Ni-Mo Alloy Research Articles

Influence of Mo Segregation at Grain Boundaries on the High Temperature Creep Behavior of Ni-Mo Alloys: An Atomistic Study.

Based on molecular dynamics simulations, the creep behaviors of nanocrystalline Ni before and after the segregation of Mo atoms at grain boundaries are comparatively investigated with the influences of external stress, grain size, temperature, and the concentration of Mo atoms taken into consideration. The results show that the creep strain rate of nanocrystalline Ni decreases significantly after the segregation of Mo atoms at grain boundaries due to the increase of the activation energy. The creep mechanisms corresponding to low, medium, and high stress states are respectively diffusion, grain boundary slip and dislocation activities based on the analysis of stress exponent and grain size exponent for both pure Ni and segregated Ni-Mo samples. Importantly, the influence of external stress and grain size on the creep strain rate of segregated Ni-Mo samples agrees well with the classical Bird-Dorn-Mukherjee model. The results also show that segregation has little effect on the creep process dominated by lattice diffusion. However, it can effectively reduce the strain rate of the creep deformation dominated by grain boundary behaviors and dislocation activities, where the creep rate decreases when increasing the concentration of Mo atoms at grain boundaries within a certain range.

Interface Catalysis of Nickel Molybdenum (NiMo) Alloys on Two-Dimensional (2D) MXene for Enhanced Hydrogen Electrochemistry.

Development of efficient bifunctional nonprecious metallic electrocatalysts for hydrogen electrochemistry in alkaline solution is of importance to enable commercialization of a low-cost alkaline hydrogen fuel cell and water electrolyzer, but it is very challenging. Two-dimensional (2D) MXene-based electrocatalysts hold tremendous potential for the applications of hydrogen fuel cell and water electrolyzer. Here, we successfully immobilized transition-metal-based NiMo nanoparticles (NPs) on 2D Ti3C2Tx (Tx: surface terminations, such as O, OH, or F) surfaces by a wet chemical method. Our results demonstrate that the NiMo NPs are monodispersed on Ti3C2Tx with surface functionalization. These monodisperse NPs resulted in superior hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) activities in an alkaline media. The NiMo NPs/Ti3C2Tx in 1.0 M KOH yielded an HER current of -10 mA cm-2 at -0.044 V vs reversible hydrogen electrode (RHE), nearly 232 mV smaller than that of the parent NiMo NPs. The NiMo NPs/Ti3C2Tx produced an HOR current density of 1.5 mA cm-2 at 0.1 V vs RHE. Density functional theory (DFT) results further reveal that Ti3C2Tx support can facilitate the charge transfer to metallic NPs and tailor the electronic structure of catalytic sites, resulting in optimized adsorption free energies of H* species for hydrogen electrochemistry. This work provides a facile and universal strategy in the development of 2D Ti3C2Tx with nonprecious metals for low-cost bifunctional hydrogen electrocatalysts.

Pulse/Pulse Reverse Deposition of NiMo Alloys for Improved Molten Salt Reactor Performance

The use of molten fluoride salts as a primary coolant within next generation nuclear reactors has the potential to improve efficiency and nuclear reactor safety by operating at low pressures and high temperatures without boiling. However, these coolants will require the development of new corrosion resistant material systems that will have to meet or supersede existing standard codes for these systems. Therefore, state of the art reactors require validation and testing of new material systems that can produce robust component structures and enable them to withstand these corrosive environments. Furthermore, any next generation process to apply protective coatings must allow for a conformal, thick, dense, and bonded materials to be formed onto any low cost ASME material (like 316H SS) that comprises the structure of heat exchanger and containment vessel components.Within this context, Faraday Technology Inc. is working on developing low cost and high value corrosion-resistant alloy coatings for next generation molten salt reactors with the goal of increasing their functional lifetime, while reducing the component cost. The manufacturing process involves electrodeposition of functionally graded NiMo alloys onto ASME certified substrates and their subsequent high temperature corrosion evaluation in molten fluoride salt electrolytes. A wide array of electrolytes and processing parameters were evaluated in order to understand these effects on the deposit composition, structure, and corrosion resistance properties towards the goal of developing an ideal alloy coating. Specifically, we demonstrated the potential to apply graded NiMo coating to the 316H SS surface (Figure 1) and found that a coating composition of ~25% Mo has the potential to improve the components lifetime. Acknowledgements: The financial support of DOE Contract No. DE-SC0019602 is acknowledged. Figure 1: Top) show a cross-sectional image of a NiMo coated 316HSS component. Bottom) shows composition of Ni (Left/Dashed) and Mo (Right/Solid) as measured by EDX trace from the SEM along the red line (Top image). Figure 1

Effect of rolling deformation on microstructure and properties of Cu–Ni–Mo alloy prepared by aluminothermic reaction

The metallic element Mo has almost no solid solubility in copper and can be used as a nucleation particle to refine the grain size and increase the recrystallization temperature of the alloy during solidification. It is expected to obtain copper alloys with good comprehensive properties by reasonably controlling the addition amount of Mo. However, it is difficult to prepare Cu–Mo alloys with uniform structure and there are few related literatures. In this paper, the aluminothermic reaction method, which has the advantages of simple process, low cost, and large size of the prepared alloy, was adopted, and a cluster model with the atomic ratio of Mo and Ni of 1:12 was introduced to design the alloy composition. Here, five alloys with different copper contents were prepared and followed by room temperature rolling with 40%, 60%, and 80% deformation. The results show that the as-cast Cu–Ni–Mo alloys exhibit good formability, have no macroscopic defects and present a small amount of precipitates. With the increase of alloy elements Ni and Mo, the hardness and strength of the alloys increase obviously, while the electrical conductivity decreases gradually. For the rolled alloys, a large number of lamellar deformed structures are formed, the grains are obviously refined, the precipitated phases are broken and the distribution is more uniform, thus the strength and hardness of the alloy increase significantly, the plasticity decrease significantly, while the conductivity changed little. In this study, high-strength samples were obtained, which may be a valuable exploration for the preparation of Cu–Ni–Mo alloy sheets with excellent microstructure and mechanical properties.

Effect of Support for Non‐Noble NiMo Electrocatalyst in Alkaline Hydrogen Oxidation

AbstractThe development of high‐performance platinum group metal (PGM)‐free electrocatalysts for the hydrogen oxidation reaction (HOR) in anion exchange membrane fuel cells (AEMFCs) remains a great challenge. Here, a novel design strategy for improving the catalytic activity of PGM‐free catalysts by adopting N‐doped large‐porous carbon as a support material is reported. This paper shows the effect of support on the activity of non‐noble NiMo in HOR by comparing NiMo alloy on N‐doped mesocellular carbon foam (NiMo/N‐MSUF‐C) with NiMo/MSUF‐C and NiMo on N‐doped CMK‐3 (NiMo/N‐CMK‐3). The strong interaction between NiMo and N species in N‐MSUF‐C alters the electronic structure of NiMo toward optimal binding energies for H and OH. The large pores in N‐MSUF‐C facilitate the diffusion of OH− into the catalyst layer, thereby increasing the limiting current density, which is higher compared with that of NiMo/N‐CMK‐3. The AEMFC with NiMo/N‐MSUF‐C as the anode shows a higher peak power density of 152 mW cm−2 in H2/O2 compared with that of previously reported PGM‐free catalysts. These results can lead to efficient designing of highly effective AEMFCs for practical applications.

Selective aqueous-phase hydrogenation of furfural to cyclopentanol over Ni-based catalysts prepared from Ni-MOF composite

Metal-organic frameworks (MOFs) as an emerging class of porous materials exhibit some unique advantages, including controllable composition, a large surface area, high porosity, and so on. In this work, the spherical NiMo bimetal catalysts supported on porous carbon matrix were prepared using a simple wet impregnation method and studied for selective hydrogenation of furfural (FFA). Three different catalysts were investigated including Ni/C-Mo-BTC, Ni/C-Mo-DHTA and Ni/C-Mo-PTA. Of the catalysts studied the Ni/C-Mo-BTC catalyst could achieve the highest selectivity of CPL (up to 90%) under moderate reaction conditions (140 °C, 2 MPa, 2 h) in aqueous medium. In addition, other Ni-based catalysts (Ni/C-Fe, Ni/C-Zn, Ni/C-Cu, Ni/C-Ce) were also investigated to achieve yields of 20–70% under the same reaction conditions. The influence of temperature, H2 pressure, time and solvent were investigated for the best performing catalyst. Based on the optimal reaction condition, various of furfural derivatives could also be effectively transferred to produce corresponding products. The detailed physicochemical characterization was carried out by means of XRD, SEM, TEM, XPS, NH3-TPD and Raman analysis. In the end, the optimal Ni/C-Mo0.4 catalyst could be recycled magnetically and efficiently applied in the next run for five consecutive recycling tests in the FFA hydrogenation to CPL. The results suggested Ni/C-Mo0.4 catalyst occurred to increasingly favor the formation of Ni-Mo alloys and suggested a metallic active site in FFA hydrogenation with the addition of element Mo. Mechanism study indicated that water was a key factor contributing to the formation of different desired products, which was responsible for the arrangement of furan compound.

In situ structural reconstruction of NiMo alloy as a versatile organic oxidation electrode for boosting hydrogen production

In situ structural reconstruction of NiMo alloy as a versatile organic oxidation electrode for boosting hydrogen production

Rapid solidification and physical properties of a refractory Mo-Ni alloy under containerless microgravity condition

<p indent="0mm">The solidification kinetics and physical properties of Mo-48%Ni alloy were studied using the free fall technique. The cooling rate and undercooling of this alloy both increased exponentially as the droplet diameter decreased, and they could reach <sc>2.41×10⁴ K s⁻¹</sc> and <sc>322 K</sc> (0.19 <italic>T</italic>_L), respectively. The high cooling rate significantly suppressed the subsequent solid state transformation process. The primary NiMo phase exhibited a morphological transition from coarse dendrite to a remarkably refined structure, and the regular lamellar (Ni+NiMo) eutectics changed into anomalous eutectic. The maximum length of the primary NiMo phase fell from 142.2 to <sc>28.4 μm</sc>, whereas its volume fraction initially rose and then fell, with a maximum of 60.1%. Moreover, the variation in the Mo content of the primary phase coincided well with that of the eutectic structure. As regards mechanical properties, the nanoindentation measurements indicated that the elastic moduli of the primary phase and the eutectic structure both showed a downward trend along with the microstructure evolution. The eutectic hardness decreased monotonously from 14.1 to <sc>8.7 GPa</sc>, whereas the primary phase hardness increased slightly from 8.0 to <sc>8.5 GPa</sc> and finally fell to <sc>5.4 GPa</sc>. In addition, the growth morphology of the (Ni) solid solution within the eutectic structure was shown to have an obvious effect on the magnetic properties of the Mo-48%Ni alloy. As the rate of cooling increased, the saturation magnetization and residual magnetization diminished. The alloy’s coercivity increased from 11.8 to <sc>25.7 A m⁻¹</sc>, indicating enhancement of the temperature resistance induced by microstructure refinement. The rapid solidification under space simulation conditions affected the mechanical and magnetic properties of the Mo-48%Ni alloy to a certain degree.

Cooperative Effects between Ni-Mo Alloy Sites and Defective Structures over Hierarchical Ni-Mo Bimetallic Catalysts Enable the Enhanced Hydrodeoxygenation Activity

Currently, the rational design of non-noble metal catalysts for highly efficient biomass upgrading into biofuels and chemicals is quite desired. In this regard, tuning the oxophilic property of cat...

Establishing relationships between bath composition and the properties of amorphous Ni–Mo alloys obtained by electrodeposition

In this study, the Response Surface Methodology (RSM) was used as an optimization tool along with a complete 3² factorial experimental design with 4 central points to determine the significant factors on the electrodeposition process of Ni-Mo alloys and support establishing relationships between the independent variables and the properties of the coatings. Specifically, the influence of the concentrations of nickel sulfate and sodium molybdate on different electroplating responses was evaluated. The models proposed in this work were validated with experiments performed within the level considered for both entry variables; no experimental combination of any level was considered for this purpose. Coatings with a high Mo percentage and distinct morphologies were produced. XRD diffractograms indicated that they were all amorphous. Variations in nickel sulfate (Ni) and sodium molybdate (Mo) concentrations in the bath produced coatings with different properties. The optimal bath condition found for Mo at% was constituted by a Ni:Mo concentration ratio of 7.5:5, producing a film with 29 at% of Mo. The optimal Ni:Mo for CE% and Rp was 10:3; highest CE% and Rp were 47% and 19,314 Ω/cm², respectively. The films produced in this work can be applied as anticorrosive coatings

Machine learning enhanced empirical potentials for metals and alloys

Interatomic potential (i.e. force-field) plays a vital role in atomistic simulation of materials. Empirical potentials like the embedded atom method (EAM) and its variant angular-dependent potential (ADP) have proven successful in many metals. In the past few years, machine learning has become a compelling approach for modeling interatomic interactions. Powered by big data and efficient optimizers, machine learning interatomic potentials can generally approximate to the accuracy of the first-principles calculations based on the quantum mechanics theory. In this works, we successfully developed a route to express EAM and ADP within machine learning framework in highly-vectorizable form and further incorporated several physical constraints into the training. As it is proved in this work, the performances of empirical potentials can be significantly boosted with few training data. For energy and force predictions, machine tuned EAM and ADP, can be almost as accurate as the computationally expensive spectral neighbor analysis potential (SNAP) on the fcc Ni, bcc Mo and Mo-Ni alloy systems. Machine learned EAM and ADP can also reproduce some key materials properties, such as elastic constants, melting temperatures and surface energies, close to the first-principles accuracy. Our results suggest a new and systematic route for developing machine learning interatomic potentials. All the new algorithms have been implemented in our program TensorAlloy. Program summaryProgram Title: TensorAlloyCPC Library link to program files:https://doi.org/10.17632/w8htd7vmwh.2Code Ocean capsule:https://codeocean.com/capsule/1671487Licensing provisions: LGPLProgramming language: Python 3.7Journal reference of previous version: Comput. Phys. Commun. 250 (2020) 107057, https://doi.org/10.1016/j.cpc.2019.107057Does the new version supersede the previous version?: YesReasons for the new version: This new version is a significant extension to the previous version. Now machine learning approaches and physical constraints can be used together to tune empirical potentials (for example the embedded atom method). Machine learning optimized empirical potentials can be almost as accurate as machine learning interaction potentials but run much faster.Nature of problem: Optimizing empirical potentials with machine learning approaches and physical constraints.Solution method: The TensorAlloy program is built upon TensorFlow and the virtual-atom approach. We successfully developed a route to express the embedded atom method and the angular-dependent potential within machine learning framework in highly-vectorizable form and further enhanced the potentials with physical constraints. Machine learning can significantly boost their performances with few training data.Additional comments including restrictions and unusual features: This program needs TensorFlow 1.14.*. Neither newer or older TensorFlow is supported.

Joining of SiC ceramics using the Ni-Mo filler alloy for heat exchanger applications

In order to meet the sealing demands of SiC heat exchanger, the Ni-Mo filler alloy was designed, prepared and employed to braze SiC ceramics. Wetting behavior of the Ni-Mo filler alloy on SiC ceramics and interfacial microstructure of the brazed joints were systematically characterized using optical observation furnace and XRD, SEM, EDS, TEM, respectively. Flexural strengths of the brazed joints at room temperature and high temperature were measured with four-point flexural strength method. HCl immersion test was performed to evaluate the corrosion resistance of the joints. The Ni-Mo filler alloy exhibited excellent wettability on SiC ceramics. During the process of brazing, SiC reacted with element Ni of the Ni-Mo filler alloy, resulting in the formation of Ni2Si + graphite reaction layer adjacent to the SiC substrate. Ni3Mo3C and Ni2Si compounds were precipitated at the center of brazing seam. When the brazing temperature increased from 1250 ℃ to 1400 ℃, the thickness of Ni2Si + graphite layer increased gradually. The maximum room-temperature flexural strength of 174 ± 33 MPa was obtained when brazed at 1300 ℃ for 40 min. The joints also exhibited stable high-temperature strength and acid corrosion resistance. When the test temperature was 700 ℃, 800 ℃, 900 ℃, the joints gave the strength retention rate of 92.5 %, 79.8 %, 67.2 %, respectively. It was believed that the formation of high melting point phases played an important role. Residual strength of the joints after HCl corrosion exceeded 130 MPa, revealing a good potential for applications in corrosion environment.

DELORO STELLITE 21

Abstract Deloro Stellite 21 (UNS R30021), previously known as Stellite 8, is similar to the medical implant alloy ASTM F75. It is a Co-Cr- Mo-Ni alloy that was developed in the mid-1930s as a corrosion resistant alloy, and rapidly found application as a biocompatible hip implant and denture alloy. This alloy consists of a CoCrMo alloy matrix containing dispersed hard carbides that strengthen the alloy and increase its hardness, but that also decrease its ductility. The type, shape, size, and distribution of the carbides are strongly influenced by the processing history of the alloy, and for this reason, the mechanical properties of Deloro Stellite 21 depend greatly on the manufacturing route and any subsequent heat treatments. This datasheet provides information on composition, physical properties, microstructure, hardness, and tensile properties. It also includes information on corrosion resistance as well as machining. Filing Code: Co-139. Producer or source: Deloro Wear Solutions GmbH.

On the role of failure analysis investigations in alloy development illustrated with case study involving Ni-Mo alloy

During thermo-mechanical processing of a Ni-Mo alloy, three hot-rolled slabs at 1250 °C have been stacked on top of each other during air-cooling. Upon reaching ambient temperature, the middle slab is found to develop a mid-length transverse crack running through the entire thickness. However, no cracks have been detected in the other slabs. It is shown that the middle slab has been embrittled by ordering to Ni4Mo due to comparative slower cooling rate. An investigation of the ordering behavior of stoichiometric Ni4Mo alloy has shown that ordering occurs homogeneously during the earlier stages of thermal aging at elevated temperatures which results in nanosized structure of ordered Ni4Mo domains capable of deforming by twinning and characterized by high strength and high ductility However, due to self-induced recrystallization by grain boundary migration during extended thermal exposure, the homogeneous nanosized structure is replaced by coarse platelets in the matrix and coarse lamellar structure at grain boundaries resulting in severe embrittlement. It is demonstrated that this problem can be combated by doping with either boron or yttrium which tend to segregate at grain boundaries and reduce their tendency toward migration and therefore self-induced recrystallization. Therefore, the desirable nanosized morphology of Ni4Mo is restored in the matrix phase and the lamellar grain boundary morphology is replaced by nanosized layers of Ni-Mo solid-solutions with compositions not susceptible to Ni4Mo ordering. As a result, the doped alloys become able to maintain high strength and high ductility after extended thermal aging at elevated temperatures.

Macroporous Array Induced Multiscale Modulation at the Surface/Interface of Co(OH)2/NiMo Self‐Supporting Electrode for Effective Overall Water Splitting

AbstractOutstanding electrocatalysts for high‐efficiency water splitting demand not only the high intrinsic activity determined by the electronic structure but also a favorable mass transfer (electrolyte diffusion and bubble desorption) and strong structural stability. Here, a 3D core–shell electrocatalyst consisting of Co(OH)2 cavity array‐encapsulated NiMo alloy on the flexible carbon cloth substrate (Co(OH)2/NiMo CA@CC) is proposed. Density functional theory reveals that coupling NiMo with Co(OH)2 can better optimize the water adsorption/dissociation and hydrogen adsorption energies in hydrogen evolution reaction, and also accelerate the kinetics of oxygen evolution reaction. Based on this, the open porous structure of the outer Co(OH)2 cavity array further promotes the diffusion of the electrolyte into the heterogeneous interface between NiMo and Co(OH)2, significantly shortening the electron transfer pathways and exposing multiple active sites. In addition, the macroporous array structure accelerates the bubble evolution and desorption process, thus ensuring a rapid mass transfer. When served as bifunctional electrocatalysts toward alkaline overall water splitting, Co(OH)2/NiMo CA@CC delivers a current density of 10 mA cm−2 at a low cell voltage of 1.52 V. Results support the multiscale optimization of the surface/interface engineering induced by the macroporous array.

Correction to: Stepwise Microstructure Development and Investigation of Mechanical Behavior of Pure Mo, Mo-Ni, and Nano-Y2O3-Dispersed Mo-Ni Alloys Fabricated by Mechanical Alloying and Pressureless Sintering

Correction to: Stepwise Microstructure Development and Investigation of Mechanical Behavior of Pure Mo, Mo-Ni, and Nano-Y2O3-Dispersed Mo-Ni Alloys Fabricated by Mechanical Alloying and Pressureless Sintering

Phase, microstructure and service character of as-deposited and short-time heat-treated Ni-Mo alloys with mixed state.

Considering the amorphous and nano-crystalline cluster structure and their activity, on the basis of the mixed structure Ni-Mo alloys, the crystallization kinetics of the alloys and the performance of the alloys after heat treatment with different mixed structure were studied. The phase structure and composition were determined by X-ray powder diffraction. The crystallization activation energy of the mixed structure was obtained by differential scanning calorimetry. The electrochemical activity of the mixed structure alloy was determined by electrochemical analysis. The experimental results show that the structural stability of the mixed-structure alloy is better, but the crystallization activation energy is much lower than that of the amorphous alloy. The crystallization process consists of a meta-stable structure transition and a new phase formation. The electrochemical properties of the alloy indicated that the alloy with the mixed structure has higher electrochemical activity, with higher hardness and better corrosion resistance, which results from the large true contact surface and the large number of active centers in this material structure.

Electrocatalytic properties for the hydrogen evolution of the electrodeposited Ni–Mo/WC composites

The catalytical activity for the hydrogen evolution reaction (HER) of the electrodeposited Ni–Mo/WC composites is examined in 1 M KOH solution. The structure, surface morphology and surface composition is investigated using the scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The electrocatalytic properties for the HER is evaluated based on the cathodic polarization, electrochemical impedance, cyclic voltammetry and chronopotentiometry methods. The obtained results prove the superior catalytic activity for the HER of Ni–Mo/WC composites to Ni–Mo alloy. The catalytic activity of Ni–Mo/WC electrodes is determined by the presence of WC nanoparticles and Mo content in the metallic matrix. The best electrocatalytic properties are identified for Ni–Mo/WC composite with the highest Mo content and the most oxidized surface among the studied coatings. The impedance results reveal that the observed improvement in the catalytic activity is the consequence of high real surface area and high intrinsic catalytic activity of the composite.

Stepwise Microstructure Development and Investigation of Mechanical Behavior of Pure Mo, Mo-Ni, and Nano-Y2O3-Dispersed Mo-Ni Alloys Fabricated by Mechanical Alloying and Pressureless Sintering

Stepwise Microstructure Development and Investigation of Mechanical Behavior of Pure Mo, Mo-Ni, and Nano-Y2O3-Dispersed Mo-Ni Alloys Fabricated by Mechanical Alloying and Pressureless Sintering

High-efficient electrocatalyst of MoNi4@MoO3-x nanorod for hydrogen evolution reaction in alkaline solutions

Hydrogen evolution reaction (HER) in alkaline media is expected to become a renewable and economical technology for hydrogen production. Various non-noble electrocatalysts have been explored for HER, in which Ni-Mo alloy is one of the best media. However, its syntheses are complicated and costly. In this work, we contribute an in-situ reduction method of porous MoNi4@MoO3-x nanorods. The synthesized MoNi4@MoO3-x exhibits a remarkable HER activity with 10 mA/cm2 constant current under 58.6 mV extremely low overpotential, small Tafel slope of 44.8 mV/decade, and high durability in 1 M potassium hydroxide electrolyte. Its remarkable activity is found to originate from the highly activity of MoNi4, excellent conductivity and favorable porous structure. This work is believed to provide a promising strategy for the HER development of highly active and cost-effective electrocatalysts.