Directional solidification and characterization of Al₂O ₃/Er₃Al₅O₁₂ eutectic in situ composite by laser zone remelting

Directionally solidified (DS) oxide eutectic in situ composites are attracting increasing attention because of their unique properties and potential applications to high temperature structural materials, optical or electronic devices. Among the alumina-based eutectic composites, DS Al₂O ₃/Er₃Al₅O₁₂(EAG) eutectic is considered to be promising candidate for use as selective emitter at high temperature. In this work, eutectic in situ composites of Al₂O ₃/EAG rods having smooth surface and full density are successfully prepared by directional solidification using the laser zone remelting method, aiming to investigate the growth characteristic of this novel binary eutectic under high temperature gradient. The microstructure is investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The Al₂O₃/EAG eutectic presents a very fine irregular network structure consisting of only α-Al₂O ₃ and Er₃Al₅O₁₂ phases without grain boundaries and amorphous phases between interfaces. The eutectic interphase spacing is strongly dependent on the laser scanning rate, rapidly decreasing at the sub-micron levels for the samples grown at high rate. Furthermore, the microstructural formation and evolution of the composite are analyzed and discussed.