Fabrication and Characterization of Al_2O_3/GdAlO_3 Eutectic Ceramic in situ Composite by Laser Zone Remelting

摘要

In situ composite of Al_2O_3/GdAlO_3(GAP) ceramic eutectic prepared by directional solidification is an interesting candidate for the manufacture of turbine blades because of its excellent mechanical properties. In the present paper, directionally solidified Al_2O_3/GAP eutectic in situ composite ceramics are manufactured by the laser zone remelting technique to investigate the rapid solidification process. The laser power and scanning rate necessary to carry out the ceramic melt growth is determined. The characteristic microstructure is investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The as-solidified Al_2O_3/GAP eutectic presents an elongated colony structure consisting of only α-Al_2O_3 and GAP phases with an oriented growth array. The eutectic spacing is strongly dependent on the laser scanning rate, rapidly decreasing to the sub-micron range for the samples grown at the highest rate. Besides, the formation condition and evolution of the particular microstructure of the composite during rapid solidification are discussed.