NiAl Alloys Research Articles

Development of an interatomic potential for L12 precipitates in Fe–Ni–Al alloys

Fe–Ni-based alloys have been considered as candidate structural materials for advanced nuclear reactors, and some of their excellent properties are particularly associated with L12 precipitates dispersed in the alloys. For a better understanding of the irradiation response, classical molecular dynamics is an essential tool to simulate the irradiation-induced defect formation and subsequent microstructural evolution. We here develop an interatomic potential for L12(Ni,Fe)3Al precipitates in the ternary Fe–Ni–Al system. The fitting parameters are tuned to describe the lattice and elastic constants of NiFe solid solutions and defect formation/vacancy migration energies in the fcc matrix. Furthermore, the lattice properties and defect energies of L12(Ni,Fe)3Al are considered for the fitting. We demonstrate the developed potential reproduces the lattice and defect properties with reasonable accuracy by comparison with density functional theory calculations, existing empirical potentials, and experimental data. This potential will be useful to investigate the defect formation and evolution of (Ni,Fe)3Al precipitates in the alloys under irradiation, which would provide critical insights into the materials design strategy to achieve enhanced properties.

The potential application of Ru in aluminide coatings with reduced Al contents: A combined experimental and theoretical study

Aluminide coatings are widely used on turbine blades due to their excellent oxidation resistance. However, the interdiffusion between these coatings and superalloy substrates can lead to a deterioration of mechanical properties in the coated alloys. In the present study, Ni-Al alloys (Ni-50Al, Ni-40Al, and Ni-30Al), both with and without the addition of 10 at. % Ru, are prepared and used to form diffusion couples with a single crystal superalloy SCA21. After a diffusion process at 1150 ℃ for 100 h, interdiffusion layers with the matrix of β-NiAl or γ ′-Ni3Al form at the diffusion couple interfaces. The formation of L12-ordered Ni3Al phases is found to impede elemental interdiffusion. Consequently, Ni-30Al/SCA21, which exhibits only Ni3Al-based interdiffusion layers, displays the lowest interdiffusion coefficients among the diffusion couples without Ru addition. Furthermore, first-principles studies reveal that the addition of Ru increases the formation energies of point defects and defect clusters involved in elemental interdiffusion in stoichiometric NiAl, Ni-rich NiAl, and Ni3Al phases, particularly when Ru occupies the Al site of Ni3Al phases at high temperatures. The remarkable diffusion barrier effects of Ru in Ni-30Al coatings have the potential to significantly enhance their performance and broaden their application prospects.

Insight into the microstructure and micromechanical behavior and mechanism of the constitutional phase of FeNiCrAl0.63 multi-principal element alloy

The mechanical properties of quaternary Fe–Cr–Ni–Al alloys have been extensively studied due to their potential application in high temperature structural components. However, the work hardening mechanism originating from the two BCC phase states is not clear. Herein, we systematically investigate the constituent phases and the micromechanical behavior of the FeCrNiAlx (x = 0.63, 0.71, 0.77) alloys. Dual-phase microstructural characterizations indicate that the ordered BCC2 phase is enriched in Ni–Al elements and the disordered BCC1 phase is enriched in Fe–Cr elements, giving rise to an increase in the partition ratio of dual phases. The work-hardening exponents of the BCC1 and BCC2 phases were evaluated to be 0.459 and 0.464, implying the difference of work hardening behavior and coordinate deformation of the two BCC phases. Meanwhile, the constitutive relationships including the modified Ludwik description of the work-hardening behavior of Al0.63 alloy are investigated by nanoindentation measurements. Results show that the outstanding work-hardening response is associated with coordinated deformation of the soft and hard two BCC phases. Furthermore, the first-principles calculation illustrates that the stronger bonding strength of the BCC2 phase contributes to the higher work hardening capability than the BCC1 phase.

Binary nanocrystalline alloys with strong glass forming interfacial regions: Complexion stability, segregation competition, and diffusion pathways

Stabilization of grain structure is important for nanocrystalline alloys, and grain boundary segregation is a common approach to restrict coarsening. Doping can alter grain boundary structure, with high temperature states such as amorphous complexions being particularly promising for stabilization. Dopant enrichment at grain boundaries may also result in precipitate formation, giving rise to dopant partitioning between these two types of features. The present study elucidates the effect of dopant choice on the retention of amorphous complexions and the stabilization of grain size due to various forms of interfacial segregation in three binary nanocrystalline Al-rich systems, AlMg, AlNi, and AlY as investigated in detail using transmission electron microscopy. Amorphous complexions were retained in AlY even for very slow cooling conditions, suggesting that Y is the most efficient complexion stabilizer. Moreover, this system exhibited the highest number density of nanorod precipitates, reinforcing a recently observed correlation between amorphous complexions and grain boundary precipitation events. The dopant concentration at the grain boundaries in AlY is lower than in the other two systems, although enrichment compared to the matrix is similar, while secondary segregation to nanorod precipitate edges is much stronger in AlY than in AlMg and AlNi. Y is generally observed to be an efficient doping additive, as it stabilizes amorphous features and nanorod precipitates, and leaves very few atoms trapped in the matrix. As a result, all grains in AlY remained nanosized whereas abnormal grain growth occurred in the AlMg and AlNi alloys. The present study demonstrates nanocrystalline stability via simple alloy formulations and fewer dopant elements, which further encourage the usage of bulk nanostructured materials.

Investigation of mechanical and microstructural properties of sputter-deposited Zr-Ni3Al coatings

Zr-doped Ni3Al alloy coatings were deposited on a silicon substrate using DC magnetron cosputtering at a substrate temperature of 400 °C. The transformation of phase, microstructure, and surface topography was investigated using GIXRD, field emission scanning electron microscopy, and atomic force microscopy, respectively. The effect of zirconium (Zr) concentration on the microstructure and mechanical properties of Ni3Al coatings has been discussed. It is observed that the high concentration of Zr in Ni3Al coatings led to the evolution of microcracks that further contributes to increasing the surface roughness of the coatings. Results revealed that the Ni3Al coating without Zr content exhibited the highest hardness of 12.8 GPa. It is also found that with the increase in Zr content in host Ni3Al coatings, the hardness decreases, whereas the contact angle increases. Ni3Al coatings with 40 W Zr enrichment showed a hydrophobic nature with a contact angle of 101°.

Dislocation breakaway from nanoparticle array linear complexions: Plasticity mechanisms and strength scaling laws

Linear complexions are stable defect states, where the stress field associated with a dislocation induces a local phase transformation that remains restricted to nanoscale dimensions. As these complexions are born at the defects which control plasticity in metals, it is crucial to understand their impact on subsequent mechanical properties. In this work, atomistic modeling is used to understand how dislocation mechanics are altered by the presence of nanoparticle array linear complexions in a Ni-Al alloy. Molecular dynamics simulations are used to identify the critical shear stress needed to drive dislocation breakaway, first for nanoparticle arrays formed by Monte Carlo/molecular dynamics methods to represent realistic configurations and subsequently for simplified models that allow the effects of particle spacing and size to be varied in a controlled manner. A combined bowing and progressive unpinning mechanism is uncovered, leading to the demonstration of a new strength scaling law that differs in keys ways from classical Orowan bowing.

Thermo-Calc determination of phase diagram and thermodynamic properties of Ni-Al binary system

Ni-Al alloys have good corrosion-resistant properties making them preferable as a material of choice compared to ordinary metals. A good understanding of the phase diagram and thermodynamic properties of the Ni-Al alloy binary system is essential in determining relevant industrial applications of the system. The Ni-Al phase diagram is being reassessed since those found in the literature are based on old experimental studies. The phase diagram and thermodynamic properties of the Ni-Al alloy is determined using the Thermo-Calc 2022b software over a temperature range of 200 K to 2000 K and 1 atm of pressure. A total of nineteen fields (including elemental Al and Ni) comprising five single solid phases, one liquid phase, and twelve double regions were obtained from the equilibrium calculation. The thermodynamic calculation has six invariant reactions containing two eutectic reactions (914.83 ± 0.025 K and 1641.80 ± 0.025 K), three peritectic reactions (1123.55 ± 0.025 K, 1400.72 ± 0.025 K and 1642.65 ± 0.025 K), and one peritectoid reaction (913.96 ± 0.025 K). The solubility of Al in Ni is also determined. The Gibbs free energy, the molar enthalpy and the activities of Al in Ni are all calculated at temperatures 913 K, 1642 K, and 1953 K. The Thermo-Calc temperature – composition of the Ni-Al alloy is compared with the existing experimental studies to identify the physical properties of the different thermodynamic properties of the Ni-Al alloy binary system.

Accelerating formation of α-Al2O3 scale on a nanograined Ni-Al alloy by self-generated NiO top layer

Alfa (α)-Al2O3 is widely used to resist oxidation at high temperature. However, presence of some transient phases can reduce the oxidation resistance. Several strategies have been proposed to solve this issue. Here, we found that nucleation of α-Al2O3 can be accelerated by a NiO layer on the surface of nanostructured Ni-7 wt%Al alloy. The oxidation rate constant is an order of magnitude lower than that of β-NiAl after 1000 °C oxidation. The enhanced growth compressive stress in scale is supposed to facilitate the α nucleation. This provides a novel strategy to develop advanced engineering alloys with high temperature applications.

Fabrication of NiAl alloy hollow thin-walled component through hot gas forming of Ni/Al laminated tube and conversion process

The NiAl intermetallic compounds have higher service temperature and lower density than traditional Ni-based super-alloy. In this work, for overcoming the fabricating bottleneck of NiAl alloy hollow thin-walled component, a typical NiAl alloy square-section component was obtained by hot gas forming of NiAl laminated tube and conversion. Firstly, the Ni/Al laminated tubes with tight interfacial bonding between layers and considerable plasticity was prepared by controlling the thickness and distribution of intermediate layer (NiAl3 and Ni2Al3). Then, the hot gas forming behavior and micro-damage control method of the Ni/Al laminated square-section component were studied under different process parameters. Finally, the Ni/Al laminated square-section components were converted into NiAl alloy components at 1200 °C/1 h. The results show that the forming temperature and gas pressure loading rate are the key parameters for hot gas forming of Ni/Al laminated materials. At an optimal temperature, the micro-damage can be avoided and the fillet accuracy can be controlled by adjusting the strain rate through using different gas pressure loading rates.

Features of formation of the Al–Ni–Zr system alloy structure obtained by reducing oxide compounds by aluminothermy using SHS metallurgy

This work is focused on establishing the regularity of the effect of zirconium (2.21; 3.29; 3.69 and 6.92 wt.% Zr) on structure formation, the nature of distribution of elements and the microhardness of structural components in the Al–Ni–Zr system alloys obtained by aluminothermy using the SHS metallurgy. Regularities of the formation of structural components and their microhardness depending on the content of zirconium in Al–Ni alloys (50 wt.%) have been identified and scientifically substantiated. Structural components were identified by the methods of electromicroscopic studies and X-ray microanalysis of elements. The structure of the initial alloy consists of Al3Ni2 (β′-phase) and Al3Ni nickel aluminides. Zirconium doping of the alloy in the amount of 2.21 wt.% leads to crystallization of zirconium nickel aluminide Al2(Ni,Zr). With further increase in the content of zirconium (more than 2.21 wt.% Zr), complex alloyed intermetallic compounds crystallize – Zr, W, Si aluminides and Ni zirconides. A regularity was established in the decrease of the solubility of nickel in nickel aluminides Al3Ni2 and Al3Ni and their microhardness as the zirconium content increases in the Al–Ni–Zr alloys from 2.21 to 6.92 wt.%. In nickel aluminide with zirconium Al2(Ni,Zr), this contributes to a decrease in the solubility of Ni, Al and increase in the concentration of Si and Zr. Zirconium doping of the Al–Ni alloy in the amount over 2.21 wt.% contributes to an increase in hardness (HRA), despite a decrease in the microhardness of the metal base (Al3Ni2, Al3Ni and Al2(Ni,Zr)). The main reason for increasing the hardness of the Al–Ni–Zr alloys is the crystallization of complex-alloyed intermetallides – Zr, W, Si aluminides and nickel zirconide, which probably have an increased microhardness. Thus, zirconium doping of the Al–Ni alloy makes it possible to obtain a plastic metal base from nickel aluminides Al3Ni2, Al3Ni and Al2(Ni,Zr) and complex-alloyed intermetallides with high hardness.

Fabrication and Damping Property of Porous Cu–Al–Ni Shape Memory Alloys Fabricated using Different Raw Materials

Porous Cu–Al–Ni shape memory alloys (SMAs) are fabricated via powder metallurgy method using Cu, Al, Ni powders and Cu–Al–Ni alloy powder as raw materials, respectively. It is found that the two kinds of specimens have similar macroscopic morphologies: connected pores are uniformly distributed in the Cu–Al–Ni matrix, forming a 3D network structure. By comparison, the specimen fabricated using alloy powder has much finer microstructures than the specimens fabricated using Cu, Al, Ni powders. After adding Ce element to the latter, the microstructure of the Cu–Al–Ni matrix is significantly refined because of the formation of Ce‐rich particles. Damping tests show that the latter has superior damping capacity than the former. With the increase of Ce content, the damping of the latter increases first and then decreases. When the Ce content reaches 0.05 wt%, the highest damping can be achieved. Correlated mechanisms are discussed based on the microstructural observations.

Tribological Performance and Model Establishment of Self-Compensating Lubrication Film Inspired by the Functional Surfaces of Scapharca subcrenata Shells

Composite surface structures inspired by the functional surface of Scapharca subcrenata shells can improve the tribological properties effectively, composed of the ordered “U”- shape micro-grooves and solid lubricant Sn-3.0Ag-0.5Cu (SAC305) alloys. A series of wear tests were conducted to further investigate the formation characteristics of the self-compensating lubrication film, and then the mathematical model of the spreading tribofilm could be proposed. The results showed that the appropriate surface texturing parameters (NBCSS-28) had a great effect on the formation of the self-compensating lubrication film, which exhibited a lower friction coefficient (0.386) and wear volume (0.682 mm3) than the other NBCSS samples. The tribofilm, with a thickness of a few microns, was deposited on the contact surface after the wear tests. The interfacial reactants (the Ni/Ni3Sn2 interface) of the SAC305 alloys, and Ni3Al alloys confirmed by the wetting experiments and the thermogravimetric analysis, could promote the deposition and diffusion of the tribofilm during the sliding process. Hence, distinguishable layered structures could be observed on the fractured surfaces of the NBCSS samples. Moreover, the formation process of the tribofilm exhibited an obvious relationship with the reduction in the dynamic friction coefficient. The tribofilm formation model was proposed by the accumulation behaviors of the spreading tribofilm randomly in the form of multiple discrete irregular film shapes on the worn surface, which could predict the formation characteristics of the self-compensating lubrication film to improve the optimization design of the parameters.

Artificial intelligence inspired design of non-isothermal aging for γ–γ′ two-phase, Ni–Al alloys

In this paper, a state-of-the-art Artificial Intelligence (AI) technique is used for a precipitation hardening of Ni-based alloy to predict more flexible non-isothermal aging (NIA) and to examine the possible routes for the enhancement in strength that may be practically achieved. Additionally, AI is used to integrate with Materials Integration by Network Technology, which is a computational workflow utilized to model the microstructure evolution and evaluate the 0.2% proof stress for isothermal aging and NIA. As a result, it is possible to find enhanced 0.2% proof stress for NIA for a fixed time of 10 min compared to the isothermal aging benchmark. The entire search space for aging scheduling was ~ 3 billion. Out of 1620 NIA schedules, we succeeded in designing the 110 NIA schedules that outperformed the isothermal aging benchmark. Interestingly, it is found that early-stage high-temperature aging for a shorter time increases the γ′ precipitate size up to the critical size and later aging at lower temperature increases the γ′ fraction with no anomalous change in γ′ size. Therefore, employing this essence from AI, we designed an optimum aging route in which we attained an outperformed 0.2% proof stress to AI-designed NIA routes.

Effect of cerium addition on microstructure, thermal and rheological properties of hypoeutectic Al-Ni alloy

The microstructure, mechanical properties, electrical/thermal conductivity, and rheological behavior of Al-5Ni alloy with different Ce contents were systematically investigated. The experimental results demonstrate that an appropriate addition of Ce reduces the recalescence and growth temperatures of the Al-Ni eutectic structure, resulting in a reduction in precipitation phase size and the formation of a spherical Al3Ni eutectic structure. It leads to improvement in electrical conductivity and mechanical properties. But excessive addition of Ce leads to the formation of slatted Al23Ce4Ni6 on the Al-Ni eutectic boundary, causing the samples with higher Ce content to exhibit lower strength and thermal conductivity. Additionally, the investigation of alloy viscosity indicates significant shear thinning behavior of Al-Ni alloys, which contributes to obtaining uniformly filled and good quality cast products. The variation of melt viscosity suggested that Ce elements could improve the morphology and distribution of α-Al precipitates in the alloy, leading to an increase in viscosity in a specific temperature range.

Separation of Anionic Chlorinated Dyes from Polluted Aqueous Streams Using Ionic Liquids and Their Subsequent Recycling.

The effect of ionic liquids on the separation of chlorinated anionic dyes such as Mordant Blue 9 (MB9) or Acid Yellow 17 (AY17) via ion exchange has been investigated in model aqueous solutions that simulate wastewater from the textile dyeing industry. The effect of ionic liquids chemical nature on the separation efficiency of mentioned dyes has been compared. It was found that especially ionic liquid based on quaternary ammonium salts comprising two or three long alkyl chains bound to the quaternary ammonium nitrogen (typically benzalkonium chloride or Aliquat 336) are very effective for the separation of both studied MB9 and AY17 from aqueous solution. In addition, the innovative technique has been developed for the reactivation of spent ionic liquids which is based on the chemical reduction of the formed ion pairs using NaBH4/NiSO4, NaBH4/Na2S2O5 or Raney Al-Ni alloy/NaOH. Thus, only NaBH4/NiSO4 in co-action with Al-Ni alloy enables both effective reduction of the azo bond and subsequent hydrodechlorination of emerging chlorinated aromatic amines. The efficiency of tested dyes separation or regeneration of ion pairs was evaluated by determination of the absorbance at wavelength of the maximum absorbance, of the Chemical Oxidation Demand (COD), and of the Adsorbables Organically bound Halogens (AOX). The formation of ion pairs or products of reduction and hydrodechlorination of these ion pairs has been studied using the 1H NMR and LC-MS techniques.

Differential effects of Sn and Si solutes on the microstructure and properties of Cu–Ni–Al alloys with coherent L12-γ′ phases

In order to solve the discontinuous precipitation of nano-spherical γ′ coherent precipitates strengthened Cu–Ni–Al alloys and explore the influence mechanism of trace elements on the microstructure and properties. Herein, the Si and Sn, with same main group but showing different elemental interaction, was selected as the fourth element, and series of alloy composition were designed and prepared in a wide Cu content, and the effect of Si or Sn addition on microstructure, properties at room temperature and thermal stability are investigated. The results demonstrate that Si is completely dissolved into γ and γ′ phase, but a little of Sn solid solution into γ′ phase. The two adding elements can accelerate the precipitation of γ′ phases, suppress the grain boundaries discontinuous precipitation and provide dual-nanostructure strengthening effect, which enhance the hardness and conductivity, and Si exhibits more preferable effect. The thermodynamic calculation and the work function results indicate that the addition of Sn would induce the descending thermal stability of γ and γ′ phase, but Si is beneficial to the improvement of thermal stability of γ and γ′ phase. Compared to Sn, Si is more suitable to be a candidate for the multi-component design of Cu–Ni–Al alloys.

Preparation of Al-Ni Alloys of Different Phases Through Direct Electro-Deoxidation of Al2O3-NiO in CaCl2-NaCl Molten Salt

Al-Ni alloys have several common thermodynamically stable alloy phases. These alloys showed distinct physical properties and were applied in different fields, including aerospace and electrochemical catalysis. However, it is difficult to prepare Al-Ni alloys with the certain phase composition through traditional preparation methods, such as casting and mechanical alloying. Herein, Al-Ni alloys were prepared through electro-deoxidation in CaCl2-NaCl molten salt. Pure Al-Ni alloys phases (AlNi3, AlNi and Al3Ni2) were obtained after optimizing the electro-deoxidation conditions, such as the molar ratio of Al and Ni in the original tablet, the sintering temperature of the precursor, electro-deoxidation time and the molten salt temperature. The deoxidation processes of the Al2O3-NiO composite were investigated through various electrochemical methods, such as cyclic voltammetry, chronoamperometric curve and constant potential electro-deoxidation experiment. The loss of Al2O3 in the molten salt was confirmed to be responsible for the loss of Al in the electro-deoxidation processes. Meanwhile, it was proposed that the loss of Al could be efficiently delayed by increasing the precursor’s sintering temperature and the molten salt temperature. The obtained Al-Ni alloys (AlNi3, AlNi and Al3Ni2) could be used as efficient additives in the cathode of lithium–sulfur batteries to improve the charging/discharging capacity.

Understanding cellular structure formation in rapidly solidified Al–Ni alloys by constructing solidification microstructure selection maps

Understanding cellular structure formation in rapidly solidified Al–Ni alloys by constructing solidification microstructure selection maps

Phase-Field Simulation of the Microstructure Evolution in the Eutectic Alloy NiAl-31Cr-3Mo

The directionally solidified eutectic alloy NiAl-(Cr,Mo) is a promising candidate for structural applications at high temperatures, due to its increased creep resistance compared to its single phase B2ordered NiAl counterpart. This system yields an eutectic trough connecting the invariant reactions of the ternary alloys NiAl-Cr and NiAl-Mo. During directional solidification (DS) along this trough the evolved microstructures of the two-phase eutectic is changing from fibrous to lamellar and back to fibrous morphology while increasing and decreasing the amounts of Mo and Cr, respectively. To investigate these effects in the morphology, the phase-field method has proven to be predestined in the last decades. However, as the modeling of quaternary systems is challenging for the simulation with a grand potential based phase-field model, the focus of this work is on the generation of a material model for one defined compound namely NiAl-31Cr-3Mo. The modeling is validated by investigating the microstructure evolution in two- and three-dimensional simulations of the DS process for two different growth velocities and by investigating their undercooling spacing relationships. The evolving microstructures obtained from three-dimensional large-scale simulations are presented and validated with corresponding micrographs from scanning electron microscopy (SEM) of directionally solidified samples with the same growth velocities. The simulation results show the theoretically expected behaviors and are in qualitative and quantitative accordance with DS experiments. The study of NiAl-31Cr-3Mo serves as the basis for a comprehensive data-driven analysis of microstructure properties and system quantities of the entire quaternary material NiAl-(Cr,Mo). With this, an accelerated design of advanced materials is promoted.

Ab-initio study on electronic, mechanical and dynamical properties of maraging steel containing coherent B2 type (Fe, Al)Ni nanoprecipitates

The ultrastrong maraging steel containing coherent B2 type (Fe, Al)Ni nanoprecipitates possesses outstanding strength and ductility with the potential to meet the demands in aerospace, advanced energy, etc. However, its transport properties including electrical and thermal conductivities have not been systematically studied. Based on the first-principles calculations, a model of Fe-7 at%(Fe, Al)Ni alloy containing B2 type (Fe, Al)Ni coherent nanoprecipitates was constructed, and its electronic, mechanical, and dynamical properties were calculated. The results showed that its bulk modulus is 169.6 GPa and the Poisson's ratio is 0.31, which are consistent with the experimental strength and ductility reported in Nature before. In addition, its unfolding band structure and phonon dispersion spectrum prove that the ultrastrong steel also has good electrical and thermal conductivities theoretically, which is similar to that of pure Fe metal. The experimental results of electrical resistivity and thermal conductivity verify the correctness and accuracy of the calculations.