Equiaxed colony growth in the small undercooled Y2O3-doped Al2O3–ZrO2 eutectic ceramic melt.

Al 2 O 3 /ZrO 2 eutectic bulks (20 mm in diameter) with different Y 2 O 3 contents (0–4.5 mol %) were grown using the conventional casting method. Variations in the microstructural characteristics and colony tip growth behavior caused by Y 2 O 3 addition in the central equiaxed grain zone were investigated. As Y 2 O 3 was added to the Al 2 O 3 /ZrO 2 binary eutectic, except for a decrease in colony size, the colony tip radius reduced drastically and then increased slightly. Colony growth behavior can be well predicted using the Lipton–Glicksman–Kurz (LGK) model. A critical Y 2 O 3 content (0.5–1.1 mol%) exists below which the eutectic colony growth is accelerated owing to the Y 2 O 3 addition, but slowed down otherwise. However, the average interphase spacing and ZrO 2 rod diameter inside the colonies varied with Y 2 O 3 content, converse to the growth rate. [ABSTRACT FROM AUTHOR]