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.