Behaviour of hydrogenated lead–lithium alloy

Eutectic Pb–Li (lithium 15.6 at.%) alloy has been tested by means of thermogravimetric analysis under different hydrogenation conditions in the temperature range 25–650 °C. The melting temperature of the material changes irreversibly after the first heating ramp, from that of the eutectic alloy (240 °C) to that of pure lead (330 °C). The capacity to upload hydrogen depends on the thermal cycling and on the humidity presence. Particularly, it has observed that the presence of water traces in the environment leads to the formation of lithium hydroxide. This reaction affects dramatically the hydrogen uploading of the Pb–Li. Such a behavior is discussed in details by considering the change of weight of the Pb–Li along hydrogenation and thermal cycling.     

Electrochemical corrosion of an AlMgCrMn alloy containing Fe and Si in inhibited alkaline solutions

The electrochemical corrosion of Al2.7%Mg0.19%Cr0.04%Mn alloy containing 0.27% Fe and 0.14% Si, using open-circuit potential measurements, corrosion rate determinants, potentiodynamic and galvanostatic transients and anode efficiency experiments together with optical microscopy, scanning electron microscopy, transmission electron microscopy and energy dispersion X-ray has been studied to ascertain the effect of Cr and Mn. The experiments were performed at 25 and 50 °C in non-deaerated and stirred 4 M KOH containing K₂MnO₄ and combinations of NaVO₃, NaBiO₃, NaMoO₄, ZnO and Al₂O₃. The open-circuit potentials were rapidly stabilized in values in the range between −1.4 and −1.6 V versus Hg/HgO/OH⁻ (4 M KOH). The alloy dissolution at open circuit and also in the galvanostatic and potentiodynamic experiments were shown to be uniform, this being correlated with the homogeneous distribution of Mg in the material. The anodic oxidation took place with the formation and dissolution of a conducting aluminium oxide film. However, limiting values were found over which the anode became passivated. The limiting values depended on the temperature, being about 125 and 500 mA cm⁻² at 25 and 50 °C, respectively. The anode efficiencies were sufficiently high, that is over 90%, only at current densities approaching the limiting value at the corresponding temperature. The anode passivation was related to an excess of Cr and the anode corrosion to an excess of Mg together with the presence of Fe and Si.     

Electrochemical properties of melt-spun Al–Si–Mn alloy anodes for lithium-ion batteries

Al_60−XSi₄₀Mn_X (X = 0, 1, 3, 5, 7 and 10 at.%) ribbons were prepared by melt spinning. A supersaturated solid solution of Si and Mn in fcc α-Al with very fine microstructures have been obtained in the ribbons. The electrochemical measurements have revealed that the Al–Si–Mn alloys with some compositions can exhibit a high Li inserting specific capacity and stable cycle performance. A specific capacity of more than 500 mAh g⁻¹ and the cycle efficiency of 90% have been achieved in melt-spun Al₅₅Si₄₀Mn₅ and Al₅₃Si₄₀Mn₇ alloys after 10 cycles. An ordered phase, δ′ (Al₃Li), seems to be formed in the alloys after Li inserting, whereas no other compounds with Li have been detected. It is evident that the supersaturated solid solution plays the main role in improving the specific capacity and cycle performance. Refinement of grains could facilitate the diffusion of Li atoms. The coexistence of multi-phases has limited the alloy volume expansion during Li inserting. As a result, a high-specific capacity and a stable cycle performance have been achieved.     

Predicting hydrogen storage capacity of V–Ti–Cr–Fe alloy via ensemble machine learning

The V–Ti–Cr–Fe quaternary alloy is a promising hydrogen storage material for excellent performances, but it is difficult to take reliable multi-factor synergistic effects into account by means of experiments. At present, using the data-driven innovation method of ensemble learning, the structure-property relationship of V–Ti–Cr–Fe alloy is built and the maximum hydrogen absorption capacity is accurately predicted as well through 19 features covering the composition and various crystal parameters with the mean square error of 0.187. The feature importance ranking indicates that valence electron concentration, lattice constant, and Z/r³ play a critical role in the prediction. The genetic algorithm is furtherly used to propose 3 optimal composition ranges, which are proved to be accurate by experiments with relative errors of around 1%. The present work could provide an effective way for accurate and rapid prediction of hydrogen storage capacity and rational design of high-performance alloys.     

Evaluation of Laves-phase forming Fe–Cr alloy for SOFC interconnects in reducing atmosphere

A Laves-phase forming Fe–Cr alloy was evaluated as interconnects for solid oxide fuel cells (SOFCs) in reducing atmosphere (in H₂-H₂O). The oxide scale growth was compared between Laves-phase forming alloy and typical stainless steel (SUS430). The oxide scale growth rates were decreased in the Laves-phase forming alloy, and the area-specific resistance (ASR) of oxidized Laves-phase forming alloy showed the lower values than that of SUS430. The temperature dependence of 1/ASR for the oxidized alloy was different between Laves-phase forming alloy and SUS430. The oxygen diffusivity in the oxide scale was also evaluated by the stable isotope oxygen (¹⁸O₂) diffusion in the scale. The chemical diffusion coefficients of isotope oxygen in the oxide scale showed the smaller value for the Laves-phase forming alloy (D = 7.0 × 10⁻¹³ cm² s⁻¹) than that for SUS430 (D = 4.6 × 10⁻¹² cm² s⁻¹) at 1073 K. A relatively high diffusivity of oxygen was estimated in the Mn–Cr spinel oxide on the top surface of oxide scales. Inward diffusion of oxygen and outward diffusion of cation in the oxide scale were discussed to consider the oxide scale growth mechanism.     

Hydrogenation and dehydrogenation cycle properties of Ti–Mn based alloy Ti0.93Zr0.07Mn1.15Cr0.35 in hydrogen gas

Hydrogenation and dehydrogenation cycle tests at 0 °C for Ti_0.93Zr_0.07Mn_1.15Cr_0.35 were carried out 2000 cycles and more in the hydrogen gas with purity of 99.99% and 99.99999%. The capacity maintenance rates at the 2000th cycle for the first cycle were 82% and 97% for each purity hydrogen gas, respectively. It was found that the cycle durability of this alloy depends on the gas purity. By the X-ray diffraction and light element analysis, it was confirmed that the C14 type crystal structure of this alloy was maintained but the nitrogen concentration in the sample with large capacity reduction was increased after the cycle test. The main factor of the decrease in capacity of this alloy is degradation due to reaction with impurity gas components such as nitrogen.     

Synchrotron EXAFS and XRD studies of Ti–V–Cr hydrogen absorbing alloy

We reported extended X-ray absorption fine structure (EXAFS) measurements at the Ti, V and Cr K-absorption edges in a Ti–V–Cr alloy before and after hydrogen charging. The results indicated that all the bond lengths increased significantly after hydrogenation, and Ti atoms interacted strongly with V, while V and Cr atoms interacted weakly. The Ti and V atom's coordination numbers in hydrogenated alloy decreased obviously in comparison with the pre-hydrogenation situation. X-ray diffraction (XRD) patterns demonstrated that the structure of Ti–V–Cr alloy had transformed from BCC to FCC during hydrogenation. In addition, we investigated the nanoparticle size distribution in the as-cast and hydrogenated Ti–V–Cr alloy by small-angle X-ray scattering (SAXS) technique.     

Effect of temperature on microstructure and texture of rolled Ni–9·3 at-%W alloy

Abstract

In the present paper, the microstructure and texture of cold rolling and warm rolling Ni–9·3 at-%W alloy were investigated by electron backscatter diffraction technique. It is found that warm rolling will reduce the deformation twins and transfer the rolling texture from brass type to copper type. The forming mechanism of rolling microstructure and texture of Ni–9·3 at-%W alloys as well as the temperature effects was discussed.     

Characterisation of as cast model Mn–Si–Cr–Ni steels for reactor pressure vessel applications

Abstract

Initial results are reported from a study aimed to investigate the role and influence of the elements Cr, Ni, Mn and Si on the radiation stability of reactor pressure vessel steels. Twelve as cast model ferritic steels with basic composition typical of those used in Russian WWER-1000 and Western PWR reactor pressure vessel materials were subjected to Charpy impact, magnetic Barkhausen noise (MBN), Vickers hardness tests and SEM examination. Higher Cr content in model steels was found generally to give increased RMS values independent of Mn and Si contents. The ductile–brittle transition temperatures (DBTT) and hardness values of the model steels were found to be independent of composition. Two steels, with low concentration of Ni and high concentration of Cr or vice versa , showed high transition temperatures (?16 and ?42°C respectively). An additional heat treatment to improve the properties is being considered for these compositions. The correlation between DBTT and MBN results has potential for rapid determination of the effect of composition and irradiation on the steel properties. The next stage of the assessment will investigate the effect of irradiation of the model steels to accumulated neutron fluences of ～10¹⁹ cm^?2.     

Hydrogen-induced softening of Ti–44Al–6Nb–1Cr–2V alloy during hot deformation

The effect of hydrogen on the hot deformation behavior and microstructural evolution of Ti–44Al–6Nb–1Cr–2V (at.%) alloys were investigated at temperature range of 1373–1523 K under strain rate of 0.01 s^?1. The true stress–strain curves show that the peak stress decreases from 323 MPa to 97 MPa when deformation temperature increases from 1373 K to 1523 K. The peak stress is decreased by 30% after hydrogenation with 2% H, which corresponds to the decrease of deformation temperature by about 50 K, it denotes that hydrogen can promote a solution softening effect in TiAl alloys. This is attributed to hydrogen-promoted the dynamic recrystallization, hydrogen-induced dislocation movement and hydrogen-stabilized the B2 phase. For dynamic recrystallization, the calculated results show that hydrogen accelerates the onset of dynamic recrystallization, which means that hydrogen promotes the dynamic recrystallization kinetics. For dislocation movement, EBSD results show that the fraction of low-density dislocation region increases from 59.6% to 79.7% after hydrogenation with 2% H, which indicates that hydrogen reduces the dislocation tangles and dislocation density. For B2 phase, more softening B2 phases are observed in hydrogenated alloy compared with that in unhydrogenated alloy, which results from hydrogen-promoted the transition of L (α₂/γ) → γ + B2. The positive effect of hydrogen on TiAl alloys provides an effective method to improve the hot workability of TiAl alloys.     

Microstructural evolution and hydride precipitation mechanism in hydrogenated Ti–6Al–4V alloy

Use of hydrogen as a temporary alloying element in titanium alloys is an attractive approach for enhancing processability, and also for controlling the microstructure and improving final mechanical properties. In this study, the α + β titanium alloy, Ti–6Al–4V, was hydrogenated with hydrogen levels of 0.1, 0.3 and 0.5 wt%. The microstructure, phases and phase transformations were investigated by optical microscopy, X-ray diffraction and transmission electron microscopy. The results showed that the hydrogen addition had a noticeable influence on the microstructure of Ti–6Al–4V alloy. Hydrogen stabled the β-phase and leaded to the formation of hexagonal close packed α′ martensite as well as face-centered cubic δ hydride. Microstructural evolution and hydride precipitation mechanism in hydrogenated Ti–6Al–4V alloy was revealed.     

Ameliorated microstructure and hydrogen absorption/desorption properties of novel Mg–Ni–La alloy doped with MWCNTs and Co nanoparticles

Based on the positive influence of carbon materials and transition metals, a new type of Mg-based composites with particle size of ～800 nm has been designed by doping hydrogenated Mg–Ni–La alloy with multi-walled carbon nanotubes (MWCNTs) and/or Co nanoparticles. The microstructures, temperature related hydrogen absorption/desorption kinetics and dehydrogenation mechanisms are investigated in detail. The results demonstrate that MWCNTs and Co dispersedly distribute on the surface of Mg–Ni–La particles after high-energy ball milling due to powders’ repeated cold welding and tearing. The experimental samples exhibit improved hydrogen storage behaviors and the addition of MWCNTs and Co can further accelerate the de-/hydriding kinetics. For instance, the Mg–Ni–La–Co sample can absorb 3.63 wt% H₂ within 40 min at 343 K. Dehydrogenation analyses demonstrate that the positive effect of MWCNTs is more obvious than that of Co nanoparticles for the experimental samples. The addition of MWCNTs and Co leads to the average dehydrogenation activation energy of experimental samples decreasing to 82.1 and 84.5 kJ mol^?1, respectively, indicating a significant decrease of dehydrogenation energy barriers. In addition, analyses of dehydrogenation mechanisms indicate that the rate-limiting steps vary with the addition of MWCTNs and Co nanoparticles.     

Stress measurement of MlNi4.5Cr0·45Mn0.05 alloy during hydrogen absorption-desorption process in a cylindrical reactor

Hydrogen stored in a solid state form of metal hydrides offers a safe and efficient storage technique for hydrogen application. In a closed metal hydride tank, stresses may occur on the tank wall due to hydride expansion during hydrogen absorption process. In the present investigation, a novel testing system for stress evolution of MlNi_4.5Cr_0.45Mn_0.05 alloy in a closed cylindrical reactor during hydrogen absorption-desorption process was built. The results show that considerable swelling stress is developed on the inner reactor wall during activation process though a high free space of 45% is presented. Increasing hydrogen charging pressure and alloy loading fraction increase the as-generated swelling stress. The metal hydride particle expansion caused by hydrogen absorption is the intrinsic factor for swelling stress evolution. The presence of particle agglomerate in a closed tank in which its expansion is constrained is responsible for the observed swelling stress accumulation.     

Effect of V content on hydrogen storage properties and cyclic durability of V–Ti–Cr–Fe alloys

Vanadium-based body-centered-cubic (BCC) alloys are ideal hydrogen storage media because of their high reversible hydrogen capacities at moderate conditions. However, the rapid capacity decay in hydrogen ab-/desorption cycles prevents their practical application. In this work, V-based BCC alloys with three different V contents (V₂₀Ti₃₈Cr_41.4Fe_0.6, V₄₀Ti_28.5Cr_30.1Fe_1.4, V₆₀Ti₁₉Cr₁₉Fe₂, named as V20, V40, V60) were prepared by arc melting, and their microstructures and hydrogen ab-/desorption properties were investigated systematically. XRD results show that there is a number of C15-Laves phase presence in V20, which does not appear in V40 and V60. Meanwhile, the lattice constant of the BCC phase clearly decreases as the V content rises. These differences result in a hydrogen storage capacity of only 1.82 wt% for V20 alloy, but 2.13 wt% for V40 and 2.14 wt% for V60, and an increment in hydrogen ab-/desorption plateau pressure. The V40 and V60 alloys are chosen in de-/hydrogenation cycle test owing to higher effective storage capacities, and the results show that the V60 alloy has better cycle durability. According to the microstructural analysis of the two alloys during the cycles, the micro-strain accumulates, the cell volume expands, the particles pulverizes and the defects increase during the cycles, which eventually lead to the attenuation of the hydrogen storage capacity. The increment of the V content obviously improves the elastic properties of the alloy, which further diminishes the micro-strain accumulation, cell volume expansion, particle pulverization and defect increase, eventually resulting in a higher capacity retention and better cyclic durability.     

Characterization of high strength and high toughness Ni–Mo–Cr low alloy steels for nuclear application

The reactor pressure vessels of PWRs have mostly been made of SA508 Grade 3 (Class 1) low alloy steels which have revealed moderate mechanical properties and a moderate radiation resistance for a 40 or 60 year operation. The specified minimum yield strength of the material is 345 MPa with a ductile–brittle transition temperature of about 0 °C. While other materials, most of which are non-ferrous alloys or high alloyed steels for a higher temperature application, are being developed for the Generation-4 reactors, low alloy steels with a higher strength and toughness can help to increase the safety and economy of the advanced PWR systems which will be launched in the near future. The ASME specification for SA508 Grade 4N provides a way to increase both the strength and toughness by a chemistry modification, especially by increasing the Ni and Cr contents. However, a higher strength steel has a deficiency due to a lack of operating data for nuclear power plants. In this study, experimental heats of SA508 Grade 4N steels with different chemical compositions were characterized mechanically. The preliminary results for an irradiation embrittlement and the HAZ properties are discussed in addition to their superior baseline properties.     

Influence of high pressure hydrogen on the tensile and fatigue properties of a high strength Cu–Al–Ni–Fe alloy

Aluminum bronze CW307G was tensile and fatigue tested in 10 MPa hydrogen, 10 MPa helium and 0.1 MPa air atmosphere. Neither tensile nor S–N fatigue properties were affected when testing in H₂. Fractography on the fatigue specimens revealed similar striation morphology on the specimens tested in H₂ and He. Dissociative chemisorption as well as hydrogen absorption were identified as potential rate limiting processes being responsible for the impassivity to HEE of this alloy.