Eutectic High Entropy Alloy Research Articles

Achieving considerable wear resistance in new Ti-based high-entropy alloys through microstructural hardening by adding Nb

In this study, (CoCrNiMn)78Ti22−xNbx eutectic high-entropy alloys were successfully synthesised via an arc melting process under vacuum, and the phase structure, microstructure, mechanical properties and dry sliding tribological behaviour of the alloys were systematically investigated. The XRD results for the (CoCrNiMn)78Ti22−xNbx eutectic high-entropy alloys are almost in agreement with the JMatPro phase diagram simulations, and the volume fraction of the Laves phase increased with increasing Nb content. OM and SEM images revealed that the microstructure was composed of dendrites (BCC A2) and interdendrites (BCC B2 +Laves) and changed from a hypoeutectic to a eutectic to a BCC B2 +Laves dual-phase structure, with the average grain size decreasing from 6.715 µm to 6.391 µm. Ti promoted the growth of the layered Laves phase and provided the alloy with base hardness and wear resistance. The hardness of the alloy combination of 21 % Ti and 1 % Nb reached the maximum value of 707.04 HV, whereas the average coefficient of friction (COF) and wear rate reached the lowest values of 0.49 and 1.668 × 10−4 mm3/N·m, respectively. With increasing load, the wear mechanism was mixed fatigue, delamination wear, and abrasive wear accompanied by oxidation, and the possibility of three-body wear paths between compacted tribolayers cannot be excluded. The debris was mostly in the form of microclusters, and the particle size range was concentrated between 1 −2 µm; meanwhile, the shape of the debris tended to develop from lamellar to spherical with increasing hardness.

Effect of laser remelting on the microstructure and properties of an AlCoFeNi eutectic high-entropy alloy fabricated through double-wire arc additive manufacturing

Additive manufacturing (AM) technology is a new method for preparing eutectic high-entropy alloys (EHEAs). The resulting EHEAs have excellent mechanical properties. However, in engineering, material failure, such as wear or fatigue fracture, often occurs on the surfaces of components. There is no report on surface modification and strengthening of additively manufactured EHEAs. Therefore, this study successfully utilized laser remelting (LR) technology to enhance the surface properties of an AlCoFeNi EHEA fabricated by using double-wire arc AM technology. After LR, the distance between adjacent regular eutectic regions and lamellar spacing of the EHEAs significantly decreased, and the proportion of strictly semicoherent face-centered cubic/body-centered cubic interfaces increased. When microhardness increased from 277.7 HV to 302.3 HV, the average friction coefficient and wear rate of the alloys decreased by 32.5% and 51.1%, respectively, and hardness and wear resistance significantly improved. This study has laid a solid foundation for the engineering application of the combination of LR and AM and also provided new ideas for improving the surface performance of additively manufactured EHEAs.

Microstructure and mechanical properties of Co-free AlCrFeNiTi0.2 eutectic high-entropy alloy

Microstructure and mechanical properties of Co-free AlCrFeNiTi0.2 eutectic high-entropy alloy

Evolution of tool wear and machining quality during dry milling of AlCoCrFeNi2.1 eutectic high entropy alloy

AlCoCrFeNi2.1, a new class of eutectic high entropy alloy (EHEA) has drawn significant interest owing to the lamellar structure of alternating face-centered cubic (FCC) and B2 phases. Properties such as high strength and high plasticity render the machining of this alloy challenging. Addressing this issue, the milling experiments were conducted under dry conditions to investigate the machining quality of AlCoCrFeNi2.1 EHEA as well as the tool wear. The cutting temperature and cutting force were measured to explain the changes in tool wear and machining quality. The tool wear mechanisms and evolution modes were clarified. Finally, the change of surface roughness and surface morphology under different parameters were analyzed and the characterization method of plastic flow marked by B2 phase was proposed. Results showed that both the cutting temperature and cutting force increase as the milling parameters become larger. The width of flank wear increases with the increase of the cutting speed and the feed rate when the volume of material removal volume is constant. The tool wear modes evolved differently with different cutting parameters, for instance, abrasive wear dominated while the cutting speed was less than 80 m/min, but for higher speeds up to 110 m/min, adhesive wear and coating peeling occurred. As the cutting speed increases further, crater wear on the rake face starts to arise in addition to the flank wear. Abrasive wear and adhesive wear with increasing feed rate were dominant until a certain threshold (0.10 mm/tooth) beyond which the coating peels off the tool. Furthermore, chipping occurred for a higher feed rate of 0.14 mm/tooth. In particular, the formation of tool adhesive wear is mainly caused by the FCC phase adheres. In terms of machining quality, larger cutting parameters will worsen the surface roughness and morphology as well as lead to deeper subsurface plastic flow. The research will be conducive to promoting the applications of AlCoCrFeNi2.1 HEA.

Tuning of the mechanical properties of a laser powder bed fused eutectic high entropy alloy Ni30Co30Cr10Fe10Al18W2 through heat treatment

Eutectic high entropy alloys (EHEA) with an exceptional combination of strength and ductility are promising candidates as advanced structural materials. However, achieving an optimal balance between the properties in additively manufactured EHEAs is an outstanding challenge. In this work, Ni30Co30Cr10Fe10Al18W2 EHEA was additively manufactured using the laser powder bed fusion (LPBF) technique. In the as-fabricated state, it exhibits a dual-phase nano-lamellar structure consisting of FCC/L12 and B2 phases. Post-fabrication heat treatments were explored for modulating microstructure and, in turn, enhancing the mechanical properties, so as to achieve an optimum balance between strength and ductility. Upon heat treatment at 750 °C for 1 h, part of the B2 phase transformed into FCC, with the appearance of the tungsten-rich precipitates inside the B2 phase. The average interlayer spacing of the FCC/L12 lamellae increased to 124 nm, while that of B2 lamellae decreased to 86 nm, resulting in an alloy with an ultimate tensile strength (UTS) of 1811 MPa, although the strain to failure (εf) decreased to 2 %. Upon increasing the heat treatment temperature to 1000 °C, the average interlayer spacings of the FCC and B2 phases increased to 210 and 187 nm, respectively, which resulted in a more balanced mechanical behavior with UTS and εf of 1332 MPa and 9.3 %, respectively. This study provides an effective approach for microstructural modulation and enhancement of mechanical properties of LPBF fabricated EHEA via post-fabrication heat treatment, offering insights for developing future high-performance alloys for advanced structural applications.

Effect of Laser Energy Density on Microstructures and Properties of Additively Manufactured AlCoCrFeNi2.1 Eutectic High-Entropy Alloy

Effect of Laser Energy Density on Microstructures and Properties of Additively Manufactured AlCoCrFeNi2.1 Eutectic High-Entropy Alloy

Insights into the relationship between particulate flow characteristics and local erosion behaviour under waterjet: The role of particle-fluid-surface interaction

In this study, the erosion characteristics of eutectic high entropy alloy under the liquid–solid two-phase flow is investigated by a coupled numerical-experimental method, in order to reveal the intrinsic relationship between microscopic erosion mechanism (experimental test) and the related particle-fluid-surface interaction (CFD modelling). Furthermore, instead of the common relation between average erosion rate and mainstream flow velocity, the relationship between local erosion distribution and local particulate flow characteristics is clarified. The erosion rate and erosion pattern match well between the experiment and simulation. The results demonstrate that NiCoCrFeNb0.45 exhibits superior anti-erosion performance when compared to other widely used equipment metals. The erosion profile agrees well with the shape of surface velocity distribution, indicating a close relationship between surface erosion behaviour and flow characteristics. In particular, the erosion pattern at a normal angle appears as a symmetric ring due to the flow stagnation phenomenon, with slight erosion damage in the centre area and severe erosion in the surrounding, whereas the erosion profile at an oblique angle displays an elliptic shape, with severe erosion damage in centre. Notably, the primary erosion mechanism varies dramatically in different surface regions, induced by the various impact velocities and angles associated with the corresponding changes in the flow field. This study provides a deeper understanding of erosion behaviour in terms of the interrelationship among the material mechanical properties, particulate flow field and particle-surface impingement behaviour.

Enhanced oxidation resistance in nano-lamellar CoCrFeNiNbx (0.45 ≤ x ≤ 0.55) eutectic high entropy alloy during cyclic oxidation at 700–1100 °C

We report the superior oxidation resistance of nano-lamellar CoCrFeNiNbx (x = 0.45, 0.50, 0.55 atom ratio) eutectic high entropy alloy (EHEA) at 700–1100 °C. The as-cast microstructure comprises of nano-lamellar eutectic FCC+Laves phases. The oxidation kinetics followed the parabolic rate in between 700–800 °C, whereas, near-parabolic kinetics is followed at 900 °C. The addition of Nb improves the oxidation and spallation resistance of the EHEAs. A protective outer-oxide layer containing Cr2O3, FeCr2O4-type spinels, whereas, an inner-oxide layer containing Nb2O5, CrNbO4 were formed during oxidation. The mechanism of protection and the superiority of EHEAs as high temperature alloy are explored.

From Small Data Modeling to Large Language Model Screening: A Dual-Strategy Framework for Materials Intelligent Design.

Small data in materials present significant challenges to constructing highly accurate machine learning models, severely hindering the widespread implementation of data-driven materials intelligent design. In this study, the Dual-Strategy Materials Intelligent Design Framework (DSMID) is introduced, which integrates two innovative methods. The Adversarial domain Adaptive Embedding Generative network (AAEG) transfers data between related property datasets, even with only 90 data points, enhancing material composition characterization and improving property prediction. Additionally, to address the challenge of screening and evaluating numerous alloy designs, the Automated Material Screening and Evaluation Pipeline (AMSEP) is implemented. This pipeline utilizes large language models with extensive domain knowledge to efficiently identify promising experimental candidates through self-retrieval and self-summarization. Experimental findings demonstrate that this approach effectively identifies and prepares new eutectic High Entropy Alloy (EHEA), notably Al14(CoCrFe)19Ni28, achieving an ultimate tensile strength of 1085 MPa and 24% elongation without heat treatment or extra processing. This demonstrates significantly greater plasticity and equivalent strength compared to the typical as-cast eutectic HEA AlCoCrFeNi2.1. The DSMID framework, combining AAEG and AMSEP, addresses the challenges of small data modeling and extensive candidate screening, contributing to cost reduction and enhanced efficiency of material design. This framework offers a promising avenue for intelligent material design, particularly in scenarios constrained by limited data availability.

A novel corrosion resistant NiFeCrAlTi eutectic high entropy alloy with high strength and ductility

We present a novel corrosion resistant Ni42.6Fe24.6Cr16.4Al13.4Ti3 eutectic high entropy alloy (EHEA), which consists of FCC(L12) phase and BCC(L21) phase. The FCC and BCC phases contain numerous nano-precipitates, with sizes of ∼10 nm and 80 nm, respectively. The as-cast EHEA exhibits exceptional mechanical properties with a yield strength of ∼730 MPa, an ultimate tensile strength of 1220 MPa and elongation of 25 %, surpassing those observed in other as-cast EHEAs. The excellent mechanical properties are attributed to the extensive dislocation activities and precipitation strengthening in both BCC and FCC phases, as well as hetero-deformation induced (HDI) strengthening. Besides, the Kurdjumov-Sachs (KS) orientation relationship between adjacent phases promotes the cooperative deformation of both constituent phases, thereby enhancing the ductility of the EHEA.

Electrochemical corrosion behavior and passive film properties of Fe2Ni2CrV0.5Nbx (x=0.2, 0.4, 0.6, 0.8) eutectic high-entropy alloy coating prepared by laser cladding

The phase composition, microstructure morphology, and corrosion behavior of Fe2Ni2CrV0.5Nbx (x=0.2, 0.4, 0.6, 0.8) eutectic high-entropy alloy (EHEA) coatings produced via laser cladding were investigated. The research delved into discerning the phase structures and microstructural variations of the EHEA coatings concerning differing Nb compositions. The findings highlighted a direct correlation between Nb content and the volume fraction of the eutectic structure, specifically the FCC/Laves phases. Electrochemical evaluations, including diverse tests such as potentiodynamic polarization, electrochemical impedance spectroscopy, cyclic polarization, Mott-Schottky measurements, and X-ray photoelectron spectroscopy, revealed distinct corrosion behaviors among the EHEA variants. Notably, the Fe2Ni2CrV0.5Nb0.2 coating exhibited relatively superior corrosion resistance compared with Fe2Ni2CrV0.5Nbx (x=0.4,0.6,0.8) coatings, attributed to its lower corrosion current density (Icorr) and the formation of a thicker passive film with prolonged passivation duration. Conversely, the Fe2Ni2CrV0.5Nb0.8 coating, characterized by increased eutectic structures and grain boundary density, yielded a thicker yet non-uniform passive film with higher vacancy defects. This comprehensive exploration into the corrosion behavior and passive film properties of these EHEA coatings provides a reference for designing materials that hold promising implications for future corrosion-resistant material development in industrial parts repair applications.

Deposition, microstructure and hardness of AlCoCrFeNi2.1 eutectic high entropy alloy coatings by cold spray, HVOF, and plasma spray

Eutectic high entropy alloys (EHEAs) are reported to exhibit excellent mechanical properties which are useful for coating applications. In this study, we have produced AlCoCrFeNi2.1 EHEA coatings using the cold spray, high velocity oxygen-fuel (HVOF), and plasma spray techniques and compared their bonding characteristics, microstructure and hardness. We observe body-centered cubic (bcc) to face-centered cubic (fcc) phase transformations in all the types of coatings. The high processing temperatures in HVOF and plasma sprays lead to the segregation and depletion of Al from Ni-and Al-rich bcc/B2 regions and form Al2O3. In the cold sprayed coatings, we observe that a fraction of lamellar microstructure is preserved after cold spraying. Regarding the hardness, the cold sprayed coatings exhibit hardness in the range of 440–498 HV due to high work hardening and low oxygen content below 4 at.%; the HVOF coatings show the hardness in the range of 380–556 HV due to the effects of oxide dispersion strengthening with 13–28 at.% oxygen; The plasma sprayed coatings exhibit the hardness in the range 208–258 HV and 6.1–13.4 at.% oxygen. This study demonstrates the feasibility to produce thick and dense EHEA coatings using the above spray techniques, and the cold sprayed coatings exhibit relatively high hardness and low oxygen levels.

Directionally solidified NiCoCrFeAlW eutectic high-entropy alloy: Microstructure and mechanical properties

The NiCoCrFeAlW eutectic high-entropy alloy exhibits a balanced combination of ductility and strength. This study examines the microstructure evolution and mechanical properties of the Ni30Co30Cr10Fe10Al18W2 alloy at varying growth velocities (10, 20, 50, 100, and 200 μm/s), which in its as-cast state, features a microstructure that includes both coarse dendrites and lamellar eutectic. The structure of the coarse dendrites is characterized by an ordered body-centered cubic (B2) phase, while the lamellar eutectic, features a combination of face-centered cubic (FCC) and ordered B2 phases. The microstructure, characterized by lamellar and dendritic structures that are parallel to the growth direction after directional solidification, undergoes a morphological transition at the solid-liquid interface from a planar to a dendritic form as growth velocity increases. The tensile fracture strength initially increases with the growth velocity, reaching a peak of 1286 MPa at a velocity of 50 μm/s, and then subsequently decreases as the growth velocity continues to increase. Directional solidification results in an increase in sample elongation with increasing growth velocity, achieving an elongation of 22.5% at 200 μm/s. An examination of the deformation mechanism reveals that the lamellar structure, composed of the more ductile FCC phase and the harder B2 phase, effectively harmonizes the plasticity and strength of the alloy. Therefore, directional solidification significantly adjusts the eutectic microstructure's orientation, thereby enhancing the mechanical properties along the direction of solidification.

Simulation-guided design of novel precipitation-strengthened eutectic high entropy alloy

Eutectic high entropy alloys (EHEAs) with hard and ductile phases are promising for high-temperature applications. The mechanical properties of EHEAs can be improved by incorporating precipitates in the ductile phase. The study focuses on the CALPHAD-guided alloy design approach for developing EHEA with cuboidal L12 precipitates in the ductile phase. The newly designed alloy (Al0.17CoCrFeNiTa0.22) is subjected to a simulation-guided heat treatment cycle. The Al0.17CoCrFeNiTa0.22 alloy shows FCC phase with a needle-like Ta-rich precipitate at 12 h and Ni-Al-rich cuboidal precipitate at 24 h of heat treatment. The calculated entropy of mixing of cuboidal precipitate is higher than that of needle-like precipitate. The detailed TEM characterisation confirms the characteristics of precipitates and microstructural changes correlated with microhardness measurements. The study proposes a novel EHEA system with a nano-scale precipitation-strengthened FCC phase and eutectic colony.

Enhanced hot corrosion resistance of AlCoCrFeNi2.1 high entropy alloy coatings by extreme high-speed laser cladding

Extreme high-speed laser cladding (EHLC) and multiple laser remelting (EHLC-MR) are used to improve hot corrosion resistance of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) coatings by refining their microstructures, introducing low angle grain boundaries (LAGBs) and high densities of dislocations as well as higher compressive residual stresses (CRSs) in the coatings. The experimental results show that finer microstructure, more LAGBs and high densities of dislocations are beneficial to increase Al2O3 nucleation sites and promote the uniform formation of the oxide layer on the coating surface. On the other hand, higher CRSs suppress the initiation and propagation of cracks as well as enhance the adhesion between the oxide layer and the substrate. Thus the hot corrosion resistance of the EHEA coatings under a molten salt of 75% Na2SO4 + 25% NaCl at 900°C is improved significantly. These novel results provide effective approach for designing elevated-temperature materials.

The corrosion behavior and passive film properties of the cast and annealed AlCoCrFeNi2.1 eutectic high-entropy alloy in sulfuric acid solution

The effect of microstructure on the corrosion behavior and film properties of strengthened AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) was investigated. Annealing of the 80 % cold-rolled AlCoCrFeNi2.1 EHEA at 650–1200 ℃ effectively improved the stable passive region to 930 mV, and decreased the passive current density by 25 % to 3.5 μA/cm2 compared with the cast alloy in 0.1 M H2SO4 solution. The improved corrosion resistance of the annealed AlCoCrFeNi2.1 EHEA was attributed to the increasing oxides proportion and thickness of passive film and the reduced composition difference between FCC and B2 phases. The B2 phase in lamellae suffered the severest corrosion.

Nanoindentation behaviors of the AlCoCrFeNi2.1 eutectic high-entropy alloy: The effects of crystal structures

The AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA), as a kind of in-situ composite materials, have achieved good match of strength and plasticity due to its typical eutectic lamella structures. Although many previous studies have investigated the indentation behaviors of the AlCoCrFeNi2.1 EHEA, there are still some controversies about the hardness characteristic of different crystal structures, requiring further clarification. Accordingly, in this study, nanoindentation tests were conducted to investigate the indentation behaviors of different crystal structures (primary L12 phase, primary B2 phase, and the eutectic phase region). The residual indentation and the crystallographic orientations were characterized by the laser scanning confocal microscope, scanning electron microscope, and electron backscatter diffraction. The hardness in different crystal structures were comparatively analyzed and the material deformation mechanisms were discussed correspondingly. The statistic results showed that the eutectic phase region had the lowest hardness, and primary B2 phase had the highest hardness. Furthermore, the slip lines in the primary L12 phase were evenly distributed near the residual indentation, but the slip lines in the eutectic phase region were concentrated near the phase boundaries. These findings are expected to deepen the understanding of the microscale deformation behaviors of EHEAs.

Enhanced an eutectic carbide reinforced niobium alloy by optimizing Mo and W alloying elements

Niobium alloys play an indispensable role in aerospace technology. However, traditional niobium alloys has unsatisfactory or high-temperature strength or limited room-temperature. This work introduces Nb2MoxWyC0.25 alloys with strength-plasticity balance by optimizing refractory alloy elements and eutectic carbides drawing on the design concepts of eutectic high-entropy alloys. The influence of Mo and W contents on the microstructure and mechanical properties of the alloys was studied. The Nb2MoxWyC0.25 alloy contain body-centered cubic (BCC) primary phase and eutectic structures composed of BCC and carbide phases with semi-coherent interfaces. Appropriate additions of Mo and W refine the grain size of the primary BCC phase and cause the carbide phase to evolve from Nb2C to NbC. The Nb2Mo0.5W0.5C0.25 hypoeutectic niobium alloy composed of BCC and Nb2C phases with a relatively small lattice mismatch has a room-temperature yield strength of 1.27 ± 0.04 GPa, compressive strength of 2.03 ± 0.06 GPa, and a fracture strain of 17.8 ± 2.2 %. Solid solution strengthening in the BCC phase and second-phase strengthening of the carbide phase simultaneously enhance the alloy. The fine grain strengthening, reduced crack origination at low mismatch interface, and the crack tip by soft BCC at the phase interface improve the plasticity simultaneously. This paper provides a method to improve the room-temperature plasticity and strength of refractory niobium alloys, laying the foundation for the industrial application of refractory niobium alloys.

Effect of Alloying on Microstructure and Mechanical Properties of AlCoCrFeNi2.1 Eutectic High-Entropy Alloy.

In order to explore the effect of alloying on the microstructures and mechanical properties of AlCoCrFeNi2.1 eutectic high-entropy alloys (EHEAs), 0.1, 0.2, and 0.3 at.% V, Mo, and B were added to the AlCoCrFeNi2.1 alloy in this work. The effects of the elements and contents on the phase composition, microstructures, mechanical properties, and fracture mechanism were investigated. The results showed that the crystal structures of the AlCoCrFeNi2.1 EHEAs remained unchanged, and the alloys were still composed of FCC and BCC structures, whose content varied with the addition of alloying elements. After alloying, the aggregation of Co, Cr, Al, and Ni elements remained unchanged, and the V and Mo were distributed in both dendritic and interdendritic phases. The tensile strengths of the alloys all exceeded 1000 MPa when the V and Mo elements were added, and the Mo0.2 alloy had the highest tensile strength, of 1346.3 MPa, and fracture elongation, of 24.6%. The alloys with the addition of V and Mo elements showed a mixed ductile and brittle fracture, while the B-containing alloy presented a cleavage fracture. The fracture mechanism of Mo0.2 alloy is mainly crack propagation in the BCC lamellae, and the FCC dendritic lamellae exhibit the characteristics of plastic deformation.

Equiaxed microstructure design enables strength-ductility synergy in the eutectic high-entropy alloy

Eutectic high-entropy alloys (EHEAs) represent attractive candidate materials for overcoming the strength-ductility trade-off, which can be enhanced through the directional alignment of the lamellar structure along the loading direction. Here, we put forward a new route to optimize the strength-ductility synergy without orientation dependence. Through a combination of severe plastic deformation and annealing, we convert the initially lamellar structure into a dual-phase structure comprised of ultrafine equiaxed grains. The significant grain refinement improves the yield strength from 703 MPa to 1199 MPa without sacrificing any ductility. During deformation, the localized softening resistance of the achieved dual-phase microstructure avoids necking, and the intrinsic microcrack-arresting mechanism effectively improves the fracture resistance. Grain boundaries and phase boundaries provide nucleation sites for dislocations and restrict dislocation transfer while the strain incompatibility is accommodated by geometrically necessary dislocations. This work demonstrates that dual-phase alloys comprised of ultrafine equiaxed grains provide a pathway for strengthening without loss of ductility.