This research prepared composite ceramics between Al₂O₃ (6 mol% MgO); AM and ZrO₂ (4 mol% Y₂O₃); ZY with 50:50 ratio. The samples were sintered under two-step method with four different sintering temperature conditions. It was found that the densities and shrinkage values tended to slightly increase with the lower T₂ temperature for the length of holding times. XRD patterns showed a combination main phase between Al₂O₃ and ZrO₂. Rietveld refinement was used to calculate the percentage of phase composition. All of samples were reveled weight percentage of main composition as m-ZrO₂ c-ZrO₂ t-ZrO₂ and r-Al₂O₃ in different sintering conditions. Rietveld analysis of data revealed a high ratio of t-ZrO₂, c-ZrO₂ phases from the two stage sintering condition with T₁ temperature at 1600 °C for 60 min and T₂ temperature at 1450 °C for 10 h, and T₁ temperature at 1600 °C for 60 min and T₂ temperature at 1500 °C for 5 h. SEM micrographs revealed grain shape and size of grains. The average grain size of AM as 0.863-1.156 µm and ZY was 0.622-0.902 µm:, the size of grain tended to increase with high T₂ temperature for the length of holding time. EDX identified large grains corresponding to the Al₂O₃ phase and small round oval shapes corresponding with the ZrO₂ phase. The mechanical properties were measured by Vicker and Knoop hardness calculate the fracture toughness value. It was found that the optimum mechanical properties were obtained from composite ceramic with sintering conditions temperatures of T₁ temperature at 1600 °C for 60 min and T₂ temperature at 1450 °C for 10 h; this resulted in the highest of fracture toughness value of about 0.32 GPa∙m^1/2. The optimal two stage sintering conditions were obtained from a high ratio of t-ZrO₂ and c-ZrO₂ phases with fine grain size.

Keywords: ZrO₂, Al₂O₃, Mechanical properties, Two stage sintering, Rietveld method.