Optical and mechanical properties of amorphous bulk and eutectic ceramics in the HfO2–Al2O3–Y2O3 system

Bulk glasses containing HfO2 nano-crystallites of 20–50 nm were prepared by hot-pressing of HfO2–Al2O3–Y2O3 glass microspheres at 915 °C for 10 min. By annealing at temperatures below 1200 °C, the bulk glasses were converted into transparent glass-ceramics with HfO2 nano-crystallites of 100–200 nm, which showed the maximum transmittance of ∼70% in the infrared region. An increase of annealing temperature (>1300 °C) resulted in opaque YAG/HfO2/Al2O3 eutectic ceramics. The eutectic ceramics contained fine Al2O3 crystallites and showed a high hardness of 19.8 GPa. The fracture toughness of the eutectic ceramics increased with increasing annealing temperature, and reached the maximum of 4.0 MPa m1/2.