Effect of Melt Cooling Rate on Microstructure of Sn - Bi and Sn - Pb Eutectic Alloys

The results of microstructure investigation of eutectic alloys Sn Bi and Sn Pb, obtained at cooling rates of the melt 10 -2 K/s, 1 K/s and 10 5 K/s are represented. Various cooling rates are achieved by graphite mold casting and by ultra fast quenching from the melt. Microstructure and grain structure are investigated by scanning electron microscopy and the electron backscatter diffraction technique. It has found that the melt cooling rate increasing at rapid quenching leads to microcrystalline structure and to a change of the solidification mechanism. The reasons for the transition from lamellar to the microcrystalline structure are discussed.