High-entropy Alloys Research Articles

Expansion of thermodynamic calculation principle of multi-component alloy and its application in the study of thermodynamic properties of the Cr-Mo-Nb-V high entropy alloy

In this paper, based on the improved Miedema model and the quaternary alloy calculation model expanded by Chou model, the activity calculation model of the ternary alloy system is extended to the quaternary alloy system through the ternary alloy activity calculation model of Wagner and Ma Zhongting et al.. In addition, a new deviation function is used in the expanded quaternary alloy calculation model to calculate the thermodynamic properties of quaternary alloys, which meets the characteristics of both non-negativity and reducibility. Using the developed model, this paper calculates the thermodynamic data of each sub-binary, sub-ternary, and quaternary system in the Cr-Mo-Nb-V quaternary high entropy alloy system. Subsequently, this paper analyzes the interactions between components, predicts the possible precipitated phases in the alloy system, and explains the possibility of forming a solid solution in the alloy system. The final results are consistent with those shown in the literatures on studying the Cr-Mo-Nb-V quaternary alloy system, which verifies the applicability of the developed model in the miscible alloy system, enriches the thermodynamic database of Cr-Mo-Nb-V alloy, and provides theoretical reference and ideas for the design of multi-component alloys.

Mechanical properties and biocompatibility evaluation of TiZrNbTaFe high entropy alloy films deposited using a hybrid HiPIMS and RF sputtering system

Given the well-documented low biocompatibility issues associated with conventional metallic biomaterials, there is an urgent need to develop new biomaterials. Biological high entropy alloys (HEAs), designed with non-toxic elements for biomedical applications, represent a significant advancement in metal biomedical materials due to their tunable mechanical properties and excellent biological safety. This study employed a hybrid system that combined a high power impulse magnetron sputtering (HiPIMS) power with a radio frequency (RF) power to synthesize a series of amorphous TiZrNbTaFe HEA coatings, in which the Ti content was varied by changing the RF power applied to the Ti target. One exemplary TiZrNbTaFe film, deposited with a Ti target RF power of 75 W, was thoroughly examined. This film demonstrated several highly promising attributes as a novel metallic biomaterial, including a dense and fine microstructure, good adhesion quality, superior corrosion resistance, and exceptional biocompatibility both in vitro and in vivo. These findings could provide new insights for innovative biomaterials development and help address long-term implantation and implant failure issues.

Development of Ti-Zr-Nb-Ta-Ag high entropy alloy for dental implants: In vitro corrosion behavior, antibacterial effect, and surface characteristics

This study presents a new biological high-entropy alloy (Bio-HEA) composed of 35Ti-35Zr-20Nb-5Ta-5Ag (at. %) for potential dental implant applications. The Bio-HEA underwent processing for various durations of mechanical alloying, followed by compaction and sintering. The processed Bio-HEA was tested for corrosion resistance in an artificial saliva medium, antibacterial properties, and surface characteristics. Surface topography and wettability were investigated using atomic force microscopy, surface profilometry, and contact angle measurements. Mechanical alloying, X-ray diffraction, and scanning electron microscopy revealed the formation of a solid-solution Bio-HEA with body-centered cubic crystal structures, with phase variations depending on the processing conditions. The Bio-HEA exhibited significantly higher microhardness values (4.38 GPa and 5.35 GPa) than commercial pure titanium (CPTi) and Ti-6Al-4V alloy, respectively. An increased ball-milling time resulted in higher microhardness for Bio-HEA and enhanced in vitro corrosion resistance in artificial saliva compared to CPTi. This was evidenced by a significant nobler shift of approximately 200 mV in the corrosion potential, with a prominent decrease of approximately two orders of magnitude in the corrosion current density and a higher charge transfer resistance. Additionally, the Bio-HEA demonstrated a lower contact angle compared to that of the Ti-6Al-4V alloy and CPTi. The Bio-HEA achieved antibacterial efficiencies of 91.76 % and 93.0 % compared to Ti-6Al-4V alloy and CPTi, respectively. The enhanced microhardness, antibacterial properties, in vitro corrosion resistance in artificial saliva, and wettability of Bio-HEA compared to commercial Ti-6Al-4V alloy and CPTi makes it a promising candidate for dental bioimplant applications.

Tribological Performance Enhancement of AISI 1050 Steel through FeNiCrCoMo High-Entropy Alloy TIG Weld Cladding

The tribological behavior of tungsten inert gas (TIG) welded high entropy alloy (HEA) FeNiCrCoMo cladding deposited on AISI 1050 steel substrate was studied. The response surface methodology (RSM) optimized the TIG welding parameters. The SEM images revealed no signs of intermetallic compounds in the cladding, and the XRD analysis showed that the FeNiCrCoMo greatest peak corresponds to the BCC+FCC mixed phase. The microhardness and sliding wear resistance of the cladding were superior compared to the steel substrate owing to the solid solution strengthening and the presence of mixed phase. The worn surfaces of HEA claddings showed the presence of wear debris, grooves and micro-cutting from sliding wear as revealed by the SEM and 3-D profilometry images.

Ultrastrong and ductile superalloy joints bonded with a novel composite interlayer modified by high entropy alloy

Diffusion bonding (DB) with interlayers is sought-after for manufacturing high-performance turbine disks of powder metallurgy (PM) superalloys with precise and intricate inner cavity structures. Developing novel interlayer materials is challenging but crucial for enhancing bonding quality and joint properties. We designed a multi-interlayer composite bonding (MICB) method, employing sandwich-structured interlayers of “BNi2/high entropy alloy (HEA)/BNi2”, to join a PM superalloy FGH98. The MICB joint exhibited an ultrahigh shear strength of ∼1132 MPa and exceptional ductility, indicating a typical ductile fracture pattern with numerous dimples. Owing to the introduction of liquid BNi2 interlayer, initial bonding interfaces were eliminated and replaced by newborn grain boundaries (GBs), preventing brittle interfacial fracture. Due to the diffusion of Al/Ti/Ta from the base metals (BMs), massive ordered γ' nanoparticles also precipitated in the joint. Moreover, the addition of HEA foil reduced the stacking fault energy (SFE) of the joint and facilitated the formation of deformation twins (DTs). Thus, during the deformation process, the γ' nanoparticles, and multiple substructures like stacking faults (SFs), Lomer-Cottrell (L-C) locks, DTs, and 9R phases enhanced the work-hardening capability and strengthened the joint. Simultaneously, the multiplication and interaction of DTs induced a softening mechanism of dynamic recrystallization (DRX) during the entire deformation process and dominated when the plastic instability occurred, resulting in numerous adiabatic shear bands (ASBs) consisting of γ/γ' nano-bands, which indicates a significant improvement of the joint ductility.

Effect of high energy ball milling, heat treatment and spark plasma sintering on structure, composition, thermal stability and magnetism in CoCrFeNiGax (x = 0.5; 1) high entropy alloys

Effect of high energy ball milling, heat treatment and spark plasma sintering on structure, composition, thermal stability and magnetism in CoCrFeNiGax (x = 0.5; 1) high entropy alloys

Cryogenic deformation strengthening mechanisms in FeMnSiNiAl high-entropy alloys

The mechanical properties and deformation mechanisms of a newly developed Co-free FeMnSiNiAl high entropy alloy (HEA) at room and cryogenic temperatures were systematically investigated. The initial tensile deformation at room temperature was dominated by dislocation slipping, with modest strengthening from the Transformation-Induced Plasticity (TRIP) effect due to the deformation-induced FCC → HCP martensitic transformation. Subsequently, the TRIP effect was markedly enhanced during the middle and later stages of deformation, leading to an excellent combination of yield strength (σy, 315.1 MPa), ultimate tensile strength (σu, 773.4 MPa), and fracture elongations (εf, 78.3%). The strengthening by the TRIP effect was significantly enhanced at cryogenic temperatures as a result of enhanced FCC → HCP martensitic transformation. This resulted in a synergetic improvement in strength and ductility at 223 K, with σy of 363.6 MPa, σu of 832.1 MPa, and εf of 87.2%. The enhanced ductility at 223 K was linked to the FCC → HCP → BCC sequential martensitic transformation during the middle and later stages of deformation, which acted as an additional way to accommodate plastic strain and delay strain localization. However, the rapid FCC → HCP transformation at the early stage of deformation at 173 K and 77 K impeded the FCC → HCP → BCC sequential martensitic transformation during subsequent deformation stages, thus remarkably enhancing strength but reducing ductility. Our findings provide new insights into the design and development of TRIP-assisted single-phase FCC HEAs for cryogenic applications.

Exceptional tensile ductility and strength of a BCC structure CLAM steel with lamellar grains at 77 kelvin

The low-temperature tensile brittleness of body-centered cubic (BCC) metals and alloys can seriously compromise their service applications. In this study, we prepared a BCC structured China low activation martensitic steel (CLAM) steel with lamellar grains by regulating the rolling and heat-treatment processes, successfully reversing the decreasing trend of ductility in the steel with decrease in temperature. Compared with current face-centered cubic (FCC) structural steels and high-entropy alloys, the lamellar grained CLAM steel exhibits an excellent synergy of strength and ductility at 77K, but with lower raw material costs. The superior low temperature ductility of the lamellar grained steel can be attributed to an increase in grain strength at low temperatures which promotes the propagation of layered tearing cracks; this in turn leads to a significant increase in the necking area of the steel, thereby compensating for the decrease in ductility. We conclude that our lamellar grain structures can be utilized to significantly enhance the low-temperature tensile ductility of BCC metals and alloys, thereby expanding their service range to cryogenic temperatures.

Nanostructure-induced functional combination of vanishing magnetostriction and magnetic softness in ferromagnetic (GaNi)xCoCrFe (x = 0.4–1.6) high-entropy alloys

Searching for high-entropy alloys with functional properties that emerge from their multi-scale structure, we have investigated the (GaNi)xCoCrFe (x = 0.4–1.6) system. We have characterized structure, microstructure, nanostructure and chemical composition of the individual phases in the multi-phase alloys and determined their magnetic, magnetostrictive and electrical properties. We found that the alloys are ferromagnetic and exhibit functional combination of magnetic softness and vanishing magnetostriction, classifying them as energy-efficient “supersilent” materials (inaudible to a human ear) for alternating-current (AC) electromagnetic applications in the audio-frequency range. The alloys develop a two-phase structure, a face-centered cubic (fcc) and a body-centered cubic (bcc), where the fcc phase fraction decreases, while the bcc fraction increases with the increasing (GaNi)x content. Ferromagnetism of the alloys originates from the highly nanostructured bcc phase, with the ferromagnetic Curie temperatures in the range TC = 750–700 K, depending on x. The fcc phase is not nanostructured and is paramagnetic at room temperature, but undergoes a spin glass transition at Tf≈6.4 K. The magnetic softness and vanishing magnetostriction of the alloys are both nanomagnetic phenomena. The magnetic-softness and magnetostriction parameters of the x = 1.3 and 1.6 alloys make them relevant for supersilent AC applications at low frequencies.

Study on the High-Temperature Oxidation of AlCrFeCoNi-Based High-Entropy Alloys with Trace Si Additions

This research investigates the isothermal oxidation behavior of AlCrFeCoNiSix (x = 0, 0.04, 0.08, 0.12at.%) at 900°C for 96hours from multiple aspects, including the oxidation surface, the oxide layer microstructure, and the oxidation mechanisms. The oxidation kinetics curves of the alloys follow the parabolic oxidation law. After 96hours of oxidation at 900°C, the oxide films of the AlCrFeCoNi and AlCrFeCoNiSi0.04 alloys are primarily composed of Al2O3. In contrast, the oxide films of the Si8 and AlCrFeCoNiSi0.12 alloys consist of an outer layer of Cr2O3/spinel oxides and an inner layer of Al2O3.The results show that the third element effect triggered by the addition of Si can promote the generation of an Al2O3 layer, which has a positive effect on the antioxidant of high-entropy alloys.

Bayesian optimization of 7-component (AlVCrFeCoNiMo) single crystal alloy’s compositional space to optimize elasto-plastic properties from molecular dynamics simulations

Abstract Exploring the vast compositional space of high-entropy alloys (HEAs) promises materials with superior mechanical properties much needed in industrial applications. We demonstrate on the 7-component alloy AlVCrFeCoNiMo system with randomly ordered atoms that this exploration of the compositional space can be accelerated by combining molecular dynamics simulations with Bayesian optimization. Our algorithm is tested on maximizing the shear modulus, resulting in pure Mo, an unsurprising result based on Mo’s large density. Maximizing the yield stress results in Co-, Cr- and Ni-based alloys with the optimal composition varying depending on the presence of defects within the crystal. Finally, we optimize the plastic behaviour by aiming for high stresses while minimizing the deformation fluctuations, and find that a predominantly NiMo alloy’s high lattice distortions ensure a smooth stress response. The results suggest that mechanical properties of 2- to 4-component alloys with optimized composition may be superior to those of equiatomic HEAs without short-range order.

Microenvironment regulation to synthesize sub-3 nm Pt-based high-entropy alloy nanoparticles enabling compressed lattice to boost electrocatalysis

Platinum (Pt) is inevitably employed to facilitate various electrocatalysis including hydrogen oxidation/evolution and oxygen reduction reactions (HOR/HER/ORR), the foundation for renewable energy conversion and storage. Pt-based high-entropy-alloy (HEA) catalysts have been recently presenting promises to improve intrinsic activity of unit mass Pt. However, their current synthesis methods always produce large particles—some can control small size but have to use complicated recipe and/or highly toxic and expensive chemicals. Alternatively, a facile microenvironment regulation strategy is herein proposed to tune solvent polarity and nanoparticle-support interactions within the precursors for carbon-thermal shock pyrolysis. We found that the decreased solvent polarity and enhanced particle-support affinity can jointly control the nanoparticle size ultimately to ~2.68nm with ~10wt % Pt loading. The compressed lattice fringe in such HEA particles leads to electron accumulation at Pt atoms and build a moderate charge density rearrangement, showing superior multifunctional HER/HOR/ORR activity to Pt/C in acidic media.

A significant improvement in corrosion resistance and biocompatibility in ZrNbTiCrCu high-entropy films induced by the precipitation of Cu

Utilizing nanotechnology and composites to create a protective film on titanium alloy is an effective means of achieving the desired high performance. Self-assembly of nanocomposite structures offers a promising route to forming high entropy alloy films (HEAFs), but controlled preparation remains challenging. This work used magnetron sputtering through adjusting preparation parameters to prepare ZrNbTiCrCu HEAFs, achieving a significant improvement in corrosion resistance and biocompatibility induced by the precipitation of Cu. According to the electrochemical corrosion test, without obvious corrosion pits on the surface of S2 after corrosion, a passivation film composed of bimetallic oxide CuCrO2 formed on the film surface, indicating that ZrNbTiCrCu HEAFs have remarkable corrosion resistance performance. In the cytocompatibility experiment, the cell viability of HEAFs reached over 95 % due to the precipitation of Cu, suggesting their excellent biocompatibility. In addition, ZrNbTiCrCu HEAFs exhibit outstanding antibacterial ability, especially when the sputtering current is 0.6 A, and the in vitro antibacterial rate of the sample against Escherichia coli is close to 99 %.

Effect of annealing on microstructure and mechanical properties for as-sintered Co-free Al1·8CrCuFeNi2 high entropy alloy

Effect of annealing on microstructure and mechanical properties for as-sintered Co-free Al1·8CrCuFeNi2 high entropy alloy

Improving strength and plasticity via pre-assembled dislocation networks in additively manufactured refractory high entropy alloy

Refractory high entropy alloys (RHEAs), as a novel class of multi-principal element alloys, have attracted significant attention owing to their excellent properties. However, their low plasticity limits their potential applications, while the high melting points of the alloying elements face challenges to additive manufacturing (AM). Herein, RHEA, with extensively distributed cellular structure within their grains, was successfully fabricated using AM. Furthermore, we proposed a simple strategy to form a complete dislocation network within the cellular structure region in advance through cyclic deformation processing in the elastic stage (microplastic deformation). Dislocation networks are entangled with other dislocations, creating numerous pinned points adjacent cell walls, which impede dislocation motion. As a result, the cyclic deformation processing of RHEA achieves a yield strength of 1136 MPa while maintaining 50% deformation strain without fracturing. The cyclic deformation processing method provides a route to strengthen additively manufactured alloys, offering a solution to overcome the trade-off between strength and plasticity.

Enhancing room and cryogenic temperatures mechanical properties of FeCoCrNiMn high entropy alloys with high content of inexpensive element P

Enhancing room and cryogenic temperatures mechanical properties of FeCoCrNiMn high entropy alloys with high content of inexpensive element P

Enhanced strain-hardening in newly designed Co-free austenitic high entropy alloys with an optimised nitrogen solubility

Enhanced strain-hardening in newly designed Co-free austenitic high entropy alloys with an optimised nitrogen solubility

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.

Tailoring strength and ductility in novel Ni50Cr20Co15Al10V5 high entropy alloys by cold-rolling followed by aging treatment

Tailoring strength and ductility in novel Ni50Cr20Co15Al10V5 high entropy alloys by cold-rolling followed by aging treatment

Microstructure and mechanical properties of MoNbVTa0.5Alx refractory high entropy alloys

The specific strength of refractory high entropy alloys (RHEAs) is usually impaired due to the high density of constituent elements. In order to develop a low-density RHEA, the microstructure and mechanical property of MoNbVTa0.5-based RHEAs with various Al additions have been investigated in this study. All samples exhibited a monolithic BCC solid solution structure. The addition of Al resulted in improved yield strength but a degraded plasticity at ambient temperature. In contrast, the yield strength consistently decreased with increasing Al content at elevated temperatures, and the softening occurred at ~1000 °C. MoNbVTa0.5Al0.3 exhibited high specific strengths of 119.2 MPa cm3/g, 108.6 MPa cm3/g and 97.3 MPa cm3/g at 600 °C, 800 °C, and 1000 °C, respectively.