Research On Formation Mechanism And Properties Of SiC_p/SiC Ceramic Matrix Composites Based On SLS And PIP

With the rapidly development of aerospace engineering,thermal insulation material has become the key to the success of the flight safety of hypersonic vehicle.The advanced materials,which must bear extreme elevated temperature condition,are indeed needed.Thus,silicon carbide(SiC)ceramic matrix composite with excellent properties has been a good candidate for the high temperature structural materials of hypersonic aircraft.While there were still several problems on SiC ceramic,such as high hardness,brittleness and hardly sintering characteristic.To solve the problems of traditional process for preparation and sintering:high economic cost,long preparation cycle and difficult to form complex structures,a novel process of SiC_P/SiC ceramic matrix composite materials was proposed via combined selective laser sintering(SLS)with precursor infiltration pyrolysis(PIP).In addition,the shaping accuracy,densification extent and properties of SiC_P/SiC ceramic matrix composite materials were investigated.The effects of SiC powders with different average particle sizes on SiC ceramic green body prepared by SLS were investigated,and the orthogonal experiment was opted to analysis the effect of SLS process parameters on the forming quality of ceramic parts.The results shown that with the increased of average particle size,the porosity of SiC green body decreased,the density and the bending strength increased gradually.The densification posttreatment of SiC green body formed by SLS was selected by combined debinding with PIP process,and the effects of debinding and PIP process on the physical,mechanical properties and micro-structure of SiC ceramic matrix composites were systematically studied,on the basic of which,the effects of printing direction and resin content on the performance of composites were analyzed.The results shown that after eight PIP cycles,the weight gain of the sample was less than 1%,the open porosity was 5.05%,the total porosity was 24.32%and the density was 2.45g/cm~3.The green body of SiC ceramic was fabricated by horizontal and vertical direction.The bending strength of samples with vertical printing direction was higher than horizontal printing direction for 12.05%.With the increase of resin content,the porosity of the specimen first increased and then decreased,and the density experienced a reversal trend.The sample with 5%resin content had the best performance.SiC_P/SiC ceramic matrix composites were prepared by optimized SLS and PIP technology.Effect of high temperature and oxidation on the properties of SiC_P/SiC ceramic matrix composite materials,and the oxidation and high temperature mechanism was analyzed.The results shown that with the increase of oxidation temperature,the mass loss of the specimens increased first and then decreased,and the bending strength increased gradually.When the temperature was 1600℃,the bending strength of the specimens reached to 85.90 MPa,which was 57%of bending strength at room temperature.SiC_P/SiC ceramic matrix composite sandwich structures were designed and prepared though SLS and PIP technology.The effect of micro-structure and ambient temperature on the mechanical properties were studied.It was found that the compressive strength and modulus of SiC_P/SiC ceramic matrix composites were increased with the increased of strut’s inclination angle,but decreased with the increased of temperature.When the temperature increased from 1400℃to1800℃,the compressive strength and modulus of the specimens decreased by34.30%and 44.82%,respectively.The compression curves of the SiC_P/SiC ceramic matrix composite sandwich structures showed the obvious nonlinearity at 1800℃.Chopped carbon fiber reinforced SiC_P/SiC ceramic matrix composite materials were prepared by the SLS and PIP technology.The effects of carbon fiber with different size and content on the microstructure and mechanical properties of SiC_P/SiC ceramic composites were studied.It indicated that with the increased of fiber content,the bending strength of samples experienced the gradually decreased trend,and the fracture toughness of the sample first increased and then decreased.Under the same carbon fiber content,the SiC_P/SiC ceramic matrix composites with longer carbon fibers had better properties.Compared with the SiC_P/SiC ceramic matrix composites without carbon fiber,the fracture toughness of samples with 8%200 mesh and 300 mesh carbon fiber increased by 33.33%and 20.39%,respectively.