mn,Ni)4(N,C) compound was formed in the nitrided alloys. EMF measurements were performed on Mn-Ni-C-N alloys in the temperature interval 940-1127 K. The addition of nitrogen to Mn-Ni-C alloys was found to decrease the activity of manganese. The negative effect of nitrogen on the activity of manganese was found to decrease as the carbon content increased.

Keywords: Thermodynamic activity; Galvanic cell technique; Transition metal carbides; Transition metal nitrides; Phase equilibrium; Thermodynamics; Differential thermal analysis; Scanning electron microscopy; Transmission electron microscopy; Ab-initio calculations; CALPHAD approach;

Place, publisher, year, edition, pages
Materialvetenskap , 2004.
Keyword [en]
Materials science, thermodynamic activity, galvanic cell technique, transition metal carbides, transition metal nitrides, phase equilibrium
Keyword [sv]
Materialvetenskap
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-24ISBN: 91-7283-832-9 (print)OAI: oai:DiVA.org:kth-24DiVA: diva2:8029
Public defence
2004-10-08, Salongen, KTHB, Qsquars backe 31, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2012-03-21Bibliographically approved
List of papers
1. Thermodynamic investigations of Cr3C2 and reassessment of the Cr-C system
Open this publication in new window or tab >>Thermodynamic investigations of Cr3C2 and reassessment of the Cr-C system
2004 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 35A, no 12, 3673-3680 p.Article in journal (Refereed) Published
Abstract [en]

The Gibbs energies of formation for Cr3C2, Δ fCr3C2, have been obtained from electromotive force (EMF) measurements, in the temperature range 950 to 1150 K, using the following galvanic cells with CaF2 single crystals as the electrolyte: Cr, CrF2 CaF2 CrF2, Cr 3C2, C (950 to 1150 K) Extreme precautions were taken during the experimental measurements to avoid errors. The reliability and reproducibility of the values were confirmed by careful repetition of several of the experiments. The following equation has been obtained by a linear analysis of the EMF results as a function of temperature: ΔfCr3C2(± 1600) = - 58,857 - 22.344T (J·mo1-1) (950 to 1150 K) The generated values are compared with those reported in the literature. The values of the enthalpy of formation were evaluated by using a third-law analysis, and an average value of Δf298 = -71.7 kJ/mol was obtained. The ground-state energy of the hypothetic end-member compound CrC3 in the bcc structure at 0 K was calculated by using the ab initio method. The experimental results obtained, as well as the results from the ab initio calculations, were employed in a reassessment of the Cr-C system using the CALPHAD approach. A new set of parameters for the bcc phase was evaluated using first-principles calculations.

Keyword
Calcium compounds, Chromium alloys, Electric potential, Electrolytes, Enthalpy, Gibbs free energy, Single crystals, Temperature, Thermodynamic properties, X ray diffraction analysis
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5207 (URN)10.1007/s11661-004-0273-7 (DOI)000225448100004 ()2-s2.0-11944268075 (Scopus ID)
Note
QC 20101004. Uppdaterad från Accepted till Published (20101004).Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2017-12-04Bibliographically approved
2. Thermodynamic investigations of the C-Cr-Fe system by galvanic cell technique
Open this publication in new window or tab >>Thermodynamic investigations of the C-Cr-Fe system by galvanic cell technique
2005 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 36, no 2, 263-270 p.Article in journal (Refereed) Published
Abstract [en]

In view of the applications of intermetallic carbides in the hard materials industries, the thermodynamic properties of the C-Cr-Fe system have been measured by the use of the solid-state galvanic cell technique with CaF2 as the solid electrolyte. The thermodynamic activities of chromium have been calculated from the results of the electromotive force (EMF) measurements. For the calculations, pure b+cc-Cr was used as the standard state. X-ray diffraction (XRD) and scanning electron microscopy were used to identify the stable phases present in each investigated sample, as well as for establishing the phase compositions. The experimental results obtained were compared with data calculated by the use of the TCFE3 database available with the Thermo-Calc software.

Keyword
Carbides, Computer software, Intermetallics, Lattice constants, Phase composition, Phase diagrams, Quenching, Scanning electron microscopy, Thermodynamics, X ray diffraction analysis
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5208 (URN)10.1007/s11663-005-0028-x (DOI)000228041000012 ()2-s2.0-17144394893 (Scopus ID)
Note
QC 20101004. Uppdaterad från Accepted till Published (20101004).Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2017-12-04Bibliographically approved
3. Study of Mn activities in Mn-Ni-C alloys by EMF measurements
Open this publication in new window or tab >>Study of Mn activities in Mn-Ni-C alloys by EMF measurements
2003 (English)In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 11, no 11-12, 1229-1235 p.Article in journal (Refereed) Published
Abstract [en]

 The activities of manganese in Mn-Ni-C alloys have been studied by solid-state galvanic cell technique with CaF2 as the solid electrolyte. The measurements of electromotive force (EMF) have been carried out in the temperature range 920-1240 K. The main phase compositions of the alloys have been analyzed by X-ray diffraction (XRD). It was established that the substitution of Mn by Ni in the (MnNi)(23)C-6 carbide was limited, that the lattice parameter decreased slightly with increase in the Ni content and that a solid solution is formed between Mn and Ni. It was also found that the activity of manganese decreases with increase in the nickel content when the ratio of C/(Mn+C) is less than 8.3 wt.%, and that the negative effect of Ni on the activity of Mn in Mn-Ni-C ternary system decreases as the carbon content increases. However, when the ratio of C/(Mn+C) is equal to 8.3 wt.% or more, the activity of manganese is independent of the nickel content.

Keyword
A. Ternary alloy systems, B. Thermodynamic and thermochemical properties
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5209 (URN)10.1016/S0966-9795(03)00163-8 (DOI)000186687100020 ()
Note
QC 20100930Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2017-12-04Bibliographically approved
4. Phase relationships and thermodynamic properties in the Mn-Ni-C system
Open this publication in new window or tab >>Phase relationships and thermodynamic properties in the Mn-Ni-C system
2005 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 36, no 10, 2585-2593 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, phase relationships in selected phase regions of the Mn-Ni-C system have been investigated at 1073 and 1223 K by use of an equilibration technique. Alloys of Mn-Ni-C were prepared from pure Mn, Ni, and C powders by the powder metallurgy method. The phase identification of the heat-treated samples was carried out by scanning electron microscope (SEM) and transmission electron microscope (TEM). The main phase compositions of the alloys have been analyzed by X-ray diffraction (XRD). The experimental results show that the site fraction of Ni in the metallic sublattice of the carbides M23C6, M7C3, and M5C2 is quite low and the value is around 0.02 to 0.03. The thermodynamic activities of manganese in 16 different Mn-Ni-C alloys have been studied by solid-state galvanic cell technique with single-crystal CaF2 as the solid electrolyte in the temperature range 940 to 1165 K. The results are discussed in light of the available thermochemical information.

Keyword
Heat treatment, Phase composition, Powder metallurgy, Scanning electron microscopy, Single crystals, Solid electrolytes, Thermodynamic properties, Transmission electron microscopy, X ray diffraction analysis
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5210 (URN)10.1007/s11661-005-0256-3 (DOI)000232076800002 ()2-s2.0-27144549607 (Scopus ID)
Note
QC 20100927. Uppdaterad från In press till Published (20100927).Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2017-12-04Bibliographically approved
5. Thermodynamic investigations of the Mn-Ni-C-N quarternary alloys by solid-state galvanic cell technique
Open this publication in new window or tab >>Thermodynamic investigations of the Mn-Ni-C-N quarternary alloys by solid-state galvanic cell technique
2005 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 388, no 2, 250-257 p.Article in journal (Refereed) Published
Abstract [en]

In view of the important applications of carbides and nitrides of transition metals in the hard materials industries, the thermodynamic activities of manganese in Mn-Ni-C-N alloys have been studied by solid-state galvanic cell technique with CaF2 as the solid electrolyte. The phase compositions and microstructure of various alloys have been analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Nitrogen was introduced into the alloy by equilibrating with N-2 gas. It was established during the experiments that the solubility of nitrogen in the alloys was affected by the carbon content. A (Mn,Ni)(4)(N,C) nitride was formed during the nitriding procedure in the alloys. The electromotive force (EMF) measurements were carried out in the temperature range 940-1127 K in order to determine the activities of Mn in the alloys. The activities of manganese were calculated and compared with those of the corresponding Mn-Ni-C ternary alloys.

Keyword
interstitial alloys, powder metallurgy, scanning electron microscopy, thermodynamics, galvanic cell, phase-diagram, system
Identifiers
urn:nbn:se:kth:diva-14476 (URN)10.1016/j.jallcom.2004.07.032 (DOI)000226556700015 ()2-s2.0-11344258943 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved

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