Preparation and microstructure evolution of directionally solidified Al₂O₃/YAG/YSZ ternary eutectic ceramics by a modified electron beam floating zone melting

We report the first growth of Al₂O₃/YAG/YSZ ternary eutectic in-situ composite ceramics by a modified electron beam floating zone melting technique with high temperature gradient. At optimized solidification conditions, high density (>99.5%) Al₂O₃/YAG/YSZ bulk eutectic ceramic rods with diameter of 2-4 mm and length up to 50 mm are successfully obtained. The grown composite ceramics present highly aligned irregular eutectic lamellae parallel to growth direction in stable growth zone at low rates, consisting of homogeneously distributed Al₂O ₃, YAG and YSZ phases in the submicron size. The coarse primary Al₂O₃ or YAG phases with strong faceted characteristic are preferred to form in the initial growth zone. The phase size and mean interphase spacing λ rapidly decrease with increasing solidification rate V where the relationship λ²V=constant is obeyed at V<90 mm/h. The cellular eutectic structures with regular lamellae in the intra-cellular region are produced at high growth rate.