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Section I: Basic and Applied Research

A Thermodynamic Description of the Al-Cr-Si System Yu Liang, Cuiping Guo, Changrong Li, and Zhenmin Du

(Submitted March 28, 2009; in revised form June 28, 2009) The Al-Cr-Si system was critically assessed using the CALPHAD technique. The solution phases (liquid, bcc, fcc, and diamond) were described by a substitutional solution model. The compounds CrSi2, Cr3Si, AlCr2, aAl8Cr5, bAl8Cr5, Al4Cr, and Al11Cr2 in the Al-Cr-Si system were treated with sublattice models (Cr, Si)(Al, Cr, Si)2, (Cr, Si)3(Al, Cr, Si), (Al, Cr, Si)(Al, Cr)2, a(Al, Cr, Si)8(Al, Cr, Si)5, b(Al, Cr, Si)8(Al, Cr, Si)5, (Al, Si)4(Al, Cr), and (Al, Si)11(Al, Cr)2, respectively. The ternary intermetallic compounds s1, s2, and s3 were treated as the formulae Al13Cr4Si4, Al9Cr3Si, and (Al,Si)11Cr4, respectively. A set of self-consistent thermodynamic description of the Al-Cr-Si system was obtained.

Keywords

metals and alloys, phase diagram, CALPHAD technique, thermodynamic properties, thermodynamic modeling

1. Introduction Al-Cr-Si alloys show good oxidation resistance with no mass loss after oxidation in air during the melting process.[1] They might be used as promising coating materials for carbon/carbon composites for application at high temperatures.[2] Knowledge of phase equilibria is significant for the optimization of alloy compositions and heat-treatment conditions. The CALPHAD technique[3] was used to analyze the thermodynamic properties of the system in this study. Robinson[4,5] determined the crystal structure of the s1 phase in the Al-Cr-Si system, which is a ternary compound a(AlCrSi) in the early studies carried out by Pratt and Raynor.[6,7] Subsequently, Esslinger et al.[8] investigated the phase equilibria in the Al-rich corner of the Al-Cr-Si system and confirmed that the composition of the s1 phase is Al13Cr4Si4. Another ternary compound b(AlCrSi) reported by Pratt and Raynor[6] and Mondolfo[9] turned out to be a

This article is an invited paper selected from participants of the 14th National Conference and Multilateral Symposium on Phase Diagrams and Materials Design in honor of Prof. Zhanpeng Jin’s 70th birthday, held November 3-5, 2008, in Changsha, China. The conference was organized by the Phase Diagrams Committee of the Chinese Physical Society with Drs. Huashan Liu and Libin Liu as the key organizers. Publication in Journal of Phase Equilibria and Diffusion was organized by J.-C. Zhao, The Ohio State University; Yong Du, Central South University; and Qing Chen, Thermo-Calc Software AB. Yu Liang, Cuiping Guo, Changrong Li, and Zhenmin Du, Department of Materials Science and Engineering, University of Science and Technology, Beijing 100083, P.R. China. Contact e-mail: [email protected].

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solid solution of Al in the binary compound CrSi2.[5] The investigation of Brukl et al.[10] also indicated that b(AlCrSi) was the binary intermetallic CrSi2 with extended solubility of Al up to 25 at.% Al with Al replacing Si in the sublattice of the intermetallic compound. The AlCr2 phase was reporte