The impact of the composition and solidification rate on the microstructure and the crystallographic orientations of Al(2)O(3)–YAG–ZrO(2) eutectic solidified by the micro-pulling down technique

Directional solidification experiments have been carried out in eutectic and off eutectic composition in Al(2)O(3)–YAG–ZrO(2) system using the micro-pulling down (μ-PD) technique. The formation of different microstructures of stable phases, over a range of velocities studied, is discussed. During the solidification process, coupled growth microsctrucure can occur at off eutectic composition. Colonies and dendrites were analysed as a function of the composition and velocity. Increasing the solidification rate resulted in a smaller grain size and instability of the crystallization interface with respect to ZrO(2) segregation at the solidification front. Increasing ZrO(2) in the eutectic composition showed enhanced tendency for colony and dendrite formation. When the velocity was extended to the rapid solidification regime (>1.75 mm min(−1)), the geometrical pattern microstructure was found to grow and a change in the growth orientation of Al(2)O(3) corresponding to c-axis (0 0 01) was observed. Whatever the pulling rate, during the eutectic solidification the Al(2)O(3) and ZrO(2):Y phases' growth competition was observed, and 〈100〉 YAG orientation was grown along the pulling direction.