Use the phase diagram provided for the following questions: What is the composit

Question

Use the phase diagram provided for the following questions: What is the composition of the eutectic Sn-Bi liquid? What is the maximum solubility of Bi in Sn? If 100 gm of molten Sn is held at 250degreeC, hew mu Ch Bi can be added to this molten metal pot while remain liquid? (must show work) Draw the expected equilibrium microstructures for a 80-20 Sn-Bi alloy at room temperature. A molten 70-30 Sn-Bi alloy is fully solidified by equilibrium cooling. What microconstituent(s) can be found? What is the weight fraction of each microconstituent found for question? (must show work)

Explanation / Answer

Bi–Sn binary system. Nagasaki and Fujita [4] experimentally defined a (Sn) solvus curve that was not in good agreement with that from Oelsen and Golucke [ ¨ 5]. Experimental results from Ohtani and Ishida [6] were also in contradiction with those from [4]. Nevertheless, Ohtani and Ishida [6] (contradicting their own experimental results) and Lee et al. [7] used only the experimental data from Nagasaki and Fujita [4] in their thermodynamic assessment. Concerning Bi–Zn, there was a significant discrepancy between the (Bi) solvus estimated by Massalski [8] and that calculated by Malakhov [9] (few wt% of Zn). Thus, targeted experimental alloys were prepared to determine the solubility of Zn in (Bi). With the aim of clarifying the above indicated aspects of the binaries and ternary, almost all of the samples were studied by SEM/EDS/WDS (Wavelength-Dispersive crystal Spectrometer), RT-XRD/HT-XRD and by DTA/DSC. 2. Experimental The Bi–Sn and Bi–Sn–Zn systems were objects of two different studies. One more devoted to phase transitions as well as to temperature measurements and the other to the equilibrium study. Hence, the experimental details were different according to the objective of the study and therefore will be presented in two different sections. 2.1. Phase transitions study of the Bi–Sn system Eight samples of 20 mm diameter, 3 mm height and weighing 2 g were prepared by mixing pure Bi (>99.8%) and Sn (>99.5%). The samples were then put in alumina crucibles and melted in a resistance furnace under an argon atmosphere. The nominal compositions of the samples were Bi(1 x)Snx (x = 12.5, 23.5, 36.5, 74.5, 80.1, 84.9, 89.9 and 95.6, wt%). These were confirmed by X-ray Fluorescence (XRF) and Atomic Absorption Spectroscopy (AAS). All samples were homogenized at 120 C for 60 min and slowly cooled down to the room temperature at a rate less than 2 C/min. Samples were studied by Light Optical Microscopy (LOM) and by SEM in a JEOL JSM 6301 F. The SEM is equipped with an INCA Energy 350 EDS analyzer from Oxford Instruments. A backscattered beam with 15 keV is employed. Internal standards are used for the EDS analysis. The experimental uncertainties of the chemical analysis done by EDS are: Bi ±1.2 wt% and Sn ±0.9 wt%. The Panalytical X’Pert Pro MPD was used for RTXRD experiments with bulk samples. CuK or primary monochromated CuK1 radiations were used to collect patterns from 5 to 120 (2) with steps of 0.01 and counting time of 10 s. The powder HT-XRD was not performed due to problems related with the samples’ grinding (the apparatus used only allows powder HT-XRD).

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