| C/C composites is a new type of material,which is composed of carbon fiber and carbon matrix.C/C composites has the advantages of high temperature strength,corrosion resistance,low coefficient of thermal expansion,ablation resistance,good biocompatibility and so on.It is widely used in aerospace,military,nuclear energy,biomedical and other fields.Up to now,many methods have been developed to prepare C/C composites,such as chemical vapor infiltration(CVI),liquid impregnation method,isothermal chemical vapor infiltration(ICVI),thermal gradient chemical vapor infiltration(TG-CVI),forced flow chemical vapor infiltration(FCVI),pulse chemical vapor infiltration,etc.CVI is the most commonly used method to prepare high performance C/C composites.In terms of actual large-scale production,the ICVI method is mainly used because of its simplicity.However,due to its long preparation cycle,the price of C/C composites remains high,which limits the application of C/C composites in many fields.In order to solve the problem of long preparation period of C/C composites,the C/C composites are prepared in a short time by using intermittent heating directional pulsed airflow TG-CVI process,and the effects of different process parameters on the microstructure and properties of C/C composites are studied.The main research results are as follows:(1)The preparation process of C/C composites in this project combines the advantages of intermittent heating,TG-CVI,directional flow CVI and pulse CVI,which significantly reduces the preparation cycle of C/C composites and improves the densification rate,The densification rate is 3 times of that of traditional ICVI and 1.4times of that of directional pulse flow TG-CVI.(2)In the same deposition time,the densification rate and the apparent density of C/C composites increase obviously with the increase of intermittent heating temperature range.When the temperature difference is 150?,the densification rate is35.2×10-3g·cm-3·h-1.When the sample is completely densified,the apparent density can reach 1.82 g·cm-3 and the bending strength is 119.64 MPa.(3)The densification rate of C/C composites(35.7×10-3g·cm-3·h-1)can be further increased by controlling the outside temperature unchanged at 850?on the basis of the intermittent heating temperature difference of 100?,and the composites has high density(1.785 g·cm-3)and bending strength(111.67 MPa).(4)The microstructure of C/C composites prepared by the directional pulse flow TG-CVI method with intermittent heating is smooth lamellar structure,and the effect of the temperature difference of intermittent heating on the graphitization degree and apparent microcrystalline size of C/C composites is not obvious.(5)The change of intermittent heating temperature difference has a significant effect on the mechanical properties of C/C composites.When the temperature difference of intermittent heating is 150?,the bending strength of C/C composites is up to 119.64 MPa,and the fracture mode is brittle fracture.When the temperature difference of intermittent heating is 0?,the bending strength of C/C composites decreases and it appears as pseudoplastic fracture. |
PDF Full Text Request