Solid-liquid interface and growth rate range of Al₂O₃-based eutectic in situ composites grown by laser floating zone melting

Directionally solidified Al₂O₃/Er₃Al₅O₁₂(EAG) eutectic in situ composites are prepared by laser floating zone melting (LFZM) to investigate the solid-liquid interface characteristic and growth rate range under non-equilibrium solidification conditions. The solid-liquid (S-L) interface is in situ obtained by rapidly quenching, and its microstructure morphology and primary phase based on different eutectic compositions are analyzed. In stable growth zone, the composite presents typically "Chinese script" (CS) irregular eutectic structure consisting of interpenetrated Al₂O₃ and EAG phases, but in quenched region the regular eutectic lamellae and CS structure are coexisted. Primary Al₂O₃ phase in hypoeutectic composition is found both in S-L interface front and quenched region. Different from the stable growth zone, in quenched region as the solidification rate increases, the eutectic lamellae spacing does not show obvious decrease. The minimum eutectic lamellae spacing is refined to about 200 nm when the solidification rate is increased up to 100 μm/s. On the basis, according to the Jackson-Hunt (J-H) model, the maximum solidification rate in quenched region is calculated to be smaller than 1.26 × 10³ μm/s, and the undercooling degree is 4.15 K.