To develop high-strength Al-Mg-Mn alloys with balanced corrosion resistance, a novel and cost-effective approach of introducing Ce via in-situ reduction of CeO2 is proposed. The addition of CeO2 powders in the molten high-Mg content Al-Mg-Mn alloys enables the formation of Ce-containing Al-Mg-Mn alloys through insitu reduction reactions. Ce exists in the alloy in the form of Al20Mn2Ce and Al13CeMg6, which can enhance corrosion resistance of the alloy at no expense of mechanical properties. The as-stabilized alloy with 0.5 wt% CeO2 addition exhibits the highest YTS (368 MPa) and UTS (515 MPa), which are 9.5% and 6.6% higher than the counterparts of the base alloy, respectively. The pitting corrosion rate of the alloy with the addition of 0.3 wt% CeO2 in the sensitized state is about 57.0% of that of the base alloy. The corrosion resistance improvement can be attributed to the enhanced stability of the oxide film associated with the addition of CeO2 and the reduced corrosion susceptibility of the Al20Mn2Ce phase. In comparison with the base alloy, the alloy with the addition of 0.5 wt% CeO2 demonstrates an enhanced intergranular corrosion (IGC) resistance, with the IGC mass loss about 12.9% lower, which is associated with the formation of the Al13CeMg6 phase. This phase effectively reduces the super-saturation of Mg atoms in the Al matrix, diminishing the driving force for the formation of (3-Al3Mg2 and thereby reducing the thickness of the (3-Al3Mg2 phase at grain boundaries. The incorporation of cerium oxide can comprehensively enhance both pitting corrosion and intergranular corrosion of the Al-Mg-Mn alloy.

First-principles calculations were performed to investigate the physical properties including structural stability, electronic structures and hydrogen trapping characteristics of various impurities in α-U. The impurities were selected based on relevant literature including 14 metallic elements (Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo) and 13 non-metallic elements (H, He, B, C, N, O, F, Ne, Si, Cl, Ar, Kr, Xe). Three interstitial sites and one substitutional site were taken into consideration. It is found that non-metallic impurities including H, C, N and O preferentially occupy interstitial sites, whereas other non-metallic impurities tend to occupy substitutional sites, and all the metallic impurities favor substitutional positions. The incorporation of impurities in α-U is governed by atomic sizes and electron hybridizations. Compared with non-metallic impurities, metallic impurities in α-U exhibit a higher propensity to act as hydrogen traps, particularly Cr, Mn, Fe, Co, Ni, and Cu. These results provide theoretical insights into the microstructure evolution of uranium and the underlying mechanisms controlling the complex failure behaviors of metallic nuclear materials, such as corrosion, swelling, and irradiation damage.

This study has systematically investigated the effects of unidirectional quasi-beta forging deformation (20 %, 40 %, 60 %) plus duplex ageing on microstructure and mechanical properties of TC18 titanium alloy. The alloy forged at 900 degrees C with the height reduction of 40 % exhibits the optimal microstructure, with the beta grain size of 47.7 mu m, the dynamic recrystallisation volume fraction of 3.9 %, and the geometrically necessary dislocation density of 0.48 & times; 1014 m-2. This microstructure provides favorable conditions for the uniform and fine precipitation of secondary alpha phase (alpha s) during the subsequent ageing. After an optimized duplex ageing treatment (350 degrees C/1h + 600 degrees C/4h), the alloy achieves a favorable balance of strength and ductility, with ultimate tensile strength of 1577 MPa, yield strength of 1513 MPa and elongation to rupture of 6.6 %, the ultimate tensile strength of which is approximately 77.2 % higher than the as-forged state. The synergistic optimization of both strength and ductility in TC18 alloy can be ascribed to the adjustment of the size and the distribution of alpha sprecipitates, which provide theoretical foundations and process guidance for the industrial production of high-performance titanium alloy components.

Irradiation can cause severe property degradation of materials (i.e., radioactive aging), which has drawn general interest in both scientific research and engineering applications. In nuclear areas, this is significantly important due to many nuclear materials being radioactive or exposed to radiation environments. Although the basic process of the self-irradiation of actinides and their derivatives has been studied, there is still much that remains elusive, especially for Pu-Ga alloys, one of the most mysterious nuclear materials. Here, we utilize molecular dynamics simulations to study the influence of the incident angle of the U nucleus on the self-irradiation of delta-phase Pu-Ga alloys, also concerning the effect of Ga concentration in the alloys. The generation of defects shows obvious dependence on the U incident angles, where the maximum and ultimate numbers of defects change up to 59% and 38%, respectively. Besides, the ultimate local atomic structures of the materials are also affected. Different U incident angles lead to different collision kinematics and energy transfer efficiencies, which subsequently cause cascade collisions with different paths and scales. Specifically, the coupling of thermal vibrations and geometric alignment in certain directions leads to high variability in defect production. The self-irradiation of delta-phase Ga alloys with a series of Ga concentrations (ranging from 2 to 7 at. %) is also studied, and the ultimate defect number is found to be the smallest for the alloys with the middle concentration of 5 at. %. This work shows importance of considering the irradiation angle and element content for the primary damage formation underlying radioactive aging of nuclear materials, which will be useful for the development of strategies to manage aged nuclear materials.

Surface protective nitride layers are crucial for enhancing corrosion resistance of uranium (U) alloys, but the protective efficiency is influenced by its thickness discontinuity. Herein, the asynchronous nitridation behavior of constituent α and γ phases in duplex U-2.0 wt.% Nb alloys is investigated via experimental microstructure characterizations and theoretical analysis. Following plasma nitriding, a UN2-x surface layer is formed on the alloy substrate, yet exhibiting a distinct phase-dependent discontinuity of thickness: thick in the α phase but thin in the γ phase. The density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations reveal the intrinsic mechanism underlying this phenomenon: the Nb element thermodynamically suppresses nitride formation while kinetically facilitating nitrogen diffusion along the γ phase, collectively leading to UN2-x thickness discontinuity. This work clarifies the phase-related asynchronous growth mechanism of surface nitride layers in duplex U-2.0Nb alloys, which enriches the fundamental understanding of plasma nitriding in multi-phase U alloys.

Laser-induced breakdown thermometry (LIBT) is a promising technique for gas temperature measurements. However, in practical flows, dynamically varying temperature gradients can induce non-negligible drift in measurement locations, potentially compromising measurement accuracy. To address this challenge, we introduced temporal modulation of laser pulse in LIBT. Specifically, by chopping the pulse duration with a pressure chamber, the expansion of laser-induced plasma was confined to its early stage, where the plasma location remained insensitive to temperature gradients, thereby stabilizing the measurement location. Spatial resolution was concurrently improved due to the reduced plasma size. Gas temperature was then calibrated against the deposited energy, and a correction model was built to suppress the modulation-induced increased shot-to-shot fluctuations. Finally, the temporally modulated laser-induced breakdown thermometry (TMLIBT) method was validated in a hot-cold gas flow interface with steep temperature gradients, which yielded improved trueness and maintained acceptable single-shot precision, demonstrating its feasibility under practical conditions.

Given the intrinsic brittleness of Be, there is still a dearth of understanding regarding its microstructure and properties under conditions of high accumulated plastic strain. In the present study, bulk nanostructured Be was successfully prepared by high pressure torsion (HPT) at room temperature, and the resulting microstructure and mechanical properties were investigated. The brittle Be exhibited plastic flow characteristics under HPT. The steady-state grain size was approximately 61 nm, and the fraction of high angle grain boundaries reached approximately 76 %. The nanostructured Be displayed an anomalous phenomenon, whereby the grain size could be reduced to tens of nanometers while maintaining a relatively low dislocation density (similar to 1.7 x 10(14) m(-2)), in contrast to the typical metals obtained by severe plastic deformation. It is postulated that the strong dynamic recovery is responsible for this phenomenon, which relies on the unique properties of Be, namely high stacking fault energy and distinct cross slip. Hydrostatic pressure not only inhibits cracks but also serves as a prerequisite for the unique dislocation activities observed in Be.

It is important to enhance the room temperature ductility of titanium alloy for its application in complex structural parts. In this study, high strain rate multi-direction forging (MDF) technique is used to refine the grain size of TC4 alloy, and both the evolution regularity and the formation mechanism of the microstructure are elucidated. Dynamic recrystallization (DRX) is enhanced by high strain rate deformation, and thus the fine uniform equiaxed alpha phase is obtained. After 2 passes of MDF at 880 degrees C with the strain rate of 13 s(-1), the mean grain size of alpha phase is refined to 3.2 mu m, and the samples exhibit a high ductility of up to 25.9 % with the yield strength and the ultimate tensile strength of 944 MPa and 1060 MPa, respectively. The ductility enhancement mechanism is due to the refined equiaxial alpha phase, which increases the strain hardening rate of the alloy by the high density of geometrically necessary dislocation (GND) and the activated slip system, and thus the crack initiation is inhibited.

A combination of electro-probe microanalysis, transmission electron microscopy and atom probe tomography was employed to investigate the effects of high-temperature oxidation on the gradient of the microstructure and microchemistry of the oxygen-rich layer on a near-alpha Ti alloy, Ti6242s, with a bimodal microstructure. alpha(2) precipitation occurred within the oxygen-rich layer, more pronounced inside the primary alpha grains than within the secondary alpha laths. The degree of alpha(2) precipitation increases with increasing oxygen content, and the critical amount of oxygen triggering alpha(2) is similar to 3 at. % in the primary alpha grains, and even higher within the secondary alpha laths. These values are far greater than the reported value, similar to 0.6-0.75 at. %, for the bulk alloy. Heterogeneous Al segregation was observed within the secondary alpha laths while bcc-beta phase persisted even at the very surface where the oxygen content was highest. These findings indicate that oxygen ingress accelerates precipitation of alpha(2) at elevated temperature, and faster O diffusion along the dislocations and boundaries stimulates heterogeneous Al segregation. The lower degree of ordering within the secondary alpha laths was probably owing to the lower Si content and Al supersaturation.

A novel tri-modal microstructure of Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy featured by gradient equiaxed alpha phase and nano-scale lamellar alpha phase was developed via two-step hot deformation plus duplex aging in this study, and the corresponding microstructure evolutions, mechanical behaviors and strengthening mechanisms were revealed in detail. The achievement of this tri-modal microstructure is attributed to the beta trans (beta transformed microstructure) re-construction process of initial bimodal alloy. Specifically, the coarser alpha s in the beta trans of as-received bimodal alloy are transformed to beta phase firstly via 40 % compression at 900 degrees C, coupled with the decreased proportion of alpha p. Then, the preferred alpha precipitation around alpha p occurs when the compressed alloy is multi-directional forged at 840 degrees C, leading to the coexistence of micron scale alpha p, sub-micron scale dynamic precipitated alpha phase and retained beta phase. Finally, the retained beta phase is transformed to beta trans again by duplex aging at 350 degrees C-1.5 h + 600 degrees C-0.5/ 2.5/5 h, which containing dense nano-scale alpha s. The alloy aged at 350 degrees C-1.5 h+ 600 degrees C-2.5 h exhibits the best strength-ductility matching, i.e., the yield strength, ultimate tensile strength and elongation are 1371 MPa, 1427 MPa and 5.1 % respectively. The alpha s precipitation strengthening is the dominated strengthening mechanism of tri-modal alloy and it offers - 70 % contribution of the yield strength increment compared with the asreceived bimodal alloy. Also, it displays a mixed fracture mechanism in which the broken of alpha p and deflections of crack propagation are helpful to delay fracture.

This paper investigates the effects of aging at 175 °C on microstructure and corrosion behavior of the Mg-6.5Gd-0.9Y-0.5Zr (wt.%) alloy. After aging treatment, β′ precipitates are formed within grains and at grain boundaries in the alloy except for the original Zr nucleus, Mg 5 (Gd,Y), and Mg 3 Y 3 Gd 2 second phase particles. Both immersion weight loss testing and electrochemical measurement in 3.5 wt.% NaCl shows that the corrosion resistance of the alloy increases at first and then decrease with the prolonged aging time. The alloy in the peak aging state demonstrates the highest corrosion resistance, with P w of 0.443 mm/y and I corr of 6.79 μA/cm². The aging treatment consumes the high density of dislocations in the as-extruded alloy, resulting in the enhanced localized corrosion resistance. The high corrosion resistance of alloys in the peakaging state can be primarily attributed to the protective effect of the β′ precipitates, which are distributed in a reticulated manner within grains and continuously at the grain boundaries. Additionally, the formation of a dense film of corrosion products contributes to this resistance.

Uranium (U) and its alloys are frequently subjected to dynamic deformation during their applications in nuclear industry. Owning to the low-symmetry crystal structure of alpha-U (the allotropic form of uranium stable up to 940 K), twinning and kinking play critical roles in its dynamic plastic deformation. However, the twinning and kinking behaviors of alpha-U under dynamic deformation have not yet been fully understood. In this work, we employed a split Hopkinson pressure bar (SHPB) to dynamically compress coarse-grained alpha-U to strains of 5%, 15%, 25%, and 27%. The resulting twin and kink bands were characterized using electron back-scatter diffraction (EBSD). Our results reveal that both the width and density of twins increase with increasing impact strain. Four types of twins were identified: {130}, '{172}', {112}, and '{176}'. Kink bands emerged after 15% impact strain, with their boundaries perpendicular to the [100] direction of matrix and their [100] directions oriented at a 45 degrees angle relative to that of matrix. The {130}, '{172}', and {112} twins were observed within the kink bands, and the {112} twins inside the kink bands were found to initiate secondary {130} twin. Fine and randomly oriented grains were observed inside the adiabatic shear bands of alpha-U. Based on these findings, we propose a twin-induced rotational dynamic recrystallization to describe the formation of adiabatic shear band in uranium. This study provides new insights into the plastic deformation mechanisms of uranium under dynamic loading.

Hydride growth behaviors are known to be governed by microstructure and stress, but the interplay of the two factors remain unclear. In this work, the growth behaviors of uranium hydride (UH3) in lamellar U-2Nb alloy were systematically investigated. The growth of UH3 in U-2Nb samples was controlled by cathodically hydrogen charging with different current densities. The hydrides were categorized into three types based on their growth rate and nucleation sites: (1) blisters at alpha-U lamellae, (2) fast growth families around inclusions, and (3) fishbonelike families at prior alpha-U grain boundaries (GBs). Surface and cross-sectional morphologies of these hydrides were examined by focused-ion-beam (FIB) milling and scanning electron microscope (SEM). The results showed that, governed by lamellar microstructure, the hydride propagation along the lamellar direction (LD) was observed throughout the hydriding progress. Meanwhile, the preference of spherical hydrides was enhanced by increasing strain energy. The volume expansion induced tensile fields and cracks were found dominating the formation of acicular UH3, and the hydrides could penetrate far into the matrix through the alpha-U lamellae. Furthermore, the hydride growth behaviors and their corresponding hydriding mechanisms in lamellar U-2Nb alloy, covering microscopic and early macro scale, are elucidated in this work.

Uranium-niobium (U-Nb) alloys as structural materials play an important role in nuclear industry. During their utilizing, U-Nb alloys tend to dynamically fracture along the adiabatic shear bands, which affects their performances. In order to understand the formation process and mechanisms, we systematically investigate the adiabatic shear bands formed in U-5.7Nb alloys, where systematical characterization methods were applied, such as optical microscope, scanning electron microscope, and high-resolution transmission electron microscope. Using stopper rings, the U-5.7Nb alloy was impacted by a split Hopkinson pressure bar at a strain rate of 8 000 s-1 to perform seven strain levels. The formation process of adiabatic shear bands in U-5.7Nb alloys was characterized, and we found two types of adiabatic shear bands: the deformed ones together with the transformed ones. They are formed at different stage of severe shear localization. The deformed adiabatic shear bands mainly included highly deformed and elongated grains, and the transformed adiabatic shear bands were basically composed of ultrafine equiaxed grains with size of about 150 nm. High density of dislocations or dislocation cells were found in these ultrafine equiaxed grains. The occurrence of ultrafine equiaxed grains in the adiabatic shear bands of U-5.7Nb alloys was deduced to be rotational dynamic recrystallization mechanism.

The corrosion resistance of uranium to hydrogen has been significantly enhanced by niobium addition while its mechanism remains unknown. To better understanding the underlying effect of niobium addition, behaviours of hydrogen in alpha-U, dilute U-Nb alloy and concentrated U-Nb alloy have been systematically explored by ab-initio calculations and experimental observations. Our findings suggest that Nb atoms play distinct roles in the dilute and concentrated single-phase U-Nb alloys, shifting from hydrogen traps to rapid hydrogen diffusion channels. Moreover, the dominant mechanisms enhancing hydrogen corrosion resistance differ between dilute and concentrated U-Nb alloys.

The βtrans (β transformed microstructure) of a bimodal Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy was refined via high strain rate ( 13.5 s− 1) forging at 900 °C followed with duplex aging (350 °C/1.5, 2, 2.5 h + 600 °C/2.5 h) treatments. The microstructure evolutions, mechanical properties and deformation mechanisms of alloy suffering this processing were studied in detail. Results show that the forging deformation promotes the α→β transformation, dynamic recrystallization and dislocation multiplication of β phase. The yield strength (σ0.2) and ultimate tensile strength (σb) of as-forged alloy are lower than the as-received alloy (σ0.2:1073 MPa, σb:1134 MPa), but the elongation (δ) is increased (maximum to 24

Effects of aging treatment on microstructure, tensile properties, impact toughness and three-point bending properties of as-extruded Mg-6Gd-1Y-0.5Zr alloy were investigated. The significant precipitation strengthening effect was involved after aging treatment at 175 °C, primarily attributed to the β′ phase. The alloy aged at 175 °C for 270 h exhibited the best combination of tensile properties, with yield strength of 252 MPa, ultimate tensile strength of 354 MPa and elongation to rupture of 11.7 1012 tensile twins, with a lesser occurrence in the middle and outer zones. As the precipitates in the alloy increased, both the number and the area fraction of twins near the fracture surface decreased.

In this review, we examine the hydrogen corrosion behavior of uranium and its alloys, with a focus on its impact on their mechanical performance, including hydrogen embrittlement and hydrogen-induced stress corrosion cracking (HISCC). Alloying with elements such as Nb and Mo has been shown to improve hydrogen corrosion resistance of uranium alloys, thereby reducing susceptibility to hydrogen embrittlement and hydrogen-induced stress corrosion cracking. Although studies about uranium hydrogen embrittlement under high strain deformation remain limited, existing evidence suggests that increasing strain rate can alleviate hydrogen embrittlement. The mechanisms underlying hydrogen embrittlement and hydrogen-induced stress corrosion cracking in uranium are still under debate, particularly regarding whether uranium hydrides formation or solid-solution hydrogen plays the dominant role in the embrittlement process. Future research should integrate advanced characterization techniques with multiscale modelling, spanning from atomic scale to continuum scale, to elucidate these mechanisms.

Niobium is introduced to uranium to enhance the corrosion resistance of metallic uranium, while duplex U-Nb alloy exhibits anomalous degradation to hydrogen corrosion. To understand the underlying mechanism, we employed high-resolution transmission electron microscopy (HRTEM) and density functional theory (DFT) calculations to characterize the structure of the phase interface in duplex U-Nb alloy and its interaction with hydrogen and vacancy. Combined with the different behaviors of hydrogen in the two phases of the duplex U-Nb alloy, a mechanism contributing to the observed abnormal degradation is proposed, corroborated by the special distribution of hydride within the duplex U-Nb alloy.