Research On Preparation Technology Of ZrO₂/Al₂O₃ Nanocomposite Ceramics

Zirconia ceramic has more excellent physical and mechanical properties than the general ceramics. It can be used to improve the strength and fracture toughness of materials as it owns crystal transition characteristic in the sintering process, but its mechanical properties is poor in high temperature and the price is high. However, alumina ceramic has superior mechanical properties at room temperature, stable chemical properties and low price. In order to reduce the cost and improve performance, alumina is doped into the zirconia ceramic. In this research, two factors were discussed, including the compositions of specimens and the process of sintering. This article chose three different kinds of zirconia, 3Y-ZrO₂, 5Y-ZrO₂ and 8Y-ZrO₂ then designed five different components. The compound powder was mixed, stirred, ball-milled, sieved, shaped and sintered from 1560℃ to 1640℃. Using scanning electron microscopy and X-ray diffraction to analysis the microstructure and phase composition.3Y-ZrO₂/Al₂O₃ composite ceramic shows evident effect to moderate shrinkage, more stable density and weight loss ratio when the temperature is from 1600℃ to 1640℃. Especially at 1640℃, the content of tetragonal and cubic phase zirconia is much higher than other temperature, but many pores are formed in the surface. It is not obvious to reinforce and toughen the samples. While at 1600℃, the samples are denser and have much superior combination properties even their phase transition rate is not high. 5Y-ZrO₂/Al₂O₃ composite ceramic shows evident effect to moderate shrinkage and more stable density and weight loss ratio when the temperature is from 1580℃ to 1620℃. When the samples are sintering at 1600℃, the tetragonal and cubic phase zirconia content is relatively high, and grain size is uniform, surface porosity is lower, the sample is compact, with high hardness and strength to achieve the best overall performance. 8Y-ZrO₂/Al₂O₃ composite ceramic shows poor overall performance in this experimental set-temperature regions, between 1560℃ and1640℃. As the sintering temperature increases, the number of pore gradually increased, the shrinkage, density and hardness values decreased, the content of monoclinic phase zirconia gradually increased. Therefore the proper temperature for 8Y-ZrO₂/Al₂O₃ is 1560℃ or below 1560℃. The value of fracture toughness, 6.935MPa×m1/2 is highest, with the amount of yttria is 5mol%. When the amount of yttria are 3mol% and 8mol% in the samples, their disappointing fracture toughness are 4.675MPa×m1/2 and 5.045MPa×m1/2, respectively. As the second phase component, alumina impacts the performance of the samples. When alumina content is high, the density is low and the porosity is high. But when the content of alumina is about 35%, The stability of tetragonal and cubic phase zirconia is promoted. It was found that M54-3 with moderate sintering temperature and higher content of alumina has good compactness, excellent hardness and fracture toughness, its hardness is up to 1287.85 HV and the overall performance is best. The patterns of crack propagation include inter-phase boundary fracture, inter-crystalline boundary fracture, trans-crystalline fracture and hiding fracture.