NiAl Phase Research Articles

Properties and Microstructure Evaluation in NiAl-xWC (x = 0 − 90 wt.%) Intermetallic-Based Composites Prepared by Mechanical Alloying

In this work, NiAl-xWC (x = 0 - 90 wt.% WC) intermetallic-based composites were successfully synthesized by mechanical alloying (MA) and a hot-pressing approach. As initial powders, a mixture of nickel, aluminum and tungsten carbide was used. The phase changes in analyzed systems after mechanical alloying and hot pressing were evaluated by an X-ray diffraction method. Scanning electron microscopy and hardness test examination were used for evaluating microstructure and properties for all fabricated systems from the initial powder to the final sinter stage. The basic sinter properties were evaluated to estimate their relative densities. Synthesized and fabricated NiAl-xWC composites showed an interesting relationship between the structure of the constituting phases, analyzed by planimetric and structural methods and sintering temperature. The analyzed relationship proves that the structural order reconstructed by sintering strongly depends on the initial formulation and its decomposition after MA processing. The results confirm that it is possible to obtain an intermetallic NiAl phase after 10 h of MA. For processed powder mixtures, the results showed that increased WC content intensifies fragmentation and structural disintegration. The final structure of the sinters fabricated in lower (800 °C) and higher temperature regimes (1100 °C), consisted of recrystallized NiAl and WC phases. The macro hardness of sinters obtained at 1100 °C increased from 409 HV (NiAl) to 1800 HV (NiAl + 90% WC). Obtained results reveal a new applicable perspective in the field of intermetallic-based composites and remain highly anticipated for possible application in severe-wear or high-temperature conditions.

Laser cladding of IN713 LC superalloy with Amdry 997 powder: microstructural evolution

In this research, Amdry 997 powder was applied by a laser cladding process to the IN713 Low Carbon (IN713 LC) nickel-based superalloy. To evaluate the microstructural behaviors of the clad zones, different variables (the laser speed, laser frequency, and pulse width) were used in the laser cladding process. The final aim of this study was to achieve a clad zone without obvious cracks and pores with a low dilution ratio. The results showed that the upper region of the cladding includes very small equiaxed dendrites. The middle region of the cladding includes columnar dendrites. Equiaxed and columnar grains can be formed at the interface region. With an increase in the heat input of the laser (increasing the pulse width and laser frequency or decreasing the laser speed), the solidification rate reduces and consequently, a longer solidification time exists. Hence, more elongated grains are formed at the interface region. The microstructure of coatings in the upper and middle regions includes γ-Ni, β-NiAl and γ′-Ni3Al phases and TaC carbide, whereas the microstructure of the coatings at the interface region includes γ and β-NiAl and γ′-Ni3Al phases and M (Mo, Ta)C carbide. The optimum laser parameters that result in a low dilution ratio (14%) and a dense clad zone without obvious crack and porosity are a laser speed of 140 mm min−1,laser frequency of 14 Hz, and pulse width of 9 ms.

Effect of refractory elements M (=Re, W, Mo or Ta) on the diffusion properties of boron in nickel-based single crystal superalloys

Boron (B) is known as a melting-point depressant for the middle interlayer to transient liquid phase (TLP) bonding of the nickel-based single crystal superalloys (Ni-SCS). However, the mechanisms for the effect of refractory elements M (=Re, W, Mo or Ta) on B diffusion in Ni-SCS remain unclear till now. Thus, the refractory elements M (=Re, W, Mo or Ta)'s effects on the diffusion of B in Ni-SCS is investigated using the density functional theory in this paper. It is found that Mo and Re atoms are mainly distributed in the γ-Ni phase, while majority of W and Ta atoms are mostly located in the Al site in γ′-Ni3Al phase. The octahedral interstices of γ-Ni and γ′-Ni3Al are preferentially occupied by B atoms. The results indicate that the M (=Re, W, Mo or Ta) atoms doped in the structures prevent B diffusion, and the change trend of B diffusion E(BFP) follows Re < Mo < W < Ta. Electronic structure analysis shows that the different atomic radiuses from Re to Ta and different hybrid orbitals between M d and B 2p from Re to Ta play important roles in the diffusion properties of B in the nickel-based single crystal superalloys.

Effect of V on microstructure, wear and corrosion properties in AlCoCrMoVx high entropy alloy coatings by laser cladding

To improve the service life and wear resistance of the agitator blade, AlCoCrMoVx (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 at.%) high entropy alloy (HEA) coatings were prepared on the 904L-stainless-steel substrate by laser cladding, and the effect of V content on the microstructure, wear and corrosion behavior were investigated. The HEA coatings consist of body-centered cubic (BCC) phase, needle-like σ phase, and irregular black AlN phase. As the V content increases, the σ phase gradually disappears. The trend of microhardness decreases firstly and then increases. AlCoCrMoV1.0 HEA coating has the highest microhardness (942.6 HV0.1). The average friction coefficient of HEA coatings firstly increases and then decreases, but the specific wear rate is the lowest when x = 0.8 (about 0.630 × 10−5 mm3 N−1 m−1). The addition of V improves the corrosion resistance of the coatings, AlCoCrMoV0.8 coating has the lowest Icorr value of 2.74 × 10−5 A cm−2 and the largest impedance radius. In a word, the addition of V in AlCoCrMoVx HEA coatings greatly improves the performance of coatings.

Alloying-Triggered Phase Engineering of NiFe System via Laser-Assisted Al Incorporation for Full Water Splitting.

It is challenging to design one non-noble material with balanced bifunctional performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for commercial sustainability at a low cost since the different electrocatalytic mechanisms are not easily matchable for each other. Herein, a self-standing hybrid system Ni18 Fe12 Al70 , consisting of Ni2 Al3 and Ni3 Fe phases, was constructed by laser-assisted aluminum (Al) incorporation towards full water splitting. It was found that the incorporation of Al could effectively tune the morphologies, compositions and phases. The results indicate that Ni18 Fe12 Al70 delivers an extremely low overpotential to trigger both HER (η100 =188 mV) and OER (η100 =345 mV) processes and maintains a stable overpotential for 100 h, comparable to state-of-the-art electrocatalysts. The synergistic effect of Ni2 Al3 and Ni3 Fe alloys on the HER process is confirmed based on theoretical calculation.

Alloying‐Triggered Phase Engineering of NiFe System via Laser‐Assisted Al Incorporation for Full Water Splitting

AbstractIt is challenging to design one non‐noble material with balanced bifunctional performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for commercial sustainability at a low cost since the different electrocatalytic mechanisms are not easily matchable for each other. Herein, a self‐standing hybrid system Ni18Fe12Al70, consisting of Ni2Al3 and Ni3Fe phases, was constructed by laser‐assisted aluminum (Al) incorporation towards full water splitting. It was found that the incorporation of Al could effectively tune the morphologies, compositions and phases. The results indicate that Ni18Fe12Al70 delivers an extremely low overpotential to trigger both HER (η100=188 mV) and OER (η100=345 mV) processes and maintains a stable overpotential for 100 h, comparable to state‐of‐the‐art electrocatalysts. The synergistic effect of Ni2Al3 and Ni3Fe alloys on the HER process is confirmed based on theoretical calculation.

Electrocatalytic Performance of Ethanol Oxidation on Ni and Ni/Pd Surface-Decorated Porous Structures Obtained by Molten Salts Deposition/Dissolution of Al-Ni Alloys.

Ni coatings with high catalytic efficiency were synthesised in this work, obtained by increasing the active surface and modifying Pd as a noble metal. Porous Ni foam electrodes were obtained by electrodeposition of Al on a nickel substrate. Deposition of Al was carried out with potential -1.9 V for a time of 60 min in NaCl-KCl-3.5 mol%AlF3 molten salt mixture at 900 °C, which is connected with the formation of the Al-Ni phase in the solid state. Dissolution of Al and Al-Ni phases was performed by application of the potential -0.5 V, which provided the porous layer formation. The obtained porous material was compared to flat Ni plates in terms of electrocatalytic properties for ethanol oxidation in alkaline solutions. Cyclic voltammetry measurements in the non-Faradaic region revealed the improvement in morphology development for Ni foams, with an active surface area 5.5-times more developed than flat Ni electrodes. The catalytic activity was improved by the galvanic displacement process of Pd(II) ions from dilute chloride solutions (1 mM) at different times. In cyclic voltammetry scans, the highest catalytic activity was registered for porous Ni/Pd decorated at 60 min, where the maximum oxidation peak for 1 M ethanol achieved +393 mA cm-2 compared to the porous unmodified Ni electrode at +152 mA cm-2 and flat Ni at +55 mA cm-2. Chronoamperometric measurements in ethanol oxidation showed that porous electrodes were characterised by higher catalytic activity than flat electrodes. In addition, applying a thin layer of precious metal on the surface of nickel increased the recorded anode current density associated with the electrochemical oxidation process. The highest activity was recorded for porous coatings after modification in a solution containing palladium ions, obtaining a current density value of about 55 mA cm-2, and for a flat unmodified electrode, only 5 mA cm-2 after 1800 s.

Microstructure and mechanical properties of FeCoCrNiAl0.1N high entropy alloy nitride coatings synthesized by cathodic arc ion plating using alloy target

To promote the industrial application of high entropy alloy nitride (HEAN) coatings, the cathodic arc ion plating deposition process was explored to deposit FeCoCrNiAl0.1 N using casting HEA alloy targets. We investigated the impacts of nitrogen pressure and bias voltage on the microstructure, mechanical characteristics, and friction behaviors. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to analyze the microstructures. It was found that compositions for all coatings were uniformly and the coatings mainly consisted of FCC-HEA, CrN, AlN, and FeN phases. The nano hardness and plastic deformation resistance, characterized by nano-indentation, both increased with the nitrogen pressure and certain bias voltage (<150 V). Coating deposited with 2.0 Pa and 150 V presented the maximum hardness of 32.9 GPa and the highest H3/E2 value of 0.1 GPa. The hardening mechanism was focused. Coatings deposited with low nitrogen pressure presented better crack resistance under scratch load. The friction behaviors were presented based on the combined studies of friction curves, wear track profiles, and morphologies. FeCoCrNiAl0.1 N coatings revealed excellent wear resistance with relatively lower COF (ranging from 0.43 to 0.51).

Superior oxidation resistance of the chemically complex but structurally simple Ti-Al-Ta-Ce-Si-La-B-nitride

Alloying (Ti,Al)N with Ta, CeSi2 or LaB6 is beneficial for both hardness and thermal stability. Here we show that their different mechanisms allow for a cumulative improvement when alloyed together, which is especially pronounced for the oxidation resistance. During isothermal oxidation treatments in ambient air at 900 °C (for up to 25 h), Ti0.44Al0.44Ta0.12N allows for a parabolic scale growth rate constant kp of 6.039 × 10-5 µm2/s. This is reduced to 2.074 × 10-5 and even 0.399 × 10-5 µm2/s when alloying with 2 mol% CeSi2 respectively CeSi2 + LaB6 (1 mol% each). The oxide scale growth kinetics for the latter can be even better described by a logarithmic or cubic law. In the as-deposited state the CeSi2 and CeSi2 + LaB6 alloyed (Ti,Al,Ta)N are single-phase fcc structured providing an indentation hardness of 32.6 ± 1.5 and 37.8 ± 1.5 GPa, combined with an indentation modulus of 496 ± 22 and 496 ± 14 GPa, respectively. After vacuum-annealing at 1000 °C, their hardness is still 33.0 ± 1.6 and 34.8 ± 1.1 GPa, and noticeable formation of hexagonal AlN and TaNx phases can only be detected by X-ray diffraction when annealed at temperatures above 1200 °C.Using CeSi2 and LaB6 instead of their elemental form is furthermore beneficial for the target production itself, as Ce and La are highly reactive.

Structural design and high temperature tribological behavior of a new turbine blade tip protective coating

Severe damage to the blade tip usually occurs when the turbine blade tip scratches against the abradable coating. Therefore, blade tip strengthening is a hot research topic. To improve the wear resistance of turbine blade tips, NiAlTa coatings were prepared on K417G superalloy by electro spark deposition. The microstructure and phase composition of the coating were analyzed by scanning electron microscope and X-ray diffraction. Microhardness tester and scratch method were used to test the microhardness and bonding strength of the coating. Using ZrO2 balls as friction pair, the tribological behavior and wear mechanism of the coating were investigated by a self-developed tribometer at 25 °C and 800 °C. The NiAlTa coating mainly consists of the β phase NiAl and the laves phase NiTaAl. The laves phase NiTaAl encapsulates the NiAl phase, and this plant-like “cell wall” structure endows the coating with excellent mechanical properties, wear resistance, and cutting performance. Compared with the substrate, NiAlTa coating has higher microhardness (~797.18 HV0.2) and lower wear rate (~10−6 mm3·N−1·m−1). The wear process of NiAlTa coatings is dominated by plastic deformation, with little evidence of material loss from the brittle fracture. The competition between the anti-wear lubricating effect of the “glaze” layer and the plowing effect of oxides and ZrO2 debris affects the tribological behavior of the coating. The cutting performance of the NiAlTa coating can be attributed to the two-body or three-body abrasive wear caused by the oxides and ZrO2 debris embedded in the “glaze” layer.

Characterizations on Precipitations in the Cu-Rich Corner of Cu-Ni-Al Ternary Phase Diagram

Three kinds of Cu-Ni-Al alloys, whose chemical compositions are located in the Cu-rich corner of the isothermal section of the Cu-Ni-Al ternary phase diagram, were prepared by melting and casting firstly, and then solution and aging treatments were carried out. The microstructure was characterized and the competitive formation process of Ni-Al intermetallics were discussed. The results show that there are little amounts of NiAl phase at the grain boundary and needle- or particle-like Ni3Al phase inside the Cu matrix in all the as-cast alloys, although they are in the single-phase area. Solution and aging treatments mainly result in the disappearance and precipitation of Ni3Al phase, but the precipitations during aging are much smaller than those in the as-cast alloys. Thermodynamics and kinetics calculation indicate that the NiAl intermetallic wins out in the solidification process because of its lower change in Gibbs free energy, while Ni3Al phase is first to precipitate during aging due to its lower formation enthalpy and required Al concentration. The most important contribution of this work is that it proves that intermetallics can precipitate from the so-called single-phase zone in the Cu-rich corner of the Cu-Ni-Al phase diagram, which is the necessary prerequisite for the realization of high strength and high electrical conductivity.

The Formation Mechanism of a Multilayer-Structure Oxide Film during the Oxidation of FeCrAl in Air at 700 °C

A protective oxide film is the key to the corrosion resistance of the FeCrAl alloy. The mechanism of the formation of the multilayer oxide film of the FeCrAl alloy in 700 °C air was explored by studying the structure evolution of the oxide film and the oxidation kinetics of FeCrAl. The results show that a multilayer oxide layer is formed on the surface of the FeCrAl alloy after 1344 h, with a (Fe,Cr)2O3 layer, an Al-rich oxide layer, an Al-depleted zone, and a new Al-rich oxide layer sequentially arranged from the surface to the matrix. This indicates that the Al element plays an important role in the formation of the oxide film. The Al in the matrix is depleted to form the Al-rich oxide layer, resulting in the Al-depleted zone. The new Al-rich oxide layer is formed under the Al-depleted zone by internal oxidation. It should be noted that the precipitation of the AlN phase in the matrix is observed, which might be a probable factor for the Al-depleted zone in the matrix.

Study of Microstructure Regulation and In Situ Tensile Performance of Ni-Al Films

In this paper, Ni-Al films were prepared using magnetron sputtering technology. The microstructure of the films and the relationship between the residual stress and the adhesion strength were studied. More importantly, the mechanical strength–ductility properties of Ni-Al films were evaluated by in situ tensile testing. The results showed that the film mainly consisted of Ni3Al phase and Ni-based solid solution at the low power of Al target. The phase transition occurred, and the NiAl phase appeared when the Al sputtering power was increased. The complex structure, with the coexistence of Ni-based solid solution, Ni3Al, and NiAl phases, possessed increased residual stress and reduced adhesion strength. Meanwhile, the crack was easily penetrated through the inside and outside of the film, falling off during in situ tensile testing. While the small residual stress and large adhesion strength were obtained, only Ni3Al and NiAl coexisted, and the film fell off with difficulty. When the Al sputtering power was 400 W, the film showed the largest adhesion strength and the smallest residual stress. The best comprehensive performance was achieved with a tensile strength of 854 MPa and a yield strength of 90 MPa. The Al content of the film was up to 23.03 at.%, which was beneficial to the application and performance improvement of the film in molten salt corrosion resistance.

Synergistic effect of Pd+Rh on the microstructure and oxidation resistance of aluminide coatings

The Pd+Rh modified aluminide coatings were deposited on nickel and CMSX-4 nickel superalloy. The Pd layer (2.5 ?m thick) and the subsequent Rh layer (0.5 ?m thick) were electroplated on both nickel and CMSX-4. The aluminization of the substrates with Pd+Rh layers was carried out using the CVD method. Two zones (outer and interdiffusing) were observed on both coatings. The ?-NiAl phase doped in palladium was formed in the outer zones and ?-NiAl phase doped with palladium and rhodium was formed at the boundary between the outer and interdiffusion zones of both coatings. The ??- Ni3Al phase and ?-Co7Mo6 precipitates in the ?-NiAl matrix were found in the interdiffusion zone on nickel and CMSX-4 superalloy respectively. The simultaneous use of Pd and Rh in the aluminide coating slowed down their oxidation rate. Moreover, Pd+Rh co-doping is more efficient than Pd+Hf in reducing the oxidation rate of aluminide coating on CMSX-4 superalloy.

Microstructural and electrical properties of AlN–CoCrFeMnNi cermet obtained by hot pressing

AlN and equimolar ratio of gas atomized CoCrFeMnNi HEA powders were used to prepare AlN–CoCrFeMnNi cermets by ball milling followed by hot pressing sintering at 1240 °C for 2 h. The microstructure characteristics and electrical properties of the cermets were investigated. The sintered cermet bulks were composed of a FCC-structured CoCrFeMnNi solid solution binder phase, AlN phase, and a small amount of Cr 7 C 3 type carbide. No obvious interfacial reaction occurred between AlN and CoCrFeMnNi HEA. The resistivity of AlN–CoCrFeMnNi cermets nonlinearly increased with increasing AlN content and temperature. A conductivity model of AlN–CoCrFeMnNi cermets at room temperature and 600 o C was established based on the generalized effective medium (GEM) equation. Results indicated that AlN–CoCrFeMnNi cermets had a typical percolation threshold phenomenon, which allowed to continuously regulate their resistivity between 10 2 μΩ cm to 10 3 μΩ cm as AlN was in the range of 10–50 wt% under room temperature. Therefore, the AlN–CoCrFeMnNi cermets are promising materials for applications in the e-cigarette field.

Structural composition of electrospark coatings obtained by Ni—Al alloys on steels

Coatings were obtained by electrospark deposition using anode materials based on the Ni-Al system. According to the research results it is most expedient to use two alloys based on Ni3Al and NiAl with an additional content of the Ni5Al3 phase for the coatings formation. The microstructure of the resulting coatings consists of columnar crystallites, in which the concentration of the anode components (Ni, Al) increases, and the content of the cathode component (Fe) decreases along the height of the coating from the surface to the base. It has been established that the content of Fe in crystallites in different areas of the coating changes most significantly.

Effect of Diluent Amount on Properties of Porous NiAl

Porous NiAl parts were formed by using Ni and Al elemental powders, preformed NiAl as diluent and NaCl particles as space holder (SH). The aim of utilizing preformed NiAl (30%-40%) as a diluent was to preserve the shape of the products. The amounts of the SH NaCl particles in NiAl were 25-50-75 vol.% and their sizes were in 300-500 µm range. Porous NiAl samples were prepared by volume combustion synthesis (VCS). The adiabatic temperatures of the Ni+Al mixtures having 30 and 40% diluent NiAl were calculated as 1638.9 and 1460.8°C, respectively. Formation of NiAl phase was verified by XRD analyses. In the green pellets, the total porosity amount was higher than the added NaCl amount. Also it was slightly higher in the product pellets than in the green pellets before VCS. Compressive strength and microhardness values of the samples which contained 30% diluent NiAl were higher than the samples which contained 40% diluent. Average compressive strength values of the products that were obtained by 25% NaCl and 30 and 40% diluent NiAl additions were 112.0±29.5 and 66.0±20.5 MPa, respectively.

Investigation of the structure and properties of highly damped alloys of the Cu-Mn system

Currently, there is a rapid development of technology, an increase in speed and an increase in the power of machinery and equipment. This leads to an increase in harmful noise and vibration, which negatively affects working conditions. One of the highly effective ways to reduce harmful noise and vibration is the use of damping materials. Alloys of the manganese-copper system belong to this group of materials. In some cases, this method is the only possible noise reduction method. Therefore, the development and study of new materials, the provision of new opportunities, their application is relevant. In the course of the study, methods of X-ray fluorescence spectroscopy, tests for the wear resistance of the material under unsteady friction, the method of homogenization, methods of microstructure research were used. It has been found that in quaternary alloys of the Mn-Cu-Ni-Al system, the effect of nickel slowing down the decomposition processes can be balanced with aluminum in a nickel-aluminum ratio of 2:1. It is known that the formation of the Ni-Al phase can further strengthen the alloy. The obtained results of tests on the wear resistance of the zirconium-doped alloy provided the basis for further research in the development of new Mn-Cu-based alloys. Before and after heat treatment, the alloy structure was studied, the chemical composition was determined, hardness and microhardness were measured, and the coefficient of wear resistance was determined. The results can be used to determine the direction of further development in the field of structural materials.

First‐Principles Study on Interfacial Bonding Characteristics and Tensile Deformation Behavior of Ni (001)/Ni3Al (001) in K418 Superalloy

AbstractIn order to theoretically explore the interfacial bonding properties between the main phase (γ) and the second precipitated phase (γ') in K418 superalloy formed by direct laser deposition. First‐principles calculation is utilized to study the adhesion work, interfacial energy, electronic structure, bonding properties, and tensile properties between γ phase (Ni (001)) and γ' phase (Ni3Al (001)). The results show that the interface energy of the NiAl‐center (0.35–1.19 J m−2) is the smallest and therefore it is with the highest interface bonding strength. The electronic analysis suggests that strong Ni‐Al covalent and ionic bonds as well as Ni‐Ni metal bonds at the interface of the NiAl‐center model are formed with the appearance of obvious orbital hybridization. The yield strength of the NiAl‐top model reaches up to 19.38 GPa under the uniaxial tensile test, which is further increased when doped with those atoms of Re, Ta, and W, up to 20.38, 20.42, and 20.93 GPa, respectively. A fundamental understanding is presented here for the design of superalloys.

Deformation behavior of cell walls in an additively manufactured hybrid metallic foam

A hybrid Al-Al3Ni metallic foam was synthesized in-situ via directed energy deposition (DED) of Ni-coated Al 6061 powder, without the need for a foaming agent. Three-dimensional characterization via X-ray computed tomography shows that the foam contains approximately 61.5 % porosity and a high volume fraction of the Al3Ni phase (∼60 vol. %) within the cell walls. This microstructure is notably distinct from the eutectic structure that is typically observed in conventionally processed Al-Ni alloys. To investigate the mechanical properties and deformation mechanisms of the Al-Al3Ni cell walls, in-situ micro-pillar compression was performed, and the results reveal a notable yield strength of 560 MPa and a compressive strain that exceeds 30 %. These properties are attributable to the presence of a high volume fraction of Al3Ni particles, in combination with the characteristics of the Al/Al3Ni interfaces. To provide insight into the deformation mechanisms in the cell walls we used in-situ mechanical testing, transmission electron microscopy and precession electron diffraction characterization, together with molecular dynamics simulations. Our results reveal two distinct mechanisms: uniform dislocation-based deformation of the Al alloy phase and localized deformation within the slip bands in the Al3Ni phase. The results further highlight the importance of the Al/Al3Ni interfaces in mechanical strengthening and the transfer of plastic deformation from the Al phase to the Al3Ni phase. At high mechanical loads, cracks form due to the large stress concentration at the slip bands and slip band intersections in the Al3Ni, giving rise to intragranular fracture of Al3Ni and finally interfacial debonding and cracking.