CrMnFeCoNi High-entropy Alloy Research Articles

Microstructure and corrosion properties of CrMnFeCoNi high entropy alloy coating by temperature field-assisted laser cladding

The CrMnFeCoNi high entropy alloy coatings were prepared on the surface of Q345 steel using a temperature field-assisted laser cladding process, and the effects of the applied temperature field on the cladding coatings were studied. The microstructures and corrosion morphologies of the coatings were observed, and the elemental distribution, hardness, effective elastic modulus, electrochemical corrosion performance, and corrosion products of different coatings were analyzed. The results show that the porosity of the HEA coatings prepared with a temperature field is reduced to below 50 % of the initial level. The microstructure of the coating changed, with the nanoindentation hardness of the coating increasing by up to 0.55 GPa, enhancing the mechanical properties. Among all the coatings, the coating prepared at 250 °C temperature field exhibited the best corrosion resistance, with corrosion potential and current density of −0.27 V and 0.15 μA/cm2, respectively, improving the corrosion potential by 0.1 V and reducing the current density by 1.08 μA/cm2 compared to the sample prepared at room temperature. After incorporating the temperature field, the stability of the passive film on the coating during corrosion improved, and the nucleation rate of pitting decreased. Therefore, incorporating an appropriate temperature field during laser cladding can effectively enhance the overall performance of the CrMnFeCoNi HEA coating.

Nanosecond pulsed laser coloring of the CrMnFeCoNi high entropy alloy

High-entropy alloys (HEAs) possess great potential for applications in the aerospace and military fields due to their excellent performance. Surface coloring can endow HEAs diverse functions. However, achieving a multi-color surface with minimal surface damage and cost remains a significant challenge. In this study, surface coloring of the CrMnFeCoNi HEA was attempted by nanosecond pulsed laser irradiation in air, and the multi-color surface was achieved. The evolution of surface color and morphology with laser parameters was analyzed. Then, five typical colors were selected, and the corresponding morphologies and chemical compositions were characterized by various techniques. The results showed that the change in oxide layer thickness as well as the formation of chromium-rich β-spinel and Cr (VI) compounds induced noticeable changes in surface color. Accordingly, complex surface patterns with various stable colors were prepared on the HEA surface, demonstrating the potential application of nanosecond pulsed laser coloring of HEAs.

A comparative study on nanoscale mechanical properties of CrMnFeCoNi high-entropy alloys fabricated by casting and additive manufacturing

Additive manufacturing (AM) has emerged as a pioneering method for fabricating high entropy alloys (HEAs), yet a comprehensive comparison of their nanoscale mechanical properties with those produced by the conventional casting method remains unexplored. In this study, the nanoindentation was utilized to investigate the nanoscale elastic and plastic characteristics in both additive-manufactured (AM-ed) and as-casted single-phase face-centered cubic (FCC) equiatomic CrMnFeCoNi HEAs. Herein, the hardness, reduced modulus, indentation size effect (ISE), yield strength, fracture toughness, and strain rate sensitivity were comprehensively investigated. The results indicated that the hardness of AM-ed HEA was higher than the as-casted HEA, and the reduced modulus values showed no notable distinction between the two samples. The AM-ed HEA demonstrated simultaneous enhancements in yield strength and fracture toughness compared to the as-casted HEA. The as-casted HEA possessed a more distinct indentation size effect (ISE) than the AM-ed HEA. It was observed that the AM-ed HEA exhibited relatively lower strain rate sensitivity and a larger activation volume. This direct comparison of the mechanical properties and deformation mechanisms from a nanoscale view offers unique insights for optimizing and advancing AM techniques in the fabrication of HEAs.

Antiferromagnetism and Phase Stability of CrMnFeCoNi High-Entropy Alloy.

It has long been suspected that magnetism could play a vital role in the phase stability of multicomponent high-entropy alloys. However, the nature of the magnetic order, if any, has remained elusive. Here, by using elastic and inelastic neutron scattering, we demonstrate evidence of antiferromagnetic order below ∼80 K and strong spin fluctuations persisting to room temperature in a single-phase face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy. Despite the chemical complexity, the magnetic structure in CrMnFeCoNi can be described as γ-Mn-like, with the magnetic moments confined in alternating (001) planes and pointing toward the ⟨111⟩ direction. Combined with first-principles calculation results, it is shown that the antiferromagnetic order and spin fluctuations help stabilized the fcc phase in CrMnFeCoNi high-entropy alloy.

Effective Atomic Radii of Constituent Elements and Their Temperature Dependence in Quaternary and Ternary Subset Alloys Derived from CrMnFeCoNi High-Entropy Alloy

Effective Atomic Radii of Constituent Elements and Their Temperature Dependence in Quaternary and Ternary Subset Alloys Derived from CrMnFeCoNi High-Entropy Alloy

Effect of Laser Multiple Remelting on the Geometric Parameters and Component Distribution of CrMnFeCoNi High-Entropy Alloys Coatings Fabricated on Al Alloy by Laser Cladding

Effect of Laser Multiple Remelting on the Geometric Parameters and Component Distribution of CrMnFeCoNi High-Entropy Alloys Coatings Fabricated on Al Alloy by Laser Cladding

In situ atomic-scale observation of deformation-induced reversible martensitic transformation in a CrMnFeCoNi high entropy alloy

High entropy alloys (HEAs) have attracted much attention for their excellent mechanical properties stemming from diverse deformation mechanisms. Particularly, face-centered cubic (FCC) to body-centered cubic (BCC) martensitic transformation is crucial for enhancing the strength and plasticity of HEAs, particularly at cryogenic temperatures. However, the fundamental atomic mechanism underlying martensitic transformation remains elusive, and the impact of martensitic transformation on the mechanical properties of HEAs at room temperature is unknown. Here, we report in situ atomic-scale observations of a reversible martensitic transformation from FCC to body-centered tetragonal (BCT) and ultimately back to FCC in nanostructured CrMnFeCoNi HEA at room temperature under deformation. This martensitic transformation is completed by the synergistic action of 90° partial dislocations slip on (111)FCC plane and atom shuffling, involving the periodic arrangement and slip of two 90° half Shockley partial dislocations a/12[1¯1¯2](111) and one 90° Shockley partial dislocation –a/6[1¯1¯2](111) on three successive (111)FCC atomic planes. Additionally, the reversible phase transformation induced by high stress dissipates strain energies and hinders crack propagation, thereby enhancing the fracture toughness of HEAs. Our findings contribute to a deeper comprehension of the martensitic transformation mechanisms in HEAs, offering valuable insights for improving their mechanical properties.

Dynamic response of equiatomic and non-equiatomic CrMnFeCoNi high-entropy alloys under plate impact

A typical Fe-rich non-equiatomic CrMnFeCoNi high-entropy alloy (HEA), Cr10Mn10Fe60Co10Ni10, and the equiatomic Cr20Mn20Fe20Co20Ni20 HEA, are investigated via plate impact experiments along with in situ free surface velocity measurements. Both the initial and postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. These two HEAs contain a single face-centered cubic phase, are texture-free, and have similar grain sizes. Dynamic yield stress and spall strength of the non-equiatomic CrMnFeCoNi are lower by ∼55 % and 15 % than those of its equiatomic counterpart, respectively. After shock compression, dislocation slips, stacking faults, Lomer-Cottrell locks and nanotwins are found in the postmortem samples of both HEAs. Due to the reduced stacking fault energy in the non-equiatomic HEA, more deformation twins and newly formed hexagonal close-packed phases are found. For spallation, intergranular voids are larger in size but smaller in quantity than intragranular voids for both HEAs. Both intragranular or intergranular voids show strong dependence on grain boundary misorientation.

Effects of ultrasonic impact treatment on the corrosion resistance of laser-cladded CrMnFeCoNi high-entropy alloy coatings

Ultrasonic impact treatment (UIT) was performed on the surface of the laser-clad CrMnFeCoNi high-entropy alloy coatings. The fluences of the UIT on the microstructure, microhardness, nanoindentation metrics and corrosion resistance of the coatings were explored. Furthermore, the enhancing mechanisms of the corrosion resistance of these coatings by the UIT were clarified. The results showed that the UIT markedly enhanced the corrosion resistance of the laser-clad CrMnFeCoNi high-entropy alloy coatings, and the enhancing effect continuously improved with the increasing of the UIT time. The most significant enhancement of corrosion resistance occurred under the action of UIT with a current of 1.6 A for 20 min. Compared to the untreated group, corrosion potential rose by 65.68 %, corrosion current density fell by 74.95 %, and equivalent resistance increased by 340.37 %. Corrosion morphology analysis showed that the primary forms of corrosion before the UIT were stress corrosion and pitting, which vanished after the UIT with a significant improvement in pitting. Analysis of corrosion products revealed an increased Cr content and a decreased FeOOH and O content on the coating surface after the UIT, leading to enhanced corrosion resistance. Additionally, microstructural analysis showed that large columnar crystals in the laser-clad CrMnFeCoNi high-entropy alloy coatings transformed into finer columns, drastically reducing the grain size of the surface. Concurrently, surface microhardness and nanoindentation mechanical properties markedly improved after the UIT, with the effects growing stronger over time. After the UIT with the current of 1.6 A for 20 min, the increasement of surface microhardness reached 109.01 %. A comprehensive analysis of the fluences on the corrosion resistance of laser-clad CrMnFeCoNi high-entropy alloy coatings by the UIT indicated that the refinement of grain size, improvement of the stress state of the coating, increasement of Cr element and its compounds, and decreasement of FeOOH content are the main reasons of enhanced corrosion resistance.

Microstructure and Wear Property of In-Situ Oxide Reinforced CrMnFeCoNi High Entropy Alloy Composite Fabricated by Selective Laser Melting

CrMnFeCoNi high entropy alloy (HEA) which had nano oxide particles formed during additive manufacturing process was fabricated using a selective laser melting (SLM) process (hereinafter SLM Cantor HEA). The microstructure of the fabricated SLM Cantor HEA and the wear properties according to the applied load (5 N, 15 N) were investigated. SLM Cantor HEA was consist of nano-size oxides and high dislocation density, resulting in superior hardness compared to conventional processed CrMnFeCoNi HEA. As a result of the wear test, it showed abrasive and oxidative wear behavior regardless of applied load. But in case of 15 N load condition, it showed more finer worn microstructure with increased wear load, and had a contradictory effect on each friction coefficient and wear rate. Based on the above results, the wear mechanism of in-situ oxide reinforced SLM Cantor HEA was discussed in relation with the microstructure.

Optimization of tensile properties and anisotropy in a cryogenically treated laser additively manufactured high entropy alloy

Repetitive deep cryogenic soaking treatment (DCT) of laser metal deposition (LMD) processed CrMnFeCoNi high entropy alloy (HEA) significantly enhances its strength without compromising ductility. This is attributed to the compressive stress induced nanotwin formation, which in turn facilitates twin induced plasticity. In this work, a parametric study on the effect of the residual stress profile and the DCT cycles on the tensile properties of the HEA, along the build and scan directions is conducted. Towards this end, builds fabricated with 5 different laser powers, 1100, 1400, 1700, 2000 and 2300 W, are examined and the ones with highest and lowest residual stress gradient are considered for further DCT treatments. Results indicate that the build fabricated with 1400 W laser power, which has the highest gradient in initial residual stresses, exhibits a greater enhancement in dislocation and twin density with increasing number of DCT treatments. Compared to its as-built state the peak yield and tensile strength of the HEA (along the scanning direction) increases to 592 ± 13 and 778 ± 15 MPa, without significant decrease in its ductility after 12 DCT cycles. However, the enhancement in the dislocation, twin density and therefore, the strength, is minimal after it is treated to 15 DCT cycles. Anisotropy in both strength and ductility, which is of the order of 20-25 %, is also observed in the DCT treated builds along the build and scan directions. These observations were rationalized on the basis of dislocation and twin evolution and distribution during DCT and deformation of the build when deformed in different directions. Implications of these results in the context of employing DCT for strengthening LMD fabricated HEA components are discussed.

Effect of nitrogen addition on sintering behavior of high-entropy alloy CrMnFeCoNi powder

The effect of nitrogen addition on sintering behavior of high-entropy alloy CrMnFeCoNi powder has been investigated. CrMnFeCoNi alloy powders were nitrided to add nitrogen and then consolidated at three different temperatures. The microstructure of the nitrided CrMnFeCoNi alloy powders and sintered compacts was characterized using electron probe microanalysis (EPMA) system. In the compact sintered at 800 °C, a high-nitrogen-content region formed a continuous network structure around the low-nitrogen-content substrate. The hardness of the sintered compacts with nitrogen was higher than that of the compacts without nitrogen. The high-nitrogen-content region expanded into the substrate region. The Vickers hardness of the sintered compacts increased with an increase of sintering temperature up to 950 °C. Sintering at 1100 °C did not completely finish; the vacuum pressure in the sintering chamber rapidly increased because chromium nitride (CrN) decomposed. The results indicate that high-temperature sintering is ineffective for nitrogen-added CrMnFeCoNi alloy powder.

Significant improvement in surface hardness of CrMnFeCoNi high entropy alloy via nanosecond pulse laser grain refinement

The CrMnFeCoNi alloy with a stable single face-centered cubic (FCC) phase, representing a typical class of high-entropy alloys (HEAs), has garnered considerable attention owing to their exceptional mechanical properties. However, the inherent low hardness has impeded their utilization in structural or contact components. This study attempted to improve the surface hardness of CrMnFeCoNi HEA via grain refinement realized by nanosecond pulse laser irradiation. The effects of laser parameters on the surface microstructures, chemical composition, and mechanical properties were investigated, and the mechanism for grain refinement was analyzed. The experimental results showed that the hardness of the laser-irradiated surface was significantly improved without altering the chemical composition. This study provides a simple but effective method to refine the grain of HEAs and improve their surface hardness.

Theoretical study on the influence of grain size on the strength, toughness and plastic deformation mechanism of pre-cracked polycrystalline high entropy alloys

High entropy alloys (HEAs) is a kind of structural material with excellent mechanical properties. The material exhibits excellent damage tolerance at low temperature, which is closely related to its potential crack tip plastic mechanism and overall fracture mode. In the research, the plastic deformation and fracture mechanical properties of polycrystalline CrMnFeCoNi HEAs with pre-crack under type I tensile load were investigated by molecular dynamics (MD) simulation. The effects of grain size and crack length on the strength, toughness and microstructural deformation of the alloy were analyzed. It is found that with the increase of grain size, the strength of the material increases and the toughness decreases. With the increase of crack length, the strength and toughness decrease, and the influence of grain size on the strength is weakened. The plastic mechanism of crack initiation in nanocrystalline HEAs is ductile cracking under the joint action of dislocations, amorphization and grain boundary plasticity, which provides high damage tolerance. As the grain size increases, additional cavities appear near the crack tip or at the grain boundary, resulting in brittle fracture mode along the grain boundary or at the end of the cavity, which greatly affects the plastic properties of the material. The initial crack length has a significant effect on the transformation of the fracture mode. With the increase of the initial crack size, the critical grain size of the brittle fracture mode increases, and its proportion in the whole fracture mode decreases. This study provides a theoretical reference for the design and application of nanocrystalline HEAs.

Machine learning optimization strategy of shaped charge liner structure based on jet penetration efficiency

Shaped charge liner (SCL) has been extensively applied in oil recovery and defense industries. Achieving superior penetration capability through optimizing SCL structures presents a substantial challenge due to intricate rate-dependent processes involving detonation-driven liner collapse, high-speed jet stretching, and penetration. This study introduces an innovative optimization strategy for SCL structures that employs jet penetration efficiency as the primary objective function. The strategy combines experimentally validated finite element method with machine learning (FEM-ML). We propose a novel jet penetration efficiency index derived from enhanced cutoff velocity and shape characteristics of the jet via machine learning. This index effectively evaluates the jet penetration performance. Furthermore, a multi-model fusion based on a machine learning optimization method, called XGBOOST-MFO, is put forward to optimize SCL structure over a large input space. The strategy's feasibility is demonstrated through the optimization of copper SCL implemented via the FEM-ML strategy. Finally, this strategy is extended to optimize the structure of the recently emerging CrMnFeCoNi high-entropy alloy conical liners and hemispherical copper liners. Therefore, the strategy can provide helpful guidance for the engineering design of SCL.

Constructing dual-scale high-entropy alloy/polymer interpenetrating networks to develop a lightweight composite with high strength and excellent damping capacity

Lightweight materials with high strength and excellent damping capacity are of great significance for reducing weight and vibration and maintaining stability in industrial applications. However, these characteristics are usually difficult to achieve simultaneously in traditional damping materials. Here, we provide a design strategy for dual-scale interpenetrating networks. By infiltrating the viscoelastic polymer containing CrMnFeCoNi nanoalloy/carbon nanotube networks into CrMnFeCoNi high-entropy shape memory alloy foam with a three-dimensional network structure, the dual-scale CrMnFeCoNi/polymer interpenetrating phase composite was developed. When the carbon nanotube loading is 2 wt%, the composite exhibits a compressive strength of 37.2 MPa and an energy absorption capacity of 22.5 MJ·m−3 (ε = 65 %), with a mere density of 2.528 g·cm−3. In the temperature range of 20 ∼ 150℃, its loss factor exceeds 0.132 with a peak value of 0.206. Compared with CrMnFeCoNi foam, its compressive strength, energy absorption capacity and peak internal friction are increased by 85 %, 65 % and 156 %, respectively. The construction of dual-scale interpenetrating networks introduces high-density interfaces, and the coupling of multi-scale intrinsic damping and interface damping endows the composite with high ground-state damping. The superposition of the phase transformation peak of CrMnFeCoNi foam and the glass transition peak of polymer composite matrix enables a wide damping temperature window. This study offers a new perspective for developing high-performance damping materials.

Influence of Al addition on microstructure and electrochemical behaviour of CrMnFeCoNi high-entropy alloy

To develop new corrosion-resistant materials for structural applications, CrMnFeCoNiAlx high-entropy alloys (HEAs) are produced via semi-industrial induction casting. The study aimed to investigate the influence of Al content (x = 0–0.3) on both microstructure evolution and corrosion properties of the alloys. X-ray diffraction and scanning electron microscopy (SEM) analysis revealed that all the alloys exhibited a single-phase face-centered cubic structure, with dendritic (Fe, Co, Cr-rich) and interdendritic (Mn, Ni, Al-rich) regions distinguished by elemental segregations. Furthermore, the incorporation of Al atoms into the solid solution led to an increase in the lattice parameter, indicating alloy strengthening. The corrosion resistance of the CrMnFeCoNiAlx alloy improved with higher Al addition. Electrochemical polarisation tests demonstrated a slight increase in the corrosion potential (Ecorr) and a significant decrease in the corrosion current density (icorr) upon Al addition. Additionally, slower kinetics for pit nucleation (higher E'corr) were observed, particularly notable for x = 0.3. Analysis of the corroded surfaces revealed a mixed degradation mechanism, involving pitting corrosion and selective dissolution of the interdendritic zone, which decreased as the Al content of the HEA increased. These findings underscore the effectiveness of Al addition in not only enhancing the mechanical properties of the Cantor alloy through solid solution strengthening, but also improving its corrosion resistance.

A low-density polymer/CrMnFeCoNi composite with high strength and high damping capacity

A novel damping composite was successfully prepared by taking a porous CrMnFeCoNi high-entropy shape memory alloy as the skeleton and filling its pores with the composite composed of carbon nanotubes and polyurethane/epoxy interpenetrating polymer networks. When the porosity, pore size and CNT loading are 80 %, 1.2 mm and 2 wt%, respectively, the compressive strength, elastic modulus and energy absorption capacity of the composite are 35.7 MPa, 1.31 GPa and 23.1 MJ/m3 (ε = 65 %), respectively. Furthermore, it has a mere density of 2.525 g/cm3. Its loss factor is greater than 0.093 and can reach a maximum of 0.145 within the temperature and frequency range of 20 ∼ 150 ℃ and 0.1 ∼ 200 Hz. A triple-phase micromechanical model was utilized to explore the damping mechanism of composites. Results indicate the coupling of multiple damping mechanisms is the reason for the high ground-state damping of composites, and interface damping is the primary damping mechanism. The superposition of the ε → γ reverse martensite transformation peak of the CrMnFeCoNi HESMA skeleton and the glass transition peak of the CNTs/polymer composite matrix realizes the wide damping temperature range of the composite.

Mechanical properties and deformation mechanisms of C-doped interstitial high-entropy alloy CrMnFeCoNi: Effects of strain rate and C content

The effects of strain rate on mechanical properties, microstructural evolution and underlying deformation mechanisms of two kinds of interstitial CrMnFeCoNi high entropy alloys (HEAs), (CrMnFeCoNi)99.5C0.5 and (CrMnFeCoNi)99.0C1.0, are investigated under quasi-static and dynamic tension. Dynamic loading is carried out via a split Hopkinson tension bar system. The pre- and post-deformation microstructures are characterized with electron back scatter diffraction and transmission electron microscopy. Both yield strength and work hardening increase remarkably with increasing strain rate. Plastic deformation in both alloys under quasi-static and dynamic loading are dominated by dislocations, stacking faults, kink bands and deformation twins. Twinning is activated easier under dynamic loading, and twin density decreases with increasing carbon content due to the increased stacking fault energy. The Khan-Liu constitutive model can describe the experimental results for these two interstitial HEAs in a wide strain range.

Anomalies in the short-range local environment and atomic diffusion in single crystalline equiatomic CrMnFeCoNi high-entropy alloy

Multi-edge extended X-ray absorption fine structure (EXAFS) spectroscopy combined with reverse Monte Carlo (RMC) simulations was used to probe the details of element-specific local coordinations and component-dependent structure relaxations in single crystalline equiatomic CrMnFeCoNi high-entropy alloy as a function of the annealing temperature. Two representative states, namely a high-temperature state, created by annealing at 1373 K, and a low-temperature state, produced by long-term annealing at 993 K, were compared in detail. Specific features identified in atomic configurations of particular principal components indicate variations in the local environment distortions connected to different degrees of compositional disorder at the chosen representative temperatures. The detected changes provide new atomistic insights and correlate with the existence of kinks previously observed in the Arrhenius dependencies of component diffusion rates in the CrMnFeCoNi high-entropy alloy.