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

The micro-pulling down method has been applied to grow Al₂O₃/ZrO₂ eutectic fibers and to investigate their microstructural properties as a function of solidification rate. Al₂O₃/ZrO₂ eutectic fibers 0.2 to approximately 2 mm in diameter and 500 mm in length have been grown with a pulling rate of 0.1 to approximately 15 mm/min. The eutectic microstructures changed as a function of pulling rate from rod shape to cellular shape containing some thin lamellae. Typical lamellar thickness decreased from about 380 to 110 nm as the pulling rate increased from 1 to 15 mm/min. The interlamellar spacing, λ fits the inverse-square-root dependence on the pulling rate, ν according to λ = 1×ν^-1/2, where λ has the dimension of μm and ν is in μ/s. Hardness value reached 13.1 GPa for fibers grown at a pulling rate of 15 mm/min and tensile strength of 900 MPa was achieved at a pulling rate of 10 mm/min. The hardness also increased as the interlamellar spacing decreased.