Mechanical and thermal properties of Al₂O₃-ZrO₂ composite ceramics at cryogenic temperatures

The alumina with zirconia of 15% (in mass)(ZTA) composite ceramics were prepared by a pressureless sintering process. The mechanical properties of ZTA composite ceramics in a temperature range of 293 to 77 K and the thermal properties in a temperature range of 300 to 5 K were investigated. The phase transformation volume and zone width of ZrO₂ in the fracture surface of ZTA composite ceramics at various temperatures were also analyzed. The results reveal that the bending strength, fracture toughness and Vickers hardness of ZTA composite ceramics increase linearly with decreasing temperature, and they are increased by 10.8%, 19.7% and 10.4% at 77 K, respectively, compared to those at 293 K. The thermal conductivity of ZTA composite ceramics at 97 K firstly increased to a maximum value, and then decreased with decreasing the temperature. The improvement of mechanical properties of ZTA composite ceramics at cryogenic temperatures was due to the enhanced stress-induced tetragonal to monoclinic phase transformation toughening. The thermal conductivity of ZTA composite ceramics at cryogenic temperatures was rather low, which could meet the demand of cryogenic engineering. The ZTA composite ceramics could be one of the most promising materials in cryogenic structural applications.