Microstructure And Mechanical Properties Of Al₂O₃/ZrO₂ Composite Ceramics

Tetragonal polycrystalline zirconia（TZP）is a widely used ceramic material with good mechanical properties and special crystal structure,which is often used in manufacturing engineering structural components and tools,medical devices,digital products,etc.,especially with the advent of the era of 5G,the higher requirements for signal reception of intelligent terminal products-mobile phones,have given the opportunity to develop ceramic mobile phone backplanes,and at present,the material used for the back of ceramic mobile phone is Y-TZP.However,TZP still has some shortcomings such as brittleness and poor stability,so it is necessary to further improve its comprehensive performance from the perspective of raw material components and preparation processes to meet its further applications and development.The fracture toughness of TZP can be improved to a great extent by introducing a second phase into the ceramic matrix,such as nanoparticles,whiskers（or fibers）,etc.Al₂O₃particles,Al₂O₃ whiskers and Si C whiskers are commonly used in the existing research as the reinforcing phase.However,it is difficult to disperse nanoparticles or whiskers evenly in the matrix,moreover,the preparation process of the whiskers is complex and agglomeration is easy to occur,which affects the mechanical properties of the composite.In this work,this thesis is devoted to studying the effect and mechanism of different Al₂O₃ content on the density,microstructure and mechanical properties of zirconia with different stabilizer contents in a well-dispersed state,and make use of in-situ growth of long rod-shaped grains instead of adding whiskers in order to improve Al₂O₃/Zr O₂ composite ceramics so that it can obtain excellent comprehensive mechanical properties.In this study,Zr O₂ and Al₂O₃ powders with different stabilizer contents（2.3 mol%and 3 mol%Y₂O₃）were first used as raw materials.Zr O₂ based ceramic composites were prepared by mechanical mixing and sintering in air.XRD,SEM,EDS and other methods were used to analyze the microstructure then the influence of Al₂O₃ second phase particles on the microstructure and mechanical properties of Zr O₂ ceramics and the mechanism of strengthening and toughening were studied.The results showed that the optimal sintering temperature of 2.3Y series samples was 1500℃,and the optimal sintering temperature of 3Y series and 2.3/3Y series were 1550℃.A proper amount of Al₂O₃ could promote the sintering and densification of composite materials.The m-Zr O₂ content of the polished surface of the sintered sample decreased with the increase of Al₂O₃ content,and Al₂O₃ could inhibit the growth of Zr O₂ grains,so that the Zr O₂ grain size decreased.The mechanical properties of the samples were influenced by the sintering temperature and the Al₂O₃ content.The sample 2.3Y5A sintered at 1550℃had the best performance which the bending strength and fracture toughness were 924±34MPa and 6.2±0.4 MPa·m^1/2,respectively.The fracture mode of the sample was a mixed fracture mode with mainly intergranular fracture and partly transgranular fracture.The main toughening mechanisms were stress-induced phase transformation toughening and crack deflection toughening.On this basis,La₂O₃ was added to the composite material,and La₂O₃ reacted with Al₂O₃ at high temperature to generate long rod-shaped La Al₁₁O₁₈.In order to explore the effect of La₂O₃on the phase composition,microstructure and mechanical properties of the composite material,0.4 wt.%,0.8 wt.%and 1.2 wt.%La₂O₃ were added with 2.3Y5A as the reference.La₂O₃ has the effect of refining the zirconia grain size,the grain size decreased from 670 nm to 535 nm.Although the flexural strength of the composite ceramic samples decreased slightly,the fracture toughness improved.The fracture toughness of 2.3Y5A0.4La sample,2.3Y5A0.8La sample,and 2.3Y5A0.8La sample were 6.1±0.2 MPa·m^1/2,6.5±0.1 MPa·m^1/2 and 6.3±0.2 MPa·m^1/2,respectively.The variation trend of fracture toughness was different from that of the fracture phase variable,the long rod-shaped La Al₁₁O₁₈ grains had effect on the deflection,bridging and pull out of the crack so the fracture toughness increased.The effect of the proportion of phase components in Al₂O₃/Zr O₂ composite ceramics with different Al₂O₃ contents under the optimum La₂O₃ addition on the mechanical properties of composites were further investigated.The fracture toughness increased with the increase of Al₂O₃ and La Al₁₁O₁₈content,and compared with the samples without La₂O₃,the fracture toughness had been improved,and the increase rate had been increased gradually,2.3Y20A0.3La obtained a maximum fracture toughness of 7.1±0.2 MPa·m^1/2 increasing by29%.When the amount of Al₂O₃ addition was more than 10 wt.%,the crack deflection,bridging and grain pull-out toughening mechanisms caused by long rod-shaped grains played a dominant role in improving the fracture toughness.