Ni-Al System Research Articles

Structure and Properties of Ni˗Al˗Ti Systems Formed by Combustion Synthesis

Ni-Al-Ti system is one of the intermetallic systems that attract wide interest for high-temperature application. In this work, combustion synthesis was used to produce intermetallic materials prepared by Ni/Al with varied Ti content using 3%, 10%, 20%, and 30%. The reactant mixtures were compressed in a steel die to form compacted pellets. The ignition of the combustion process was conducted using an arch flame. Sequential tests of SEM, EDS, and XRD were conducted to characterize the microstructure of the synthesized products, whereas the mechanical properties of the product were measured using a Vickers microhardness test and wear test. The result shows that the phases formed in the product were dominated by Ni-Al and Ti-Ni systems. An increase in the Ti content from 3% to 20% increases the hardness. The formation of several intermetallic phases was responsible for the harder products. An increase of Ti content decreases the wear rate. This work shows that the content of 10% Ti can be used to achieve the optimized properties of hardness and wear resistance.

Composition and Crystalline Structure of Ternary Phases in the Ta–Ni–Al System

The composition and crystal structure of compounds produced by self-propagating high-temperature synthesis (SHS) from the 5Ta–2Ni–3Al (at %) powder mixture followed by vacuum remelting at 3000°C are studied. The SHS product contains the following phases: TaNiAl (Laves τ1 phase), NiAl, Ni2Al3, and Ta. Its microstructure includes Ta85Ni7Al8, Ta52Ni20Al28, and Ta53Ni25Al22 ternary phases according to elemental analysis data. Reflections belonging to no known ternary phases in the Ta–Ni–Al system under consideration are revealed in the X-ray diffraction pattern of the remelted material. Based on the homological approach, it is found that these reflections belong to three phases with the structural types W6Fe7 ( $$R\bar {3}m$$ ), Ti2Ni ( $$Fd\bar {3}m$$ ), and Ta3Al ( $${{P{{4}_{2}}} \mathord{\left/ {\vphantom {{P{{4}_{2}}} {mnm}}} \right. \kern-0em} {mnm}}$$ ). They are identified as reflections of three compounds, Ta6.5Ni6.5, Ti2Ni, and Ta2.84Al0.91, with unit-cell parameters differing from these for the same compounds with the conservation of the structural type. An increase in the unit-cell parameters of all revealed phases is noted when compared with known binary intermetallic compounds. This can be associated with the presence of Al atoms in the crystal lattice from the Ta6.5Ni6.5 phase and Al and Ta atoms in the phase with the Ti2Ni structural type. Phases Ta6.5Ni6.5 and Ti2Ni phases are identified as Ta6Ni6Al and Ta2Ni0.5Al0.5 by X-ray structural analysis and crystal-chemical modeling, and their structural type, composition, and unit-cell parameters are determined. The structure and composition are refined by the full-profile analysis, and the unit-cell parameters of the phases and their quantitative ratio in the material are determined. The phase composition of the material is as follows, wt %: 47 Ta6Ni6Al, 16 Ta2Ni0.5Al0.5, and 37 Ta3Al.

Ab-initio investigations on the energetic, opto-electronic and magnetic characteristics of alkali metal (AM) atom substituted monatomic AlN layer

Physical properties of AM atom substituted monolayer AlN are studied using first-principles calculations. During Li@Al substitution, AlN carries narrow/wide (0.3/2.95 eV) band gaps for spin up/down bands. The Na@Al substitution produces thin band semiconductor with (1.9/1.3 eV) energy gaps during spin up/down bands, respectively. Both K@Al and Na@N doping in AlN produced (0.5/0.4 eV) band gaps, respectively. The Li@N doped AlN is a half metal/wide band semiconductor for spin up/down bands, respectively. The K@N doped system displays (0.7/0.8 eV) energy gaps through spin up/down bands, respectively. Various optics parameters are improved in low energy range for all AM-doped AlN systems.

Composition and crystal structure of ternary phases in the Ta-Ni-Al system

The study covers the composition and crystal structure of compounds produced by self-propagating high-temperature synthesis (SHS) from the 5Ta—2Ni—3Al (at.%) powder mixture followed by vacuum remelting at 3000 °C. The SHS product contains the following phases: TaNiAl (Laves τ 1 -phase), NiAl, Ni 2 Al 3 , and Ta. Its microstructure features by the presence ofternary phases with the composi­tion Ta 85 Ni 7 Al 8 , Ta 52 Ni 20 Al 28 and Ta 53 Ni 25 Al 22 according to elemental analysis. The X -ray diffraction pattern of the remelted material revealed reflections that do not belong to any of the known ternary phases in the Ta—Ni—Al system considered. Based on the homological approach, it was found that these reflections belong to three phases with the structural types W 6 Fe 7 ( R 3 m ), Ti 2 Ni ( Fd 3 m ) and Ta3Al (P 4 2 /mnm). It was possible to define them as reflections of three compounds — Ta 6,5 Ni 6,5 , Ti 2 Ni and Ta 2,84 Al 0,91 with unit cell parameters different from those for the same compounds with the retained structural type. The increase in the unit cell parameters for all the phases identified was noted as compared to the known binary intermetallics. It may be associated with the presence of Al atoms in the crystal lattice for the Ta 6.5 Ni 6.5 phase and Al and Ta atoms in the phase with the structural type Ti 2 Ni. X -ray diffraction analysis and crystal-chemical modeling made it possible to identify Ta 6.5 Ni 6.5 and Ti 2 Ni phases as Ta 6 Ni 6 Al and Ta 2 Ni 0.5 Al 0.5 , to determine their structural type, composition and unit cell parameters. Full-profile analysis was conducted to specify the structure and composition and determine unit cell parameters of the phases and their quantitative ratio in the material. The material phase composition is 47 wt.% Ta 6 Ni 6 Al, 16 wt.% Ta 2 Ni 0.5 Al 0.5 and 37 wt.% Ta 3 Al.

STUDY OF THE STRUCTURE AND PHASE COMPOSITION OF THE OXIDE FILM ON THE SURFACE OF A LAYERED COATING OF THE Al-Ni SYSTEM

This work is aimed to the study of the structure and phase composition of the 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 atmospheric oxygen, separate sections of Al2O3 oxide are formed on its surface, which are agglomerates of plate crystals of α-modification of nanometer thickness, which increase and grow together with increasing exposure time continuous protective oxide film. An increase in the heating temperature leads to an intensification of oxidation processes and the formation of a complex oxide film of AlO and spinel NiAlO.

Estimation of the Service Lifetime of Layered Heat-Resistant Ni-Al and Ni-Cr-Al Coatings

This paper describes the method and results of calculation of the service lifetime of layered heat-resistant Ni-Al and Ni-Cr-Al coatings by known empirical methods. It is shown, that alloying the Ni-Al system coatings by Cr leads to a five-fold increase of durability at high temperatures.

Intermetallic compounds of the Ti–Al–Ni system suitable for hydrogen accumulation

The paper studies how intermetallic compounds of the titanium-aluminum-niobium system could be used as a getter. It was found that with an increase in the niobium content in the alloy from 16 to 40 at.%, the volume of absorbed hydrogen increases from 0.47 to 2.2 wt.%. It is shown that the maximum amount of absorbed hydrogen is observed in alloys with a dendritic structure. Recommendations are given for future directions of research.

Structural and Energy Characteristics of NiAl Alloys with Deviations from Stoichiometric Composition. General Provisions. Part 1

The research results are presented in two parts. The first part presents data describing the general state of the problem of low-stability pre-transitional structural phase states in intermetallides of the Ni-Al system. Physical interpretations of low-stability structural phase states in condensed systems are described along with the applied physical-mathematical model based on a calculated block of 32x32x32 elementary cells (65536 atoms) of an ordered BCC structure (superstructure B2, Pearson symbol cP2). The study is carried out by Monte Carlo methods using the Metropolis algorithm for an intermetallic NiAl sample of stoichiometric composition (used as an example). It is found out that a kind of hysteresis is observed during thermal cycling. The presence of such hysteresis indicates the irreversibility of the occurring processes. This implies a difference in the structural phase states at the heating and cooling stages.
 The second part of the paper will demonstrate the results of a computer simulation of changes in structural phase states. The focus will be made on the low-stability pre-transitional structural phase states and energy characteristics of intermetallides образом with deviations from the stoichiometric composition of Ni45Al55 and Ni55Al45.

Formation of New Intermetallic Phases in the Ta–Ni–Al System

Formation of New Intermetallic Phases in the Ta–Ni–Al System

A comparative atomic simulation study of the configurations in M-Al (M = Mg, Ni, and Fe) nanoalloys: influence of alloying ability, surface energy, atomic radius, and atomic arrangement

The structure evolution behavior of M-Al (M = Mg, Ni, and Fe) nanoalloys with three sizes (N = 13, 55, and 147) at different compositions were studied through basin-hopping Monte Carlo and molecular dynamics simulations. The atomic interaction was described using the embedded atom method. Results showed that the particle size and composition ratio of each element affected the final configuration of nanoparticles mainly due to the competition between the alloying effect and surface segregation. Among three different systems, the Ni-Al system had the strongest alloying effect, followed by Fe-Al and Mg-Al systems. Among three types of nanoalloys with 13 atoms, the icosahedra (ICO) structure had the most stable configuration. For nanoalloys with 55 and 147 atoms, poly-icosahedral (pIh), three-layer onion-like, rhombohedra (RHO), and core-shell structures were observed by controlling the composition ratio of two different metals. This study can provide theoretical guidance for the laboratory synthesis of nanoalloys with different structures.

In-situ TiB2–NiAl composites synthesised by arc melting: oxidation behaviour, oxidation kinetics and oxidation mechanism

ABSTRACT Endogenetic particles TiB2 (5 and 10 vol.-%)-reinforced NiAl matrix composites were fabricated in-situ from Ti–B–Ni–Al system by arc melting. The oxidation behaviour and anti-oxidant mechanism of TiB2–NiAl composite were investigated at 1173 K in air atmosphere. The composite had a rapid rate of oxidation during the first 20 h. With the increase in oxidation time, α-Al2O3 oxidation films and needle-shaped TiO2 phases were formed on the surface of the composite. As the Al oxidised into Al2O3, the NiAl phase transformed into γ-Ni3Al phase. The oxides were beneficial for improving the oxidation resistance of the composite. The mass change of the composite was less than 2.5 mg cm−2 after being oxidised at 1173 K in air atmosphere for 100 h. The composite showed excellent high-temperature oxidation resistance.

Influence of micropores on structural instability of the combustion wave

The article shows examples of visualization of the process of heat transfer by radiation in unstable combustion modes of porous powder materials, which are in good agreement with the results of high-speed video recording and micropyrometry. The mathematical model and the results of calculating the structure of the combustion wave in the Ni-Al system are presented. The contribution of radiative heat transfer at an adiabatic combustion temperature in the range of 810 % and the effect of its trigger shutdown with decreasing temperature were revealed.

The effect of various factors on the strength and ignition of the used Ni-Al system

The aim of this work was to obtain structural reactive materials from high-energy mixtures. The effect of various additives on the parameters of the burning rate and the ignition temperature was studied. The object of the study was a powder mixture based on nickel and aluminum in a stoichiometric ratio with a particle size of less than 50 microns. Boron and tungsten fibers were used as reinforcing and energy elements. Mixtures of powders were compacted to a relative density of 0.7 and 0.8. Specimens were made in the form of a parallelepiped. The strength of the samples was studied using three-point bending. It was possible to increase the initial strength of the samples by 9 times when reinforced with tungsten fibers.

Evaluation of neutron activation of intermetallic matrices for dispersive nuclear fuel obtained by SH-synthesis

The paper describes a technique for obtaining intermetallic matrix materials based on Zr-Al and Ni-Al systems for dispersive nuclear fuel. This type of fuel is planned to be used in existing and future high-temperature nuclear reactors. Physical and mathematical modelling of the process of activation of matrices by neutron radiation showed that upon reaching the value of thermal neutron fluence of the order of 2.76⋅1021 n⋅cm−2, the activity of Zr-Al and Ni-Al matrices was 1.3 ⋅ 1010 and 0.2⋅1010 Bq/g, respectively. The analysis showed that in terms of exposure of irradiated fuel it is preferable to use a matrix based on the zirconium-aluminium system.

ИЗГОТОВЛЕНИЕ ЭКСПЕРИМЕНТАЛЬНОГО КОНСТРУКТИВНО-ПОДОБНОГО ОБРАЗЦА СЕКТОРА СОПЛОВОГО АППАРАТА И ПРОВЕДЕНИЕ ЕГО ИСПЫТАНИЙ ПРИ ТЕМПЕРАТУРЕ 1500 °С

The interaction of the SiC–SiCw–B4C–AlN system ceramic composite material (CCM) with the EP648 alloy in the process of high-temperature brazing was studied. The smallest erosion activity both in relation to CCM, and to the EP648 alloy, has HMP solder VPr50. An experimental constructionally similar sample of the nozzle assembly sector was made using uncooled nozzle blade prototypes from CCM. Tests of an experimental constructionally similar sample of the nozzle assembly sector at a temperature of 1500 °C were carried out. No traces of material ablation from the surface of the CMC were found.

Precision measurement of the velocity of propagation SHS wave by the method of chrono-topographical analysis

The paper presents the capabilities of the chrono-topographical analysis method for studying the discrete nature of the propagation of the SHS process on the scale of the combustion source and the reaction cell. Using the approach of chrono-topographic analysis, thermal imaging studies of the microheterogeneous combustion mode in the Ni-Al system were carried out. The regularities of the dynamics of individual foci in the SHS wave are revealed. Using chronographic maps of the SHS process, it is shown that there are two types of foci in the combustion wave, which differ in the nature of the propagation dynamics. On the scale of the reaction cells in the experiment, the relationship of the combustion dynamics with the moments of the formation of new reaction sites was studied. According to the results, it was concluded that an increase in the heat deficit in microheterogeneous combustion regimes leads to an i ncrease in the dispersion of the resulting product. This work was supported by the Russian Foundation for Basic Research in research projects No. 18-08-01475, 18-08-01152, as well as grant No. 13-01-20 / 28 "Leading Scientific School of Yugra State University".

Zr-based nickel aluminides: Crystal structure and electronic properties

In our motive to contribute to a better understanding of phase transitions, structural changes and physical properties of Zr-based alloys, we have studied three zirconium-rich compounds in the Zr–Ni–Al system annealed at 800 °C. For Zr6NiAl2, which was investigated hitherto only by the use of X-ray powder film data, the precise crystal structure has been derived from Rietveld refinement of powder X-ray diffraction data revealing a significant disorder of Al (81.3% Al+18.7% Ni in 2d) and Ni (76.1%Ni+23.9% Al in 1a) atomic sites rendering final composition Zr6Ni1.14Al1.86 in accord with energy dispersive X-ray (EDX) spectroscopy analysis. The crystal structures of ZrNiAl and Zr5Ni4Al have been confirmed; despite the disorder of certain atom sites (94% Al+6% Ni in 3g and 90% Ni+10%Al in 2d for ZrNiAl; 93% Zr+7% Al in 2e and 95% Al+5% Zr in 2f for Zr5Ni4Al; Rietveld refinements of powder X-ray diffraction data), the deviations from the stoichiometry for these compounds are negligible. Cell parameters and atomic coordinates have been also refined in the scope of local density approximation being in good agreement with experimental data. For all compounds the electronic density of states has been calculated. Electrical resistivity measurements characterize ZrNiAl, Zr6NiAl2 and Zr5Ni4Al as metals in concord with electronic band structure calculations.

In-Situ Synthesis of Aluminum Matrix Composite from Al–NiO System by Mechanical Alloying

In this paper, Al-based composites reinforced by Alumina and Al–Ni intermetallic compounds have been successfully fabricated by mechanical alloying technique. The intermetallic phase, i.e., NiAl, NiAl3, Ni2Al3, as well as Alumina, were formed in the aluminum matrix by in situ solid-state reactions between pure Al and NiO powders. The effects of NiO content (7–10–13 vol%) on the characteristics of the fabricated composites were examined, the hardness, wear properties, phase constituent, and composite microstructure with different NiO content in particular. The results showed that the addition of NiO to Al increases the formation of Al–Ni system intermetallic compounds and enhance the surface hardness. Further, it is ascertained that Al–10 vol% NiO nanocomposite has better wear properties in comparison with samples with 7 and 13 vol% NiO due to the better matrix integrity and reinforcement distribution in the Al matrix.

Synthesis of Ni-Al intermetallic surface alloys produced by using a low-energy high-current electron beam

Ni-Al surface alloy electron beam synthesis results are presented. Surface alloy was formed on a carbon steel substrate by multilayer Ni-Al system deposition and subsequent one pulse low-energy high-current electron beam (LEHCEB) treatment in single vacuum cycle. It is shown that surface alloy containing mainly intermetallic phase NiAl is formed as a result of one pulse LEHCEB treatment. It is established that NiAl surface alloy microhardness and wear resistance are higher in comparison to steel substrate parameters.

Instability of the Ni-Al combustion wave in the Zeldovich-Barenblatt parameters

The study of the thermal structure of the combustion wave of self-propagating high-temperature synthesis using differential chronoscopy (DCS), using the example of the Ni-Al system, demonstrates the possibility of estimating the criterion of thermal diffusion instability of the front in accordance with the Zeldovich-Barenblatt model. The application of standard image recognition methods, in the form of a high-speed Trace-transform algorithm, to a 2D chronogram of the interframe difference in the coordinates of the combustion front, calculated from high-speed video recording of the propagation of a SHS wave as a DCS-map, demonstrates the ability to control the sustainability mode of the burning wave in situ.