Preparation And Study Of Multidimensional Aluminosilicate Fiber Reinforced Mullite Matrix Composite

In view of the urgent demand for high-temperature structural materials in the aerospace field,it was particularly urgent to conduct in-depth research on the preparation and properties of oxide fiber reinforced mullite matrix composites,improving the damage tolerance and thermal shock resistance of mullite ceramic and fabricating high-performance oxide fiber reinforced mullite matrix composites.In this study,mullite?Mu?and aluminosilicate fiber?AF?were used as raw materials to fabricate multidimensional aluminosilicate fiber reinforced mullite matrix composite?AF/Mu composite?via hot pressing and pressureless sintering process,to improve the fracture toughness of mullite ceramic.The influences of powder particle size on the sintering behavior and mechanical properties of mullite ceramic were studied,and the low-temperature densification of mullite ceramic was realized.Based on the structural design of the composite and investigation of the high-temperature evolution behavior of organization and property of AF,the high-performance multidimensional AF/Mu composites meeting different requirements were successfully prepared.SiC was fabricated on the AF surface to inhibit fiber structure damage and property degradation during the preparation process,using polycarbosilane?PCS?as precursor.Finally,the thermal shock resistance of the AF/Mu composites were investigated.The densification behavior,microstructure and properties of mullite ceramic fabricated via different particle sizes were investigated to choose the optimal particle size of mullite powder and realize low-temperature sintering,which could reduce the fiber damage during the preparation process of AF/Mu composite.Dense mullite ceramic with a high flexural strength 245.7 MPa and fracture toughness 2.5 MPa?m^1/2 could be prepared after sintering at 1500°C for 1h,using mullite micron powder.And dense mullite ceramic with a higher flexural strength 251.2 MPa and fracture toughness 2.8 MPa?m^1/2 could be obtained at 1300°C,using the nano powder and greatly reduced the sintering temperature.According to the different requirements of the high temperature components such as the aircraft wing and rudder,flat component and engine combustor lining,three kinds of AF/Mu composites?unidirectional,bidirectional and three directional?were designed,and the stiffness of the composites were predicted by finite element simulation.The simulation results showed that the elastic modulus and shear modulus of unidirectional AF/Mu composite in the axial direction of fiber were higher than those of other directions,which could meet the unidirectional bearing demand.The elastic modulus and shear modulus of bidirectional AF/Mu composite in the plane of fiber cloth along 0o/90odirections were higher than other directions,satisfying the demands of bidirectional bearing.The elastic modulus and shear modulus of three directional AF/Mu composite were similar in three directions,and the microstructure and property of three directional AF/Mu composite were isotropic in three directions,which could meet the three directional bearing demand.The effects of heat treatment temperature on the microstructure and property of aluminosilicate fibers were studied.When the heat treatment temperature was below 1300oC,the microstructure and property of the fiber were stable and the tensile strength retention rate was above 85%.As the heat treatment temperature rised above 1400oC,the grain of AF fiber grew rapidly and the tensile strength decreased seriously.Based on above results,it was proposed that the sintering temperature of AF/Mu composite should be lower than 1400oC.The preparation technology of AF/Mu composite was investigated.The effects of sintering temperature and aluminosilicate fiber content on the microstructure and properties of unidirectional and bidirectional AF/Mu composite were investigated.The unidirectional and bidirectional AF/Mu composites with 30 vol%fiber content sintered at 1300oC for 1 h displayed a high density and mechanical properties.The unidirectional AF/Mu composite exhibited a high density 91.5%,flexural strength 208.8 MPa and fracture toughness 4.85 MPa?m^1/2.The correctness of the simulation results about unidirectional AF/Mu composite were verified by comparing the mechanical properties of the composite in different directions.The bidirectional AF/Mu composite exhibited a high density 90.3%,flexural strength 134.6 MPa and fracture toughness 4.13 MPa?m^1/2.The mechanical properties of bidirectional AF/Mu composite were little different in the plane of fiber cloth along 0o/90odirections.The density of bidirectional AF/Mu composite prepared by optimized PIP-LBL increased from 90.3%to 91.8%,and flexural strength and fracture toughness increased to 163.2 MPa and 4.55 MPa?m^1/2,respectively.The three directional AF/Mu composite with a high density could be obtained by precursor infiltration and pyrolysis?PIP?method.The density of the three directional AF/Mu composite increased with the increase of PIP cycle,and the composite prepared by PIP for 6 cycles displayed a high density 77.5%,flexural strength 130.1 MPa and fracture toughness 4.91 MPa?m^1/2.The three directional AF/Mu composite showed isotropic in X,Y and Z directions.To reduce the fiber damage during the preparation process,adjust the interfacial bonding force between the fiber and the matrix and improve the fracture toughness of AF/Mu composite,0.01 mol/L PCS solution was used to prepare SiC coating on the surface of AF by PIP method.The fracture toughness of unidirectional AF/Mu composite with 30 vol%fiber content increased from 4.87 MPa?m^1/2 to 5.33 MPa?m^1/2;the fracture toughness of bidirectional AF/Mu composite with 20 vol%fiber content increased from3.67 MPa?m^1/2 to 4.22 MPa?m^1/2;and the fracture toughness of three directional AF/Mu composite increased from 4.93 MPa?m^1/2 to 5.14 MPa?m^1/2.Three kinds of AF/Mu composites exhibited damage-tolerant behaviour during the failure process.The thermal shock resistance of three kinds of AF/Mu composites were evaluated through cyclic heat treatment?from 1300oC to RT?for several cycles.The residual flexural strength of AF/Mu composites decreased gradually with the increase of cycle number.After 10 cycles and 15 cycles heat treatment,the flexural strength retention rate of AF/Mu composites was above 85%and 70%,respectively.The critical thermal shock temperature differences of AF/Mu composites were obtained by water quenching method.The critical thermal shock temperature differences of unidirectional,bidirectional and three directional AF/Mu composite were 617.7oC,746.2oC and 843.9oC,respectively.The three kinds of AF/Mu composites exhibited excellent thermal shock resistance.