Study On Properties Of ZrO₂-Al₂O₃ Laminated Ceramics

Laminated composite ceramics are attached great importance to because of their high toughness. Mechanical properties of laminated ceramics are not in relation close to flaw, and such ceramics become flaw-tolerance materials, therefore their toughness is improved more.In this paper, mechanical properties of ZrO2—Al2O3 laminated ceramics prepared by dry-pressing, pressureless-sintering were studied, which have three-layer structure and thickness of their surface and center layers are separately 0.3(0.1mm, 5.4(0.2mm. For knowing the relation of composition and properties, mechanical properties of different laminated ceramic which surface layer's composition is separately 20wt％,30wt％ and 40wt％ Al2O3+ ZrO2 were studied under 5wt％Al2O3+ ZrO2 center layer condition, and properties of monolayer ceramics of different composition were compared; the reason of properties' change and mechanism of strengthening and toughening were analyzed by microstructure research of laminated ceramics with the helps of lots of modern analyzing instruments. The results showed that hardness, strength and toughness of this kind of three layer composite ceramics were higher than those of monolayer ceramics under same conditions, especially toughness of laminated ceramics was higher 60％ than that of monolayer ceramics. When composition of surface layers is 30wt％Al2O3— ZrO2,the total mechanical properties of laminated ceramic were the best: (f＝786MPa,KIC＝18.37MPa·m1/2,HV＝14.99GPa. Strengthening and toughening mechanisms of laminated ceramics were from residual stress caused by different thermal-expansion of laminated structure, layer's interface, martensite phase transformation of zirconia and dispersion of alumina grains together, in which effect of laminated structure was the most. Laminated composite ceramics of residual compressive stress in surface layers and tensile stress in center layer were brought by above laminated structure and composition. Toughening effect of phase transformation of zirconia were increased and energy of main crack were decreased by compressive stress in the surface layers, and micro-cracks were formed to decentralize energy of main crack by tensile stress in the center layer.Currently two sorts of theories and formulae of thermal-shock-resistance of ceramics are too contradictive each other to be forecasted and explained exactly. In this paper, thermal-shock-resistance of the ZrO2—Al2O3 laminated and monolayer ceramicswere measured by residual strength method and crack extension method, difference of thermal-shock-resistant properties were compared, two sorts of traditional theories of thermal-shock-resistance were analyzed and validated according to test results, and these theories were revised based on above study. The results indicated that critical thermal-shock-resistant temperature (Tc of ZrO2—Al2O3 laminated ceramics was higher than that of monolayer ceramics under same test conditions, and (Tc of laminated ceramics which composition of surface layer was 30wt％Al2O3+ ZrO2 was the highest which was 550℃ measured by residual strength method and 500℃ by crack extension method. Formulae of critical thermal-shock-resistant temperature of ZrO2—Al2O3 laminated and monolayer ceramics were put forward firstly as follow based on practical test conditions and were validated based on test results. The results showed that rules of thermal-shock-resistance of ceramics were discovered by those formulae, and the forecast results of (Tc of ceramics were equal to test results. ((Tc of monolayer ceramics under quick cooling speed) ((Tc of monolayer ceramics under a constant cooling speed) ((Tc of laminated ceramics under quick cooling speed) ((Tc of laminated ceramics under a constant cooling speed)Besides, tribology properties of the ZrO2—Al2O3 laminated and monolayer ceramics were studied systemically under different lubrication medium, load, speed...