Study On C/C Composites Based On SR-μ-CT And In-site Electron Irradiation

Molten salt reactor(MSR)is considered as one of the most promising systems in the fourth generation nuclear reactor systems due to its inherent safety,effective utilization of nuclear resources,neutron economy,fuel cycle,nuclear proliferation prevention,etc.In the long run,higher temperature is required to improve the efficiency of MSR and provide high temperature for hydrogen production.However,the alloys will lose strength at higher temperature.C/C composites are high temperature materials with excellent performance.They are the highest temperature resistant materials known at present,and have been recognized as candidate materials for the fourth generation nuclear power plants.C/C composites are compatible with molten salt,and their potential applications in molten salt reactor are control rod sleeves and materials used as substitute for metal alloys.However,the progress of C/C composites in nuclear applications is relatively slow,and the corresponding database is limited.A lot of researches and tests are needed to evaluate the stability of C/C composites in reactor environment.In order to further explore the microstructure,tensile fracture properties and radiation damage of C/C composites to promote the improvement of the corresponding databases,this paper explored the C/C composites by synchrotron radiation μ-CT technology and in-situ electron irradiation.In this paper,three-dimensional reconstruction of C/C-31 sample was performed by applying synchrotron radiation μ-CT technology,and the dynamic process of insitu tensile fracture of the sample was studied by adopting CT projected images.Through CT reconstruction,the porosity of C/C-31 sample is 20.82%,the connected porosity is 18.61%,the isolated porosity is 2.21%,and the connected porosity accounts for 89.39% of the total porosity.A large number of isolated pores that are similar to the fiber trend distribution can be seen from the isolated pore model,and a large number of throats with fiber trend distribution can be observed in the connected pore network model,which indicates that there are a large number of pores in the fibermatrix interface.The dynamic process of 2D-C/C composites C/C-31 sample was investigated by synchrotron radiation CT projection,which reveals that the loaddisplacement curve of 2D-C/C composites C/C-31 is divided into initial damage stage,linear elastic stage and strengthening stage,without obvious yield phenomenon.During the tensile process,owing to the fracture of part of the sample structure,the load-displacement curve rose and fell.The incomplete fracture of the sample and the long fibers pulled out indicated that there are weakened bonding interfaces in the C/C composites.In this present paper,C/C-31 samples were characterized by field emission transmission electron microscopy with a voltage of 200 k V and studied by in-situ electron irradiation.The C/C-31 samples have two different kinds of interfaces,namely mutant interfaces and progressive interfaces.An obvious transition layer could be detected in the progressive interface region that is filled with amorphous carbon and a large number of nano pores.Under electron irradiation,the progressive interface shrank due to the expansion of the nearby fiber and matrix,which offset part of the expansion of the fiber and matrix.Similar to the Mrozowski cracks,the progressive interface has some certain regulating functions.