Formation Of NiAl Research Articles

CORROSION BEHAVIOUR OF ADVANCED COMPOSITES CONTAINING SURFACE MODIFIED SIC AS REINFORCEMENT

The interface structure, micro-voids, pits, delamination, intermetallic compounds and internal stresses are the utmost critical factors influencing the corrosion performance of composite materials making them unsuitable for use in structural applications. One useful technique to control such adverse effect in composites is surface modification of the reinforcement. The present investigation involved the implementation of chemical techniques, particularly electroless plating (EP), to modify the surface of silicon carbide (SiC) particles by depositing a layer of nickel phosphorous (Ni-P) onto them. These plated SiC particles were subsequently employed in the production of Al/Ni-pSiC composites using the powder metallurgy (PM) method, with different weight percentages of plated SiC content ranging from 5% to 15%. The corrosion behaviour was assessed by potentio-dynamic polarization tests in 3.5% NaCl solution at room temperature. Results confirmed that AlNi-pSiC composites exhibit a greater resistance to pitting, in contrast to pure aluminium and Al/SiC composites without plating. The enhanced corrosion resistance in Al/Ni-pSiC composites can be attributed to strong interfacial bond, grain refinement, CTE difference, formation of Ni3Al, and reduced potential difference.

Castable eutectic Ni–Ce high temperature alloys strengthened by γ/γʹ microstructure

Ni-based superalloys are the premier material for high-temperature applications but are often difficult to manufacture via solidification-based processing. Eutectic alloys typically possess good castability due to narrow solidification ranges. The Ni–Ce system possesses a eutectic reaction but has never been examined as a potential high-temperature material. This work investigates the microstructure and mechanical properties of near-eutectic alloys Ni–17Ce and Ni–17Ce–5Al (wt.%). Both alloys show outstanding high-temperature microstructure and mechanical property stability at 900 °C. The formation of Ni3Al (γʹ) precipitates is observed in the primary FCC-Ni phase of the ternary Ni–Ce–Al alloy. The precipitation hardened ternary alloy exhibits superior hardness to Inconel 718 at elevated temperatures, retaining its strength to 750 °C, or about 50 °C higher than Inconel 718. The novel hierarchical microstructure consisting of thermally stable eutectic regions combined with γʹ-strengthened primary FCC-Ni and eutectic phases show great promise as a castable material solution for high-temperature applications.

Chemical reactions of Ni/Al multilayers upon ultrahigh compressive load at ambient temperature

Energetic multilayers are peculiarized by their self-propagation reactions when giving them a thermal pulse. This work reports the chemical reactions of Ni/Al energetic multilayers can be triggered upon ultrahigh compressive load (stress >1 GPa) at ambient temperature, which is realized by micro-compressions of Ni/Al micropillars with equal molar ratio. Detailed microscopic characterizations evidence monolayer reactions of Ni20Al30 and Ni110Al140 (NixAly: x and y are average thickness of individual layers in nanometer) are triggered, forming a stoichiometric NiAl phase after micropillar compression. The as-observed reactions must be triggered by ultrahigh compressive loads, which aid for nucleation of NiAl grains at atomic intermixing zones of Ni-Al interfaces. Once occurrence, the grain growth is self-sustained by the released heat during NiAl formation. The grain textures depend strongly on the deformation extent. The self-sustained process is terminated until the whole micropillar is reacted. Analogous chemical reactions are not observed in the thickest Ni450Al620 micropillar where atomic intermixing is absent. The comparison highlights the critical role of ultrahigh compressive load to trigger monolayer reactions of Ni/Al multilayers, and could forward the advance of Ni/Al energetic multilayers for diffusion welding purpose.

Critical conditions of forced ignition in Ni-Al, Ti-Al powder systems under solid-phase synthesis

A theoretical study of the critical conditions of forced solid-phase ignition in Ti-Al, Ni-Al systems was carried out. Based on the analysis of the non-stationary diffusion equation with moving boundaries, the critical powers of the heating source and the corresponding critical temperatures were determined during the formation of NiAl, TiAl3 intermetallic compounds using the state diagrams of these binary systems. The diffusion activation energies, frequency factors, particle sizes, and heat removal conditions were considered as variable parameters. The diagrams of critical parameters which relate the corresponding specific heating powers with the indicated values were constructed. It has been established that for the same values of the parameters and under identical synthesis conditions, the critical temperatures in these systems differ by more than one hundred degrees. The latter is associated with a significant difference in the width of the solubility region for the corresponding compounds of the composition NiAl, TiAl3. The performed analysis allows separating the modes of isothermal sintering and thermal explosion which makes it possible to control the thermal and diffusion modes of synthesis. The comparison of the calculation results with the experimental data showed their satisfactory agreement.

Effect of preliminary high-energy ball milling on the structural-phase state and microhardness of Ni3Al samples obtained by spark plasma sintering

The study of the influence of the duration of preliminary high-energy ball milling on the features of the structural-phase state and the level of microhardness of consolidated Ni3Al samples obtained by the method of spark plasma sintering has been carried out. It was found that the inhomogeneous state of the precursor from the 3Ni-Al powder mixture in the case of preliminary ball milling of a short duration (1 min) is a cause of the formation of an inhomogeneous structural-phase state of the consolidated Ni3Al sample. An increase in the duration of high-energy ball milling provides a homogeneous phase composition, promotes the refinement of the grain structure and an increase in the microhardness values of the obtained Ni3Al samples. The main factors determining the processes of structural-phase transformation during the formation of Ni3Al under the conditions of spark plasma sintering, depending on the preliminary high-energy ball milling, are revealed. It is shown that grain boundary strengthening is the one of the effective mechanisms for increasing the strength of the material under study.

Role of Al additions in secondary phase formation in CoCrFeNi high entropy alloys

AlxCoCrFeNi High Entropy Alloys (HEAs), also referred to as multiprincipal element alloys, have attracted significant interest due to their promising mechanical and structural properties. Despite these attributes, AlxCoCrFeNi HEAs are susceptible to phase separation, forming a wide range of secondary phases upon aging, including NiAl–B2 and Cr-rich phases. Controlling the formation of these phases will enable the design of age-hardenable alloys with optimized corrosion resistance. In this study, we examine the critical role of Al additions and their concentration on the stability of the CoCrFeNi base alloy, uncovering the connections between Al composition and the resulting microstructure. Addition of 0.1 mol fraction of Al destabilizes the single-phase microstructure and results in the formation of Cr-rich body-centered-cubic (bcc) phases. Increasing the composition of Al (0.3–0.5 mol fraction) results in the formation of more complex coprecipitates, NiAl–B2 and Cr-rich bcc. Interestingly, we find that the increase of the Al content stimulates the formation of NiAl–B2 phases, increases the overall density of secondary phases, and influences the content of Cr in Cr-rich bcc phases. Density functional theory calculations of simple decomposition reactions of AlxCoCrFeNi HEAs corroborate the tendency for precipitate formation of these phases upon increased Al composition. Additionally, these calculations support previous results, indicating the base CoCrFeNi alloy to be unstable at low temperature. This work provides a foundation for predictive understanding of phase evolution, opening the window toward designing innovative alloys for targeted applications.

Effect of Inserted Ti Layers on the Phase Transformation of Al/Ni Multilayer Foils

The thin Ti layers were inserted in the interfaces of base Al/Ni multilayer foils to form the Al/Ti/Ni/Ti (ATNT) foils through magnetron deposition. Al and Ni were determined in the as-deposited foils, while the absence of Ti was due to the strongly textured polycrystalline structure. TEM analysis implied an asymmetric interface structure between the Ni/Ti/Al interfaces and Al/Ti/Ni interfaces. After annealing at 473 K and 573 K for 3 h, the phase composition was the same as the initial state, which changed to be Al3Ni2, Ni3(AlTi), Ni and a small amount of Al3Ti when the treating temperature reached 673 K. Further increasing the annealing temperature to 773 K and 873 K leads to the appearance of stable AlNi. The obtained results implied that the inserted Ti layers impeded atomic interdiffusion and the formation of Al3Ni at the early stage, but had less impact on the final products. This further indicated that adding the inserted transition layer provides a reference to balance the storage stability and reaction performance of Al/Ni foils with regard to the applications.

Microstructure, hardness, thermal and wear behaviours in Al–10Ni/TiO2 composites fabricated by mechanical alloying

In this study, the effects of milling time and sintering temperature on the microstructural evolutions and thermal properties of Al–10Ni/TiO2 composites fabricated by mechanical alloying were investigated. X-ray diffraction revealed that Al3Ni2 intermetallic phase appeared after 20 h of milling. Also, X-ray diffraction and scanning electron microscopy results revealed that as the milling time increased, a more homogeneous structure and particle size reduction occurred. The differential thermal analysis results showed a series of endothermic and exothermic peaks indicating phase transformation and crystallization during continuous heating. After the sintering, polishing and etching of the pressed composite samples, the surface analysis was examined with an optical microscope and the microhardness was also measured. It was observed that as the sintering temperature increased, the formation of Al3Ni and Al3Ni2 intermetallic phases and the microhardness increased. The maximum microhardness value of the pressed composites was found as 541 ± 20 HV1 in the Al–10Ni/TiO2 composite sample produced with 20 h milling and sintered at 500 °C. In addition, the wear behaviour of the composites was investigated using pin-on-disk wear test under a certain load (5–15 N). It was determined that the mass loss decreased significantly as the grinding time and sintering temperature increased.

On the Disintegration of A1050/Ni201 Explosively Welded Clads Induced by Long-Term Annealing.

The paper presents the microstructure and phase composition of the interface zone formed in the explosive welding process between technically pure aluminum and nickel. Low and high detonation velocities of 2000 and 2800 m/s were applied to expose the differences of the welded zone directly after the joining as well as subsequent long-term annealing. The large amount of the melted areas was observed composed of a variety of Al-Ni type intermetallics; however, the morphology varied from nearly flat to wavy with increasing detonation velocity. The applied heat treatment at 500 °C has resulted in the formation of Al3Ni and Al3Ni2 layers, which in the first stages of growth preserved the initial interface morphology. Due to the large differences in Al and Ni diffusivities, the porosity formation occurred for both types of clads. Faster consumption of Al3Ni phase at the expense of the growing Al3Ni2 phase, characterized by strong crystallographic texture, has been observed only for the weld obtained at low detonation velocity. As a result of the extended annealing time, the disintegration of the bond occurred due to crack propagation located at the A1050/Al3Ni2 interface.

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.

Synthesis of NiAl/TiC–Al2O3 composite by mechanically activated combustion synthesis

The NiAl/Al2O3–TiC composite was fabricated by the combustion synthesis of NiO/Al/Ti/C powder starting mixture. The effects of mechanical activation on phase formation and microstructure development were evaluated by X-ray diffraction, scanning electron microscopy using energy dispersive spectroscopy, and transmission electron microscopy. By the combustion synthesis of an as-mixed powder compact, a partial amount of NiO was reduced by molten aluminum with the formation of NiAl3 and Al2O3. Mechanical activation refined the particle size of the reactants and after combustion synthesis, Ni was reduced by the reaction of NiO/Al with molten Al giving rise to NiAl. NiAl formation is an exothermic reaction whose released energy starts the ignition resulting in the final NiAl/Al2O3–TiC composite.

Metallurgical characterization of mechanically alloyed MoNiAl-WC reinforced Fe matrix composite

Abstract MoNiAl-WC reinforced Fe matrix composites were obtained by mechanical alloying. The effect of various reinforcement ratios on microstructure change, elemental characterization and phase transformation were examined by using optical microscopy, scanning electron microscopy, energy dispersion spectroscopy, X-ray diffraction, elemental surface mapping and a microhardness test. Fe and MoNiAl-WC compound and powder mixtures were synthesized by MA and nanocrystalline solid solution was obtained. The increase in the reinforcement ratio reduced grain size in the structure and increased the carbide ratio. The composite demonstrated excellent metallurgical qualities and interface bonding. Moreover, it was found that the amount of porosities increased with increasing reinforcement. X-Ray analysis showed the formation of NiAl, Al3Ni and WC phases.

Metallurgical characterization of mechanically alloyed MoNiAl-WC reinforced Fe matrix composite

Abstract MoNiAl-WC reinforced Fe matrix composites were obtained by mechanical alloying. The effect of various reinforcement ratios on microstructure change, elemental characterization and phase transformation were examined by using optical microscopy, scanning electron microscopy, energy dispersion spectroscopy, X-ray diffraction, elemental surface mapping and a microhardness test. Fe and MoNiAl-WC compound and powder mixtures were synthesized by MA and nanocrystalline solid solution was obtained. The increase in the reinforcement ratio reduced grain size in the structure and increased the carbide ratio. The composite demonstrated excellent metallurgical qualities and interface bonding. Moreover, it was found that the amount of porosities increased with increasing reinforcement. X-Ray analysis showed the formation of NiAl, Al3Ni and WC phases.

Effect of Heat Exposure on Grain Growth and Oxidation Behavior of Cobalt Based Composite Powders by Facile Suspension Synthesis

In this study the intermetallic-matrix composite powders CoNiCrAlY-2wt. %Al2O3 were characterized in order to investigate the effect of heat exposure time on morphologies, grain growth and phases formed by facile suspension route synthesis. The as-synthesized powders were examined by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) and X-ray diffraction (XRD). The formation of NiAl phase was noticed after 1 hour of heat treatment. The average particle size of intermetallic-matrix composite powders CoNiCrAlY-2wt.%Al2O3 increased as the heat exposure time increased. It is found that the reinforcement of alumina allowed the particles to uniformly distributed when the sample was heated for 10 hours. The formation of NiAl started when the sample was heated at 1 hour and NiAl continued to form when heated at 10 hours.

Synthesis of NiAl-TiC nanocomposite during mechanical alloying of Ni–Ti–Al–C powder mixture

The formation mechanism of NiAl-TiC nanocomposite during mechanical alloying of Ni–Ti–Al-C powder mixture was evaluated. The sequence of reactions during milling was obtained by DTA. Also, x-ray analysis was used for phase development, and morphological and microstructural evaluations were carried out by SEM and TEM electron microscopes. The results showed that after 5 h milling, NiAl and TiCx were formed, and no change in the phase composition was seen by prolongation of milling time to 40 h. The XRD results showed that no reaction took place until 3 h ball milling. DTA analysis of 3 h milled powder showed a broad exothermic peak at temperature range 850 °C–950 °C related to the simultaneous formation of NiAl and TiC. Morphological characterization by TEM confirmed that the final microstructure consisted of NiAl-TiC nanocomposite.

Microstructural characterization and properties of in situ Al-Al3Ni/TiC hybrid composite fabricated by friction stir processing using reactive powder

Microstructural evolutions during in-situ fabrication of Al-Al3Ni/TiC hybrid composite by friction stir processing (FSP) of AA1050 alloy with inserting reactive powder were investigated. Reactive powder was prepared by double step mechanical alloying (MA) of elemental Ni, Ti and C powders for a total duration of 20 h. Mechanical activation of pre-milled powders resulted in the in situ synthesis of Al3Ni/TiC particles in Al matrix during FSP. By increasing the number of FSP passes, a more uniform distribution of reinforcing particles along with higher degree of in situ reaction could be achieved. Complete reaction of MAed powders was attained after 6 FSP passes which resulted in the formation of Al3Ni and TiC reinforcing particles in Al matrix. In situ composite obtained from with 6 FSP passes exhibited phase stability during high temperature exposure. Al-Al3Ni/TiC hybrid composite showed superior hardness of 70 HV and ultimate tensile strength of 179 MPa compared to those of AA1050 (25 HV, 84 MPa) and FSPed AA1050 without powder addition (30 HV, 90 MPa).

Intermetallic formation at deeply supercooled Ni/Al multilayer interfaces: A molecular dynamics study

NiAl intermetallic formation occurs along the interfaces in the Ni/Al multilayer system during molecular dynamics simulations of deep (>50%) supercooling. The simulations begin with a crystalline solid solution at the Ni/Al interfaces that melts at 800 K, a supercooling of 56% of NiAl's simulated melting temperature (1800 K), and undergoes solid-state amorphization at 650 K, a supercooling of 64%. The intermetallic phase, NiAl, then forms at the interface from the melted/amorphous region through heterogeneous nucleation followed by growth in both lateral and normal directions. Upon nucleation, the intermetallic phase retains a fraction of the composition gradient present within the initial solid solution, and that fraction is always larger at 650 K, compared to 800 K, for the same initial composition gradient. Kinetics of the transformation follows the Johnson-Mehl-Avrami model, and an Avrami exponent of 0.5 was extracted at 800 K and 0.1 at 650 K. The NiAl formation is growth-controlled and the growth rate is found to increase with the decreasing initial composition gradient. Our finding supports a growth-competition mechanism of phase selection for interfacial reactions.

Electrically activated reactive synthesis (EARS) and electro-annealing of 3Ni–Al powder compacts

The present study investigates the electrically activated reactive synthesis (EARS) and post-reaction electro-annealing of 3Ni–Al powder compacts. The effect of initial relative green density on EARS processing and on the microstructure and phases produced was investigated. Post-reaction electro-annealing was also conducted to investigate its effects on phase transformations and consolidation. The initial reaction resulted in the formation of Ni3Al as the major phase, with 3R martensite also being formed. The investigated variation in relative green density was found to have limited effect on the product porosity and microstructure. Post-reaction electro-annealing, however, resulted in harder products with unique microstructures, particularly the formation of Ni4.22Al0.9 in very high amounts.

Nickel Oxide Catalysts for Partial Oxidation of Methane to Synthesis Gas

<p class="Default">Nickel catalysts supported on different carriers (θ-Al<sub>2</sub>O<sub>3</sub>, γ-Al<sub>2</sub>O<sub>3</sub>, HZSM-5 with γ-Al<sub>2</sub>O<sub>3</sub>, HZSM-5, and NaX) have been investigated for the partial oxidation of methane. All the supported nickel catalysts showed a high activity for the formation of synthesis gas, and γ-Al<sub>2</sub>O<sub>3</sub> was the most effective among all the tested carriers. The effect of the heat-treatment temperature of the 3 wt.% Ni/γ-Al<sub>2</sub>O<sub>3</sub> catalyst on its catalytic activity was studied, and a considerable decrease in its activity was observed by the heat-treatment of the catalyst at 1000 °C compared with the catalysts prepared by the 300–800 °C – calcination. The XRD analysis suggested the formation of NiAl<sub>2</sub>O<sub>4</sub> that is a non-reducible compound at the high calcination temperature. The addition of a modifier (Co, Ce, or La) to the 3 wt.% Ni/γ-Al<sub>2</sub>O<sub>3</sub> catalyst increased the selectivity to H<sub>2</sub> and CO with the decreasing selectivity to CO<sub>2</sub>, and the highest selectivity to H<sub>2</sub> was obtained by the 5 wt.% NiLa/γ-Al<sub>2</sub>O<sub>3</sub>. The developed 5 wt.% NiLa/γ-Al<sub>2</sub>O<sub>3</sub> catalyst showed a high stability for 30 h for the partial oxidation of methane at 750 °C. The methane conversion reached 95%, selectivity to hydrogen 83% and 52% to carbon monoxide.</p>

Detailed surface study of adsorbed nickel on Al12N12 nano-cage

The geometries and electronic structures of Ni-adsorbed Al12N12 (AlN) nano-cage are studied by density functional theory. A number of different structures varying in the position and orientation of nickel on the surface of the nano-cage are studied. Binding energies, band structures, total density of states, natural bond orbital charges, and electron density differences of Ni-adsorbed Al12N12 nano-cage were calculated, and analyzed in comparison with pure AlN nano-cage. The adsorption energies are in the range of (−110)–(−113) kcalmol−1 for three adsorption sites (P1–P3), and about −86kcalmol−1 for P4. High binding energies for these geometries suggest strong chemisorption of nickel on AlN nano-cage. Moreover, dissociation of AlN bond is observed concurrent with the formation of NiAl and NiN bonds when the Ni atom is adsorbed on the nano-cage. Results from the calculations also reveal that there is significant charge transfer from the nano-cage to the metal atom which changes the location of HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) resulting in reductions in the Egap (EHOMO-ELUMO). The HOMO-LUMO gap for P4 geometry is 1.79eV which is much lower than the band gap for pure AlN nano-cage (3.93eV). The band gap for P1, P2 and P3 geometries is 2.90, 2.79 and 3.18eV, respectively. The decrease in band gap is attributed to the push of outer d electrons of the transition metals to become more diffuse like. The HOMOs in all geometries have densities on Ni atom whereas the densities in LUMO are distributed on the entire skeleton. The results revealed that Ni adsorption provides N-type conduction which makes it an ideal adsorbent for practical applications in magnetism, catalysis and other areas. Reactivity descriptors indicate an increase in electrophilic character of Ni-adsorbed nano-cages compared to pure AlN nano-cage. The electron affinity and softness are highest for P4 geometry whereas the lowest ionization potential and hardness are calculated for P4.