The effect of La2O3 on the microstructure and room temperature mechanical properties of t-ZrO2

Structural and mechanical properties of La₂O₃ added (up to 5 wt%) t-ZrO₂ compacts were examined with the aim of optimizing hardness and fracture toughness for room temperature applications. Structural examinations were performed using an X-ray diffractometer and a scanning electron microscope. Mechanical properties of the compacts were determined as modulus of elasticity, hardness and fracture toughness by conducting Vickers indentation tests under test loads of 0.5, 1 and 10 kg. Addition of 0.5 wt% La₂O₃ deteriorated the room temperature stability of t-ZrO₂ by forming m-ZrO₂ and coarse polygonal grains in the matrix. Higher concentrations (2 and 5 wt% La₂O₃) caused precipitation of La₂Zr₂O₇ at the grain boundaries, which also accompanied by a reduction in hardness. Fracture toughness increased with increasing La₂O₃ content of the compact. Finally, an optimum combination between hardness and fracture toughness was obtained for the 0.5 wt% La₂O₃ containing compact.