Search Results (747)

High-entropy alloys (HEAs) and multi-principal-element alloys (MPEAs) provide broad compositional flexibility for regulating phase stability, microstructure, and properties. However, nominal composition and average phase constitution alone are insufficient to describe the actual material state formed during processing and service. This review summarizes the thermodynamic and diffusion-kinetic basis of phase formation and compares five representative fabrication routes, including mechanical alloying, vacuum melting, severe plastic deformation, magnetron sputtering, and additive manufacturing. Particular attention is given to the effects of processing history on grain structure, texture, elemental segregation, defects, phase constitution, and local chemical order. Computational methods and multiscale characterization techniques are also discussed in relation to the identification and interpretation of processing-dependent material states. Current studies indicate that alloys with identical nominal compositions can exhibit different microstructures and properties because of differences in thermal history, strain path, elemental redistribution, defect populations, and post-processing conditions. The review further examines strength and ductility, corrosion resistance, oxidation resistance, irradiation tolerance, and catalytic performance, with emphasis on the evolution of microstructure and surface state under service conditions. These results indicate that reliable evaluation of HEAs and MPEAs requires consideration of processing reproducibility, structural heterogeneity, and long-term stability rather than isolated peak properties. This processing–structure–service perspective provides a basis for more reliable comparison, selection, and engineering assessment of HEAs and MPEAs under application-relevant conditions. Future research should focus on reproducible fabrication, integration of computational prediction with experimental validation, multiscale assessment of structural evolution, long-term service performance, scalable processing, and sustainable alloy design. Full article

Cu-based hybrid composites reinforced with AlCrFeCuNi high-entropy alloy (HEA) particles and graphene were successfully fabricated by spark plasma sintering (SPS) to investigate the combined effects of microstructure, mechanical properties, and tribological performance under electrical current. Microstructural observations revealed a dense and homogeneous distribution of HEA particles within the Cu matrix, while the addition of 2.0 wt.% graphene promoted noticeable grain refinement due to its grain boundary pinning effect. Although graphene addition provided beneficial effects in terms of grain refinement and electrical conductivity, it also increased the porosity from 2.49% to 5.08%. Consequently, the beneficial contribution of graphene to mechanical strengthening was substantially offset by the adverse effect of increased porosity, resulting in only a marginal increase in hardness from 127 HB to 129 HB. The addition of 2.0 wt.% graphene led to a pronounced change in the tribological behavior of the composites. The Cu–HEA exhibited relatively stable friction behavior but experienced a higher wear rate under all test conditions. In comparison, the Cu–HEA–2.0 Gr composite demonstrated a lower coefficient of friction and wear rate at 0–10 A, which is consistent with the possible formation of a graphene-rich lubricating surface layer. A clear transition occurred at 30 A, where the coefficient of friction and wear rate began to increase, while at 50 A, further increases in both parameters were observed, suggesting progressive disruption of the proposed protective surface layer under the investigated current-carrying sliding conditions. Full article

High-entropy alloys (HEAs) are a unique metallic alloy that was initially recognized for the possibility of stabilizing simple solid-solution phases through high configurational entropy. Research over the past two decades, however, has shown that their behavior is far more complex. Phase formation, microstructural evolution, and surface performance arise from the combined influence of composition, atomic interactions, processing history, and the surrounding environment. This paper reviews the connections between these aspects moving from the bulk alloy to the surface. The thermodynamic and empirical criteria utilized for prediction of phase formation and reasons behind ignoring the factors such as ordering, segregation, metastability, and processing defects are described. Further, the influence of casting, rapid solidification, coating deposition, and thin-film processing on the microstructure that will interact with catalytic or corrosive environment is reviewed. Electrocatalysis and corrosion resistance are considered as two strongly coupled surface phenomena rather than separate fields of application. Quantitative comparison of exemplary high-entropy alloy systems shows the influence of the alloying approach and surface development on the catalytic properties, surface reconstruction, selective dissolution, passive film formation, and localized corrosion. The potential of CALPHAD modeling, density functional theory, machine learning, and multi-objective optimization for a better alloy selection in the field of high-entropy alloys is reviewed as well. We identified that the success of HEA design is not only in choosing the right composition but rather in controlling the phases, defects, interfaces, and surface of the HEA. Full article

High-entropy alloys (HEAs), complex concentrated alloys (CCAs), medium-entropy alloys (MEAs), and multi-principal element alloys (MPEAs) are compositionally complex material classes in which design is based on multiple principal elements present in substantial, often comparable, fractions rather than on a single dominant constituent. In this Entry, the discussion focuses primarily on metallic alloy systems within this broader framework. HEAs are commonly described as alloys containing five or more principal elements and relatively high ideal configurational entropy; CCAs represent a broader, phase-agnostic category of chemically complex alloys in which multiple elements occupy significant fractions and can form solid solutions, ordered phases, intermetallic compounds, or multiphase microstructures; MEAs generally refer to systems containing fewer principal elements or lower configurational entropy than typical HEAs; and MPEAs describe alloys designed around multiple principal elements without requiring a specific entropy threshold. These terms overlap and are not universally hierarchical, and their use depends on composition, phase constitution, and research context. The large compositional space enabled by these materials provides opportunities for designing face-centered cubic, body-centered cubic, hexagonal close-packed, ordered, eutectic, refractory, interstitially alloyed, and precipitation-strengthened alloy systems. Their properties are governed by the complex interactions among composition, phase stability, chemical ordering, processing route, microstructure, and service environment. This Entry summarizes the fundamental concepts, design approaches, structural characteristics, processing methods, modeling strategies, properties, candidate engineering applications, limitations, and future perspectives of HEAs and related compositionally complex alloys. Full article

In this study, the influence of precipitated Laves particles on the metastable pitting of VCrFeTa_0.1W_0.1 and VCrFeTa_0.2W_0.2 refractory high-entropy alloys (HEAs) in 3.5 wt.% NaCl solution was investigated. Microstructures and corrosion behaviors were characterized by XRD, SEM, TEM, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS), and the underlying mechanisms were elucidated. The PDP test results demonstrate that the precipitated Laves particles reduce the pitting resistance of HEAs. The corrosion current densities of VCrFeTa_0.1W_0.1 and VCrFeTa_0.2W_0.2 HEAs are 0.066 and 1.361 μA/cm², respectively, and the pitting potentials are 1.058 and 0.881 V, respectively; that is, reducing the Laves-particle content lowers the corrosion current density by a factor of approximately 20 and raises the pitting potential by approximately 180 mV. The corrosion current density and pitting potential of VCrFeTa_0.1W_0.1 are competitive with those of reported HEAs and traditional alloys. Full article

AlCoCrFeNi-based high-entropy alloys have garnered significant attention for high-end applications in aerospace, marine engineering, and the nuclear industry due to their exceptional comprehensive properties, including high strength and good corrosion resistance. However, their widespread application is critically hindered by a fatal disadvantage: poor ductility. Optimizing the ductility of this alloy system has therefore become a key research priority. Optimizing their ductility has emerged as a key research priority in recent literature. This review systematically examined the influences of diverse fabrication techniques on the mechanical properties, particularly ductility, of these alloys. Melting routes (vacuum arc melting and vacuum induction melting), powder consolidation (spark plasma sintering and hot pressing), and additive manufacturing (selective laser melting, laser melting deposition, electron beam melting, and wire arc additive manufacturing) were covered in this review. This review underscores that while each fabrication route offers distinct advantages, future breakthroughs require multi-process hybridization, data-driven optimization, and precise control of precipitation kinetics to overcome the strength–ductility trade-off and enable large-scale applications of AlCoCrFeNi-based HEAs. Full article

This study investigated how compositional variation within the AlTiSiCrCo high-entropy alloy (HEA) system affects the microstructure, hardness, and dry sliding wear behaviour of laser-cladded coatings on Ti6Al4V. Three coatings, namely, equiatomic (HEA 1), Cr/Co-enriched (HEA 2), and Al/Ti-enriched (HEA 3), were characterized by SEM, EDS, XRD, and Vickers microhardness and tested for dry sliding wear using a ball-on-disc tribometer at 5 N and 15 N. All coatings comprise a BCC solid solution matrix reinforced by intermetallic precipitates. HEA 2 and HEA 3 gave the highest hardness (755 HV and 754 HV, respectively) against 705 HV for HEA 1 and 345 HV for the Ti6Al4V substrate. All HEA coatings reduced wear rate relative to Ti6Al4V; HEA 2 recorded the lowest rate ($4.570\times {10}^{-5}$ mm³/N.m and $2.744\times {10}^{-4}$ mm³/N.m at 5 N and 15 N, respectively), well below the substrate ($2.257\times {10}^{-4}$ mm³/N.m and $0.0014$ mm³/N.m at 5 N and 15 N, respectively). Worn surface analysis showed abrasive/delamination at 5 N transitioning to more severe abrasive, adhesive, and delamination wear at 15 N. The enhanced wear resistance of HEA 2 stems from the BCC solid solution strengthening, intermetallic reinforcement, and high chromium content, which aids in the formation of the Cr₂O₃ protective oxide film. Overall, enriching the coating with chromium and cobalt proved to be the most effective approach for improving the tribological performance of laser-cladded AlTiSiCrCo HEA coatings on Ti6Al4V. Full article

High-entropy alloys (HEAs) offer attractive combinations of mechanical performance, thermal stability, and compositional flexibility, making them promising candidates for advanced structural applications. Laser-based additive manufacturing, particularly laser powder bed fusion (LPBF) and laser-directed energy deposition (LDED), enables the fabrication of geometrically complex HEA components with non-equilibrium microstructures. However, the distinct thermal histories of LPBF and LDED, with typical cooling rates of approximately 10⁵–10⁷ K s⁻¹ and 10²–10⁴ K s⁻¹, respectively, strongly govern solidification behavior, elemental segregation, residual stress development, defect formation, and mechanical properties. Although previous reviews have discussed additively manufactured HEAs, an integrated framework linking composition design, printability, LPBF/LDED processing, microstructural evolution, post-processing, and industrial qualification remains limited. Therefore, this review establishes a unified composition–process–structure–property framework for laser additively manufactured HEAs. Fundamental HEA concepts, LPBF/LDED process characteristics, solidification behavior, phase formation, defect evolution, and mechanical performance from ambient to elevated temperatures are systematically discussed across representative FCC, refractory, and dual-phase HEA systems. This review emphasizes that printability should be considered during alloy design by correlating composition-dependent solidification characteristics, cracking susceptibility, phase stability, and defect formation with mechanical performance. Post-processing treatments are shown to modify residual stress, microsegregation, precipitation behavior, porosity, and deformation mechanisms, although their benefits must be balanced against thermal softening or brittle phase formation. Finally, CALPHAD, integrated computational materials engineering (ICME), machine learning (ML), and in situ monitoring are identified as promising tools for accelerating alloy and process optimization, while reproducible process windows, defect-control criteria, databases, and qualification protocols remain essential for industrial implementation. Full article

This study investigates the design, microstructure, and performance profile of a novel composite coating combining a high-entropy alloy (HEA) matrix with cermet reinforcement. A 50wt.%CoCrFeMnNi_0.8V–50wt.% Cr₃C₂-Ni₈₀Cr₂₀ powder mixture was successfully deposited onto steel substrates via high-velocity oxy-fuel (HVOF) thermal spraying. Microstructural analysis revealed a highly dense, well-bonded coating architecture (450–500 μm thick) where partially melted, spherical HEA splats were uniformly surrounded by the Cr₃C₂-Ni₈₀Cr₂₀ phase. X-ray diffraction confirmed a complex multiphase evolution consisting of FCC, BCC, and σ-NiCr phases driven by the rapid solidification inherent to the HVOF process. Tribological evaluations via ball-on-disc testing demonstrated that incorporating the Cr₃C₂-Ni₈₀Cr₂₀ reinforcement significantly improves wear resistance compared to the monolithic HEA coating. The composite’s wear behavior is governed by a synergistic mechanism: the ductile HEA matrix accommodates plastic deformation, while the harder carbide particles enhance load-bearing capacity, transitioning from adhesive wear to mild third-body abrasion and protective tribo-oxidation. Conversely, electrochemical testing in a 3.5 wt.% NaCl solution showed that the composite coating exhibits higher corrosion current densities (10.53 × 10⁻⁶ A/cm²) and more active corrosion potentials than the pure HEA matrix. This behavior is attributed to localized micro-galvanic cells forming at the heterogeneous interfaces between the different phases, alongside chloride-induced destabilization of the surface oxide film. Overall, the novel composite coating offers a compelling, sustainable alternative for surface engineering applications requiring a balanced trade-off between mechanical toughness and acceptable environmental durability. This behavior is also verified by the comparison with previous results dealing with monolithic CoCrFeMnNi_0.8V and 75wt.%CoCrFeMnNi_0.8V–25wt.% Cr₃C₂-Ni₈₀Cr₂₀ thermal sprayed coatings, where it is evident that the increase of the reinforcing phase leads to an optimum combination of properties. Full article

A novel (TaWZrHf)₉₅Y₅ refractory high-entropy alloy (RHEA) matrix was fabricated via vacuum hot pressing (VHP) sintering and subsequently modified through laser remelting (LR) surface treatment. Thermodynamic phase diagram calculations predicted the alloy’s dual-phase BCC structure, and the effects of LR on phase composition, microstructure, and mechanical properties were systematically investigated. LR induced a significant phase transition, promoting rapid solidification and substantial grain refinement. The surface hardness increased to 848 HV₀.₂, approximately 1.5 times higher than that of the matrix, while the compressive strength reached 1635 MPa, surpassing the matrix by 200 MPa without compromising ductility. Importantly, the LR process effectively mitigated rare-earth (yttrium) segregation and loss, a common challenge in conventional arc melting of refractory HEAs, thereby enhancing solid solution strengthening and phase stability. This work pioneers the application of laser surface engineering to VHP-sintered refractory HEAs, bridging critical gaps in fabrication, microstructural optimization, and performance enhancement, and offering valuable insights for the future design of high-performance multi-principal element alloy development. Full article

The empirical descriptors of high-entropy alloys and oxides, from the mixing entropy and atomic-size mismatch to the Miedema enthalpies and the $\mathsf{\Omega }$, $\mathrm{\Phi }$, and $\phi$ stability parameters, are quoted in nearly every design study, yet they are reimplemented ad hoc by individual groups, by closed web calculators, and now inside language-model agent frameworks, where fabrication of property values is a documented failure mode. The resulting numbers disagree and cannot be traced or reproduced. We present HEA-Bench, an open calculator in which every descriptor is a closed-form expression over a curated, literature-cited element-property table, with the six canonical phase-prediction rules reported alongside their thresholds and sources rather than as predictions. One calculation core is delivered as a dependency-free Python (version 3.10 or later) library, a zero-install browser application, an offline desktop executable, and a Model Context Protocol server that exposes it to AI agents as deterministic tools, returning every value with its unit, citation key, and version so an agent’s reasoning trace can be audited. The implementation reproduces published per-alloy and per-oxide anchor values to their printed precision and extends to high-entropy oxides in four structure families. The numerical instability of $\mathsf{\Omega }$ near zero mixing enthalpy is quantified and exposed as a callable check. Full article

Steel components in thermal power plants are vulnerable to severe wear and wall thinning induced by the high-velocity impact of pulverized coal, which significantly compromises their service life and structural integrity. To address this issue, a TiC-reinforced AlCoCrFeNi high-entropy alloy (HEA) composite coating was fabricated via laser cladding, aiming to substantially enhance the wear resistance of these critical components. The phase composition, microstructure, microhardness and tribological behaviors of the coatings were systematically investigated by XRD, SEM, EDS and dry sliding wear tests. Results show that both coatings possess dense microstructures and reliable metallurgical bonding with the substrate. The AlCoCrFeNi coating consists of a single BCC solid solution phase, while the TiC/AlCoCrFeNi composite coating contains a BCC phase and a TiC ceramic phase without brittle intermetallic compounds. The average microhardness of the TiC/AlCoCrFeNi composite coating was measured to be 823 HV_0.3, which is 85.66% greater than that of the AlCoCrFeNi coating (443 HV_0.3). Under identical wear test conditions, the AlCoCrFeNi coating exhibits a mass loss of 31.4 mg and a volumetric wear rate of 24 × 10⁻³ mm³/min, whereas the TiC/AlCoCrFeNi composite coating exhibits a mass loss of 15.6 mg and a wear rate of 13 × 10⁻³ mm³/min, corresponding to reductions of approximately 50.32% and 45.83%, respectively. The wear mechanism of the AlCoCrFeNi coating is dominated by severe abrasive wear coupled with adhesive wear, while the addition of TiC converts the wear mechanism into mild abrasive wear and oxidative wear. The incorporation of TiC particles effectively enhances the microhardness and reduces the mass loss, thereby contributing to a marked improvement in the wear properties of the laser-clad AlCoCrFeNi coating. This research provides experimental data and theoretical support for the engineering application of TiC/AlCoCrFeNi composite coatings on wear-resistant components in thermal power units. Full article

Non-equiatomic high-entropy alloys (HEAs) are promising candidates for low-dimensional magnetocaloric applications. In this work, Fe₂₅Ni₂₁Mn₂₄Si₁₃Ge₁₇ HEA-based nanoribbon arrays with spacings of 1 and 2 µm, together with companion thin films, were fabricated under the same technological conditions by magnetron co-sputtering from five sources. The effects of heat treatment and longitudinal strain (0–2%) on the structural, magnetic, and magnetocaloric properties were studied using TEM, SAED, AFM, and SQUID magnetometry. TEM, SAED, and AFM confirmed an amorphous structure with a single cubic-type short-range order and thermal stability up to 700 K. The nanoribbons exhibited shape-induced magnetic anisotropy that vanished at a 2 µm spacing, where the ribbons became magnetically decoupled. Within the elastic regime, longitudinal strain acted via magnetoelastic coupling, preserving the in-plane isotropy while enhancing the magnetic response above 100 K. Annealing at 700 K drove short-range atomic reordering and relieved fabrication-induced strain, increasing the saturation magnetization severalfold and raising the maximum isothermal magnetic entropy change −ΔS_M of the 1 µm nanoribbons from 1.25 to 1.35 JK⁻¹kg⁻¹ (at 140 K, ΔH = 50 kOe). The results demonstrate that strain engineering and thermal processing provide distinct, complementary routes for tuning the magnetic and magnetocaloric behavior of FeNiMnSiGe HEA nanoribbons. Full article

This work presents an interpretable machine learning (ML) system that uses composition- and physics-based descriptors to predict the bulk moduli of high-entropy alloys (HEAs). Extra Trees, Random Forest, Gradient Boosting, AdaBoost, and LightGBM are five ensemble ML algorithms that were systematically shaped and refined by hyperparameter fine-tuning. With a test R² of about 0.852 and an RMSE and MAE of about 5.49 GPa and 1.5 GPa, respectively, Extra Tree outperformed the other optimized models, indicating good generalization capacity for untested HEA compositions. The computational efficiency results showed that LightGBM had the fastest prediction speed (~4.24 ms), whereas Extra Trees had the shortest training time (~17.3 s). The majority of the optimized models had statistically equal prediction performance (p > 0.05), according to statistical validation using paired t-test analysis, even though residual error distributions for the Extra Tree model established consistent and unbiased predictions. To enhance the interpretability of the model, SHAP-based explainable analysis was performed, which included SHAP importance, dependence, and waterfall plots. The SHAP results revealed that the primary determinants impacting bulk modulus behavior in HEAs were Zr content, mean electronegativity, Al content, bond strength, and melting-temperature-related parameters. The proposed framework enables the rapid identification and design of next-generation HEAs by permitting precise and computationally efficient bulk modulus prediction, as well as physically significant insights into descriptor–property connections. Full article