Microstructural Investigation Of Single Crystal Sic After Helium Ion Irradiation And Post-irradiation Annealing

SiC has the advantages of high melting point,corrosion resistance and thermal conductivity,as well as low coefficient of thermal expansion and thermal neutron absorption cross section,which is an important candidate material in nuclear power field.Because of the low solibility of helium ions produced by transmutation reaction and deuterium-tritium reaction,aggregation occurred and then large sacle bubbles formed.The formation of bubbles can lead to the degeneration of mechanical properties of SiC,decreasing its service life of the reactor.Therefore,it is very important to study the microstructure evolution of SiC.In this paper,the single crystal 6H-SiC were irradiated by 400keV He+ ions and then subsequently annealed.The microstructure evolution of the samples was investigated by transmission electron microscopy and scanning electron microscopy.Only a damaged layer was observed with no visible helium bubbles formed after helium irradiation with a fiuence of 1×1016 He+/cm2 and subsequently annealed at 900? for 30min.However,after annealed at 1200? for 30 minutes,platelet-like planar bubbles were formed in the irradiated region and they were mainly distributed on the(0001)plane with a small amount lying on the(11-20)plane.Statistical analysis of the bubble size shows that the average size of the bubbles at the same annealing time is linearly increased with the annealing temperature.When 6H-SiC samples were irradiated at room temperature with a fluence of 1×1017 He+/cm2 and then subsequently annealed,the distribution of the bubbles in the irradiation layer was consistent with that of the helium concentration,bubbles at the bottom of the irradiated layer is small,and then increased sharply to the maximum,and gradually decreased with the distance from the interface.And layer of sparse bubbles in the upper area of irradiated layer were observed.Recrystallization occurred after 6H-SiC annealed at high temperature,a large number of stacking layers are formed and crystal poly-types silicon carbide with new crystal orientation were formed.When irradiated at 400?,no bubbles were observed after annealing at 600?and the bubble clusters lying on the(0001)plane appeared at both sides of the irradiated zone after annealing at 900?.Thickness of the upper bubble clusters layer was less than the lower.The bubble clusters in the interface of the irradiated zone evolved into platelet-type bubbles after annealing at 1200? for 15h.When annealed at 1400?,the bubble size in the irradiation layer drastically increased and the density was remarkably reduced.The two-dimensional bubble clusters on both sides of the irradiation zone grow into three-dimensional ellipsoidal bubbles.When the annealing time is constant,the bubble size increases exponentially with the annealing temperature.When 6H-SiC samples were irradiated and then subsequently isothermal annealed,the bubble size in the early annealing increased rapidly,and then the growth rate gradually decreased with the annealing time.Based on the statistical results of bubble size,a quantitative model of bubble size with annealing time and temperature evolution was obtained.The model can be used to calculate the corresponding values of the average size of SiC bubbles at a variety of annealing temperatures at room temperature and 400 ? irradiated with a fluence of 1 x 1017 He+/cm2.There were no visible defects formed on the surface of 6H-SiC after irradiation.Nevertheless,blistering and craters were formed after annealing at 1200?.The formation of surface blistering and craters became much easier and plenty of flaking were generated when annealed above 1500?.