Mechanical Properties of Alumina-Mullite Whisker Composites

Composite alumina ceramics with a mullite whisker content of up to 30vol% were fabricated by hot-pressing at 1400 to 1600°C under 30MPa for 30min. The bending strength, hardness, elastic modulus and fracture toughness of the hot-pressed bodies were investigated. Considerably dense alumina-mullite whisker composite ceramics were obtained by sintering at 1600°C with a whisker content of up to 30vol%. The composite with a whisker content of 10vol% and sintered at 1600°C exhibited the highest room temperature bending strength of around 750MPa. This value is still lower than the maximum strength of alumina ceramic which is about 850MPa. However, the composites exhibited greater high temperature strength and hardness than alumina. The elastic modulus decreased with an increase in whisker content. No improvement was ohserved in the fracture toughaness of the alumina by the addition of mullite whiskers, as very little crack deflection by the whiskers and pull-out of the whiskers occurred in these composites.