ZrCo alloys with Ti, Sc, Ni, Fe substitution (Zr0.8Ti0.2Co, Zr0.8Sc0.2Co, ZrCo0.8Ni0.2, ZrCo0.8Fe0.2) were prepared via arc-melting method, and then products before and after hydrogenation were ...characterized by X-ray diffraction. Results showed that the crystal structure of ZrCo alloys substituted with Ti, Sc, Ni and Fe substitution formed cubic phase, and the lattice parameters of ZrCo alloys and these hydrides decreased with Ti substituted, while increased with Sc, Ni, Fe substitution. The dehydrogenation pressure composition isotherms for all these alloys were obtained in the temperature range between 523 K and 623 K, and it was found that desorption plateau pressure increased in order of ZrCo0.8Fe0.2 < ZrCo < Zr0.8Sc0.2C < ZrCo0.8Ni0.2 < Zr0.8Ti0.2Co. Meanwhile, the enthalpy and entropy change for hydrogen desorption were calculated. And the kinetics of hydrogen-induced disproportionation in desorption mode for all these alloys was also investigated. Results demonstrated that the rate and extent of disproportionation of ZrCo alloys decreased with Ti substitution, while increased with Sc, Ni and Fe substitution. Thermal analytical method (DSC) was carried out to investigate the mechanism of thermal stability change of ZrCo alloys after Ti, Sc, Ni, Fe substitution. It could be inferred that the effect of element substitution on disproportionation of ZrCo alloys was caused by the radius change of hole sizes of hydrogen occupation sites.
•Crystallographic parameters of ZrCo alloys and their hydrides with Ti, Sc, Ni, Fe substituted were investigated.•Thermodynamic parameters were calculated for ZrCo alloys with Ti, Sc, Ni, Fe substituted.•Kinetics of disproportionation of ZrCo alloys with Ti, Sc, Ni, Fe substitution were studied.•Explained the increasing ability of anti-disproportionation of ZrCo with Ti substituted.
Ultrasonic surface rolling process (USRP) is a novel surface modification technique based on surface severe plastic deformation (SSPD). The present study aims to investigate the surface ...characteristics and micro-mechanical properties of uranium by USRP treatment. By means of theoretical calculations and experimental tests, it was concluded that the USRP treated specimen showed a smoother and more densified surface. The surface roughness Rv, Rp and Ra were reduced to 0.590 μm, 0.669 μm and 0.249 μm, respectively. Meanwhile, the U(002) basal texture and stronger residual compressive stresses were presented on the surface. The gradient microstructure including severe deformation layer and deformation twinning layer was generated after USRP treatment. Furthermore, there was a typical gradient strength distribution with significantly higher values on the top surface, followed by a gradual decrease until the matrix was reached. As a result, the improvement of surface strength was achieved and the ductility of matrix in core was maintained. These improvements in the micro-mechanical properties were attributed to the results of surface integrality, orientation of grains, residual compressive stress, severe deformation layer and deformation twinning layer. However, excessive passes of USRP treatment led to the nucleation and propagation of surface cracks and the release of residual compressive stress, which were not conducive to the improvement of micro-mechanical properties.
The microstructure evolution of uranium after USRP treatment: (a) SEM image of gradient microstructure; (b) TEM image of severe deformation layer; (c) Depths of deformation layers. Display omitted
•The smoother surface and stronger residual compressive stresses are obtained in uranium specimens after USRP treatment.•The U(002) basal texture, severe deformation layer and deformation twinning layer are presented after USRP treatment.•There is a gradient strength distribution along the depth with significant higher values on the top surface.•The micro-mechanical properties of uranium are much enhanced by USRP which can improve resource sustainability greatly.
Abstract The inherent variability of pitting poses challenges in accurately evaluating the pitting resistance due to potential disparities in test results. This study compares the pitting resistance ...of two commercial 2205 duplex stainless steels. Counterintuitively, the variant with higher Pitting Resistance Equivalent Number, exhibits a lower Critical Pitting Temperature. Through the potentiostatic pulse test and potentiostatic polarization, this variant is observed to have a greater number of pitting initiation sites. Further investigation, using SEM inclusion statistics, reveals an increased presence of inclusions rich in calcium oxides as the underlying cause of this unexpected phenomenon.
•The nitride uranium metal surfaces were formed by SGPN and PIII methods.•The initial oxidation behaviors of surfaces were analyzed by XPS in detail.•A comparative study was performed to clarify the ...initial oxidation processes.
The nitride surfaces of uranium were prepared by the surface glow plasma nitriding (SGPN) and plasma immersion ion implantation (PIII) methods. The initial oxidation behaviors of modified surfaces were studied by X-ray photoelectron spectroscopy (XPS). The SGPN on the uranium surface led to a single layer of uranium sesquinitride (U2N3), while the PIII on the surface resulted in a compound layer composed of U2N3 and uranium dioxide (UO2). The oxygen covered on these modified layers led to the formation of UO2 from U2N3 and U2N3 from UN. The oxidized nitrogen species were also observed on the two types of nitriding layers, with the discussion of the N–O coaction behaviors.
•The U2N3+xOy films were deposited by magnetic sputtering deposition method.•The initial oxidation behaviors of U2N3+xOy films were analyzed by XPS in detail.•Effective information is extracted from ...the spectra variations during oxidation and depth profile, and a cascade mechanism is proposed and discussed.
U2N3+xOy films were deposited on Si substrate by magnetic sputtering deposition method, and the oxidation behavior of U2N3+xOy films in air and oxygen atmosphere were investigated by X-ray photoelectron spectroscopy (XPS) at room temperature. During oxidation, U4f peaks gradually shift to higher binding energy accompanied with variations of satellites at 386.6eV and 397.7eV in U4f region. And similar satellites variations are observed on U2N3+xOy surface during oxidation and depth profile, which is attributed to the N-enriched intermediate product. The final product of U2N3+xOy is UO3, and oxidized nitrogen is also observed after a several-week exposure in air. A cascade mechanism is discussed and applied to explain the oxidation process, in which more than three series reactions are included.
The in-depth investigation of hydrogen behaviors in Pu-oxide overlayers (mainly PuO2 and α-Pu2O3) is critical for modeling the complex induction period of Pu hydriding. Within density functional ...theory (DFT) + U + D3 schemes, our systematic first-principles calculations and ab initio thermodynamic evaluations reveal that the hydrogen incorporation, dissolution behaviors, and diffusion mechanism in PuO2 are quite different from those in α-Pu2O3, among which the highly endothermic incorporation and dissolution of hydrogen are the primary hydrogen resistance mechanism of PuO2. Since its difficult recombination, atomic H is the preferred existence state in PuO2, but H will recombine spontaneously in α-Pu2O3. In PuO2, H diffusion is always clinging to O anions, whereas in α-Pu2O3, H2 prefers to migrate along O vacancies with higher barriers. H dissolution in intact PuO2 is very difficult, which can only be driven by extremely high pressure PH2 and temperature. Based on a series of theoretical studies, we conclude that the main interactions between hydrogen and Pu-oxide overlayers are not involved with chemical reactions, and intact PuO2 can effectively inhibit hydrogen permeation.
► Al overlayers on U were prepared by sputtering at room temperature. ► The behavior of Al/U interfaces was studied in situ by AES, EELS, and XPS. ► An island growth mode was proposed.
Aluminum ...overlayers on uranium were prepared by sputtering at room temperature in an ultra-high vacuum chamber. The growth mode of aluminum overlayers and behaviors of the Al/U interface reaction were studied in situ by auger electron spectroscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy. The results suggested that the interdiffusion took place at the Al/U interface during the initial stage of deposition. The U4f spectra of the Al/U interface showed strong correlation satellites at binding energies of 380.4 and 392.7eV and plasma loss features at 404.2eV, respectively. The interactions between aluminum and uranium yielded the intermetallic compound of UAlx, inducing the shift to a low binding energy for Al2p peaks. The results indicated that aluminum overlayers were formed on the uranium by sputtering in an island growth mode.
Nitrogen ion was implanted into uranium surface using plasma immersion ion implantation, and the corrosion resistance of modified layer was studied by corrosion experiment. SEM was used to observe ...variety of samples surface. In atmosphere, the sample surface had not changed during five months. In heat–humid environment, there was dot-corrosion appearing after two months, but it did not influence the integrity of the modified layer. AES was used to study the diffusion of oxygen and nitrogen during hot–humid corrosion, in three months, both of two elements diffused to the substrate, but the diffusion was weak. The structure of modified layer was not changed. Experimental results show that the modified layer formed by plasma immersion ion implantation has good corrosion resistance.
▸ The nitride layer was formed on uranium by glow plasma surface nitriding. ▸ Four zones were observed in the nitride layer. ▸ The chemical states of uranium, nitrogen, and oxygen were identified by ...AES.
The nitride layer was formed on uranium metal by a glow plasma surface nitriding method. The structure and composition of the layer were investigated by X-ray diffraction and Auger electron spectroscopy. The nitride layer mainly consisted of α-phase U2N3 nanocrystals with an average grain size about 10–20nm. Four zones were identified in the layer, which were the oxide surface zone, the nitride mainstay zone, the oxide-existence interface zone, and the nitrogen-diffusion matrix zone. The gradual decrease of binding energies of uranium revealed the transition from oxide to nitride to metal states with the layer depth, while the chemical states of nitrogen and oxygen showed small variation.
The anisotropic behavior of elastic properties of the low-temperature phase of uranium was studied by theoretical and experimental methods in this work. Firstly, based on the density functional ...theory, the elastic constants and compliance constants of α-U were obtained. Secondly, Young's modulus, bulk modulus, shear modulus, and Poisson's ratio of polycrystalline α-U were calculated using the Voigt-Reuss-Hill model. Then, according to the crystal symmetry of α-U, the spatial distribution characteristics of its Young's modulus were calculated and displayed. The Young's modulus of α-U in some specific crystal directions (including the typical deformation-induced twinning {1 3 0}, {1 7 2}) were also given. Nanoindentation method combined with electron backscatter diffraction (EBSD) technology were used to measure and characterize the grains with different crystal orientations, to obtain experimental values of Young's modulus of α-U in different crystal orientations. Also, the inverse pole figure of Young's modulus of α-U was given.
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