Mechanical properties and surface characteristics of SiC fibers irradiated by swift heavy ions

SiC fibers were irradiated by 414.4-MeV^(112)Sn^(27.3+)ions to different fluences(5.0×10^(12),6.0×10^(13),1.6×10^(14),and 1.92×10^(15)ions/cm^(2)).^(112)Sn^(27.3+)deposited its energy mainly via electron energy loss and passed through the SiC fiber.Then,the mechanical properties and surface characteristics of fibers were studied using a specific single filament tensile test and field emission scanning electron microscopy.Results revealed that the carbon concentration on the fiber surface increased while the silicon concentration decreased.Moreover,the addition of oxygen was found to correlate with an increase in ion fluence.Meanwhile,the fiber surface morphology of the least fluence(5.0×10^(12)ions/cm^(2))irradiated specimen displayed no obvious changes and its diameter was slightly reduced.With successive increases of ion fluence,large grains/bubbles on the fiber surface first appeared and then disappeared,and the diameter of fibers evidently increased.Moreover,at the highest fluence(1.92×10^(15)Sn ions/cm^(2))irradiated specimen,some fibers were brittle fractured.As a result,the mean tensile strength and the average elastic modulus of the fibers generally decreased with respect to the ion fluence.The degradation mechanisms of mechanical properties of SiC fibers under irradiation are discussed in detail.

Damage produced on GaN surface by highly charged Krq+irradiation

Surface morphology, compositions, microstructure and optical properties of GaN film irradiated by highly charged Kr^(q+)(q = 23, 15, 11) in two geometries to a fluence of 1×10^(15)kr^(q+)/cm^2 were studied using AFM,XPS, PL, Raman scattering and UV–visible spectroscopy.The AFM observation shows that the irradiated GaN area is a swollen terrace. The swelling rate increased with the charge state(potential energy). For the same charge state,the swelling rate of tilted incidence was greater than that for normal incidence. The XPS measurements reveal that N deficiency, Ga enrichment and Ga–O and Ga dangling bonds generated on the irradiated GaN surface increased with the charge state, and more N was lost for normal incidence than that for tilted incidence. The UV–Vis results show that the transmittance decreased with increasing charge state. For the same charge state, the transmittance for tilted incidence is higher than that for normal incidence.The PL spectra present that, with increasing charge state,the YL band intensity decreased, with a blueshift in its peak position; while the NBE peak intensity increased firstand then reduced, and a blue luminescence band appeared.A rapid quenching of both the YL and the NEB for normal incidence was observed. Raman spectra display that screw dislocations perhaps were produced near the surface for normal incidence.

Aligned Elongation of Ag Nanoparticles Embedded in Silica Irradiated with High Energy Ni Ions

Metallic nanoparticle （NP） shapes have a significant influence on the property of composite embedded with metallic NPs. Swift heavy ion irradiation is an effective way to modify shapes of metallic NPs embedded in an amorphous matrix. We investigate the shape deformation of Ag NPs with irradiation fluence, and 357 MeV Ni ions are used to irradiate the silica containing Ag NPs, which are prepared by ion implantation and vacuum annealing. The UV-vis results show that the surface plasmon resonance （SPR） peak from Ag NPs shifts from 400 to 377nm. The SPR peak has a significant shift at fluence lower than 1 × 10^14 ions/cm2 and shows less shift at fluence higher than 1 × 10^14 ions/cm2. The TEM results reveal that the shapes of Ag NPs also show significant deformation at fluence lower than 1 × 10^14 ions/cm2 and show less deformation at fluence higher than 1 × 10^14 ions/cm2. The blue shift of the SPR peak is considered to be the consequence of defect production and Ag NP shape deformation, Based on the thermal spike model calculation, the temperature of the silica surrounding Ag particles first increases rapidly, then the region of Ag NPs close to the interface of Ag/silica is gradually heated. Therefore, the driven force of Ag NPs deformation is considered as the volume expansion of the first heated silica layer surrounding Ag NPs.

Hardening of an ODS Ferritic Steel after Helium Implantation and Thermal Annealing

Specimens of an oxide dispersion strengthened（ODS） ferritic steel（15 Cr-4 Al-0.6 Zr-0.1 Ti） are implanted with multiple-energy He ions at room temperature to create a damage plateau of 0.4 dpa for the average（corresponding to an He concentration of about 7000 appm） from the near surface to a depth about 1 um. The specimen is subsequently thermally annealed at 800°C for 1 h in a vacuum so that simple defects can be formed in the as-implanted state that has undergone significant recombination, meanwhile helium bubbles at nano-scale are formed. Hardness of the specimens are tested with the nano-indentation technique. A hardening by 25% is observed. Microstructures of the specimen after irradiation/annealing are investigated with transmission electron microscopy. Helium bubbles are generally located at dislocations and grain boundaries. Using the dispersed barrier strength model, the strength factor of helium bubbles in the ODS ferritic steel is estimated to be between0.1 and 0.26, which is close to that of helium bubbles in austenitic steels.