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Phase relationships and thermodynamic properties in the Mn-Ni-C system
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
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.

Place, publisher, year, edition, pages
2005. Vol. 36, no 10, 2585-2593 p.
Keyword [en]
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: urn:nbn:se:kth:diva-5210DOI: 10.1007/s11661-005-0256-3ISI: 000232076800002Scopus ID: 2-s2.0-27144549607OAI: oai:DiVA.org:kth-5210DiVA: diva2:8027
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
In thesis
1. Thermodynamic investigations of transition metal systems containing coabon and nitrogen
Open this publication in new window or tab >>Thermodynamic investigations of transition metal systems containing coabon and nitrogen
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
Materials science, thermodynamic activity, galvanic cell technique, transition metal carbides, transition metal nitrides, phase equilibrium, Materialvetenskap
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-24 (URN)91-7283-832-9 (ISBN)
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

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