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The present work investigated the effect of a cyclic overaging pre-weld heat treatment proposed by Lim (US Patent no. 5 509 980, 1996) on the microstructure, tensile ductility, and weldability of Rene 80 nickel based superalloy (approximate composition 60Ni ± 14Cr ± 9 . 5Co ± 4Mo ± 5Ti ± 3Al ± 0 . 17C ± Zr ± B, wt-%), with a focus on the role of solution treatment and end aging temperatures. The results showed that maximum ductility corresponds to a microstructure consisting of very coarse and widely spaced g' , with ® ne g' not resolvable even at a magni® cation of 610 000. This was achieved by cyclic cooling the material from the solution temperature to a temperature in the range 500 ± 750°C followed by fast furnace cooling to suppress the precipitation of ® ne g' . The solution treatment temperature was found to control the number density of coarse g' , which, in turn, slightly in¯uenced the optimum end aging temperature. After the optimum cyclic overaging heat treatment with a solution temperature of 1080°C and an end aging temperature of 550°C, the material exhibited a tensile type fracture path with a high registered tensile ductility of ~30% in elongation. Fractographic studies revealed that the necked g ligaments were thicker and taller, with an increased frequency of cleaved coarse g' occurring at different levels in the material. Precision welding tests showed that the weldability of the optimally overaged alloy was signi® cantly improved, owing to both the resultant soft and ductile base metal and the reduced heat affected zone size.MST/5028

We are developing a high brightness nano-aperture electron impact gas ion source, which can create ion beams from a miniature ionization chamber with relatively small virtual source sizes, typically around 100 nm. A prototype source of this kind was designed and successively micro-fabricated using integrated circuit technology. Experiments to measure source brightness were performed inside a field emission scanning electron microscope. The total output current was measured to be between 200 and 300 pA. The highest estimated reduced brightness was found to be comparable to the injecting focused electron beam reduced brightness. This translates into an ion reduced brightness that is significantly better than that of conventional radio frequency ion sources, currently used in single-ended MeV accelerators.