| Because of high melting point,high thermal conductivity,low coefficient of thermal expansion,superior corrosion resistance,low neutron reaction cross section,excellent irradiation tolerance,SiC has been promising candidate material in nuclear field.SiC based materials have beem considered to be used as the structural layer of TRISO fuels,the first wall materials of fusion reactors and articulating joints of control rods.Served in the nuclear reactor core,SiC materials will be exposed to extremely harsh environment with high temperature,high pressure and high-flux neutron irradiation.Impurity atoms,such as H,He and P,will be produced by neutron irradiation.Irradiation induced effects of bubbles,blisters,cracks and hardening by ion irradiation of H,He,C and Kr and subsequent annealing were investigated in this thesis.It is of great importance to investigate the irradiation behavior,irradiation induced material degradation and understand the inherent mechanism.The thesis firstly investigated the irradiated layer in He+ irradiated samples.The evoluation of helium bubbles were studied after annealing at 900? and 1200?.The mean radius of bubbles decreased along with the increase of irradiation temperature in the range of 200?400?.This is due to that the growth of bubbles is affected by the residual defects after the He irradiation.The surface blisters of SiC material after irradiation of H2+,He+ and He++H2+ and annealing were investigated in the second part.The effects of factors of size and shape of blisters,such ions species and ion fluences were studied.The lateral radius(a)and the vertical deformation value(w0)of the blisters in the irradiated sample with low H2+ fluence was larger than that in the irradiated samples irradiated with high H2+ fluence and He+-H2+ ions.The blisters nucleated from the connection of H nano-cracks.8%?58%of implanted H atoms contributed to the formation of the blisters.Compared with other irradiated samples,the ratio of w0/a and the density of the blisters in the He+-H2+ irradiated samples was largest.The stress field of the blisters was simulated using finite element method and the inner pressure in the blisters was also calculated.Circular ripples were formed in the He+ irradiated and annealed sample.The delamination occurred at a depth of 600nm in the He+ irradiated sample.The corresponding mechanism was analyzed and discussed.The cracks of C+ irradiated and annealing SiC samples were researched.The mean length and mean width of cracks increased along with the increase of annealing time.The growth of cracks is due to the lateral stress produced by volume shrinkage of irradiated layer during the annealing process.The function of the length and width of cracks was fitted for the growth of cracks.The recrystallization induced by annealing of SiC sample irradiated with H2+,He+ and C+ at RT are investigated.Samples irradiated with He+ and C+ share the same recrystal mechanism during annealing:the random nucleation at the center area of irradiated layer dominated when annealed at 800? and epitaxial columnar growth dominated when annealed above 900?.The recrystallization rate of H2+ irradiated samples is much slower than that of He+ and C+ irradiated smaples and the recrystallization dominated by epitaxial layer-by-layer growth in the all annealing temperature range.This is because H can react with Si and C to form Si-H or C-H bonds during the irradiation.More energy and time were needed to break the bonds during annealing process.The thesis finally investigated the nano hardness of SiC irradiated with a series of Kr+irradiation.The changes of nano hardness were the same for the thress types of SiC:4H-SiC,6H-SiC and 3C-SiC.The nano hardness increased from 44±3GPa to 51±3GPa when annealed at 900?for 600min.The nano hardness decrease significantly to 17±3GPa when annealing at 1200? for 600min.Large numbers of black spots defects and dislocations lying on(0001)and {11-20} planes were observed in the irradiated samples.Based on the theory of dislocation gliding,the changes of nano hardness of SiC samples during annealing at 900? and 1200? were explained by analysis of the evolution of the dislocations. |
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