Ni High-entropy Alloys Research Articles

Cuckoo search-artificial neural network aided the composition design in Al–Cr–Co–Fe–Ni high entropy alloys

In this work, we proposed a data-driven approach combining machine learning (ML), experiments and molecular dynamic (MD) simulation to accelerate the composition design and exploration of wear behavior in Al–Cr–Co–Fe–Ni based high entropy alloys. A Cuckoo Search-Artificial Neural Network (CS-ANN) model was proposed to deal with small sample data and showed fairly strong learning ability and generalization capabilities. Elemental analysis revealed that the microhardness can be enhanced by adding Al or reducing the proportion of Fe and Ni. Then the Al1.1CrCoFe0.9Ni0.9 HEAs were designed and prepared for experimental verification. The microstructure, phase composition, hardness, and wear resistance properties of the alloy were further investigated. Al1.1CrCoFe0.9Ni0.9 HEAs were composed of BCC+B2 phases, exhibited a microhardness of 580.6 HV. The wear rate was measured as 6.04×10−6 mm3/(Nm) by the reciprocating dry wear tests, the average COF was estimated as ∼0.5. The main wear mechanisms involved abrasive wear and oxidation wear. MD simulations are used to analyze the atomic evolution and deformation mechanism during the nano scratch process. The obtained information would help either facilitate developing novel HEAs or utilize the HEAs effectively to resist wear.

High-temperature oxidation and diffusion studies on selected Al–Cr–Fe–Ni high-entropy alloys for potential application in thermal barrier coatings

In this work, the properties of two high-entropy alloys (HEAs) Al25Cr20Fe20Ni35 and Al20Cr20Fe20Ni40 (at.%) were compared for potential application as bond coats in thermal barrier coatings (TBCs). For this reason, both their oxidation resistance under isothermal and thermal shock conditions, as well as diffusion phenomena occurring at the substrate-HEA diffusion couple interface, were investigated. It was determined that both alloys demonstrate good phase stability and oxidation resistance during prolonged exposure to air atmosphere at 1000°C. In the initial 100 h period, selective aluminum oxidation is responsible for the protective scale growth on both materials under both isothermal and thermal shock conditions. However, only the Al20Cr20Fe20Ni40 high entropy alloy maintains a single Al2O3 layer for over 1000 h of oxidation with cyclic temperature changes. On the other hand, diffusion studies indicate that mainly iron and chromium travel between the ferritic steel substrate and the HEAs. Aluminum diffusion is seemingly limited by the unexpected formation of a thin aluminum nitride layer at the interface between the materials. From all these results it can be concluded that the Al20Cr20Fe20Ni40 alloy shows more promise for application in TBCs based on high entropy materials than Al25Cr20Fe20Ni35.

Mechanical properties of Al–Co–Cr–Fe–Ni high-entropy alloy: A molecular dynamics simulation

Molecular dynamics simulations were utilized to investigate the mechanical properties of the Al–Co–Cr–Fe–Ni high-entropy alloy and observe atomic microstructure and internal dislocation line changes under different parameter conditions. The findings demonstrate that the mechanical properties of the AlCoCrFeNi3 high-entropy alloy are significantly superior to those of conventional alloys in ambient temperature. During the tensile process, the face-centered structure undergoes interconversion with other structure types, while the internal dislocation lines gradually increase. The presence of grain boundaries impedes dislocation movement, resulting in lower deformation capacity and tensile strength in polycrystals compared to single crystals. Enhancing Ni content, increasing strain rate, and decreasing temperature during tensile process contributes to the enhancement of the mechanical properties of material. Among these factors, the Ni content exerts the most significant influence on the mechanical properties of the material.

Strain softening observed during nanoindentation of equimolar-ratio Co–Mn– Fe–Cr–Ni high entropy alloy

This research article presents an atomistic study on the cyclic nanoindentation of an equimolar-ratio Co–Mn–Fe–Cr–Ni high-entropy alloy (HEA) using molecular dynamics simulation. The study investigated the effects of indentation depth on the cyclic load versus the indentation depth of the HEA. The results showed that the cyclic response exhibits a pronounced shift towards plasticity with pile-up formation instead of sinking behavior at higher indentation depths. Within the realm of molecular dynamics simulations, the simulated hardness value reached up to 16 GPa for the initial indentation cycle. A steep drop in the load–displacement curve was observed during the elastic–plastic transition, signifying substantial strain softening of the substrate. It was found that the densely clustered stacking faults undergo a reverse transition during cyclic loading, contributing to the backpropagation phase responsible for elastic recovery despite subsequent strain hardening. The study provides important insights into the underlying mechanisms governing the cyclic mechanical behavior of HEAs to guide their improved micromanufacturing.

Multi-material deposition of Inconel 718 and Ti–6Al–4V using the Ti–Nb–Cr–V–Ni high entropy alloy intermediate layer

Multi-materials are required in high-tech industries that require different properties at different locations in the same structure. The successful utilization of multi-materials can be economical, space-saving, and easy to maintain in engineering applications. Regardless of the technique used, the multi-material deposition (MMD) of Ti and Ni alloys presents some unique challenges. In this study, MMD of Ti–6Al–4V and Ni–20Cr using a high-entropy alloy (HEA) intermediate layer was performed, and deposition failure causes were analyzed. Deposition failures were found to be caused by the immiscibility between materials, differences in thermal properties, and interface due to the formation of brittle intermetallic compounds (IMC). HEA causes lattice distortion owing to the difference in the size of the elements constituting the solid solution and has excellent mechanical properties owing to the lattice distortion and the unique microstructure caused by the formation of a single-phase solid solution. In addition, HEAs do not form IMC because they exhibit slow diffusion rates. Therefore, HEA could be used as an effective interlayer to inhibit IMC formation. In this study, Inconel 718 and Ti–6Al–4V were successfully deposited by applying a Ti–Nb–Cr–V–Ni HEA intermediate layer to MMD. In addition, microstructure analysis and hardness measurements were performed to analyze whether IMC inhibition and successful deposition occurred.

Machine learning-assisted analysis of dry and lubricated tribological properties of Al–Co–Cr–Fe–Ni high entropy alloy

This study marks a notable advancement in tribology by thoroughly investigating the tribological properties of a high-entropy alloy under both lubricated and dry conditions.

Analysis of contact zone of coating-substrate system exposed to irradiation with a pulse electron beam

Using the wire-arc additive manufacturing method (WAAM) on a 5083 aluminum alloy substrate, a non-equiatomic Mn – Cr – Fe – Co – Ni high-entropy alloy (HEA) coating was formed. By scanning and transmission electron diffraction microscopy we analyzed the structure, phase and elemental composition of the contact zone after irradiation with high-current low-energy electron beams with the following parameters: accelerated electron energy 18 keV, electron beam energy density 30 J/cm2, electron beam pulse duration 200 µs, number of pulses 3, pulse repetition rate 0.3 s–1. Multiphase multielement submicro- and nanocrystalline structures are formed predominantly in the substrate, which has a lower melting temperature compared to HEAs. Mutual doping of the coating – substrate system occurs in the contact layer, which has sinuous boundaries. The contact layers adjacent to the substrate and coating have the structure of high-speed cellular crystallization. In the layer adjacent to the substrate, the cells are formed by a solid solution of magnesium in aluminum. Interlayers of the second phase, enriched in atoms of the coating and substrate, are revealed along the cell boundaries. In the layer adjacent to the coating, the cells are formed by an alloy of composition 0.17Mg – 20.3Al – 4.3Cr – 16.7Fe – 9.3Co – 49.2Ni corresponding to the coating. Interlayers of the second phase, enriched mainly in magnesium and, to a lesser extent, in atoms of the HEA coating, are located along the cell boundaries. Central region of the contact zone with a thickness of ~1700 μm is formed by lamellar crystallites, which indicates the eutectic nature of its formation. Its main element is aluminum (≈77 at. %).

Effect of silicon addition on the corrosion resistance of Al0.2CoCrFe1.5Ni high-entropy alloy in saline solution

In the paper, the effect of Si content on the microstructure evolution and corrosion properties of Al0.2CoCrFe1.5NiSix (x = 0, 0.1, 0.2, 0.3) high entropy alloys (HEAs) was systematically investigated. With the addition of Si element, the microstructure changed from single face-centered cubic (FCC) phase in the Al0.2CoCrFe1.5Ni and Al0.2CoCrFe1.5NiSi0.1 HEAs to a dual-phase structure composed of FCC and body-centered cubic (BCC) phases in the Al0.2CoCrFe1.5NiSi0.2 and Al0.2CoCrFe1.5NiSi0.3 HEAs. In addition, the corrosion mechanism has been analyzed by elemental analysis and corrosion morphology. The electrochemical measurement results indicated that the Al0.2CoCrFe1.5NiSi0.1 HEA possessed the best corrosion resistance (Ecorr = − 215 mVAg/AgCl, Icorr = 256 nA/cm2) because the small amount of Si element improves the corrosion resistance of the single-phase FCC HEA. When the Si content increased to 4.08 at% (x = 0.2) and 6.00 at% (x = 0.3), the galvanic corrosion was caused by BCC, resulting in the selective dissolution of the BCC phase and the decrease of corrosion resistance. This research results will help to understand the potential applications of doped trace Si element as a matrix element in single-phase FCC HEAs with good corrosion resistance.

Variation of BCC/B2 coherent microstructure and resultant improvement in strength of Al0.7CrxFe3−xCoNi high-entropy alloys

The effects of Cr and Fe contents on the microstructure and mechanical properties of B2 nanoparticle-enhanced BCC-based Al0.7CrxFe3−xCoNi (x = 1.5–3.0) high-entropy alloys (HEAs) were studied. It was indicated that the addition of Cr and reduction of Fe in the alloys can increase the lattice misfits between the BCC and B2 phases, inducing the variations of BCC/B2 coherent microstructure and the significant improvements of the compressive yield strengths from ∼ 1485 MPa to ∼ 2252 MPa. The calculations of the yield strengths based on the microstructure of the alloys suggested that the improvements of the strengths were mainly due to the enhancements of the precipitation-strengthening effects. The interactions between dislocations and B2 particles with various shapes and sizes were also discussed on the basis of the calculations. It is demonstrated that adjusting the contents of Cr and Fe is an effective way to control BCC/B2 coherent microstructure and improve the mechanical properties of Al–Cr–Fe–Co–Ni HEAs.

Machine learning assisted optimization of tribological parameters of Al–Co–Cr–Fe–Ni high-entropy alloy

ABSTRACT High-entropy alloys (HEA) have become increasingly important in the materials world due to their ability to combine multiple principal elements in an alloy system to achieve desired mechanical and tribological properties. In this study, Al–Co–Cr–Fe–Ni HEA alloy is synthesized using vacuum induction melting and its tribological properties are analyzed under dry conditions, which is important since dry sliding is a common mode of wear in many engineering applications. To enhance its tribological performance, evolutionary data-driven modeling and optimization techniques are applied to determine the best possible solutions for the loading condition at different frequency levels. A neural net-based algorithm (EvoNN) is utilized in the data-driven modeling process to generate and train models, which are then used in the optimization process. The reference vector-based algorithm (cRVEA) is incorporated with the EvoNN to evaluate the optimum wear, coefficient of friction (COF), and surface roughness results in multidimensional hyperspace. The results obtained from this study fall within the experimental data range and satisfy the tribological requirements under optimum conditions. The excellent wear resistance of HEAs due to their high hardness, strength, and resistance to deformation makes them suitable for use in various wear applications, including cutting tools, bearings, and gears. Overall, this study highlights the potential of HEAs and data-driven modeling techniques for the development of advanced materials with superior properties and performance.

Effect of microstructural evolution on corrosion behavior of Al0.7Cr2FeCoNi high-entropy alloy

In the present study, the influence of the microstructural evolution on the corrosion behavior of the B2 nanoprecipitation-strengthened BCC-based Al0.7Cr2FeCoNi high-entropy alloy (HEA) in a 3.5 mass% NaCl solution was studied. The alloys in the as-cast state and heat-treated at 673 K for 2 h consisted of the BCC matrix and the B2 nanoparticles, and the heat treatments at 873 K and 1073 K for 2 h induced the coarsening of the B2 particles and the precipitation of the σ phase. It was found that the alloys exhibited good corrosion resistance, as evidenced by the low corrosion rates of less than 10−3 mm/year and the spontaneous passivation due to the formation of the Cr-rich surface films. It is notable that the alloys in the as-cast state and heat-treated at 673 K showed the transpassive dissolution above ∼ 0.7 V vs. SCE, while the alloys heat-treated at 873 K and 1073 K suffered localized corrosion on the B2 phase at ∼ 0.40 V and ∼ 0.37 V during the anodic polarization, respectively. This deterioration in the corrosion resistance of the alloys heat-treated at the higher temperatures was attributed to the higher potential difference between the B2 and σ phases than that between the B2 and BCC phases, as well as the coarsening of the Cr-depleted B2 particles. It is demonstrated that the coarsening of the B2 particles and the precipitation of the σ phase should be suppressed to obtain the corrosion-resistant Al–Cr–Fe–Co–Ni HEAs.

Manufacturing of Ti–Nb–Cr–V–Ni high entropy alloy using directed energy deposition and evaluation of materials properties

High entropy alloy (HEA) is a new material that can overcome the limitations of the physical properties of conventional materials, exhibit excellent mechanical properties, and be employed in various extreme environments. In particular, refractory HEA composed of refractory materials such as Ti and Ni are expected to exhibit desirable high-temperature properties. Metal additive manufacturing has a shorter manufacturing time than the conventional casting method and is suitable for HEA manufacturing using various metal materials. Specifically, directed energy deposition (DED) has a high solidification rate that is advantageous for grain refining, prevents intermetallic compounds, and averts shrinkage that occurs in the casting method, thereby reducing cracks and deformations and resulting in fewer defects and superior production quality. In this study, a HEA with desirable high-temperature characteristics that are composed of Ti–Nb–Cr–V–Ni was designed by optimizing thermodynamic parameters and deposited using DED. The deposited Ti–Nb–Cr–V–Ni exhibited a body-centered cubic structure. Tensile strength, hardness, differential scanning calorimetry (DSC), and thermal conductivity analyses were performed to analyze its mechanical and thermal properties. Ti–Nb–Cr–V–Ni exhibited a fine structure and high tensile strength at high temperatures due to the characteristics of the DED process, but low elongation at room temperature. These strength characteristics are attributed to the microstructure of Ti–Nb–Cr–V–Ni, which mainly forms the BCC phase. And Ti–Nb–Cr–V–Ni exhibited high hardness and high thermal stability enough to be used in extreme environments with high temperatures.

Organizational Evolution during Performance Meritocracy of AlSi0.5CrxCo0.2Ni Lightweight High Entropy Alloys

The Al-Si-Cr-Co-Ni High Entropy Alloy (HEA) with low density (about 5.4 g/cm3) and excellent performance had significant potential in the lightweight engineering material field. To further research and optimize the Al-Si-Cr-Co-Ni system HEA, the influences of element Cr on the microstructures and performances of lightweight AlSi0.5CrxCo0.2Ni (in mole ratio, x = 1.0, 1.2, 1.4, 1.6, and 1.8) HEAs were investigated. The experiment results manifested that AlSi0.5CrxCo0.2Ni HEAs were composed of A2 (Cr-rich), B2 (Ni-Al), and Cr3Si phases, indicating that the addition of Cr did not result in the formation of a new phase. However, ample Cr increased the Cr3Si phase composition, further ensuring the high hardness (average HV 981.2) of HEAs. Electrochemical tests demonstrated that HEAs with elevated Cr3Si and A2 phases afforded greater corrosion resistance, and the improvement in corrosion was more pronounced when x > 1.6. This work is crucial in the development of lightweight engineering HEAs, which are of tremendous practical utility in the fields of cutting tools, hard coating, etc.

Exploration of V–Cr–Fe–Co–Ni high-entropy alloys with high yield strength: A combination of machine learning and molecular dynamics simulation

Improving the strength of Cr–Fe–Co–Ni high-entropy alloys is a key issue in expanding their applicability. Herein, a framework combining machine learning and molecular dynamics is employed to improve the yield strength of Cr–Fe–Co–Ni high-entropy alloys through vanadium addition. The results indicate that by specifying the valence electron concentration, vacancy formation energy, and mismatch in cohesive energy as input features, a support vector regression model with a radial bias function kernel displays the highest performance among numerous combinations of machine learning models and material features. According to the Shapley additive explanation, the vacancy formation energy and valence electron concentration show a negative correlation with the yield strength above 1.66 eV and 7.60, respectively, and a positive correlation otherwise. The mismatch in the cohesive energy always shows a negative correlation. By utilizing a Bayesian adaptive alloy design, V5Cr16Fe9Co35Ni35 has been identified to have the highest yield strength. The simulated tensile deformation of polycrystalline high-entropy alloys confirms the predicted trend in yield strength, and the events observed during plastic deformation are consistent with previous experimental observations. The proposed framework provides a promising prospect for accelerating the design of high-entropy alloys with reduced dependence on costly trial-and-error experiments.

Tribological and corrosion performance of an atmospheric plasma sprayed AlCoCr0.5Ni high-entropy alloy coating

High entropy alloys (HEAs) are an established new class of materials exhibiting excellent mechanical and functional properties. The well-studied AlCoCrFeNi HEA has been modified to AlCoCr0.5Ni HEA in view of the latter's better oxidation resistance. The elimination of Fe and reduction in Cr content is expected to improve the HEA's corrosion and tribological performance. Thus, an AlCoCr0.5Ni HEA coating was fabricated via the atmospheric plasma spray (APS) process using mechanically alloyed (MA) feedstock. The microstructural characteristics of both the MA feedstock and coating have been investigated. The sliding wear behaviour of the HEA coating was evaluated at both room temperature and 500 °C. In addition, the electrochemical compatibility of the coating was analyzed in seawater. The microstructural results revealed that the MA feedstock was composed of BCC/B2 and FCC phases, which were retained in the HEA coating along with minor oxides. The wear resistance of the AlCoCr0.5Ni HEA coating was superior to the AlCoCrFeNi HEA coating both at room temperature and 500 °C. The high wear resistance of the coating was attributed to the formation of equal concentrations of the BCC/B2 and FCC phases. The coating exhibited a greater tendency of being cathodic (passive) than both an AlCoCrFeNi HEA coating and SS316L with identical polarization behaviour.

Notable hydrogen storage in Ti–Zr–V–Cr–Ni high entropy alloy

In the present investigation, we discussed the synthesis, structural and hydrogen storage behavior of high-entropy Ti–Zr–V–Cr–Ni equiatomic intermetallic alloy. This alloy was synthesized by arc melting in an argon atmosphere where base pressure was in the order of 10−5 atm before purging with argon gas. The X-ray diffraction study revealed that the alloy is C14 type hexagonal Laves phase. The pressure composition isotherms (PCI) of this alloy were investigated with pressure ranges at 0–40 atmosphere. The total hydrogen storage capacities were found to be 1.52 wt%. The reversible hydrogen storage capacity was quite stable and only slight decreases in the storage capacity was observed after 10 cycles during hydrogen soaking. The demonstrations of hydrogen storage capacity of the Ti–Zr–V–Cr–Ni equiatomic alloy were thus established, indicating the future potential of developing this class of high entropy intermetallic based materials for hydrogen storage.

A Review of Emerging Metallic System for High-Energy Beam Additive Manufacturing: Al–Co–Cr–Fe–Ni High Entropy Alloys

A Review of Emerging Metallic System for High-Energy Beam Additive Manufacturing: Al–Co–Cr–Fe–Ni High Entropy Alloys

Molecular dynamics study on the strengthening mechanisms of Cr–Fe–Co–Ni high-entropy alloys based on the generalized stacking fault energy

The correlation between the generalized stacking fault energy and the strengthening mechanisms of Cr–Fe–Co–Ni high-entropy alloys during uniaxial tensile deformation is investigated using molecular dynamics simulations. An increase in the Cr and Fe content decreases the generalized stacking fault energy, while an opposite trend is observed for the content of Co and Ni. A linear correlation is identified between the unstable stacking fault energy and the yield stress. Alloys with a lower Fe content and higher Co and Ni contents show a higher unstable stacking fault energy, and hence higher yield stress. A high density of Lomer–Cottrell locks or deformation twins leads to higher flow stress. The deformation twins play a more important role in enhancing the flow stress as compared to sessile dislocations. Additionally, high unstable stacking fault energy is required to stabilize the defects formed and contribute to increasing flow stress. For a low unstable stacking fault energy, the plastic deformation progresses at lower stress and a bidirectional defect transformation is observed. The results agree with recent experiments and serve as guidelines for how the composition can be used to enhance the yield strength and the efficiency of strengthening mechanisms in Cr–Fe–Co–Ni high-entropy alloys.

High-Temperature Tribological Behavior of Al0.3Cr0.5Fe1.5Mn0.5Ni High-Entropy Alloys With Addition of Titanium and Carbon

In this study, the Al0.3Cr0.5Fe1.5Mn0.5Ni high-entropy alloys (HEAs) with addition of titanium and carbon was prepared. The as-cast alloys were composed of FCC solid solution and TiC particles, and were further aged and strengthened by precipitation of B2-NiAl phase at 700°C for 10 h to increase hardness from Hv 200 to Hv 400. Tribological properties of the HEAs and commercial tool steel (AISI M2) against Al2O3 under dry sliding condition at room-temperature and elevated temperatures are compared. After high-temperature wear testing, the HEAs demonstrated exceptional oxidation resistance and a lower friction coefficient than M2 steel since the dense glazed layer on the surface of the HEAs served as a lubricant to decrease the friction coefficient, and protected the substrate from oxidation.

Phase Components, Microstructures, and Mechanical Properties of AlCoCrVX (X = Fe, Ni, and Cu) High-Entropy Alloys

Phase Components, Microstructures, and Mechanical Properties of AlCoCrVX (X = Fe, Ni, and Cu) High-Entropy Alloys