| C/C composite materials have low density,high strength,and can maintain excellent strength without degradation under high temperature.They are widely used in aerospace,military and civil fields.However,C/C composites also have their own shortcomings.For example,the bending strength and fracture toughness are still low at room temperature,and the high temperature is easy to oxidize in an aerobic environment,which limits its application in certain specific situations.In order to effectively solve this problem,this research combined with a self-made deposition device,using ordinary carbon felt as a preform,liquefied gas,and silicon powder as a deposition source.A type layered composite material was prepared by isothermal chemical vapor infiltration method(ICVI)and chemical gas solid phase reaction method(CVR).Using ICVI,CVR,and directional gas-thermal gradient chemical vapor permeation methods(TG-CVI)were used to prepare B-type and B1-type layered composite materials.The test methods for bending strength,fracture toughness,and oxidation resistance are mainly studied.The effects of different process routes on the densification behavior,microstructure and properties of A-type and B-type composite materials are mainly studied.The main results are as follows:(1)Through existing equipment and self-designed deposition equipment,changing the process conditions,it is possible to deposit pyrolytic carbon(PyC)layers and(SiC)layers with uniform thickness,denseness and good structure on the surface of carbon fibers.(2)Type A composites are compacted only through the ICVI process and CVR process,so the deposition rate is slow and crusts easily during the later densification,resulting in low density and unevenness.Type B composites use ICVI,CVR,and combined method of directional airflow TG-CVI solves the disadvantages of low density and non-uniformity of the A-type composite material,and improves the densification rate.(3)By characterizing the structure of the carbon fiber reinforced annual ring(PyC-SiC)matrix lamination composites,it is found that the layered(PyC-SiC)layer of the A-type composite material near the carbon fiber is uniform and dense,the layered structure is clear,and the layer structure is far from the carbon fiber is difficult to identify,and there is a small amount of residual Si in the matrix.Except for the layered structure of the B 1-type composite material,there is few residual Si in the matrix.(4)Through the analysis of the mechanical properties of the carbon fiber reinforced annual ring(PyC-SiC)matrix lamination composites,it was found that the interface bonding strength between the A-type composite carbon fiber-PyC matrix and the SiC layer and the PyC layer adjacent to its outer side was weak,while the interface bonding strength between the PyC layer and its adjacent SiC layer was high,and the cracks rapidly from the silicon carbide matrix extending to the interface,the stress at the crack tip is relaxed at the interface,which is manifested as composite interface peeling and fiber extraction,which plays a toughening effect,and the fracture mode is stepped fracture.The B-type composite material and the A-type composite material have similar interface bonding strength,the difference is that the outermost layer of the B-type composite carbon fiber has a thicker pyrolytic carbon layer prepared by the directional airflow TG-CVI method,and the fracture mode is pseudoplastic fracture.(5)By analyzing the microstructure and properties of A-type,B-type,and B1-type composites with different SiC contents,it is found that When the density of B-type composites except B(PyC-SiC)5 composites is slightly higher than that of C/C composites,the density of the other two composite materials is lower than that of the C/C composite material,the average fracture toughness of the B-type composite material is 115.3%higher than that of the C/C composite material.When the density and flexural strength are generally lower than those of B1 type composites,the average fracture toughness of B type composites is 101.6%higher than that of B1 type composites.(6)Compared with the oxidation resistance of carbon fiber reinforced annual ring(PyC-SiC)matrix lamination composites and C/C composites,the former has significantly improved oxidation resistance. |
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