CrMnFeCoNi High-entropy Alloy Research Articles

Exploring the Compositional Space of High-Entropy Alloys for Cost-Effective High-Temperature Applications

High-entropy alloys (HEAs) are nearly equimolar multi-principal element alloys, exhibiting exceptional thermal and mechanical properties at extreme conditions such as high-temperatures and stresses. Since the first discovery and early conceptualization of conventional HEAs nearly two decades ago, HEAs with far-from-equimolar compositions have attracted substantial interest to provide a broader range of material properties and to adjust price fluctuations and availability of commodities. Here, we present a first-principles investigation of non-equimolar chromium-manganese-iron-cobalt-nickel (CrMnFeCoNi) HEAs and effects of molybdenum (Mo) and niobium (Nb) substitutions on cost, phase stability and solubility, and mechanical and thermal performance up to 1000 K operational temperature. Virtual-crystal approximation is used to expediently approximate random solid solutions at the disordered mean-field limit. Using multi-objective metaheuristics built on a first-principles database, golden compositions are predicted for thermally well-insulated components and effective heat sinks. Replacing Co with Fe lowers commodity costs without hindering phase stability and solubility. Lower Ni concentration leads to lower thermal conductivity, indicating better thermal insulation, while reducing Mn concentration significantly increases the thermal conductivity, indicating better performing heat sinks. Moving away from equimolar ratios commonly increases the thermal expansion coefficient, which could generate higher thermal stresses. Nb and Mo substitution always lead to substantially higher commodity cost and density but with an increment in the mechanical performance due to solid-solution hardening. However, alloying with Mo and Nb is the only compositional space that reduces the thermal conductivity and thermal expansion coefficient.

Development of High-Entropy Alloy Coating by Additive Technology

In this research study, various additively fabricated coatings and bulk 3D-printed parts were prepared, using the mechanical and corrosion-resistant properties of CrMnFeCoNi (Cantor alloy) and AlCrMnFeNi high-entropy alloys (HEAs). The coatings were applied to an EN 1.0038 carbon steel substrate using direct metal laser sintering. We attempted to optimize the 3D printing parameters of HEA alloys. The effect of volumetric energy density (VED) on the microstructure was investigated by scanning electron microscopy. We also examined the change of relative concentration of alloys in the direction of 3D printing (z-axis) as well as the volumetric failures (cracks and gaps). Standard salt spray tests were performed to test the corrosion resistance of various coatings after 3D printing. The use of both raw materials applied as thick films was successful; they retained their corrosion-resistant properties even with a change in their composition. Regarding the crystal structure, no difference was found between the base material and the material applied as a coating on the basis of X-ray diffraction investigations. Bulk HEA printing experiments need further optimization concerning their structural integrity and density in the case of the Cantor alloy. Bulk 3D printing experiments of the AlCrMnFeNi alloy did not yield satisfactory results because of the formation of dendritic microstructure and brittle BCC phase, and the residual internal stress resulted in part distortion and improper printing.

Treatment by Electrocoagulation of Congo red from Aqueous Solution Using Cantor Alloy

Electrocoagulation (EC) is one of the most effective techniques in removing color and organic pollutants from wastewater. This study aims to use a new alloy system, so-called High Entropy Alloys (HEAs), which contains at least five principal elements with 5-35 at. %, as an electrode in the EC process. The well-studied equiatomic CrMnFeCoNi HEA (Cantor alloy) was used as an anode in the treatment of the synthetically prepared wastewater (congo red solution) with EC. In the EC study, COD and color removal were evaluated at different current densities (5-100 mA/cm2) for 15 min electrolysis period. The results showed that removal efficiency of above 80 % was obtained for both parameters of COD and color at the lowest current density of 5 mA/cm2. The optimum current density was determined to be 10 mA/cm2, and the COD and color removal efficiencies were found to be 84 and 99.4 %, respectively. It was shown that the Cantor alloy possesses an effective removal in the EC process.

Water Oxidation on Crmnfeconi High Entropy Alloy: Improvement Through Rejuvenation and Spin Polarization

Water Oxidation on Crmnfeconi High Entropy Alloy: Improvement Through Rejuvenation and Spin Polarization

1.45 GPa ultrastrong cryogenic strength with superior impact toughness in the in-situ nano oxide reinforced CrMnFeCoNi high-entropy alloy matrix nanocomposite manufactured by laser powder bed fusion

CrMnFeCoNi high-entropy alloys (HEAs) exhibit an excellent combination of tensile strength and ductility at cryogenic temperatures. This study led to the introduction of a new method for the development of high-performance CrMnFeCoNi HEAs at cryogenic temperatures by jointly utilizing additive manufacturing (AM) and the addition of interstitial atoms. The interstitial oxygen present in the powder feedstock was transformed into beneficial nano-sized oxides during AM processing. The HEA nanocomposite fabricated using laser powder bed fusion (L-PBF) not only contains heterogeneous grains and substructures but also a high number density of nano-sized oxides. The tensile results revealed that the L-PBF HEA nanocomposite has superior yield strengths of 0.77 GPa and 1.15 GPa, and tensile strengths of 0.92 GPa and 1.45 GPa at 298 K and 77 K, respectively. In addition, the Charpy impact energies of the samples tested at 298 K and 77 K were measured as 176.2 J and 103.7 J, respectively. These results indicate that the L-PBF HEA nanocomposite successfully overcomes the well-known strength-toughness trade-off. The tensile deformation microstructure contained a relatively large number of deformation twins (DTs) at cryogenic temperature, a possible consequence of the decrease in the stacking fault energy with decreasing temperature. On the other hand, cracks were found to propagate along the grain boundaries at room temperature, whereas a transgranular crack was observed at cryogenic temperature in the specimens fractured as a result of the Charpy impact. • In-situ oxide reinforced crmnfeconi HEA was manufactured by selective laser melting. • HEA nanocomposite reveals heterogeneous grain structure, nano-size in-situ oxide, and dislocation network induced-substructure. • HEA nanocomposite has cryogenic tensile strength of 1.45 GPa with elongation of 23.4%, while also showing cryogenic impact toughness of 103.7 J.

Effects of Stacking Fault Energy and Temperature on Grain Boundary Strengthening, Intrinsic Lattice Strength and Deformation Mechanisms in CrMnFeCoNi High-Entropy Alloys with Different Cr/Ni Ratios

Effects of Stacking Fault Energy and Temperature on Grain Boundary Strengthening, Intrinsic Lattice Strength and Deformation Mechanisms in CrMnFeCoNi High-Entropy Alloys with Different Cr/Ni Ratios

A Crmnfeconi High Entropy Alloy Boosting Oxygen Evolution/Reduction Reactions and Zinc-Air Battery Performance

A Crmnfeconi High Entropy Alloy Boosting Oxygen Evolution/Reduction Reactions and Zinc-Air Battery Performance

A Crmnfeconi High Entropy Alloy Boosting Oxygen Evolution/Reduction Reactions and Zinc-Air Battery Performance

A Crmnfeconi High Entropy Alloy Boosting Oxygen Evolution/Reduction Reactions and Zinc-Air Battery Performance

Effect of Grain Size on Critical Twinning Stress and Work Hardening Behavior in the Equiatomic CrMnFeCoNi High-Entropy Alloy

Effect of Grain Size on Critical Twinning Stress and Work Hardening Behavior in the Equiatomic CrMnFeCoNi High-Entropy Alloy

Effect of Grain Size on Fatigue Properties in Crmnfeconi High-Entropy Alloy Fabricated by Spark Plasma Sintering Under Four-Point Bending

Effect of Grain Size on Fatigue Properties in Crmnfeconi High-Entropy Alloy Fabricated by Spark Plasma Sintering Under Four-Point Bending

Density Functional Study of Atomic Arrangements in Bulk, Grain Boundary, And Stacking Fault of CrMnFeCoNi High-Entropy Alloy

Density Functional Study of Atomic Arrangements in Bulk, Grain Boundary, And Stacking Fault of CrMnFeCoNi High-Entropy Alloy

Thermodynamics Analysis of Crmnfeconi High-Entropy Alloys with Weak Local Segregation

Thermodynamics Analysis of Crmnfeconi High-Entropy Alloys with Weak Local Segregation

Exploring the Formation Mechanism of Deformation Twins in CrMnFeCoNi High Entropy Alloy

Exploring the Formation Mechanism of Deformation Twins in CrMnFeCoNi High Entropy Alloy

Electrical resistivity and short-range order in rapid-quenched CrMnFeCoNi high-entropy alloy

High-entropy alloys (HEAs) are equimolar solid solution alloys composed of more than five elements, and their atomic arrangement is chemically disordered. Some ordering in HEAs, however, is suspected from the characteristic properties, such as high strength with good ductility at low temperatures or sluggish diffusion. Herein, we report that quasi-stable states inherent in nonequilibrium systems can be extracted by applying an electric pulse current to the system (electropulsing). In this study, changes in the electrical resistivity of the rapid-quenched CrMnFeCoNi HEA were investigated after electropulsing. No step-like large decreases reflecting nanocrystallization in amorphous alloys were observed for rapid-quenched CrMnFeCoNi by electropulsing. This indicates that quasi-stable ordered atom clusters do not exist in the CrMnFeCoNi HEA. However, the resistivity showed a slight decrease and increased with increasing electropulsing current density. A tendency to form short-range order, as Cr is preferentially surrounded by Ni, is suggested by comparison with the results of NiCr alloys.

Phase transformation and morphological features in a cold-worked CrMnFeCoNi high entropy alloy with Al addition

Addition of Al to equiatomic high entropy alloy CrMnFeCoNi alloy with a single phase FCC structure is known to promote formation of a BCC phase. In addition, tetragonal intermetallic phase σ was also found to form in a (CrMnFeCoNi)92Al8 alloy when subjected to processing by caliber rolling (8 passes) at room temperature followed by annealing at 800 ∘C. Microstructure of the as-rolled alloy is complex, containing a high dislocation density and planar faults (including twins) which can be parallel and perpendicular to the rolling direction. Morphological features of the transformations induced by straining by caliber rolling have been determined by transmission electron microscopy (TEM). Two main morphologies have been determined. In one type of morphology, bundles of elongated domains of B2 ordered BCC phase form preferentially on {111} matrix planes, inside which σ phase particles nucleate on interface with the matrix. In another type of morphology called “aggregate” here, “spines” of elongated grains of σ phase form, over which domains of B2 phase nucleate driven by change in solute concentration ahead of the interface. The σ phase forms by nucleation on planar faults in the matrix with its (001) plane, forming the known orientation relationship (OR) {001}σ ∥ {111}FCC and 〈110〉σ ∥ 〈110〉FCC. Since the planar faults in a caliber rolled alloy form parallel as well as perpendicular to the rolling direction, spines of the σ phase elongated in three mutually perpendicular directions are shown to exist. OR of the B2 phase with the matrix is Kurdjumov-Sachs. The B2 phase matched pairs of close packed planes with σ phase, but no particular OR was found. Elemental concentration profiles across interfaces suggests that σ and B2 phases grow into the matrix. All the evidence suggests that the σ phase nucleates on the planar faults in the matrix, and then B2 phase forms by elemental concentration changes in the matrix caused by growth of the σ phase, forming the aggregate morphology.

Activating dispersed strain bands in tensioned nanostructure layer for high ductility: The effects of microstructure inhomogeneity

How to suppress strain localization in tensioned nanograined layer and make it ductile? This remains a great challenge. Here we explore the effects of microstructure inhomogeneity on the plastic behavior of nanostructured layer. A nanostructured CrMnFeCoNi high entropy alloy layer supported by coarse-grained substrate (in gradient architecture) is taken as an example. In the tensile deformation, strain examinations find that the nanostructure layer experiences significant strain delocalization by activating dispersed stable strain bands (SBs) and promoting the deformation of non-strain banding zone. Finite element analysis reveals that it is the intra-layer microstructure inhomogeneity which enables dispersed SBs nucleation from the mechanical weak sites. The inter-layer microstructure inhomogeneity introduces extra shear constraints from the coarse-grained substrate, which stabilizes SBs and improves the stress of non-strain banding zone, thereby suppressing the early catastrophic strain localization. Importantly, the strong nanostructure layer indeed becomes ductile (enables further work hardening) due to the activation of hierarchical nanotwinning and dislocation activity.

Atomic scale understanding of phase stability and decomposition of a nanocrystalline CrMnFeCoNi Cantor alloy

High entropy alloys (HEAs) provide superior mechanical and functional properties. However, these advantages may disappear when a metastable single-phase solid solution decomposes at low temperatures upon long-term annealing. Therefore, understanding the underlying phase separation mechanisms is important for the design of new HEAs with controlled properties. In the current work, the thermal stability of a nanocrystalline CrMnFeCoNi HEA was investigated at different annealing conditions using a combinatorial processing platform, involving fast and parallel synthesis of nanocrystalline thin films, short annealing time for a rapid phase evolution, and direct characterization by atom probe tomography. The microstructural features of the decomposed CrMnFeCoNi alloy as well as its decomposition process were analyzed in terms of elemental distributions at the near-atomic scale. The results show that the segregation of Ni and Mn to grain boundaries in the initial single-phase alloy is a prerequisite and is observed to be the only occurring physical process at the early stage of phase decomposition. When the concentrations of Ni and Mn reach a certain value, phase decomposition starts and a MnNi-rich phase forms at grain boundaries. Next, two Cr-rich phases form at the interface between the MnNi-rich phase and the matrix. Meanwhile, a FeCo-rich phase forms in the grain interior. Based on these observations, the underlying mechanisms involving nucleation, diffusivity as well as thermodynamic considerations were discussed.

Microstructure-dependent phase stability and precipitation kinetics in equiatomic CrMnFeCoNi high-entropy alloy: Role of grain boundaries

The multi-principal element CrMnFeCoNi alloy, which solidifies as a single-phase solid solution with the face-centered cubic (fcc) structure, is thermally stable above 900 °C but is known to decompose into multiple phases at temperatures between 450 and 800 °C. Although the thermal stability of Cr-Mn-Fe-Co-Ni alloys can be altered by changing the composition, there is limited knowledge of the role of microstructure on the kinetics of precipitation from the supersaturated primary fcc phase. To fill this gap, we compared the thermal stability of monocrystalline and polycrystalline thin films of the equiatomic CrMnFeCoNi alloy during synthesis and after post-deposition annealing. At the processing temperature of 700 °C, the polycrystalline film undergoes substantial phase decomposition in 3 min, consistent with earlier results that a bulk alloy of similar composition decomposes into multiple phases at this temperature. In contrast, the monocrystalline film of the same composition remains single-phase both during synthesis and subsequent annealing at 700 °C for 5 h. X-ray diffraction investigations together with comprehensive transmission electron microscopy analysis revealed that the decomposition of the supersaturated primary phase is related to the presence of structural defects, in particular grain boundaries, which promote diffusion of Cr and Mn and subsequently destabilize the primary solid solution. Correspondingly, the absence of high-diffusivity grain boundaries in the monocrystalline alloy prevents its primary phase from decomposing. The fundamental role of grain boundaries on precipitation kinetics, manifested through the short circuiting of sluggish bulk diffusion in entropy-stabilized multi-principal element alloys, is discussed together with the possibility of controlling their thermal stability by microstructural design.

Microstructure and corrosion properties of laser remelted CrFeCoNi and CrMnFeCoNi high entropy alloys coatings

CrFeCoNi and CrMnFeCoNi coatings were prepared using laser remelting technology. The microstructure and phase composition of coatings were investigated. X-ray diffraction (XRD) results indicated that CrFeCoNi and CrMnFeCoNi coatings presented face-centered cubic structure. Electrochemical measurements were used to reveal the corrosion behavior of coatings. Results showed that CrFeCoNi coating exhibited lower corrosion current density, lower passive current density and higher charge transfer resistance than CrMnFeCoNi coating in H2SO4 solution (0.5 mol/L). This indicated that CrFeCoNi coating possessed higher corrosion resistance. Mott–Schottky analysis revealed that the passive film formed in CrFeCoNi coating possessed lower donor density value in contrast with that of CrMnFeCoNi coating, suggesting that CrFeCoNi coating formed a more protective passive film. The corrosion mechanisms of coatings were also revealed.

CrMnFeCoNi high entropy alloys with carbon and nitrogen: mechanical properties, wear and corrosion resistance

The use of interstitial elements has been a key factor for the development of different kinds of steels. However, this aspect has been little explored in the field of high entropy alloys (HEAs). In this investigation, the effect of carbon and nitrogen in a near-equiatomic CrMnFeCoNi HEA is studied, analyzing their impact on the microstructure, and mechanical properties from 77K to 673K, as well as wear, and corrosion resistance. Carbon and nitrogen are part of the FCC solid solution and contribute to the formation of precipitates. An increase in the yield and ultimate tensile strength accompanied with a decrease in the ductility are the main effects of C and N. The impact toughness of the interstitial-free material is higher than that of C and C+N alloyed systems. Compared to CrNi and CrMn austenitic steels, the wear resistance of the alloys at room temperature is rather low. The surface corrosion resistance of HEAs is comparable to austenitic steels; nevertheless HEAs are more susceptible to pitting in chloride containing solutions.