High-entropy Alloy Films Research Articles

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.

Effect of C additives with 0.5 % in weight on structural, optical and superconducting properties of Ta–Nb–Hf–Zr–Ti high entropy alloy films

We investigated the superconducting (SC) properties of Ta–Nb–Hf–Zr–Ti high-entropy alloy (HEA) thin films with 0.5 % weight C additives. The C additives stabilize the structural properties and enhance the SC critical properties, including μ0Hc2 (13.45 T) and Tc (7.5 K). The reflectance of the C-added HEA film is enhanced in the low-energy region, resulting in a higher optical conductivity, which is consistent with the lower electrical resistivity. In addition, we observed SC vortices in the C-added HEA film using magnetic force microscopy. The magnetic penetration depths (λ) of the pure HEA and C-added HEA films were estimated from their Meissner force curves by comparing them with those of a reference Nb film. At 4.2 K, the λ of the C-added film is 360 nm, shorter than that of the pure HEA film (560 nm), indicating stronger superconductivity against an applied magnetic field.

High creep resistance in amorphous/crystalline dual-phase nanostructured CoCrFeNiMn high entropy alloys

Amorphous/crystalline dual-phase metallic materials received great attention owing to their synergistic combination of strength and ductility. However, the mechanisms governing creep deformation in these dual-phase materials are largely elusive. In the present letter, the creep deformation of amorphous/nanocrystalline CoCrFeNiMn high-entropy alloy (HEA) films is investigated through nanoindentation creep testing. It is suggested that dual-phase HEAs exhibit reduced creep strain compared to their monophase counterparts, and even surpass the performance of coarse-grained variants. This behavior arises from diffusion processes within the amorphous phase and the capacity for nucleation/annihilate of dislocations at amorphous/nanocrystalline interfaces. Furthermore, it is proposed that the presence of glass shell significantly influences the creep behavior of dual-phase HEAs.

Effect of Mo on surface reconstruction of FeCoNi-based high entropy alloy film electrode for oxygen evolution reaction

The selection of elements, tune of compounds types and modification of structure are important ways to improve OER activity of high-entropy alloys. The reconstruction behavior of film electrodes during OER process revealed that Mo element has a strong promoting effect on the reconstruction of FeCoNi-based films. It is shown by first-principles that electron-deficient region could be formed near Mo, and electron-rich region could be formed near surrounding elements of Mo. Charge transfer may be the reason that Mo promotes reconstruction of high-entropy alloys. Compared with FeCoNiCr film electrode, FeCoNiCrMo film electrode, the 2p3/2 binding energy peaks of Fe/Co/Ni in which are shifted forward, has more oxygen-containing species and oxygen vacancies. The study also revealed the existence of lattice oxygen mechanism during OER process. The deposition thickness of alloy film has a linear relationship with sputtering time and deposition rate of FeCoNiCrMo. There is an optimal deposition thickness of FeCoNiCrMo film electrode for OER. FeCoNiCrMo film electrodes have the most excellent OER performance: the overpotential is 268 mV, and the Tafel slope is 57.6 mVdec−1.

Performance and mechanism of electrocatalytic oxidation of urea based on carbon-doped FeCoNiCrMn high entropy alloy film

The application and research of high entropy alloy electrodes in urea oxidation reactions (UOR) are significant. In this study, FeCoNiCrMn, FeCoNiCrMnO, and FeCoNiCrMnC high entropy alloy thin films were prepared by magnetron sputtering by controlling the sputtering power, varying the sputtering atmosphere, and using double target co-sputtering, respectively. The microstructure and surface morphology of the electrode were observed and analyzed by X-ray diffraction, scanning electron microscope, transmission electron microscope, and atomic force microscope. In addition, the chemical state of the elements on the electrode surface was analyzed by X-ray photoelectron spectroscopy (XPS) to clarify the mechanism related to the excellent UOR performance of the electrode. The study found that a small amount of carbon doping can greatly improve the UOR performance of this type of electrode. The amorphous FeCoNiCrMnC electrode has more potential UOR active sites than the face-centered cubic FeCoNiCrMn electrode. After cyclic voltammetry (CV), the potential active sites of the electrode are activated, and the active substances of these electrodes are increased, furthermore, the UOR performance of these electrodes has improved. Since it has 200 cycles of CV, the 10 mA cm−2 potential of FeCoNiCrMnC electrode for UOR is only 1.337 V. After 100 days of natural aging, the catalytic ability of the electrode not only did not decrease but slightly improved, with a potential of 1.321 V at 10 mA cm−2, reflecting the good stability of the catalytic electrode.

Interfaces enhanced plasma irradiation resistance in CrMoTaWV/W multilayer films through blocking He diffusion

The performance of plasma-facing materials (PFMs) is one of the key factors that significantly impact the stability of operation in fusion reactors. Herein, a new CrMoTaWV/W (high entropy alloy (HEA)/W) multilayer structure is designed as PFM to investigate its resistance to He plasma irradiation. It was observed that the introduction of the interfaces effectively absorbed plenty of He atoms, preventing them from diffusing into the material and delaying the formation of fuzz incubation zone, therefore, enhancing the resistance to plasma irradiation. The thickness transformed to fuzz in the HEA/W multilayer films was observed to be about two-thirds of those in the CrMoTaWV (HEA) film. Additionally, the fuzz growth rates in HEA/W multilayer films are lower than the average growth rate of bulk W and HEA films combined. These findings highlight a promising new avenue for the exploration of high-performance PFMs.

Formation and characterization of Pt-containing magnetic high entropy alloy film from multilayer precursor

Pt-containing high entropy alloy films (HEAFs), FeCoNiCuxPtx (x = 0.2, 0.4, 0.6, 0.8, 1.0), have been prepared from multilayer precursors using a two-step method involving magnetron sputtering deposition and vacuum annealing. It has shown that through vacuum annealing at elevated temperatures, complete mixing of the multilayer component can be realized to form uniform high entropy alloy films. By changing their concentrations, the effects of Pt and Cu on microstructure and magnetic properties of FeCoNiCuxPtx HEAFs have been systematically investigated. The results show that FeCoNiCuxPtx HEAFs are of disordered FCC solid solution structure, exhibiting soft ferromagnetic behavior and strong in-plane magnetic anisotropy. FeCoNiCu0.2Pt0.2 HEAFs, with MS = 802 emu/cm3, HC = 52.0 Oe, HK = 2.3×104 Oe, and ρ =3.8×10−7 Ω·m, are suitable for application as the core material of high frequency thin film inductors. It is found that Pt-containing HEAFs show relatively high saturation magnetization due to the fact that Pt-containing HEAFs tend to have larger lattice parameter, which may promote the exchange interaction among the magnetic Fe, Co and Ni atoms in FeCoNiCuxPtx HEAFs. This result is further supported by DFT calculations.

Effect of Si concentration and substrate temperature on the microstructure and magnetic properties of FeCoNiCu0.5Six high entropy alloy films

It has been known that Si has the effect to increase the resistivity, permeability, and to decrease the magnetostriction coefficient in Si-containing steel as soft magnetic material. On the other hand, high-entropy alloys are intensively studied as soft magnetic materials in recent years, especially as thin films. In the present work, Si-containing (FeCoNiCu0.5Six) high entropy alloy films (HEAFs) have been prepared by magnetron co-sputtering under different deposition conditions. The microstructure and magnetic properties of FeCoNiCu0.5Six HEAFs have been investigated to clarify the effects of Si concentration on microstructure formation and magnetic properties. It has been found that Si addition strongly affects the magnetic properties of FeCoNiCu0.5Six HEAFs of FCC phase by decreasing the coercivity of the films, but hardly affects the phase formation in the films. On the other hand, it has been found that deposition of the films at moderate high substrate temperatures greatly improve the magnetic properties by increasing the saturation magnetization while keeping low coercivity.

Investigation of hardness, tribological and adhesion properties of TiAlNiVN HEA films heat treated at different temperatures

TiAlNiVN high entropy alloy (HEA) films were firstly produced in the literature using the magnetron sputtering system. These films were subjected to heat treatments at different temperatures between 750 °C and 900 °C. Strong TiN and VN crystal structures were observed in all the annealed films. The composition of each element constituting TiAlNiVN HEA films was within a concentration range of 5–35 %. The presence of TiAlNiVN HEA films was confirmed by X-ray photoelectron spectroscopy (XPS) analysis. D-850 film had the highest hardness of 25.7 GPa and exhibited the lowest wear rate at 2.45 × 10−5 mm3/(N.m), attributable to its lowest surface roughness (0.22) and friction coefficient (0.44). Subsequent to the heat treatment, there was a substantial enhancement in the adhesion performance of the films, culminating in a high critical load value of 80 N. This study revealed that nitride-based TiAlNiVN HEA films could be enhanced in terms of hardness, tribological, and adhesion properties after heat treatment. Considering the adhesion performance, it is anticipated that the films we have produced will be a promising alternative to traditional nitride-based coatings in challenging and complex service conditions.

High-temperature wear resistance improvement mechanism of TiAlCrNiSiNbx high-entropy alloy films through sliding wear-induced gradient nanostructure

TiAlCrNiSiNbx high-entropy alloy films (HEFs) with varying Nb concentrations were deposited using multi-target magnetron co-sputtering at a controlled sputtering power. At room temperature (RT), 300 ℃, 500 ℃ and 700 ℃, the average coefficients of friction (COF) and wear rates of TiAlCrNiSNbx HEFs were lower than those of TC4 alloy. TiAlCrNiSiNbx HEF with a Nb content of 12.36 at% exhibited the best wear resistance at 700 ℃. A nanocomposite layer (∼260 nm) and a plastic deformation region (∼1.2 µm) formed on the film during the wear at 700 ℃. The Al2O3, Cr2O3, SiO2, and Nb2O5 in the nanocomposite layer facilitated the formation of a dense oxide layer. The cooperative deformation effect of nanocrystalline metal oxides and amorphous phases is conducive for inhibiting strain localization and enhancing wear resistance. The grain size of the nanocomposite layer was significantly refined, with an average size of 3.98 nm. This was attributed to the grain refinement caused by the interaction of dislocations and deformation twins in the plastic deformation region, which improved the strength and hardness of the film. The gradient nanostructure of the nanocomposite layer and plastic deformation region led to a more homogeneous plastic deformation, effective inhibition of strain localization and suppression of the micro-crack.

Microstructure evolution and mechanical properties of refractory high-entropy alloy nitride film

The (TiZrNbMo)Nx refractory high-entropy alloys (RHEAs) nitride films were fabricated using reactive magnetron sputtering by modifying the N2 flow rate ratio in the mixed N2 + Ar atmosphere. The incorporation of the N element induced a phase transition in the (TiZrNbMo)Nx films from body-centered cubic (BCC) to face-centered cubic (FCC) structure, accompanied by increasing in the amorphous phase. With the introduction of N2, the hardness of (TiZrNbMo)Nx films firstly increased significantly to 25.2 GPa when the N2 flow rate ratio was at 50 % and then decreased slightly to 18.5 GPa when the N2 flow rate ratio was at 75 %. Theoretical analysis shows that the doping of N element enhances the solid strengthening effect, with the formation of nitride phases and grain boundary (GB) strengthening effect significantly contributing to the enhanced hardness. Furthermore, the addition of N element can also inhibit grain rotation and GB sliding during deformation. This work provides a new insight into understanding the structure and properties of refractory high-entropy alloy films.

Deposition of high entropy alloy sub-surface films on metal substrates via DC magnetron sputtering with a CoCrFeMnNi target

High entropy alloys and high entropy alloy films (HEFs) are gaining increasing attention in the research community due to their superior mechanical properties. CoCrFeMnNi is one of the most investigated of these alloys in the literature; however, CoCrFeMnNi HEFs have not yet been extensively reported. To improve our understanding of the processes occurring during fabrication of CoCrFeMnNi HEFs, here, DC magnetron sputtering using a CoCrFeMnNi equimolar target is used to deposit HEFs on glass substrates, A5052 aluminum sheets, and S45C steel sheets. The resulting HEFs are observed to be embedded as sub-surface bands, less than a micrometer under the substrate surface. This is attributed to implantation of the HEF elements into the base material due to the high deposition energy of sputtering. Another possibility is that substrate elements migrate to the surface in an Ar plasma-assisted process. The HEF crystallite size on glass substrates was determined by x-ray diffraction to be several nanometers, meaning that high hardness is expected in HEFs produced by DC magnetron sputtering.

Microstructure and antibacterial properties of AlCrTiZrWN high-entropy alloy nitride synthesized using HiPIMS under various N2/Ar flow ratios

This paper reports on the use of high-power impulse magnetron sputtering (HiPIMS) to deposit (AlCrTiZrW)Nx high-entropy alloy (HEA) nitride films to a thickness of 1 μm on SKH-9 high-speed steel, SUS304 stainless-steel, and Si wafers. The primary aim was to elucidate the effects of N2/Ar flow ratio (from 10/100–150/100 sccm) on the structure of the resulting materials and antibacterial properties. Co-sputtering was performed using multiple simultaneous targets to overcome the difficulties in manufacturing HEA targets at industrial scales. XRD analysis revealed a FCC structure with (111) orientation under nitrogen gas flow of 70 sccm. Increasing the nitrogen flow to 90 sccm shifted the preferred orientation to the (200) direction. The highest water contact angle (113°) and highest hardness value (27.6 GPa) were achieved under a nitrogen flow of 70 sccm, while the best Rp value (22.7 × 105 Ω‧cm2) was achieved under 110 sccm. The antibacterial performance of the coated samples exceeded that of uncoated SUS304 stainless-steel. Overall, the incorporation of nitrogen had positive effects on HEA film properties.

Terahertz characterization of nano-scale high-entropy alloy films and their high-contrast grating applications

We investigated the optical constants of thin films of the Nb25Mo25Ta25W25 alloy, which belongs to high-entropy alloys (HEAs), with a transmission terahertz (THz) measurement system and discovered that the refractive index, extinction coefficient, and conductivity of the HEA thin film measured in the range of 0.3–1.0 THz all increased as the thickness of the thin film increased (the thickness was maintained in the range between 10 and 40 nm). According to the experimental results, this alloy with a high refractive index is suitable for producing high-contrast gratings (HCGs). The principle behind achieving a high contrast with a high-reflection HEA grating is to harness the confined plasmonic energy within the grating, thereby enhancing the localized plasmonic energy within the grating. This work elucidates that we can not only fabricate THz components by controlling the thickness of the thin film but also utilize the high refractive index of this material to create HCGs.

Enhancing wear resistance: In-situ ceramic phase precipitation for strengthening and toughening FeCoNiCrNx high-entropy alloy films

FeCoNiCr high-entropy alloys have attracted widespread attention because of their excellent toughness; however, their insufficient hardness limits their application in wear-resistant films. The introduction of non-metallic elements is an effective method for strengthening high entropy alloys films. In this study, high-entropy alloy films of FeCoNiCrNx with varying nitrogen content were fabricated using reactive magnetron sputtering. The influence of nitrogen content on the structure, mechanical properties, and tribological behavior of these high-entropy alloy films was studied. With an increase in nitrogen content, the FeCoNiCrNx film undergoes amorphization and simultaneous precipitation of Cr2N phases. At lower nitrogen flow rates (0–4 sccm), the film exhibits lower hardness (8.51–10.97 GPa) and poor wear resistance. At moderate nitrogen flow rates (8 sccm), the film exhibits enhanced hardness (12.8 GPa) and toughness, leading to favorable wear resistance (4.04 × 10−6 mm3 N−1 m−1). A further increase in the nitrogen flow rates (12–16 sccm), while raising hardness (13.08–15.17 GPa), leads to a slight reduction in toughness and consequently, a mild decrease in wear resistance (4.37–5.09 × 10−6 mm3 N−1 m−1). A biphase structure design combining FeCoNiCr high entropy alloy and ceramic (Cr2N) improved the strength and toughness of FeCoNiCrNx and significantly enhanced its wear resistance, thus enhancing its application potential.

Role of the structure order in the transport and magnetic properties of high-entropy alloy films

The fabrication and development of high-entropy alloys (HEAs) with exceptional functionalities is a rapidly expanding field with numerous applications. When the role of entropy in HEAs is considered, the extrinsic factors, such as the existence of grains and different phases, need to be separated from the intrinsic configurations of the atomic lattice. Here, we fabricated the CoCrFeNi2Al0.5 HEA/muscovite heterostructures, and some were prepared as epitaxial bilayers and others were prepared as an amorphous system. These two systems are classified into atomic-site disordered (ASD) and structurally disordered (SD) states, respectively, without the extrinsic effects for the determination of the crystal lattice role in high-entropy states. In this study, we determined the role of the structure order in correlation with the structural, electronic, and magnetic properties of HEAs using a combination of energy-dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy, magneto-transport, ac magnetometry, and X-ray absorption spectroscopy with magnetic circular dichroism. The ASD state showed fully metallic behavior. In contrast, the SD state showed a metallic behavior with intense magnetic saturation, which was called Kondo-like behavior, under 50 K with a low-temperature coefficient of resistivity of ~64 ppm/°C. The difference between the saturation magnetic moment and the electron relaxation behavior in the ASD and SD states resulted from the existence of the structural order affecting the atomic distance and periodicity to modify the exchange interaction and tune the electron-phonon interaction for scattering. The ferromagnetic behavior contributed by Co, Fe, and Ni atoms was probed by X-ray absorption and magnetic circular dichroism to understand the magnetic interactions in the ASD and SD states.

Correction: Vacancy induced microstrain in high-entropy alloy film for sustainable hydrogen production under universal pH conditions

Correction for ‘Vacancy induced microstrain in high-entropy alloy film for sustainable hydrogen production under universal pH conditions’ by Yiyuan Yang et al., Energy Environ. Sci., 2024, https://doi.org/10.1039/d4ee01139b.

Vacancy induced microstrain in high-entropy alloy film for sustainable hydrogen production under universal pH conditions

A novel vacancy-induced microstrain engineering strategy is developed in FeCoNiCrPt high-entropy alloy, enabling high activity and long lifetime hydrogen evolution under universal pH conditions.

High Entropy Alloy Deposition from an Aqueous Bath

A new alloy design approach based on the concept of high entropy alloy (HEA) has attracted attention during the last few years. HEA is defined as an alloy composed of five or more principal elements with a concentration between 5 and 35 at% of each element. Depending on the combinations of the elements, HEA could show high resistance to corrosion, fatigue and fracture toughness besides unique electrical and magnetic responses. The outstanding characteristic of HEA is attributed to the high mixing entropies and the severe lattice distortion related to the addition of multiple components. Due to this unique combination of properties and the potential for designing a wide variety of new materials, interests have been directed toward high entropy alloy films and coatings for applications where corrosion and oxidation protection are strongly required. This study attempted to deposit five elements (Ni-Co–Cu–Mo-W) from an aqueous bath on a low-carbon steel substrate by the direct current. The goal was to combine the properties of Ni-Co-Cu with Ni-W and Ni-Mo coatings. In this case, a HEA coating can be produced, which might maintain corrosion and wear resistance even at high temperatures and be suitable for application in aggressive environments. To understand better the role of entropy on the coatings properties, three electroplating systems were designed, including electroplating of five elements (Ni-Co-Cu-Mo-W), which was compared with electroplating of four elements (Ni-Co-Cu-W) and (Ni-Co-Mo-W). In this case, systems with different configuration entropy can be produced, and by characterizing them, the relationship between the entropy and the properties of the coating might be cleared.Electrodeposition was carried out in Hull-cell to find the alloy deposition's proper working window. The role of different parameters such as pH, current density, and complex agent on the coating's composition was studied. The morphology and composition of the Hull-cell coatings were checked by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy along with X-ray fluorescence spectroscopy. Finally, the hardness and corrosion resistance of the coatings was studied by the nanoindentation technique and polarization in NaCl. This study developed a single aqueous bath for the electrodeposition of Ni-Co-Cu-Mo-W, Ni-Co-Cu-W and No-Co-Mo-W, and suitable deposition conditions were determined. It was shown that besides the metal concentration ratio, pH was the most influential parameter in the codeposition of elements with different deposition mechanisms. Ni and Co were the main inducing elements in the deposition of Mo and W than Cu. In addition, Ni, Co, Mo and W deposited uniformly, while Cu showed a different behavior. A competition between Mo and W deposition was seen, and Mo deposited more preferentially than W. The coatings showed weak passivity behavior and comparison between coating’s corrosion resistance was a challenge since their corrosion behavior does not only depend on coating composition but also on coatings compactness and integrity. By comparing the nano-hardness of the coatings, it was seen that the Ni-Co-Cu-W system with even the lowest configurational entropy has the highest hardness value. Keywords: Electrodeposition; High entropy alloy; Alloy deposition; hardness; Corrosion resistance

Nickel content-dependent microstructure and mechanical properties of TiZrNbHfNi high entropy alloy thin films

Alloying is known as an effective strategy to improve the mechanical properties of metallic materials. Here we show that the microstructure and mechanical behavior of a TiZrNbHf1.6 high entropy alloy film can be highly tuned by Ni addition. The newly designed TiZrNbHf1.6Nix (x = 0, 0.4, 1.2, 1.8, 2.5, 3.0, 4.6) alloy films are synthesized by co-sputtering Ti, Zr, Nb, Hf and Ni elemental targets. The microstructure and mechanical behavior of the alloy films are investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and nano/micro-indentations. The microstructural analysis indicates that the TiZrNbHf1.6 film has a single body-centered cubic with columnar-nanograined structure. As Ni content increases to 0.4 or above, the films show a complete amorphous structure. Our theoretical analysis shows that the transition from the crystalline to the amorphous structure can be attributed to the large atomic radius difference and the change of the thermodynamic parameters (e.g., mixing entropy and mixing enthalpy) due to the Ni addition. Compared to the TiZrNbHf1.6 film with a hardness of 4.8 GPa, a hardness increase of 8–35% is achieved in the Ni-doped alloy films (5.2–6.5 GPa) as measured by nanoindentation. The elevated hardness may be attributed to the severe lattice distortion and the amorphous structure induced by the Ni addition. Furthermore, microindentation reveals a diversity of deformation behavior in those films with different Ni content. A homogeneous deformation (slight plastic pileup) occurred in the films with Ni content of 1.2 and 4.6, which is close to the deformation behavior of the crystal TiZrNbHf1.6 film. While the film with a Ni content of 1.8 exhibits a catastrophic cracking deformation. Finally, multiple shear banding dominates the deformation of these films with Ni content of 0.4, 2.5 and 3.0. Our findings demonstrate that ultrastrong and highly deformable amorphous high entropy alloy thin films can be developed by appropriate element addition, making them promising materials for corrosion and wear-resistant coatings.