Paper 3.1

Thermodynamic studies of Cr3C2 and reassessment of Cr-C system

 

Teng Lidong, Lu Xiaogang, Aune Ragnhild. E., and Seetharaman S.  

 

Department of Materials Science and Engineering, Royal Institute of Technology,

SE-10044 Stockholm, Sweden

 

Chromium carbides are of considerable scientific and technical importance because of their extensive applications in cutting tool and heat-resistant steel industries. A precise knowledge of their thermodynamic properties is essential for the understanding and the prediction of their chemical behavior in various environments. The standard Gibbs energies of formation of Cr3C2, , have been obtained from electromotive force (EMF) measurements between 950 and 1150K on the following galvanic cells with CaF2 single crystals as the electrolyte:

Cr, CrF2 | CaF2 | CrF2, Cr3C2, C         (950-1150 K)

The following equation has been obtained by a linear analysis of the EMF as a function of temperature

      

The values of the Gibbs energy of formation and the entropy term for Cr3C2 agree well with those of Kulkarni [8]. The values of enthalpy of formation were evaluated by a third-law analysis. An average value of  = -71.7 kJ/mol was obtained and this value is comparable to the values reported by Kulkarni [1], Du et al [2] and Kleykamp [3].

 

The ground-state energy and its constituents for end-member compound CrC3 in bcc phase were calculated by use of the Vienna ab initio simulation package (VASP) [4]. The experimental results and the VASP calculated values were employed in a reassessment of the Cr-C system by using the computer program PARROT [5]. A new set of parameters of bcc phase have been evaluated more reliably by using of the first-principles calculations.

 

Reference

1. A. D. Kulkarni, and W. Worrell, Metall. Trans., 1972, vol.3, p. 2363-70

2. Du Sichen, S. Seetharaman, L.I. Stafansson, Met. Trans. B 20(1989) 911

3. H. Kleykamp, J. of alloys and Compounds, 321(2001) 138-145.

4. G. Kresse and J. Joubert, Phys. Rev. B. 59(1999) 1758-1761

5. Thermocalc Software, version P on WinNT, 2000, http://www.thermocalc.com.

 

E-mail: lidongt@mse.kth.se