Study Of Corundum-based Wear Resistant Composite Ceramics

With the rapid development of science technology and industrial production,the service life of wear-resistant parts in various machinery and equipment has become an important factor affecting the production efficiency of equipment.The research and development of high wear-resistant materials is of great importance on the industry and social economy.Based on the mechanical properties to be improved and the high cost of production and other deficiencies of alumina ceramic wear-resistant materials,the research of corundum-based wear-resistant ceramic materials was carried out.The corundum-based composite ceramics were prepared by pressureless sintering using corundum and silicon carbide as the starting materials.Partially stabilized zirconia（PSZ）was added to improve the densitiy and strength of the composite ceramics,and rare earth oxides were doped to further improve the sintering and mechanical properties.The basic properties（water absorption,bulk density,bending strength,etc）,wear resistance,phase composition and microstructure of the samples were analyzed by XRD,SEM and FE-SEM.The relationship between formulation,processing technology,microstructure and properties and factors affecting the density and mechanical properties of the samples were studied.The mechanism of improving the wear resistance of the samples was discussed.The results are as follows:（1）Using Al₂O₃ and SiC as starting materials,adding MgO and TiO₂ as sintering aids,the Al₂O₃/SiC composite ceramic was designed and prepared.The effects of SiC content and preparation on the structure and properties of the composite ceramics were studied.The hardness and the wear rate of the sample B5（containing SiC 20wt.%）sintered at 1640°C were 16.22 GPa and 1.83×10-5 mm³/（N·m）,respectively,and the thermal conductivity was 25.41 W/（m·K）,all were higher than those of pure alumina ceramics.The main crystal phases of sample B5 were corundum and silicon carbide.themicrostructurewasdense,andthefracturemodewas intergranular-transgranular fracture.SiC as the second phase particles,suppressed the growth of Al₂O₃ grains,and promoted grain refinement,the grain boundary strengthening and crack deflection and bridge was the main reasons of the improvement of the composite ceramic density and mechanical properties.（2）In order to improve the density and strength of the composite ceramics,the Al₂O₃/SiC/ZrO₂ composite ceramics was prepared by introducing PSZ（3 mol%Y₂O₃）on the basis of optimal formulation B5.The effect of ZrO₂ content on the structure and properties of the samples was studied,and the mechanism of strengthening the composite ceramics was discussed.The results showed that the water absorption of samples was below 0.5%when sintered at 1580°C,and the bending strength and hardness of sample C4（applied ZrO₂ 20 wt.%）sintered at 1640°C were 221.43 MPa and 17.33 GPa,density and bending strength has been greatly improved.ZrO₂particles filled in the gaps between corundum and SiC particles,refining the matrix grain together with SiC particles,thus improving the density of the composite ceramics.ZrO₂ particles formed"intergranular"and"intragranular"structures in the composite ceramics to promote the transgranular fracture of the composite ceramics,which is favorable for the deflection and branching of the crack,improving the strength of the samples,the phase transformation toughening and micro-crack toughening of ZrO₂ also played an important role in enhancing the mechanical properties of the samples.（3）In order to further improve the sintering properties and mechanical properties of the composite ceramics,two kinds of rare earth oxides,La₂O₃ and Y₂O₃,were doped on the basis of the optimal formula C4.The effects of rare earth oxides on the structure and properties of the composite ceramics were studied.The results showed that the sintering temperature of Al₂O₃/SiC/ZrO₂ composite ceramics was reduced to1540°C by adding La₂O₃,and the bending strength and hardness of sample E3（applied La₂O₃ 3 wt.%）sinteried at 1540°C were 183 MPa and 18.46 GPa.The addition of La₂O₃ promoted the liquid phase during the sintering process,and suppressed the grain growth,which could improve the density of the samples.The grain refinement and grain boundary strengthening were beneficial to the improvement of the strength.The bending strength and hardness of sample F1（applied Y₂O₃ 2 wt.%）sintered at 1640°C were 250.14 MPa and 20.64 GPa,respectively.Y₂O₃ could effectively hinder the instability of zirconia crystal transition,so that ZrO₂ were stabilized to tetragonal phase,thereby improving the mechanical properties of composite ceramics.