The Investigation Of Dispersion, Sintering And Mechanical Properties For The Composites Of Nanoscale M-ZrO₂ And Al₂O₃

The toughening effect of ZrO2 comes from its t-m transformation, which is related to grain size of ZrO2. In this paper, we used nanoscale ZrO2 grain to toughen submicron A^Os and specially investigated the relationship between the volume fraction of nanoscale m-ZrOi and the toughening effect. At the same time, we discussed the influence of sintering behavior and zirconia's morphology to the toughening effect.We carefully studied the influence of dispersant content and pH value of suspension on dispersive property of suspension by measuring the rheology curve of Al2O3 and m-ZrO2 suspension whose content of solid is 15vol.%, in which PMAA-NH4 is dispersant. The results denoted that PMAA-NH4 has distinct effect to Al2O3 and nanoscale m-ZrO2, but the despersive conditions are different. So we selected the despersive condition that the content of PMAA-NFU was 0.3wt.% and pH value was 9 for simultaneous stability of two kinds of grain. The electrosteric stabilization of PMAA-NH4 plays a important role in dispersion.The experiment results denoted that ultrasonic surge has no positive effect to the stability of nanoscale m-ZrO2, which perhaps is related to the insuited technology. The experiment results denoted that the best dispersive condition of 3Y-TZP was that pH value is 9. This result has distinct difference to nanoscale m-ZrO2. The main reason is that the absorb ability has weaken result from the reducing of specific surface.We investigated the sintering behavior of Al2O3 and the Al2O3 composites which content 10vol.% nanoscale m-ZrO2. We found that the samples initial sintering temprature has increased from 1033 to 1216, the sample's ultimate shrink ratios are 18.2% and 16.0% at 1600℃ from the heating up curves. These phenomena indicated that nanoscale m-ZrO2 hinders the sintering property of composites. From the logarithm isothermal curve, we found that the slope of ln(AL/Ln)-Int curve of Al2O3 is approximately 0.4 in the forepart of sintering. This result was according with the theory of Coble, but the respective slope has changed to 1/3 after adding ZrO2. The samples sintering behavior was similar with ZrO2.After adding nanoscale m-ZrO2, there was 50.3vol.% t-ZrO2 reserved at the roomtemperature in the sample contained 2vol.% nanoscale m-ZrO2. This reason was the constraining effect of Al2O3 matrix to ZrO2. The content of t-ZrO2 was only 31.2vol% when the volume fraction of ZrO2 is 10vol.%. This indicated that the content of reserved t-ZrO2 has dropped with the increasing of the content of ZrO2 in the green compacts.We have measured the fracture toughness, fracture strength and hardness of samples which nanoscale m-ZrO2 contents are different. The results indicated that the sample s fracture toughness was the maximum of 5.84MPa-ml/2 when the content of ZrO2 was 4vol.%; the fracture strength was almost equal of 395.0MPa and 391.0MPa when the contents of nanoscale m-ZrOa are 2vol.% and 4vol.%. The hardness of sample s has dropped distinctly after adding nanoscale m-ZrO2, which is 12.76GPa when the content of m-ZrO2 is 4vol.%. The hardness of samples has dropped no more when the content of m-ZrO2 has exceeded 4vol.% and even increaseed again a little.In this paper, the result of experiment has been discussed carefully useing transformation toughening and microcrack toughening mechanism.