NiAl Intermetallic Compound Research Articles

Investigation of structural-phase transformations in a foundry structural alloy based on Ni3Al intermetallic compound after high-temperature exposures and during the operation of the alloy as a nozzle blade

The paper presents studies of structural and phase transformations in intermetallic compositions based on the Ni3Al compound depending on alloying and high-temperature treatments, carried out in the process of creating a cast structural alloy for operation in the temperature range of 900–1200°C. Experimentally, when testing the developed intermetallic alloy as nozzle blades of the 1st stage of a high-pressure turbine, it was confirmed that the alloy is thermally stable at temperatures up to 1200°C.

High temperature shear and thermal aging behavior of dissimilar transient liquid phase bonded Hastelloy X to Ni3Al intermetallic compound

Nickel super alloys and intermetallic compounds (IMCs) are candidate as strategic materials for turbine industry, because of its excellent high temperature properties. In this study, mechanical properties and thermal aging behavior (post thermal exposure) of the transient liquid phase (TLP) bonds between Hastelloy X to Ni3Al IMC at temperature range of 800–900 °C were investigated. The microstructure and fracture surfaces of the joints were examined by optical and scanning electron microscopes as well as XRD analysis. The optimum joint bonding strength was achieved for the sample treated at 1100 °C–180 min equaling to 355 ± 4.5 MPa. XRD patterns of semi-cleavage fracture surfaces revealed nickel solid solution matrix containing BNi3 and Ni3Si compounds generated at ASZ/ISA interface. The ultimate tensile strength reaches 36.5 ± 1 and 20.5 ± 1 MPa at temperatures of 800 °C and 900 °C, respectively. Fracture occurred in the IMC substrates for both temperatures were due to shrinkage porosity during solidification of IMC and mismatch of crystal lattice constants with the matrix. The thermal aging process at 900 °C for 50–500 h had a minor effect on the joint microstructure but generated TCP phases in the Hastelloy X.

Preparation of Ni–Al intermetallic compounds by plasma arc melting deposition through double-wire feeding

Double-wire plasma arc melting deposition was used to fabricated Ni–Al intermetallic compounds by the optimization of feeding position of Ni and Al wires with big difference in melting point. The proposed double-wire synchronous feeding method cleverly solved the problem that the weld bead could not be effectively formed due to the preferential melting of Al wire with low melting point. After the optimization of double-wire feeding position, the effects of heat input on the microstructure uniformity of deposited Ni–Al intermetallic compounds were also studied. It was found that with the increase of heat input from 2.453 to 3.143 kJ/mm, the deposited microstructures transferred from M-NiAl + Ni3Al to M-NiAl+γ′-Ni3Al/γ-Ni, and the amount of γ′-Ni3Al/γ-Ni was increased and became uniformly distributed. These combined improvements benefited to reduce the difference in the microhardness from top to bottom areas of deposited Ni–Al intermetallic compounds. The related results provide new ideas for the high-efficiency and low-cost manufacturing of intermetallic compounds or other difficult-to-deposit metals.

Electrochemical partial reduction of Ni(OH)2 to Ni(OH)2/Ni via coupled oxidation of an interfacing NiAl intermetallic compound for robust hydrogen evolution

Ni-based porous electrocatalysts have been widely used in the hydrogen evolution reaction (HER) in alkaline water electrolysis, and the catalysts are produced by selective leaching of Al from Ni-Al alloys. It is well known that chemical leaching of Ni-Al intermetallic compound (IMC) generates a high surface area in Ni(OH)2. However, the Ni(OH)2 produced by leaching the Ni-Al intermetallic compound retards the hydrogen evolution reaction, which is attributed to its weak hydrogen adsorption energy. In this study, we controlled the chemical state of Ni using plasma vapor deposition (PVD) followed by heat treatment, selective Al leaching, and electrochemical reduction. X-ray diffraction (XRD), scanning microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) were used to confirm the phase evolution of the electrocatalysts during fabrication. We reveal that the heat-treated Ni-Al alloy with a thick Ni2Al3 surface layer underwent selective Al leaching and produced biphasic interfaces comprising Ni(OH)2 and NiAl IMCs at the edges of the grains in the outermost surface layer. Coupled oxidation of the interfacing NiAl IMCs facilitated the partial reduction of Ni(OH)2 to Ni(OH)2/Ni in the grains during electrochemical reduction, as confirmed by X-ray photoelectron spectroscopy (XPS). An electrocatalyst containing partially reduced Ni(OH)2/Ni exhibited an overpotential of 54 mV at 10 mA/cm2 in a half-cell measurement, and a cell voltage of 1.675 V at 0.4 A/cm2 for single-cell operation. A combined experimental and theoretical study (density functional theory calculations) revealed that the superior HER activity was attributed to the presence of partially reduced metallic Ni with various defects and residual Al, which facilitated water adsorption, dissociation, and finally hydrogen evolution.

Macrokinetics of thermal explosion in a 3Ni-Al system mechanically activated in a low-energy mill

Two-step mechanosynthesis in the 3Ni - Al system has been investigated by experimental and theoretical methods using the developed macrokinetic theory of mechanochemical synthesis (MS). The first step included the grinding and mechanical activation (MA) of the starting reaction mixture in the mill, and the second step included the explosive synthesis of the Ni3Al intermetallic compound outside the mill. The effect of mechanical pre-treatment on the temperature-time parameters of the synthesis of the Ni3Al intermetallic compound was found. The phase composition of the activated mixture of nickel, aluminum, and synthesized products was characterized by X-ray diffraction. Preliminary low-energy mechanical activation (LEMA) of the mixture in a laboratory mill eliminates the negative phenomena associated with the grinding and formation of intermediate phases. Kinetic and thermophysical constants characterizing the two-step MS were determined using the inverse problem. The contribution of mechanical activation factors to the acceleration of Ni3Al synthesis was quantitatively evaluated.

Comparative strengthening of intermetallic compounds produced in situ by friction stir processing on different aluminum alloy matrixes

The composite technology based on friction stir processing (FSP) can enhance the strength of Al alloys while retaining the original toughness and ductility of Al alloys, thus achieving an improvement in the overall performance of the composites. Ni/Al composites were prepared in three typical Al matrixes by optimized FSP, and the effect of in situ generated intermetallic compounds on the strengthening of different Al substrates during the FSP was investigated. It was found that the reinforcing phase of Ni/Al composites was mainly in situ generation of Al3Ni intermetallic compound using energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM), and the more the number and more uniform the distribution of Al3Ni reinforcing phase, the better the mechanical properties of Ni/Al composites. The results indicate that the Ni/Al composites formed from different series of Al alloy matrix, the Ni/6061Al composite has the most remarkable microstructure uniformity, the greatest strength increase and the least elongation decrease, which is conducive to improving its strength without affecting the processing properties of the 6061 Al alloy. The finding opens new opportunities for the preparation of Ni/Al composites with excellent properties from 6061 Al alloys.

Formation of grain structure and microhardness of Ni3Al intermetallic compound as a result of SHS extrusion

In the work the possibility of improving the strength properties of Ni3Al intermetallic compound by reducing its average grain size was studied using the example of microhardness. The authors investigated the effect of reaction mixture deformation during self-propagating high-temperature synthesis (SHS) on the grain size and microhardness of Ni3Al intermetallic compound. SHS extrusion was carried out on the experimental stand, which allows continuous monitoring of synthesis parameters. It was established that one of the key factors affecting the characteristics of the grain structure and microhardness is degree of the synthesis product deformation. An increase in diameter of the extrusion hole from 3 to 5 mm leads to an increase in the maximum linear displacement of the press plunger due to active output of the material through a hole of the larger diameter. The above assumes a decrease in the material resistance to deformation when pressure is applied and an increase in degree of the material deformation inside the die and its decrease in the extruded material. Furthermore, the average grain size of Ni3Al remaining in the mold volume after synthesis decreases by 40 % (from 7 to 5 μm), and the material that passed through the extrusion hole increases by 2 times (from 3 to 6 µm). Compared to Ni3Al obtained by SHS compaction, the average grain size of the extruded intermetallic compound is 5.6 times smaller (from 17 to 3 μm). A decrease in the average grain size of extruded Ni3Al leads to an increase in microhardness by 600 MPa. The results obtained make it possible to develop recommendations for producing intermetallic compounds and alloys based on them with a fine grain size and high microhardness.

Wire arc additive manufacturing of Ni-Al intermetallic compounds through synchronous wire-powder feeding

Here we proposed a new method to solve the difficulty existing in wire arc additive manufacturing of Ni-Al intermetallic compounds (IMCs), i.e., no welding wire available owing to the brittle fracture occurring in wire drawing. A synchronous wire-powder hybrid manufacturing by using Ni wire as forming material and auxiliary filling Al powder was employed. Based on the optimized feeding rate of Al powder (VAl) at 0.77 g/min, the deposited microstructure including γ-Ni matrix and grid-like γ'-Ni3Al/γ-Ni was obtained, which increased the ultimate tensile strength by 8% while maintaining the elongation by 90 % compared with the deposited thin-wall without filling Al powder. When the VAl increased to 1.39 g/min, the deposited microstructure remained unchanged, but the distribution of precipitated γ'-Ni3Al/γ-Ni transferred to block-like shape due to its increasing average content from 18.22 % to 50.48 %. It then directly resulted in cracks at the bead surface after the deposition height reached 11 mm. This study mainly investigated the effects of adding amount of Al powder on microstructure transformation of deposited Ni-Al IMCs, as well as its influence mechanisms on mechanical properties and cracking tendency.

Investigation of the phase composition and structure of stationary catalysts to increase safety of agrarian-and-food production

The phase composition and structure of stationary nickel-aluminum promoted catalysts have been studied. It is shown that the phase composition of the catalysts consists of intermetallic compounds NiAl, NiAl3, Ni2Al3. Changes in the microscopic structure of the alloys are determined. Modern methods for evaluating hydrogenation catalysts, as well as methods for analyzing raw materials and products of catalytic hydrogenation, have been established. The highest hydrogenation performance is characteristic of stationary catalysts whose alloys consist of Ni2Al3×4NiAl3 intermetallic compounds. New modifications of stationary alloyed nickel-copper-aluminum catalysts with the addition of vanadium (0.5-2.5 %), rhodium (0.5 %) and palladium (0.05 %) in the process of pre- contact hydrogenation of cottonseed oil have been studied and developed. It has been shown that the lowest content of transisomerized acids in tallow is achieved at a content of 1.5 % vanadium in a stationary promoted catalyst. The content ratio of the fatty-acid composition in the triglycerides of target dietary fats was determined, ensuring their increase in nutritional value and safety. The conditions under which the highest results were obtained are presented.

A brief review of processing techniques for NiAl intermetallic composites

In recent decades, NiAl intermetallic compounds have become a potential candidate for elevated temperature structural materials for aerospace applications due to their exceptional properties. In-spite of having lucrative properties, one thing that restricts their application are low ductility and fracture toughness at room temperature. Several attempts have been made by the researchers to overcome these bottlenecks by adopting feasible processing routes. In this paper, an attempt has been made to highlight the various processing techniques with a view to indicate the most suitable technique for the development of NiAl intermetallic composites.

Fabrication and interface optimization of continuous CF/Al composites with different reinforcement volume fraction

Interface is the key factor to determine the properties of composites. In this work, the Ni coated continuous CF/Al composites were fabricated via twin-roll casting method. After interface optimization, the interfacial bonding strength was enhanced and the dispersion of carbon fibers was improved. The effect of reinforcement volume fraction on microstructure, mechanical properties and strengthening mechanism of CF/Al composites was studied. The microstructural showed that the increase of reinforcement volume fraction was easy to cause more defects in composites. Transmission electron microscopy (TEM) and thermodynamic calculation were used to characterize the interfacial phase composition of composites after interface optimization. The results revealed that the exterior of carbon fibers bundle was mainly composed of Al3Ni intermetallic phase, and there was no obvious Al4C3 phases were found interior of the CFs bundle. In addition, the composites with 13.6 vol% CFs had the best UTS of 218.7 MPa and well dispersion. Furthermore, Vickers hardness test and Nano-indentation results showed that Al-Ni intermetallic compound can enhance the whole hardness of CF/Al composites. Dislocation strengthening in the Al-Ni intermetallic compound region was observed by TEM. The interface evolution mechanism of CF/Al composites were revealed for the first time.

Effects of Ag2Mo2O7 nano-shapes on the mechanical and tribological properties of NiAl intermetallic compound over a wide temperature range

Ag2Mo2O7 has attracted considerable interest as excellent high-temperature solid lubricant. The effect of Ag2Mo2O7 nano-shape on the mechanical and tribological performances of NiAl-Ag2Mo2O7 composites was investigated in the study. Ag2Mo2O7 with three different shapes (nanowires, nanorods, and nanoparticles) were prepared by hydrothermal method. The synthesized Ag2Mo2O7 completely decomposes to Ag and MoO3 during sintering of NiAl-Ag2Mo2O7 composites. The decomposed Ag and MoO3 can improve the microhardness of the composites due to the grain refinement and enhancement of strain strength. In particular, Ag2Mo2O7 nanowires can increase the hardness of NiAl by 27%. With the specific decreasing of surface area of Ag2Mo2O7, the friction coefficients of the composites slightly decrease over a wide temperature range. Moreover, Ag2Mo2O7 could be obtained again by a high-temperature tribochemical reaction at 800 °C. The tribo-layer comprising NiO, MoO3, NiMoO4, and Ag2Mo2O7 renderes excellent tribological performances to the composites at 800 °C. Especially for the composite with addition of Ag2Mo2O7 nanoparticles, the friction coefficient and wear rate could be as low as 0.27 and 4.6 × 10−6 mm3/Nm respectively.

Определение когерентности интерфейса твердорастворной и интерметаллидной фазыв монокристаллических литейных сплавах на основе интерметаллида Ni3Al рентгенодифрактометрическим методом

The paper considers splitting of the solid solution gamma phase diffraction peaks in the nickel heat-resistant alloys, including alloys based on the Ni3Al intermetallic compound with the heterophase structure. It is shown that the effect of splitting the solid solution gamma phase diffraction peaks is missing in the alloys based on the Ni3Al intermetallic compound with heterophase structure, in contrast to the nickel heat-resistant alloys. It was established that splitting of the solid solution gamma phase diffraction peaks in the diffraction pattern was caused by tetragonal distortion of the gamma phase crystal lattice (solid solution) exposed to the interphase stresses. Only under condition of the interphase boundary coherence exposed to the interfacial stresses the tetragonal distortion of the gamma phase crystal lattice (solid solution) appeared. Therefore, a conclusion could be made based on the absence of splitting the gamma phase diffraction peaks that the interphase boundary (interface) coherence was missing in alloys based on the Ni3Al intermetallic compound with the heterophase structure.

Synthesis of NiAl Intermetallic Compound under Shock-Wave Extrusion.

This paper presents the implementation of the first stage of a study on the synthesis of the intermetallic compound in the Ni-Al system under shock-wave extrusion (SWE). A method was developed and experiments involving SWE of the reactive Ni–Al powder mixture were carried out. As a result, it was possible to obtain up to 56 vol.% of the final product and achieve 100% synthesis of NiAl. The results of metallographic analysis indicate that the process of high-velocity collapse of the tube created conditions for the formation of a cumulative flow, which directly affects the phase formation in NiAl. It was shown that the presence of the central hole in the powder sample reduced the effect of the Mach stem on the homogeneity of the NiAl structure. It was also determined that with a central hole with a 5 mm diameter, the effect of the Mach stem could not be observed at all. The goals of further studies are achieving 90–100 vol.% of the final product and reducing the porosity in the final product. Preliminary experimental studies have shown great potential for SWE to produce composite metal–intermetallic materials.

Effect of the heating rate on the thermal explosion behavior and oxidation resistance of 3D-structure porous NiAl intermetallic

Porous NiAl intermetallic compounds demonstrate great potential in various applications by their high porosity and excellent oxidation resistance. However, to obtain a controllable NiAl intermetallic structure by tuning different process parameters remains unclear. In this work, porous NiAl intermetallic compounds were fabricated by economic and energy-saving thermal explosion (TE) reaction. The relationship between microstructure and process parameters was revealed using three-dimensional X-ray microscopy (3D-XRM) with high resolution and non-destructive characteristics. The geometrical features and quantitative statistics of the porous NiAl obtained at different heating rates (2, 10, 20 °C min−1) were compared. The result of the closed porosity calculation showed that a lower heating rate (2 °C min−1) promoted the Kirkendall reaction between Ni and Al, resulting in a high closed porosity (5.25%). However, at a higher heating rate (20 °C min−1), a homogeneous NiAl phase was observed using the threshold segmentation method, indicating uniform and complete TE reaction can be achieved at a high heating rate. The result of the 3D fluid simulation showed that the sample heated at 10 °C min−1 had the highest permeability (2434.6 md). In this study, we systematically investigated the relationship between the heating rates and properties of the porous NiAl intermetallic, including the phase composition, porosity, exothermic mechanism, oxidation resistance, and compression resistance. Our work provides constructive directions for designing and tailoring the performance of porous NiAl intermetallic compounds.

Evaluating of the microstructure, texture, and mechanical properties of AA2024-Al3NiCu composites fabricated by the stir casting process

The formation of nickel aluminides and their uniform distribution in the aluminum matrix due to their high thermal stability can improve the thermal instability of Al-Cu-Mg alloys. This research aims to study the effect of stir casting parameters, including stirring speed, stirring time, and temperature, on the microstructure, and mechanical properties of AA2024 aluminum alloy composite reinforced with Al-Ni intermetallic compounds. Also, the effect of time and temperature of artificial aging treatment on mechanical properties of AA2024-Al 3 NiCu composite investigated. To produce in-situ Al-Ni intermetallic compounds in aluminum, nickel additive was inserted to the molten aluminum during stir casting process. The results indicated that the amount of S-Al 2 CuMg precipitates decreased, and the number of Al 3 NiCu intermetallic compounds increased either by increasing the stirring temperature from 750° to 850°C or increasing the stirring time from 10 to 20 min. With increasing the stirring time from 10 to 20 min and increasing the stirring speed from 300 to 450 rpm, the preferred orientation of the aluminum matrix changed to the (220) plane with a P of 1.31 and 1.34, respectively. By adding 3 wt% Ni at stirring temperature of 750 °C, stirring time of 10 min, and stirring speed of 300 rpm, the maximum hardness 144.05 ± 9.27 HV, tensile strength 230.76 ± 8.45 MPa, and toughness 1.87 ± 0.14 MJ.m −3 were achieved.

Magnetron sputtered NiAl/TiBx multilayer thin films

Transition metal diboride-based thin films are currently receiving strong interest in fundamental and applied research. Multilayer thin films based on transition metal diborides are, however, not yet explored in detail. This study presents results on the constitution and microstructure of multilayer thin films composed of TiBx and the intermetallic compound NiAl. Single layer NiAl and TiBx and NiAl/TiBx multilayer thin films with a variation of the individual layer thickness and bilayer period were deposited by D.C. and R.F. magnetron sputtering on silicon substrates. The impact of the operation mode of the sputtering targets on the microstructure of the thin films was investigated by detailed compositional and structural characterization. The NiAl single layer thin films showed an operation mode-dependent growth in a polycrystalline B2 CsCl structure with a cubic lattice with and without preferred orientation. The TiBx single layer thin films exhibited an operation mode independent crystalline structure with a hexagonal lattice and a pronounced (001) texture. These TiBx layers were significantly Ti-deficient and showed B-excess, resulting in stoichiometry in the range TiB2.64–TiB2.72. Both thin film materials were deposited in a regime corresponding with zone 1 or zone T in the structure zone model of Thornton. Transmission electron microscopy studies revealed, however, very homogeneous, dense thin-film microstructures, as well as the existence of dislocation lines in both materials. In the multilayer stacks with various microscale and nanoscale designs, the TiBx layers grew in a similar microstructure with (001) texture, while the NiAl layers were polycrystalline without preferred orientation in microscale design and tended to grow polycrystalline with (211) preferred orientation in nanoscale designs. The dislocation densities at the NiAl/TiBx phase boundaries changed with the multilayer design, suggesting more smooth interfaces for multilayers with microscale design and more disturbed, strained interfaces in multilayers with nanoscale design. In conclusion, the volume fraction of the two-layer materials, their grain size and crystalline structure, and the nature of the interfaces have an impact on the dislocation density and ability to form dislocations in these NiAl/TiBx-based multilayer structures.

Effect of Nb content on the stacking fault energy, microstructure and mechanical properties of Fe-25Mn-9Al-8Ni-1C alloy

In this study, Fe-25Mn-9Al-8Ni-1C-xNb alloys (x = 0, 0.1%, 0.2%, 0.3%, and 0.4%) were prepared by vacuum arc melting, and the effects of Nb content on the stacking fault energy, microstructure, hardness and room temperature tensile properties of the alloys were systematically studied. It is deduced from the literature on the estimation of stacking fault energy that the stacking fault energy of the Fe-25Mn-9Al-8Ni-1 C-xNb alloys increases the increase of Nb content. Within this range of stacking fault energies, twinning-induced plastic deformation is dominant. Microstructure analysis shows that main phases of the series alloys are austenite, ferrite, k-carbide, NiAl intermetallic compound and NbC phase. As the Nb content increases, the NbC quantity gradually increases. With increasing Nb content, the hardness and elongation of the material gradually increase, while the tensile strength first increases and then decreases. When the Nb content is 0.3%, the alloy has enhanced comprehensive properties, and the average tensile strength is about 853 MPa, and its average elongation is about 30%, which about 8 times higher than that of Fe-25Mn-9Al-8Ni-1C alloy.

ПОЛУЧЕНИЕ МЕТАЛЛОМАТРИЧНЫХ СПЛАВОВ ДЛЯ ИЗНОСОСТОЙКИХ ЭЛЕКТРОИСКРОВЫХ ПОКРЫТИЙ

The study objective is to obtain and study metal matrix alloys based on NiAl intermetallic compound with different concentrations of Ni for forming wear-resistant coatings on steel 45. 
 The problems to which the paper is devoted are: obtaining electrode materials based on NiAl intermetallic compound with different concentrations of Ni and studying their structure; studying the mass transfer during electrospark deposition on steel 45; studying the comparative wear resistance of the coatings obtained. 
 Research methods: electrode alloys are obtained by the method of liquid-phase self-propagating high-temperature synthesis; electro spark alloying is used to create wear-resistant coatings; the microstructure of the obtained alloys is studied by the method of metallographic analysis.
 The novelty of the work: for the first time, the influence of different Ni concentration values on the wear resistance of NiAl electrospark coatings on steel 45 is studied.
 Study results: the microstructure of the obtained alloys consists of doped Cr and Co grains of NiAl matrix with a different Ni/Al ratio, along the boundaries of which the compounds of all alloy components are located. When forming coatings by electrospark method, time dependences of changes in anode erosion, cathode gain and mass transfer coefficient are obtained. 
 Conclusions: NiAl metal-based alloys with different concentrations of Ni were smelted using a liquid-phase SHS method using charge consisting of metal oxides and mineral concentrates containing tungsten and zirconium; the microstructure of the obtained alloys consists of doped Cr and Co grains baseds on NiAl, along which boundaries compounds of all the constituent components of the alloy are concentrated, including Zr and W. Experimental results of anode erosion, cathode gain, and mass transfer coefficient were obtained while forming the coatings with the alloys using electrospark method, and it was found during wear resistance tests that with an increase of Ni concentration in the alloy, the wear resistance increases.

Microstructure evolution and interfacial bonding mechanisms of ultrasonically soldered sapphire/Al dissimilar joints using Sn-based solders

Sapphire and 5A06 Al were ultrasonically soldered with Sn9Zn, SAC305 alloy solders and NiCu alloy foam added Sn-based composite solders, respectively. The microstructure and mechanical properties of joints were investigated and the interfacial bonding mechanism was analyzed. Cracks were observed at the sapphire/Sn matrix interface in joints soldered with alloy solders, which were disappeared in the joints soldered with composite solders. In the joint using NiCu–Sn9Zn composite solder, the solder seam was uneven and Al3Ni intermetallic compound (IMC) layer was formed on the surface of NiCu alloy skeletons. While in the joint using NiCu-SAC305 composite solder, fine particles of (Ni,Zn)3Sn4 were largely formed and homogeneously distributed in the solder seam. An amorphous Al2O3 transition layer was formed at the sapphire/Sn matrix interface, and Zn enrichment was found at the Sn matrix/amorphous Al2O3 interface. The action mechanism of Zn was analyzed by first-principles calculation. The joints soldered with NiCu-SAC305 composite solder exhibited the highest shear strength of 74.42 MPa, the shearing failure mainly happened in the soldering seam.