Ni-Al System Research Articles

Combustion in Ni–Al system with Cu additive (powder or rod) Experiment and mathematical model

Experimental studies were carried out with theoretical calculations of wave synthesis in the Ni–Al–Cu system were performed using the mathematical model developed. Approximate analytical formulas were obtained for synthesis performance evaluation. The inverse problem method was used to get kinetic constants that determine process dynamics based on the experimental data and analytical relationships. It is shown that the combustion front propagation velocity increases monotonically with an increase in the reaction sample relative density in the range of relative density values of 0.4 to 0.6. The depth of copper melt penetration from the center of the sample into the nickel-aluminum matrix depends on the relative density of the sample and copper wire diameter: higher densities and larger diameters lead to an increase in the liquid-phase impregnation area. The rate of nickel and aluminum powder frame wetting with copper melt is limited by the synthesis wave speed. Based on the experimental data and analytical ratios, we estimated the effective kinetic constants describing the high-temperature synthesis of the Ni + Al reaction mixture in the presence of copper additives. The thermal effect of the NiAl intermetallic formation reaction and the preexponential factor in the chemical transformation equation are calculated, the exponent value in the ratio for the mixture thermal conductivity is established; a constant determining the process of nickel-aluminum matrix impregnation with copper melt is found. The macroscopic approach used to analyze the NiAl intermetallic synthesis makes it possible to determine all the desired physicochemical characteristics and model parameters. The mathematical model is suitable for predictive estimates and experimental data analysis in the macroscopic approximation. Approximate analytical formulas are obtained for calculating the NiAl intermetallic synthesis characteristics. They allow for calculating the through channel characteristics and can be used in the design of NiAl products.

Alloy design and properties optimization of multi-component alloy based on solidification characteristics

The current design strategies focus on the solidification characteristics to discover new MACs with promising properties in an enormous search space composed of considerable composition combinations in a specific system. In the present study, the associated correlations between alloying elements and solidification interval characteristics are uncovered via machine learning (ML) in the multi-component systems. Given the Fe–Cr–Ni–Al system, testing accuracy value using FNN model in identifying the input and output features is above 89%, and the Cr and Al are the critical elements. With these understanding, FeCrNiAl0.8 alloy was successfully designed and prepared, and the properties are tested to confirm the reliability of the alloy design strategies. The experimental investigations not only provide strong evidence for the predicted accuracy, but also find superior mechanical properties. The designed FeCrNiAl0.8 alloy exhibits fracture strength and plastic strain of 2839 MPa and 41%, respectively, accompanied with remarkable work hardening capacity. Beyond that, the extraordinary specific strength make it competitive against virtually known high performance metals and polycrystalline superalloys even in high temperature applications. Our work provides new ideas to search for compositionally complex alloys and is also applicable to assist in developing advanced MACs for engineering applications.

Electrochemical Corrosion of Composite Ceramics and Thermal Spray Coatings in the ZrB2–SiC–AlN System

Polarization studies of the ZrB2–SiC–AlN compact ceramic material and thermal spray coatings of the same composition were conducted in a 3% NaCl solid solution to analyze their cathodic and anodic behavior. The compact ceramic material was produced by hot pressing, the plasma-sprayed coating 240 μm thick was deposited onto a C/C–SiC graphite substrate, and the detonation-sprayed coating 340 μm thick was applied to 12Kh18N9T stainless steel. The microstructure and phase composition of the compact sample and thermal spray coatings were examined. The microstructure was heterophase in all cases. The compact sample and plasma-sprayed coating contained SiC, AlN, and ZrB2 as the main phases, and the detonation-sprayed coating additionally had a small amount of nickel and zirconium oxide. Electron microprobe analysis showed that the plasma-sprayed coating had 20 wt.% oxygen; i.e., the coating contained oxide phases in the amount not revealed by X-rays. The compact ceramic sample showed exceptionally high resistance to electrochemical oxidation: electrochemical potential, Ecorr, at which corrosion current occurs is very high and constitutes +1.51 eV. For the detonation- and plasma-sprayed coatings, Ecorr = –0.25 and –0.05 eV, respectively. The great resistance of the compact ceramic material to electrochemical oxidation correlates with its resistance to high-temperature oxidation above 1700°C. This is due to the formation of an Al2O3–SiO2 mullite film on the surface. The lower resistance of the coatings to electrochemical oxidation compared to the compact material is associated with their increased porosity.

High-temperature synthesis in activated powder mixtures under conditions of linear heating: Ni–Al system

In the present paper, a mathematical modeling of high-temperature synthesis process in powder system Ni+Al under linear heating conditions was carried out. A comparative analysis of numerical modeling results and experimental data which were obtained for mechanically activated powder mixtures is presented. The criterion for determining the characteristic ignition temperature in the case of forced ignition was proposed. This criterion makes it possible to establish a relationship between the thermokinetic parameters at the ignition limit. With the use of the model, the dependencies of the ignition temperature, the induction time, and the conversion degree on the effective activation energy were established. It was found that these dependencies are close to linear that allows making the predictive estimates. It was shown that the ignition temperature depends most significantly on the activation energy of the synthesis while its dependence on other kinetic parameters is of secondary importance. Based on the criterion proposed, an alternative method for determining the effective activation energy of synthesis was considered.

Computer molecular-dynamic simulation of shs microkinetics in the atomic structure with a checkerboard-like arrangement of nanoscale blocks of Ni and Al atoms

The article presents the results of computer simulation of the propagation of the combustion wave of "self-propagating high-temperature synthesis (SHS)" process in an atomic layered structure. In each layer of the structure, nanosized blocks of two types alternate: a block of the first type is composed as a packet of unit cells of Ni atoms, and a block of the second type is composed of a packet of elementary cells of Al atoms. In each pair of layers adjacent to each other, sequences of alternating blocks of two types are shifted relative to each other by one block, so the full layered structure of the layers with alternating blocks in them is associated with a chessboard pattern. Computer simulation of SHS in such a structure was carried out using the LAMMPS software package taking into account parallel computations, which uses the molecular dynamics method and the interatomic interaction potential in the embedded atom" model (EAM). In addition to the LAMMPS package, the authors implemented program procedures for calculating the temperature and density profiles of the substance along the motion direction of the SHS combustion wave front, which made it possible to carry out temperature analysis of the SHS microkinetics (to estimate the velocity of the combustion wave front) and recognition of intermetallic phases in the reaction volume of the Ni-Al system when using the OVITO package.

Mechanism of structural formation in the combustion wave of the Ni-Al system with strengthening additives

In the work, microstructures formed in the combustion wave of the Ni-Al system with hardening additives of high-temperature ceramic particles consisting of titanium diboride and corundum were studied. Microstructures and shapes vary depending on the content of ceramic additives in the NiAl matrix. Particles of TiB2 take the most diverse elementary forms, such as bars, plates, herringbones, regular cubic structures and cuboids. These results outline a real-time strategy of self-assembly processes to create diversified microstructures. Some grains of titanium diboride 2-5 m in size are embedded in corundum clusters, and a small number of TiB2 particles are dispersed in the NiAl matrix. It is assumed that the higher the content of reinforcing additives, the more uniform the distribution of the ceramic skeleton will be present in the NiAl matrix.

Investigation of fine metal films of the Ni-Al system by physical methods

The article describes the results of investigations of ultrathin Ni-Al films, obtained by the resistive method of thermal evaporation and having characteristic islands sizes of 700-1000 nm with a film thickness of about 500 nm. The work presents a method for producing a film using an installation for creating a high vacuum and subsequent film deposition. Investigations of the obtained film sample were carried out with the help of an optic microscope, a scanning probe microscope and a Fourier analyzer. Kinetic characteristics and relief of the film, characteristic islands sizes are established, the search for regularities in the island structure of films is carried out, and its electrical conductivity is determined.

Surface Properties of Liquid Al-Ni Alloys: Experiments Vs Theory

The present study is an overview of the surface properties of liquid Al-Ni alloys, which are of great importance for the design and development of new Al-Ni and Ni-based industrial alloys, widely used as functional and structural materials. The solidification and thus, the microstructural evolution are directly dependent on the interface/surface properties of metallic melts. Therefore, numerical simulation of microstructure evolution requires reliable property data as input to such models. Taking into account the experimental difficulties related to a high reactivity of liquid Al-Ni alloys and the effects of impurities on their surface properties, the surface tension over the whole concentration range has been determined in the frameworks of three international research projects. Namely, the surface tension measurements have been carried out by both traditional container-based and as an alternative, containerless methods within the ESA-MAP ThermoProp and ESA-MAP Thermolab Projects and also under the EU FP6-IMPRESS Project. The obtained datasets were analysed and subsequently compared with the model predicted values as well as with the literature data. A strong exothermic mixing characterises the Al-Ni system and the presence of a few intermetallic compounds in the solid state leads to the formation of short range ordered elements or complexes in the liquid phase, at least near the melting temperature, which significantly affects the surface properties of alloy melts. Aiming to estimate the effects of short range ordering on these properties, the Compound Formation Model (CFM) and the Quasi Chemical Approximation (QCA) for regular solution were applied.

Modeling of molar volume for the Ni–Al γ/γ′ binary phases within the framework of CALPHAD method

Assisted by the first-principles calculations, the molar volumes of γ and γ′ phases in the binary Ni–Al system were modeled within the framework of the CALPHAD method. A CALPHAD database integrating thermodynamic and molar volume descriptions was established. The present Ni–Al binary database was validated to make good predictions of molar volumes/lattice parameters and thermal expansivities for both γ and γ′ phases. The predicted γ/γ′ lattice misfits from low to high temperatures turn out to be reasonable.

The oxidation behaviour of layered Al-Ni coating at high-temperature heating

The aim of the work is to study of the structure and phase composition of an oxide film formed on the surface of the layered coating of the Al-Ni system during high-temperature heating. It was experimentally established that at the initial stages of heat treatment, as a result of the interaction of the Al-Ni system layered coating with air oxygen, individual sections of Al2O3 oxide are formed on its surface, which are agglomerates of nanometre-thick plate crystals, which increase and grow into a continuous oxide film with increasing exposure time. Along with stable α-modification, transitional metastable δ- and θ-modifications are present in the film. An increase in the heating temperature leads to an intensification of the oxidation processes and the formation of a complex oxide film of Al2O3 and spinel NiAl2O4, 1–3 μm thick.

Thermal Barrier Stability and Wear Behavior of CVD Deposited Aluminide Coatings for MAR 247 Nickel Superalloy.

In this paper, aluminide coatings of various thicknesses and microstructural uniformity obtained using chemical vapor deposition (CVD) were studied in detail. The optimized CVD process parameters of 1040 °C for 12 h in a protective hydrogen atmosphere enabled the production of high density and porosity-free aluminide coatings. These coatings were characterized by beneficial mechanical features including thermal stability, wear resistance and good adhesion strength to MAR 247 nickel superalloy substrate. The microstructure of the coating was characterized through scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis. Mechanical properties and wear resistance of aluminide coatings were examined using microhardness, scratch test and standardized wear tests, respectively. Intermetallic phases from the Ni-Al system at specific thicknesses (20–30 µm), and the chemical and phase composition were successfully evaluated at optimized CVD process parameters. The optimization of the CVD process was verified to offer high performance coating properties including improved heat, adhesion and abrasion resistance.

Optimization of the coating process by cold gas dynamic spraying applied to production conditions of Ni–Ti and Ni–Al systems

This study developed practical recommendations for using the method of cold gas dynamic spraying to obtain functional coatings in a production environment using powders of nickel, titanium and aluminum of the grades: PNE-1 (Ni), PTOM-1 (Ti) and PA-VCh (Al). The temperature and speed parameters of the process were optimized using mechanical mixtures (Ni + Ti) and (Ni + Al) as an example. High adhesion of the coating and coefficient of powder use were ensured with maximum productivity at the DIMET-403 installation.

DFT-CEF Approach for the Thermodynamic Properties and Volume of Stable and Metastable Al–Ni Compounds

The Al–Ni system has been intensively studied both experimentally and theoretically. Previous first-principles calculations based on density-functional theory (DFT) typically investigate the stable phases of this system in their experimental stoichiometry. In this work, we present DFT calculations for the Al–Ni system that cover stable and metastable phases across the whole composition range for each phase. The considered metastable phases are relevant for applications as they are observed in engineering alloys based on Al–Ni. To model the Gibbs energies of solid phases of the Al–Ni system, we combine our DFT calculations with the compound energy formalism (CEF) that takes the Bragg–Williams–Gorsky approximation for the configurational entropy. Our results indicate that the majority of the investigated configurations have negative energy of formation with respect to Al fcc and Ni fcc. The calculated molar volumes for all investigated phases show negative deviations from Zen’s law. The thermodynamic properties at finite temperatures of individual phases allow one to predict the configurational contributions to the Gibbs energy. By applying a fully predictive approach without excess parameters, an acceptable topology of the DFT-based equilibrium phase diagram is obtained at low and intermediate temperatures. Further contributions can be added to improve the predictability of the method, such as phonons or going beyond the Bragg–Williams–Gorsky approximation that overestimates the stability range of the ordered phases. This is clearly demonstrated in the fcc order/disorder predicted metastable phase diagram.

Effect of Deposition Parameters on the Reactivity of Al/Ni Multilayer Thin Films

Nanoscale multilayers can be used as highly localized heat sources, making them attractive for several applications, in particular for joining and as igniters. Over the last decades, academia and industry have given particular emphasis to nanoscale multilayers from the Ni–Al system. In this study, Al/Ni (V) multilayer thin films with periods of nominally 25 and 50 nm (bilayer thickness) and near equiatomic average stoichiometry were produced by d.c. magnetron sputtering from Al (99.999% pure) and Ni (93 wt % Ni, 7 wt % V) targets (vanadium was added to the Ni target to make it non-magnetic). Deposition parameters such as the substrate rotation speed and substrate bias were varied in order to evaluate their effect on the reactivity of the multilayers. The influence of in situ ion bombardment of the multilayer thin films was also studied. Phase identification was carried out by X-ray diffraction, while the microstructure was analyzed in detail by transmission electron microscopy, distinguishing alternating layers throughout the entire thickness of the films. Although the films mainly consist of Al- and Ni-rich layers, the presence of the Al3Ni intermetallic phase was detected, except in the multilayers produced with the ion gun switched on during the deposition process. The ion bombardment, as well as the increase of the substrate bias, promote some microstructural disorder and thus affect the multilayers’ reactivity.

Leveraging Anisotropy for Coupled Optimization of Thermal Transport and Light Transmission in Micro‐Structured Materials for High‐Power Laser Applications

AbstractMaximum operating power densities in ceramic laser media scale with thermal conductivity k. This requires larger grain sizes in polycrystalline ceramics to reduce phonon scattering at grain boundaries. However, smaller grain sizes are preferred to minimize light scattering in the Rayleigh regime in polycrystals made from birefringent materials such as AlN and Al2O3, which are otherwise appealing for their high k. An optimization challenge arises from the opposite scaling laws governing the effects of grain sizes on k and light transmission. Here, this is tackled by introducing anisotropically microstructured materials (columnar/disk‐shaped grains) as the lasing media, and allowing orthogonal heat transfer and lasing directions. For columnar grains, larger grain sizes along the c‐axis help maintain high k for good heat dissipation, while preserving light transmission properties in the orthogonal lasing and pumping directions. Analytical models for the thermal conductivity in such structures are presented and verified using Monte‐Carlo ray‐tracing simulations. Similarly, an approximate Rayleigh–Gans–Debye model is used to predict light transmission and verified with exact simulations using FEM software. Finally, the tradeoff between thermal and optical phenomena is captured in a new anisotropic figure‐of‐merit tensor, which is optimized for the microstructure that maximizes lasing media performance in AlN and Al2O3 model systems.

Synthesis of a Crystalline and Transparent Aerogel Composed of Ni–Al Layered Double Hydroxide Nanoparticles through Crystallization from Amorphous Hydrogel

Enormous efforts have been devoted to the development of crystalline aerogels toward heterogeneous catalysis, energy storage, ion/molecular absorption, and luminescence. However, properties of aerogels are not fully exploited due to their low content of functional moieties embedded in their solid networks, low crystallinity, and limited chemical compositions. Herein, we develop a one-pot approach based on crystallization from amorphous metal hydroxides modified with a β-diketone ligand, toward crystalline transition-metal hydroxide aerogels. Synthesis of monolithic and crystalline aerogels of layered double hydroxide (LDH) was performed in a Ni-Al system starting from aqueous ethanol solutions of NiCl2·6H2O and AlCl3·6H2O with acetylacetone as an organic ligand. Propylene oxide as an alkalization reagent was added into precursory solutions to yield monolithic wet gels. The successive pH increase induces the formation of 3-dimentional (3-D) solid framework composed of amorphous Al(OH)3. Then, amphoteric Al(OH)3 undergoes crystallization into Ni-Al LDH via an acetylacetone-driven dissolution-crystallization of metal hydroxides without destroying the preformed 3-D solid framework. The process allows us to obtain crystalline aerogel monoliths with high porosity and high transparency after supercritical CO2 drying of wet gels. The present scheme can be expected to synthesize functionalized aerogel composed of crystalline transition-metal oxide/hydroxides nano-building-blocks.

Heat-Treatment of Aluminium-Nickel Composite Cold Sprayed Coating

Intermetallic compounds, especially aluminides, show good high-temperature strength, oxidation resistance, high melting points, and thus have received considerable attention as potential substitutes for superalloys in high-temperature applications. Aluminides are especially interesting because they are stable up to the critical temperature of ordering, which is close to the melting temperature. In the Al-Ni system, the most studied intermetallics are Ni3Al, NiAl and NiAl3. In the presented study, Al and Ni powders were mixed together with Al2O3 in various proportions to produce dense coatings by low-temperature cold spraying. Two types of post-deposition treatments were applied to produce aluminides, namely furnace heating and resistance spot welding. The former caused a long time diffusion while the latter a self-propagating high temperature synthesis. Both heating methods enabled formations of intermetallic phases. However, the furnace heating provides high porosity. The microstructure of the samples was analyzed by SEM (scanning electron microscope), EDS (energy dispersive X-ray spectroscopy) and XRD (X-ray diffraction) together with microhardness measurements.

Structure refinement, mechanical properties and feasibility of deformation of hypereutectic Al–Fe–Zr and Al–Ni–Zr alloys subjected to ultrasonic melt processing

Hypereutectic Al–Fe and Al–Ni alloys offer a potentially attractive combination of properties, e.g. high-temperature strength and stability, high elastic modulus and low coefficient of thermal expansion. This potential, however, cannot be reached unless the structure of these alloys is refined so that their processing becomes possible. In this study, we for the first time apply ultrasonic melt processing for refining the structure of hypereutectic Al-4% Fe and Al-8% Ni alloys with 0.3 wt% Zr addition. Both primary Al3Fe and Al3Ni particles as well as aluminum/eutectic grains are significantly refined. It is suggested that cavitation-induced fragmentation of primary Al3Zr crystals plays a significant role in the nucleation of intermetallics as well as aluminum. Furthermore, the hardness and tensile properties of the alloys substantially increase after ultrasonic treatment due to the refined structure, which also contributes to the considerably enhanced ductility of the alloys. As a result, the fracture mode changes from brittle fracture to ductile fracture. The increase in ductility makes the alloys suitable for hot deformation, which is demonstrated by lab-scale hot rolling. In addition, precipitation hardening of the alloys can be achieved by high-temperature annealing at 450 °C due to retained Zr in the Al solid solution upon solidification. The results are supported by the analysis of the composition of a supersaturated solid solution of Zr in Al and scanning and transmission electron microscopy that confirms the precipitation of coherent Al3Zr nanoparticles. It is demonstrated that a combination of ultrasonic melt processing and alloying with Zr makes it feasible to develop new class of hypereutectic casting and wrought alloys based on the Al–Fe and Al–Ni systems.

Improving the Characteristics of Wear-Resistant Coatings Obtained by HDTV-Boration, their Modification by Intermetallic Compounds of Fe-Al and Ni-Al Systems

Innovative technology of HDTV-borating, that is distinguished by high hardness, strength, wear resistance and corrosion resistance occupies a special place among the hardening processes for steels and construction materials. During the new technology process HDTV-boration of structural steel 65Mn (65Г in Russian) under a mix layer of charge mixture based on fused borate fluxing agent P-0.66, boron carbide and intermetallic compounds FexAly, NixAly. Using the methods of X-ray phase analysis, spectrography and metallography, the composition and structure of coatings were determined, the microhardness distribution over the coating thickness was studied. In the coatings, new phases of intermetallic compounds, the double superhard boride Fe2AlB2, were found; in the coatings, the base iron boride is FeB, what leads to an increase in their hardness and wear resistance. Modification of boride coatings formed by intermetallic compounds with melting temperatures close to the process temperature of HFC surfacing leads to a decrease in the cracks number and the appearance of new consumer qualities of the material.

Effect of Ti Contents on the Microstructure and Mechanical Properties of Ni˗Al˗Ti System

In this work, a ternary system prepared by Ni-Al-Ti mixed powder was synthesized using self-propagation high-temperature synthesis (SHS) process. The weight of the reactant was varied using 3%, 10%, 20% and 30% of the Ti content. The mixtures were compressed in a steel die to form compacted pellets, and subsequently ignited using an external heat source to initiate the combustion process. The synthesized products were characterized using SEM, EDS, and XRD, whereas the mechanical property of the product was measured using a Vickers microhardness test. The identification of the formed phase indicates that Ni-Al, Ti-Al and Ti-Ni systems were formed during the reaction. An increase of Ti content from 3% to 10% improves the density of the synthesized product. Further increase of Ti content to 20% results in the generation of cracks. The addition of Ti with 30% leads to the formation of a porous product. The heat released by the SHS process due to the formation of several intermetallic phases was responsible for the formation of defect products. The highest hardness of the product was achieved in the product prepared by 20% Ti content. However, the higher Ti content than 20% results in hardness reduction. This work shows that the content of 10% of Ti produced a dense and hard product.