Bingsheng Li

Structural Distortion and Defects in Ti

Ti3AlC2 samples are irradiated in advance by 3.5MeV Fe-ion to the fluence of 1.0×10 16 ion/cm 2 , and then are implanted by 500 keV He-ion with the fluence of 1.0×10 17 ion/cm 2 at room temperature. The irradiated samples are investigated by grazing incidence x-ray diffraction (GIXRD) and transmission electron microscopy (TEM). GIXRD results show serious structural distortion, but without amorphization in the irradiated samples. Fe-ion irradiation and He-ion implantation create much more serious structural distortion than single Fe-ion irradiation. TEM results reveal that there are a large number of defect clusters in the damage region, and dense spherical He bubbles appear in the He depositional region. It seems that the pre-damage does not influence the growth of He bubbles, but He-ion implantation influences the pre-created defect configurations.

_{3}

The evolution of the recrystallization phase in amorphous 6H-SiC formed by He implantation followed by thermal annealing is investigated. Microstructures of recrystallized layers in 15 keV He ion implanted 6H-SiC (0001) wafers are characterized by means of cross-sectional transmission electron microscopy (XTEM) and high-resolution TEM. Epitaxial recrystallization of buried amorphous layers is observed at an annealing temperature of 900°C. The recrystallization region contains a 3C-SiC structure and a 6H-SiC structure with different crystalline orientations. A high density of lattice defects is observed at the interface of different phases and in the periphery of He bubbles. With increasing annealing to 1000°C, 3C-SiC and columnar epitaxial growth 6H-SiC become unstable, instead of [0001] orientated 6H-SiC. In addition, the density of lattice defects increases slightly with increasing annealing. The possible mechanisms for explanation are also discussed.

AlC

A type of home-made reduced activation martensitic steel, high silicon (SIMP) steel, is homogeneously irradiated with energetic Fe ions to the doses of 0.1, 0.25 and 1 displacement per atom (dpa), respectively, at 300°C and 1 dpa, at 400°C. Microstructural changes are investigated in detail by transmission electron microscopy with cross-section technique. Interstitial defects and defect clusters induced by Fe-ion irradiation are observed in all the specimens under different conditions. It is found that with increasing irradiation temperature, size of defect clusters increases while the density drops quickly. The results of element chemical mapping from the STEM images indicate that the Si element enrichment and Ta element depletion occur inside the precipitates in the matrix of SIMP steel irradiated to a dose of 1 dpa at 300°C. Correlations between the microstructure and irradiation conditions are briefly discussed.