Mechanical anisotropy in the zirconia toughened alumina

The two kinds of the hydrothermally crystallised zirconia powders were used to toughen alumina matrix. The one composed of isometric crystallites of tetragonal symmetry, the other one of elongated monoclinic particles. In the sintered ZTA material either isometric or elongated particles form tetragonal disk shaped inclusions. Zirconia inclusions originating from the elongated particles tend to arrange crystallographically on the uniaxial compaction. This resulted in the material showing different ultrasonic wave velocity, Young modulus, crack lengths and fracture toughness along directions perpendicular and parallel to the compaction force. An explanation of this phenomenon is suggested. Zirconia inclusions originating from the powder composed of isometric crystallites lead to the material of isotropic mechanical properties. (C) 1999 Kluwer Academic Publishers.