Ni-Al System Research Articles

Structure of multilayer microcomposite Ni/Al obtained by diffusion welding

The article discusses the study of the structure of composite materials of layered type, in which alteration of layers of brittle heat-resistant and relatively plastic components should provide nonbrittle behavior of the composite in general at temperatures higher than 1000°C. The possibility of obtaining such materials is demonstrated for the case of the Ni-Al system. Diffusion welding under pressure at temperatures not higher than aluminum melting point is applied at first to produce multilayered composites Ni/Al, in which at subsequent higher temperatures multilayered structures are generated from chemical compounds formed as a consequence of mutual diffusion of nickel and aluminum. The compound NiAl has the highest interest. Flat samples are obtained consisting of a sufficiently high amount of diffusion layers of NiAl with thickness of ∼110 μm.

A new approach to establish both stable and metastable phase equilibria for fcc ordered/disordered phase transition: application to the Al–Ni and Ni–Si systems

Both two-sublattice (2SL) and four-sublattice (4SL) models in the framework of the compound energy formalism can be used to describe the fcc ordered/disordered transitions. When transferring the parameters of 2SL disregarding the metastable ordered states into those of 4SL, inconsistence in either stable or metastable phase diagrams could appear, as detected in both Al–Ni and Ni–Si systems. To avoid such a kind of drawback, this behavior was analyzed and investigated in the Ni–Si and Al–Ni systems with the aid of first–principle calculations. Furthermore, a new approach considering both the stable and metastable fcc ordered phase equilibria deduced from the first–principles calculations was proposed to perform a reliable thermodynamic modeling for the fcc ordered/disordered transition. The Ni–Si system was then thermodynamically assessed using the presently proposed approach. The good agreement between the calculation and experiments demonstrates the reliability of the proposed approach. It is expected that the approach is valid for other systems showing complex ordered/disordered transitions.

Phase-field modelling of self-propagating high-temperature synthesis of NiAl

A phase-field model is developed and used to simulate high-temperature synthesis of intermetallic compounds. The model is based on a thermodynamic formulation, which incorporates the formation of chemically ordered phases and the associated heat generation. In contrast to previous approaches to modelling of high-temperature synthesis of intermetallics, the present model can be used to analyse the kinetics of the process at the microstructure level. The model takes general thermodynamic and kinetic parameters as input and gives as output a spatially resolved sequence of phase formation, from which the overall reaction kinetics can be inferred. Thus, no additional assumption has to be made on the nature of the kinetic mechanisms or on the magnitude of the overall reaction rate. Beside prediction of the microstructure, the model captures the key thermal characteristics of the combustion synthesis in both modes of thermal explosion and self-propagation. The results of simulations, as applied to the case of intermetallic formation in a simplified Ni–Al system, are shown to be consistent with the existing experimental data.

Optimisation of Nickel Aluminising by CVD

Results Concerning Nickel Aluminisation with Application of Chemical Vapour Deposition Method Are Presented. Two-Step Processing under Investigation Consists of Al Chloride Formation in the Primary Vessel and Al Deposition in the Secondary One. the Initial Gas Stream Is Composed of Hcl Dissolved in H2 at Various Ratios. it Was Shown that the Choice of the [HCl]/[H2] Ratio and the Determination of the Optimum Temperature to Produce Most Preferential β-Nial Phase May Be Done with the Use of Thermodynamic Calculations. the Results Obtained with Application of Factsage Program Confirm Essential Influence of both Initial [HCl]/[H2] Ratio (in the Range between 0,05 and 100) and the Temperature in the Second Vessel (1123 K – 1323 K) on Aluminium Chloride Partial Pressures and Hence Aluminium Content in its Gaseous Donors and at the Substrate Surface (boundary Condition for Interdiffusion in Ni-Al System). it Was Confirmed that β-Nial Growth Is Favoured at Low [HCl]/[H2] Ratios and High Temperatures for which Alcl and AlCl2 Partial Pressures Increase with Respect to that of AlCl3. the Thermodynamic Predictions Remain in Agreement with CVD Experiments. the Presented Thermodynamic Data May Be Used as a Source of Essential Information for Designing Further Experiments in this Field as Well as for Modelling of Solid-State Diffusion in Ni-Al System.

Mechanically activated SHS of NiAl: Effect of Ni morphology and mechanoactivation conditions

Explored was the effect of the morphology of Ni particles in green mixtures on the mechanoactivated SHS reactions in the Ni-Al system. In case of fluffy Ni particles (produced in a carbonyl process), the mean size of the agglomerates formed in the course of MA was higher than in case of dense Ni particles (produced in an electrolytic process). The absolute values of combustion temperature and burning velocity were higher in case of carbonyl-derived Ni, while an increment in burning velocity caused by MA was higher in case of electrolytically produced Ni.

Thermal conductivity mapping of the Ni–Al system and the beta-NiAl phase in the Ni–Al–Cr system

We use two examples to highlight the power of micron-scale-resolution thermal conductivity mapping on graded compositions created in a diffusion-multiple sample in rapid establishment of composition–phase–property relationships. The Ni–NiAl diffusion couple example clearly shows the effects of solid solutioning, order–disorder transition, and compositional point defects on thermal conductivity. Thermal conductivity mapping of the beta-NiAl phase region of an Ni–Cr–NiAl diffusion triple clearly shows that Cr substitutes for both Ni and Al sites in beta-NiAl without a strong preference, which is also found not to be strongly composition dependent.

Enhanced reactivity of mechanically-activated nano-scale gasless reactive materials consolidated by coldspray

The present study presents a novel method to prepare nano-scale energetic materials with high reactivity, low porosity and controllable shape. The experiments have been focused on the Ni–Al system. To increase the reactivity, an initial mechanical activation was achieved by the ball milling technique. The consolidation of the materials was achieved via the use of the Cold Gas Dynamic Spray (also known as Cold Spray) technique, where the particles are accelerated to high speeds and consolidated via plastic deformation upon impact, forming activated nanocomposites in arbitrary shapes with porosity levels close to zero. This technique permits to retain the powder microstructure in the coatings and prevents any reactions during the consolidation phase. The material reactivity is addressed through the flame propagation velocity, which showed an increase in the flame speed of the cold sprayed samples by up to one order of magnitude compared to their cold pressed counterparts.

Effect of TiO2 addition on thermal and mechanical properties of Y–Si–Al–O–N glasses

Abstract Y–Si–Al–O–N glasses are intergranular phases in silicon nitride based ceramics in which the composition and volume fraction of oxynitride glass phases determine the sintering/shrinkage behaviour. Several investigations on oxynitride glass formation and properties have shown that addition of nitrogen increases glass transition and softening temperatures, viscosity, elastic modulus and hardness. In the present study, effect of TiO2 addition on thermal and mechanical properties of Y–Si–Al–O–N glasses is investigated since the most typical Si3N4 ceramics for bearing applications are fabricated using a Si3N4–Y2O3–Al2O3–TiO2–AlN system. Addition of TiO2 is effective in preparing Y–Si–Al–O–N glasses with lower glass transition temperatures and with higher hardness.

Microstructural Characteristics of Accumulative Roll-Bonded Ni-Al-Based Metal-Intermetallic Laminate Composite

The present investigation is an attempt to develop metal-intermetallic laminate composites based on Ni-Al system. In this study, Ni sheets and Al foils have been used for the development of Ni-Al laminate using accumulative roll-bonding technique at 773 K. The laminate composites were then subjected to the controlled annealing to affect reactive diffusion at the Ni/Al interface leading to intermetallic compound formation. The accumulative roll-bonded laminates showed good bonding of layers. Annealing treatment at 773 K led to formation of reaction product and maintained the interface integrity. A qualitative compositional analysis at the interfaces reflected the formation of Al-Ni compounds, and a gradual compositional gradient also across the interface. This process seems to be of promise so far as the continuous production of large scale metal-intermetallic laminate composites is concerned.

Investigation of the heterogeneous nucleation in a peritectic AlNi alloy

The goal of this research is a systematic investigation aiming at a quantitative understanding of the four different stages of peritectic solidification: 1) heterogeneous nucleation, 2) peritectic reaction, 3) peritectic transformation and 4) direct growth of the peritectic phase. Solidification experiments of the peritectic alloy Al-36wt.% Ni are carried out in differential scanning calorimetry (DSC), and the recently developed multi-phase-field techniques are employed to quantitatively model and simulate the peritectic phase transformation, by taking into account the precise thermodynamic description of the Al-Ni system. A previously developed phase-field model that had been successfully employed in the Al-Ni system is adapted here and calibrated by a novel method that simulates not only the final solidification microstructure but also DSC traces. The resulting kinetics of the phase-transformation processes are presented underlying the above four stages of phase transformation in detail.

Crystal structure of τ5–TiNi2−xAl5 (x = 0.48) and isotypic {Zr,Hf}Ni2−xAl5−y

The crystal structure of the compound in the Al-rich region of the Ti–Ni–Al system, τ5–TiNi2−xAl5, x=0.48, has been derived from X-ray powder and single crystal, neutron powder and electron diffraction (space group I4/mmm, a=0.3984(2)nm, c=1.4073(3)nm, RF2=0.0133). Titanium atoms were unambiguously located from neutron powder data. τ5 is isotypic with the crystal structure of ZrNi2Al5. Detailed transmission electron microscopy (TEM) in several crystallographic directions confirmed the lattice parameters and crystal symmetry. Although occupancy of Ni in the 4e site revealed a defect (occ.=0.76), no significant homogeneity region was observed for this phase at 1020°C. Rietveld analyses of X-ray powder diffraction data for the Zr- and Hf-homologues confirmed for both compounds isotypism and revealed defects in the Ni sites and to a lesser extent also in the Al sites: ZrNi2−xAl5−y, x=0.4, y=0.4 and HfNi2−xAl5−y, x=0.5, y=0.2. The crystallographic relations among the structure types of Cu, TiAl3, ZrNi2Al5 and Zr(Ni,Ga)7 have been defined in terms of a Bärnighausen scheme.

Molecular dynamics simulations of nanometric metallic multilayers: Reactivity of the Ni-Al system

The reactivity of a layered Ni-Al-Ni system is studied by means of molecular dynamics simulations, using an embedded-atom method type potential. The system, made of an fcc-Al layer embedded in fcc-Ni, is initially thermalized at the fixed temperature of 600 K. The early interdiffusion of Ni and Al at interfaces is followed by the massive diffusion of Ni in the Al layer and by the spontaneous phase formation of $B2$-NiAl. The solid-state reaction is associated with a rapid system heating, which further enhances the diffusion processes. For longer times, the system may partly lose some its $B2$-NiAl microstructure in favor of the formation of $L{1}_{2}$-${\mathrm{Ni}}_{3}\mathrm{Al}$. This stage is controlled by the diffusion of Al in the Ni-rich phase, and a layer-by-layer development of the new phase is observed.

Microstructural analysis of rapidly solidified aluminium–nickel alloys

Powders of Al–50 wt-%Ni and Al–36 wt-%Ni were produced using the impulse atomisation technique, a rapid solidification technique. The molten droplets were cooled in flight by the stagnant helium or nitrogen in the atomising chamber. The resulting powders were sieved into different size ranges. X-ray diffraction and neutron diffraction were used in order to quantify the phase fractions in the samples. Profile refinement, using the computer software GSAS, was used to calculate the weight fraction of the existing phases, namely Al3Ni2, Al3Ni and Al, as a result of different processing parameters. The Scheil–Gulliver model was applied to investigate the extent to which it can predict phase fractions in the Al–Ni system. In Al–50 wt-%Ni, by increasing cooling rate, the ratio of Al3Ni to Al3Ni2 approaches that of Scheil–Gulliver’s prediction. Opposite behaviour was observed in Al–36 wt-%Ni. In addition, from the profile refinement, the effect of composition and cooling rate on the lattice parameter of Al3Ni2 was investigated. In Al–36 wt-%Ni, the c/a ratio is significantly smaller than the stoichiometric c/a ratio of Al3Ni2, and it decreases with increasing cooling rate. On the other hand, for Al–50 wt-%Ni, the c/a ratio is much closer to the stoichiometric value and it increases with increasing cooling rate.On a produit des poudres d’Al-50% en poids de Ni et d’Al-36% en poids de Ni en utilisant la technique d’atomisation par impulsion, une technique de solidification rapide. Les gouttelettes fondues étaient refroidies en vol par l’hélium ou l’azote stagnants dans la chambre d’atomisation. Les poudres résultantes étaient tamisées en différentes gammes de taille. On a utilisé la diffraction des rayons X et la diffraction des neutrons pour quantifier les fractions de phase dans les échantillons. Le raffinement du profil, obtenu grâce au logiciel d’ordinateur GSAS, était utilisé pour calculer la fraction de poids des phases existantes, soit Al3Ni2, Al3Ni et Al, comme résultat des différents paramètres de traitement. On a appliqué le modèle de Scheil-Gulliver pour vérifier à quel point il peut prédire les fractions de phase du système Al-Ni. Pour l’Al-50% en poids de Ni, en augmentant la vitesse de refroidissement, le rapport d’Al3Ni à Al3Ni2 s’approche de celui de la prédiction de Scheil-Gulliver. On a observé le comportement opposé pour l’Al-36% en poids de Ni. De plus, à partir du raffinement du profil, on a étudié l’effet de la composition et de la vitesse de refroidissement sur le paramètre de réseau de l’Al3Ni2. Pour l’Al-36% en poids de Ni, le rapport c/a est significativement plus petit que le rapport c/a stoechiométrique de l’Al3Ni2, et il diminue avec une augmentation de la vitesse de refroidissement. D’un autre côté, pour l’Al-50% en poids de Ni, le rapport c/a est beaucoup plus près de la valeur stoechiométrique et il augmente avec une augmentation de la vitesse de refroidissement.

A Tersoff‐based interatomic potential for wurtzite AlN

AbstractAluminum nitride (AlN) is a popular buffer layer and interlayer. The understanding of how AlN serves as a wetting and fracture‐mitigating layer relies on molecular pictures of the AlN layer and the interfaces. However, molecular dynamics (MD) simulation studies on AlN system, particularly on its wurtzite phase, have been limited. This is because most existing interatomic force fields of AlN target the less common zinc blende phase. Here, we report a new Tersoff‐based AlN force field for its wurtzite structure. This potential has been extensively tested in terms of lattice parameters, bulk modulus, cohesive energy, and heat capacity. In addition, thermal expansion coefficient (TEC) of wurtzite AlN, a key property to precisely model heterostructures, has been calculated using MD method. The value of 2.66 × 10−6 K−1 calculated at 300 K for TEC is in excellent agreement with the reported experimental value.

Electronic Structure Magnetic Properties and Optical Properties of Co-doped AlN from First Principles

The electronic structure, magnetic properties, and optical properties of Co-doped AlN are investigated based upon the Perdew—Burke—Ernzerhof form of generalized gradient approximation within the density functional theory. The band gaps narrowing of Al1−xCoxN are found with the increase of Co concentrations. The analyses of the band structures and density of states show that Al1−xCoxN alloys exhibit a half-metallic character. Moreover, we have succeeded in demonstrating that Co doped AlN system in x = 0.125 is always antiferromagnetic, which is in good agreement with the experimental results. Besides, it is shown that the insertion of Co atom leads to redshift of the optical absorption edge. Finally, the optical constants of pure AlN and Al1−xCoxN alloy, such as loss function, refractive index and reflectivity, are discussed.

Synthesis and structural characterization of nanocrystalline (Ni, Fe)3Al intermetallic compound prepared by mechanical alloying

Synthesis of (Ni, Fe)3Al intermetallic compound by mechanical alloying (MA) of Ni, Fe and Al elemental powder mixtures with composition Ni50Fe25Al25 was successfully investigated. The effects of Fe-substitution in Ni3Al alloy on mechanical alloying process and on the final products were investigated. The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry, scanning electron microscopy and microhardness measurements. At the early stages, mechanical alloying resulted in a Ni (Al, Fe) solid solution with a layered nanocrystalline structure consisting of cold welded Ni, Al and Fe layers. By continued milling, this structure transformed to the disordered (Ni, Fe)3Al intermetallic compound which increased the degree of L12 ordering upon heating. In comparison to Ni–Al system, Ni (Al, Fe) solid solution formed at longer milling times. Meanwhile, the substitution of Fe in Ni3Al alloy delayed the formation of Ni (Al, Fe) solid solution and (Ni, Fe)3Al intermetallic compound. The microhardness for (Ni, Fe)3Al phase produced after 80h milling was measured to be about 1170HV which is due to formation of nanocrystalline (Ni, Fe)3Al intermetallic compound.

Synthesis of rhombic and triangular cross-sectional AlN nanorods on Si substrate via thermal CVD

Faceted one-dimensional (1D) nanostructures have some peculiar properties over circular-cross-section ones, therefore their preparation have attracted much attention over the past decades. In this contribution, wurtzite AlN nanorods with rhombic and triangular cross-sections were obtained on bare Si substrate through the nitridation of Al powder in ammonia/nitrogen atmosphere. The formation of the faceted AlN nanostuctures was briefly discussed. The novel AlN nanostructures obtained are of significance for further enriching the 1D AlN systems.

Preparation of Ni-Al System Intermetallic Compound by Reactive Sintering and Their Applications to Coating

Preparation of Ni-Al System Intermetallic Compound by Reactive Sintering and Their Applications to Coating

Effect of aluminum content on the mechanochemical synthesis of in-situ TiN in the Al–Ti–AlN system and subsequent shock consolidation

To determine the effect of aluminum content on the formation of in-situ TiN in the Al–Ti–AlN system, a mixture of aluminum, titanium and aluminum nitride powders was subjected to high energy milling. Al content of the mixture was changed according to the following stoichiometric reaction: Ti+AlN+ XAl→TiN+(1+ X)Al. The value of X was varied from 5.35 to 19.65 based on the stoichiometric calculation of the molar mass of each component expected to result in aluminum matrix composite with TiN weights of 30%, 20% and 10%, respectively, in addition to reaction corresponding to X=0(Ti+AlN→TiN+Al). Thermodynamic factors determine that the amount of Al in the mixture plays a key role in the formation of in-situ TiN. XRD and EPMA results showed that at lower Al content ( X=0, 5.35), reaction proceed through a gradual mode. By increasing Al content ( X=19.65), no mechanochemical reaction occurred between Ti and AlN. Continuation of the milling process allowed acquisition of in-situ TiN in the designed compositions of AlN–TiN, Al–Ti–AlN–30%TiN, and to some extent, of Al–Ti–AlN–20%TiN. A nanocrystalline solid solution evolved by mechanical alloying (MA) was sustained for prolonged milling time. The mean TiN crystallite size obtained was 10 nm for the AlN–TiN composition. The end product milled powder after 40 h of milling time, equating to the Al–Ti–AlN–30%TiN composition was consolidated into bulk compact using the underwater shock compaction method. The milled specimens were characterized by XRD, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and microhardness testing. The sample had a uniform and fine-grained composite structure with 99% theoretical density and average microhardness of 434 HV0.1. The results confirmed the possibility of fabricating reliable bulk nanostructured materials by imposing shock compaction on submicron sized powders.

Atomic mobilities and diffusivities in the fcc, L12and B2 phases of the Ni-Al system

AbstractA phenomenological model was utilized to describe diffusivities in the γ (fcc) /γü (L12) and A2/B2 phases of the NiüAl system. An effective strategy, which takes the homogeneity range and defect concentration into account, was developed in the present work to optimize the atomic mobilities of γü phase. Such a strategy results in a dramatic decrease in the number of atomic mobility parameters to be evaluated for the L12phase. The measured composition- and temperature- dependent diffusivities in the NiüAl system have been well replicated by the present mobility descriptions. For the L12phase, comprehensive comparisons show that with fewer model parameters the presently obtained mobilities yield a better fit to experimental diffusivities, compared with previous assessments. The mobility descriptions are further validated by comparing calculated and measured concentration profiles for various diffusion couples. The time-dependent Al composition profile for the annealed vapor Al / γ couple is accurately described for the first time.