Hydrogen accumulation in and at the perimeter of U–C–N–O inclusions in uranium – A SIMS analysis

Abstract

a b s t r a c tWe use imaging secondary ion mass spectrometry (SIMS) with a Cameca NanoSIMS 50 to determine the distribution and relative concentration of H in two uranium metal samples: sample1(LANL), as cast with less than 1 wppm H, sample2(Y12), outgassed 6 h in vacuum at 630°C to remove hydrogen. H ion counts appear almost exclusively associated with 'carbide' inclusions, based on H À , C À and O À ion images for uranium surfaces sputter-cleaned in situ with a 16 keV Cs + ion beam. Two classes of inclusions are identified:small, micrometer to sub-micrometer inclusions and larger, clearly angular inclusion (P3 lm). In sample1(LANL) the large inclusions (P250/mm 2 ) show a low H À /C À ratio inside, and have H À /C À ratios at their perimeters comparable in magnitude to that seen in lm-size inclusions. Small inclusions ($2500/mm 2 ) contain H more uniformly throughout and, averaged over the inclusion, the small inclusions have approximately 50 times higher relative H concentration than the large inclusions. Sample2(Y12) was found to have comparable H À /C À ratios in the large carbides, but no small inclusions were observed. Because of the matrix-sensitivity of SIMS, H/C ratios representing the actual composition of the inclusions cannot be derived from the H À /C À ratios without calibration UC samples with known H content, which are not currently available.

Effect of surface rolling extrusion processing on corrosion resistance of U–5.7Nb alloy

“…The existence of inclusions can destroy the continuity of the matrix, and when the inclusion is noncoherent with the matrix, stress will exist at the interface. Inclusions in matrix can lead to a significant reduction of the elongation, meanwhile, inclusions exposed on the surface will destroy the continuity of the material, form galvanic couple in the humid environment and often become the nucleation site during the hydrogen corrosion process [23-26]. It is known that the deformation of monoclinic α″-phase U–5.7Nb alloy at room temperature is mainly due to the formation of twins and the migration of the twin interface.…”