| The ternary Mg-Mn-Ce phase diagram was experimentally studied and thermodynamically calculated at the Mg-rich corner. More than twenty binary and ternary alloys were synthesized and heat-treated at both ambient and elevated temperatures. The microstructures and lattice parameters of the samples were studied via XRD, SEM/EDS and EPMA to determine phase equilibria. The ternary phase diagram was also calculated via thermodynamic calculation software FactSage. The results from both experiment and the assessment were compared and discussed.;The binary phase diagram study was also extended to the Ce-rich side of Mg-Ce system. A new phase, Mg4Ce, was found in the study of phase Mg3Ce. Based on the investigation of the intermetallics in the Mg-Ce binary system, a modified phase diagram was suggested to accommodate the stoichiometry of Mg11Ce, Mg39Ce5, and Mg3Ce.;The experimental study on the ternary phase diagram was conducted on three isopleths: 0.6, 1.8 and 2.5wt% Mn, respectively, and Ce varied between 0 and 25wt%. All alloys were synthesized from high purity starting materials. Two types of thermal analyses, namely, cooling curve analysis (CCA) and differential scanning calorimetry (DSC), were used to determine the liquidus and solid phase transformation temperatures. The heating/quenching tests on selected samples were conducted for phase analysis. The results showed that only one invariant point for ternary eutectic reaction was observed in the three isopleths, and the composition is 1wt% Mn and 22wt% Ce at 592°C. Furthermore, a solid-solution type of ternary intermetallic compound (Mg, Mn)11Ce is formed, holding the same tetragonal structure as Mg12Ce. The solid solution of Mn in Mg12Ce varies between 0.3∼0.6 at%, depending on alloy composition and quenching temperature.;Finally, the phase diagram calculation with FactSage program was conducted and the small disagreement between the modeling results and present experimental data were found, especially for the eutectic temperature for L → Mg(hcp) + Mg12Ce. This is mainly because the present experimental data were not available when the thermodynamic modeling had been performed. The Gibbs energy of Mg12Ce phase was re-optimized and the revised data can accurately reproduce the experimental results within experimental error limits.;The binary phase diagrams were re-examined, especially the Mg-Ce system. In order to investigate the composition range of the intermetallic compounds Mg12Ce and Mg41Ce5, and to clarify data in the existing phase diagram, both the solid-liquid diffusion couple method and alloys synthesized with target phases were analyzed. Pure Mg - Ce contact was vacuum-encapsulated in quartz tube and the Mg and Ce inter-diffused at 400°C. Alloys prepared were cast and annealed at a temperature range of 300-550°C. All the four single-phase zones corresponding to the Mg-Ce phase diagram were observed via the diffusion couple technique. However, the stoichiometry of Mg12Ce studied on the synthesized and annealed alloys showed that on the Mg rich side of the present phase diagram, the compositional range of Mg12Ce should be redesignated as Mg(11.17-10.81) Ce at ambient temperature, and Mg(11.31-10.75)Ce at 530°C. Mg41Ce5, on the other hand, has been confirmed as a line compound, but with composition 11.3at% Ce, rather than 10.9at% Ce. |
