Behavior Of High-entropy Alloys Research Articles

Effects of annealing and cold rolling on microstructural features, magnetic properties, tensile behavior and electrical resistance of FeCoNi(MnAl)x high entropy alloys

In this study, the microstructure, magnetic properties, and tensile behavior of high entropy alloys of FeCoNi(MnAl)x (x = 0–0.6, in molar ratios) were investigated after casting, cold rolling and annealing. X-ray diffractometry (XRD), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometer (VSM), and also tensile tests were used to evaluate phase formation, microstructure, magnetic behavior and tensile properties of the samples, respectively. The results showed that as the indices of x value increase to 0.6, crystallographic structures transform from FCC to FCC + BCC. This in turn decreased the magnetic saturation of FeCoNi(MnAl)0.6 from 151 to 36 emu/g. Increasing x to 0.6, also raised the values of Hc from 3 to 16 Oe. This behavior was also observed in annealed and cold rolled alloys. Annealing treatment also released the residual stresses and resulted in reduction of Hc values. However, the highest values of Hc was observed in cold rolled samples which ranged from 5 to 25 Oe. The tensile strength of cold rolled and annealed alloys for x values of 0, 0.2, and 0.4, were 510, 635, and 910 Mpa, respectively. Furthermore, the electrical resistance augmented monotonously with an increasing value of x. It is therefore concluded that cold rolled and annealed high entropy alloys of FeCoNi(AlMn)x can present a variety combinations of tensile, magnetic, and electrical behavior when compared to other soft magnetic materials.

Relationship between the unique microstructures and behaviors of high-entropy alloys

Relationship between the unique microstructures and behaviors of high-entropy alloys

Wear and corrosion behavior of high entropy alloys

High entropy alloys are the most recent and advanced class of materials that have drawn the attention of researchers and engineers due to their distinct and unique properties. HEAs are different from conventional alloys due to their different alloying approach as in conventional alloys two or three constituent elements are present whereas, HEAs constitute five or more principal elements in equal proportion as there is no difference between solute and solvent elements. HEAs derived their properties from well-established four core effects. HEAs can play a vital role in industrial applications as they have already proven their better tribological and corrosion resistance than traditional alloys. In this article, we studied different attributes that are crucial in improving wear and corrosion resistance properties.

Corrosion Behavior of High Entropy Alloys and Their Application in the Nuclear Industry—An Overview

With multiple principal components, high entropy alloys (HEAs) have aroused great interest due to their unique microstructures and outstanding properties. Recently, the corrosion behavior of HEAs has become a scientific hotspot in the area of material science and engineering, and HEAs can exhibit good protection against corrosive environments. A comprehensive understanding of the corrosion mechanism of HEAs is important for further design of HEAs with better performance. This paper reviews the corrosion properties and mechanisms of HEAs (mainly Cantor alloy and its variants) in various environments. More crucially, this paper is focused on the influences of composition and microstructure on the evolution of the corrosion process, especially passive film stability and localized corrosion resistance. The corrosion behavior of HEAs as structural materials in nuclear industry applications is emphasized. Finally, based on this review, the possible perspectives for scientific research and engineering applications of HEAs are proposed.

Irradiation hardening behavior of high entropy alloys using random field theory informed discrete dislocation dynamics simulation

High entropy alloys (HEAs) exhibit outstanding radiation resistance over traditional alloys owing to severe lattice distortion, and therefore, would be regarded as candidate materials for advanced reactors. However, the complex evolution of dislocation configurations in the irradiated HEAs subjected to the external loads has not been uncovered at the micron scale. To elucidate this key mechanism, we develop the random field theory informed discrete dislocation dynamics simulations based on high-resolution transmission electron microscopy, to systematically clarify the role of heterogeneous lattice strain on the complex interactions between the dislocation loop and dislocation in three-dimensional (3D) space. The results show that the lattice-strain-induced irradiation hardening decreases, in agreement with the excellent irradiation hardening resistance of the HEAs from the recent experiment. Based on the analysis of the micrometer-scale dislocation multiplication process, a new cross-slip mechanism through the collinear reaction between dislocations and rhombus perfect loops is revealed. The peaks and valleys of the heterogeneous lattice strains induced by severe lattice distortion are randomly distributed in a 3D space, reducing an aggregation of lattice point and dislocation density at the local region. The cross-slip process occurs by the joint action of the lattice distortion and rhombus-perfect-loop dislocation reaction, leading to the strong irradiation resistance attributed to a large number of narrow defect-free channel under a relatively random strain localization. The present study gives an insight into the fundamental irradiation damage behavior at the mesoscopic scale, thereby guiding the development of advanced HEA materials through the regulation of heterogeneous lattice strain for nuclear energy applications.

Corrosion behavior and mechanism of dual phase Fe1.125Ni1.06CrAl high entropy alloy

This investigation explores the corrosion behavior and mechanism of as-cast dual phase Fe1.125Ni1.06CrAl high entropy alloy with low density (6.65 g/cm3) and high hardness (460.67 kgf/mm2) in 3.5 wt% NaCl solution. The microstructure, elemental distribution and corrosion behavior of high entropy alloys before and after the corrosion process were investigated via electrochemical quantitative analysis and then the corrosion mechanism of high entropy alloys was obtained by the first principles and experimental modeling approaches. The results show that quaternary Fe1.125Ni1.06CrAl high entropy alloy display spinodal decomposition microstructure of dual BCC phase with high hardness and distinguished corrosion resistance compared with other established alloys. The self-corrosion current density of 9.262 × 10−9 A/cm2 and corrosion potential of − 0.228 V are gotten for this alloy via potentiodynamic polarization measurements and the calculated parameters of high entropy alloys were analyzed by fitting equivalent circuit. Corrosive pits emerged on the alloy surface when the Fe1.125Ni1.06CrAl and Fe1.125Ni1.125CrAl specimens have experienced preferentially localized corrosion at the areas enriched in Ni and Al characterized by scanning electronic microscope and atomic force microscope. Oxides and hydroxides films of constitutional elements on the alloy surface are formed by X-ray photoelectron spectroscopy analysis, which indicates that corrosion properties of high entropy alloys possess. Chloride anions are easier to be adsorbed and attacked on the BCC2 phase surface based on the adsorption behavior analysis, accelerating the localized pitting and micro-galvanic corrosion processes.

Interface-affected mechanical properties and strengthening mechanisms in heterogeneous high entropy alloy nanolaminates

Introducing heterogeneous interfaces by constructing laminated structure is a promising avenue to achieve the controllable strengthening behavior of high entropy alloys. In this work, the microstructural evolution and mechanical properties of magnetron sputtered Ni/Fe50Mn30Co10Ni10 nanolaminates with equal layer thickness h ranging from 5 to 150 nm were investigated systematically. With reducing h, the nanoindentation hardness of Ni/FeMnCoNi nanolaminates firstly increased and subsequently decreased, emerging a maximum value at the critical h of ~25 nm due to the transformation of constraining barrier for dislocation slipping from the heterogeneous interfaces to columnar grain boundaries. Microstructural observation demonstrated that the interfacial structure of Ni/FeMnCoNi transformed from incoherent to completely coherent at h below ~25 nm, and both the constituent layers made comparable contribution to the plastic deformation of Ni/FeMnCoNi nanolaminates. The strong h-dependent mechanical behavior could be rationalized in terms of the co-deformation of constituent layers and the structural evolution of Ni/FeMnCoNi interface. Additionally, the strengthening mechanisms were discussed based on the confined slip of dislocation within the constituent layers and columnar grains.

Tensile deformation behavior of twist grain boundaries in CoCrFeMnNi high entropy alloy bicrystals

High entropy alloys (HEA) are a class of materials that consist of multiple elemental species in similar concentrations. The use of elements in far from dilute concentrations introduces a multi-dimensional composition design space by which the properties of metallic systems can be tailored. While the mechanical behavior of HEAs has been the subject of active research recently, the role of grain boundaries (GBs) in their deformation behavior remains poorly understood. Motivated by recent experiments on HEAs demonstrating that GBs act as nucleation sites for deformation twins, herein, we leverage atomistic simulations to construct a series of equiatomic CoCrFeMnNi HEA bicrystals with langle 110 rangle and langle 111 rangle symmetric twist GBs and examine their tensile behavior and underlying deformation mechanisms at 77 K. Simulation results reveal that plastic deformation proceeds by the nucleation of partial dislocations from GBs, which then grow with further loading by bowing into the bulk crystals leaving behind stacking faults. Variations in the nucleation stress exist as function of GB character, defined in this work by the twist angle. Our results provide future avenues to explore GBs as a microstructure design tool to develop HEAs with tailored properties.

Laser re-melting influence on isothermal oxidation behavior of electric current assisted sintered CoCrFeNi, CoCrFeNiAl0.5 and CoCrFeNiTi0.5Al0.5 high entropy alloys

In this study, it was aimed to determine the effect of laser re-melting on the oxidation behavior of high entropy alloys produced with electric current assisted sintering (ECAS). CoCrFeNi, CoCrFeNiAl0.5 and CoCrFeNiAl0.5Ti0.5 high entropy alloys (HEAs) were produced using ECAS. After the production of HEAs, the laser re-melting (LR) process was applied to the surface of sintered samples. Then, isothermal oxidation tests were carried out to HEAs at 1000 °C for 5, 25 and 75 h. Before and after the oxidation tests, the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) mapping analysis. The obtained results show that the LR process significantly improved the microstructural properties of ECAS-HEAs. More homogeneous microstructure, lower porosity and single-phase formations were observed in HEAs after LR. This has enabled a more stable microstructure compared to ECAS samples. After the oxidation tests, lower oxide layer thickness, lower oxide growth rates and lower inner oxide formation were obtained in laser re-melted HEAs. The presence of Al-rich phases enables the formation of alumina layer on the surface of HEAs. The best oxidation performance was obtained with laser re-melted CoCrFeNiAl0.5.

Outstanding radiation tolerance and mechanical behavior in ultra-fine nanocrystalline Al1.5CoCrFeNi high entropy alloy films under He ion irradiation

The enhancement of helium ion (He+) radiation tolerance and mechanical behavior of high entropy alloys (HEAs) have triggered significant research interest. In this work, the ultra-fine nano-crystalline Al1.5CoCrFeNi HEA films with single phase structure were prepared, which were irradiated at 300 K with 60 keV He+ in a wide fluence ranging from 1 × 1016 cm−2 to 1 × 1017 cm−2. The effects of ultra-fine nano-crystalline on He evolution behavior, radiation tolerance and mechanical behavior in Al1.5CoCrFeNi HEA films were investigated. The results show that the He clusters preferentially distributed along the grain boundaries (GBs) rather than in grains due to the defect sink effect of nano-GBs. No observable He bubbles were observed in the peak damage region of the films even though the He concentration is up to 8.50 at.% at the fluence of 1 × 1017 cm−2. Some grains with limited irradiation damage keep their stability and integrity by eliminating the irradiated defects at GBs, exhibiting enhanced radiation tolerance in the ultra-fine nano-crystalline HEA film. The dependence of phase stability on the suppression of radiation-induced segregation level owing to the design of ultra-fine nano-crystalline and high lattice distortion was revealed in detail. Moreover, the ultra-fine nano-crystalline HEA films display higher swelling resistance than that of bulk coarse-grained HEA materials by reducing the size of He clusters. Higher relative hardness(H/H0) was observed in the irradiated ultra-fine nano-crystalline HEA film compared to that of the bulk coarse-grained HEA, Finally the relevant hardening mechanisms were also discussed.

Micromechanical modeling of work hardening for coupling microstructure evolution, dynamic recovery and recrystallization: Application to high entropy alloys

A dislocation density-based multiscale constitutive model is developed to describe the hot deformation of high entropy alloys. The work hardening process of high entropy alloy is divided into several stages according to the change of hardening rate. As crystalline material, high entropy alloys are regarded as two-phase materials. In the current study, a physical-based constitutive model with three key microstructural state variables, cell mobile dislocation density, cell immobile dislocation density and wall immobile dislocation density, is proposed to simulate the phases deformations. The physical mechanisms including strain hardening, dynamic recovery, and recrystallization are considered in describing the evolution of dislocation densities. It is noted that the competition and interaction among the three mechanisms result in a typical hardening behavior of high entropy alloys. The dislocation density-based constitutive model is embedded in the modified Mori-Tanaka scheme to describe the hardening behaviors of two-phase materials with an elastic phase cell wall and an elastic-inelastic phase cell interior. The model is applied for simulating the hardening curves of CoCrFeMnNiC0.5 high entropy alloy at different temperatures and strain rates. Compared with experimental data, it shows that the developed model can describe hot deformation of high entropy alloys with reasonable accuracy. The macroscopic inelastic strain in the Mori-Tanaka scheme is calculated by a classical plasticity method. The simulation results show that the modified method can give a more accurate prediction compared to the average inelastic strain of all phases.

Influence of ZnO nanoparticles on the microstructure of a CoCrFeMoNi matrix via powder metallurgy

In the last decade, extensive research has been carried out on the microstructural behavior of high-entropy alloys (HEA), for which the in-situ formation of nanoparticles has been reported. However, studies of the incorporation of nanoparticles in HEA have been rarely reported. In this work, the addition of zinc oxide nanoparticles (ZnO NP) as reinforcement in a CoCrFeMoNi high-entropy alloy matrix, as well as the morphological, structural, and microstructural evolution of composites synthesized via powder metallurgy, were studied. Scanning electron microscopy and X-ray diffraction analysis were performed in order to study the microstructural and phase characterization of the composites. After sintering, it was found that the ZnO NP addition (0.5wt%, 1wt% and 2wt%) had a significant influence on the micro-structure and hardness of the CoCrFeMoNi high-entropy alloy. Stronger bonding among metal particles was promoted with the additions of ZnO NP. A reduction in porosity as a function of ZnO NP content was also observed. The microhardness results showed that the composite reached its highest reinforcement in bulk samples with 1wt% ZnO NP (HV 870), which represented a 20% improvement over the unrein-forced HEA matrix.

Nanoindentation behavior of high entropy alloys with transformation-induced plasticity

Nanoindentation of three metastable dual-phase high entropy alloys (HEAs) was performed to obtain their inherent elastoplastic deformation responses. Excellent combination of hardness and elastic modulus in as-cast condition confirmed that, their inherently higher strength compared to other HEAs reported in literature, can be attributed to alloy chemistry induced phase stability. Further, hardness of 8.28 GPa combined with modulus of 221.8 GPa was obtained in Fe-Mn-Co-Cr-Si-Cu HEA by annealing the as-cast material, which is the best hardness-modulus combination obtained to date in HEAs from nanoindentation. On the other hand, although Fe-Mn-Co-Cr-Si HEA showed lower hardness and modulus than Fe-Mn-Co-Cr-Si-Al and Fe-Mn-Co-Cr-Si-Cu HEAs, the former alloy exhibited the highest strain rate sensitivity, as determined from tests performed at five different strain rates. The three alloys also had subtle differences in incipient plasticity and elastoplastic behavior, while retaining similar levels of hardness; and nanoindentation response showed microstructural dependence in friction stir processed, annealed and tensile-deformed specimens. Thus, the study highlighted that while higher strength was achieved by designing a class of HEAs with similar composition, any of the individual alloys can be tuned to obtain enhanced properties.

Influence of Al content on high temperature oxidation behavior of AlxCoCrFeNiTi0.5 high entropy alloys

Studies on the oxidation behavior of high entropy alloys (HEAs) from the AlxCoCrFeNiTi0.5 (x = 0.5, 1.0, 1.5) metallic systems are conducted. In this work, the alloys are synthesized using arc-melting method, and the microstructure, anti-oxidant properties and oxidation products of the alloys at 700 °C, 900 °C and 1100 °C up to 100 h have been studied. The main substrate phases constitution in the arc-melted AlxCoCrFeNiTi0.5 HEAs was inter-dendritic FeCr-rich BCC1 and dendritic FeCr-poor BCC2 phases. With the increase of Al content, the fraction of the BCC2 phase increases while the BCC1 phase decreases, meanwhile the formation of FCC and σ inter-metallic phases are suppressed. At 700 °C −1100 °C, all alloys exhibit initial transient oxidation followed by various degrees of parabolic oxide growth; the Al1.5CoCrFeNiTi0.5 alloy exhibits excellent oxidation resistance because a continuous compact layer of (Al0.9Cr0.1)2O3 oxide films are produced on the alloy surface. The Kp values for the Al1.5CoCrFeNiTi0.5 alloy oxidized at 1100 °C for 100 h can be up to about 1.03×10−12 g2cm−4s−1.

Deformation Behavior of Bulk Metallic Glasses and High Entropy Alloys under Complex Stress Fields: A Review.

The plastic deformation of bulk metallic glasses (BMGs) depends significantly on applied stress states, and more importantly, in practical applications of BMGs as structural materials, they always deform under complex stress fields. The understanding of deformation behavior of BMGs under complex stress fields is important not only for uncovering the plastic deformation mechanisms of BMGs, but also for developing BMG components with excellent mechanical performance. In this article, we briefly summarize the recent research progress on the deformation behavior of BMGs under complex stress fields, including the formation and propagation of shear bands, tunable macroscopic plasticity, and serrated plastic flows. The effect of complex stress fields on the plastic deformation mechanisms of BMGs is discussed from simple stress gradient to tailored complex stress fields. The deformation behavior of high entropy alloys (HEAs) under complex stress states has also been discussed. Challenges, potential implications and some unresolved issues are proposed.

Corrosion Behaviour in Human Stimulation Media of a High Entropy Titan-Based Alloy

The paper presents results on the corrosion behavior of high entropy alloys, commonly called BIOHEA in human physiological simulating media, respectively in the NaCl infusion solution and Ringer’s lactate infusion solution. Corrosion tests were performed by potendiodinamic test using AUTOLAB type potentiostat equipped with specialized corrosion software including the PGSTAT302N, BA and SCAN250 modules. Three entropy alloy systems were investigated: FeTa0.5Nb0.5Ti1.5Zr0.5 (BIOHEA 1), FeMnNb0.5TiZr0.5 (BIOHEA 3), FeTa0.5Nb0.5TiZr0.5 (BIOHEA 4), and BIOHEA alloy 2 was obtained by remelting BIOHEA 1. A comparison of the results obtained in the present tests and the data from the literature shows, on the one hand, that the global results can be compared with the different results from the literature, and, on the other hand, the results are new, in the sense that in any work there are no combinations of alloys studied here or human simulating medians used for testing. The conclusion of the experimental investigations in the present paper is the fact that regardless of the simulation test environment, all the alloys experimental alloys have similar behaviors, there is a difference between the chemical composition of the experimental alloy and the displacement of the corrosion potential values at electropositive values, decreasing of corrosion current, and corrosion rates. The experimental results allow the corrosion resistance of the investigated alloys, alloy BIOHEA 2 having the best corrosion behavior in both test media, with very low corrosion rates (respectivelly 0.067 μm/year in NaCl infusion solution, and 0.021 μm / year in Ringer’s lactate infusion solution).

Reciprocating sliding wear behavior of high entropy alloys in dry and marine environments

The reciprocating sliding wear behavior of two high entropy alloys, CoCrFeMnNi and Al0.1CoCrFeNi, was evaluated in dry and marine environments. Both the alloys showed better wear performance in marine environment as compared to dry condition, indicating negative synergy of wear and corrosion. Al0.1CoCrFeNi was more wear resistant compared to CoCrFeMnNi in both environments. Accelerated electrochemical corrosion tests were carried out to quantify the effect of passive layer on marine wear behavior. Al0.1CoCrFeNi showed lower corrosion rate, higher pitting resistance and greater degree of passivation. A strong correlation was found between the electrochemical polarization resistance and wear resistance.

Effect of temperature on wear behavior of high-entropy alloys

The wear behavior of a FeCoNiCrMn (counterbody)–Ti30Zr25Hf15Nb20Ta10 (finger) friction pair in the temperature range of 77–873 K has been determined. It has been found out that the finger wear significantly decreases with an temperature increase compared with the counterbody due to the spur increase in the hardness of the friction surface structures of up to 18.0 GPa due to the formation of a high-temperature oxide. It has been revealed that the depth of secondary structures increases with temperature, while at 523 K and higher, it reaches 40 μm.

Wear behavior of high entropy alloys containing soft dispersoids (Pb, Bi)

Intrinsic high entropy alloys (HEAs) exhibit superior mechanical properties (hardness, strength, ductility, toughness etc.) and hence, they are considered as potential candidates for wear resistance applications. Wear resistance of HEAs can further be improved by engineering microstructure using various novel design concepts. One of such concepts involves the usages of soft dispersoids (Sn, Pb, Bi, Sb etc.) in the HEA matrix. However, the challenge is to engineer the novel microstructure consisting of soft dispersoids, dispersed uniformly in the HEA matrix, using suitable processing techniques. In this connection, the present work reports the effect of soft dispersoids, such as Pb and Bi on the wear behavior in equiatomic CuCrFeTiZn and AlCrFeMnV HEAs. The alloys containing Pb and Bi were synthesized using mechanical alloying (MA) followed by spark plasma sintering (SPS) in inert argon atmosphere. Phases and microstructure of milled powder and sintered alloys were investigated using XRD, SEM equipped with EDS. Sliding wear tests were also carried out for all the sintered samples at 2N, 5N, 7N and 10N load for various sliding speeds. Wear results indicate coefficient of friction (COF) does not vary much with varying the Pb concentration in HEAs. However, wear rate decreases significantly with increasing the Pb content in the alloys. For HEAs containing Bi, there is considerable decrease in the COF as well as in the wear rate even for a lower (5%) Bi content. Increasing load does not cause any change in the COF in both cases. However, wear rate decreases substantially due to increase of load. In addition, SEM analysis of the worn surface and wear debris were performed and it has been found that oxidative wear is the dominant wear mechanism in these systems. However wear tracks indicate the presence of abrasive wear. Analysis of Raman spectroscopy of wear debris confirms the presence of Fe2O3, Bi2O3 and PbO.

Influence of Cu content on high temperature oxidation behavior of AlCoCrCuxFeNi high entropy alloys (x = 0; 0.5; 1)

Studies on the oxidation behavior of high entropy alloys from the Al-Co-Cr-Cu-Fe-Ni metallic system were conducted. Three different high entropy alloys were synthesized using arc-melting method: AlCoCrFeNi, AlCoCrCu0.5FeNi and AlCoCrCuFeNi, with their crystal structures being respectively BCC, BCC and BCC + FCC. All alloys were oxidized in the air atmosphere at temperature of 1273 K for different time periods. Basing on the thermogravimetric result, the oxidation rate of the materials decreased with the increase of Cu content and the values of parabolic constants were on the level similar to those observed in Ni-Al intermetallic alloys. In all cases the oxide scale consisted of α-Al2O3, which exhibited poor adhesion to the surface during the cooling process, what was especially visible in alloys with Cu addition. In all oxidized samples a tendency towards formation of the Al-depleted FCC phase directly beneath the scale was observed. The phase constitution of all materials changed significantly during the oxidation process, with multiple new phases appearing in the system.