Mechanical Properties,Phase Composition And Microstructure Of Al₂O₃-ZrO₂ Composite Ceramics By Three-Roller Mixing Method

The homogeneous dispersion of the raw materials was the key process to prepare 3Y-ZrO₂/Al₂O₃ ceramics.The three-roller mixing was suitable for dispersing the high viscosity slurries containing the fine ceramic powders,which benefited reducing the amount of dispersion medium and drying time.The Al₂O₃-ZrO₂ composite ceramics were prepared by the three-roller milling,dry pressing and sintering.The phase composition,microstructure,and mechanical properties were analyzed using XRD,SEM,EDS,high and low-temperature double-column testing machine,and so on.The effects of alumina particle size and additives on the mechanical properties and microstructure of Al₂O₃-ZrO₂ composite ceramics were investigated with the change of 3Y-ZrO₂ volume fraction.The results show that the distribution of Al₂O₃ and ZrO₂ in Al₂O₃-ZrO₂ ceramics is closely related to the zirconia phase transition and the mechanical properties of the composite ceramics.For the sample with the coarse Al₂O₃ of 3 ?m addition,when 3Y-ZrO₂ is dispersed in the Al₂O₃ matrix,the tensile stress existing in the ZrO₂ grains,the generation of the m phase and the low density make the bending strength of Al₂O₃-ZrO₂ ceramics do not increase compared with the alumina ceramics.When the 3Y-ZrO₂ content increases to become the continuous phase,the compressive stress appears in the ZrO₂ grains and the m-ZrO₂ content decreases make the bending strength of the composite ceramic sintered at 1500-1600 °C significantly increase.Therefore,the proper amount of Al₂O₃ addition can improve the bending strength and toughness of ZrO₂ ceramics.The maximum bending strength and fracture toughness are increased by 17% and 52% compared with those of the single ZrO₂ ceramics respectively.For the sample with the fine alumina powder of 0.3 ?m addition,the m phase is not detected,and the t-phase diffraction peak is significantly shifted.Compared with the coarse Al₂O₃,the temperature at which this shift occurs is lower,related to the solid solution between alumina and zirconia.At the same time,the alumina micro-aggregation area can be found,with the size range of 5-10 ?m.As the volume fraction of Al₂O₃ increases,the bending strengths of composite ceramics prepared from both coarse and fine alumina powders decrease.However,the decrease from fine alumina powders is more gradual.Due to the large difference in sintering temperature between alumina and zirconia,the effects of different additives on the microstructure and properties of Al₂O₃-ZrO₂ composite ceramics were studied.When adding 1 wt% Ba Ti O3 to the ZTA?containing 30 vol% ZrO₂?,the grain sizes of Al₂O₃ and ZrO₂ both increase and the crack propagation was inhibited,which is associated with the bridging and piezoelectric effect of Ba Ti O3 in ZTA matrix.Mg O can increase the density of ZTA ceramics with the intergranular-transgranular mixed fracture mode.The intergranular pores are few and the grain bonding is strong.Therefore,ZTA composite ceramics are most resistant to crack propagation and produce the bending strength of 492 MPa.When CaO-SiO₂ is added,the sintering performance of the two phases of alumina and zirconia can be improved at lower sintering temperatures.The composite ceramics display the obvious transgranular fracture and the bending strength has also been improved.For the addition of micron alumina powder,compared with the traditional ball mill mixing,the three-roll mixing method benefits achieving denser ATZ ceramics.However,the ball milling method can get a higher density of ZTA ceramics.This is associated with the strong interaction between alumina and zirconia in the three-roller mixing.For the samples with submicron alumina addition,the micro-aggregates of alumina with the size of 5-10?m both exist in the samples prepared under the two mixing methods,which indicates that the dispersion effect of the two mixing methods is similar.