Study On The Process And Microstructure Properties Of C/C Composites Prepared By Rotating Temperature Intermittent Liquid Phase Vaporization TG-CVI Method

C/C composites are widely used in aerospace,medicine,military and other science and technology frontier fields because of their high specific strength,high specific modulus and good high temperature performance.The main methods of preparing C/C composites are ICVI and liquid impregnation carbonization.Among them,the ICVI method is easy to"shell on the surface",which needs repeated machining in a material preparation cycle,with long preparation cycle and high cost;the liquid phase impregnation carbonization technology needs to use high pressure to press the resin into the preform,which requires high equipment requirements,and the deposited carbon is"glass carbon",with low graphitization degree and poor material performance.In order to solve the problems of long densification cycle and high cost of preparation of C/C composites,cyclohexane was used as carbon source precursor,ordinary annular carbon felt was used as preform,and self-made deposition device was used to rapidly prepare C/C composites by rotating uniform temperature intermittent liquid phase vaporization TG-CVI method.The effects of processing conditions on the densification behavior,microstructure and properties of the composites were studied by means of PLM,SEM,XRD and three-point bending(1)The effects of different deposition temperatures on densification behavior,microstructure,physical and mechanical properties of C/C composites were studied under the same intermittent heating temperature difference.The results show that at the same intermittent heating temperature difference,with the increase of deposition temperature,the average density and densification rate of the material increase significantly,the radial and circumferential density uniformity of the material is good,the pyrolytic carbon structure changes from smooth layer to rough layer,and the bending strength of the material increases.(2)The effects of different intermittent heating temperature differences on densification behavior,microstructure,physical properties and mechanical properties of C/C composites were studied at the same deposition temperature.The results show that at the same deposition temperature,with the increase of intermittent heating temperature difference,the average density and densification rate of the material decrease gradually,the pyrolytic carbon structure changes from the coexistence of smooth layer and rough layer to smooth layer,and the bending strength of the material decreases.(3)The optimal process parameters for the preparation of C/C composites by rotating uniform temperature intermittent liquid phase vaporization TG-CVI method are as follows:deposition temperature of 1000?,intermittent heating temperature difference of 50?and deposition time of 40 h.under this process,the ordinary ring preform with initial density of 0.14 g·cm^-3 can be densified to 1.721 g·cm^-3,and the densification rate is about 0.0395 g·cm^-3·h^-1.The pyrolytic carbon structure is a mixture of smooth layer and rough layer,and the bending strength is about 73.80 MPa.The fracture mode of the material is brittle fracture.(4)The main reasons for the rapid and uniform preparation of C/C composites by rotating uniform temperature intermittent liquid phase vaporization TG-CVI are the large temperature difference in the radial direction of the annular preform,the uniform heating in the circumferential direction,and the use of high concentration of liquid carbon precursor.