Phase relationships and thermodynamic properties in the Mn-Ni-C system
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I. INTRODUCTION
THE knowledge of the phase relationships in the Mn-Ni-C ternary system is of great importance for an understanding of the properties of alloy steels. The thermodynamics of the three binary subsystems in the Mn-Ni-C ternary system, i.e., Mn-C,[1,2] Ni-C,[3,4] and Mn-Ni,[5,6] are relatively well established, but, to the knowledge of the present authors, there is no experimental information available on the solid-phase relationships of the ternary system Mn-Ni-C.[7] Because of the lack of the experimental data, there is no thermodynamic assessment available for the Mn-Ni-C ternary system. In the TCFE3 database,[8] the Mn-C binary system has been assessed by Huang[9] and Ni-C by Gabriel et al.[10] The parameters of Mn-Ni binary system were obtained from an NPL (National Physical Laboratory, Teddington, United Kingdom) unpublished work (1989). Based on the extrapolations of the binary subsystems,[9,10] the preliminary calculations of Mn-Ni-C ternary system have been carried out using Thermo-Calc software.[11] In a previous article,[12] some of the thermodynamic activities of Mn in the Mn-Ni-C ternary system have been reported. As a continuation of the earlier study, the present work is aimed at more experimental results of the activities of manganese in the system by the galvanic cell method as well as phase relationships by use of X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. II. EXPERIMENTAL The nominal compositions and sample numbers are identical to those described in a previous work[12] and are listed in Table I. Figure 1 presents an isothermal section of the Mn-NiC system at 1073 K on the basis of the preliminary calculation
LIDONG TENG and RAGNHILD E. AUNE, Doctors, and SESHADRI SEETHARAMAN, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, 10044 Stockholm, Sweden. Contact e-mail: [email protected] WENCHAO LI, Professor, is with the Department of Physical Chemistry, University of Science and Technology Beijing, 100083 Beijing, P.R.China. Manuscript submitted July 30, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
by extrapolations of the binary systems. The locations of the alloy compositions and corresponding sample numbers are presented in Figure 1. Alloys of Mn-Ni-C were prepared from Mn (99.9 pct pure; 150 m; supplied by E. Merck, Darmstadt, West Germany), Ni (99.8 pct pure; 10 m; supplied by E. Merck), and graphite (99.999 pct pure; 325 mesh; supplied by Aldrich, Stockholm, Sweden) powders by mixing the components in required proportions, compacting into pellets, and sintering them in a closed alumina crucible at 1273 K for 2 weeks under a stream of purified argon. Details of the argon gas cleaning apparatus and the oxygen meter used in this study have been reported elsewhere.[13] The sintered samples were placed inside quartz capsules and sealed under vacuum (0.1 Pa). The capsules were then placed in the uniform temperature zone (0.5 K) of a vertical alumina reaction tube and heat
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