NiAl Phase Research Articles

Increasing the high-temperature mechanical properties of Mg-Gd-Y-Zn alloys by adding AlN/Al particles

The AlN particles reinforced Mg-10Gd-3Y-1Zn (GWZ) composites were prepared by mixing AlN/Al particles using ball milling followed by stirring casting method. The influence of AlN/Al particles on the microstructural evolution and high-temperature mechanical properties of GWZ alloys were revealed and discussed. With AlN/Al particles added into the as-cast alloys, the Mg3RE phase was transformed into lamellar LPSO phase, while the content of Al2RE and LPSO phase increased. Since the Al2RE and AlN were effective nucleation sites for α-Mg, the grain size of AlN/Al-GWZ composites was reduced obviously from 126.1 to 39.8 μm. After homogenization, due to the coherent lattice matching relationships between 18R-LPSO phase and Al2RE or AlN particles, the 18R-LPSO phase nucleated on the Al2RE and AlN particles. After ageing treatment, the 2AlN/Al-GWZ composite showed the optimum mechanical properties at 250 °C, with the yield strength, ultimate tensile strength and elongation of 247.1 MPa, 265.5 MPa and 4.0%, respectively. The strengthening effect was primarily originated from the AlN particles, Al2RE and LPSO phases in the 2AlN/Al-GWZ composite. Besides, the composites can achieve the enhancement of high-temperature strength without the sacrifice of plasticity due to the coordinated deformation of AlN particles as well as the refinement of grains.

Microstructural evolution and mechanical properties of Al-4Ni-0.4V alloyed with Zr and Ti at elevated temperatures

The influence of Zr and Ti alloying on the microstructural evolution and mechanical properties of an Al-4Ni-0.4V alloy at elevated temperatures was investigated. The results showed that the coarsening rate of the eutectic Al3Ni phase in the Al-4Ni-0.4V-0.2Zr-0.2Ti alloy decreased from 21.1 nm3/s in the Al-4Ni-0.4V alloy to 7.4 nm3/s after annealing at 350 °C for 0 h to 120 h. The tensile strength, yield strength, and elongation at room temperature of the annealed Al-4Ni-0.4V-0.2Zr-0.2Ti alloy (350 °C, 8 h) were 181 MPa, 108 MPa, and 27.2 %, respectively. After tensile test at 350 °C, these values of the annealed Al-4Ni-0.4V-0.2Zr-0.2Ti alloy were 108 MPa, 72 MPa, and 29.8 %, respectively. Transmission electron microscopy results revealed the precipitation of the L12 ordered structure of the Al3M (M = Zr, V, Ti) phase, approximately 2 nm in size, in the α-Al after annealing. These phases exhibited excellent lattice matching with the α-Al and considerable precipitation strengthening. Segregation of Zr, V, and Ti elements at the α-Al/Al3Ni interface hindered Ni diffusion in the matrix, thereby reducing Al3Ni phase coarsening. Moreover, the Al3M phase precipitated at the interface exhibited favorable matching with the lattice planes of the α-Al and Al3Ni phase, which improved the thermal stability of the eutectic structure and the mechanical properties at elevated temperatures.

Design of non-heat-treatable Al-Fe-Ni alloys with high electrical conductivity and high strength via CALPHAD approach

Electrical conductivity and strength are two critical properties concerned for rotors materials in electric vehicles. However, the two properties are often mutually exclusive in cast Al alloys. The present work proposes a novel non-heat-treatable Al-Fe-Ni alloy by considering the intermetallic compound’s content and morphology. With the modification of Ni and Fe content, the solidification path of designed alloy were calculated to predict the phase composition, which would greatly impact their performance. The as-cast Al-2Fe-1Ni (wt%) alloy exhibits comprehensive properties with an ultimate tensile strength of 131.2±2.5 MPa, an elongation of 20.2±3.6 % and an electrical conductivity up to 52.0±0.1 %IACS. The eutectic microstructure of Al13(Fe,Ni)4+α-Al in Al-2Fe-1Ni alloy accounts for over 90 %, much larger than the eutectic content in Al-0.4Fe-3.4Ni and Al-1Fe-1Ni alloys. The fine eutectics in Al-2Fe-1Ni alloy improve the second-phase strengthening effects and plastic deformation capability. In addition, the fibrous rod-like intermetallic reduces the electron scattering during the propagation process and leaves more space for free electron movement. The dominant second phase transforms from Al3Ni phase to Al9FeNi phase, further enhancing the thermal stability of the alloy. After aging treatment at 180 °C for 100 h, it shows no noticeable change in electrical conductivity and mechanical properties. It is hoped that this work can provide a new design approach for high-strength and high-conductivity Al alloys.

The Effect of Spray Distance on the Hot Corrosion Behavior of HVOF‐Sprayed NiCrAlY Coatings in a Simulated Gas Turbine Environment

ABSTRACTTo utilize the unique properties of coatings produced using the high‐velocity oxy‐fuel (HVOF) method, this study examined the effect of spray distance on the hot corrosion behavior of NiCrAlY coatings deposited on a steel substrate. The coating samples were obtained at spray distances of 20, 25, and 30 cm. The flow rates of oxygen and propane were maintained constant at 300 and 60 lit/min, respectively. Additionally, the powder feeding rate was 32 g/min. The samples were then subjected to the hot corrosion test in a salt mixture of Na2SO4−60% V2O5 at 900°C in an ambient atmosphere. The surface and the cross section of the samples were observed using a scanning electron microscope (SEM) and the chemical composition of different sections was determined by energy‐dispersive spectroscopy (EDS). The phases were also characterized using X‐ray diffraction analysis (XRD). The best corrosion resistance was found in the sample coating formed at a spraying distance of 20 cm, as the results showed that increasing the spraying distance led to a reduction in the thermal and kinetic energy of the flame, resulting in increased porosity in the coating. This behavior can be attributed to the low oxide content of the coating, the higher aluminum content, and the richer NiAl phase, which serves as a reservoir for aluminum.

Microstructural evaluation and optimization of wear behaviour of vacuum arc melted AlFeCrNiSi high entropy alloy

High-entropy alloys (HEA) are equiatomic, multi-element systems that, while having several elements with various crystal geometries to form a single phase. In this study, a novel equiatomic AlFeCrNiSi HEA is prepared using the vacuum arc melting process. The resulting microstructure featured dendritic and inter-dendritic structures with formations of intermetallic compounds such as Al₃Fe₂Si, NiAl, and AlCrNi phases. EDS analysis confirmed the presence of alloying elements and EBSD analysis revealed refined grains with an average size of 1 ± 0.15 µm size. Pin-on-Disc wear test with varying test parameters is conducted to optimize the wear parameters. Signal-to-noise ratio and analysis of variance identified the most significant wear parameters, with load being the most influential, followed by sliding distance and velocity. The wear rate is minimum at the lowest conditions of applied load, sliding distance, and sliding velocity. The improved microhardness also contributed to the improved wear resistance of the cast alloy. The subsequent worn morphology revealed the formation of grooves, microcracks, and oxide layers on the worn surface.

Study on the tensile behaviour and nano deformation mechanism of Nickel-based single crystal superalloys with γ/γ' structure at atomic scale

To study the deformation mechanism of nickel-based single crystal superalloys (NBSC) during tensile process, tensile experiments on NBSC are carried out by molecular dynamics to systematically analyze stress-strain, shear strain, atomic migration and defect evolution. The effects of the structure of the two phases and the strengthening elements on the tensile behavior are analyzed by comparing the pure Ni phase, the pure Ni3Al phase and the Ni phase containing the strengthening elements Cr and Co from a microscopic view. The results show that the interaction between the two-phase structural dislocations during tensile process balances the stress concentration and reduces the degree of plastic deformation that occurs within the matrix. The γ/γ' interface separates the strain morphology and inhibits the slip of the shear band between the two phases, resulting in enhanced deformation resistance of the matrix. By comparing the three single-phase structures, the γ/γ' structure has the highest yield point. From the shear strain distribution pattern, the portion of the two-phase structure with a larger degree of shear strain mainly occurs at the interface as well as at the edge of the matrix.

The effect of aluminum addition on plasma nitriding for 42CrMo steel

In order to enhance the efficiency and performances of nitriding layer, aluminum was primarily introduced in the furnace during plasma nitriding by adding some FeAl around the samples. The results show that the process efficiency is dramatically enhanced more than 5 times comparing with traditional plasma nitriding (PN), with the effective hardening layer increasing from 224 μm to 1246 μm at 520 ℃/4h. Meanwhile, ultra-high surface hardness and excellent wear behaviors are obtained by Al-PN due to the formation of dispersed strengthening phases of AlN and FexAl in the nitriding layer, with the surface hardness increasing from 755 HV0.025 to 1251 HV0.025, and the wear rate decreased by a factor of approximately 2.

Microstructural refinement in a high elastic modulus Al-18Si-8Ni casting alloy

A new Al-Si-based casting alloy with high elastic modulus in the range of 90‐100 GPa and low density, less than 3 g/cm3, was developed by alloy design and microstructural refinement approaches. The addition of 8 wt.% Ni to a hypereutectic Al-18Si alloy introduces large volume fractions (∼40 vol.%) of hard primary Si and primary Al3Ni phases. Coarse primary Si and primary Al3Ni formed in the early stage of solidification, however, can interfere with the melt flow, reducing the castability, and also were deleterious to elongation. By the assessments of the crystallographic misfit between a nucleant substrate and a nucleated solid, we discovered key inoculants, AlP and TiB2, which can successfully refine such coarse and brittle primary phases, Si and Al3Ni, respectively. More importantly, along with the improved elastic modulus, the combined addition of AlP and TiB2 results in a significant increase in the elongation up to 1% with an advantageous yield strength of over 230 MPa. The important role of an inoculant, particularly TiB2 in nucleating the Al3Ni phase is also discussed based on the theoretical lattice misfit calculations and experimental characterization, further confirming their orientation relationship between the Al3Ni and the TiB2 as (110)[11¯0]Al3Ni∥ (0001)[12¯10]TiB2.

Oxidation of Sintered Refractory Alloy (Ni3Al)

Ni3Al is a superalloy which is of particular interest at high temperatures due to its high resistance to oxidation with the formation of a protective oxide layer that performs better than NiO and Cr2O3. Among the factors likely to affect the reaction mechanism and modification of the oxidation kinetics, the surface state appears to be a very important parameter. In the case of sintered materials, the surface condition will be linked to the porosity of the material and therefore to densification. This work essentially has two parts. The first consists of developing Ni3Al sinters intended for oxidation, studying the densification mechanisms and bringing together the results obtained by dilatometry at variable temperature and by differential thermal analysis which made it possible to demonstrate sintering in a reactive liquid phase extremely fast SHS type, with instantaneous formation of the Ni3Al phase. The second part is devoted to the isothermal oxidation between 1100 and 1350°C of cubic-shaped sinters (4mm edge) under a flow of oxygen for 24 hours. The shape of the parabolic curves is correlated with morphological and microstructural observations to deduce the diffusional kinetic regime which controls the speed of the reaction. On the other hand, these observations highlighted a very strong adhesion due to the indentations of the Al2O3 oxide in the metal at the oxide/metal interface. Various techniques (Density – XRD – SEM and Microanalysis) to characterize the sinters and the oxidation products complete our study.

Phase composition and microstructure of intermetallic alloys obtained using electron-beam additive manufacturing

The paper investigates the microstructure and phase composition of nickel- and aluminum-based intermetallic alloys obtained using two-wire electron-beam additive manufacturing (EBAM). Relevance of the research is related to the widespread use of intermetallic alloys based on nickel and aluminum (mainly Ni3Al) in various high-temperature applications and the need to use modern production methods when creating machine parts and mechanisms from these alloys. Using EBAM, the billets from intermetallic alloys with different ratios of the content of main components were obtained. Change in concentrations of the basic elements was carried out varying the ratio of feed rates of nickel and aluminum wires during additive manufacturing in the range from 1:1 to 3:1, respectively. The results of microscopic studies of the obtained alloys showed that, regardless of nickel content, the obtained alloys are characterized by a large–crystalline structure with grain sizes in the range of 100 – 300 μm for alloys with a component ratio of 1:1 and 150 – 400 μm for alloys with a component ratio of 2:1 and 3:1. At the same time, the alloy with an equal content of base components is characterized by more uniform grain and microstructure compared to those with high content of Ni. By changing the concentration ratio of the components, phase composition of the resulting billet can be purposefully controlled. In the case of an “equiatomic” content of the base components in the alloy, a NiAl-based compound with a small phase content based on the intermetallides Ni3Al5 and Ni3Al is formed. At high concent­rations of nickel, the intermetallic Ni3Al phase is formed, and at a component ratio of 3:1, structure of the resulting billet consists mainly of Ni3Al phase and the γ solid substitutional solution based on nickel. The paper demonstrates the possibility of direct production of intermetallic alloys with a given phase composition during electron-beam additive manufacturing.

Oxidation behavior of SiC‐AlN ceramics exposed to dry oxygen and water oxygen environments at 1100–1300°C

AbstractThe corrosion of SiCf/SiC composites in gas environment threatens their long‐term service in aeroengines as hot‐end structure components. Addition of corrosion‐resistant phases into SiC matrix is a potential strategy to improve the service performance of SiCf/SiC materials. Here, AlN added SiC ceramics were prepared by reactive melt infiltration, and the effect of AlN phase on the oxidation resistance of the ceramics was emphasized. The oxidation tests were performed in dry oxygen and water oxygen atmospheres at 1100°C–1300°C, respectively. The oxidation mechanism was discussed based on the microstructure evolution of the oxide layer. The results show that the oxide layer is composed of aluminum silicate glass and Al2O3 flakes dispersedly distributed in the glass phase. As the temperature rises, the oxide layer gradually grows and thickens. Finally, a smooth and dense protective layer could be formed on the surface of ceramics to resist oxidation. This study can provide a profound insight to construct SiCf/SiC composites with excellent oxidation resistance.

Effect of Microstructure on Energy Release Characteristics of Al/Ni Energetic Structural Material Prepared by Cold Spraying.

Al/Ni energetic structural material with both high strength structural properties and high energy release functional properties can undergo a strong exothermic reaction under heating or impact loading conditions. In order to investigate the influence of microstructure on the mechanical properties and energy release characteristics of the Al/Ni energetic structural material, the materials with different Ni contents were prepared by cold spraying. With the increase of Ni particles, the microstructure inside the energetic structural material gradually changes from a continuous network structure of Al to a continuous network structure of Ni. The contact between Ni particles will make the stress transfer more uniform during the compression process of the energetic structural material, which enhances their strength. The results of heat-induced exothermic and shock-induced energy release show that the Al/Ni energetic structural material exhibits the best exothermic performance when Ni particles are uniformly dispersed and there are enough Al and Ni to make the material completely transform into the AlNi phase. The increase in the contact interface between Al and Ni particles facilitates the occurrence of a solid/solid reaction exothermic reaction between Al and Ni as well as the diffusion of Ni into the Al melt to generate the AlNi phase. The formation of the Ni continuous phase will lead to a reduction in the contact interface between Al and Ni, as well as an increase in porosity, which will result in a decrease in the amount of heat released during the diffusion reaction. This study will provide insights into the preparation of an Al/Ni energetic structural material with excellent properties.

Characterization of Sm-rich phase and properties of hypereutectic Al-Ni alloys modified by Sm

The impact of Samarium (Sm) addition on hypereutectic Al-Ni alloys was systematically investigated, focusing on microstructural changes and thermal-physical, mechanical properties. The addition of 0.1–0.5 wt% Sm resulted in the refinement of primary Al3Ni phases from coarse lath-like structures to small particles, enhancing mechanical properties and reducing thermal expansion coefficients (CTE). Thermal conductivity (TC) improved with 0.1–0.3 wt% Sm addition, but declined at the amount of 0.5 wt%. Excessive Sm addition leads to the formation of a Sm-rich phase, characterized by a two-phase mixed structure of Al11(Ni, Sm)3 surrounded by Al4Sm. Sm addition lowered the precipitation temperature of the primary Al3Ni phase, inducing significant constitutional undercooling and exhibiting a phase refinement effect. The Al-9Ni-0.3Sm alloy showed excellent performance, with a TC of 211.8 W/(m·K), CTE of 17.3×10−6/K (@25–100 °C), ultimate tensile strength of 169.5 MPa, and elongation of 10.4 %. Optimal addition of Sm improved TC, mechanical properties as well as reduced the CTE in the Al alloy at the same time and showed a good modification effect.

Effect of heat treatment on microstructure of near-eutectic Al-Ni-Mn alloy, and determination of mechanical and thermoelectrical properties

This study examined the impact of solution heat treatment on the microstructure, mechanical characteristics, thermophysical properties, and electrical resistivity of an Al-Ni-Mn near-eutectic alloy. The investigation focused on varying temperatures and holding periods. The composition of the Al-Ni-Mn near-eutectic alloy system was chosen as Al-5.3%Ni-1.0%Mn (wt). In the non-heat-treated sample, the matrix phase (α-Al) is in equilibrium with the intermetallic Al9(Mn,Ni)2 and Al3Ni phases. The hardness value of the non-heat-treated sample (49.8 kg mm−2) increased to 70.1 kg mm−2 with 2 h of solution heat treatment at 570 °C and then 8 h of artificial aging at 180 °C. The hardness value increased by approximately 41%. TE: 651.81 °C for the non-heat-treated sample and TE:648.79 °C for the heat-treated sample. Fusion enthalpy (ΔH) value was determined as 336.79 (J g−1) for the non-heat-treated sample and 516.36 (J g−1) for the heat-treated sample. Heat Capacity (Cpl) value was found to be 0.364 J g−1.K for the non-heat-treated sample and 0.560 J g−1.K for the heat-treated sample. The electrical resistivity value of the 2 h’ solution heat-treated sample at 600 °C reached its highest value.

Influence of additional intermediate thick Al layers on the reaction propagation and heat flow of Al/Ni reactive multilayers

This study investigates the effects of sputtering and electron beam evaporation (e‐beam) on the microstructure and reactive properties of Al/Ni reactive multilayers (RML). The intermixing zone, a critical factor influencing reaction kinetics, was characterized using high‐resolution transmission electron microscopy and found to be consistently 3 nm for both fabrication methods. Differential scanning calorimetry revealed that e‐beam samples, with thicker Al layers, exhibited slightly higher total molar enthalpy and maintained high reaction temperatures despite reduced reaction velocities in comparison to sputtered samples. X‐ray diffraction confirmed the formation of both Al3Ni2 and AlNi phases in the e‐beam samples. These findings indicate that while thicker bilayer structures reduce reaction velocity, they keep thermal output and mitigate the impact of intermixing zones, leading to similar total molar enthalpy. This analysis underscores the significance of deposition technique and bilayer thickness in optimizing the performance of Al/Ni RML, offering the possibility to establish different phase formations in thicker RML. It advances the control over the reactive properties of reactive multilayers in their applications, for example reactive bonding.This article is protected by copyright. All rights reserved.

The Atomic Atmosphere at the Antiphase Domain Boundary in Ni3Al: A Phase‐Field Study

The atomic atmosphere and formation mechanism of the antiphase domain boundary (APB) may depend on the environmental variables of the phase transformation for the L12‐structural Ni3Al phase, which is the first important precipitate phase for Ni‐based superalloys. Herein, a discrete phase field method is used to reproduce the complete formation process of an APB without preset restrictions. Numerical calculations are performed to classify the atomic atmosphere, and its formation mechanism is revealed by calculating and analyzing the functional properties of the driving force. The formation process shows that four types of antiphase domains survive to form the APB. The numerical calculation results demonstrate that the atomic atmosphere has the same temperature dependence for hypostoichiometric, stoichiometric, and hyperstoichiometric systems. However, Al plays two opposite roles in influencing the atomic atmosphere according to the changes in the alloy system. The positive and negative values of the driving force determine whether the atomic atmosphere is segregated or depleted, and the magnitude of the absolute value determines the atomic atmosphere level. This atomic‐scale study of nanoscale ordered domain boundaries can provide theoretical information for further understanding of these and similar interfaces in ordered precipitation‐strengthened phases.

Study on the structure, growth pattern and corrosion behavior of CoCrFeNiAl high entropy alloy coatings - base on hollow cathode effect

The surface of TC18 titanium alloy was coated with a CoCrFeNiAl HEA coating using double-glow plasma surface metallurgy. The structure, phase, and growth mode of the coating were investigated, along with its electrochemical corrosion behavior. The prepared HEA coating, under the influence of the hollow cathode effect and non-equilibrium diffusion, exhibits a composite structure consisting of a deposited layer and an interdiffused layer. It demonstrates robust metallurgical bonding with the substrate, and it exhibits a hardness of 12.66 GPa and an elastic modulus of 158.52 GPa, along with exceptional hardness and high elastic modulus. The primary phase of the coating consists of an FCC solid solution, with a minor presence of Ni3Al and Al8Cr5 phases. TEM results demonstrate that hollow cathode enhanced sputtering effectively refines the grain structure on the substrate surface. The high entropy alloy coating, characterized by a significant abundance of nanocrystalline and amorphous structures, is obtained under the bombardment of high-energy particles. Gradually increasing from the interface to the deposited layer, there is an augmentation in the content of nanocrystals. The transition from the substrate to the sedimentary layer comprises three distinct regions: a surface fine crystal region, a nanocrystalline structure region, and a nanocrystalline and amorphous precipitated phase-rich region. In 3.5 wt% NaCl solution, the electrochemical corrosion rate of the coating is 1.36 × 10−1 μm·year−1, which is about ten times lower than that of the substrate. Moreover, pre-soaking forms a stable oxide film on the coating's surface, effectively preventing corrosion and demonstrating its remarkable corrosion resistance.

Phase Relations of the Sm–Ni–Al Ternary System at 800 °C in the 30–100 at.% Al Region

The Sm–Ni–Al phase relationships at 800 °C have been investigated by using several well–focused experimental techniques such as X–Ray Powder Diffraction (XRPD), Light Optical Microscopy (LOM) and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Microprobe Analysis (EPMA). The isothermal section of the Sm–Ni–Al system at 800 °C was constructed according to the present experimental results. More than 50 alloys have been synthesized and characterized in the 30–100 at.% Al region. At 800 °C, 9 intermetallic phases have been confirmed, characterized and their relationships have been established. In the Al-rich corner, the presence of two ternary invariant reactions have been postulated whilst along the 16.67 at.% Sm isopleth, the presence of two structurally related extended solid solutions have been observed. The determined phase equilibria at 800 °C are discussed and compared with the isothermal section at 500 °C already reported in literature.

Fabrication and Characterization of Nickel‐Aluminide Cladding by Dual‐Wire Arc Additive Manufacturing

Nickel aluminide is a widely utilized intermetallic compound, prized for its high strength, low density, and resistance to both corrosion and creep. This study investigates the impact of heat input during the fabrication of nickel‐aluminide intermetallic compounds using the dual‐wire gas tungsten arc welding process. The results indicate that an increase in clad layer dilution from 28.9% to 33.4% reduces the amount of aluminum in the molten pool from 32.46 to 21.96 wt% while increasing the presence of the Ni3Al phase. Additionally, the NiAl phase decreases when moving from the upper side of the coating to the fusion line. When the arc current is increased from 110 to 150 A, a coarse dendritic structure forms, and the dendritic arms increase from 2.6 ± 0.4 to 5.5 ± 0.3 μm. This increase in current also results in yield strength and tensile strength values of 500.21 ± 14.56 and 752.32 ± 25.12 MPa, respectively, representing decreases of 15.2% and 5.1%. Furthermore, as the arc current increases from 110 to 150 A, both the friction coefficient and the wear rate increase to 0.43 and 0.29 ± 0.02 μg m−1, respectively. However, corrosion resistance improves by 66.3%.

Preparation of transparent MgAlON ceramics with tunable compositions

MgAlON ceramics with excellent optical properties were synthesized using high-purity AlON and commercially available MgO powder. The effect of MgO amount on ceramic sintering was examined in terms of microstructural evolution and grain growth. Furthermore, the process of MgAlON phase formation through the reaction between AlON and MgO was studied. The results revealed that the addition of MgO significantly hindered the formation of α-Al2O3 and AlN phases at temperatures ranging from 1350 °C to 1600 °C, thereby facilitating the stabilization of the spinel-type phase. The optical transmittance and Vickers hardness of MgAlON were investigated through pressureless sintering followed by hot isostatic pressing (HIP). The resulting ceramics, with a MgO mass ratio of 10.0 wt%, exhibited an excellent in-line transmittance of ∼82.9 % at 0.6 μm and 87.7 % at 3.7 μm, and a remarkable Vickers hardness of approximately 13.65 ± 0.21 GPa.