United Nations has estimated that 130 million people would suffer from osteoarthritis worldwide by 2050. This disease would require patients to undergo a surgery known as Total Hip Replacement (THR) which has a failure rate of approximately 1 % with a lifespan of 20 years. The biomaterials used to manufacture this total hip artroplasty are mainly made of Zirconia-Toughened Alumina. In this work, Zirconia Toughened Alumina (ZTA) composites with 10 vol% Y-TZP content were doped with small amount (0.01 to 1 wt%) of graphene oxide (GO). The GO-doped ZTA composites were produced via two-stage sintering with T1 ranging between 1400°C and 1550°C, heating rate of 20°C/min, followed by T2 of 1350°C and 12 hours holding time. The sintered ZTA samples were then evaluated on its microstructure and mechanical properties such as bulk density, Vickers hardness, Young’s modulus and fracture toughness to investigate the effect of GO addition on ZTA samples prepared via two-stage sintering. The results showed that ZTA composites containing up 0.1 wt% GO is beneficial in improving the microstructural and mechanical properties of ZTA composites prepared via two-stage sintering. The sample recorded a high hardness of up to 18.5 GPa, Young’s modulus of 406 GPa and fracture toughness of 5.8 MPam1/2 when sintered at T1 of 1450℃.

The microstructure and mechanical properties of Zirconia Toughened Alumina (ZTA) produced via two-stage sintering at various sintering temperature of T1 and T2 in addition to effect of various holding time were investigated. T1 temperature was set between the range of 1400°C to 1500°C with a heating rate of 20°C/min. The samples were then sintered at T2 ranging from 1350°C to 1400°C followed by various holding time between 2 hours to 12 hours. The sintered samples’ microstructural properties, bulk density, hardness (Vickers hardness), elastic modulus (Young’s modulus) and fracture toughness (K1C) were then determined. Compared to standard holding time of two-stage sintering which is 12 hours, results show that ZTA produced via two-stage sintering with shorter holding time of 4 hours with T1 set at 1500°C and T2 of 1450°C are capable of achieving full densification. In addition, the same sample were also able to achieve hardness up to 19 GPa, Young’s modulus of 390 GPa and fracture toughness of 6.1 MPam1/2. The improvement in mechanical properties can be mainly attributed to the absent of surface diffusion at T2 above 1400°C and also presence of Y-TZP which contributed to lower grain growth due to the pinning effect.

Ceria stabilized zirconia with critical grain size is found to exhibit higher strength and higher resistance towards low temperature moisture degradation, The mechanical properties are greatly influenced by the size of the tetragonal grains. The effectiveness of doping with MnO2 (0.2 to wt %) in retarding degradation mechanical properties of ceria stabilized tetragonal zirconia (Ce-ZrO2) was evaluated by pressureless sintering within a temperature range from 1250°C-1550°C. Impact of manganese oxide to the mechanical properties and ageing resistance to the Ce-ZrO2 is truly beneficial. 0.4 wt% MnO2 at 1450°C revealed that, the tetragonal grain size was not affected by dopant level.With optimum dopant the 3 mol% ceria (3Ce-ZrO2) ceramic demonstarted the Vicker hardness of 11.8 GPa , fracture toughnessof 10.0 MPam1/2, flexural strength 920 MPa and Young modulus of 210 GPa. The 3Ce-ZrO2 doped with 0.4wt% MnO2 sintered 1450°C could be the best building block for biomedical applications.

Hydroxyapatite (HA)-Zirconia (ZrO2) composite with varying zirconia composition ranging from 1 to 10 wt% was investigated for biomedical applications in order to produce high compressive strength. Precipitation method was used to prepare both hydroxyapatite and zirconia powders. To find the ideal composition, mixture-containing 1, 3, 5 and 10 wt% ZrO2 powder was added. Each mixture was sintered for 4 hours at 750oC, 1050oC and 1250oC. Hardness and compressive strength test were used for evaluation. It was found that with 1 wt% of ZrO2 sintered at 1250oC showed the greatest structural strength as its volume fraction porosity is the lowest. The hardness and compressive strength of this sample were found to be 2.75 GPa and 72.0 MPa respectively. This can be useful for biomedical applications especially in promoting osteo-integration.

The effect of doping small amounts of Magnesium Oxide ranging between 0 to 1 vol% on Zirconia Toughened Alumina (ZTA) composites which is one of main biomaterial used for production of total hip arthroplasty were investigated. The samples were produced via conventional two-stage sintering with T1 varies between 1450°C and 1550°C with heating rate of 20°C/min. The samples were then rapid cooled to T2 set at 1400°C with holding time of 12 hours. The microstructural and mechanical properties of the two-stage sintered ZTA are then investigated to determine the feasibility of MgO addition. Combination of two-stage sintering at T1 above 1500 and also small amount of MgO up to 0.5 vol% were shown to have positive effect on ZTA which exhibited improvement on its grain size, mechanical properties such as Vickers hardness, Young’s modulus and fracture toughness compared to undoped ZTA composites. The sample with 0.5 vol% MgO addition sintered at T1 of 1500°C and T2 1400°C was able to achieve Vickers hardness of 19.6 GPa, Young’s modulus of 408 GPa and fracture toughness of 6.8 MPam1/2 without significant grain growth compared to undoped ZTA composites.