Thermal and structural characterization of ultrasonicated Bi-Sn alloy in the eutectic composition

Irradiation of the molten eutectic Bi43Sn57 alloy with ultrasonic energy produced different bismuth–tin phases that were not reported in the equilibrium binary phase diagram. The X-ray powder diffraction data, refined using the Rietveld method, allowed the identification of these metastable phases and their crystal structure. The Bi2Sn and b0-Sn phases, with distorted b-Sn type structure, were obtained in the sample which was rapidly quenched after ultrasonication. On the other hand, the equiatomic phase BiSn was obtained in the quenched sample when the ultrasonication was continued during the rapid cooling below the eutectic point. The ultrasonicated samples were characterized by differential scanning calorimetry. The results suggested that the metastable phases, which were kinetically stable at RT, decomposed into equilibrium components during the heating treatment at 320 C, and that this conversion is an irreversible process. Observations by scanning electron microscopy and energy dispersive X-ray analysis complete the characterization of samples.