Fabrication And Mechanical Properties Of 3D-Al₂O₃/Al₂O₃ Composite Based On Water-based Slurry Infiltration

As one type of continuous ceramic fiber-reinforced ceramic matrix composites that emerged in the 1990s,Al₂O₃/Al₂O₃composites has developed into a major category of ceramic matrix composites alongside non-oxide ceramic matrix composites such as Si C/Si C and C/Si C composites.With the unique advantages of long-time oxidation resistance,high-temperature corrosion resistance and low cost,it has shown broad application prospects in the field of dual-use thermal structural materials such as aerospace engines and gas turbines.In this paper,we studied the fabrication of3D-Al₂O₃/Al₂O₃composites by vacuum impregnation with aqueous ceramic slurry process using stitched 3D fabric preforms as fiber reinforcement,the microscopic morphology,micro-macro mechanical properties of the composites were investigated.The work in this paper provides an appropriate exploration for the research and application of 3D alumina/alumina composites in thedomestic field.Firstly,the basic characteristics of Al₂O₃slurry and stitched preforms were studied.water-based Al₂O₃slurry was selected from sub-micron Al₂O₃powder with a particle size of about 150-250 nm.20 vol.%～45 vol.%solid content slurry has low viscosity,good wettability and high solid content,and shows good dispersion and stability.Three-dimensional stitched fiber preforms are used as reinforcement,and the raw material is Nextel610,which has high integrity and complex internal pore structure.The tensile breaking strengths of the fiber fabric before and after stitching were 36.46±10.65 Kg/cm and 23.32±7.62 Kg/cm,respectively.The stitching process decreased the strength of the fiber fabric by about 36%,indicating that would cause significant damage to the flat fabric.The effect of cycle number on 3D-Al₂O₃/Al₂O₃composites was investigated by selecting composites with 30 vol.%slurry with 3,6 and 9 impregnation cycles.The effect of the solid content of the impregnated slurry on the composite was investigated using slurries with different solid contents（20 vol.%,30 vol.%,40 vol.%and 45vol.%）The composites impregnated with 40 vol.%slurry for 6 cycles showed the best performance.The 3D-Al₂O₃/Al₂O₃composite prepared by the optimal process has a density of2.94±0.01 g/cm3,and the flexrual strength,interlaminar shear strength,and fracture toughness reach 332.4±18.51 MPa,25.22±0.32 MPa,and 11.60±0.79 MPa·m^0.5,respectively,compared to the performance of the composite was prepared by sol gel process of mechanicscomprehensive promotion,the transthickness tensile strength reaches 5.9±0.8 MPa,which is about 203%higher than the 2D-composites reported in the literature,showing excellent structural integrity,delamination and damage resistance,and the interlayer properties are significantly better than those of commercial2D-Al₂O₃/Al₂O₃composites.The thermal aging properties of 3D-Al₂O₃/Al₂O₃composites were investigated,and their long-time service performance in thermal examination service at 900oC was excellent.The retention rates of flexural strength,interlaminar shear strength and fracture toughness of the composites after thermal examination at 900oC for 300 h were82.47%,114.81%,and 76.38%,respectively.The interlaminar shear strength showed a slight increase after thermal examination due to the matrix secondary sintering.The retention rates at 1100oC were 67.52%,101.72%,and 54.91%,respectively,and the decrease in mechanical properties was mainly due to the secondary sintering of matrix,the decrease of mechanical properties of the fibers and excessive interfacial bonding strength.