Study On Structural Design And Mechanical Analysis Of Al₂O₃-ZrO₂ Composite Ceramics

Ceramic materials have the advantages of low density,high modulus of elasticity,high hardness and high temperature resistance,which become the primary research and object of the material industry in the future.Al₂O₃-ZrO₂ composite ceramics can achieve complementary performances on the basis of keeping the excellent characteristics of each component,so the mechanical properties are effectively improved.However,a large number of microcracks produced by phase transformation toughening of traditional Al₂O₃-ZrO₂ composite ceramics destroy the overall structure of the material,so it is difficult to achieve the common improvement of strength and toughness.At present,a reasonable structural design is one of the effective ways to improve this phenomenon.By studying the mechanical properties of different structural composite ceramics,we can provide theoretical basis for a reasonable structural design,so as to prepare composite structural ceramics with excellent mechanical properties.In this paper,two different composite structural ceramic are designed,namely,Al₂O₃-ZrO₂ composite ceramics with three-dimensional network and layered Al₂O₃-ZrO₂ composite ceramics.The influence of structural design on the mechanical properties of composite structural ceramics is analyzed systematically,especially the crack growth and deflection of Al₂O₃-ZrO₂ composite ceramics during the fracturing process and the influence of internal defects of Al₂O₃-ZrO₂ composite ceramics on the formation,deflection and mechanical properties of cracks.The three-dimensional network Al₂O₃-ZrO₂ composite ceramic is constructed by two steps: the three-dimensional network matrix and the secondary phase filler.The influences of different component proportion,pore size of spong,filling amount and sintering process on the porosity,relative density,mechanical properties and crack growth of the three-dimensional network Al₂O₃-ZrO₂ composite ceramic are explored in the experiment.The results show that Al₂O₃ is filled in85%ZrO₂+15%ZrO₂（ATZ）slurry,which is used as the raw material of three-dimensional network framework.The internal structure of Al₂O₃-ZrO₂ composite ceramics with three-dimensional network prepared by vacuum hot pressing sintering deforms greatly,forming three-dimensional Al₂O₃ irregular block mosaic structure.The interface has a high bonding strength,with low energy consumption during the process of crack deflection and dispersion.Although the average flexural strength is only 266.47 MPa with the relative density of 98.3%,the continuous three-dimensional ATZ phase still has a good deformation resistance.By associating the part with thewhole,the deformation resistance of the three-dimensional network Al₂O₃-ZrO₂ composite ceramics is significantly greater than that of the dispersion Al₂O₃-ZrO₂ composite ceramics,and the fracture toughness reaches the standard of the traditional dispersion Al₂O₃-ZrO₂ composite ceramics,which is 3.24MPa·m1/2.The above results show that the three-dimensional network structure design can effectively realize the reinforcement and toughening of materials,but it fails to meet the design requirements due to the limitation of process conditions.Al₂O₃ substrate with different thickness（120μm-180μm）are prepared by roller pressing,and ZrO₂ interface layer with thickness of 10μm is sprayed on the surface of Al₂O₃ matrix layer so as to obtain the layered Al₂O₃-ZrO₂ composite ceramics,which is synthesized by convebtional sintering methods.The mechanical properties of Al₂O₃-ZrO₂ composite ceramics with different thickness of Al₂O₃ matrix layer were studied.With the help of SEM,loading curve and industrial CT,the crack growth of layered Al₂O₃-ZrO₂ composite ceramics in the failure process was analyzed,and the relationship between crack growth and strengthening and toughening mechanism of materials was obtained.The results show that when the thickness of Al₂O₃ matrix layer is 120μm,the mechanical properties of the laminated composite Al₂O₃-ZrO₂ ceramics prepared by pressureless sintering at 1500℃ are excellent,i.e.,the flexural strength is 426.63 MPa,and the fracture toughness is 6.18MPa·m1/2.However,due to the high bonding strength between the layers,the cracks fail to deflect greatly at the interface between the layers during the fracture process,and the cross section is neat and flat,showing the characteristic of brittle fracture.Graphite is introduced between Al₂O₃ matrix layer and ZrO₂ interface layer by dip coating method.During the sintering process,graphite decomposition can effectively weaken the bonding strength between Al₂O₃-ZrO₂ composite ceramic layers.The results show that when the solid content of graphite slurry is 0.5wt%,the average relative density of layered Al₂O₃-ZrO₂ composite ceramics is 94.3%,and the average flexural strength is 343.78 MPa as well as,the average fracture toughness is7.11MPa·m1/2.In the fracture process,the cracks deflect and disperse between layers,which increases the propagation path of the cracks and energy consumption,showing the characteristic of ducture.It is concluded that the flexural strength of the laminated Al₂O₃-ZrO₂ composite ceramics is related to the thickness ratio and the residual stress at the interface,and the deflection and dispersion of the cracks are related to the interlaminar bonding strength,while the fracture toughness is concermed with the total energy wasted in the fracture process and elastic modulus.