Ni-Al System Research Articles

Numerical Study of Epitaxial Growth after Partial Remelting during Selective Electron Beam Melting in the Context of Ni–Al

In the selective electron beam melting approach an electron beam is used to partially melt the material powder. Based on the local high energy input, the solidification conditions and likewise the microstructures strongly deviate from conventional investment casting processes. The repeated energy input into the material during processing leads to the partial remelting of the already existing microstructure. To closer investigative this effect of partial remelting, in the present work the phase-field model is applied. In the first part the solidification of the referenced Ni–Al system is simulated in respect to selective electron beam melting. The model is calibrated such to reproduce the solidification kinetics of the superalloy CMSX-4. By comparison to experimental observations reported in the literature, the model is validated and is subsequently applied to study the effect of partial remelting. In the numerical approach the microstructures obtained from the solidification simulations are taken as starting condition. By systematically varying the temperature of the liquid built layer, the effect of remelting on the existing microstructure can be investigated. Based on these results, the experimental processing can be optimized further to produce parts with significantly more homogenous element distributions.

Self-diffusion in melts of Ni-Al and Ti-Al systems: molecular dynamics study

Self-diffusion in liquid alloys of Ni-Al and Ti-Al systems, depending on the concentration of the components, as well as in pure metals Al, Ni, and Ti, has been studied using the molecular dynamics method. Knowledge of the diffusion parameters in melts of binary systems, such as Ni-Al and Ti-Al, is necessary for a more detailed understanding and prediction of the processes occurring during combustion synthesis and in the manufacture of wares by melt casting. For the considered systems, self-diffusion characteristics (activation energy and preexponential factor in the corresponding Arrhenius equation) are found separately for atoms of different types. Good agreement of diffusion characteristics with experimental data was obtained for pure metal melts, which indicates the physical realism of the molecular dynamics model and EAM potentials used. In addition to pure metals, three component ratios were considered for each system: A75B25, A50B50 and A25B75. According to the data obtained, the activation energy of diffusion substantially depends on the concentration of the components, and the highest, among the considered compositions, for Ni75Al25 for Ni-Al system and for Ti50Al50 for Ti-Al system. At the same time, no significant predominance of diffusion mobility of atoms of different types was observed for all the mixture compositions considered.

Processing of intermetallic laminates by Self-Propagating High–Temperature Synthesis initiated with concentrated solar energy

The intermetallic compounds are very interesting in a multitude of structural and functional applications, such as in turbomachines or engine parts, due to their good behaviour at high temperatures, as well as their high resistance to corrosion and oxidation. In the present work, the study of processing of the Ni-Al system intermetallics has been carried out by means of Self-Propagating High–Temperature Synthesis initiated by concentrated solar energy (SHS–CSE). Synthesis by this high-energy exothermic reaction often causes the appearance of porosity, lack of interlayer adhesion, volumetric expansion, and even the total loss of sample shape. To obtain high-quality systems, a study has been carried out on one-layer and multi-layer configurations from powder materials, considering the influence of the heating rate and time. The use of concentrated solar energy has allowed to obtain fully densified nickel parts at 1000°C in just 15 min, compared to the 1325°C and more than 12h required by conventional techniques to obtain lower relative densities (~97%). The best results in multilayer configurations have been achieved in Ni-Ni/Al-Ni system with the synthesis of intermetallic compounds type Ni2Al3, NiAl and Ni3Al. The control of volumetric expansion and porosity, full densified nickel layers perfectly adhered to the interlayer and hardness values up to 900 HV have been obtained in just 2 min. This work highlights the wide possibilities of the use of CSE in metal treatment, which allows efficient and sustainable synthesis of new systems and the improvement of the final properties of the parts.

Alternative Thermal Cycling Treatment to Produce Abnormal Grain Growth in FeMnAlNi Alloys: Study of Composition Variations and Effects on the Relative Phase Stabilities

An alternative method to obtain abnormal grain growth in Fe–Mn–Al–Ni system is presented. A crucible is used to control the cooling speed of the samples from 1200 °C enabling the nucleation of the equilibrium fcc phase. This fcc structure leads to an abnormal grain growth after heating to 1200 °C, temperature at which the bcc phase is stable. In this way, crystals with a mean diameter of 18 mm are obtained after 4 thermal cycles which take approximately 2 h. Additionally, precise composition measurements using neutron activation allowed the detection of a decrease in Mn content after each thermal cycle. Using electrical resistivity measurements, the effect of the variation of Mn content on the relative phase stability between the bcc austenite and the fcc martensite has been observed and is discussed here.

Microstructure characteristics of wire arc additive manufactured Ni Al intermetallic compounds

An initial attempt had been made to fabricate NiAl intermetallic compounds (IMCs) by wire arc additive manufacturing (WAAM) in order to overcome the disadvantages of traditional casting-melting method such as complex process and long production cycle. The effects of wire Ni content on the microstructure and mechanical properties of the deposited thin-wall samples were studied. It was found that the deposited microstructure varied from M-NiAl/Ni3Al to bulk-like Ni3Al + γ-Ni/γ′-Ni3Al by increasing the Ni content. The average microhardness of the deposition firstly decreased from 437.6 HV0.3 to the minimum of 255.4 HV0.3 with the increase of the Ni content because of the decrease of the M-NiAl with high hardness. It then increased to 302.1 HV0.3 owing to the increase of the strengthened phase of γ′. The thermodynamic behavior in NiAl system was calculated to discuss the transformation mechanism of the WAAMed NiAl IMCs.

Electronic Structure of Ternary Alloys of Group III and Rare Earth Nitrides.

Electronic structures of ternary alloys of group III (Al, Ga, In) and rare earth (Sc, Y, Lu) nitrides were investigated from first principles. The general gradient approximation (GGA) was employed in predictions of structural parameters, whereas electronic properties of the alloys were studied with the modified Becke–Johnson GGA approach. The evolution of structural parameters in the materials reveals a strong tendency to flattening of the wurtzite type atomic layers. The introduction of rare earth (RE) ions into Al- and In-based nitrides leads to narrowing and widening of a band gap, respectively. Al-based materials doped with Y and Lu may also exhibit a strong band gap bowing. The increase of a band gap was obtained for GaScN alloys. Relatively small modifications of electronic structure related to a RE ion content are expected in GaYN and GaLuN systems. The findings presented in this work may encourage further experimental investigations of electronic structures of mixed group III and RE nitride materials because, except for Sc-doped GaN and AlN systems, these novel semiconductors were not obtained up to now.

Influence of (Li/Na/K) doping and point defect (VAl, Hi) on the magnetic and photocatalytic performance of AlN: A first-principles study

Although extensive reports on the influence of Li/Na/K doping on the physical properties of AlN systems exist, the effects of Li/Na/K doping and point defects (VAl, Hi) coexisting in AlN systems on magneto-optical properties are often neglected. Experimentally, Li/Na/K doping and point defects (VAl, Hi) cannot be precisely controlled. In this study, the generalized gradient approximation (GGA) plane wave ultrasoft pseudopotential + U method based on spin density functional theory is adopted to solve the abovementioned problem. The first-principles method is utilized to study the effects of point defects (VAl, Hi) and Li/Na/K doping on the photocatalytic performance of AlN systems. Compared with the Al34MN36 (M = Li/Na/K) system, the Al34MHiN36 (M = Li/Na/K) system presents reduced formation energy and improved stability. The Al34NaHiN36 system has the smallest formation energy and the highest stability. In particular, compared with all doped systems, the Al34NaHiN36 system has the best absorption spectrum redshift, the best carrier activity, the longest carrier lifetime, and the strongest oxidation capacity, that is, the best photocatalytic performance. The first-principles study indicates that N atoms in all Al34MN36 (M = Li/Na/K) and Al34MHiN36 (M = Li/Na/K) systems have acceptor and donor characteristics. The magnetic source of all doped systems is related to the double exchange of carriers as mediators, the itinerant electron polarization of unpaired N2− atoms and electric polarization. This study has certain theoretical guidance for the experimental design and preparation of new AlN magneto-optical functional materials.

The influence of high-energy ball milling and nanoadditives on the kinetics of heterogeneous reaction in Ni-Al system

Kinetic studies were performed utilizing high-speed temperature scanner in the Ni-Al system including those with and without mechanical activation (MA) of different duration in a planetary ball mill, with and without using carbon nanoadditives (NA). The temperature profiles were taken and treated at different heating rates from 100 up to 2600 °C/min considering the influence of activation duration and the role of nanoadditive on the characteristic points of thermograms. Kissinger method allowed to evaluate activation energy (Ea) for non-activated, activated (1, 2, 3, 5 min), nanoadditive (1 wt.%) containing and nanoadditive (1 wt.%) containing mechanoactivated (1, 3, 5 min) mixtures. The beneficial influence of NA on the interaction between Ni and Al in the non-activated and moderately mechanoactivated mixtures was demonstrated. The influence of MA and NA on the microstructure features and phase formation sequence at various heating rates were revealed. For all the mixtures under study, T* characteristic temperatures (the temperature, where the maximum exothermic effect was observed) were found to increase with increasing heating rates. It was unravelled that mechanical treatment leads to significant changes in the reaction kinetics and phase formation laws. Particularly, in an activated mixture, the formation of Ni3Al is followed by NiAl intermetallic, in contrast to non-activated mixture, where the reaction proceeds only with the NiAl formation. The both MA in 1 min and addition of 1 wt.% NA decreased the activation energy of the Ni-Al reaction, exhibiting commensurate impact on the effective activation energy value of the Ni-Al system. However, > 3 min MA in the presence of 1 wt.% NA have prohibitive effect on the reaction in the Ni-Al system.

Obtaining of Composite Alloys Based on Nickel Aluminides with Rare Metals

The paper presents the research results on the production of doped composite materials by the method of out-of-furnace liquid-phase self-propagating high-temperature synthesis using oxides and mineral concentrates containing Zr and W as a charge. The positive experience of producing ingots of intermetallic alloys based on the Ni-Al system in one stage of the reduction process of joint metallothermy is shown. The use of Zr in the charge leads to grinding of microstructure of the ingots and the formation of intermetallic compounds containing Zr. The additional use of C, B2O3, and W in the charge results in the formation of complex borides and tungsten carbides in the ingots. Additional introduction of Cr2O3 into the charge is necessary for the formation of W carbides in the nickel aluminide matrix.

SHS in the Ni–Al System: Influence of Green Density and Mechanoactivation

SHS in the Ni–Al System: Influence of Green Density and Mechanoactivation

Computational study on the effects of vacancy in wurtzite AlN (0001) and (000[formula omitted]) surfaces

In this study, the effects of vacancies in wurtzite AlN (0001) and (0001(—)) surfaces were investigated by performing CASTEP calculations in Materials Studio software. In particular, we comparatively analyzed the electronic structure, magnetism, and partial optical properties of AlN with surface vacancies. The results show that after introducing a vacancy, the band gap of the systems became zero, which represented a metallic characteristic. In addition, both the vacant (0001) and (0001(—)) surfaces as well as their corresponding systems exhibited non-magnetic. Contrastingly, the original systems with an intact (0001) or (0001(—)) surface were ferrimagnetic. Finally, it was found that the presence of the vacancy did not have any evident impact on the absorption and reflection of the AlN systems. Compared with the (0001) system, the (0001(—)) one had greater maximum absorption coefficient and maximum reflectivity.

High temperature wear behavior of δ-Ni2Al3 and β-NiAl coatings formed on pure nickel using pack cementation process and diffusion heat treatment

Nickel aluminide coatings with three different compositions, namely δ-Ni2Al3, Al-rich β-NiAl and Ni-rich β-NiAl were produced by chemical vapor deposition on pure nickel with successive diffusion heat treatments. The influence of the coating composition on the wear resistance is systematically studied and discussed based on the stability region of the δ-Ni2Al3 to the hypo-stoichiometric β-NiAl phase using a ball-on-disk setup up to 600 °C in air with alumina as the counterpart material. Wear resistance generally increased with decreasing Al contents of the coatings tested. Nanoindentation measurements showed that Young's moduli and hardness decreased for decreasing Al contents in the NiAl system. This change is accompanied with an increase in ductility, resulting in higher resistance against cracking of the coating, which is found to be the main wear mechanism for Al-rich coatings.

Nanoscale twinning and superstructures of martensite in the Fe–Mn–Al–Ni system

Fe–Mn–Al–Ni-based shape memory alloys are regarded as promising shape memory materials, which can be utilized due to its pseudoelastic properties in a wide field of applications. Based on a detailed microstructural analysis, it is demonstrated that the formation of different austenitic superstructures and their impact on the resulting structure of the martensite tremendously affect the reversibility of the martensitic transformation. In addition to the usually investigated chemical compositions, which produce a nanoscopic A2 + B2 austenitic state, Mn-rich Fe–Mn–Al–Ni alloys, relying on a fully ordered D03/L21 austenite, may be suggested to constitute a potentially new group of SMAs in the Fe–Mn–Al–Ni system.

Combustion in Ni–Al System with Cu Additive (Powder or Rod). Experiment and Mathematical Model

Combustion in Ni–Al System with Cu Additive (Powder or Rod). Experiment and Mathematical Model

Study of Surface and Electrical Conductivity of Thin Metal Films of the Ni–Al System

The results of studies of thin Ni–Al films obtained by the resistive thermal evaporation method and having characteristic island sizes of 700–1000 nm with a film thickness of ~500 nm are described. A brief description of the method for producing a film using an installation for creating a high vacuum and subsequent film deposition is presented. The obtained film sample was studied with an optical microscope, a scanning probe microscope, and a Fourier analyzer. The kinetic characteristics of the film, its film, and the characteristic sizes of the islands have been established; regularities in the island structure of the films were sought, and its electrical conductivity has been determined.

The effect of La2O3 and CeO2 modifiers on properties of Ni–Al catalysts for LNG prereforming

Ni/La–Al2O3 and Ni/Ce–Al2O3 catalysts with a small amount of promoters intended for prereforming of LNG were characterized by XRF, N2 adsorption-desorption, XRD, H2 chemisorption, HRTEM and XPS. The catalytic activity was evaluated in methane steam reforming both in the kinetic and diffusion regime, at temperatures characteristic of pre-reforming. Carbonaceous deposit was analysed by TPO-MS method. The nature and location of the coke were studied by HRTEM.La or Ce addition into Ni–Al system causes the increase of the active surface area of Ni by enhancing its dispersion. Studies at kinetic regime have shown that the promoted catalysts have almost twice the activity than reference Ni–Al catalyst. This effect was not confirmed by measurements in the diffusion regime on whole catalyst tablets. Almost identical textural properties of catalysts and diffusive limitations related to them but not the catalytic properties of the material itself appeared to be crucial factors. The presence of La (but not Ce) causes a significant increase in resistance to coking.

ТЕХНОЛОГИЧЕСКИЕ ПУТИ СОЗДАНИЯ КОМПОЗИЦИОННЫХ МАТЕРИАЛОВ НА ОСНОВЕ ЖАРОПРОЧНЫХ ТУГОПЛАВКИХ СОЕДИНЕНИЙ (обзор)

The article discusses the main technological approaches to obtain heat-resistant and heat-resistant materials based on compounds in the Ni–Al system in order to use them in promising products of aviation and rocket technology. It is shown that when receiving materials based on compounds in the Ni-Al system, a phase of eutectic origin is formed based on the Ni3Al compound, which reduces the technological plasticity of the alloys of this system. The use of powder metallurgy methods eliminates such phases in the structure of alloys obtained using granule metallurgy technology, as well as with the use of special methods of powder metallurgy. Technological approaches are presented to obtain similar materials using powder metallurgy methods combined with thermomechanical processing.

Composite Metal-Matrix Alloys Based on Ni-Al for Obtaining Wear-Resistant Coatings by Electric Spark Deposition

The paper presents the research results on produsing by the method of liquid-phase self-propagating high-temperature synthesis (SHS) the composite metal-matrix alloys intended for the obtaining of wear-resistant coatings by electric spark deposition (ESD). Oxides NiO, Cr2O3 and mineral concentrate ZrO2 were used as a melting charge. Alloys based on the Ni-Al system with aluminides of complex composition containing Cr and Zr were obtained by means of the alumothermic SHS reaction. Wear-resistant coatings were formed on steel 45 by the ESD method by means of the newly obtained alloys,. The maximum wear resistance of the coatings was obtained using the alloys containing Cr (wt% 18) and Zr (wt% 1.9).

Application of two-step diffusion couple technique in high-throughput screening of optimal composition and aging temperatures for alloys design: A demonstration in binary Ni-Al system

In this paper, four binary Ni-13.4 at.% Al/Ni-17.7 at.% Al diffusion couples were first prepared and subjected to homogenization at 1573 K for 10,800 s, from which a continuous concentration profile formed. The three diffusion couples were then cooled down for aging at respective temperatures, i.e., 1173, 1123, and 1073 K, for 14400 s. The effect of composition and aging temperature on the aging microstructure was studied in detail by means of different experimental techniques and statistical analysis. The volume fraction, grain size, and shape factor of ?? precipitates in the three diffusion couples were plotted as a function of alloy composition and annealing temperatures. Together with the previously proposed evaluation function in which the phase fraction, grain size, and shape factor of ?? precipitates were chosen as the evaluation indicators, the optimal alloy composition and aging temperature for binary Ni-Al alloys with the best mechanical properties were evaluated, and finally validated by the measured hardness values. The successful demonstration of alloy design in the present binary Ni-Al alloys indicated that the two-step diffusion couple, together with the evaluation function for mechanic properties, should be of generality for high-throughput screening of optimal alloy composition and heat treatment process in different alloys.

Tailoring spintronic and opto-electronic characteristics of bilayer AlN through MnO x clusters intercalation; an ab initio study.

Adopting ab initio density functional theory (DFT) technique, the spintronic and opto-electronic characteristics of MnOx (i.e., Mn, MnO, MnO2, MnO3 and MnO4) clusters intercalated bilayer AlN (BL/AlN) systems are investigated in this paper. In terms of electron transfer, charge transfer occurs from BL/AlN to the MnOx clusters. MnOx clusters intercalation induces magnetic behavior in the non-magnetic AlN system. The splitting of electronic bands occurs, thus producing spintronic trends in the electronic structure of BL/AlN system. Further, MnOx intercalation converts insulating BL/AlN to a half metal/semiconductor material during spin up/down bands depending upon the type of impurity cluster present in its lattice. For instance, Mn, MnO and MnO2 intercalation in BL/AlN produces a half metallic BL/AlN system as surface states are available at the Fermi Energy (EF) level for spin up and down band channels, accordingly. Whereas, MnO3 and MnO4 intercalation produces a conducting BL/AlN system having a 0.5 eV and 0.6 eV band gap during the spin down band channel, respectively. During spin up band channels these systems behave as semiconductors with band gaps of 1.4 eV and 1.2 eV, respectively. In terms of optical characteristics (i.e., absorption coefficient, reflectivity and energy loss spectrum (ELS)), it was found that MnOx intercalation improves the absorption spectrum in the low electron energy range and absorption peaks are observed in the 0–3 eV energy range, which are not present in the absorption spectrum of pure BL/AlN. The static reflectivity parameter of BL/AlN is increased after MnOx intercalation and the ELS parameter obtains significant peak intensities in the 0–2 eV energy range, whereas for pure BL/AlN, ELS contains negligible value in this energy range. Outcomes of this study indicate that, MnOx clusters intercalation in BL/AlN is a suitable technique to tailor its spintronic and opto-electronic trends. Thus, experimental investigation can be carried out on the systems discussed in this work, so as to fabricate practical layered AlN systems that are functional in the field of nano-technology.