CoCrCuFeNi High-entropy Alloy Research Articles

Thermophysical properties of AlxCoCrCuFeNi high entropy alloys

The AlxCoCrCuFeNi (x = 0.25, 0.5, 1, 2) high entropy alloys (HEAs) were prepared by arc melting and spray casting techniques. Their microstructures, hardness, and thermophysical properties such as fusion enthalpy, entropy, thermal diffusion coefficients, thermal expansion coefficients, were investigated. XRD results indicated that AlxCoCrCuFeNi (x = 0.25 and 0.5) alloys were composed of a high-entropy FCC phase and Cu-rich nanophase. As the Al content increased to 1 and 2, the phase structures included the AlNi-rich B2 phase, FeCr-rich A2 phase and Cu-rich nanophase. With the increased Al content, the microstructures of AlxCoCrCuFeNi HEAs transitioned from coarse dendrites to petal-like dendrites, and the grains were continuously refined. Moreover, the Al additions reduced the density whereas increased the Vickers hardness of the alloys. The maximum hardness observed in Al2CoCrCuFeNi HEA was approximately 2.4 times greater than that of the Al0.25CoCrCuFeNi HEA. The thermal diffusion coefficients of alloys initially increased and subsequently decreased as the temperature elevated. The phase transformation induced by Al content was an effective method for rapidly homogenizing the internal temperature of alloys. Furthermore, the crystal structure, elemental segregation, lattice distortion, enthalpy and entropy of fusion, and lattice vibration frequency all mutually affected the thermal diffusion and expansion coefficients of AlxCoCrCuFeNi HEAs.

Microstructure evolution and mechanical properties of diffusion bonding CoCrCuFeNi high entropy alloy to Inconel 600 alloy

In this study, the CoCrCuFeNi high entropy alloy was diffusion bonded with the Inconel 600 superalloy at bonding temperatures ranging from 950 to1100 °C for a bonding time of 2h under a pressure of 20 MPa in a vacuum. The microstructure and mechanical properties of the diffusion bonded joints were investigated. The diffusion zone of the welded joint contains of two distinct zones: a coarse grain zone (on the Inconel 600 superalloy side) and the diffusion interface layer. The blocks Cr23C6 phase and Cu-rich phase were formed in the diffusion interface layer at 950 °C. As the bonding temperature increased, the Cr23C6 gradually disappeared and the blocks Cu-rich phase transformed into nano Cu-rich precipitate in the diffusion interlayer at 1100 °C. The hardness of the interface layer was significantly higher than that of the base metal at all temperature. When the bonding temperature increased from 950 °C to 1100 °C, the ultimate tensile strength of the welded joints increased from 521 MPa to 558 MPa, and the elongation increased from 10.3 % to 31.2%, respectively. The ultimate tensile strength reached 96 % and 82 % than that of the CoCrCuFeNi HEA and Inconel 600 base metal, and the elongation is comparable to that of the base metals. All the welded joint fracture near the diffusion interface layer. As the bonding temperature increased, the fracture mode of the joint transformed brittle to ductile. At an elevated temperature of 300 °C, the ultimate tensile strength and elongation of the welded joint are 325 MPa and 9.8 %, respectively. The welded joint exhibits a mixed fracture mode of ductile and cleavage fractures.

Microstructure and Mechanical Properties of Nanocrystalline CoCrCuFeNi High-Entropy Alloy Coating Manufactured by Atmospheric Plasma Spraying

Microstructure and Mechanical Properties of Nanocrystalline CoCrCuFeNi High-Entropy Alloy Coating Manufactured by Atmospheric Plasma Spraying

Simultaneous enhancement of strength and ductility of Al matrix composites enabled by submicron-sized high-entropy alloy phases

Our study investigated the reinforcing effect of submicron-sized (100–500 nm) Al0.5CoCrCuFeNi high-entropy alloy particles (HEAps) on the tensile properties of Al matrix composites. The HEAps were refined to the submicron-sized level via a thermal plasma process to maximize reinforcing efficiency by increasing specific surface (i.e., interface) area. The Al/HEA composites were produced by hot rolling of mechanically milled Al/HEA composite powder. The microstructural analysis demonstrated that the HEAps were uniformly dispersed within the Al matrix by forming a sound interface without interdiffusion brittle intermetallic layers or any noticeable voids. Moreover, the addition of 2 vol% HEAps resulted in a simultaneous increase in both yield strength from 355 to 403 MPa and tensile elongation from 1.3 to 3.3%. As a result, the composite experienced a synergistic effect due to the combination of intrinsic strengthening to promote uniform plastic deformation and extrinsic strengthening to mitigate plastic instability and crack propagation.

SUPERIOR ANTIBACTERIAL PROPERTIES OF COPPER-BEARING HIGH ENTROPY ALLOY COATED STAINLESS STEEL SURFACE FABRICATED USING LASER CLADDING

A high-entropy alloy (HEA) coating is applied to a stainless-steel surface using the laser cladding (LC) process. This coating offers a broad-spectrum antibacterial ability and favorable mechanical properties. The release of copper ions from the HEA effectively inhibits the growth of Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), enhancing the alloy’s suitability for various applications requiring antibacterial properties. The elemental compositions, sizes, and morphologies of the constructed HEAs are revealed through X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). This study validates the feasibility of applying the antibacterial CoCrFeCuNi HEA alloy coating to stainless steel via LC. The antibacterial evaluation showcases the enhanced efficacy of the CoCrCuFeNi HEA coating, demonstrating an antibacterial effectiveness of approximately 89% against E. coli and 98% against S. aureus. In contrast, the CoCrFeNi HEA coating exhibits an antibacterial effectiveness of about 40% against E. coli and 93% against S. aureus. The Vickers hardness of the stainless steel coated with CoCrCuFeNi HEA has significantly increased to 352 HV, compared to the CoCrFeNi coating with a hardness of 300.6 HV and the uncoated stainless steel with a hardness of 256.6 HV. This HEA alloy demonstrates considerable potential for use in medical applications or other settings that require antibacterial features.

AlxCoCrCuFeNi (X = 0, 0.8) high entropy alloys fabricated by laser powder bed fusion

ABSTRACT The AlxCoCrCuFeNi (x = 0, 0.8) high entropy alloys (HEAs) were prepared by laser powder bed fusion (LPBF), and the effects of volumetric energy density (VED) and heat treatment on microstructures and mechanical properties of HEAs were investigated. The results show that the CoCrCuFeNi HEA has a single FCC phase structure and exhibits good ductility. Its yield strength is relatively low, being 520 MPa. After the alloy composition was adjusted from CoCrCuFeNi to Al0.8CoCrCuFeNi, the HEA changed from FCC single-phase to FCC + BCC dual-phase structure and the hardness and compressive properties were significantly improved. Among them, the Al0.8CoCrCuFeNi HEA prepared with the VED of 167 J/mm3 has the best mechanical properties, with a compressive yield strength of 652 MPa and good plasticity. After annealing at 600°C and 900°C for 1 h, the mechanical properties of HEAs are significantly improved. In particular, the microhardness and compressive yield strength of the Al0.8CoCrCuFeNi HEA annealed at 600°C for 1 h are 378 HV and 810 MPa, respectively. The coordinated deformation between FCC and BCC domains, back stress strengthening, solid solution strengthening and precipitation strengthening after heat treatment make the Al0.8CoCrCuFeNi HEA achieve a balance of high strength and good ductility.

Atomistic study of CoCrCuFeNi high entropy alloy nanoparticles: Role of chemical complexity

High entropy alloy nanoparticles are envisaged as one of the most interesting materials compared to monoatomic materials due to their modulated properties in terms of their convenient surface-to-volume ratio. However, studies are still missing to unveil how composition or nanoparticle size can influence nanoparticle morphology. Based on molecular dynamics simulations, we perform a structural characterization as a function of nanoparticle size and the chemical composition of high entropy alloy nanoparticles subject to multiple annealing cycles. After the multiple thermal loads, we observe a substantial migration of copper atoms towards the np surface, consistent with the experimental results of Cu-based high entropy alloys. The resulting high entropy alloy nanoparticle behaves as a core–shell nanostructure with a rich fcc phase on the surface (50% of Cu) and 5% fcc phase in the nanoparticle core. Inspecting the nanoparticle surface, it is observed that high entropy alloy nanoparticles have a lack of surface facets, leading to a more spherical shape, quite different from mono-metallic nanoparticles with a high number of facets. Performing an average atoms simulation, it showed that nanoparticles are prone to form 111 surface facets independent of the nanoparticle size, suggesting that for high entropy alloy nanoparticles, the chemical complexity avoids the formation of surface facets. The latter can be explained in terms of the lattice distortion inducing tensile/compressive stress that drives the surface reconstruction. All in all our results match extremely well with experimental evidence of FeNiCrCoCu nanocrystalline materials, explaining the Cu segregation in terms of surface energy and mixing enthalpy criteria. We believe that our results provide a detailed characterization of high entropy nanoparticles focusing on how chemical complexity induces morphological changes compared to mono-crystalline nanoparticles. Besides, our findings are valuable for experimental works aimed at designing the shape and composition of multicomponent nanoparticles.

Effect of Silver Addition on Microstructure, Phase Composition, Microhardness and Surface Oxide Layer Formation of Al0.5CoCrCu0.5FeNi and Al0.5CoCrCuFeNi High-Entropy Alloys

Effect of Silver Addition on Microstructure, Phase Composition, Microhardness and Surface Oxide Layer Formation of Al0.5CoCrCu0.5FeNi and Al0.5CoCrCuFeNi High-Entropy Alloys

Interfacial coherence regulation and stabilization of molybdenum/Kovar alloy welded joint by CoCrCuFeNi high entropy alloy

The crux of molybdenum/Fe-base alloy welded joint is embrittlement and consequently deteriorated strength. The current researches just attribute it to brittle intermetallic compound inside the weld. However, no brittle phase continuously precipitates at the fracture location of the molybdenum/Kovar alloy electron beam welded joint, meaning that the unstable phase interface is the real fundamental reason for the brittleness of joint, instead of the phases themselves. Noncoherent interfaces are formed between α-Mo and eutectoid α-Fe + μ(Fe3Mo2) deriving from solid-state phase transition. To optimize interfacial coherence and stabilize the interface, CoCrCuFeNi high entropy alloy is added into the weld. The new interfaces between α-Mo and eutectic face-centered cubic (fcc) + laves are transformed into coherent interfaces. σ(FeCr) nanoparticles precipitate at α-Mo/fcc interface, indicating the decreased interfacial energy and more stable interface. The tensile strength of the joint is increased from 262 to 366 MPa. The present work provides guidance for optimizing welding quality between molybdenum and Fe-base alloy.

The Effect of La on the Surface Properties of Plasma Nitrided CoCrCuFeNi High-Entropy Alloys at 440 Degrees Celsius

This paper investigates the effect of the element La on plasma nitriding of the CoCrCuFeNi high-entropy alloy (HEA) at 440 °C for 8, 16, and 24 h. The phase composition, morphology, and hardness distribution of the nitrided layer are characterized using XRD, optical microscopy, and a microhardness tester. Furthermore, the corrosion resistance is tested using an electrochemical workstation. The study evaluated the friction and wear performance using a testing machine and scanning electron microscope. The thickness of the effective hardening layer after 16 h of treatment with La was similar to that after 24 h of treatment without La. The addition of La significantly increased the growth rate constant of the effective hardening layer from 0.53 × 10−14 m2/s to 0.72 × 10−14 m2/s. In addition, an expanded FCC phase with greater interplanar spacing can be formed on the surface of the sample by introducing La into the plasma nitriding process. This indicates that the expanded FCC phase, with a higher concentration of interstitial nitrogen atoms, can effectively improve the corrosion resistance of the specimen surface. The corrosion rate of the specimen surface was reduced by 27.5% and the wear rate was reduced by 41.7% after 16 h of treatment with the addition of La compared to 24 h of nitriding without the addition of La. It has been shown that the addition of La to the plasma nitriding process results in a higher quality nitrided layer in a shorter time and also demonstrates that La has the potential to optimize the surface properties of plasma nitrided HEAs.

Metastable phase separation and crystalline orientation feature of electromagnetic levitation processed CoCrCuFeNi high entropy alloy

The metastable liquid phase separation and rapid solidification kinetics of CoCrCuFeNi high entropy alloy (HEA) has been investigated by electromagnetic levitation (EML) technique. The maximum liquid undercooling attained 452 K (0.27TL), and the critical undercooling to initiate phase separation was determined as 172 K. By modulating the degree of alloy undercooling, the overall macrosegragation pattern achieved a transition from homogeneous dendrites into dispersed structures and finally into core-shell structures. Both microstructure and electron backscatter diffraction (EBSD) characterizations revealed that liquid undercooling played a crucial role in the modulation of dendritic anisotropy correlated with crystalline orientations. Coarse high entropy face-centered cubic (HEF) dendrites were produced with 〈100〉 preferred orientation at small undercoolings. Once undercooling exceeded the threshold of 172 K, the previously uniform liquid alloy was separated into Cu-depleted and Cu-rich zones. Numerous equiaxed HEF grains of relatively random orientation together with some twin crystals were displayed in Cu-depleted zone, whereas in Cu-rich zone HEF phase solidified into many slender dendrites. Theoretical analyses indicated that equiaxed grains were produced in the regime of thermal diffusion-controlled dendritic growth with actual solidifying velocity up to 42.7 m s−1. Furthermore, physical properties examinations demonstrated that large liquid undercoolings enhanced the alloy microhardness and low temperature saturated magnetization but reduced its electrical resistivities.

Impact of edge dislocation and grain boundaries on mechanical properties in CoCrCuFeNi high entropy alloy

This study uses molecular dynamics simulations to explore the mechanical behavior of a CoCrCuFeNi high-entropy alloy (HEA) with Σ5 and Σ13 grain boundaries (GBs) as well as without GBs and dislocation. The analysis focused on understanding the influence mechanisms of these grain boundaries on the mechanical behavior of the HEA. Our findings reveal that the atomic size disparity among the constituent elements induces lattice distortion, leading to deformation in HEAs. The determined elastic constants met Born stability requirements, ensuring mechanical stability across both the examined GBs. Higher elastic moduli were associated with increased strength and stiffness, particularly evident in HEAs with Σ5 GB, surpassing those of non-GB structures. Notably, GB Σ5 demonstrated enhanced strength and hardness, indicated by larger elastic moduli compared with those of non-GB structures. Conversely, GB Σ13 exhibited increased Cauchy pressure and Poisson and Pugh's ratios. The ductility of face-centered cubic HEAs was found to be significantly influenced by the GBs, affecting mechanical properties. The Kleinman parameter highlighted a bending-type bonding with reduced strength at the GBs. Machinability indices indicated high machinability of the CoCrCuFeNi alloy, further enhanced by the presence of the GBs. Direction-dependent parameters underscored the anisotropic nature of the HEA, mitigated by the GBs. Overall, this study elucidates the nuanced influence of different GBs on the mechanical properties of HEAs, offering valuable insights for materials design and applications. The results of this investigation shed light on HEAs with improved mechanical properties via GB engineering.

Modeling of the Flow Field and Clad Geometry of a Molten Pool during Laser Cladding of CoCrCuFeNi High-Entropy Alloys

A flow field analysis was performed in this research using the ANSYS Fluent module, and a dynamic heat source employing UDF was constructed using the DEFINE_PROFILE macro. A VOF model was developed to track the volume fraction of each fluid throughout the computational domain as well as the steady-state or transient condition of the liquid–gas interface in the free liquid surface area. To determine the distribution state and regularity of the molten pool flow field, the flow field velocity was calculated iteratively by linking the Simple algorithm with the horizontal set method. The molten pool was concave, indicating that the key hole was distributed narrowly. Inserting cross-sections at different depths yielded the vector distribution of the molten pool flow velocity along the depth direction. We set up monitoring sites along the molten pool’s depth direction and watched the flow change over time. We investigated the effects of the process parameters on the flow field’s vector distribution.

Elucidating the warm compression of CoCrCuFeNi high entropy alloy: Modeling and microstructural evolution

The warm compression tests were carried out at various temperatures of 400, 550, and 700 °C and strain rates of 0.01, 0.001, and 0.0001 s−1 to unravel the warm deformation behavior of CoCrCuFeNi high entropy alloy (HEA). The microstructural evolutions were characterized using x-ray diffraction (XRD), differential scanning calorimetry (DSC), a field emission gun scanning electron microscope (FESEM) equipped with energy dispersive spectroscopy (EDS), and electron backscattered diffraction (EBSD) detector. These microstructure studies show a dendritic structure containing a bright phase rich in Cu and a darker phase rich in Fe, Cr, and Co. The solidification and melting points of the bright phase are 1136 °C and 904 °C, respectively and the dark phase nucleates at 1365 °C based on DSC results. A Zener-Hollomon parameter was employed to model and predict the warm compression behavior by calculating the activation energy (∼451 kJ/mol), developing a precise constitutive equation (correlation coefficient: R = 0.99), and constructing a processing map for determining the stable temperature and strain rate (strain rates lower than 10−2.75 s−1 and temperatures between 400 and 700 °C) of the plastic flow behavior of the alloy. The FESEM results confirmed the stability and instability domains predicted by the processing map. Moreover, the EBSD analysis indicated that the continuous dynamic recrystallization (CDRX) grains nucleated in the strain rate of 0.0001 s−1 at temperatures higher than 400 °C. Larger grains were formed at 550 and 700 °C due to lower Z parameters in higher temperatures.

High-Temperature Oxidation Behaviour of High Entropy Alloys

High-temperature operation, such as in gas turbine engines, is typically limited by the ability of materials to withstand extreme operating conditions. The need for a combination of high-temperature strength and oxidation resistance, as well as microstructural stability, has led to the continued use of nickel-based superalloys as materials for turbine blades, the most critical component in aero gas turbine engines. Due to their limited melting points, materials beyond superalloys are needed to meet increasing fuel efficiency requirements. High entropy alloys have recently been considered as candidates for materials to replace nickel-based superalloys. This paper discusses the microstructures and high-temperature oxidation behavior of Al0.75CoCrCuFeNi high entropy alloy at 900, 1000, and 1100°C. It was found that the oxidation rate constants for Al0.75CoCrCuFeNi oxidized at 900, 1000, and 1100°C are 3.84 x 10-10, 5.99 x 10-10, and 8.97 x 10-10 (mg/cm2.s), respectively, with an activation energy for oxidation of 66.58 kJ/mol.

Microstructure and Mechanical Properties of CoCrCuFeNi High-Entropy Alloys Synthesized by Powder Metallurgy and Spark Plasma Sintering

Microstructure and Mechanical Properties of CoCrCuFeNi High-Entropy Alloys Synthesized by Powder Metallurgy and Spark Plasma Sintering

Molecular dynamics simulation of tension and compression deformation behavior in CoCrCuFeNi high-entropy alloy: Effects of temperature and orientation

This study utilizes molecular dynamics (MD) simulations to investigate the uniaxial tensile and compressive deformation behavior of the face-centered cubic (FCC) CoCrCuFeNi high-entropy alloy (HEA) with varying orientations at different temperatures. The results indicate that the material experiences temperature-induced softening in all simulation cases. In addition, it has been observed that the mechanical properties of the CoCrCuFeNi HEA exhibit orientation dependence and tension-compression asymmetry. Analysis of the Schmid factor of the leading and trailing partial dislocations suggests that the yield asymmetry is contingent upon the leading Schmid factor asymmetry. Microstructure evolution analysis and quantitative statistics of deformation defects indicate that the plastic deformation mechanisms of uniaxial tensile deformation along the [001], [111], and [112] orientations and compressive deformation along the [110], [111], and [112] orientations can be characterized by the formation and annihilation of intrinsic stacking fault (ISF), extrinsic stacking fault (ESF), and a few twins resulting from the gliding of Shockley partial dislocations. Twins play a crucial role in compression along the [001] direction and tension along the [110] direction due to the proliferation of twin boundaries (TBs)-assisted dislocations. The interactions between stacking faults (SF) and abundant TBs cause an increase in dislocation density in the later stage of plastic deformation in the aforementioned models. A comparison with low-entropy materials and theoretical calculations reveals that alloying reduces the stacking fault energy (SFE) of the CoCrCuFeNi crystal and enhances its twinnability.

Friction stir welding of AA5010 aluminum alloy to St-12 carbon steel using CoCrCuFeNi high entropy alloy interlayer

Dissimilar friction stir welding (FSW) of AA5010 aluminum alloy to St-12 carbon steel using an equiatomic CoCrCuFeNi high-entropy alloy (HEA) interlayer was investigated. Mechanical properties of the joints fabricated under different plunge depths of the FSW tool were examined and correlated to microstructural evolutions. The incorporation of the HEA interlayer successfully prohibited the formation of AlFe intermetallic compounds (IMCs). Also, the interlayer was metallurgically consistent with both base metals, although quite thin complex IMC layer was formed at the aluminum/HEA interface as a result of sluggish diffusion of constituent elements of HEA towards the aluminum. The application of suitable plunge depth in the steel part, i.e. 0.2 mm, resulted in the perturbation of the HEA/steel interface and then the formation of interfacial mechanical interlocks that were beneficial to the strength of the joints. However, excessive FSW tool plunge depth caused large voids to form near hooks, acting as stress concentration areas during shear-tensile test. An appropriate plunge depth of the tool achieved an ideal joint that exhibited fracture from the aluminum side rather than the joint interfaces. It also provided a strength value as high as 80 % of the nominal strength of aluminum base metal.

The effect of grain boundary on irradiation resistance of CoCrCuFeNi high entropy alloy

Defect traps have been well known to influence the irradiation resistance of traditional structural materials, but to what extent is not fully clear for high entropy alloys. Herein, the effect of grain boundary on irradiation resistance of CoCrCuFeNi is investigated through defects capture, strength variation, and void annihilation via molecular dynamics simulations and compared to that of pure Ni, taking ∑5(210) as a representative grain boundary. The grain boundaries in both CoCrCuFeNi and Ni are effective in capturing point defects. The number of captured defects is related to the distance between primary knock-on atoms and grain boundary. The change in tensile stress of CoCrCuFeNi after irradiation is smaller than that of Ni. The grain boundary of CoCrCuFeNi can annihilate voids at room temperature. However, that of Ni is hindered in the migration process and cannot annihilate voids completely. Our results provide atomistic insights into the mechanism of radiation resistance via grain boundaries as recombination centers.

Real-time atomic deformation behavior of nano CoCrCuFeNi high-entropy alloy

Tensile tests were performed by molecular dynamics at various strain rates ranging from 2×108 to 1×1010 s−1 and various temperatures ranging from 10 to 1200 K, and the real-time deformation behavior of a nanocrystalline CoCrCuFeNi high-entropy alloy was investigated. The results indicate that the main deformation mechanism is grain boundary slip at high temperatures and low strain rates. Dislocation slip replaces grain boundary slip to control plastic deformation with decreasing temperature and increasing strain rate, correspondingly enhancing the strength of the alloy. Furthermore, the alloys with different grain sizes were simulated to evaluate the effects of grain boundaries on the mechanical behavior. It is found that the strength of the nanocrystalline high-entropy alloys increases with increasing grain sizes when the grain size is too small, exhibiting an inverse Hall—Petch relationship.