Active learning of eutectic phase diagram in engineering courses

The present article shows a new strategy used to cover phase diagrams for undergraduate mechanical engineering students. It is based on active learning in which students are required to investigate experimentally three different eutectic alloys by using X-ray diffraction and metallography. The first technique allows students to use Rietveld analysis to obtain the mass fraction of the present phases and they must compare their results with those obtained theoretically whilst the second one is used to characterize those phases and measured their area fractions. From these results, they can also compare them with those obtained theoretically, but considering the density of different phases. The results have shown that students understood more clearly concepts such as the lever rule, and the very interpretation of phase diagram: the liquidus and solidus curve and finally the eutectic point.

Phase equilibria in the SnBi2Te4MnBi2Te4 system and characterization of the Sn1-xMnxBi2Te4 solid solutions

The phase diagram of the SnBi2Te4-MnBi2Te4 system was established over the entire concentration range by means of differential thermal analysis and powder X-ray diffraction techniques. It was shown that the system is non-quasi-binary due to the incongruent melting character of SnBi2Te4 and MnBi2Te4 compounds, but it is stable below solidus. The formation of a continuous series of solid solutions with the tetradymite-like layered structure was observed. Due to ionic radius differences of Mn2+ and Sn2+, both unit cell parameters of solid solutions increase linearly with the increasing amount of Sn. Phase equilibria above the solidus curve cannot be completed until the SnTe-MnTe-Bi2Te3 system fully studied.

A Preliminary Investigation of the Cr3Si-Mo Pseudo-Binary Phase Diagram

An investigation was undertaken to study the phase relations in Cr3Si alloyed with Mo varying from 10 to 83.5 wt. % of the material. Specimens were prepared from arc-melted buttons that were subsequently heat treated at 1673 K for 200 h and air quenched to room temperature to preserve the high temperature microstructures. Alloys containing more than 20 wt. % Mo were primarily two-phase materials of M3Si and M5Si3, where M is (Cr,Mo). Three alloys contained less than 5 % of a third phase, which also had the M5Si3 crystal structure. Differential thermal analysis (DTA) was performed on several specimens at temperatures up to 2073 K in order to determine a solidus curve for the M3Si phase. Since only one DTA peak was observed in each alloy, the M5Si3 phase must melt above 2073 K, the maximum temperature examined. A preliminary pseudo-binary phase diagram for (Cr,Mo)3Si and a portion of the 1673 K isothermal section of the Cr-Mo-Si ternary phase diagram are presented.