Search Results (87)

Intermetallic Fe₃Al-based alloys reinforced with Laves-phase precipitates are emerging as potential replacements for conventional high-alloy steels and possibly polycrystalline Ni-based superalloys in structural applications up to 700 °C. Their impressive mechanical properties, however, are offset by limited fabricability and poor machinability due to their severe brittleness. High tool wear during finish-machining, which is still required for components such as turbine blades, remains a key barrier to their broader adoption. In contrast to conventional manufacturing routes, additive manufacturing offers a viable solution by enabling near-net-shape manufacturing of difficult-to-machine iron aluminides. In the present study, laser powder bed fusion was used to produce an Fe-25Al-1.5Ta intermetallic containing strengthening Laves-phase precipitates, and the porosity, microstructure and phase composition were characterized as a function of the process parameters. The results showed that preheating the build plate to 650 °C effectively suppressed delamination and macrocrack formation, even though noticeable cracking still occurred at the high scan speed of 1000 mm/s. X-ray tomography revealed that samples fabricated with a lower scan speed (500 mm/s) and a higher layer thickness (0.1 mm) contained larger, irregularly shaped pores, whereas specimens printed at the same volumetric energy density (40 J/mm³) but with different parameter sets exhibited smaller fractions of predominantly spherical pores. All samples contained mostly elongated grains that were either oriented close to <001> relative to the build direction or largely texture-free. X-ray diffraction confirmed the presence of Fe₃Al and C14-type (Fe, Al)₂Ta Laves phase in all samples. Hardness values fell within a narrow range (378–398 HV10), with only a slight reduction in the specimen exhibiting higher porosity. Full article

High-entropy alloys (HEAs) are a class of multi-principal element materials composed of five or more elements in near-equimolar ratios. This unique compositional design generates high configurational entropy, which stabilizes simple solid solution phases and reduces the tendency for intermetallic compound formation. Unlike conventional alloys, HEAs exhibit a combination of properties that are often mutually exclusive, such as high strength and ductility, excellent thermal stability, superior corrosion and oxidation resistance. The exceptional mechanical performance of HEAs is attributed to mechanisms including lattice distortion strengthening, sluggish diffusion, and multiple active deformation pathways such as dislocation slip, twinning, and phase transformation. Advanced characterization techniques such as transmission electron microscopy (TEM), atom probe tomography (APT), and in situ mechanical testing have revealed the complex interplay between microstructure and properties. Computational approaches, including CALPHAD modeling, density functional theory (DFT), and machine learning, have significantly accelerated HEA design, allowing prediction of phase stability, mechanical behavior, and environmental resistance. Representative examples include the FCC-structured CoCrFeMnNi alloy, known for its exceptional cryogenic toughness, Al-containing dual-phase HEAs, such as AlCoCrFeNi, which exhibit high hardness and moderate ductility and refractory HEAs, such as NbMoTaW, which maintain ultra-high strength at temperatures above 1200 °C. Despite these advances, challenges remain in controlling microstructural homogeneity, understanding long-term environmental stability, and developing cost-effective manufacturing routes. This review provides a comprehensive and analytical study of recent progress in HEA research (focusing on literature from 2022–2025), covering thermodynamic fundamentals, design strategies, processing techniques, mechanical and chemical properties, and emerging applications, through highlighting opportunities and directions for future research. In summary, the review’s unique contribution lies in offering an up-to-date, mechanistically grounded, and computationally informed study on the HEAs research-linking composition, processing, structure, and properties to guide the next phase of alloy design and application. Full article

To investigate the radiation stability of the intermetallic in PH 13–8 Mo steel, precipitates with different sizes were generated and then the samples are irradiated with 400 keV Fe⁺ at room temperature with maximum damage up to 8 dpa. The pre- and post-irradiation samples are examined with selected area electron diffraction (SAED), scanning transmission electron microscopy (STEM) and Energy Dispersive Spectroscopy (EDS). Before the irradiation, B2 NiAl precipitates are uniformly distributed in matrix with increased sizes of 2.5, 4.9 and 8.1 nm. After the irradiation, the intensity of SAED superlattice pattern of B2 NiAl with 8.1 nm diminishes rather than disappeared in the remaining samples, indicating that the ordered B2 structure of NiAl precipitates of smaller size are mostly destroyed. EDS results proves that no elemental diffusion took place between the precipitates and matrix. Moiré fringes are found to be located beside dissolved precipitates attributed to radiation-enhanced diffusion. This work will provide advice for the material design of other intermetallic strengthened alloys especially in nuclear applications. Full article

In the present study, aluminum matrix composites (AMCs) were fabricated by friction stir processing (FSP) using Ni-Cu particles. Ni-Cu particles were added to the Al matrix in two ways. First, without any treatment and in the form of a mixture of as-received powders. Second, treated through mechanical alloying to form Monel solid-solution particles. The particles were added to a groove to be processed by the FSP tool to produce a local AMC. To investigate the kinetics of intermetallic compounds (IMCs) growth in reinforcement particles, the produced AMCs were annealed at 500 °C for 2 h. To characterize the reinforcing particles, several analyses were performed on the samples. Field-emission scanning electron microscopy (FE-SEM) was used to study the size, morphology, and IMC thickness. TEM was performed to characterize the IMCs through high-resolution chemical analyses. Tensile testing was used to understand the mechanical properties and fracture behavior of AMCs. Tensile testing revealed a noticeable improvement in strength for the as-mixed sample, with a UTS of 90.3 MPa, approximately 22% higher than that of the base aluminum. In contrast, the mechanical alloying sample with annealing heat treatment exhibited a severe drop in ductility, with elongation decreasing from 17.98% in the as-mixed sample to 1.52%. The results showed that heat treatment thickened the IMC layer around the reinforcing particles formed during the FSP process with as-mixed particles. In the AMC reinforced with mechanically alloyed Ni-Cu powders, IMC formation during FSP was significantly suppressed compared to that of as-mixed particles, despite the finer size resulting from milling. Additionally, the heat treatment resulted in only a slight increase in IMC thickness. The IMC layer thickness after heat treatment in both the mechanically alloyed sample and the as-mixed sample was approximately 2 µm and 20–40 µm, respectively. The reason behind this difference and its effect on the fracture behavior of the composite were elaborated in this study, giving insights into metal-matrix production with controlled reaction. Full article

Dissimilar material welding enables the integration of the superior properties of different materials, thereby achieving optimal structural performance and economic efficiency while meeting specific service requirements. The presence of solid-solution strengthening elements such as Ti, Co, and Al, and trace elements such as P and S, in GH3030 nickel-based superalloy leads to their segregation and the formation of intermetallic compounds in the welded joint, resulting in deterioration of joint performance. High-entropy alloys (HEAs), with their high-entropy effect and delayed diffusion effect working synergistically, can effectively suppress compositional segregation caused by uneven elemental diffusion and the formation of intermetallic compounds at interfaces, thereby improving the quality of welded joints and demonstrating great potential for dissimilar material joining. Therefore, in this study, fiber laser welding was used to effectively join AlCoCrFeNi2.1 eutectic high-entropy alloy and GH3030 nickel-based superalloy, with the expectation to improve welded joint element segregation, suppressing the formation of intermetallic compounds, and enhance the welded joint quality and its performance. The AlCoCrFeNi2.1/GH3030 joint exhibits an average yield strength of 1.31 GPa, which is significantly higher than that of the GH3030/GH3030 joint (1.07 GPa). In addition, the AlCoCrFeNi2.1/GH3030 joint shows a higher average work-hardening exponent of 0.337 compared with 0.30 for the GH3030/GH3030 joint, indicating improved plasticity. The results showed that under appropriate welding process parameters, the hardness of the weld zone, transitioning from the nickel-based superalloy to the eutectic high-entropy alloy, exhibited a stable increasing trend, and the joint exhibits good plasticity, with brittle fracture being unlikely. Full article

During active brazing of alumina ceramics, active elements react with the ceramic to form a reaction layer, which has significant influence on the mechanical property of the brazed joint. However, the composition and formation mechanism of this layer remain unclear among researchers. To fill this gap, different brazing temperatures (900–1100 °C) and heating rates (2.5 °C/min and 10 °C/min) were used to braze 95% Al₂O₃ ceramics and a Kovar 4J34 alloy using a Ag-Cu-2Ti active brazing filler, and the microstructure and mechanical properties of the joints were investigated. The results show that the joint could be divided into five layers: Al₂O₃, ceramic-side reaction layer, filler layer, Kovar-side reaction layer, and Kovar. The ceramic-side reaction layer could be further divided into a Ti-O-rich layer and an intermetallics (IMC)-rich layer, and the Kovar-side reaction layer consists of TiFe₂ particles, Ag-Cu eutectic, and the remaining Kovar. A belt-like TiFe₂+TiNi₃ IMC could be found in the filler layer. Increasing the brazing temperature enlarged the belt-like TiFe₂+TiNi₃ IMC in the filler layer and increased the thickness of the IMC-rich layer in the ceramic-side reaction layer, but had no significant effect on the thickness of the Ti-O-rich layer in the ceramic-side reaction layer. A lower heating rate (2.5 °C/min) was found to suppress the formation of the IMC-rich layer and shift the fracture location in shear tests from the ceramic-side reaction layer to the filler layer, indicating that the strength of the ceramic-side reaction layer was enhanced by controlling the formation of the IMC-rich layer. A maximum shear strength of 170 ± 61 MPa was obtained at a heating rate of 2.5 °C/min and a brazing temperature of 940 °C. Full article

The application of laser powder bed fusion (LPBF) to 7xxx-series aluminum alloys is fundamentally limited by hot cracking and porosity. This study demonstrates that adding 5 wt.% AlCoCrFeNi_2.1 high-entropy alloy (HEA) particles to 7075 aluminum alloy (AA7075) powder can effectively mitigate these issues. Microstructural characterization revealed that the HEA particles remained largely intact and formed a strong metallurgical bond with the α-Al matrix. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis confirmed that this bonding is facilitated via the in situ formation of new intermetallic phases at the particle/matrix interface. X-ray diffraction (XRD) identified these phases as primarily Al₅Co₂ and Fe₃Ni₂. A key consequence of this reinforced interface is a significant change in cracking behavior; optical microscopy (OM) showed that long, continuous cracks typical of AA7075 were replaced by shorter, deflected cracks in the composite. While porosity was not eliminated, the addition of HEA stabilized the process, yielding a consistent density improvement of 0.5–1.5% across the processing window. This microstructural modification resulted in a substantial ~64% increase in average microhardness, which increased from 96.41 ± 9.81 HV_0.5 to 158.46 ± 11.33 HV_0.5. These results indicate that HEA reinforcement is a promising route for engineering the microstructure and improving the LPBF processability of high-strength aluminum alloys. Full article

Nickel–iron (Ni-Fe) catalysts are widely used in industry due to their cost-effectiveness and versatile catalytic properties. This work investigates the structural and morphological characteristics of Ni-Fe catalysts supported on γ-Al₂O₃, synthesized with varying Ni/Fe atomic ratios (from 1:1 to 20:1). The catalysts were characterized using a combination of experimental techniques including X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM), and selected-area electron diffraction (SAED). Theoretical modeling using the USPEX evolutionary algorithm complemented the experimental data by predicting stable Ni-Fe crystal structures. The results revealed uniform metal distribution on the support with particle sizes ranging from 4.1 to 4.5 nm. SAED analysis confirmed the formation of an intermetallic FeNi phase, particularly in samples with higher iron content. This study demonstrates Ni-Fe interaction effects and will be of interest to researchers in catalysis and materials science working on the development of bimetallic systems. Full article

High-entropy alloys (HEAs) are highly concentrated, multicomponent alloys that have received significant attention due to their superior properties compared to conventional alloys. The mechanical properties and hardness are interrelated, and it is widely known that the hardness of HEAs depends on the principal alloying elements and their composition. Therefore, the desired hardness prediction to develop new HEAs is more interesting. However, the relationship of these compositions with the HEA hardness is very complex and nonlinear. In this study, we develop an artificial neural network (ANN) model using experimental data sets (535). The compositional elements—Al, Co, Cr, Cu, Mn, Ni, Fe, W, Mo, and Ti—are considered input parameters, and hardness is considered as an output parameter. The developed model shows excellent correlation coefficients (Adj R2) of 99.84% and 99.3% for training and testing data sets, respectively. We developed a user-friendly graphical interface for the model. The developed model was used to understand the effect of alloying elements on hardness. It was identified that the Al, Cr, and Mn were found to significantly enhance hardness by promoting the formation and stabilization of BCC and B2 phases, which are inherently harder due to limited active slip systems. In contrast, elements such as Co, Cu, Fe, and Ni led to a reduction in hardness, primarily due to their role in stabilizing the ductile FCC phase. The addition of W markedly increased the hardness by inducing severe lattice distortion and promoting the formation of hard intermetallic compounds. Full article

In the present study, the diffusion couple of solid CoCrFeMnNi HEA and liquid pure Al was prepared. The microstructure evolution and relevant interdiffusion behavior of CoCrFeMnNi HEA/Al solid–liquid diffusion couple processed by different parameters were characterized and investigated. Results demonstrated that the interfacial compounds in the order of Al(Co, Cr, Fe, Mn, Ni), Al₁₃(Co, Cr, Fe, Mn, Ni)₄ and Al₄(Co, Cr, Fe, Mn, Ni) were determined in the interdiffusion area along the direction from CoCrFeMnNi HEA to Al, and the precipitated Al₄(Cr, Mn) and Al₉(Co, Fe, Ni) phases were formed in the center of Al couple. In addition, the diffusion mechanism and activation energy of growth for each diffusion layer were revealed and determined. More importantly, the growth mechanism of each diffusion layer was also investigated and uncovered in detail. Meanwhile, the activation energy of each intermetallic layer was obtained by the Arrhenius equation and the linear regression method. It is anticipated that this present study would provide a fundamental understanding and theoretical basis for the high-entropy alloy CoCrFeMnNi HEA, potentially applied as the cast mold material for cast aluminum alloy. Full article

High-entropy alloys (HEAs) exhibit superior properties for extreme environments, yet the effects of laser scanning speed on the microstructure and performance of laser-clad NiAlNbTiV HEA coatings remain unclear. This study systematically investigates NiAlNbTiV coatings on 316 stainless steel fabricated at scanning speeds of 800–1100 mm/min via laser cladding. Characterizations via XRD, SEM/EDS, microhardness testing, high-temperature wear testing, and electrochemical measurements reveal that increasing scanning speed enhances the cooling rate, promoting γ-(Ni, Fe) solid solution formation, intensifying TiV peaks, and reducing Fe-Nb intermetallics. Higher speeds refine grains and needle-like crystal distributions but introduce point defects and cracks at 1100 mm/min. Microhardness decreases from 606.2 HV (800 mm/min) to 522.4 HV (1100 mm/min). The 800 mm/min coating shows optimal wear resistance (wear volume: 0.0117 mm³) due to dense eutectic hard phases, while higher speeds degrade wear performance via increased defects. Corrosion resistance follows a non-linear trend, with the 900 mm/min coating achieving the lowest corrosion current density (1.656 μA·cm⁻²) due to fine grains and minimal defects. This work provides parametric optimization guidance for laser-clad HEA coatings in extreme-condition engineering applications. Full article

To our knowledge, no magnetic B2 phase in the Al–Mn system of near-equiatomic compositions has been reported so far. Here, we investigate the structural and magnetic characteristics of Al₄₅Mn_41.8X_13.2 (X = Fe, Co or Ni) alloys. We demonstrate that adding 13.2 atomic percent magnetic 3d metal to AlMn stabilizes a ferromagnetic B2 structure, where Al and X occupy different sublattices. We employ density functional theory calculations and experimental characterizations to underscore the role of the late 3d metals for the phase stability of the quasi-ordered ternary systems. We show that these alloys possess large local magnetic moments primarily due to Mn atoms partitioned to the Al-free sublattice. The revealed magneto-chemical effect opens alternative routes for tailoring the magnetic properties of B2 intermetallic compounds for various magnetic applications. Full article

Aluminum/steel bimetal combines the advantages of aluminum alloy and steel, greatly leveraging the value of various industrial fields, especially in improving engine performance and fuel economy. However, it is very difficult to prepare products with good interface bonding strength. The fundamental issue stems from the presence of an excessively thick interface layer and brittle intermetallic compounds. Therefore, this study employed a 50 μm-thick Ni interlayer to control the interface layer thickness, thereby enhancing the Al/steel interfacial bonding strength. A systematic investigation was conducted on the effects of hot dip duration on the interfacial microstructure and mechanical properties of Al/steel bimetal. The influence of hot dip duration on the microstructure and mechanical properties of aluminum/steel bimetal interface was systematically studied. The results show that the 50 μm Ni intermediate layer was used to effectively control the transition layer thickness and improve the interfacial bonding strength of aluminum steel. The thickness of the interface layer gradually increases with the increase in the hot-immersion time. The thickness of the interface layer composed of the two phases of τ₁-Al₂Fe₃Si₃ and FeAl₃ on the steel side increases first and then decreases, while the interface layer composed of the two phases of τ₅-Al₈Fe₂Si and Fe₂Al₅ on the aluminum side decreases first and then increases. When the hot dip time is 240 s, the shear strength of Al/steel bimetal with 50 μm Ni interlayer showed 75% enhancement compared to Ni-free counterparts. Full article

This study examines the microstructure and corrosion resistance of FeCrNiAl_0.7Cu_0.3Si_x (x = 0, 0.1, 0.3, and 0.5) high-entropy alloys (HEAs) in a 3.5% NaCl solution. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electrochemical testing were employed to systematically analyze the alloys’ microstructures and corrosion behavior. The XRD results indicate that the addition of Si affects the phase structure of the alloy. At Si = 0, the alloy exhibits a single BCC phase. By increasing the Si content to 0.1 and 0.3, a BCC₂ phase appears. At Si = 0.5, Si-containing intermetallic compounds form. SEM observations reveal that as the Si content increases, the alloy develops a distinct dendritic structure. Polarization tests in the 3.5% NaCl solution show that the corrosion current density first decreases and then increases with increasing Si content. At Si contents of 0.1, 0.3, and 0.5, the corrosion current densities are 4.275 × 10⁻⁶ A·cm⁻², 4.841 × 10⁻⁷ A·cm⁻², and 2.137 × 10⁻⁶ A·cm⁻², respectively. FeCrNiAl_0.7Cu_0.3S_0.3 HEA exhibits the lowest corrosion current density, indicating a lower corrosion rate. Electrochemical impedance spectroscopy (EIS) tests show that at Si = 0.3, the alloy has the largest capacitive arc radius. The charge-transfer resistance (RCT) for the alloys with the Si contents of 0.1, 0.3, and 0.5 are 2.532 × 10⁵ Ω·cm², 4.088 × 10⁵ Ω·cm², 4.484 × 10⁵ Ω·cm², and 2.083 × 10⁵ Ω·cm², respectively. FeCrNiAl_0.7Cu_0.3Si_0.3 HEA has the highest RCT, which indicates a more stable passivation film and better resistance to chloride ion intrusion. The corrosion morphology observed after polarization testing shows that all alloys exhibit intergranular corrosion characteristics. The Si content alters the distribution of passivation film-forming elements, Cr and Ni. Compared to other alloys, the corrosion morphology of FeCrNiAl_0.7Cu_0.3Si_0.3 HEA is more complete. Combining the polarization, EIS, and corrosion morphology results, it can be concluded that FeCrNiAl_0.7Cu_0.3Si_0.3 HEA exhibits the best corrosion resistance in the 3.5% NaCl solution. Full article

AlCrCoFeNi high-entropy alloys (HEAs) have been successfully synthesized by laser cladding. The AlCrFeCoNi HEA coatings were composed of planar crystal, columnar grain, and equiaxed grain from bottom to top. Face-centered cubic (FCC) was the major phase in coatings, and its content decreased when increasing laser power or reducing scanning speed. The precipitation in the HEA coatings were Al-Ni enriched B2 phase and FeAl₃ intermetallic compounds. The interface zone had higher microhardness than the cladding zone due to the addition of Fe from the dilution role. The C2 (3 kW, 4 mm/s) and C9 (3.5 kW, 6 mm/s) coatings displayed the best corrosion resistance when taking the E_corr (−0.327 V, −0.335 V), I_corr (0.236 μA·cm⁻², 0.475 μA·cm⁻²), and R_ct (224.2 kΩ/cm², 121.1 kΩ/cm²) into consideration. Pitting dominated the corrosion process of the AlCrFeCoNi HEA coatings. Large grain boundary areas generated by the fine grain in the C2 and C9 coatings enhanced difficulty of ion transport along the grain boundary. Then, multiple corrosion sites on the surface promoted uniform corrosion and formed a protective oxide film, inhibiting serious pitting. This work provided an approach of laser cladding AlCrCoFeNi HEAs with different laser powers and scanning speeds, and insights into the correlation of anti-corrosion properties with the microstructure of AlCrCoFeNi coatings. Full article