Ab initio study of H/O trapping and clustering on U/Al interface

Al coating on U surfaces is one of the methods to protect U against environmental corrosion. The behaviors of hydrogen and oxygen impurities near the Al/α-U interface have been studied in the density functional theory framework. It turns out that U vacancies tend to segregate to the interface with segregation energies of around 0.5-0.8 eV. The segregated U vacancy can act as a sink for H and O impurities, which is saturated when filled with 8 H or 6 O atoms, respectively.Moreover, the O impurities tend to stay in the Al layer while the H impurities prefer to diffuse into the U lattice, suggesting that the Al coating can play a significant role against oxidation but not against hydrogenation of U.

An Incremental Model for Defect Production upon Cascade Overlapping

An analytic incremental model is proposed to predict the defect production upon cascade overlapping.By resolving the coupled annealing events during cascade overlapping,this model handles cascade overlapping with multiple pre-existing defects of different sizes and number densities.The model is first parameterized and then applied to bcc-Fe.The proposed model satisfyingly reproduces the defect production obtained by molecular dynamics simulations with various radiation damage levels and defect cluster size distributions.The present model provides an essential description of the primary source of radiation damage,especially for high dose irradiation,and could be used in conjunction with reactive diffusion models for better understanding of radiation damage.

Oxygen-penetration-induced large hardness enhancement in nanoscale Nb/Ti multilayers

Nb/Ti multilayers with different modulation periods were prepared by magnetron sputtering deposition. Microstructure and mechanical properties were investigated by XRD, SEM and Nanoindentation. It turns out that hardness of samples increases with decreasing modulation wavelength （A） and then dropped at small A. Through scrutinizing other results in literature, we found that the coherent stress rather than modulus mismatch played more important role for hardness enhancement with de- creasing A of the bcc-hcp multilayers. Annealing of samples in low （or high） vacuum at 400 ~C for 30 min led to large （or medium） enhancement of hardness, while the modulated structure was still maintained. It was found that annealing in low vac- uum resulted in oxygen penetration into the multilayers as revealed by auger electron spectroscopy, but hardly changed metallic sheet resistivity. XRD results suggested that some niobium oxides were formed in Nb layers and oxygen distributed intersti- tially in Ti layers. The large hardness enhancement after annealing is mainly due to the strengthening effect from dispersive distribution of nano-scale niobium oxides and interstitial oxygen in the multilayers. In addition, interfaces between adjacent layers were more distinct after annealing which indicated good thermal stability of laminated structure.

Radiation damage of 1Cr18Ni9Ti and Zr-Ti-Al alloys due to energetic particle irradiation

The radiation damage of 1Cr18Ni9Ti stainless steel and the Zr-Ti-Al alloy by 200 keV Xe＋ ions bombardment at the fluence ranging from 1×1014 to 8×1015 ions/cm2 has been investigated by conventional transmission electron microscope, X-ray diffraction line profile analysis （XRDLPA） and nanoindentation. XRDLPA shows that the order of magnitude of dislocation density in both materials remains almost unchanged up to the highest irradiation dose. Selected-area electron diffraction combined with bright and dark field image indicates that 1Cr18Ni9Ti is more easily damaged than the Zr-Ti-Al alloy. With increasing the ions fluence, the radiation damage became more severe in 1Cr18Ni9Ti, accompanied with phase transition and partial amorphization. The nano-hardness was found to increase rapidly with increasing ion fluence till the dose of 1×1015 ions/cm2, and then gradually saturate with dose. The enhancement of hardness in irradiated materials is due to irradiation-induced defects acting as barriers to dislocation motion.