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Many studies attribute the excellent properties of high-entropy alloys to the ordering-phenomena. It can be known from density functional theory that the macroscopic properties of the system can be described by the electron density. Electronegativity is related to electron density, and models describing ordering can be established based on electronegativity scales through machine learning. In this study, a large dataset was established and predicted the ordered state corresponding to the alloy composition. The accuracy of the model on the test set was 94%. Furthermore, this study used different methods to explain the machine learning model and learned more model information. [ABSTRACT FROM AUTHOR]

The high-temperature properties of new alloys need to be investigated to guide the hot working process. The temperature sensitivity of various microstructures of Fe45Mn15Cr15Ni25 and Fe35Mn15Cr15Ni25Al10 cobalt-free high-entropy alloys was investigated using high-temperature tensile tests. For recrystallized alloys, the increase in aluminum (Al) atoms exacerbates the emergence of serration behavior, prolongs the strain hardening capacity, and delays the decrease in plasticity. The Fe35Mn15Cr15Ni25Al10 alloy, with a high-density precipitated phase, exhibits excellent mechanical properties at 673 K. It has a yield strength of 735 MPa, an ultimate tensile strength of 1030 MPa, and an elongation of 11%. Ultimately, it has been found that the addition of the element Al improves the strength, oxidation resistance, and thermal stability of the alloy. According to the solid solution strengthening model fitting and nanoindentation results, the temperature sensitivity of the yield strength of the alloy is primarily attributed to the solid solution strengthening and phase interface forces. There is relatively less variation in grain boundary strengthening and precipitation strengthening. The relationship between the mechanical properties and temperature of the alloy can be predicted to guide the machining process of the alloy. [ABSTRACT FROM AUTHOR]

Transformation induced plasticity (TRIP) effect in high entropy alloys (HEAs) overcomes the strength–ductility "trade-off" and leads to the synchronous improvement of strength and ductility. In this work, we studied a TRIP Fe60Mn20Co10Cr10 HEA with a dual-phase structure consisting of face-centered cubic matrix and hexagonal close-packed (HCP) martensite. By warm-rolling and subsequent annealing, three samples with different recrystallization conditions and HCP phase volume fractions were obtained. The alloys exhibit a good combination of ultimate tensile strength (∼700–900 MPa) and elongation (∼45%–55%), representing sustainable strain hardening behavior over extended deformation regime. To reveal the deformation mechanism of the present TRIP HEA, the method to determine the stacking fault energy (SFE) via a regular solution model was discussed, and the SFE of Fe60Mn20Co10Cr10 alloys at 300 K was estimated as 15.3 mJ/m2. The low SFE promotes the formation and overlapping of stacking faults via dislocation interaction, which provides nucleation sites of HCP martensite and further contributes to the striking strain hardening capacity upon tension. [ABSTRACT FROM AUTHOR]

A triple-phase eutectic high-entropy alloy (TEHEA) Al10Co18Cr18Fe18Nb10Ni26 is designed and successfully prepared by electric arc melting. The alloy is proved to consist of disordered face-centered cubic (FCC) phase, ordered body centered cubic (B2) phase and Laves phase with hexagonal close-packed (HCP) structure. Furthermore, a simple mixing method can be adopted to design TEHEAs and to locate the eutectic point composition. This class of alloys provides a new approach for the exploration of multicomponent triple-phase eutectic alloys with unique microstructure and properties. [ABSTRACT FROM AUTHOR]

High strength-ductility is the prerequisite requirement for the widely used steel wires in engineering applications. Traditional strengthening strategies on these wires are suffocated inevitably by strength-ductility trade-off dilemma. Recent emerging medium-entropy alloys (MEAs) usually exhibits excellent ductility but relatively lower strength. In this paper, a novel CoCrNi MEA wire with superior mechanical properties was successfully fabricated by heavily drawing process. The yield strength, ultimate tensile strength and elongation could reach 1.5 GPa, 1.8 GPa and 37.4% at liquid-nitrogen temperature, respectively. In-depth microstructure characterization indicates this superior strength-ductility derives from the synergy of dislocations, high-density twins and clear FCC-HCP phase transition. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The equiatomic GaInSnZn (GISZ) high-entropy alloys (HEAs) are considered to have the potential as coolants to engage the thermal management owing to their high thermal conductivity. However, the incompatibility between them and other structural materials hinders these practical applications. On the way to seeking suitable structural metals with liquid metal embrittlement (LME) resistance in GISZ environment, the Al 0.7 CoCrFeNi alloys are selected and their temperature-dependent LME sensitivity is investigated through high temperature and slow strain-rate tensile tests at 100, 300 and 500 ℃. The sharp decrease in tensile ductility and serious LME phenomenon are explicitly inspected at all temperatures. The transformation of the LME mechanism, which shifts from adsorption-induced reduction in cohesion of the interior or boundaries of grain colonies to grain/phase boundary wetting with temperature increasing, is corroborated by the fractographic analysis and crack propagation path. This study not only provides guidance for the LME of this new system, but also encourages a promising landscape for searching for protective measures of Al 0.7 CoCrFeNi alloys and new materials adapted to GISZ, thereby laying a solid foundation for promoting liquid metal cooling applied to the actual industry. • The Al 0.7 CoCrFeNi HEAs in GaInSnZn show a sharp decrease in tensile ductility and serious LME behavior at 100, 300 and 500 ℃. • The LME sensitivity has a strong temperature dependence and its severity is correlated positively with temperature. • The LME mechanism transforms from adsorption-induced reduction in cohesion to grain/phase boundary wetting. [ABSTRACT FROM AUTHOR]

A series of AlCoCr x FeNi 2 (x = 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4) high entropy alloys (HEAs) were designed to investigate the structural evolution and tensile properties variation with Cr content. It was found that all the alloys were composed of face-centered cubic (FCC) phase and disordered body-centered cubic (BCC) plus ordered body-centered cubic (B2) region. However, the volume fraction of FCC phase first increased and then decreased with increasing Cr content, while the valence electron concentration (VEC) values kept decreasing, which contradicts with the universal VEC criterion. Here, the partition ratio of Cr element in FCC/(BCC + B2) region was introduced to describe the structural evolution and phase stability. Our work reveals that Cr is FCC stabilizer at low concentration, and promotes the formation of BCC phase at high concentration. Similarly, the strength and ductility exhibit a non-monotonic variation with increasing Cr content. • Cr is not always a BCC forming element in HEAs as previously thought. • VEC criterion fails to explain phase stability from qualitative perspective for the first time. • Partition ratio is introduced to describe the structural evolution and phase stability. [ABSTRACT FROM AUTHOR]

Abstract The current study reports a novel heterogeneous AlCoCr 2 FeNi 2 high entropy alloy (HEA) with an innovative structure and outstanding mechanical properties at various temperatures. The alloy is composed of the alternating face centered cubic (FCC) phase and the body centered cubic (BCC) phase, with the cubic ordered body centered cubic (B2) phase embedded in the BCC phase and the fusiform BCC phase embedded in the FCC phase homogeneously. The as-cast alloy shows excellent mechanical properties with an ultimate tensile strength of 1330 ± 44 MPa and a total elongation of 7.4%. The mechanical properties are superior to most reported HEAs and are attributed to the strong back stress strengthening effect. [ABSTRACT FROM AUTHOR]

Face-centered cubic (FCC)/ordered body-centered cubic (B2)-structured Al–Co–Cr–Fe–Ni system eutectic high-entropy alloys (EHEAs) have a favorable combination of high strength and ductility in the as-cast state. However, the mechanical properties of this type of alloy vary significantly with composition. In this study, we attempted to determine the yield strength differences in FCC/B2 EHEAs. Based on reported Al 0.8 CrFeNi 2.2 , we successfully prepared three low-cost Co-free EHEAs: Al 0.82 Cr 0.8 Fe 1.2 Ni 2.18 , Al 0.83 Cr 0.6 Fe 1.4 Ni 2.17 , and Al 0.85 Cr 0.4 Fe 1.6 Ni 2.15. All the EHEAs are shown to exhibit the same phase constituent (FCC/B2) and complete eutectic microstructure, with similar lamellar thickness but different tensile properties. We constructed a theoretical calculation model based on the Hall-Petch regime which fits the measured yield strength σ 0.2. The yield differences for current FCC/B2 EHEAs results mainly from different intrinsic strengths of their soft FCC phases. [ABSTRACT FROM AUTHOR]

Metallic wires with high strength-ductility at both room and cryogenic temperatures are always pursued for engineering applications. However, traditional metallic wires are tortured inevitably by strength-ductility trade-off dilemma. In this work, a gradient heterogeneous lamella structure, characterized with hard gradient-distributed B2 lamellae embedded in soft FCC lamellae matrix, is introduced into AlCoCrFeNi 2.1 eutectic high entropy alloy (EHEA) wire by well-designed multiple-stage heavy-drawn and heat treatment processes, which achieves an outstanding strength-ductility synergy. This EHEA wire exhibits not only high tensile strength of 1.85 GPa and sufficient uniform elongation of ∼12% at room temperature, but also ultra-high tensile strength of 2.52 GPa and even slightly elevated uniform elongation of ∼14% at cryogenic temperature. In-depth microstructure characterization indicates that the gradient heterogeneous lamella structure facilitates a radial gradient distribution of geometrically necessary dislocation (GND) during tension, i.e., the GND density decreases gradually from the surface region to the central region of EHEA wire, which induces pronounced strain gradient strengthening effect and thus greatly benefits the mechanical properties. Intriguingly, at cryogenic temperature, dense cross-slip which gives rise to intensively dynamic microstructure refinement is firstly observed in the B2 phase of EHEA wire. The activation of cross-slip provides sufficient ductility while inducing evidently dynamic Hall-Petch effect, becoming the most effective deformation mechanism contributing to the unprecedented cryogenic tension properties. This work sheds light on designing ultra-strong EHEA wire and other advanced metallic wires. [Display omitted] [ABSTRACT FROM AUTHOR]

The tribological behavior of hot-rolled and boronized Fe40Mn20Cr20Ni20 high-entropy alloys (HEAs) sliding against a Si3N4 ball was investigated in the air, deionized water and seawater. The results showed that the hot-rolled Fe40Mn20Cr20Ni20 HEA was composed of an FCC (face-centered cubic) phase. In addition, the boronized HEA was composed of a great number of borides, including CrB, FeB, MnB, Fe2B, Fe3B and MnB2. The hardness increased from 139 HV to 970 HV after boronizing. In air, the wear rate decreased from 4.51 × 10−4 mm3/Nm to 0.72 × 10−4 mm3/Nm after boronizing. The wear mechanism transformed from abrasive wear and oxidative wear to the polishing effect. After boronizing, in the deionized water, the wear rate decreased from 1.27 × 10−4 mm3/Nm to 8.43 × 10−5 mm3/Nm. The wear mechanism transformed from abrasive wear and delamination wear to delamination wear. In the seawater, the wear rate decreased by about ten times that of hot-rolled alloy. [ABSTRACT FROM AUTHOR]

Micron-sized CoCrNi medium-entropy alloy (MEA) wires are successfully fabricated by Taylor-Ulitovsky method for the first time. The wires of two different sizes, with diameters of 40 and 100 microns, exhibit an excellent combination of tensile strength and ductility. In-depth microstructure characterization indicates the superior mechanical properties stem from the synergy of Lomer-Cottrell locks, mechanical nano-twinning and HCP stacking. Surprisingly, an anomalous size effect is presented in the tension of these microwires, i.e., the much higher tension strength and ductility are observed in the 40 micron-wire, in sharp contrast to conventional single-principal element alloys only showing negligibly minor tension size effect. Much higher density of geometrically necessary dislocation accompanying heterogeneous deformation is observed in 40 micron-wire, leading to a high strain gradient, which is in turn joined with multiple deformation twins giving rise to high strength and ductility in 40 micron-wire. [Display omitted] [ABSTRACT FROM AUTHOR]

Comprehensive investigations on the impact of Ce doping on the pitting resistance of Fe 40 Mn 20 Cr 20 Ni 20 high-entropy alloys in 3.5% NaCl solution were conducted with an emphasis on the inclusions involved. The correlation between the variations of the type, number and size of inclusions and the doping of Ce were identified. The increased pitting resistance of the alloy induced by the doping of Ce was found associated with higher metastable pitting potentials and steady-state pitting potentials. The morphology evolution with the inclusions captured by SEM images and EDS mapping strongly indicated an existence a double-layer structure in Ce-doped Fe 40 Mn 20 Cr 20 Ni 20 high-entropy alloys. An evident irregular pitting propagation path was probed in Ce-doped samples. • Ce-doping improved the pitting resistance of Fe 40 Mn 20 Cr 20 Ni 20 HEAs. • The addition of Ce can refine the grain size of alloys. • Doping of Ce is beneficial to the metastable pitting process in Fe 40 Mn 20 Cr 20 Ni 20 HEAs. • Ce-doped HEAs exhibited an irregular pitting propagation path. • Doping of Ce resulted in a double-layer structure of inclusions in Fe 40 Mn 20 Cr 20 Ni 20 HEAs. [ABSTRACT FROM AUTHOR]

The evolution of microstructure and tensile properties of a newly designed cobalt-free high entropy alloy, Fe 35 Mn 15 Cr 15 Ni 25 Al 10 (at.%), has been investigated during the annealing and aging processes. A dual-phase alloy with a face-centered cubic (FCC) and body-centered cubic (BCC) or ordered B2 structure, along with multiscale heterogeneous precipitates, has been formed. The precipitated phases consist of bulk primary B2–NiAl and secondary BCC/B2 particles that range in size from the nanometer to micrometer scale. By prolonging the aging time, the yield strength is strongly enhanced, increasing from 250 MPa to 860 MPa at the peak aging stage. The primary sources of strengthening are precipitation hardening and hetero-deformation-induced strengthening from the BCC or ordered B2 phase. Furthermore, the incorporation of various strengthening mechanisms and high-strain hardening capability at cryogenic temperatures (77 K) results in improved strength and ductility simultaneously. A highly cost-effective high-entropy alloy, doped with a high concentration of aluminum, has been developed. • A highly cost-effective high-entropy alloy (HEA) doped with a high aluminum content has finally been developed. • The dual-phase face-centered-cubic (FCC) and body-centered-cubic (BCC) or ordered B2 structured alloy with multi-scale heterogeneous precipitates was formed. • The strength and ductility are simultaneously improved by multiple strengthening mechanisms and a high-strain hardening capability at cryogenic temperatures (77 K). [ABSTRACT FROM AUTHOR]

As a surface modification technique, chromization is often used in steels to improve their wear, corrosion, and oxidation resistances. High-entropy alloys (HEAs) with excellent properties can be applied in extreme environments, perhaps to further improve their resistance to external environments by chromization. In this work, the chromization of hot-rolled Fe 40 Mn 20 Cr 20 Ni 20 HEA was carried out by pack cementation. A chromized coating of 120 µm with the body-centered cubic (BCC) structure and a diffusion layer of 30 µm were obtained by chromizing at 1473 K for 12 h. Based on the growth kinetics of the coating, the relationship between the thickness of the chromized coating and chromized temperature as well as the time was modeled to visualize. After chromization, due to the higher chromium content of the coating, the Vickers hardness of was increased from 150 HV0.1 of hot-rolled HEA to more than 500 HV0.1, the wear rate was significantly reduced, and the dominant wear mechanisms for both hot-rolled and chromized HEAs under three test environments involved abrasion and adhesive wears. Besides, the corrosion resistance was promoted in NaCl solution (3.5 wt%). Thereby, the present work provides guidances for chromization on HEAs. [Display omitted] • The chromization of Fe 40 Mn 20 Cr 20 Ni 20 HEA is carried out by pack cementation. • Tribological behavior of chromized HEA under different environments is examined. • The relationship between the thickness of coating, temperature and time is modeled. [ABSTRACT FROM AUTHOR]

The electrochemical corrosion behavior and passive film properties formed on the as-cast Co-free Al 0.8 CrFeNi 2.2 eutectic high entropy alloy (EHEA) in different media (0.5 M NaCl, 0.5 M Na 2 SO 4 , 0.5 M H 2 SO 4 and 0.5 M HCl) were investigated by the electrochemical test methods, SEM analysis and XPS characterization. The potentiodynamic polarization tests and SEM morphologies examination demonstrated the inhomogeneity of eutectic dual-phase structure led to the preferential corrosion of BCC phase regardless the corrosion media. The values of the defect diffusivity (D O) and donor density (N D) of the passive film suggested the quality of the film formed in H 2 SO 4 solution is inferior to that of other media. Further XPS measurements provided compositional information in support of above observation. • Corrosion resistance of the EHEA in H 2 SO 4 and NaCl media is better than some conventional alloys and comparable to some HEAs. • The inhomogeneity of the dual-phase structure leads to the preferential corrosion of the BCC phase regardless the corrosion media. • The defect diffusivity D O were obtained, which can explain the discrepancy of passive current densities in different media. • XPS results show the higher content of Cr and its oxides of films in H 2 SO 4 solution, is due to the low stability of Fe. [ABSTRACT FROM AUTHOR]