Study On The Process And Properties Of Disk Like C/C Composites Prepared By Directional Airflow TG-CVI Method

C/C composites have many excellent properties,such as high specific strength,high specific modulus,good tribological properties,low density,low expansion coefficient,good thermal conductivity and so on.It can be widely used in aerospace,weaponry,nuclear energy and other fields,and has a wide application p rospect.However,the traditional CVI technology for the preparation of C/C composite has many outstanding problems,such as long process cycle,high cost,and easy to shell the surface,which seriously restricts the development of C/C composites.The temperature gradient CVI(Temperature gradient chemical vapor infiltration,TG-CVI)process is a highly efficient densification process derived from the traditional CVI process,which can effectively suppress the surface of the crust and reduce the cost of preparation.On the basis of the TG-CVI process,this paper studies the densification rate,porosity and pore volume,the crystallization degree of pyrolysis carbon,the microstructure and mechanical properties of the disk like composites by the combination of directional airflow and temperature gradient,that is the directional air flow TG-CVI method.Found:(1)The average densification rate of C/C composites increases with the increase of deposition temperature.The average densification rate of C/C composi tes decreases with increasing chamber pressure.(2)When the pressure of the deposition chamber is 0KPa,10 KPa,and the deposition temperature is 980 ?,1080 ?,the density of C/C composite exhibits a decreasing trend along the direction of radius,and the change of porosity is the opposite.It is indicated that sequential deposition can be achieved at this temperature.When the deposition temperature is 1180 ?,the density and porosity of C/C composites fluctuate larger along the radius increasing direction,and there is no obvious change rule.(3)Under the same pressure in the deposition chamber,the opening volume of C/C composites decreases with the increase of deposition temperature,but the pore size is larger at 1180 C.With the same deposition tempera ture,the pore volume of C/C composite decreases gradually with the increase of the pressure in the deposition chamber.(4)With the same pressure in the deposition chamber,the diffraction peak intensity of C/C composites increases with the increase of de position temperature,the higher the crystallization degree of the pyrolytic carbon,the transition from amorphous to graphite crystal structure,indicating that the base carbon of the C/C composite prepared by the directional air flow TG-CVI method is easier to graphitization.(5)The microstructure of C/C composites at different deposition temperatures was observed.It was found that the pyrolytic carbon particles deposited at 980 ? were larger than those at 1080?,and the corresponding pyrolysis layers were thicker,and the smallest particles were deposited at 1180 ?,but there were obvious pores between the pyrolytic carbon and the fiber.(6)The pyrolytic carbon structure is different from the different deposition temperature.When the deposition temperat ure is 1080 ?,the deposited pyrolytic carbon is all rough layer structure(RL).At 980 ?,the structure of pyrolytic carbon is about 8mm thick layer pyrolysis carbon(RL)along the radius,and the rest part is smooth layer structure(SL).When the depositio n temperature is 1180?,the structure of pyrolytic carbon is anisotropic along the radius of radius.The same sex(ISO)transition to the rough layer(RL)structure.(7)The test of three point bending mechanical properties of C/C composites prepared at different deposition temperatures showed that the bending strength of the C/C composites prepared at the deposition temperature of 1080 ? were higher than the C/C composites prepared at the deposition temperature of 980 ? and 1180?.