NiAl Alloys Research Articles

Combinatorial synthesis of AlNi alloys by low-pressure cold spray deposition and post-laser alloying process

Aluminum-Nickel (AlNi) alloys are of great interest due to their exceptional high-temperature wear and corrosion resistance, making them valuable in transport, energy, and materials processing applications. However, challenges in the production and shaping of these alloys, particularly as thick coatings, remain significant. This study introduces an innovative method for the high-throughput synthesis of AlNi coatings, utilizing a two-step process: low-pressure cold spray deposition followed by laser surface alloying. The combination of these two techniques not only improves the synthesis process but also opens avenues for exploring new material compositions with specific application requirements. This approach holds significant potential for accelerating the development and optimization of advanced coatings and multiphase compounds in applications such as repair and additive manufacturing.Aluminum and nickel powders were co-sprayed to create coatings with controlled compositions ranging from 50Al50Ni to 10Al90Ni (wt%). Subsequent laser treatment induced in-situ alloying and homogenization, resulting in dense, uniform AlNi coatings. The microstructure and chemical composition were characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), while X-ray Diffraction (XRD) identified the formation of various phases, including Al3Ni and AlNi3 phases. The process demonstrated effective alloying and microstructural homogeneity, with residual alumina present at the surface. Despite the presence of some microstructural defects, such as cracking, this method provides a robust foundation for further refinement and opens new possibilities for tailoring alloy properties through combinatorial cold spray and laser alloying techniques.

Corrosion Susceptibility and Microhardness of Al-Ni Alloys with Different Grain Structures

The development of Al-Ni alloys with a controlled microstructure has had a great impact on the field of study of aluminum-based alloys. In the present research, the influence of thermal parameters on the grain structures resulting from the directional solidification process of Al-Ni alloys with different alloy content has been studied. It has also been evaluated how different structures and the distribution of second phases influence the corrosion behavior and microhardness of alloys. The columnar-to-equiaxed transition (CET) was observed to occur when the temperature gradient in the melt decreased to values between 1.3 and 2.9 °C/cm. In addition, a small increase in the microhardness values was observed as a function of the Ni content. When the Ni content increases, the resistance to polarization decreases for samples with equiaxed grain structure throughout the range of compositions studied. Furthermore, the equiaxed grain structure presents higher resistance to polarization values than the columnar grain zone for alloys with a composition equal to or lower than the eutectic composition.

Thermal conductivity of binary Al alloys with different alloying elements

This work investigates the physical properties of several binary Al-Si/Ni/Fe/Cu/Mg alloys with varying alloying element contents and microstructures. The findings indicate that as the content of alloying elements increases, the number of secondary phases in binary Al alloys rises, and these phases become coarser. In hypereutectic compositions, primary phases in Al-Ni and Al-Fe alloys take on a needle-like morphology with high aspect ratios, forming a dendritic network. Regarding properties, in the hypoeutectic region, both thermal conductivity and electrical conductivity of binary alloys initially decrease sharply, followed by a more gradual decline with the addition of alloying elements. This trend occurs because thermal conductivity is mainly influenced by supersaturated solid solutions. In hypereutectic Al-Ni and Al-Fe alloys, the presence of large, needle-like primary phases significantly hinder the heat transfer, resulting in a more apparent reduction in both thermal conductivity and electrical conductivity. Among the five binary alloys, Al-Ni and Al-Fe alloys, which have lower solute concentrations of alloying elements in the Al matrix, exhibit the highest thermal and electrical conductivity. Furthermore, with increasing alloying element contents, the phonon thermal conductivity of Al-Si alloy increases more markedly compared to other alloys. The study will offer a fundamental understanding for the development of advanced alloy.

Effect of Cr, Al and Mo additives on the wetting characteristics of molten Ni on (Ti, Zr, Hf, Nb, Ta)C high entropy ceramics

For the first time, the wetting behavior of the (Ti, Zr, Hf, Nb, Ta)C) high entropy carbide ceramics by molten Ni-based alloys was investigated using a sessile drop technique in a vacuum environment. Adding 10wt% of Cr, Mo, or Al into Ni resulted in final contact angles of 14°, 10°, and 14° on the (Ti, Zr, Hf, Nb, Ta)C substrate, respectively. The interaction mechanism between (Ti, Zr, Hf, Nb, Ta)C and Ni-based alloys occurs in two stages: the dissolution and interaction of the elements Ti, Zr, Hf with the alloys and the dissolution of NbC and TaC at the grain boundaries. SEM observations revealed that Cr and Al additives do not interact with carbides, while Mo was dissolved in carbides. Due to the low contact angle, minimal interaction region between alloy and ceramic, and short time of drop spreading, NiAl alloy is proven to be a promising binder for the HEC-based composites.

Sealing Ni-Cr/Ni-Al alloys with borosilicate glass: Bonding strength, sealing interface, and fracture behavior

Encapsulation of the cold junction of sheathed thermocouples by incorporating glass-to-metal seal, which substitutes for the conventionally used organic sealants, is expected to improve the reliability of thermocouples. In this study, the sealing of borosilicate glass with thermocouple wire materials, i.e., Ni-Cr and Ni-Al alloys, was investigated. Three types of specimens were prepared for both alloys: nonoxidized, mildly preoxidized, and deeply preoxidized. High-temperature sealing with borosilicate glass was conducted for each specimen. The results revealed that grain boundaries were preferentially oxidized in both alloys and that preoxidation significantly increased the bonding strength between the alloys and borosilicate glass. However, the preoxidation conditions corresponding to the optimal bonding strength differed between the two alloys, which necessitates tailored pretreatment of the metal surface. For the Ni-Cr alloy, the sealing interfaces indicated that the deeply preoxidized specimens achieved the optimal bonding strength because of the synergistic effect of the glass saturation mechanism and mechanical interlocking mechanism, whereas the mildly preoxidized specimens were affected by unexpected chemical reactions and the consequent microscopic defects at the sealing interface. For the Ni-Al alloy, the deeply preoxidized specimens exhibited inferior bonding strengths compared with the mildly preoxidized specimens, which was attributed to their overmature intergranular oxidation, in which the grain boundaries were eroded by molten glass during sealing and trapped the glass after cooling. The glass in the grain boundaries was stressed by the cooling contraction of the metals and became prone to cracking. This study reveals the microscopic bonding mechanisms for the sealing of glass to Ni-based alloys and the causes of failure, providing a new perspective on the regulation and optimization of the sealing interface.

Self-exothermic reaction behavior and pore structures of Ni-Al intermetallics with more than 70% porosity

Abstract In this study, high-porosity Ni-Al alloys with complete shape and controllable pore structures were prepared by combining the self-exothermic reaction with the space holder method. The observations show that porous Ni-Al sintered discs appeared to melt and deform after a violent reaction without adding space holder particles. The link between the volume content of urea particles and macroscopic morphology, combustion behavior, phase composition and pore structures of porous Ni-Al compounds were studied. The space holder pores acts as a heat absorber, greatly increasing the open porosity to 76.0% when adding 50 vol% urea particles. This leachable space holder method can be an effective strategy to regulate the sample shape and pore characteristics of porous Al-containing intermetallics.

Influence of martensite and grain size on the mechanical behavior of austenitic Fe–C–Mn–Ni–Al medium Mn steels with TWIP mechanism under uniaxial tension/compression and micromechanical creep

Medium Mn steels with induced plasticity mechanisms have effectively addressed the high-strength and ductility requirements for structural applications. However, there is still uncertainty about the impact of residual martensite on medium Mn steels with an austenitic matrix under uniaxial tension and compression. Furthermore, research on the influence of grain size through incomplete recrystallization in medium Mn alloys is scarce. In this context, our study focused on design and manufacturing a medium Mn Fe–C–Mn–Ni–Al alloy through controlled atmosphere casting incorporating martensite, aiming to analyze its effects under uniaxial stress conditions. Thermomechanical and annealing heat treatments were applied to control grain growth and nucleation of new grains, allowing us to explore how grain size affects the twinning process and mechanical reinforcement in the alloy. Microstructural characterization techniques, including optical and scanning electron microscopy, were employed to assess the mechanical response and damage mechanisms. Mechanical tests included tension, compression, and nanoindentation. The results indicated that residual martensite generates an accelerated damage mechanism under tension due to co-deformation at the interface with austenite, resulting in crack nucleation and rapid propagation through mode I fracture. Consequently, ductility in tension significantly decreases, while no apparent failure is observed during the compression deformation process. Furthermore, incomplete recrystallization was observed to enhance the creep response in both tension and compression. The strain hardening rate results revealed the activation of primary twinning in tension and both primary and secondary twinning in compression for annealed samples. Nanoindentation tests confirmed the presence of twinning and revealed that diffusion creep and grain boundary sliding are the predominant creep mechanisms.

Effect of Cr Additions on the Coarsening Resistance of β′ Precipitates in Ferritic Fe–Ni–Al Alloys

The effect of Cr additions ON the coarsening of β′(NiAl) precipitates in (Fe,Cr)‐α matrix is studied using Fe–10%Ni–15%Al–15%Cr (FAN15Cr) and Fe–10%Ni–15%Al–22%Cr (FAN22Cr) alloys. Specimens are homogenized and subsequently aged at 850, 900, and 950 °C for different periods of time. The characterization is carried out with conventional and high‐resolution scanning electron microscopy, transmission electron microscopy, and Vickers hardness tests. Results indicate that the addition of Cr leads to an increase in the activation energy and the coarsening kinetics at high temperatures. The precipitate morphology during aging evolves from spheres with a random distribution, followed by cuboids aligned in preferential orientations and the formation of clusters. As aging progresses further, the morphology changes to semirounded precipitates with a polyhedral surface as revealed by the etching process. Transmission electron microscopy results reveal the formation of a dislocation network indicating a state of semicoherency in the precipitate–matrix interface. The activation energy for the coarsening process is determined from the coarsening kinetic constants. While the activation energy for the coarsening in FANCr15 is close to similar alloys, the value for FAN22Cr is unusually high and probably related to the dislocation networks observed.

Prediction of Time–Temperature–Transformation Diagrams of NiAl Alloy: An Evaluation of Intelligent Algorithms

Time‐temperature‐transformation diagrams are essential in the field of metallurgy. However, constructing these diagrams through empirical and simulating methods can be time‐consuming and expensive. Therefore, there is a need to develop accurate and affordable alternatives that can rapidly predict TTT diagrams. The present study offers a novel analysis of multiple algorithms for predicting TTT diagrams, as well as an examination of various data preprocessing techniques (data augmentation ‐ DA and exploratory data analysis ‐ EDA). A database is created by integrating multiple data sources and increased using DA by ensuring the synthetic data remains physically realistic and meaningful. Subsequently, an EDA is performed to prepare the data before its use in training. The influence of each hyperparameter on the prediction was studied and optimal hyperparameter configuration was defined for each algorithm. The performance of the algorithms is evaluated using RMSLE, RMSE, R2, Mean IoU, and SMAPE. The multilayer perceptron demonstrated the greatest robustness in predicting TTT curves. Additionally, the Ft‐Transformer is a viable alternative if an appropriately sized dataset is available. These results provide valuable insights into the use of Machine Learning techniques as a new alternative in predicting isothermal transformation curves.

Unveiling the thermodynamic landscape of liquid Ti–Al–Ni alloys through first-principles simulations

We conducted ab initio molecular dynamics simulations to systematically examine the composition-dependent thermodynamic properties and atomic-scale interactions in liquid Ti–Al–Ni alloys throughout the entire ternary phase space at 2033 K. The calculated enthalpies of mixing demonstrated exothermic tendencies, with a distinct minimum in the composition of Ti0.0Al0.50Ni0.50, indicating significant Al–Ni attractive interactions. Incorporating ternary interaction parameters into the Redlich-Kister-Muggianu equation enabled accurate modeling of the complex variations in mixing enthalpy. Analysis of partial pair correlation functions and structure factors revealed chemical and topological short-range ordering (SRO), as well as medium-range ordering, within the liquid alloy. Quantifying deviations from ideal configurational entropy clarifies the coupling between chemical SRO and topological SRO, significantly impacting the overall Gibbs energy of mixing. This comprehensive atomistic study provides insights into the thermodynamics of Ti–Al–Ni alloys, paving the way for tailoring their properties for high-performance applications.

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.

Characteristics of Gasless Combustion of Core-Shell Al@NiO Microparticles with Boosted Exothermic Performance.

The microstructures and thermochemical behavior of the energetic composites composed of core-shell structured μAl@NiO microparticles were characterized. These core-shell microparticles were synthesized using a wet-chemistry-based one-pot process, where the assembly was proposed to be driven by the electrostatic force between negatively charged Al and positively charged Ni-NH3 ions. Electron microscopic images demonstrated the formation of NiO nanoparticles adhering to the surface of microsized Al particles with different equivalence ratios. Thermal analysis revealed two consecutive exothermic peaks resulting from the initial thermite reaction between 890 and 960 °C and subsequently the intermetallic/alloy formation reactions between 1000 and 1040 °C. The latter was further confirmed by the endothermic peaks of Al-Ni alloy melting at higher temperatures. The formation of alloy was substantiated by the melting of AlNi3, AlNi, and Al3Ni. The onset temperature of the first exothermic peak decreased with increasing nominal equivalence ratio of the core-shell. Compared to the physically mixed (PM) composite, the core-shell structures decreased the activation energy of the thermite reaction by a mere 9.24 kJ/mol; however, it increased the combustibility by the manifold. The PM composite was not able to be ignited at all by a 5 W laser, while the core-shell counterpart ignited at 2.55 ms and was completely combusted within 6.50 ms accompanying a violent impulse.

Effect of NiAl alloy microparticles deposited in flexible SERS substrates on the limit of detection of rhodamine B molecules.

Flexible-SERS (FSERS) substrates were fabricated by depositing Ni64Al36(NiAl)-alloy-microparticles and/or spherical Ag-NPs (sizes of 10-40 nm) on recycled plastics, which had an aluminum layer on their surface. First, FSERS substrates made of Al + Ag-NPs and an area of 1 cm2 were used to detect rhodamine B (RhB) molecules. The limit-of-detection (LOD) for RhB was 8.35 × 10-22 moles (∼503 molecules), and the enhancement factor (EF) was 3.11 × 1015. After adding NiAl-microparticles to the substrate, the LOD decreased to 8.35 × 10-24 moles (∼5 molecules) and the EF was increased to 2.05 × 1017. Such EF values were calculated with respect to substrates made only with Al + NiAl-alloy (without Ag-NPs), which did not show any Raman signal. Other FSERS substrates were made with graphene-layer + Ag-NPs or graphene-layer + NiAl-alloy + Ag-Nps, and the best LOD and EF values were 8.35 × 10-22 moles and 6.89 × 1015, respectively. Overall, combining the Ag-NPs and NiAl-alloy microparticles allowed for the zeptomole detection of RhB. This was possible due to the formation of Ag aggregates around the alloy microparticles, which enhanced the number of hotspots. If no alloy is present in the FSERS substrates, the detection of RhB is lowered. Overall, we presented a low-cost FSERS substrate that does not require expensive Au films or Au-NPs (as previously reported) to detect RhB at the zeptomole level.

First-Principles Kinetic Monte Carlo Modeling of Passivation in Ni-Based Alloys

Corrosion by metal oxidation is a major problem for many structural materials, including Ni-based alloys in high-temperature applications. Passivation can be achieved through various alloying strategies, but common theoretical approaches to understanding key factors such as the critical concentration of the minor element are limited in their predictive capability. In particular, existing models often do not explicitly capture competing metal cation migration mechanisms in the oxide. In this study, we examine passivation kinetics of Ni-Cr and Ni-Al alloys by modeling the evolution of initial NiO oxide films as Cr/Al are incorporated. Surrogate models for the energies of various oxide configurations and the migration barriers of metal cations are parameterized from density functional theory calculations. These inputs are used to drive kinetic Monte Carlo simulations over long time scales. By tracking the time-dependent oxidation behavior across alloy composition, we predict critical concentrations of Cr/Al to form continuous passivation layers. Compositional and structural analyses of the simulated oxides are used to quantify fractions of different phases and provide insight into the nature of passivation in each alloy system. The effect of increasing or decreasing the exchange rate of metal atoms near the alloy-oxide interface, which can be related to alloy processing, is also explored. We discuss the applicability of our method to other systems and its incorporation into an existing open-source software package.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Determination of γ/γ' interface free energy for solid state precipitation in Ni-Al alloys from molecular dynamics simulation.

Interface free energy is a fundamental material parameter needed to predict the nucleation and growth of new phases. The high cost of experimentally determining this parameter makes it an ideal target for calculation through a physically informed simulation. Direct determination of interface free energy has many challenges, especially for solid-solid transformations. Indirect determination of the interface free energy from the nucleation data has been done in the case of solidification. However, a slow on molecular dynamics (MD) simulation time scale atomic diffusion makes this method not applicable to the case of nucleation from the solid phase when precipitate composition is different from that in matrix. To address this challenge, we outline the development of a new technique for determining the critical nucleus size from an MD simulation using a recently developed method to accelerate solid-state diffusion. The accuracy of our approach for the Ni-Al system for Ni3Al (γ') precipitates in a Ni-Al (γ) matrix is demonstrated well within experimental accuracy and greatly improves upon previous computational methods [Herrnring et al., Acta Mater. 215(8), 117053 (2021)].

Laser-based directed energy deposition and characterisation of cBN-reinforced NiAl-based coatings

Within this study, the alloy NiAl–2.5Ta–7.5Cr is investigated as a new matrix material for cBN-reinforced abrasive turbine blade tip coatings as currently used NiCoCrAlY matrix alloys suffer from insufficient strength at the high operating temperatures. Laser-based directed energy deposition with blown powder was applied to produce cBN reinforced NiAl-based coatings on monocrystalline CMSX-4 substrates. For this, powdery titanium-coated cBN and NiAl–2.5Ta–7.5Cr material were co-injected into the process zone to achieve an in situ formation of a NiAl–2.5Ta–7.5Cr/cBN composite. In order to overcome challenges such as cracking susceptibility, inductive preheating of the substrate up to 800 °C was used. Optical and scanning electron microscopy, energy dispersive X-ray spectroscopy, as well as electron backscatter diffraction were applied to analyse the fabricated samples’ microstructure. Additionally, the mechanical properties were evaluated by means of microhardness mappings. This work demonstrates the feasibility of in situ forming a metal matrix composite with a homogeneous distribution of cBN particles. The results show the beneficial effect of high-temperature preheating on the crack formation. However, the study also reveals challenges such as cracking induced by the injected cBN particles as well as severe intermixing of substrate and coating, which yields spatially resolved deviations in the chemical composition and resulting variations in microstructure and hardness.Graphical abstract

Ultrasounds Induced Microstructure Transition and Improved Mechanical Property of Directionally Solidified Ternary Cu–Al–Ni Alloy

Ultrasounds Induced Microstructure Transition and Improved Mechanical Property of Directionally Solidified Ternary Cu–Al–Ni Alloy

Effects of external static electrical field on thermal and electrical conductivity in the Al-Cu, Al-Ni, and Al-Si eutectic alloys

This study aims to investigate the effects of external positive and negative static electric fields (E+ and E- respectively) on thermal conductivity (K) and electrical conductivity (σ) in Al-33 wt. % Cu, Al-6.4 wt. % Ni and Al-12 wt. % Si eutectic alloys. For this purpose, the solidifications of Al-Cu, Al-Ni, and Al-Si eutectic alloys were directionally done under E+ and E-. The directions of E were chosen to be parallel (E+) and antiparallel (E-) to the solid-liquid (S-L) growth direction and the magnitudes of E were approximately (+10) and (−10) kV cm−1 and (+16) and (-16) kV cm−1 for the Al-Cu, Al-Ni, and Al-Si eutectic alloys, respectively. The effects of E+ and E− on the K and σ were determined by the longitudinal heat flow and the four-point probe methods, respectively. While the K and σ values decreased with increasing temperature, the K and σ were increased and decreased with E+ and E−, respectively.

Improved elevated-temperature strength and thermal stability of additive manufactured Al–Ni–Sc–Zr alloys reinforced by cellular structures

Laser powder bed fusion (LPBF) processed Al–Ni alloys typically exhibit cellular structures, contributing to superior strength at ambient temperature as the cell walls can effectively impede dislocation motion during plastic deformation. However, it is still unclear whether cellular structures can lead to excellent elevated-temperature performance. In this study, we conducted a systematic investigation into the elevated-temperature mechanical properties and thermal stability of an LPBF Al–Ni–Sc–Zr alloy with cellular structures. The as-built alloy exhibits a yield strength of 368 MPa at 25℃ and 332 MPa at 250℃, with an exceptional strength retention rate of ∼90 % at 250℃. Moreover, the alloy maintains a hardness of ∼146 HV following exposure at 250℃ for 100 h and shows no apparent decrease despite increasing the exposure time to 500 h. The excellent elevated-temperature performance can be attributed to the cellular structures. The cell walls effectively confine dislocations at elevated temperatures, suppressing the dislocation annihilation and leading to exceptional strength retention. On the other hand, even if the cell walls decompose into nanoparticles after prolonged thermal exposure, the reduction in strength due to the decomposition can be compensated by the strengthening of the nanoparticles, resulting in excellent thermal stability. By studying the influence of the cellular structures on elevated-temperature performance, this study could provide valuable insights into developing high-performance Al alloys for elevated-temperature applications by additive manufacturing.

Effect of microalloying additions on microstructural evolution and thermal stability in cast Al-Ni alloys

Enhancement of thermal stability in Al-Ni alloys through microalloying with slow-diffusing elements, specifically Zr, has been previously reported which is attributed to Zr segregation at the Al/Al3Ni interface. In this study, we explore the influence of microalloying Al-Ni alloys with Zr, Ti, V, and Fe on microstructural evolution, hardness, and electrical and thermal conductivity across a range of heat-treatment temperatures from 300 to 450 °C. The distribution of microalloying elements and precipitates after heat treatment is characterized using atom probe tomography (APT). Our investigation confirms Zr segregation to the Al/Al3Ni interface, while similar interfacial segregation is absent with the addition of Ti, V, and Fe. Additionally, our analysis of the Al3Ni microfiber morphology reveals that their coarsening and spheroidization rates are similar with and without interfacial segregation; thus, retaining the fiber reinforcement through interfacial segregation of slow diffusing elements may not be an effective strategy. Precipitation of L12 nanoparticles was found to be the dominant mechanism affecting enhanced hardness and electrical conductivity in Al-Ni-Zr alloys, attributed to precipitation strengthening and solute depletion, respectively. Similar precipitation was not observed for additions of Ti, V, and Fe following heat treatment. We provide a thermodynamic explanation for this limitation. The findings of this study suggest that an effective approach for designing Al-Ni alloys should involve prioritizing microalloying elements to maximize L12 precipitation and minimize solute content in the FCC-Al matrix post heat treatment, rather than focusing on Al/Al3Ni interfacial segregation.