Abstract
This work deals with the study of the volume ratio of α(Sn) and β(Bi) phases in the as-cast eutectic Bi-43 wt % Sn alloy, as well as in this alloy after casting, followed by compression in a hydraulic press to a degree of deformation of ∼70%, and in this alloy aged for various time intervals. This alloy demonstrates superplastic behavior even at room temperature. The experiments were carried out using scanning electron microscopy and electron-microprobe analysis using a JSM-6390LV scanning electron microscope equipped with an INCA-350 attachment for EDS analysis. Based on the obtained cooling curves, it has been found that, under the selected experimental conditions, the crystallization of the alloy is nonequilibrium. The original phase state of the alloy is characterized by an excessive relative amount of the α(Sn) phase compared to the equilibrium amount even for the eutectic temperature, which is indicative of the quenching of the liquid melt. The phase state of the alloy formed in the course of crystallization is metastable. This is confirmed by the volume ratio of the phases in the specimens subjected to fairly long aging. The data on the earlier discovered effect of the enrichment of open outer surfaces of the specimens in tin in the course of aging are presented. As a cause of the metastability of the phase state of the alloy, internal compression stresses are considered, which arise in the course of crystallization due to an increase in the specific volume of the bismuth phase in going from the liquid to the solid state. The results presented are first reported and are significant for gaining insight into the physical nature of the effect of superplasticity.
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Original Russian Text © V.F. Korshak, P.V. Mateychenko, Yu.A. Shapovalov, 2014, published in Fizika Metallov i Metallovedenie, 2014, Vol. 115, No. 12, pp. 1318–1327.
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Korshak, V.F., Mateychenko, P.V. & Shapovalov, Y.A. Peculiarities of the volume ratio of α and β phases in the superplastic eutectic Bi-43 wt % Sn Alloy. Phys. Metals Metallogr. 115, 1249–1258 (2014). https://doi.org/10.1134/S0031918X14120047
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DOI: https://doi.org/10.1134/S0031918X14120047