FeCoNiCrMn High Entropy Alloy Research Articles

Fabrication of Fe-based metallic glass reinforced FeCoNiCrMn high-entropy alloy through additive manufacturing: mechanical property enhancement and corrosion resistance improvement

In recent years, high entropy alloys (HEA) receive extensive attention for their excellent mechanical performance. In this paper, the FeCoNiCrMn high-entropy alloy reinforced material is produced by laser powder bed fusion (LPBF). The excellent tensile performance can be achieved through many strengthening mechanisms, e.g., solution strengthening, dislocation strengthening, fine-grain refinement, and dispersion strengthening. The reinforced material with additive Fe-based metallic glass shows a yield strength of 675 MPa, 29.8% higher than FeCoNiCrMn (520 MPa), and an average hardness of 241.9 HV, 12.7% higher than FeCoNiCrMn (214.6 HV). Meanwhile, the plasticity of the reinforced material is maintained at a good level. In comparison with FeCoNiCrMn, the corrosion current density is reduced by 18.9%, and the corrosion resistance is significantly improved. The high strength and corrosion resistance are achieved by the addition of Fe-based metallic glass, which provides a feasible approach for the preparation of HEA with enhanced mechanical properties in the future.

Effect of Mo addition on structures and properties of FeCoNiCrMn high entropy alloy film by direct current magnetron sputtering

FeCoNiCrMnMox high-entropy alloy (HEA) films were prepared by direct current (DC) magnetron co-sputtering. The influence of the Mo content on the microstructures and mechanical properties of the HEA films were systematically studied by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Vickers hardness test and tribological test. The addition of Mo results in the formation of a denser film with refined grain size, and promotes the transformation from a face-centered cubic (FCC) phase to a mixture of FCC and body-centered cubic (BCC) phases. The hardness of the films increases from 8.5 GPa (x = 0) to 12 GPa (x = 1) and the friction coefficient decreases from 0.5 (x = 0) to 0.3 (x = 1), which greatly enhance the damage tolerance of the film. The improved mechanical and tribological properties of the HEA films are attributed to the formation of the hard BCC phase and grain refinement at high contents of Mo. The FeCoNiCrMnMox HEA films are suitable candidates for structural application as protective coatings.

Dislocation-driven high catalytic performance of FeCoNiCrMn high-entropy alloy for the hydrolysis of NaBH4

A high-entropy alloy Fe10Co10Ni10Cr10Mn60 ribbon catalyst with a face-centered cubic structure was designed by using Co and Ni as the main catalytic elements and combining various co-catalytic elements, such as Fe, Mn, and Cr. Substantial element selective corrosion occurs during the acid solution corrosion process, which induces the exposure of many Co and Ni atoms, increases the specific surface area, and further results in the formation of many vacancies and dislocations. This unique structure generates a positive electron effect, that is the peaks of Ni2p3/2 and Co2p3/2 shift to lower binding energies, namely, approximately 1 eV for Ni and 0.8 eV for Co, indicating the Co and Ni enrich electrons. The catalyst shows an excellent catalytic performance for the hydrolysis of NaBH4 after corrosion for 90 s, whose hydrogen production rate approaches 18.46 l/(m2·min). This work opens up a direction for the application of the macroscopic scale high-entropy alloy in the catalytic hydrogen field.

Microstructure and mechanical properties of a laser welded Ti–6Al–4V titanium alloy/FeCoNiCrMn high entropy alloy with a Cu filler layer

A high-power solid-state laser was used to weld the Ti–6Al–4V titanium alloy and the FeCoNiCrMn high-entropy alloy. By adding a pure Cu filler layer for the laser welding, a strong welded joint is obtained and the average tensile strength of the laser welded Ti–6Al–4V/FeCoNiCrMn joint exceeds 140 MPa. Composition and mechanical properties of phases in the laser welded Ti–6Al–4V/FeCoNiCrMn joint were investigated by the optical microscope, the electron probe microanalysis technique, the scanning electron microscope and the nanoindentation technique. The fusion zone is mainly composed of the Cu-rich and the FeCoNiCrMn-rich regions. The Cu-rich phases can disperse brittle intermetallic compounds such as Ti–Fe, to prevent the formation of a continuous brittle compound layer, thereby improving the plasticity of the welded joint and promoting the formation of the joint. The temperature distribution model in the fusion zone was established, and combined with the element distribution and phase composition analysis results in the fusion zone, microstructure mechanism for formation of the fusion zone was proposed.

Effects of W addition on the Corrosion Behaviors of FeCoNiCrMn High Entropy Alloy Composites in the 3.5 wt.% NaCl solution

The effects of W addition on the corrosion behaviors of FeCoNiCrMn high entropy alloy composites in 3.5 wt.%NaCl solution are investigated in this study. The X-ray diffraction and scanning electron microscopy suggest that the quantity of added W particles results in the increasing quantity of particles in the composites and large amount of cohesionless phases covering the matrix occur in the alloy with 1.0 molar ratio of W element. The trend of corrosion potential current density means that all W-added high entropy alloy composites have a better corrosion resistance referring to the base high entropy alloy composites and 0.8 molar ratio of W element into base generates a best corrosion resistance in the current work. The Electrochemical impedance spectra and compositional analysis of corroded surface of as-cast high entropy alloys demonstrate that W particles act as anode in the composites and Fe-Mn-Cr is as the cathode.

Microstructure and wear behavior of FeCoNiCrMn high entropy alloy coating deposited by plasma spraying

FeCoNiCrMn high entropy alloy coatings were deposited on steel substrate by atmospheric plasma spraying at different H2 flow rates and subsequently annealed. The microstructure and the phase composition of the prepared coatings were investigated, and the hardness of the coating was determined. The wear behavior of the as-sprayed and annealed FeCoNiCrMn coatings against WC-Co ball was evaluated under dry sliding condition. The results show that the fluffy structures characterized on the surfaces of as-sprayed coatings were formed due to the volatilization and oxidation of Mn element. The coatings were single FCC phase along with some oxides. The wear rate of the as-sprayed coatings was reduced by half as the H2 flow rate increasing from 3 to 6 L/min. Annealing can greatly improve the wear resistance and scratch resistance of the as-sprayed coatings. The characterization of wear tracks demonstrates that splat spalling was the dominating wear mechanism for the as-sprayed coatings. The improvement of wear resistance by increasing H2 flow rate and annealing was attributed to the enhancement of cohesive strength among splats.

Mechanical properties and microstructure of laser welded FeCoNiCrMn high-entropy alloy

In this study, the high-power solid-state laser was successfully employed to weld the FeCoNiCrMn high entropy alloy plates. The tensile strength of the joint achieves 524 MPa. The FeCoNiCrMn high-entropy alloy joint has improved hardness and excellent cyclic deformation resistance. In the fusion zone, dendrites become finer and elements Mn are distributed at the end of dendrites. Refined grains and ultrafine Mn–C rich precipitates can effectively enhance the mechanical properties of joints.

Microstructure and corrosion properties of FeCoNiCrMn high entropy alloy coatings prepared by high speed laser cladding and ultrasonic surface mechanical rolling treatment

Abstract The FeCoNiCrMn high-entropy alloy (HEA) coatings were prepared by high-speed laser cladding (HSLC) technology, and the surface was subjected to ultrasonic surface mechanical rolling treatment (SMRT). After SMRT, the surface of the coatings show a gradient structure. The coatings consist of planar crystal, columnar dendrites and equiaxed crystals from inside to outside. Corrosion behavior in a 3.5% NaCl solution indicates that SMRTed coatings exhibit higher corrosion resistance than the coatings without SMRT. Anti-corrosion mechanism was discussed based on grain refinement, grain boundary wetting phase transitions and compressive residual stress.

Effects of Al Addition on Microstructure and Wear Resistance of High-Velocity-Oxygen-Fuel-Sprayed FeCoNiCrMn High Entropy Alloy Coating

Effects of Al Addition on Microstructure and Wear Resistance of High-Velocity-Oxygen-Fuel-Sprayed FeCoNiCrMn High Entropy Alloy Coating

The corrosion of an equimolar FeCoNiCrMn high-entropy alloy in various CO2/CO mixed gases at 700 and 950 °C

The corrosion behavior of an equimolar FeCoNiCrMn high-entropy alloy was studied in various combination of CO2/COmixed gases at 700 and 950 °C, with the oxygen partial pressure range from 5.0 × 10−16 to 7.9 × 10−8 Pa. The alloy exclusively experienced oxidation, and its kinetics followed the parabolic rate law at both temperatures with the oxidation rates steadily increasing with oxygen pressure. This result demonstrated that a typical oxide scale exhibited a p-type semiconductivity. The scale formed on the alloy at 700 °C was thin, consisting of a mixture of MnO, (Mn,Fe)3O4, and (Mn,Cr)3O4, while the duplex scales formed at 950 °C consisted of an outer layer of (Mn,Fe)3O4 and, MnO, and an inner layer of (Mn,Cr)3O4 andMnO.

Deposition of FeCoNiCrMn high entropy alloy (HEA) coating via cold spraying

High entropy alloys (HEAs) are of great interest in the community of materials science and engineering due to their unique phase structure. They are constructed with five or more principal alloying elements in equimolar or near-equimolar ratio. Therefore, HEAs can derive their performance from multiple principal elements rather than a single element. In this work, solid-state cold spraying (CS) was applied for the first time to produce FeCoNiCrMn HEA coating. The experimental results confirm that CS can be used to produce a thick HEA coating with low porosity. As a low-temperature deposition process, CS completely retained the HEA phase structure in the coating without any phase transformation. The characterization also reveals that the grains in the CSed HEA coating had experienced significant refinement as compared to those in the as-received HEA powder due the occurrence of dynamic recrystallization at the highly deformed interparticle region. Due to the increased dislocation density and grain boundaries, CSed HEA coating was much harder than the as-received powder. The tribological study shows that the CSed FeCoNiCrMn HEA coating resulted in lower wear rate than laser cladded HEA coatings.

Effects of milling time, sintering temperature, Al content on the chemical nature, microhardness and microstructure of mechanochemically synthesized FeCoNiCrMn high entropy alloy

FeCoNiCrMn(Al)-based powdered high entropy alloys were synthesized by a short time mechanical alloying process in a high energy planetary ball milling from mixtures of elemental powders, and subsequently sintered by a pressureless procedure. The composition and microstructure of the HEA phases before and after the sintering process were studied by X-ray diffraction, energy dispersive X-ray analysis (EDX) and scanning electron microscopy. The microhardness and tensile strength values for Fe1,8Co1,8Ni1,8Cr1,8Mn1,8Al1,0 HEA sintered at 1400 °C sample were 3,7 GPa and 1011 MPa, respectively. Statistical Fisher-Pearson coefficient of skewness and kurtosis were played to determine the optimum synthesis milling time. The use of NaCl as additive led on to a reduction of the as-milled grain size. After sintering, SEM study confirmed a segregation of the initial HEA phase directly related to the melting temperature of the elements. Three melting temperature groups were described (Cr, FeCoNi and Mn) and they agree with the observation in the elemental mapping study. The presence of Al favored the segregation of Cr.

Dynamic deformation behavior of a face-centered cubic FeCoNiCrMn high-entropy alloy

In this study, mechanical tests were conducted on a face-centered cubic FeCoNiCrMn high-entropy alloy, both in tension and compression, in a wide range of strain rates (10−4–104 s−1) to systematically investigate its dynamic response and underlying deformation mechanism. Materials with different grain sizes were tested to understand the effect of grain size, thus grain boundary volume, on the mechanical properties. Microstructures of various samples both before and after deformation were examined using electron backscatter diffraction and transmission electron microscopy. The dislocation structure as well as deformation-induced twins were analyzed and correlated with the measured mechanical properties. Plastic stability during tension of the current high-entropy alloy (HEA), in particular, at dynamic strain rates, was discussed in lights of strain-rate sensitivity and work hardening rate. It was found that, under dynamic conditions, the strength and uniform ductility increased simultaneously as a result of the massive formation of deformation twins. Specifically, an ultimate tensile strength of 734 MPa and uniform elongation of ∼63% are obtained at 2.3 × 103 s−1, indicating that the alloy has great potential for energy absorption upon impact loading.

Preparation of FeCoNiCrMn High Entropy Alloy by Electrochemical Reduction of Solid Oxides in Molten Salt and Its Corrosion Behavior in Aqueous Solution

For the first time, powdery FeCoNiCrMn high entropy alloy (HEA) with homogeneous grain size was prepared by one-step electrolysis of solid oxides in molten CaCl2 at 850°C. The HEA with FCC structure and uniform distribution of components was formed during the electrochemical reduction of the oxides, no melting step was needed. In addition, a certain amount of carbon was introduced to the alloy during the electrolysis in a form of chromium carbide due to the dissolution of the carbon anode. The HEA powders were then made into a bulk material and its corrosion behaviors in different aqueous solution were investigated by polarization curve tests. The HEA exhibits a very low corrosion rate, 0.778 μA cm−2 in 1M KOH, 0.879 μA cm−2 in 3.5 wt% NaCl, 32.9 μA cm−2 in 1M HCl solution, respectively. The robust precursors and relatively simple process suggest an economical and environmentally friendly method for preparing HEA powders.

Lattice Distortions in the FeCoNiCrMn High Entropy Alloy Studied by Theory and Experiment

Lattice distortions constitute one of the main features characterizing high entropy alloys. Local lattice distortions have, however, only rarely been investigated in these multi-component alloys. We, therefore, employ a combined theoretical electronic structure and experimental approach to study the atomistic distortions in the FeCoNiCrMn high entropy (Cantor) alloy by means of density-functional theory and extended X-ray absorption fine structure spectroscopy. Particular attention is paid to element-resolved distortions for each constituent. The individual mean distortions are small on average, <1%, but their fluctuations (i.e., standard deviations) are an order of magnitude larger, in particular for Cr and Mn. Good agreement between theory and experiment is found.

The oxidation behavior of an equimolar FeCoNiCrMn high-entropy alloy at 950 °C in various oxygen-containing atmospheres

The oxidation behavior of an equimolar FeCoNiCrMn high-entropy alloy was studied in four oxygen-containing atmospheres over the oxygen partial pressure range from 10 to 105Pa at 950°C. The oxidation kinetics of the alloy followed the parabolic rate law, and the oxidation rate constants increased with increasing oxygen partial pressure. Triplex scales formed on the alloy consisted of an exclusive outer layer of Mn3O4, a heterophasic intermediate layer of Mn3O4, (Mn,Cr)3O4, and Cr2O3, and an exclusive inner layer of Cr2O3.

Steady state flow of the FeCoNiCrMn high entropy alloy at elevated temperatures

Steady state flow behavior of the FeCoNiCrMn high-entropy alloy at temperatures ranging from 1023 to 1123 K was systematically characterized. It was found that the stress exponent (i.e., the reciprocal of strain-rate sensitivity) was dependent on the applied strain rate, and specifically the stress exponent is high (∼5) in the high strain rate regime, but decreases with decreasing strain rate. Microstructural examinations of the samples before and after deformation were performed to understand the interplay of the microstructures with the corresponding properties. Based on the observations, it was proposed that, at high strain rates, the deformation of the current high-entropy alloy was controlled by dislocation climb and the rate limiting process was the diffusion of Ni. At low strain rates, however, the deformation appeared to be controlled by the viscous glide of dislocations. Moreover, at the slowest strain rate (i.e., the longest thermal exposure time), new phases evolved, which caused elemental redistribution and weakening of the material.

Effects of Al addition on structural evolution and tensile properties of the FeCoNiCrMn high-entropy alloy system

A series of six-component (FeCoNiCrMn)100−xAlx (x=0–20at.%) high-entropy alloys (HEAs) was synthesized to investigate the alloying effect of Al on the structure and tensile properties. The microstructures of these alloys were examined using transmission electron microscopy, and crystalline phase evolution was characterized and compared with existing models. It was found that the crystalline structure changed from the initial single face-centered cubic (fcc) structure to a duplex fcc plus body-centered cubic (bcc) structure and then a single bcc structure as the Al concentration was increased. Resulting from the structural changes there were also corresponding variations in tensile properties. In the single fcc region, alloys behaved like a solid solution with relatively low strength but extended ductility. In the mixed structure region, alloys behaved like a composite with a sharp increase in strength but reduced ductility. In the single bcc region, alloys became extremely brittle. In this study, close correlation between the microstructure and mechanical properties was also discussed and presented.