Study On Preparation And Properties Of ZTA Ceramics Using Blast Furnace Slag As Sintering Aids

The excellent properties such as high hardness,high toughness,corrosion resistance,wear-resistance and high cost-effective have made Zirconia Toughened Alumina（ZTA）ceramics famous in engineering ceramics materials.But the high processing cost caused because of its high sintering temperature has restricted the wild range application of ZTA ceramics.One practical way to solve this issue is introducing sintering aids into ZTA ceramics.Among the regular sintering aids,usage of solid phase sintering aids has difficulties in the reduce of the sintering temperature and make the densification of ZTA ceramics ineffective.The usage of liquid phase sintering aids introduces glass phase into ZTA ceramics which is a potential damage factor for its mechanical properties.In this paper,we use blast furnace slag（BFS）as sintering aids,which is a simple,eco-friendly,utility way to reduce the sintering temperature and improve mechanical properties of ZTA ceramics.To fully investigate the physical and mechanical properties of the ZTA ceramics with FBS as sintering aid,firstly the chemical composition,physical characteristic,thermal characteristic and microstructure of BFS were studied by X-ray Fluorescence Spectrometry（XRF）,X-ray diffraction（XRD）,differential scanning calorimetry（DSC）,laser particle size analyzer and Scanning Electron Microscope（SEM）.The results show that the main constitution of BFS is glass phase composition with CaO,MgO,Al₂O₃,SiO₂,the crystal phase is gehlenite and the crystal temperature is 850⁹50℃.Gehlenite is the main ingredient of sintering aid and the grain size is about 1μm.And then,the effects of the ratio of ZrO₂ and Al₂O₃,the content of traditional solid-phase additive（TiO₂）,liquid compound additive（SiO₂/CaO）and the blast furnace slag on ZTA performance were studied respectively.The results show that when the sample has 30wt% ZrO₂ and sintered for 2 hours at 1600℃,its bending strength is 225 MPa and fracture toughness is 2.63MPa·m1/2.The SEM analysis showed that the material was difficult to be densified at this sintering temperature without the sintering aids.When 2wt% TiO₂ was added as solid phase activator and sintered at 1600 ℃for 2hours,ZTA ceramics sample’s bending strength reaches 330 MPa and relative density is only 90%,which implied that the solid phase activator is not the best choice.When 5wt% composite activator was added into ZTA ceramics and sintered at 1600 for 2 hours,its relative density reaches 94%,but the bending ℃strength drops to 300 MPa because of the glass phase introduced by liquid phase activator.The sample that added 5wt% BFS was sintered at 1550 ℃for 2 hours and insulated 1 hour at 950℃,its relative density reaches 97%,bending strength is 375 MPa and fracture toughness is 3.97MPa·m1/2.XRD and SEM show the existence of gehlenite at the grain boundary,which improves the mechanical properties of ZTA ceramics.Finally,the effects of particle size and molding pressure on the properties of ZTA ceramics were studied.The results show that high-energy ball milling can significantly reduce the particle size of Al₂O₃ powder.The powder particle size can reach 0.43μm after ball milling 40 min and the powder would come to reunion if the time is longer.When the formula is invariant,the molding pressure has a certain impaction on the ZTA density.The larger forming pressure will lead to stress concentration in body,which is harmful to sintered density.When particle size of Al₂O₃ is 0.43μm,forming pressure is 120 MPa,the samples were sintered at 1550℃ for 2 hours,the bulk density of the ZTA ceramics is 4.36g/cm3,its bending strength is 430 MPa,fracture toughness is 4.81MPa·m1/2,and hardness is 10.20 GPa,the sintered activity of ZTA ceramics can be improved by using the raw material powder with large specific surface area.