Microstructure, mechanical and tribological properties of microwave sintered calcia-doped zirconia for biomedical applications

Among the available ceramics materials for load bearing bio-implant applications, Y-TZP is superior (fracture toughness: ∼10 MPa m0.5) for its better mechanical properties. However, due to concerns related to property degradation of Y-TZP during long exposure in body fluid, the current work is taken up to study the feasibility of developing stabilised zirconia ceramics in CaO–ZrO2 system, using microwave sintering (MW) technique. The present paper reports the processing, microstructure and tribological properties of microwave sintered Ca-doped ZrO2 based ceramics. An important experimental result is that MW sintering to greater than 90% theoretical density can be achieved in Ca-PSZ (8 mol% CaO) and Ca-FSZ (16 mol% CaO) ceramics by sintering at 1585 °C for 1 h. The sintered materials exhibit Vickers hardness ∼8–10 GPa, which would allow them to be used as load bearing implants. Also, a modest fracture toughness (∼6 MPa m0.5) was measured for Ca-PSZ, which is better than commercial grade alumina. So, it is possible to synthesize a material which has better combination of hardness and toughness than other commercially available bioceramics like alumina, hydroxyapatite, TCP, etc. Considering its specific application for THR (total hip replacement), tribological experiments using fretting wear tester serve to provide data about the wear behaviour of the proposed materials. The fretting experiments were conducted against a bearing-steel counterbody in air as well as in a SBF (simulated body fluid) environment. The wear behaviour of the investigated tribocouple is dominated by the formation of Fe oxide/chloride layer at the worn surface.