NiAl Phase Research Articles

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.

Microwave absorption, thermal and mechanical properties of amorphous nano carbon doped aluminium nitride composite ceramics

Low-cost amorphous nano-carbon (ANC) was employed as an absorbent to modify the microwave performance of AlN ceramics (AlN-4 wt% Y2O3-x wt% C, x = 0, 2.0, 3.8, 3.9, 4.0) via hot-pressing sintering, and the thermal and mechanical properties were also investigated. With the increase of ANC content from 0 to 4.0 wt%, the relative density of AlN composite decreases from 3.28 g cm−3 to 3.16 g cm−3 when sintered at 1800 °C for 2 h, and with the increase of sintering temperature from 1700 °C, the density of the 4.0 wt% ANC doped AlN composite presents trend of increase and reaches the maximum value of 3.16 g cm−3 at 1800 °C and then decreases. The XRD pattern shows that the composites are composed of AlN and Y–Al–O (YAG, YAP, YAM et al.) phases. SEM results indicate that average grain sizes for AlN and secondary phases gradually decrease with increasing carbon content, suggesting inhibited grain growth due to ANC addition. No obvious changes in phase constitution nor intensity changes were detected with the increase in carbon content and sintering temperature. As the carbon content increases from 0 to 4.0 wt%, the dielectric constant gradually increases from ∼9 to 13.89 at 10 GHz, the dielectric loss gradually increases from the vicinity of 10−3 to 0.38 at 10 GHz, and the reflective loss decreases from −27.92 dB to −49.40 dB, the thermal conductivity of the AlN-ANC composite decreases from 116.63 W m−1 K−1 to 50.13 W m−1 K−1. In addition, with 4.0 wt% ANC addition, the dielectric constant, dielectric loss, reflective loss, hardness, elastic modulus, bending strength, and fracture toughness are 13.89, 0.38, 49.40 dB, 6.4 ± 0.4 GPa, 262 GPa, 268.78 MPa, and 1.4 ± 0.1 MPa m1/2, respectively. Its ability to efficiently absorb microwave energy enhances the performance of devices including radar systems, communication equipment, and microwave heating systems, making it a promising candidate for microwave vacuum electronic applications.

Revealing microstructural degradation mechanism induced by interdiffusion between Amdry365 coating and IN792 superalloy

Metallic coatings are widely employed to improve the oxidation resistance of superalloys. However, the interdiffusion between the metallic coatings and the superalloys leads to microstructural degradation in both. Some of the underlying degradation mechanisms are still elusive, e.g., the γ′ (Ni3Al) phase depletion in superalloys, where a large amount of γ′ precipitates are dissolved in the γ matrix even though the incoming Al from coatings indeed increases the Al content. Here, we investigated the interdiffusion behavior between the Amdry365 coating and the IN792 superalloy at 1100 °C, using multiple microscopic techniques and thermodynamics calculations. Our results showed an excellent agreement between experiments and thermodynamics simulations, indicating the dominant role of Al on the initial diffusion-induced phase transitions. We proposed the Al-Cr interference effect to account for the pile-up behavior of Cr and the reduced Al content near the coating/superalloy interface. The local phase equilibrium calculations revealed that the γ′ depletion in the superalloy is primarily attributed to the loss of γ′-forming elements, such as Ta and Ti. Our findings opened up an avenue for studies on the superalloy/coating interdiffusion, contributing to reducing this damaging impact.

Impact toughness and fracture propagation mechanism of NiAl precipitation-strengthened HSLA steels

Impact toughness is essential for evaluating the mechanical properties of ship hull steels. This study focused on understanding the embrittlement mechanism of NiAl precipitation-strengthened HSLA steels by integrating advanced characterization and atomic-scale calculations. The factors causing the deterioration of the impact toughness of NiAl precipitation-strengthened steels, which have been contentious, were identified. The embrittlement mechanism and crack propagation mode were revealed using first-principles calculations and 3D impact fracture morphology, respectively. The results suggested that the numerous homogeneous NiAl nanoparticles within the bcc-Fe matrix reduced the impact toughness of the HSLA steels. As the precipitate interparticle spacing (L) decreased, the impact toughness decreased until it attained a critical value (∼27 nm). This is interpreted effectively by the calculations indicating that the shear modulus (75 GPa) and fracture energy (4.5 J/m2) of the NiAl phase, particularly the NiAlMn phase (46 GPa, 4 J/m2), are significantly lower than those of bcc-Fe (83 GPa, 5 J/m2). This induces the fracture of nanoparticles under rapid impact loading, which functions as numerous crack initiations before plastic deformation of the matrix. The small L achieved after peak-hardening aging can result in the interconnection of these crack sources and cause instantaneous cleavage fractures, similar to brittle materials.

Effect of biphasic interface on mechanical properties and deformation mechanism of nickel base alloy

The tensile properties of biphasic nickel-based nanopolycrystalline alloys (Ni–Ni3Al) at different temperatures were simulated by molecular dynamics. The results show that the tensile properties of the dual-phase nano-polycrystalline alloy are obviously better than those of the conventional nickel metal. The γ 'phase (Ni3Al) is LI2 type structure, which shows higher stability and reduces grain boundary migration during deformation due to the lower atomic potential energy of γ′ phase. As the temperature increases, the mechanical behavior of the biphasic alloy and nickel metal shows the same decreasing trend. Dislocation is an important factor affecting the strength of γ 'phase plastic deformation. The current study provides an atomic perspective on the deformation process and mechanism of biphasic nickel-based nanopolycrystalline alloys, and provides a new perspective for the design of novel superalloys with excellent mechanical properties.

Mechanical and thermal properties of in situ AlN/Al-12Si composite fabricated by laser powder bed fusion

This work reports on the synthesis, mechanical, and thermal properties of in situ AlN/Al-12Si composite through laser powder bed fusion (LPBF) by blending Al-12Si powder with 5 vol% nano-sized BN particles. Incorporating nano-BN particles results in (i) formation of thermally stable AlN phase, preventing Si diffusion and breakdown of cellular structure, (ii) improvement of compressive yield strength (CYS), and (iii) reduction in coefficients of thermal expansion (CTE) and thermal conductivity. In addition, compared to Al-12Si alloy, the composite exhibits grain refinement from 38.8 to 1.2 μm in size, and the alteration of columnar grains (Al-12Si) to equiaxed grains (AlN/Al-12Si). At annealing temperatures above 573 K, the CYS of the unadulterated Al-12Si alloy had a ∼ 2.1 times greater reduction (from 285 to 200 MPa) compared to that of the composites (from 301 to 260 MPa). The formation of the AlN phase mitigates the significant reduction in CYS. The CTE of Al-12Si and AlN/Al-12Si are 27.3 × 10−6 K−1 and 24.3 × 10−6 K−1 respectively. There is good agreement between the measured CYS results and the calculated strengthening mechanisms. This work offers both theoretical insights and experimental data to support the use of LPBF AlN/Al-12Si composite in low- and moderate-temperature applications.

Fast epitaxial brazing of DD6 single crystal superalloy using novel NiCoCrAlNbTi high entropy filler alloy

In recent years, Ni-based single crystal superalloys are widely applied in the fabrication of blades and vanes in aero-engine industry due to the excellent high temperature properties. In this study, a novel high entropy filler without Si and B was proposed. The melting point of the newly developed Ni-Co-Cr-Al-Nb-Ti filler was 1155ºC and fast epitaxial brazing DD6 single crystal superalloy was realized under the brazing condition of 1200ºC for 30 min. Furthermore, the influence of aging heat treatment on the interface microstructure and joint strength was investigated. The as-brazed joint interface mainly consisted of γ, γ’, γ’’-(Ni,Co,Cr)3Nb and NiAl phase. After aging treatment, element distribution became more uniform and the size of intermetallic phase was refined. The γ+γ’ phase in brazing seam exhibits same [001] orientation with DD6 substrate. The orientation relationship between γ and γ’’ was also analyzed. The joint tensile strength tested at 980ºC was 559 MPa.

An ab initio guided study on the shear-induced fcc-hcp transition: A case study of (Ti,Al)N/ZrN multilayers

The cubic-wurtzite phase transition of (Ti,Al)N-based thin films at high temperatures is the chief determing factor for their thermal stability. Nevertheless, its mechanism of atomic shear is not yet well explored theoretically. Here, we correlate the coherent interfaces with wurtzite formation within (Ti,Al)N/ZrN multilayers by a combined ab initio and experimental study. Compared to (Ti,Al)N, the multilayer exhibits a delayed formation of hexagonal close-packed (hcp) wurtzite-type AlN phase, which is encapsulated by face-centered cubic (fcc-)(Ti,Zr)N and fcc-(Zr,Ti)N layers when annealed at 1200 °C. Based on the orientation relationships of (200)fcc//(0001)hcp and (220)fcc//(01-10)hcp among hcp-AlN and neighboring fcc-(Ti,Zr)N as well as fcc-(Zr,Ti)N by the solid-state nudged elastic band (SS-NEB) method, two mechanisms for atomic shear during fcc-hcp transition are proposed. The introduction of ZrN layers effectively suppresses the fcc-hcp transition, due to higher activation energies induced by the coherent interfaces.

Short study on mechanism of morphology change of γ′ precipitates in IN718 Plus

γ′ Ni3Al phase (L12 structure) strengthened superalloy has become an important strengthening phase in Ni based superalloys because of its excellent high-temperature service performance, and has been widely used. The process of γ′ phase precipitation has also received a lot of attention and research. However, most studies focused on its growth rate. There were few studies on the morphology transformation of γ′ phase, and the morphology transformation process is complex. The mechanism of γ′ phase transformation process was systematically analyzed in this paper. Firstly, through molecular dynamics calculation, the most stable morphology of the γ′ phase in the nickel matrix was obtained under ideal conditions. The stability of spherical precipitates is higher than that of cubic precipitates. When the temperature is greater than 800 K, the stability is more obvious.Then through the micro EDS analysis of the γ′ phase in the morphology transformation process, it was shown that the soft impingement phenomenon exists in the nickel base alloy with high γ′ phase volume fraction. Further, by the derivation of the formula of solid-state phase transformation, it was found that the growth rate of precipitate is directly proportional to the concentration gradient of Al in the matrix at the interface, while increases with the rising of the Al concentration in the matrix at the interface. Finally, the way and mechanism of soft impingement affecting the morphology transformation were analyzed. The precipitates formed by soft impingement are nearly cubic precipitates with rounded edges and corners.

Combustion-synthesised TiAl/NiAl layered intermetallic composite: synthesis, phase composition, and microstructure

ABSTRACT The joining of different intermetallics (e.g. NiAl, TiAl) is important for high-temperature applications. In this study, self-propagating high-temperature synthesis was used for simultaneous joining of (Ni+Al) and (Ti+Al) layered samples of the stoichiometric compositions. The main advantage of such joining by self-propagating high-temperature synthesis is that it could be done at ambient temperature without the use of a furnace. The applied load during combustion synthesis was used to improve the contact between the Ni-Al and Ti-Al layers. The obtained results demonstrate that TiAl/NiAl intermetallics were successfully joined together with a bonding interface of about 170 μm thickness. XRD analysis has shown that the joining area consists of NiAl, TiAl, Ti3Al, and NiTiAl2 phases. The SEM data analysis of the transition zone of NiAl-TiAl conjunction has revealed that the transition zone consists of several intermediate layers: a polycrystalline NiAl layer; an intermediate layer based on Ni-Al-Ti containing NiTiAl2 phase; a layer based on Ni-Al-Ti with mixed dendritic and eutectic regions; and a polycrystalline TiAl layer.The measured microhardness of the transition zone varies from 3200 up to 13,600 MPa with the maximum microhardness of 1355 ± 45 MPa corresponding to the layer identified as the NiTiAl2 phase.

Microstructure evolution and mechanical behavior of Cu-7Ni-7Al-4Fe-2Mn alloy via a quenching-aging heat treatment

The effects of solution and aging treatment on the microstructure and mechanical properties of Cu-7Ni-7Al-4Fe-2Mn alloy were studied by means of optical microscope(OM), scanning electron microscope(SEM), transmission electron microscope(TEM) and an electronic tensile testing machine. The results show that the microstructure of the as-cast alloy is mainly composed of an α-Cu matrix, Fe3Al particles and NiAl phase distributed at the grain boundaries. After solution treatment, the distribution of bean-shaped Fe3Al particles in the microstructure of the alloy is more uniform than that of the as-cast state, and the larger square Fe3Al phase is redissolved and disappears. During the aging process, the NiAl phase is continuously precipitated in the grains. The strength and hardness of the alloy first increase and then decrease with the extension of the aging time. After aging treatment at 500 °C × 6 h, the hardness of the alloy is 231.4 HV, and the tensile strength is 538.5 MPa. The hardness is 78.8% higher than that of the as-cast state, and the tensile strength is 41.9% higher than that of the as-cast state.

Effect of Vanadium Addition on Solidification Microstructure and Mechanical Properties of Al-4Ni Alloy.

The effects of vanadium addition on the solidification microstructure and mechanical properties of Al-4Ni alloy were investigated via thermodynamic computation, thermal analysis, microstructural observations, and mechanical properties testing. The results show that the nucleation temperature of primary α-Al increased with increased vanadium addition. A transition from columnar to equiaxed growth took place when adding vanadium to Al-4Ni alloys, and the average grain size of primary α-Al was reduced from 1105 μm to 252 μm. When the vanadium addition was 0.2 wt%, the eutectic nucleation temperature increased from 636.2 °C for the Al-4Ni alloy to 640.5 °C, and the eutectic solidification time decreased from 310 s to 282 s. The average diameter of the eutectic Al3Ni phases in the Al-4Ni-0.2V alloy reduced to 0.14 μm from 0.26 μm for the Al-4Ni alloy. As the vanadium additions exceeded 0.2 wt%, the eutectic nucleation temperature had no obvious change and the eutectic solidification time increased. The eutectic Al3Ni phases began to coarsen, and the number of lamellar eutectic boundaries increased. The mechanical properties of Al-4Ni alloys gradually increased with vanadium addition (0-0.4 wt%). The Al-4Ni-0.4V alloy obtained the maximum tensile strength and elongation values, which were 136.4 MPa and 23.5%, respectively. As the vanadium addition exceeded 0.4 wt%, the strength and elongation decreased, while the hardness continued to increase. Fracture in the Al-4Ni-0.4V alloy exhibited ductile fracture, while fracture in the Al-4Ni-0.6V alloy was composed of dimples, tear edges, and cleavage planes, demonstrating mixed ductile-brittle fracture. The cleavage planes were caused by the primary Al10V and coarse Al3Ni phases at the boundary of eutectic cells.

Fuel-clad interactions: Uranium nitride and uranium dioxide with FeCrAl and Ti-modified stainless steel

This study elucidates on the compatibility of fuel and clad materials for potential use in lead cooled fast reactors. Diffusion couples were performed on representative, unirradiated fuel forms (UN and UO2) with potential cladding materials, a Ti-modified stainless steel (D9) and a FeCrAl alloy (Kanthal APMT). Temperatures of 800–1200°C, with durations up to 100 h, were investigated. Chemical interaction between all combinations of the fuel and cladding candidates was found to be minimal, with no diffusion gradients observed or extensive interface phases formed. When interaction occurred, it was in the production of a minor discrete phase. At the highest temperatures, D9 with UN resulted in the formation of a Ti-C-N phase. D9 with UO2 resulted in the formation of a Ti-C-O phase. FeCrAl with UN resulted in the formation of an Al-N phase. FeCrAl with UO2 results in the formation of an Al-O phase. Despite the observed mechanical bonding between fuel and cladding material, no evidence of any chemical interaction with the uranium in the fuel material was found. At the higher temperatures investigated (>1000°C) there was evidence of clad softening resulting in transfer of material to the fuel surface.

Aluminizing as a method of improvement of Mar-M247 alloy lifetime

Environmentally friendly high temperature high-activity (HTHA) and high temperature low- activity (HTLA) CVD aluminizing processes were realized on the Mar-M247 heat resistant superalloy substrate that is widely used in the hot section of aircraft engines. Additionally, commercial aluminide coatings deposited in the above-the-pack aluminiznig process were analyzed. The aluminizing of the Mar-M247 superalloy by the HTHA, HTLA and above-the-pack processes led to formation of two layers of the coatings. The outer layer of the coatings formed by the above-the-pack process consisted of the ?-NiAl phase with precipitates, while the outer layer of coatings formed by the HTHA and HTLA processes consisted of the pure ?-NiAl phase. Aluminizing successfully improved the lifetime of Mar-M247 superalloy. Despite the fact that the coatings formed by the above-the-pack process are thicker and have a higher aluminium concentration than the coatings formed by the HTLA aluminizing and process, the lifetime of the coated superalloy was lower. Moreover the oxidation resistance of the coated superalloy in the HTLA aluminizing process was better than that of the coating in the HTHA aluminizing process. The removal of impurities in the HTLA aluminizing process ensured a ?pure? outer layer of the coatings. Clean aluminide coatings may create a purer alumina oxide and may prolong its lifetime.

Design of a 2.7 GPa ultra-high-strength high Co–Ni secondary hardening steel by two-step nano-size precipitation tailoring

High Co–Ni secondary hardening steels are valuable in the field of aviation materials. With the increasing demand of lightweight, further enhancing its strength has received widespread attention. In this study, instead of using only M2C carbides as the reinforcements in the traditional high Co–Ni secondary hardening steels, nano-size NiAl phases were introduced to provide additional strength. To obtain the collaborative precipitation of these two reinforcements, systematically thermodynamic calculation, including the driving force, coarsening rate, etc., was made to quantitatively tailor the composition and the two-step aging parameters. The calculation results showed that adding 1 % Al into the standard composition of M54 is a plan with high potential and a second aging process at 450 °C should be added to promote NiAl precipitation. Based on the experimental validation, the target microstructure formed as the design. With the dual-phase strengthening of NiAl particles and M2C carbides, the yield and tensile strength are greater than 2.3 and 2.7 GPa, respectively, which increases the strength of M54 steel by >30 %, retaining sufficient elongation and relatively low cost. This new designed alloy increased the strength–ductility balance of high Co–Ni secondary hardening steels and aviation maraging steels from ∼12.5 to 13.5 GPa%.

Transforming microstructures and mechanical properties of (CoCrNi)93-xAl7Ndx medium entropy alloy films by annealing

In this context, we aim to investigate the effects of Nd content and annealing on the microstructures and mechanical properties of a series of (CoCrNi)93-xAl7Ndx (x = 0, 0.22, 0.56, 1.05, 1.73, 2.55, 3.53) medium entropy alloy films. The results showed that doping with Nd resulted in grain refinement and triggered a transition from a single FCC solid solution to nanocrystalline and amorphous structures. The mechanical properties, evaluated using nanoindentation and micropillar compression tests, showed that 0.56 at.% Nd doping yielded the optimum outcome due to the formation of a solid solution and grain refinement. However, the mechanical properties dropped sharply with further increases in Nd content due to the inverse Hall-Petch effect and the transition from an FCC to an amorphous matrix. The annealing treatment (550 °C for 10 min) was found to enhance atomic diffusion and migration, facilitating lattice rearrangement and the formation of a large number of precipitates, including BCC Cr-rich, B2 NiAl, L12 Ni3Al, and HCP NdNi5 phases. In addition, we also found that annealing resulted in an increase in strength and a decrease in ductility, which was contrary to the behavior of conventional metal materials.

Investigation on Ni-Al Intermetallic Compounds Fabricated through Reactive Sintering Processes

The utilization of nickel aluminide compounds in high-temperature structural applications is advantageous due to their desirable properties. One efficient method for producing nickel aluminide samples with desirable chemical reactions using minimal energy is reactive sintering. In this study, Ni-Al (20 wt.%-80 wt.%) compounds were fabricated by initially cold pressing them, followed by reactive sintering. The reactive sintering process resulted in the formation of NiAl3 and Ni2Al3 phases within the Ni-Al compounds. The microstructure, porosity, and hardness of the samples were thoroughly examined and analyzed. Generally, the compounds produced through reactive sintering exhibited significant porosity attributed to shrinkage and the Kirkendall effect. Microstructural analysis confirmed the presence of porosity, NiAl3, and Ni2Al3 phases. The sintered sample processed at 400 °C demonstrated higher density and hardness. Additionally, the wear test indicated a low wear rate and friction coefficient for the sintered sample processed at 400 °C.

Brazing of Cr2AlC and 316H stainless steel using BNi-2 filler: Microstructure, properties and joining mechanism

Cr2AlC, a ternary carbide, has been successfully brazed with 316H stainless steel using the BNi-2 filler, thereby expanding their potential applications. The diffusion of Ni from the filler into both Cr2AlC and 316H dominates the formation of the joint microstructure. High temperature leads to the detachment of Al from the Cr2AlC matrix, retaining the porous Cr7C3 along the diffusion interface. Along with the inward diffusion of Ni from the filler, the NiAl phase will be formed within the porous Cr7C3, collectively constituting the reaction layer. However, these void defects cannot be completely filled, leaving micro-voids along the Cr2AlC interface. It weakens the performance of the brazed joints. Elevated temperature and longer holding time will lead to a thicker reaction layer along the matrix interface, consequently decreasing the joint strength. A maximum joint shear strength of 248 MPa is achieved at 1000 °C/1 min. Inhibiting the excessive detachment of Al can be an efficient way to reduce the thickness of the reaction layer and increase joint performance.