Microstructure of Y₂O₃ doped Al₂O₃/ZrO₂ eutectic fibers grown by the micro-pulling-down method

Al₂O₃/ZrO₂ eutectic crystal fibers containing various amounts of Y₂O₃ were grown by the micro-pulling-down method. The eutectic microstructures and some mechanical properties were investigated as a function of growth rate and doping amount of Y₂O₃. Doped with Y₂O₃, Al₂O₃/ZrO₂ eutectic fibers 0.3-2 mm in diameter and 500 mm in length have been grown over the range of pulling rate 0.1-15 mm/min. The dominant zirconia phase was changed from monoclinic to cubic as the doping amount of Y₂O₃ increased. The eutectic microstructures were oriented to a common direction which depended on the growth rate and doping amount of Y₂O₃. The uniform lamellar structure obtained at a lower growth rate below 1 mm/min transformed to an ellipsoidal cellular structure at a growth rate above 10 mm/min, and circular or triply facetted cellular patterns were observed at intermediate growth rates. The intercellular spacing increased as the doping amount of Y₂O₃ increased. The hardness value reached 20 GPa for 9 mol% Y₂O₃ doped fibers grown at a rate of 15 mm/min. The highest tensile strength reached 2000 MPa at room temperature and 560 MPa at 1500°C for the 3 mol% Y₂O₃ doped fibers grown at a rate of 15 mm/min.