In present study,the microstructure,mechanical and electrochemical properties of aluminum-graphene nanoplatelets(GNPs) composites were investigated before and after extrusion.The contents of graphene ...nanoplatelets(GNPs) were varied from 0.25 to 1.0 wt.%in aluminum matrix.The composites were fabricated thorough powder metallurgy method,and the experimental results revealed that Al-0.25%GNPs composite showed better mechanical properties compared with pure Al,Al-0.50%GNPs and Al-0.1.0%GNPs composites.Before extrusion,the Al-0.25%GNPs composite showed ~13.5%improvement in ultimate tensile strength(UTS) and ~50%enhancement in failure strain over monolithic matrix.On the other hand,Al-0.50%GNPs and Al-0.1.0%GNPs composites showed the tensile strength lower than monolithic matrix.No significant change was observed in 0.2%yield strength(YS) of the composites.However,the extruded materials showed different trends.The0.2%YS of composites increased with increase in GNPs filler weight fractions.Surprisingly,UTS of composites with 0.25 and 0.50%GNPs was lower than monolithic matrix.The failure strain of the baseline matrix was enhanced by ~46%with 0.25%graphene nanoplatelets.The superior mechanical properties(in terms of failure strain) of the Al-0.25%GNPs composite maybe attributed to 2-D structure,high surface area and curled nature of graphene.In addition,the corrosion resistance of pure Al and its composites reinforced with 0.5 and 1.0 wt%GNPs was also investigated.It was found that the corrosion rate increased considerably by the presence of GNPs.
Outstanding mechanical properties of graphene nanoplatelets (GNPs) make them ideal reinforcement for mass production of composites. In this research, the composites were fabricated by stir-casting ...method. GNPs were added in 1.5 and 3.0 wt.% into Mg–3wt.% Al–1wt.% Zn (AZ31) magnesium alloy. As cast ingots were preheated for one hour and extruded at 350 °C with extrusion ratio of 5.2:1. As extruded AZ31-GNPs composites were micro-structurally characterized with X-ray diffraction, optical microscopy and scanning electron microscopy. Vickers micro-hardness of synthesized materials was investigated both in parallel and perpendicular to extrusion directions. Room temperature mechanical testing revealed that with increasing GNP's content, tensile fracture strain was remarkably increased without significant compromise in tensile strength. Furthermore, as extruded AZ31-3GNPs composites were subjected to tensile testing at temperatures ranging from 75 °C to 300 °C with initial strain rate of 2 × 10−3 s−1 to evaluate high temperature formability of composite. It was found that like CNTs, GNPs also have the potential to sustain tensile strength at high temperatures.
Based on the experimental data of phase diagram and thermodynamic properties, the U-Sn system was assessed using the CALculation of PHAse Diagrams (CALPHAD) method. The Redlich-Kister model was used ...for the description of the liquid phase. A set of self-consistent thermodynamic parameters describing all condensed phases was obtained. The calculated results in this work are in good agreement with available phase equilibria data and thermodynamic data. The tentative U-Zr-Sn ternary system was constructed by extrapolation method and the available ternary experimental data from literature can be reasonably reproduced using the current thermodynamic description.
Co-adsorption of multi-components in ZrCo-based hydrogen storage materials can lead to a number of synergistic effects, such as the modification of adsorption sites, and further worsen the hydrogen ...storage capability. In this work, we explore the co-adsorption of H and CO on the ZrCo(110) surface and find that the molecular CO can be adsorbed on the clean alloy surface and thus decrease the hydrogen storage ability of the alloy. Moreover, CO occupies the adsorption site of H and therefore prevents the adsorption and diffusion into the interior of the lattice. Fortunately, the Hf dopant reduces the number of adsorption sites of the CO molecule and inhibits the formation of carbides to a certain extent. In addition, the partial density of states (PDOS) result shows that there is almost no interaction between the s orbital of H and the s orbital of Co on the pure surface of pre-adsorbed CO, while on the Hf-doped surface of pre-adsorbed CO, the s orbital of H overlapped greatly with the s orbital of Co, indicating that Hf doping inhibits CO toxicity in the interaction between H and the surface. Hence, the doping of Hf has the effect of giving resistance to CO toxicity and is conducive to the adsorption of H.
Zirconium alloys are subjected to a fast neutron flux in nuclear reactors, inducing the creation of a large number of point defects, both vacancy and self-interstitial. These point defects then ...diffuse and can be trapped by their different sinks or can cluster to form larger defects, such as vacancy and interstitial clusters. In this work, the trapping capability of small-vacancy clusters (two/three vacancies, V2/V3) in the α-Zr doped with alloying elements (Sn, Fe, Cr, and Nb) has been investigated by first-principle calculations. Calculation results show that for the supercells of α-Zr containing 142-zirconium atoms with the two-vacancy cluster, alloying elements of Sn and Nb in the second vacant site (V2) and Cr in the first vacant site (V1) are more easily trapped by two vacancies, respectively. However, the two sites are both captured more easily by two vacancies for Fe in the supercells of α-Zr containing 142-zirconium atoms inside due to the similar value of the Fermi level. For the supercells of α-Zr containing 141-zirconium atoms with the three-vacancy cluster, the alloying element of Sn in the third vacant site (V’3), Fe in the first vacant site (V’1), and Cr and Nb in the second vacant site (V’2) are more easily trapped by three vacancies, respectively.
In a fusion environment, tungsten, a plasma-facing material in a reactor, is subject to the irradiation of high-energy neutrons, generating a large amount of displacement damage and transmutation ...products (such as rhenium, Re). We studied the evolution of defects under irradiation in W and W-Re systems using the density functional theory (DFT) and rate theory (RT) method. The results indicate that the evolution of irradiation defects is mainly affected by the irradiation dose, dose rate, and temperature. During irradiation, loops form first in W, followed by the generation of voids, which are due to the different migration energies of point defects. Higher dose rates result in a higher density and larger size of defects in tungsten. Higher temperatures cause a decrease in void density and an increase in size. The results obtained at 600 °C were in good agreement with the reported TEM data. In W-Re alloys, it is indicated that the formation of loops is delayed because Re suppresses the nucleation of loops. The dynamic introduction of Re in W stabilizes the growth of defects compared to W-Re alloys, suggesting that transmuting elements have less detrimental effects on irradiation than alloying. As defect densities and sizes were quantified under different irradiation conditions, the results provide data for the multi-scale simulation of the radiation damage and thermal/mechanical properties in plasma-facing materials under fusion conditions.
U
3
Si
2
is a potential accident-tolerant fuel (ATF) due to its high thermal conductivity and uranium density relative to UO
2
. The grain size and distribution play an essential role in the service ...performance of U
3
Si
2
. However, the grain evolution is quite complicated and remains unclear, which limits further application of U
3
Si
2
in the ATF assembly. In the present work, a phase-field model is employed to investigate the nucleation and growth of grains in U
3
Si
2.
Our results show that the number of grains rises rapidly at the nucleation stage until they occupy the whole system. After that, the grain radius and area continue to grow, and the grain number decays. The grain area increases in time according to the linear law, while the mean grain radius increases with time in a power law form with the scaling growth exponent z = 0.42, which is quite close to the theoretically predicted value. Finally, we performed statistical analysis and found that the grain size evolution of U
3
Si
2
obeys Rayleigh distribution. Our simulation not only elucidates the nucleation and evolution of grains in U
3
Si
2
during the thermal treatment process unambiguously but also provides a fundamental study on the investigation of grain growth, subdivision, and even amorphization in the irradiated condition, which is very important for U
3
Si
2
used as ATF in the light water reactor.
Abstract
The effects of Nb concentration and temperature on the generalized stacking fault energy (GSFE) of basal, prismatic I, pyramidal I and II plane for Zr-Nb alloys are investigated by molecular ...dynamics simulations (MD). The stable and unstable SFEs of different slip systems show no significant change with the increasing Nb concentration (0, 0.5, 1.0, 1.5, 2.0, and 2.5 at.%) in Zr-Nb alloys at 0 K. Basal, pyramidal I and II planes slip of Zr-Nb alloys prefer to deform by full dislocation with the temperature increases. Additionally, plastic deformation anisotropy of Zr-Nb alloy is improved with the increasing temperature using both embedded atom method (EAM) and angular-dependent potentials (ADP). The present work provides a theoretical basis for understanding enhanced plasticity of Zr-Nb alloys under finite temperature.
Due to the superior thermal conductivity and high uranium density, U
3
Si
2
is an excellent candidate for conventional UO
2
nuclear fuel and shows great potential application in accident-tolerant ...fuel (ATF) assembly of light water reactors (LWRs). Currently, the behavior of Xe bubbles with internal or applied stress is rarely investigated, restricting further understanding of swelling in U
3
Si
2
. The mesoscopic phase-field method has been developed in this work to study the spatial and temporal Xe bubble evolution in U
3
Si
2
. The results show that the bubble density and its average size increase as the fission rate increases. Applied stress accelerates the nucleation and growth of gas bubbles, reshaping the bubbles’ morphology from spherical in a stress-free state into elongated along the applied direction in a stressed state. The gas bubbles in a local dislocation stress field nucleate preferentially at stress-concentrated sites and spread over the whole system in succession, and the bubble coarsening is controlled by the stress overlap of the dislocation pair. The results show a practical phase-field method for Xe bubble evolution study in U
3
Si
2,
which can be expanded into swelling behavior investigation in other fuels and lay a solid foundation for the development of ATF assembly.
•Electron–phonon coupling shows its obvious effect when unconnected subcascades dominate.•Electron–phonon coupling can restrict the generation of large defect clusters that contributes to subcascade ...formation.•With increasing the capacity of electron–phonon coupling, more defects survive.
Molecular dynamics (MD) is an important tool for investigating primary radiation damage in materials. Electronic effects, including electronic stopping power (se) and electron–phonon coupling (EPC), have a significant influence on high-energy radiation damage in many metals. Based on MD, this study investigated the role played by electronic effects on the collision cascade in α-zirconium (α-Zr). The results show that when the dominant type of cascades is unconnected subcascades, EPC obviously affects the evolution of collision cascades. The incorporation of EPC can promote the generation of subcascades, which reduces large defect clusters. Furthermore, more defects survive when EPC is applied, where the number of residual defects increases with the capacity of EPC. In contrast, the application of se on low-energy atoms impels the aggregation of the defects into large clusters. However, both EPC and se only slightly affect the spatial distribution of the defect clusters. The influence of cutoff energy choice on the simulation results was also discussed.
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