Radiation Resistance Of SiC With Hetero–interfaces

The high–temperature mechanical properties,oxidation and corrosion resistance,radiation resistance of SiC are excellent,and its thermal neutron absorption cross section and induced radioactivity are relatively low,which can replace Zr alloy as accident–tolerant cladding material.For this reason,it is also considered to be one of the candidate materials for the Gen.IV fission reactors.At present,some achievements have been obtained based on the irradiation effect of single crystal and micro crystal SiC.The results show that single crystal and micro crystal SiC are amorphized at low temperature and the accompanying swelling is large,the amorphous swelling will lead to the degradation of material properties,especially the thermal conductivity,which limits the application of SiC in the nuclear field significantly.In this thesis,the influence of Hetero–interface structure on the radiation resistance of SiC was studied.The main research contents and results are as follows:（1）The radiation damage evolution behavior of Si/SiC hetero–interface materials using RMI（Reactive Melt Infiltration）method was studied.The swelling behavior,defect evolution（including generation,aggregation and reconstruction）of He⁺irradiated Si–rich SiC were observed using in–situ HIM（Helium Ion Microscopy）.It showed that there is no obvious“interface driven shrink”behavior of Si/SiC hetero–interface materials under He⁺irradiation,and the irradiation induced swelling increases with the increase of SiC grain size,when the size of SiC reaches 750 nm,the swelling increases exponentially;the irradiation induced defects first appear in the Si phase.Compared with the ones used on pure SiC and C/SiC,the dose of He ion irradiation to produce defects in Si/SiC is lower;the defects in Si/SiC is repairable,however,due to the defect generation rate is much higher than the repair rate under room temperature irradiation,the defects accumulate continuously,therefore the radiation resistance is poor.（2）The radiation resistance of carbon nanotube modified polycarbosilane（PCS）derived SiCs was studied.The pyrolysis temperature and the dosage of multi–wall carbon nanotubes（MWNTs）for PCS derived SiCs were optimized.Promoting defect recombination is the key to design super radiation tolerance materials.It showed that PCS–derived SiC and MWCNTs were used to construct C/SiC hetero–interface.By elevating the pyrolysis temperature,the SiC grains in PCS derived ceramic gradually grow up,and the carbon clusters transform into nano graphite（NG）,at 1400°C,the bulk density was the highest and the open porosity was the lowest.The aspect ratio of carbon nanotube is large,and thus it can form rich internal interface with the matrix,which can act as a place for recombination of radiation defects and therefore improve the radiation resistance of materials.Sample with carbon tube content of 3 wt.%,the MWCNTs were uniformly dispersed and had high density and excellent mechanical properties.2 Me V Au²⁺room temperature irradiations show that the addition of CNTs can improve the radiation resistance of PCS transformed nano SiC ceramics.Compared with the critical amorphous dose of single crystal SiC under the same irradiation condition,the sample with 3 wt.%MWCNTs content has better amorphous resistance ability（>0.25 dpa）.