Molybdenum Alloy Research Articles

The origin of exceptionally large ductility in molybdenum alloys dispersed with irregular-shaped La2O3 nano-particles

Molybdenum and its alloys are known for their superior strength among body-centered cubic materials. However, their widespread application is hindered by a significant decrease in ductility at lower temperatures. In this study, we demonstrate the achievement of exceptional ductility in a Mo alloy containing rare-earth La2O3 nanoparticles through rotary-swaging, a rarity in Mo-based materials. Our analysis reveals that the large ductility originates from substantial variations in the electronic density of states, a characteristic intrinsic to rare-earth elements. This characteristic can accelerate the generation of oxygen vacancies, facilitating the amorphization of the oxide-matrix interface. This process promotes vacancy absorption and modification of dislocation configurations. Furthermore, by inducing irregular shapes in the La2O3 nanoparticles through rotary-swaging, incoming dislocations interact with them, creating multiple dislocation sources near the interface. These dislocation sources act as potent initiators at even reduced temperatures, fostering diverse dislocation types and intricate networks, ultimately enhancing dislocation plasticity.

Implementation and Verification of a Micro-Jet-Vane System of a Solid Rocket Motor for a Micro-Nano Satellite

To achieve rapid vector maneuvering of a space micro-nano satellite, a micro-sized solid rocket motor was utilized as its propulsion system, and a micro-jet-vane-thrust-vector control system was devised. Computational fluid dynamics (CFD) numerical simulations were conducted on the designed micro-vane structure at various deflection angles to ascertain the lateral force and flow field characteristics. The motor’s combustion temperature is 1380 K. Therefore, materials such as 45 steel, alumina ceramics, and tungsten–molybdenum alloy were chosen for the jet vanes to carry out ground-based-motor-jet-ablation experiments and measure the ablation amount. Concurrently, experimental data, including lateral force, were gathered. The tests demonstrated that despite 45 steel having a higher melting point than the combustion temperature significant ablation still occurred. Alumina ceramics exhibited defects and experienced ablation and fragmentation post-test. In contrast, tungsten–molybdenum alloy, being a refractory metal, showed minimal ablation after testing, making it an ideal material for micro-jet vanes. At a 20° deflection of the jet vanes, the lateral force calculated via numerical simulation was 3.76 N, whereas the lateral force obtained from the test was approximately 3.8 N, resulting in an error within 1% and validating the numerical simulation’s validity and accuracy. The jet vanes can generate a maximum steering angle of 8°, thus ensuring the micro-nano satellite’s swift vector maneuvering at large angles.

Effects of filler materials on the microstructural characteristics and mechanical properties of laser-welded lap joints of TZM alloys

The poor weldability of molybdenum (Mo) alloys has always been the main problem that impedes their application as large-sized structural components. Two types of laser-welded lap joints, namely LW-Ti and LW-Nb joints, were prepared using titanium (Ti) and niobium (Nb) as filler materials to investigate the alterations in microstructures and mechanical properties of TZM (Mo-0.5Ti-0.08Zr-0.02C) alloy joints. The results indicate that both Ti and Nb have excellent metallurgical compatibility with Mo, resulting in well-formed joints. Due to solid-solution strengthening, the microhardness of the fusion zone (FZ) significantly increases from 269.9 HV to 397.1 HV for LW-Ti joints and reaches 389.6 HV for LW-Nb joints. Furthermore, the shear strength of LW-Ti joints is approximately 2.05 times that of LW-Nb joints, measuring at 110.97 MPa. Fractures in LW-Ti joints primarily occur at the base metal (BM) and display lamellar ductile fracture characteristics, while fractures in LW-Nb joints mainly occur at the FZ and exhibit coarse brittle intergranular fractures. The mechanical properties of LW-Nb joints are compromised due to the larger maximum pore diameter (300 μm) in the FZ compared to LW-Ti joints (50 μm), which can be attributed to the higher viscosity of liquid niobium. Additionally, the average grain size in the FZ of LW-Nb joints (86.37 μm) is larger than that in LW-Ti joints (53.28 μm). The reduction in grain size observed in LW-Ti joints also increases the grain boundary area, decreases oxygen concentration along the grain boundaries, and enhances binding strength at Mo grain boundaries. Given Ti's stronger affinity for oxygen compared to Mo, the abundant formation of second-phase TiO2 particles within LW-Ti joints hinders the specific formation of MoO2 along grain boundaries. Consequently, the proposed welding technology was employed to weld a large-scale cylinder-flange component made from Mo alloy, which is expected to greatly facilitate the widespread utilization of welded structures made from Mo alloys.

A direct evidence for lattice selective rotation of molybdenum alloys single crystals in tensile deformation

The Mo-Nb-W-Zr quaternary single crystals were prepared using the electron beam floating zone melting technique. Samples fractured under tension were sectioned along the axial direction. The results revealed an absence of the single crystal-to-polycrystal transition during the tensile process. However, there was a noticeable alteration in crystal orientation between regions near and far from the fracture site. Upon analyzing three distinct regions, it was observed that the axial crystal plane index gradually shifted from the original (-1–11) towards the direction of (-110), passing through (-2–21), (-3–31), and (-4–41). The fracture occurred precisely when the crystal plane twisted to this (-110) direction. This implies that {110} represents a lattice-selective rotation for molybdenum-based single crystal torsion when subjected to stretching along the <111> direction.

First-principles study of behaviors of point defects in Mo-14 Re alloy

Molybdenum alloys with rhenium additions of 14 % (Mo-14 Re) are regarded as structural materials for advanced nuclear reactors. The performance of Mo-14 Re alloy under irradiation is crucial for its application. Irradiation performance is related to the behaviors of point defects produced by irradiation. The behaviors of point defects in Mo-14 Re alloy were investigated using first-principles methods in this work. Compared with the results in pure Mo alloy, the formation energy and the migration energy of vacancy in Mo-14 Re were both reduced, and the migration energy of interstitial dumbbell increased while the formation energy decreased in Mo-14 Re. In Mo-14 Re, vacancy preferred to form and diffuse faster in Re-enriched environment. Knowing the number of Re atoms in the 1NN (first nearest neighbor) shell of the vacancy and saddle point, the vacancy formation energy and migration energy can be estimated. Since the interstitial atom has a certain orientation, the distribution of the atoms around it is anisotropic. To estimate the interstitial formation energy, it was necessary to count the number of Re atoms at the tensile and compressive sites at the 1NN shell around the interstitial. The interstitial motion was three-dimensional (3D) in Mo-14 Re. At 1200 K, the diffusion coefficient of Re atom was a little higher than that of Mo atom, which could lead to the segregation of Re atoms at defect sinks and the formation of Re-enriched phase. It is possible to investigate the longer-term evolution of microstructure using cluster dynamics (CD) or kinetic monte carlo (KMC) techniques based on these results.

Evaluation of Efficacy of MV Loop for En masse Anterior Retraction as Compared to Opus and Snail Loop Using Finite Element Method and Clinical Intervention: A Research Protocol

Abstract Background: In orthodontics, space closure after extraction is crucial. Frictionless mechanics in preadjusted “edgewise appliance” treatment in orthodontics are better alternatives to friction mechanics. The major benefit is dissipation of force, a high M: F ratio and a low load-deflection rate which is not there in friction mechanics. The retraction loops are Snail loop, Opus loop, K Sir loop, L loop etc. which are used as force system in frictionless mechanics. Objectives: To evaluate and compare the efficacy of Multiple Variability (MV) loop for qualitative and quantitative en masse anterior retraction as compared to Opus and Snail loop. Materials and Methods: The study will be carried out in the Department of Orthodontics and Dentofacial Orthopaedics, Sharad Pawar Dental College, Sawangi (M), Wardha with the technical assistance from NIT Engineering College, Pune. MV loop, Opus loop and Snail loop will be fabricated in “0.019 × 0.025, 0.017 × 0.025 inch Titanium Molybdenum alloy (TMA) and 0.017 × 0.025 inch Stainless Steel (SS) wire” with 1 and 2 mm preactivation bends will be analysed on Finite element method (FEM) Software. Then clinical trials will be carried out based on qualitative and quantitative assessment of records for evaluation of MV loop, opus loop and Snail loop. Expected Results: The FEM analysis and clinical trials will predict the perfect design of loop with adequate preactivation bends. Mainly on data access layer (DHAL) analysis MV loop showed 10:1 Moment to Force (M:F). Similar results are expected on FEM analysis and clinical trials. MV loop will show superior results as compared to Opus and Snail loop. Conclusion: Loop mechanics provide efficient intrusion and retraction in extraction cases. A loop to be effective and efficient needs to clinically as well as mechanically evaluated. MV loop was fabricated to fulfill all the requirements of loop. Clinical evaluation of loop will provide complete effectiveness of loop.

Interfacial coherence regulation and stabilization of molybdenum/Kovar alloy welded joint by CoCrCuFeNi high entropy alloy

The crux of molybdenum/Fe-base alloy welded joint is embrittlement and consequently deteriorated strength. The current researches just attribute it to brittle intermetallic compound inside the weld. However, no brittle phase continuously precipitates at the fracture location of the molybdenum/Kovar alloy electron beam welded joint, meaning that the unstable phase interface is the real fundamental reason for the brittleness of joint, instead of the phases themselves. Noncoherent interfaces are formed between α-Mo and eutectoid α-Fe + μ(Fe3Mo2) deriving from solid-state phase transition. To optimize interfacial coherence and stabilize the interface, CoCrCuFeNi high entropy alloy is added into the weld. The new interfaces between α-Mo and eutectic face-centered cubic (fcc) + laves are transformed into coherent interfaces. σ(FeCr) nanoparticles precipitate at α-Mo/fcc interface, indicating the decreased interfacial energy and more stable interface. The tensile strength of the joint is increased from 262 to 366 MPa. The present work provides guidance for optimizing welding quality between molybdenum and Fe-base alloy.

In English

The total reorganization energy of the system and its components, the solvent reorganization energy and the transformation energy of reactants (water clusters [(H2O)nOH]-), during electrocatalytic hydrogen evolution on binary alloys of molybdenum with iron subgroup metals (Fe, Co, Ni) in an alkaline medium (30 wt. % NaOH solution) have been calculated. The calculated values of the solvent reorganization energy and the reorganization energy of water clusters are in agreement with the Marcus – Dogonadze – Kuznetsov theory. The dependence of the total reorganization energy of the system, the solvent reorganization energy, and the reorganization energy of discharging species (water clusters) on the electrolyte temperature has been calculated. It was shown that the total reorganization energy of the system and the activation energy of the electron-transfer reaction of electrocatalytic hydrogen evolution (HER) on binary alloys of molybdenum with iron subgroup metals in an alcaline vedium (30 wt. % NaOH solution) decrease linearly with increasing electrolyte temperature in the following order: Fe-54 at. % Mo &gt; Ni-54 at. % Mo &gt; Co-52 at. % Mo. The temperature dependences of the water cluster discharge reorganization energy and the activation energy on binary molybdenum alloys are linear and intersect in the boiling point region of 30 wt. % NaOH solution 384.7 K. At this temperature, the electrode process is limited by the diffusion of regenerating water clusters to the electrode surface. The calculated diffusion activation energy Ad is 9.9 kJ·mol–1. The value of the system reorganization energy lt is 39.8 kJ·mol–1, which is consistent with the theory of Markus – Dogonadze – Kuznetsov. Electrocatalytic activity of binary alloys of molybdenum with iron subgroup m

A European manufacturing line for monolithic U–Mo bare foil production

The nuclear research reactor Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II), operated by the Technical University of Munich (TUM) in Germany, provides intense thermal neutron beams for the international scientific community. The uranium fuel currently used for the compact core is an assembly of fuel plates composed of dispersed U3Si2 powder with an enrichment up to 93%, dispersed in aluminium (Al) powder and cladded with an Al alloy. Within the international efforts to minimise the usage of HEU (Highly Enriched Uranium), the FRM II aims to convert its compact core to LEU (Low Enriched Uranium), i.e., a fuel with an enrichment in 235U lower than 20%. The most promising candidate is the metallic monolithic uranium–molybdenum alloy (U–Mo) with zirconium (Zr) coating and Al-based cladding. Here, we show the first European pilot line for U–Mo bare foil manufacturing, implemented in collaboration with the European fuel manufacturer Framatome-CERCATM in Romans-sur-Isère, France. This line involves innovative manufacturing processes, including casting, laser welding, hot rolling, and laser cutting. An overview of the bare foil development with the first results is presented, including visual inspections of foils produced from the hot rolling, the laser cutting and the manufacturing tools used. These first depleted uranium (DU) bare foils are analysed to extract the best manufacturing parameters for future industrialisation. This European manufacturing process gives an alternative solution to the US development for U–Mo monolithic bare foil manufacturing. It represents the first step for European monolithic fuel manufacturing, which could push other European research reactors to use the monolithic U–Mo for their conversion.

In Vitro Comparison to Evaluate Metal Ion Release: Nickel-Titanium vs. Titanium-Molybdenum Orthodontic Archwires.

Background When metals used in orthodontic materials are exposed to the oral environment, teeth, and gingivae over an extended period of time, they may gradually deteriorate. As a result, the patient is exposed to higher concentrations of metals and metal ions than what they would be exposed to through food and other sources. The goal of the current in vitro experiment was to evaluate and contrast the metal ion release from orthodontic archwires made of titanium-molybdenum alloy (TMA) and nickel-titanium (NiTi). Methods For 90 days, 20 orthodontic archwires in each group were immersed in 50 milliliters of simulated saliva using different containers. Atomic Absorption Spectrometry (AAS) (Shimadzu Corporation, Kyoto, Japan) was used to assess and compare metal ion emission. The unit of measurement is parts per million (PPM). Results The findings indicated that the discharge of nickel metal from the NiTi archwire (Group A) was much higher than that from the TMA archwire (Group B), with a statistical significance level of p < 0.001. It was discovered that Group B's release of titanium was statistically significantly (p < 0.05) higher than Group A's titanium release, which did not include the release of any other metals. Conclusion The study findings indicated that the amounts of metal ions released from the orthodontic archwires made of titanium molybdenum and nickel-titanium alloy were within safety limits.

Orientation-dependent ion-irradiation responses in molybdenum and molybdenum-rhenium alloys

Helium ion-irradiation responses in molybdenum (Mo) and molybdenum-rhenium (Mo-Re) alloys at room temperature were evaluated via micro-pillar compression. Irradiation-induced hardening is closely dependent on orientation in Mo-Re alloys with low Re content, while is weak orientation-dependence on high Re alloys. Irradiated pillars with [100] orientation all shows higher flow stresses than pillars with [110] orientation after yield, which is distinguishing from pillars before irradiation that has been shown in our previous work. High density of dislocation loops and helium bubbles after irradiation at room temperature induces severe hardening in Mo. Voids / small loops induced by irradiation lead to less hardening in Mo-Re alloy than in Mo. No precipitation is observed in all samples, which may be attributed to low irradiated temperature and implantation energy.

Current-carrying tribological behavior of copper alloy matrix and molybdenum alloy coating at high current density

Improving the current-carrying friction and wear resistance of copper alloy current-carrying friction subsets effectively is a hot topic. In this paper, a method of preparing high melting point molybdenum-based coating on copper alloy surfaces by laser cladding technology is presented. A large current (106 A/m2) comparison experiment is carried out with a self-made current-carrying friction device, and the failure mechanism is analyzed. The results show that the molybdenum-based coating significantly improves the adhesion problem between the friction partner and the copper alloy substrate, while the thickness of the stress layer caused by the current-carrying friction is reduced by about 7 times. The molybdenum-based coating significantly reduces the surface arc rate and has a lower friction interface temperature, thus retaining the Al2O3 self-lubricating phase. The research in this paper is expected to provide extended research ideas for the surface protection of current-carrying friction subsets of copper alloys.

Influences of Si-Ti combined alloying on microstructures and properties of laser welded socket joints of molybdenum

This study selected silicon (Si) and titanium (Ti) as alloying elements to explore influences of the Si:Ti mass ratio on performance of molybdenum bead on plate laser welded joints. When the Si:Ti ratio was 1:1, the silicides exhibited a uniform continuous distribution, and significantly increased room temperature tensile strength of molybdenum bead on plate from 48 MPa to 231.6 MPa. In addition, Si-Ti combined alloying was applied to Mo tube-end plug socket joints with the optimal Si:Ti ratio. Results showed that Si and Ti were uniformly distributed in the weld of laser welded socket joints. Addition of Si and Ti in the weld increased the fraction of low-angle grain boundaries (LAGBs), which was conducive to improving the bonding strength of grain boundaries. The second-phase particles Mo3Si and Ti5Si3 were observed in the weld after adding Si and Ti, which played a role in second-phase strengthening. The room-temperature tensile strength of laser welded socket joints of Mo with the Si:Ti mass ratio of 1:1 reached 301 MPa, and the joint showed mixed fractures. The fractures in the FZ exhibited morphologies of cleavage fractures, while those in the heat affected zone (HAZ) showed mixed morphologies of intergranular and cleavage fractures. Finally, the results of high-temperature nanoindentation creep testing showed that after applying a load of 8 mN for 600 s at 400℃, the creep displacement of the LW-socket joint was measured at 20.28 nm, whereas the LW-SiTi socket joint exhibited a creep displacement of only 6.63 nm. The research findings of this paper provide references for alloying methods in laser welding of molybdenum and molybdenum alloys.

Functional characterization of biomechanical loading and biocorrosion resistance properties of novel additively manufactured porous CoCrMo implant: Comparative analysis with gyroid and rhombic dodecahedron

Notably, successful clinical outcomes of additively manufactured porous metallic implants require careful consideration of factors such as porosity, pore size, and pore interconnectivity. Applying the SLM technique in Cobalt chrome molybdenum (CoCrMo) alloy fabrication has shown excellent results for prosthetic restorations. However, the corrosion performance of 3D-printed interpenetrating lattices or a combination of minimal surface and strut lattices such as BD.05 (both based on TPMS and struts lattice cells) remains unexplored. This study explores additively manufactured BD.05 structures using CoCrMo as a bulk biomaterial to address the stiffness mismatch, a common cause of stress shielding between implants and bones. Comparative characterization of TPMS-based gyroid and stress lattice-based Rhombic dodecahedron (RH) shows a distinct deformation pattern under quasi-compressive loading. The gyroid exhibits higher yield stress (126.05 MPa), followed by BD-0.5 (25.46 MPa) and RH (9.36 MPa). BD.05 shows an impact strength of 3.17 ± 0.03J/cm2 and a microhardness of 556HV1. Electrochemical measurements demonstrate the inherent corrosion resistance of the fabricated structures. This indicates the appropriate and successful promise of these lightweight interpenetrating-based lattice metamaterial implants in orthopedic applications.

Corrosion-induced changes in surface properties and roughness of orthodontic wires

This study aimed to investigate the surface free energy and surface roughness (SR) of metallic alloys under the influence of acid solutions. The experiment involved the use of 270 rectangular wire samples measuring 0.019 × 0.025-in. These samples were sourced from 3 different commercial brands: Dentsply GAC, American Orthodontics, and Orthoclassic. This invitro study categorized the samples into 3 groups based on the solutions employed: deionized water, citric acid, and phosphoric acid. Each group consisted of 90 samples, with 30 samples representing each type of alloy-stainless steel, nickel-titanium, and titanium molybdenum alloy (TMA). The wire segments were immersed in their respective solutions for 72 hours at a controlled temperature of 37°C, with continuous orbital agitation at 130 rpm. After the immersion period, the study analyzed both surface free energy and SR. The mean values obtained were subjected to an analysis of variance at a significance level of 5%. All alloys displayed hydrophobic behavior, as indicated by interaction free energy values<0. In acidic environments (phosphoric acid and citric acid), significant differences were observed among different brands and alloys, affecting surface energy and interaction free energy. Variations in SR among metallic alloys included steel with the lowest SR variations, followed by nickel-titanium and TMA. Notably, the TMA alloy stood out with significantly higher surface energy compared with that of the other alloys (P<0.001). In this study, all examined alloys demonstrated a hydrophobic nature, suggesting a limited attraction to water. Notably, TMA exhibited the least hydrophobic behavior among the alloys studied. However, when exposed to citric acid, TMA displayed the most substantial alterations in its surface properties. These results underscored the significance of accounting for the distinctive properties of each alloy and their responses to diverse challenges, such as exposure to acidic solutions, during the selection of orthodontic wires for orthodontics treatment.

Effect of the addition of titanium filler on high temperature strength and microstructural characteristics of laser welded tube-end plug socket joints of molybdenum alloy

Three types of Mo alloy socket joints were prepared in this study: a joint without alloying (LW joint), a joint with a trace amount of titanium (Ti) added to the fusion zone (FZ) (LW-Ti-A joint), and a joint with Ti separately added to the FZ and the heat affected zone (HAZ) (LW-Ti-B joint). Tensile tests were carried out on the three types of joints at 360, 900, and 1200 °C. The results showed that the tensile strengths of the base metal (BM) of the Mo tubes were 368.7, 239.9, and 189.6 MPa at 360, 900, and 1200 °C, respectively. At all temperatures, the tensile strengths of the welded joints increased in the order of LW, LW-Ti-A, and LW-Ti-B, which indicates that adding Ti to the FZ and HAZ separately had an obvious strengthening effect. The fracture positions of the joints were primarily affected by the Ti alloying scheme. The LW joints are always fractured at the FZ, showing brittle intergranular fractures; the LW-Ti-A joints fractured at the BM or the HAZ near the FZ; and the LW-Ti-B joints fractured at the BM far from the FZ, exhibiting ductile fracture. Adding Ti to the FZ can induced a solid-solution strengthening effect, which refined the grain size in the FZ by approximately 30–40% and reduced the amount of Mo oxide on the grain boundaries in the FZ, thus improving the joint strength. Presetting a Ti foil on the overlapping interface in the HAZ realized metallurgical bonding between the Mo tube and Mo end plug in the HAZ of the laser-welded joints, enlarge the bearing area, and improve the joint strength. And a new metallurgical bond zone is formed on the overlapping interface in the HAZ during the high-temperature tensile tests of the welded joints, which further improve the joint strength.

Excellent combination of strength and elongation of TZM alloys achieved by c-ZrO2 and single cross rolling

In this study, new TZM-xZrO2 (x = 0, 0.5, 1, 1.5) (wt%) alloys were designed by powder metallurgy solid-solid mixing method combined with single cross rolling. The results show that c-ZrO2 in TZM alloys was mainly spherical, and the average size of c-ZrO2 particle increases gradually from 1.28 μm to 1.71 μm with the increase of its content. c-ZrO2 can effectively refine the molybdenum grain and adsorb the free brittle element O in grain boundaries in the form of TiO2 layer. The interface was composed of three phase: c-ZrO2, Y2O3 and TiO2, with the presence of [0−11] c-ZrO2 ǁ [−11−2] Y2O3 ǁ [−10−3] TiO2 crystal relationship. The rolled plates mainly exist 〈100〉//ND and 〈111〉//ND two kinds of grain orientation, the addition of c-ZrO2 particles promote <100>//ND orientation ratio, thus weakening the texture strength (maximum pole density value from 8.34 to 5.39), conducive to the improvement of plasticity. When the c-ZrO2 content was 0.5 wt%, the best performance was achieved, with good strength and elongation (ultimate tensile strength: 958 MPa; Elongation: 17.3%), showing excellent strength and elongation product (16.6 GPa·%), 31% higher than TZM alloy, better than most reported molybdenum alloys. With the further increase of c-ZrO2 content, the particles gradually coarsened, the hindering effect on dislocations was weakened, and it was easy to become the nucleation site of main cracks, resulting in the decrease of strength and plasticity. Fine grain strengthening and dislocation strengthening were important factors to improve the strength. The excellent ductility was mainly due to the deflection mechanism of microcracks and the blocking effect of grain boundary enrichment on crack propagation.

Surface-sulphurated nickel–molybdenum alloy film as enhanced electrocatalysts for alkaline overall water splitting

Nickel-molybdenum (NiMo) alloys are a kind of promising HER electrocatalysts to supersede precious metal based materials due to their highly active hydrogen evolution reaction (HER) kinetics in alkaline solution. However, the poor stability of NiMo, caused by the Mo dissolution mainly due to the thermodynamically instability of Mo in alkaline media, significantly limits its practical applications. Herein, a facile strategy is developed to modify the surface of the electrodeposited NiMo alloy film via a simple surface sulphuration treatment. Material characterizations show that the NiS homogeneously covers the surface of the NiMo alloy, resulting in a NiS/NiMo heterostructure. Electrochemical measurements show that the NiS/NiMo heterostructure exhibits outstanding HER activity (η-10 mA cm-2 = 77 mV) and good stability for 24 h stability test. Surprisingly, the heterostructure also displays excellent OER kinetics by delivering an ultra-low overpotential of 245 mV (10 mA cm−2). The constructed electrolyzer with NiS/NiMo acted as both cathode and anode needs only 1.547 V to power the water splitting at 10 mA cm−2. The formation of heterostructure and the enhanced electrochemically active surface area are responsible for the exceptional HER/OER electrocatalytic performance. This work offers a simple way to build sulfide/alloy heterostructures to improve the electrocatalytic activity of electrocatalysts.

Accelerating Hydrogen Desorption of Nickel Molybdenum Cathode via Copper Modulation for Pure‐Water‐Fed Hydroxide Exchange Membrane Electrolyzer

AbstractThe more sluggish kinetics of hydrogen evolution catalysts in base as compare to that in acid to some degree restricts hydrogen production performance of hydroxide exchange membrane electrolyzers, especially when using earth‐abundant catalysts. Here a ternary nickel–copper–molybdenum hydrogen evolution catalyst is reported that exhibits ≈5 times higher turnover frequency than without copper doping. The X‐ray absorption near‐edge structure and valence band spectrum demonstrate that the light doping of copper into nickel–molybdenum alloy modulates the electronic structure and downshifts the d‐band center, resulting in accelerated hydrogen desorption, as consolidated by H2 temperature programmed desorption and theoretical calculation. An electrolyzer employing this cathode catalyst and a nickel–iron anode, gives a current density of 1.7 A cm−2 at 2.0 V with a pure‐water feed through the anode, which outperforms the 2025 target proposed by the United States Department of Energy, and even is operated continuously for over 1000 h with a decay rate of as low as 0.5 mV h−1. Post‐mortem analysis discloses that hydroxide exchange ionomer migration is one of the key factors affecting long‐term durability. This work demonstrates the feasibility of a low‐cost, water‐fed hydroxide exchange membrane electrolyzer achieving industrial‐level performance and lifetime.

Effect of Electron Beam Oscillation Welding of Molybdenum and Titanium

Electron beam welding of pure molybdenum (Mo) and titanium alloy (Ti-6Al-4V) was performed with beam oscillation. The effects of beam oscillation with offset on the welded joints were analyzed in terms of microstructure, element distribution, chemical composition, microhardness, and tensile strength. The results showed that the fusion zone expanded with beam oscillation. Reaction layers were generated in both joints welded with and without beam oscillation. The thickness of the reaction layers decreased along the perpendicular direction. The reaction layers were (Mo, Ti) solid solutions. Both welded joints consisted of single-phase Mo, the β-Ti phase, and Mo-Ti solid solutions. The microhardness distribution of the joint welded with beam oscillation was more consistent than that of the joint welded without beam oscillation, and the maximum hardness was reduced from 340 HV to 270 HV. The tensile strength increased from 124 MPa to 204 MPa.