Study On The Composition Structure And Performance Of ZrO₂-Y₂O₃ Multi-phase Ceramics

Zirconia-based materials have a series of unique physical,chemical,electrical and mechanical properties including high strength,high hardness,high toughness,good abrasion resistance,high melting point,chemically inert,low thermal conductivity,high coefficient of thermal expansion and biocompatibility Sex is good,etc^[1].Therefore,it is determined that it is a very ideal material for high temperature refractory materials,abrasive materials and high temperature thermal insulation material^[2-4].In addition,zirconia also has the characteristics of martensitic transformation^[5],which is used to improve the toughness of ceramic materials.However,with the increase and decrease of sintering temperature,the mutual transformation of monoclinic phase and tetragonal phase occurs in zirconia with a certain amount of volume effect.Therefore,in the preparation of zirconia-based products,the stability of zirconia crystal phase has become the focus of research.Compared with other physicochemical methods such as adding alkaline earth metal oxides,the addition of rare earth metal oxide Y₂O₃ is a better and less expensive method for stabilizing tetragonal zirconia to room temperature.At present,there are many researches on the addition of Y₂O₃ as zirconia phase change stabilizer at home and abroad,but most of them are not systematic,and the research scope is often limited to5-12wt.%Y₂O₃ content.However,little has been reported on the structure and properties of ZrO₂-Y₂O₃ composite with Y₂O₃ addition exceeding 12wt.%.And few studies have investigated the relationship between the composition,microstructure and properties of ZrO₂-Y₂O₃ multiphase materials powders.This subject systematically studied the effect of Y₂O₃ on the phase composition,unit cell structure and solid solution forms of Y-ZrO₂,while the Y₂O₃ content within 3-21wt.%,and through its microstructure study to explore the impact of microstructure on sintering performance,mechanical properties and thermal properties of Y-ZrO₂,in order to lay the theoretical foundation to further expand the scope of application of ZrO₂-Y₂O₃ composite material.The phase composition of the YSZ sample was analyzed by X-ray diffraction.As the content of Y₂O₃ increased from 3wt.%to 21wt.%,the phase of YSZ sample changed from monoclinic phase to tetragonal phase to cubic phase,and the relationship between Y₂O₃ content and the mass fraction of monoclinic phase,tetragonal phase and cubic phase was obtained.Besides,through the optimization and calculation of the unit cell parameters,it is found that the increase of the tetragonal phase content can reduce the Y³⁺ion solid solubility which stabilizes the metastable tetragonal phase to room temperature,that is to say,when increasing the Y₂O₃ content,the Y³⁺ions are more inclined to turn more monoclinic phase to tetragonal phase instead of increasing the solid solubility of the Y³⁺ions in the existing tetragonal phase.In addition,assuming that the solution of Y³⁺ions into the ZrO₂ lattice is the substitutional solution and the interstitial solution,respectively,and the theoretical density is calculated.By comparing the substitutional solution theoretical density and the interstitial solution theoretical density with true density,it is concluded that the tetragonal YSZ and cubic phase YSZ are substitutional solid solution.The best sintering temperature of YSZ samples is 1650°C.With the increase of Y₂O₃ content,the bulk density of YSZ first increases and then decreases,the apparent porosity first decreases and then increases,reaching the maximum value at 7YSZ while the sintering is the most compact.When the Y₂O₃ content is 3-7 wt.%,the grain size of YSZ sample is small and fine,and the sintering of the sample is promoted with the increase of Y₂O₃ content.When Y₂O₃ content is 9-21 wt.%,Vacancies generated by solid solution migrate to grain boundaries to form atmospheric pores.The tetragonal phase will occur phase transformation induced by stress to improve the mechanical properties of the sample,5YSZ sample is of the largest flexural strength,7YSZ is of maximum compressive strength.The thermal conductivity of 3YSZ sample with monoclinic phase as the main crystalline phase was significantly higher than that of9YSZ sample with tetragonal phase as the main crystalline phase,and the thermal conductivity of two-phase 5YSZ sample and 7YSZ sample were much lower than single phase samples due to more complex phase composition.In addition,the thermal expansion coefficient of YSZ samples present a law:tetragonal phase>cubic phase>monoclinic,and the presence of tetragonal phase in the complex phase YSZ sample composed of monoclinic and tetragonal phases can reduce the monoclinic phase transition temperature,making the phase change easier to happen.