Objective To evaluate mechanical properties of zirconia toughened composite alumina（ZTCA） ceramic used for dental application, characterize the effect of different zirconia contents on mechanical properties of ZTCA. Methods Dental alumina ceramic powder was prepared by sol- gel method, and four groups of ZTCA powders with different zirconia contents were prepared via surface- induced precipitation method. All five groups of powders were dry- pressed and then sintered to make standard specimens for mechanical tests. The flexural strength and fracture toughness of these specimens were evaluated, and the fractography was characterized by scanning electronic microsc pe （SEM）. Phases of ZTCA were also determined using X- ray diffraction（XRD）. Results It was found that the flexural strength of ZTCA ceramics increases with ZrO2 content up to 30%, and decreases thereafter. ZTCA specimens containing 30% ZrO2 show the highest flexural strength, and the corresponding fracture toughness was 1.85 MPa·m1/2. The XRD results of ZTCA ceramics showed the phase constituents of α- Al2O3, t - ZrO2 and a small amount of m- ZrO2. Conclusion The strengthening and toughening mechanisms of ZTCA depend on ZrO2 content. In the range of 15%～ 30% ZrO2, the stress- induced phase transformation toughening mechanism is dominant, while microcrack and deflection exist as the additional toughening mechanism when ZrO2 addition amount is above 30%.
