Preparation And Microstructure Of Fiber Reinforced Ti Matrix Composites

Hypersonic aircraft is the aircraft with flying high speed,which put forward more and more stringent requirements for structural materials,especially for skin structural materials.It is very important to develop skin structural materials with long life,corrosion resistance,high strength,high temperature resistance and lightweight for the development of hypersonic aircraft.The temperature resistance range and mechanical properties of SiCf/Ti composite are consistent with the service environment requirements of hypersonic vehicles.Its high specific strength and high specific modulus,good electrical and thermal conductivity,low coefficient of thermal expansion,high temperature resistance,wear resistance,high dimensional stability and other characteristics are the ideal choice of skin materials for hypersonic vehicles.In this paper,in China,the SiCf/Ti composite skin structure is taken as the application object,aiming to the needs of the development of hypersonic vehicles.The advantages of high temperature resistance and lightweight of titanium matrix composites are brought and the key technologies of fiber preparation and arrangement,interface control are focused.The evolution law of microstructure and the fracture failure mechanism of composite materials are explored,and the development and assessment of skin structure parts are completed,to promote the application of titanium matrix composite skin in hypersonic aircraft.The vertical CVD equipment with DC heating was built,and the design and manufacture of reactor,flange,gas supply system and heating system were completed.The Continuous SiC fiber was prepared by DC heating tungsten wire and multi-stage chemical vapor deposition.The best CVD process for preparing SiC fiber was obtained:H2(1.2 L/min)+CH3SiCl3(1.8 L/min)+Ar(1.0 L/min),in which CH3SiCl3 of 1.8 L/min was heated in a water bath at 40?,deposition temperature at 1300? and wire speed at 1.2 m/min.The diameter of SiC fiber is about 100?m.The tensile strength is more than 2000 MPa.The layout optimization and structure design of SiC fiber were studied by numerical simulation and experiment.The results show that the fiber volume fraction of titanium matrix composites with fiber spacing of 0.15 mm,0.2 mm and 0.25 mm is 32.4%,26.4%and 22.3%,respectively.The optimal fiber cloth spacing is 0.2 mm,which ensures high fiber volume fraction and avoids fiber lap.Compared with the square fiber arrangement model,the maximum radial compressive stress and circumferential tensile stress of the hexagonal fiber arrangement model are 108 MPa and 196 MPa,respectively.The hexagonal fiber arrangement model is better than the square fiber arrangement model.The preparation process of SiC fiber reinforced titanium matrix composites and analyzing the microstructure were investigated,the results show that the best process to remove PMMA adhesive is to raise the temperature to 400? with 3?/min and keep the temperature for 2 h.The best hot pressing process of SiC fiber reinforced titanium matrix composite is to keep the temperature at 880?and pressure at 40MPa for 2h.The results show that the SiC fiber reinforced titanium matrix composites have uniform fiber distribution,compact matrix structure and no micro defects such as holes and no welding.The interface behavior of SiC fiber reinforced titanium matrix composites was studied and thermodynamic dynamics analysis.The results show that the thickness of reaction layer is 0.5 at 840?,880? and 920?,respectively 0.5 ?m,1 ?m and 3 ?m.The reaction product of the fiber/Ti interface is TiC,the reaction rate of the interface is mainly controlled by the diffusion of C element.The composition of the interface reaction layer is SiC fiber/TiC/Ti matrix.The mechanical properties of SiC fiber reinforced titanium matrix composites were studied by means of room temperature tensile test,high temperature tensile test and fatigue test.The results show that SiCf/TB8 composites have excellent room temperature properties,high temperature properties and fatigue properties.The tensile strength at room temperature reaches 1500 MPa,the elastic modulus reaches 180 GPa,the tensile strength at 600?reaches 960 MPa,At the stress of 350 MPa,the number of cycles exceeds 1 x 107?The feasibility of the process route for the preparation of SiC reinforced titanium matrix composite skin structure is analyzed,process optimization and performance evaluation.The results show that the multi-layer structure of SiC reinforced titanium matrix composite is prepared by superplastic forming/diffusion connection technology,with the size of 120 mm×120 mm.The inner defects of SiCf/TB8 composite skin structure were characterized by ultrasonic nondestructive testing,and the feasibility of the process route was verified.The temperature difference of the skin is 100? under 700? thermal balance condition.It is proved that the structure of SiC reinforced titanium matrix composite skin has excellent thermal insulation performance and can meet the service requirements of hypersonic vehicle.