Laser zone remelting of Al₂O₃/Er₃Al ₅O₁₂ bulk oxide in situ composite thermal emission ceramics: Influence of rapid solidification

A modified laser zone remelting was performed to prepare novel crack-free bulk Al₂O₃/Er₃Al₅O₁₂(EAG) oxide in situ composite thermal emission ceramics, aiming to investigate the influence of rapid solidification on the ceramic melting process and microstructure characteristics. The grown Al₂O₃/EAG ceramic showed a near full density value of >99% and smooth surface, and it was sensitive to rapid solidification. The density increased with decreasing laser scanning rate, which led to a decrease of smoothness in surface finishing. At low scanning rate of 20 μm/s, fine faceted-grown EAG phases of 1-2 μm were homogeneously embedded in the Al₂O₃ matrix, presenting typical irregular patterned lamellar microstructures. The eutectic spacing was rapidly refined with the increase of laser scanning rate due to high temperature gradient and rapid solidification rate. The minimal spacing was reduced below 300 nm. Furthermore, at high scanning rate the faceting growth tendency was decreased and particular dendrite eutectic structures were produced, whose formation mechanisms were discussed.