Study On Ion Irradiation Effects Of Single Crystal 4H-SiC And SiC_f/SiC Composites

SiC and SiC_f/SiC composites have the advantages of high temperature strength,low activation,relatively low neutron absorption,and irradiation resistance,making them candidate materials for cladding of light water reactors.Evaluating the microstructure and mechanical properties of SiC and SiC_f/SiC composites under irradiation is the prerequisite for the application in reactors.In this paper,the single crystal 4H-SiC and SiC_f/SiC composites were irradiated by Si²⁺and He⁺+Si²⁺at 320?.Scanning electron microscope(SEM)and Raman spectroscopy were used to study the irradiation effects on the micromorphology and structure of single crystal 4H-SiC and SiC_f/SiC.Nanoindentation experiments were used to study the irradiation effects on the hardness and elastic modulus of single crystal4H-SiC and SiC_f/SiC composites.Three kinds of composite SiC/C models that SiC(100),(110)and(111)crystal planes connected with graphite were established by molecular dynamics simulation.In order to study the irradiation effects on the defect distribution and interface mechanical properties of the SiC/C models,14 and 28 silicon atoms were selected as PKAs to bombard the interfaces.The main conclusions are as follows:1.Ion irradiation effects of single crystal 4H-SiCRaman spectroscopy show that homonuclear Si-Si bonds and homonuclear C-C bonds appear after irradiation,and the E₂(TO)and A₁(LO)peaks related to Si-C bonds shift and broaden,indicating that the crystallinity decreases.Nanoindentation results show that the hardness of 4H-SiC increases due to the pinning effect after ion irradiation;the elastic modulus decreases due to the expansion of 4H-SiC.2.Ion irradiation effects of SiC_f/SiC compositesRaman spectroscopy show that the fibers and matrix have homonuclear Si-Si bonds similar to single crystal 4H-SiC,and the TO and LO peaks related to Si-C bonds shift and broaden,indicating that the crystallinity decreases.Nanoindentation results show that the fiber and matrix hardness increase due to the pinning effect after Si²⁺irradiation;the elastic modulus decreases because of the matrix lattice expands,and the fiber may shrink and the elastic modulus increases.The mechanical properties of SiC_f/SiC after He⁺+Si²⁺irradiation are different from those of Si²⁺,which may be the effect of helium bubbles.The single fiber push-in experiments show that the interface shear strength increases after irradiation,which may be attributed to the interface mixing effect caused by irradiation.3.Molecular dynamics simulation of SiC/CAfter irradiation,the SiC structure is destroyed at the interface,and some interstitials exist at the interface.Besides,an atomic mixing region is formed at the interfaces after irradiation.As the number of PKA increases,the number of interstitials and vacancies in SiC increases;vacancies are more likely to exist in the form of vacant clusters.In the absence of irradiation,the interface energy of the(110)model is the lowest,and the debonding position and strength are the highest.After irradiation,the debonding position and strength of the(100)and(110)models increase,which is more pronounced at high PKAs.For the(111)model,the debonding position and strength under 14 PKAs are close to those without irradiation,and the debonding position and strength are significantly increased under 28 PKAs.