Ni-C Alloys Research Articles

Thermal stability and coarsening of eutectic and near-eutectic Ni–Ce alloys

Ni–Ce alloys are currently being studied as a castable alternative to conventional Ni-based superalloys. To understand the evolution of microstructure and mechanical behavior at elevated temperatures, this study investigates the mechanism of coarsening behavior in eutectic and near eutectic Ni–Ce at 900 °C. The as-cast eutectic Ni–Ce consists of a combination of fine lamellar and rod eutectic colonies with coarser boundary regions. Upon annealing, continuous coarsening, via process of globularization, initiates at colony boundaries or primary dendrites where faults (termination and branches) in the lamellar structure are plentiful. Coarsening then proceeds by a combination of fault migration mechanism and lamellar boundary splitting, growing toward the center of the eutectic colonies with increasing annealing time. Coarsening near the center of a colony is extremely slow, indicating the eutectic microstructure itself is very stable. The near-eutectic alloys containing primary dendrites coarsen and stabilize faster compared to the fully eutectic alloy. Moreover, an anomaly is observed in the hardness of the fully eutectic alloy after long exposure at elevated temperature compared to the near-eutectic alloys.

Effect of loading current on the arc erosion behavior of in-situ composite fiber-reinforced Ag–Cu–Ni–Ce alloy

To reveal the arc erosion behavior of in-situ composite fiber-reinforced electrical contact materials, arc erosion tests of an Ag–Cu–Ni–Ce alloy with the voltage of 24 V DC and a current ranging from 10 to 20 A were performed and the surface morphology, elemental distribution, and mass variations caused by arc erosion were investigated. The results found that, with the increase of load current, the arc erosion ratio and mass loss of contacts gradually increase. With a load current of 10 A, the contact resistance was lower, approximately one mΩ. The direction of material transfer was from the anode to the cathode, and the erosion mechanism was dominated by splashing and evaporation of the anode metal by short arc action. When the load current increased to 12 A, the contact resistance reached the maximum value of 5 mΩ. Then, it gradually decreased with increasing load current. The direction of material transfer was from the cathode to the anode, and the mechanism of erosion was mainly the bombardment of the cathode by gaseous positive ions by the long arc. At the same time, the results of the comparative analysis demonstrate that the in-situ composite fiber-reinforced Ag–Cu–Ni–Ce alloy has excellent arc erosion resistance.

Optimizing thermal stability and mechanical behavior in segregation-engineered nanocrystalline Al–Ni–Ce alloys: A combinatorial study

Optimizing thermal stability and mechanical behavior in segregation-engineered nanocrystalline Al–Ni–Ce alloys: A combinatorial study

Mechanical Loss Spectrum of the Fe-20%Ni-C Alloys in the Temperature Interval 300 K–700 K

Mechanical Loss Spectrum of the Fe-20%Ni-C Alloys in the Temperature Interval 300 K–700 K

Effect of temperature on the mechanical properties of Al–Si–Cu–Mg–Ni–Ce alloy

High-temperature performance is a key factor to concern for the application of cast Al–Si alloys. The evolution of microstructures and mechanical properties of a multiphase Al–Si–Cu–Mg–Ni–Ce alloy during tension in a temperature range from 25 °C (ambient temperature) to 425 °C was investigated. The results show that the main strengthening precipitates of the alloy are θ′ and Q phases. They are stable at 25–250 °C, while dissolve rapidly above 250 °C during tension. The damage initiates and propagates in the form of cracking of brittle phases. The fracture mechanism transforms from quasi-cleavage to coexistence of quasi-cleavage and dimple as temperature increases. The Ce-bearing phase Al20Ti2Ce promotes the damage occurrence below 350 °C while hinders crack propagation at 425 °C. The ultimate tensile strength (UTS) and yield strength (YS) decrease as the tensile temperature increases. The decreasing rate of UTS can be divided into three stages which is associated with the decreasing rate of strengthening precipitates. An empirical constitutive equation is proposed to describe the relationship between UTS and tensile temperature. It provides a good estimation for both cast and wrought Al alloys and the predicted strengths are in good agreement with the experimental results.

Disordered interfaces enable high temperature thermal stability and strength in a nanocrystalline aluminum alloy

Lightweighting of structural materials has proven indispensable in the energy economy, predicated on alloy design with high strength-to-weight ratios. Modern aluminum alloys have made great strides in ambient temperature performance and are amenable to advanced manufacturing routes such as additive manufacturing, but lack elevated temperature robustness where gains in efficiency can be obtained. Here, we demonstrate the intentional design of disorder at interfaces, a notion generally associated with thermal runaway in traditional materials, in a segregation-engineered ternary nanocrystalline Al–Ni–Ce alloy that exhibits exceptional thermal stability and elevated temperature strength. In-situ transmission electron microscopy in concert with ultrafast calorimetry and X-ray total scattering point to synergistic co-segregation of Ce and Ni driving the evolution of amorphous intergranular films separating sub-10 nm Al-rich grains, which gives rise to emergent thermal stability. We ascribe this intriguing behavior to near-equilibrium interface conditions followed by kinetically sluggish intermetallic precipitation in the confined disordered region. The resulting outstanding mechanical performance at high homologous temperatures lends credence to the efficacy of promoting disorder in alloy design and discovery.

Mechanical Loss Spectrum of the Fe-20%Ni-C Alloys at Negative Temperatures

Mechanical Loss Spectrum of the Fe-20%Ni-C Alloys at Negative Temperatures

Improved Absorption and Desorption Kinetics of Mg–Ni–Ce Alloy Activated under Elevated Hydrogen Pressure

Improved Absorption and Desorption Kinetics of Mg–Ni–Ce Alloy Activated under Elevated Hydrogen Pressure

Enhanced hydrogen generation behaviors and hydrolysis thermodynamics of as-cast Mg–Ni–Ce magnesium-rich alloys in simulate seawater

In this study, we developed as-cast (Mg10Ni)1-xCex (x = 0, 5, 10, 15 wt%) ternary alloys by using a flux protection melting method and investigated their hydrolysis hydrogen generation behaviour in simulate seawater. The phase compositions and microstructures of as-cast (Mg10Ni)1-xCex ternary alloys are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with electron energy dispersion spectrum (EDS) and transition electron microscope (TEM). Their kinetics, thermodynamics, rate-limiting steps and apparent activation energies are investigated by fitting the hydrogen generation curves at different temperatures. With increasing Ce content, the (Mg10Ni)1-xCex ternary alloys show increased electrochemical activities and decreased eutectic. When 10 wt% and 15 wt% Ce added, the active intermediate phase of Mg12Ce has been observed. The hydrogen generation capacity of (Mg10Ni)95Ce5 is as high as 887 mLg−1 with a hydrolysis conversion yield of 92%, which is higher than that of Mg10Ni alloys (678 mLg−1) with a yield only 75% at 291 K. The initial hydrolysis reaction kinetics of Mg–Ni–Ce alloys is mainly controlled by the electrochemical activity and the mass transfer channels formed in the alloys. Such a structure-property relationship will provide a possible strategy to prepare Mg-based alloys with high hydrogen conversion yield and controlled hydrolysis kinetics/thermodynamics.

Activity of Ni/CeO2 catalyst for gasification of phenol in supercritical water

An effective Ni/CeO2 catalyst prepared by the polyol reduction method for degrading phenol into CH4, H2 and CO2 in supercritical water (SCW) was developed. About 80% carbon gasification efficiency can be achieved at 525 °C and 60 min with 5 wt% phenol, 0.098 kg/m3 water density and 0.5 g Ni/CeO2/g phenol catalyst, forming CH4 and H2 as the main gaseous products. Comparison study indicated that the efficiency of present Ni/CeO2 catalyst was about 20% higher than that of a commercial catalyst, i.e., Ni/SiO2Al2O3 from Sigma-Aldrich with 65 wt%Ni, at a reaction conditions of 500 °C and 30 min. The characterization analyses of BET, TPR, XRD, XPS and TEM indicated that there was a NiCe alloy formed in Ni/CeO2, which could be important to enhance the activities of the carbon gasification efficiencies and gas yields. A kinetic modelings were conducted and the results showed that the lnA and the activation energy (Ea) of gasification were 7.1 ± 0.5 and 58.1 ± 3.2 kJ/mol for the gaseous product, and were 2.6 ± 0.9 and Ea is 36.6 ± 5.6 kJ/mol for the char formation, respectively. The present Ni-based-metal Ni/CeO2 catalyst is cheaper and has a potential application for the gasification to convert phenol into gases fuels in SCW process.

Influence of Silicon on Nucleation and Growth Process of Spherical Graphite in Ni-C Alloys Solidification Structure

Plasma etching, SEM and quantitative metallographic analysis technology were used to study the influence of Si on nucleation and growth process of spherical graphite in Ni-C alloys solidification microstructure. Pure Si, Ni-Si alloys and Fe-Si alloys were added into Ni-C melts respectively, and the solid microstructures were compared. The density, diameter size and roundness of spherical graphite were studied in this work to reveal the influence of Si on the morphology of graphite. The Ni-C alloy was etched by plasma etch, and the morphologies and composition of graphite nucleus were observed by scanning electron microscope (SEM) and electron energy spectrum analysis (EDS). The results suggested that the high Si melt zone in melt strongly promoted the enrichment and carbide of graphite, which both promoted the nucleation and growth of graphite. The change in Si content had a large effect on the roundness of the graphite, the higher the Si content, the better the roundness of the graphite.

Probing the role of carbon solubility in transition metal catalyzing single-walled carbon nanotubes growth

Metal catalysts supporting the growth of Single Wall Carbon Nanotubes display different carbon solubilities and chemical reactivities. In order to specifically assess the role of carbon solubility, we take advantage of the physical transparency of a tight binding model established for Ni-C alloys, to develop metal carbon models where all properties, except carbon solubility, are similar. These models are used to analyze carbon incorporation mechanisms, modifications of metal/carbon wall interfacial properties induced thereby, and the associated nanotube growth mechanisms. Fine tuning carbon solubility is shown to be essential to support sustainable growth, preventing growth termination by either nanoparticle encapsulation or detachment.

Microstructure and Characterization of Ni-C Films Fabricated by Dual-Source Deposition System

Ni-C composite films were prepared by co-deposition using a combined technique of plasma CVD and ion beam sputtering deposition. Depending on the deposition conditions, Ni-C thin films manifested three kinds of microstructure: (1) nanocrystallites of non-equilibrium carbide of nickel, (2) amorphous Ni-C film, and (3) granular Ni-C film. The electrical resistivity was also found to vary from about 102 μΩcm for the carbide films to about 104 μΩcm for the amorphous Ni-C films. The Ni-C films deposited at ambient temperatures showed very low TCR values compared with that of metallic nickel film, and all the films showed ohmic characterization, even those in the amorphous state with very high resistivity. The TCR value decreased slightly with increasing of the flow rate of CH4. For the films deposited at 200 °C, TCR decreased with increasing CH4 flow rate; especially, it changed sign from positive to negative at a CH4 flow rate of 0.35 sccm. By increasing the CH4 flow rate, the amorphous component in the film increased; thus, the portion of Ni3C grains separated from each other became larger, and the contribution to electrical conductivity due to thermally activated tunneling became dominant. This also accounts for the sign change of TCR when the filme was deposited at higher flow rate of CH4. The microstructures of the Ni-C films deposited in these ways range from amorphous Ni-C alloy to granular structures with Ni3C nanocrystallites. These films are characterized by high resistivity and low TCR values; the electrical properties can be adjusted over a wide range by controlling the microstructures and compositions of the films.

Separation of radiation defects in Ni and Ni-C alloys under electron and neutron irradiation

Complex investigations of radiation damage of Ni and Ni- 880 at. ppm C alloy under electron and neutron irradiation in the region of room temperature hardened and deformed state. In pure nickel, with the deformation microstructure, both in electron and in the neutron irradiation is observed separation of radiation-induced defects. When electron irradiation in the alloy Ni-C separation effect is observed, and when neutron irradiation there is no. This is due to the interaction of carbon atoms with radiation defects. The main sinks for radiation-induced defects are the areas with a high concentration of defects in cascades of atomic displacements.

Electrocatalytic Activity of Nickel-Cerium Alloys for Hydrogen Evolution in Alkaline Water Electrolysis

Nickel-cerium (Ni-Ce) alloys of different compositions were fabricated and evaluated as electrodes for hydrogen evolution reaction (HER) in alkaline media. HER at Ni-Ce electrodes was studied in 8 M KOH solution for temperatures ranging from 25 to 85°C. Polarization curves were recorded using both Ni-Ce alloys and pure Ni electrode, and further analyzed enabling determination of main kinetic parameters. The parameters determined, namely Tafel coefficients, charge transfer coefficients, exchange current densities and activation energies, made possible a direct comparison of the studied electrodes performances for the HER. It was observed that low amounts of Ce in the alloys did not result in significant improvement of the catalytic activity of the Ni-based electrodes. Nevertheless, the present results are encouraging and support further investigation to determine the optimal composition of Ni-Ce alloys for hydrogen evolution.

Nickel and Nickel-Cerium Alloy Anodes for Direct Borohydride Fuel Cells

The borohydride oxidation reaction (BOR) was studied at nickel and nickel-cerium (Ni-Ce, with 5 and 10 at% Ce) alloy electrodes in alkaline media. The samples were prepared by arc-melting and their microstructure and phase composition were determined by scanning electron microscopy and electron probe microanalysis based on energy dispersive X-ray spectroscopy. BOR was investigated using cyclic voltammetry and chronoamperometry and kinetic parameters such as charge transfer coefficients, number of electrons exchanged and standard heterogeneous rate constants, were evaluated. The three studied electrodes exhibited similar performance for BOR with Ni95Ce5 alloy electrode giving the highest current densities. Direct borohydride-peroxide fuel cell (DBPFC) was constructed employing Ni95Ce5 alloy electrode as anode and main cell parameters (e.g., maximum cell voltage, peak power density) were determined. Influence of temperature on the BOR on Ni and Ni-Ce alloy electrodes, as well as on the DBPFC performance was explored in the 25–45°C range. A peak power density of 110 mW cm−2 was obtained at 45°C for a cell voltage of 0.50 V and current density of 219 mA cm−2.

Nickel-Cerium Electrodes for Hydrogen Evolution in Alkaline Water Electrolysis

The electrocatalytic activity of nickel-cerium (Ni-Ce) alloys towards the hydrogen evolution reaction (HER) in alkaline solution has been evaluated. Ni-Ce alloy electrodes with different low amounts of the rare earth element were prepared and tested in 8 M KOH aqueous electrolytes at temperatures ranging from 25 to 85 ºC. Polarization measurements are done to evaluate the HER on the Ni-Ce alloy electrodes and to determine several kinetic parameters, namely the Tafel coefficients, charge-transfer coefficients, and exchange current densities, allowing a direct comparison of the intrinsic HER activity of these electrodes with single Ni metal electrode prepared according to the same procedures

Glass forming ability and primary crystallization behavior of Al–Ni–Ce alloys

Wedge-shaped samples of Al–Ni–Ce alloys were prepared by suction casting with preparation conditions controlled. Glass forming ability (GFA) of the alloys was characterized. The primary crystallization process was investigated by X-ray diffraction and differential scanning calorimetry. The results show that the optimum glass forming composition is located at Al85.5Ni9.5Ce5, but the GFA parameters such as Trg and γ are the highest in Al85Ni8Ce7. The value of the topological instability parameter λ of the Al–Ni–Ce alloy with the best GFA is 0.085 rather than 0.1. The GFA was analyzed from the topological and crystallization points of view.

Application of Density Functional Theory to Point Defect Anelasticity of Carbon-Containing Austenitic Alloys

We have used density functional theory (DFT) to determine binding energies (BE’s) of carbon-vacancy (C-v) point-defect complexes of probable importance to C-based anelastic relaxation processes in fcc iron alloys. Calculations are presented for three types of stable point defect clusters: C-v pairs, di-C-v triplets, and tri-C-v quadruplets. We demonstrate semi-quantitative consistency of the calculated BE’s with internal friction results on Fe-36%Ni-C alloys. The BE’s, which are in the range-0.37 eV to-0.64 eV, were determined for a hypothetical non-magnetic (NM) fcc Fe. The effect of the magnetic state of fcc Fe on some of these quantities was investigated by DFT and is shown to be significant; the BE’s appear to be reduced in antiferromagnetic (AFM) fcc Fe.

Microstructure and mechanical properties of Al–Si–Ni–Ce alloys prepared by gas-atomization spark plasma sintering and hot-extrusion

Al–Si–Ni–Ce alloys with the composition of Al 78.5Si 19Ni 2Ce 0.5, Al 76Si 19Ni 4Ce 1 and Al 73Si 19Ni 7Ce 1 were atomized and then sintered by using spark plasma method. The microstructure of the as-atomized powders, sintered and hot-extruded samples was analyzed. The influences of granularity and sintering parameters including time and temperature on the density of sintered alloy were also discussed. It is shown that the atomized powders are composed of Si, Al 11Ce 3, Al 3Ni and alpha Al. Tiny Al 3Ni particles precipitate from supersaturated matrix near the powder boundaries during SPS. Hot-extrusion process leads to the layer structure and more homogeneous distribution of precipitates. These alloys exhibit high comprehensive mechanical properties with combination of high Vicker's micro-hardness, moderate tensile properties and elongation, which provide a novel kind of promising engineering materials.