Fe Ni Al Alloy Research Articles

Modification of short-range repulsive interactions in ReaxFF reactive force field for Fe–Ni–Al alloy* *Project supported by the National Magnetic Confinement Fusion Energy Research Project (Grant Nos. 2019YFE03120003, 2018YFE0307100, and 2017YFE0302500) and the National Natural Science Foundation of China (Grant Nos. 11975034, 11921006, 12004010, and U20B2025).

The short-range repulsive interactions of any force field must be modified to be applicable for high energy atomic collisions because of extremely far from equilibrium state when used in molecular dynamics (MD) simulations. In this work, the short-range repulsive interaction of a reactive force field (ReaxFF), describing Fe–Ni–Al alloy system, is well modified by adding a tabulated function form based on Ziegler–Biersack–Littmark (ZBL) potential. The modified interaction covers three ranges, including short range, smooth range, and primordial range. The short range is totally predominated by ZBL potential. The primordial range means the interactions in this range is the as-is ReaxFF with no changes. The smooth range links the short-range ZBL and primordial-range ReaxFF potentials with a taper function. Both energies and forces are guaranteed to be continuous, and qualified to the consistent requirement in LAMMPS. This modified force field is applicable for simulations of energetic particle bombardments and reproducing point defects' booming and recombination effectively.

Positron Annihilation Spectroscopy of the Accumulation of Vacancy Defects in an Aging Fe–Ni–Al Alloy Irradiated at 573 K

The influence of intermetallic Ni3Al precipitates on the accumulation of vacancy defects in aged Fe–Ni–Al alloy at the initial stages of electron irradiation (5 × 10–4 dpa) at a temperature of 573 K has been studied using positron annihilation spectroscopy. The obtained results demonstrate that intermetallic precipitates inhibit the process of the accumulation of vacancy defects under irradiation. It has been found that these precipitates facilitate the mutual recombination of point defects that form under irradiation. This effect has been attributed to elastic stresses at the precipitate–matrix boundaries.

Effect of Cu on Nanoscale Precipitation Evolution and Mechanical Properties of a Fe-NiAl Alloy.

The microstructural evolution of precipitation in two model alloys, Fe-NiAl and Fe-NiAl-Cu, was investigated during aging at 500°C for different times using atom probe tomography (APT). The APT results reveal that the addition of Cu effectively increases the number density of NiAl precipitates. This is attributed to Cu promoting the nucleation of NiAl particles by increasing the chemical driving force and decreasing the interfacial energy. The NiAl precipitates of the Fe-NiAl-Cu alloy grow and coarsen at a slower rate than that of the Fe-NiAl alloy, mainly due to the slower diffusion rate of the Cu atoms. The mechanical properties of the two alloys were characterized by Vickers hardness and tension tests. It was found that the addition of Cu results in the formation of core-shell precipitates with a Cu-rich core and a NiAl shell, leading to a dramatic improvement of peak hardness and strength. The effect of Cu on precipitation strengthening is discussed in terms of chemical strength and coherency strength.

Dynamic aging in an Fe–Ni–Al alloy upon megaplastic deformation. Effect of the temperature and deformation rate

The method of Mossbauer spectroscopy has been used to investigate the effect of the temperature and the rate of megaplastic deformation on the processes of dissolution–precipitation of intermetallic compounds in aging austenitic alloy with a composition of Fe–36Ni–9Al. It has been established that, upon deformation in revolving Bridgman anvils, in the temperature range of cryogenic temperatures (liquid nitrogen) up to 573 K, a change occurs in the character of phase transitions from atomic disordering and the dissolution of intermetallic compounds to their additional accelerated precipitation. The factor that affects the kinetics of the processes of dissolution–precipitation of intermetallic compounds in the metallic matrix is dynamic aging. Dynamic aging is activated with an increase in the temperature and a decrease in the deformation rate.

Formation and evolution of intermetallic nanoparticles and vacancy defects under irradiation in Fe[sbnd]Ni[sbnd]Al ageing alloy characterized by resistivity measurements and positron annihilation

In this paper, we study the effects of intermetallic nanoparticles like Ni3Al on the evolution of vacancy defects in the fcc FeNiAl alloy under electron irradiation using positron annihilation spectroscopy. Electrical resistivity measurements have been used as a testing method for characterizing the evolution in the underlying precipitate microstructure due to heat treatment and irradiation. It was shown that the nanosized (∼4.5 nm) intermetallic precipitates homogeneously distributed in the alloy matrix caused a several-fold decrease in the accumulation of vacancies as compared to their accumulation in the pre-quenched alloy. This effect was enhanced with the irradiation temperature. The irradiation-induced growth of intermetallic nanoparticles was also observed in the pre-quenched FeNiAl alloy under irradiation at 573 K. Thus, resistivity measurement and positron confinement in ultrafine intermetallic particles, which we revealed earlier, provided the control over the evolution of coherent precipitates, along with vacancy defects, during irradiation and annealing.

The anomalous diffusion processes “dissolution-precipitation” of THE γ′ Phase Ni3Al in AN Fe–Ni–Al alloy during low-temperature deformation

An anomalous deformation-induced dissolution of the intermetallics Ni3Al in the matrix of austenitic Fe–Ni–Al alloy has been revealed in experiment at cryogenic temperatures (down to 77K) under high pressure torsion. The observed phenomenon is explained as the result of deformation-stipulated migration of interstitial atoms from a particle into the matrix in the stress field of moving dislocations. With increasing the temperature of deformation, the dissolution is replaced by the deformation-induced precipitation of the intermetallics, which is accelerated due to a sufficient amount of point defects in the matrix, gained as well in the course of deformation at lower temperatures.

Positron-annihilation studies of the influence of nanodimensional intermetallic precipitates on the evolution of radiation defects in the Fe–Ni–Al alloy

The influence of precipitates of the Ni3Al intermetallic compound on the accumulation of vacancy defects in the aged Fe–Ni–Al alloy upon electron irradiation has been studied by the method of positron annihilation spectroscopy. The samples of the alloy with different initial microstructures (quenched, aged under different conditions) were irradiated at temperatures of 300 and 423 K to a damaging dose of 5 × 10–4 displacements per atom (dpa), after which they were isochronously annealed in the temperature range of 300–850 K. The results obtained have shown that the presence of particles of the intermetallic precipitates leads to the retardation of the accumulation of vacancy defects. The rate of accumulation substantially depends on the irradiation temperature. Furthermore, the effect of precipitates depends on the size, density, and type of particles. An analysis of the experimental data has shown that this effect is caused by the presence of elastic stresses at the precipitate–matrix boundaries.

Stable and inexpensive electrodes for the hydrogen evolution reaction

The HER activities of Raney–Ni electrodes obtained by partial leaching of Al in a Ni–Al–Fe alloy doped with Mo, Cr or Pd were studied in 28% KOH. PTFE bonded Gas Diffusion Electrodes (GDEs) were prepared by the rolling method before sintering at 300 °C under N2. Ni in alkaline electrolyte has a lower intrinsic HER activity than Pt in acid. However, the spongy and highly porous character of Raney–Ni greatly enhances HER resulting in a cheap material with outstanding catalytic performance. The polarization behavior of GDEs consisting mainly of Raney–Ni catalysts with optional addition of co-catalyst or conductivity enhancing powders, such as carbonyl iron, carbonyl nickel, copper and molybdenum oxide are studied as a function of temperature and time in order to determine activities, behavior in the high current density regime, and long term stability in view of potential exploitation in industrial electrolysis. Cr and Pd-doped Raney–Ni initially achieve outstanding performances with unusually low “Tafel slopes”. After weeks long cathodic treatments, these GDEs eventually attain inferior but stable activities due to an apparently irreversible aging of Raney–Ni. The aging of Mo-doped Raney–Ni is less conspicuous, and relevant performances are sometimes improved by additives. A clear picture is emerging of the mechanisms controlling polarization and aging behavior of Raney–Ni GDEs. From this picture, suggestions are put forward on how to improve stability and performances of full electrode assemblies and make them suitable for use in advanced alkaline electrolyzers.

Microalloying effects on the microstructure and kinetics of nanoscale precipitation in Ni–Al–Fe alloy

The aim of this study is to investigate the influence of 3d transition metal (Co, Mn and V) microalloying on the microstructural evolution, thermomagnetic properties and kinetics of nanoscale precipitation in Ni–25Al–25Fe alloy. The three phase solidification microstructure comprising of dendritic β-phase (ordered bcc) and interdendritic β + γ (disordered fcc) + γ′ (ordered fcc) phases in the as-cast state is significantly altered by annealing. Needle-like disordered γ-phase precipitates are observed within β-phase dendrites, and, dissolution of ordered γ′-phase into the γ matrix promotes the growth of β-phase particles in the interdendritic region of Mn- and Co-modified alloys. Disappearance of dendritic microstructure and formation of large volume fraction needle-like disordered γ-phase precipitates within β-matrix are observed in V-modified alloy. In all studied alloys, annealing at an intermediate temperature promotes significant hardening of the β-phase associated with bcc α-phase precipitation at the nanoscale. Isothermal precipitation kinetics of the ferromagnetic α-phase is studied by a magnetic monitoring approach via magnetically assessed time–temperature-transformation diagrams. It is found that V microalloying suppresses the growth of α-phase precipitates at high temperatures and large transformed fractions serving as a promising route to maintain balanced mechanical properties for long-term high temperature applications.

Effect of Process on Microstructure and Elevated Temperature Mechanical Behavior of Multi-Phase NiAl-Fe(Nb) Alloy

The microstructure and elevated temperature mechanical behavior of as-cast, HIPed and directionally solidified NiAl-Fe(Nb) Alloys have been investigated. The results show that the microstructure of as-cast NiAl-Fe(Nb) alloy consists of dendritic regions (b) and interdendritic regions (g/g¢) with non-continuous NbNiAl(Laves) phase segregating at the interfaces of b and g/g¢ phases. The HIP processing does not alter the microstructure of as-cast alloy. The longitudinal dendritic microstructure of the DS NiAl-Fe(Nb) alloy is regular. Room temperature elongations of as-cast and HIPed NiAl-Fe(Nb) alloys are all zero, however, 0.4% for the DS alloy. The strength and elongation of the HIPed alloy are higher than that of as-cast alloy. The yield strength and ultimate strength of the DS alloy are equivalent to that of as-cast alloy, but elongation of the DS alloy is higher than that of as-cast alloy, the elongation exceed 100% at 1273K, which indicates that the DS alloy can be deformed superplastically.

Role of intermetallic nanoparticles in radiation damage of austenitic Fe–Ni-based alloys studied by positron annihilation

The effect of homogeneous distributed nanosized (1–8 nm) intermetallic particles on the evolution of the vacancy defects in fcc Fe–Ni-based alloys during electron irradiation at temperatures 300, 423 and 573 K was studied by the positron annihilation spectroscopy. It was shown that coherent intermetallic nanoparticles like Ni 3Al(Ti) inhibited accumulation of the sub-nanometer vacancy clusters. The efficiency of this process depends on type, size and density of nanoparticles and it increases at the elevated irradiation temperatures. It is also observed that in Fe–Ni–Al alloy radiation-induced nucleation of intermetallic particles of Ni 3Al type occurs during irradiation at 573 K. In addition, possible mechanisms of the absorption of point defects by nanoparticles are discussed.

Positron annihilation studies of microstructural changes in cold-worked Fe–Ni-base aging alloys

Microstructural evolution of cold-worked fcc Fe–Ni–Ti(Al) aging alloys subjected to isochronal annealing has been investigated using positron annihilation. The stages corresponding to vacancy defect annealing, heterogeneous nucleation of γ′-phase particles and recrystallization have been clearly identified. It has been found that, due to strong interaction of vacancies with titanium atoms in the Fe–Ni–Ti alloy, low-temperature (450–700 K) segregation of titanium and formation of Ni 3Ti particles at dislocations are observed. The Ni 3Ti particles strongly pin the dislocations, leading to recrystallization retardation. At the same time, particles block positron trapping at dislocations. Decomposition of cold-worked Fe–Ni–Al alloy takes place over the same temperature range (800–900 K) as in the solution annealed state of this alloy. Precipitation of the Ni 3Al and high-temperature bcc-phase particles also leads to dislocation pinning and inhibiting recovery of the microstructure in cold-worked Fe–Ni–Al alloy.

The effect of alloying elements on the vacancy defect evolution in electron-irradiated austenitic Fe–Ni alloys studied by positron annihilation

The vacancy defect evolution under electron irradiation in austenitic Fe–34.2 wt% Ni alloys containing oversized (aluminum) and undersized (silicon) alloying elements was investigated by positron annihilation spectroscopy at temperatures between 300 and 573 K. It is found that the accumulation of vacancy defects is considerably suppressed in the silicon-doped alloy. This effect is observed at all the irradiation temperatures. The obtained results provide evidence that the silicon-doped alloy forms stable low-mobility clusters involving several Si and interstitial atoms, which are centers of the enhanced recombination of migrating vacancies. The clusters of Si-interstitial atoms also modify the annealing of vacancy defects in the Fe–Ni–Si alloy. The interaction between small vacancy agglomerates and solute Al atoms is observed in the Fe–Ni–Al alloy under irradiation at 300–423 K.

Influence of nanoprecipitates on the creep strength and ductility of a Fe–Ni–Al alloy

Creep studies of a duplex Fe–Ni–Al intermetallic alloy, in two microstructural states, have been carried out at temperatures between 725 and 800 °C (about 0.6 T m). In the as-cast state, the alloy contains a large volume fraction of nanoprecipitates (50–100 nm) which confer a very high creep strength with a stress exponent of 3 and an activation energy of 280 kJ/mol. The different microstructure obtained in the second state of the alloy, obtained after annealing at 1000 °C for 24 h, leads to a much lower creep strength with a higher stress exponent as well as a large value of the apparent activation energy. While volume diffusion appears to control creep in the as-cast state, both thermal and athermal processes seem to contribute to the different creep rate of material in the annealed state. The latter also exhibits a much larger ductility (12%) relative to that observed in the as-cast material (3%), due to the presence of large numbers of interfaces between the two phases present where strain incompatibilities can be accommodated.

Coarsening kinetics of metastable nanoprecipitates in a Fe–Ni–Al alloy

Microstructure evolution of a Fe–Ni–Al alloy has been examined during annealing at temperatures between about 700 and 800 °C. This material is brittle in the cast state but shows good strength with ductility after a stabilising anneal at 1100 °C when it has a duplex microstructure of B2 dendrites with fcc interdendritic phase. The 700–800 °C ageing leads to the formation of metastable bcc precipitates within the dendrites with less change within the interdendritic regions. The long-term coarsening of these precipitates is controlled by diffusion within the B2 phase. The composition of the B2 phase changes with annealing temperature, which is believed to modify the diffusion rate and, correspondingly, the rate of particle coarsening. The present coarsening study serves to define annealing conditions for preparation of optimum microstructure before material testing, as well as define upper temperature limits for possible long-term application, where stable microstructures are required.

Positron annihilation spectroscopy characterization of effect of intermetallic nanoparticles on accumulation and annealing of vacancy defects in electron-irradiated Fe–Ni–Al alloy

The effect of intermetallic nanoparticles like Ni3Al and nanoparticles of an Fe-rich bcc phase on the evolution of vacancy defects in an fcc Fe–34.2 wt% Ni–5.4 wt% Al model alloy under electron irradiation at elevated temperatures (423 and 573 K) was investigated using positron annihilation spectroscopy. Nanosized (1–8 nm) particles, which are homogeneously distributed in the alloy matrix, cause a several-fold decrease in the accumulation of vacancies as compared to their accumulation in a quenched alloy. This effect depends on the size and the type of nanoparticles. The effect of the nanoparticles increases when the irradiation temperature increases. The irradiation-induced nucleation and the growth of intermetallic nanoparticles were also observed in an alloy pre-aged at 1023 K under irradiation at 573 K. Thus, a quantum-dot-like positron state within ultrafine intermetallic particles, which we revealed earlier, allows control of the evolution of coherent precipitates like Ni3Al, along with vacancy defects, during irradiation and subsequent annealing. Possible mechanisms of the absorption of point defects by nanoparticles are discussed.

Electrical discharge machining of a NiAlFe ternary shape memory alloy

Abstract The electro-discharge machining (EDM) characteristics of a NiAlFe ternary shape memory alloy (SMA) have been investigated in this study. Experimental results reveal that the material removal rates (MRRs) of Ni 60 Al 24.5 Fe 15.5 and Ti 35.5 Ni 49.5 Zr 15 alloys in the EDM process exhibit a reverse relationship to the product of the alloy's melting temperature and thermal conductivity. In addition, a precise EDM machining of NiAlFe SMA can be obtained by setting the machine parameters at low pulse energy. The surface roughness (Ra) of the EDMed NiAlFe SMA is found to follow the empirical equation of Ra = λ ( I P × τ P ) β . Having a less T Θ × K T value, Ni 60 Al 24.5 Fe 15.5 alloy has a larger Ra value than that of Ti 35.5 Ni 49.5 Zr 15 alloy after electro-discharge machining. The recast layer consists of the oxides Fe 2 O 3 , Al 2 O 3 , NiO and the deposition particles of the consumed Cu electrode and dissolved dielectric medium. The hardening effect near the outer surface for EDMed NiAlFe alloy originates from the recast layer. The thickness of the recast layer varies with the pulse duration and exhibits a minimum value at the maximal MRR.

Microstructure and mechanical behaviour of a Fe–Ni–Al alloy

The microstructure of a cast Fe–35% Ni–20% Al alloy has been examined and changes occurring on annealing examined in relation to the ternary equilibrium diagram for these conditions. Significant changes occur with various precipitations inside the initial dendritic cast structure. As cast material is brittle due to cleavage across the B2 regions, despite the presence of ductile fcc interdendritic phase, precipitation on annealing softens the material and allows notable room temperature ductility.

Effects of intermetallic nanoparticles on the evolution of vacancy defects in electron-irradiatedFe–Ni–Al material

In this paper we study the effects of intermetallic nanoparticles likeNi3Al on the evolution of vacancy defects in the fcc Fe–Ni–Al alloy under electron irradiationusing positron annihilation spectroscopy. It was shown that the nanosized(∼4.5 nm) intermetallic particles homogeneously distributed in the alloy matrix causeda several-fold decrease in the accumulation of vacancies as compared to theiraccumulation in the quenched alloy. This effect was enhanced with the irradiationtemperature. The irradiation-induced growth of intermetallic nanoparticles was alsoobserved in the pre-quenched Fe–Ni–Al alloy under irradiation at 573 K. Thus, aquantum-dot-like positron state in ultrafine intermetallic particles, which we revealedearlier, provided the control over the evolution of coherent precipitates, along withvacancy defects, during irradiation and annealing. Possible mechanisms of theabsorption of point defects by coherent nanoparticles have been discussed too.

Positron confinement in intermetallic nanoparticles embedded in Fe–Ni–Al material

The affinity-induced positron state was detected in ‘defect-free’ intermetallicparticles using angular correlation of annihilation radiation. It was found thatapproximately 98% of the positrons annihilate within nanosized and subnanosizedintermetallic particles embedded in an fcc Fe–Ni–Al alloy. These particles werecreated by means of thermal ageing. The ultrafine particles had a structure of theNi3Al type with addition of Fe atoms. The nanoparticles were three-dimensional and had noopen-volume defects at the interfaces, which could trap a positron. These observationssuggest that this positron state promises to be a powerful tool for studies of mesoscopicsystems in condensed matter.