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Fretting wear is the main factor restricting the application of titanium alloy as compressor blades. Preparing a kind of high entropy alloy (HEA) coating is an effective way to improve the fretting wear resistance under high temperature conditions. Thus, in the present work, the FeCrAlMoxNby HEA coating was fabricated on a Ti-64 substrate by the laser cladding technology. The phase composition, microstructure and fretting wear resistance of the coating at high temperatures (200 °C, 300 °C and 400 °C) were investigated. It was demonstrated that the laser cladding FeCrAlMoxNby HEA coatings exhibited dense and uniform microstructures consisting of a BCC phase and a Laves phase (Cr2Nb). In addition, the changing trend of phase content of BCC and Laves phase is the same as the trend of atomic content of Mo and Nb respectively. The presence of the Laves phase increases the hardness of the coating. Due to its high hardness and the formation of a protective oxide layer, the coating demonstrated significantly superior resistance to high-temperature fretting wear compared to the substrate. The lowest wear rate is Mo0·5Nb0.5 coating at 300 °C, only 1.3 × 10−6 mm3/N·m. The current results provide a new method to protect titanium alloy's surface from fretting wear damage in high-temperature service environments.

High entropy alloys have excellent wear resistance, so they have great application prospects in the fields of wear resistance and surface protection. In this study, the wear resistance of the FeNiCrCoCu high entropy alloy coating was systematically analyzed by the molecular dynamics method. FeNiCrCoCu high entropy alloy was used as a coating material to adhere to the surface of a Cu matrix. The friction and nanoindentation simulation of this coating material were carried out by controlling the ambient temperature. The influence of temperature on its friction properties was analyzed on five aspects: lattice structure, dislocation evolution, friction coefficient, hardness, and elastic modulus. The results show that with the increase of temperature, the disorder of the lattice structure increases, which leads to an increase of the tangential force and friction coefficient in the friction process. At 300 K and 600 K, the ordered lattice structure of the high entropy alloy coating material is basically the same, and thus its hardness is basically the same. However, the dislocation density at 600 K is significantly reduced compared with that at 300 K, resulting in an increase of the elastic modulus of the material from 173 GPa to 219 GPa. At temperatures of 900 K and 1200 K, lattice disorder takes place rapidly, and dislocation density also decreases significantly, resulting in a significant decrease in the hardness and elastic modulus of the material. When the temperature reaches 900 K, the wear resistance of the FeNiCrCoCu high entropy alloy coating decreases sharply. This work is of great value in the analysis of wear resistance of high entropy alloys at high temperature. [ABSTRACT FROM AUTHOR]

(AlCu)3.5CoCrNiSnx (x = 0 and 1) high entropy alloy (HEA) coatings were prepared on AZ91 magnesium alloy substrate by laser cladding technology. Both the HEA coatings consisted of FCC phase and BCC phase. The addition of Sn could lead to an increase in the relative proportion of the BCC phase and the formation of coarse dendritic structure in the HEA coating. The average microhardness and average wear weight loss of the (AlCu)3.5CoCrNi coating (612.2 HV and 2.9 mg) and (AlCu)3.5CoCrNiSn coating (562.1 HV and 3.9 mg) were both higher and lower than those of the AZ91 substrate (70.5 HV and 5.5 mg), indicating that the prepared HEA coatings could significantly improve the properties of the substrate. The (AlCu)3.5CoCrNi coating showed better performance than the (AlCu)3.5CoCrNiSn coating due to the grain refinement effect.

(AlCu)3.5CoCrNiFe and (AlCu)3.5CoCrNiTi high entropy alloy (HEA) coatings were prepared on AZ91 magnesium alloy by using laser cladding technology. The phase constitution, microstructure, microhardness, corrosion resistance and wear resistance of the prepared HEA coatings were investigated. Both the HEA coatings consisted of BCC and FCC phases. The microhardness of the (AlCu)3.5CoCrNiFe coating and (AlCu)3.5CoCrNiTi coating was 642.1 HV and 656.2 HV respectively, and both of them were about 9 times higher than that of the AZ91 substrate (71.9 HV). The addition of Ti element led to the formation of dense TiO2 passivation film, thus improving the corrosion resistance of the (AlCu)3.5CoCrNiTi coating. The wear loss of the (AlCu)3.5CoCrNiFe coating and (AlCu)3.5CoCrNiTi coating was 29% and 20% of that of the AZ91 substrate, respectively. The prepared HEA coatings could significantly improve the surface properties of the AZ91 alloy substrate, and the (AlCu)3.5CoCrNiTi coating showed better performance compared to the (AlCu)3.5CoCrNiFe coating.

Surface modification of magnesium alloys was performed using a coating process to optimize their performance. Friction stir processing for preparing magnesium-based high-entropy alloy coatings effectively addressed issues such as oxidation, pores, cracks, and poor coating quality found in existing processes. In addition, it substantially enhanced the hardness and wear resistance of magnesium alloys. The micro-structure and elemental distribution for the cross-section and surface for the magnesium-based high-entropy alloy coating had been studied. The impact of magnesium-based high-entropy alloy upon hardness and wear resistance of the magnesium alloy had been analyzed, focusing on its favorable forming and binding characteristics. Finally, the heat conduction process during friction stir processing were discussed in detail. The theoretical basis for the preparation of magnesium-based high entropy coatings was improved.

In this paper, CrMnFeCoNiMo high entropy alloy coating was prepared on 304 stainless steel by plasma cladding technology. The effects of different heat treatment processes on the microstructure, hardness, wear resistance and corrosion resistance of high entropy alloy coatings were studied. The XRD and SEM images of the coating show that the phase structure is mainly Ni–Cr–Co–Mo phase. The impurity phase-[CrFe] solid solution and Ni3Fe phase will be formed between 950 °C and 1050 °C. The homogenization effect of the coating composition is more excellent under the heat treatment conditions of 950 °C and more than 1 h holding time. The hardness of the coating is relatively high at 850 °C heat treatment temperature and holding for 1 h, which is 670 HV0.2. When the temperature rises to 950 °C and 1050 °C, the hardness of the coating decreases. The coating has relatively high wear resistance at 950 °C heat treatment temperature and holding for 1 h, and the friction coefficient is about 0.27. Moreover, under this heat treatment condition, the surface composition of the coating is uniform and the corrosion resistance is good. The self-corrosion current is 1.325 × 10−7 A and the self-corrosion potential is −0.202 V.

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The high entropy alloy coating is considered as one of the most promising methods to improve the high-temperature oxidation resistance of titanium aluminum alloys due to its fine mechanical property and thermal stability. However, the high entropy alloy coating prepared so far has poor coating quality, and low coating forming efficiency and there are certain requirements for the substrate alloys. To this end, a NiCoCrAl high entropy alloy coating was developed using the double glow plasma alloying technique on the TiAl alloy. The morphology, phase structure, and high temperature oxidation resistance of the coating were comprehensively studied. The results indicate that a uniform and dense coating with a single solid solution of face-centered cube phase formed on the alloy surface. Furthermore, isothermal oxidation test was performed, and the oxidation failure process of the TiAl substrate and the NiCoCrAl-coated sample with different oxidation times was analyzed. It is found that the coating efficiently prevented the TiAl alloy from degeneration for up to 100 h at 900 °C. [ABSTRACT FROM AUTHOR]

High entropy alloys have excellent wear resistance, so they have great application prospects in the fields of wear resistance and surface protection. In this study, the wear resistance of the FeNiCrCoCu high entropy alloy coating was systematically analyzed by the molecular dynamics method. FeNiCrCoCu high entropy alloy was used as a coating material to adhere to the surface of a Cu matrix. The friction and nanoindentation simulation of this coating material were carried out by controlling the ambient temperature. The influence of temperature on its friction properties was analyzed on five aspects: lattice structure, dislocation evolution, friction coefficient, hardness, and elastic modulus. The results show that with the increase of temperature, the disorder of the lattice structure increases, which leads to an increase of the tangential force and friction coefficient in the friction process. At 300 K and 600 K, the ordered lattice structure of the high entropy alloy coating material is basically the same, and thus its hardness is basically the same. However, the dislocation density at 600 K is significantly reduced compared with that at 300 K, resulting in an increase of the elastic modulus of the material from 173 GPa to 219 GPa. At temperatures of 900 K and 1200 K, lattice disorder takes place rapidly, and dislocation density also decreases significantly, resulting in a significant decrease in the hardness and elastic modulus of the material. When the temperature reaches 900 K, the wear resistance of the FeNiCrCoCu high entropy alloy coating decreases sharply. This work is of great value in the analysis of wear resistance of high entropy alloys at high temperature.

It is one of the main ideas of developing ATF cladding materials to improve the accident resistance of zirconium alloy by coating. In the existing research on the protection mechanism of the coating on zirconium alloy substrate, the main focus is on the oxidation resistance of the coating. It is often concluded that all kinds of coating can effectively improve the accident resistance of zirconium alloy. But in fact, the embrittlement of zirconium alloy cladding under accident conditions depends not only on the degree of oxidation, but also on the change of hydrogen content in zirconium alloy. The increase of hydrogen content will greatly reduce the plasticity of zirconium alloy under accident conditions. In this study, the high-temperature steam oxidation quenching experiment at 1 200 ℃ was carried out on the AlCrNbSiTi high entropy alloy coating zirconium alloy prepared by multi-arc ion plating process. The plasticity of zirconium alloy coated with high entropy alloy after oxidation was evaluated by ring compression. The embrittlement mechanism of zirconium alloy was investigated by weighing, metallography, scanning electron microscope, electron probe X-ray microanalysis and inert gas pulse melting infrared absorption method. After oxidation for 335 seconds, no oxide layer is observed on the coating side, which indicates that the coating can effectively prevent the oxidation of zirconium matrix under this oxidation condition. The result of testing the hydrogen content of the matrix is about 100 ppm (under the same conditions, the Zirlo alloy is about 10 ppm), and the result of testing the offset strain of the matrix is more than 20%, which indicates that the coating can not prevent the hydrogen content in the zirconium alloy matrix from increasing under this oxidation condition, but plays a reverse role. However, 100 ppm hydrogen is not enough to reduce the plasticity of high matrix, and oxidation still plays a major role. After oxidation for 500 seconds, no oxide layer is observed on the coating side, which indicates that the coating can still effectively prevent the oxidation of zirconium matrix under this oxidation condition. The result of testing the hydrogen content of the matrix is about 240 ppm (under the same conditions, the Zirlo alloy is about 10 ppm), and the result of testing the offset strain of the matrix is more than 5%. This indicates that the increase of hydrogen content caused by the coating is the main reason for the loss of plasticity of the zirconium alloy matrix. The results show that high entropy alloy coating can effectively prevent the oxidation of zirconium matrix, and the loss of plasticity of zirconium matrix may be due to the synergistic effect of hydrogen embrittlement and oxidation embrittlement.

In order to increase the wear and corrosion resistance of the surface of the steel structures, four kinds of CoCrMnNiMox (x=0.1, 0.2, 0.3, 0.4) high entropy alloy (HEA) coatings with different compositions were prepared on N80 steel substrate by laser cladding. The effect of Mo content on microstructure, wear resistance and corrosion resistance of HEA coating was studied. Results showed that the CoCrMnNiMox coating structure was a single FCC phase. With the increase of Mo content, the coating hardness increased. The average Vickers hardness of the CoCrMnNiMo0.4 HEA coating was up to 628 HV, which was 3.8 times higher than that of N80 steel substrate (165 HV). The friction coefficient decreased first and then increased, reaching the lowest (0.38) at Mo content of 0.3, which reduced by 0.40 compared to that of N80 substrate. The wear mechanism of clad layer changed from adhesive wear to abrasive wear and the wear resistance increased. The dynamic corrosion and static corrosion of clad layer reached the optimum at Mo content of 0.3. Compared with the substrate, the dynamic corrosion potential increased by 0.2 V at Mo content of 0.3, and the corrosion current density decreased by one order of magnitude. However, the corrosion resistance of the clad layer was greatly reduced compared with the static corrosion due to the promoting effect of wear on corrosion. The corrosion wear coupling test results showed that with the increase of Mo content, the potential first gradually increased and then decreased. The potential reached the highest (-0.28 V) at Mo content of 0.3. The corrosion resistance under friction condition was the best, which was 0.22 V higher than that of N80 substrate (-0.50 V). The wear and corrosion resistance of the substrate surface were well improved. The friction coefficient of the sample under corrosion increased first and then decreased. Except for the high friction coefficient at Mo content of 0.2, the friction coefficient of the other samples was low in the stable run-in stage, and the wear resistance under corrosion condition was relatively good.

Noble metal electrocatalytic electrodes used in water electrolysis for hydrogen production are expensive and non-noble metal nanoparticle catalysts are not conducive to large-scale production. In this paper, the CoCrFeNiMn high entropy alloy (HEA) coating was prepared by high-velocity oxygen fuel (HVOF) spraying on the surface of stainless steel as a self-supporting oxygen evolution electrode, and the electrocatalytic activity of the electrode was further improved by plasma nitriding. The results show that the CoCrFeNiMn coating is mainly composed of FCC solid solution phase and MnCr2O4 spinel phase, and the thickness of the coating is approximately 100 μm. After nitriding, the surface of the coating is reshaped from the original semi-molten morphology to cauliflower-like structure, and the N atoms are mainly enriched in the MnCr2O4 phase. In addition, the binding energies of Co, Cr, and Ni to O in the nitrided coating decrease by 0.7 eV, while the binding energies of Fe and Mn to O are not significantly affected. The overpotential of the nitrided CoCrFeNiMn coating decreases from 363 mV to 309 mV at the current density of 10 mA cm−2, and it has a smaller Tafel slope and charge transfer resistance, and larger double-layer capacitance compared to the CoCrFeNiMn coating. Both the CoCrFeNiMn coated electrodes with and without nitriding show good long-term stability during the 60 h stability test. The high entropy alloy coating coupled with plasma nitriding technique provides a new research idea for the eletrocatalytic field of the water splitting.

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to improve the wear properties of FeCoCrNi high entropy alloy (HEA), laser cladding was applied to fabricate FeCoCrNiAlx HEA coatings with different Al additions. The Al-modified coatings exhibited excellent metallurgical bonding interfaces with the substrates. The microstructure of FeCoCrNiAl0.5 coating was the same as of the FeCoCrNi coating: face-centered cubic (FCC). However, the microstructure of FeCoCrNiAl was different: body-centered cubic (BCC) with more Al atoms distributed inside the grains. As the Al content in the coating was increased, the hardness increased as well from 202 to 546 HV0.2, while CoF and wear rate decreased from 0.62 to 0.1 and from 8.55 × 10−7 to 8.24 × 10−9 mm3/(Nm), respectively. The wear mechanisms changed from the mixture of abrasive, adhesive, and oxidative wear patterns to the mixture of abrasive and oxidative patterns. Such a change indicates that the Al addition indeed improved the wear resistance of FeCoCrNiAlx HEA coatings. Our results expand knowledge on HEA coating applications as wear-resistant materials in various applied industrial fields. [ABSTRACT FROM AUTHOR]

In this paper, two groups of high-entropy alloy coatings, Fe35Co14Ni17Cr15Nb19 and Fe33Co14Ni15Cr12Nb26, were prepared on a 304 stainless steel substrate using TIG. Both groups of coatings are composed of FCC + Laves phase and the Laves phase increases with the increase of Nb element content. In the Nb29 coating, a transition from sub-eutectic to fully eutectic structure occurs from the bottom to the top. The average microhardness of the two groups of high-entropy alloy coatings was 508.56 HV0.5 and 617.64 HV0.5, respectively, which was increased by 2.3 and 2.8 times compared with the substrate. The two groups of high-entropy alloy coatings were superior to the 304 substrate in wear and corrosion resistance, and the Nb26 coating had the best performance. [ABSTRACT FROM AUTHOR]

Developing a high entropy alloy (HEA) coating with high ductility and high strength has been a tremendous challenge since the inherent solid solution strengthening usually compromises its ductility. Herein, we present a fine-grained strengthening approach through the generation of a second phase induced by the short-range ordering (SRO) characteristics of HEA, which leads to the greatly enhanced ductility property of the FeCrAlTi x HEA coating that surmounts the strength-ductility trade-off. The quantitative microstructure- and composition-property relationships are revealed. The prepared FeCrAlTi x HEA coating comprises a biphasic structure of a BCC parent phase and a B2 second phase anchored on BCC, which exhibits a bio-like dendritic skeleton microframework. The introduced Ti acts not only as a strengthening element to enhance solid solution strengthening, but also as an SRO promoter to generate the well-grain-refining agent B2 phase for fine grain strengthening, and further serves as a promoter to trigger the formation of a bio-dendrite-like structure. When x = 0.75, these three factors are balanced, which optimizes the strength and ductility of HEA coating, with hardness, elastic modulus, ultimate tensile strength, uniform elongation, and coefficient of friction of 910.7 HV, 278.2 GPa, 1061.9 MPa, 25.9 %, and 0.477, respectively. [Display omitted] • Bifunctional Ti realizes dendritic skeleton structure and grain refinement in HEA. • Strengthen-toughen HEA by solid solution strengthening and fine grain strengthening. • Diphasic FeCrAlTi x HEA coating with BCC phase + B2 second phase was prepared by laser cladding. • Diphasic FeCrAlTi 0.75 HEA coating exhibits favorable mechanical properties. [ABSTRACT FROM AUTHOR]

• Novel CoCrFeNiMnMo x HEA coatings were prepared by laser cladding. • Strengthening mechanisms of Mo solid solution in HEA coating were investigated. • Mo 1.0 coating with fine grains presented the excellent wear resistance. • Mo 0.5 retarded Mo and Cr enriching at grain boundaries, avoiding coupling corrosion. • Passive film formed at Mo 0.5 coating surface, proving corrosion-cavitation synergism. The CoCrFeNiMnMo high entropy alloy (HEA) coatings with various Mo contents (0.1, 0.5, 0.8, 1.0 in atomic ratio) were prepared by laser cladding, aiming at determining the optimum Mo content and the effect of Mo on the microstructure and properties of CoCrFeNiMnMo x HEA. The synergistic cavitation failure-corrosion impact of the coatings was also studied in 3.5 wt% NaCl solution. Experimental results showed that HEA coatings were only composed of FCC matrix and the grains were refined gradually with the increase of Mo contents. Meanwhile, the corrosion resistance of the coatings increased first and then decreased. The CoCrFeNiMnMo 05 possessed the highest corrosion resistance as indicated by the highest polarization resistance, strongest passivation tendency and lowest carrier concentration. The wear resistance of the coatings was significantly higher than that of the substract. The enhanced wear resistance was contributed to the grain refinement and solid solution strengthening. After 8h cavitation failure, the CoCrFeNiMnMo 05 showed the lowest mean depth failure of 0.05 μm as it maintains the highest self-healing ability and integrity of passive film during the synergistic effect of cavitation failure and corrosion. In this study, the optimum Mo content was determined and the effect of Mo on the microstructure and properties of CoCrFeNiMnMo x HEA was described. [ABSTRACT FROM AUTHOR]

The W and extra/in-situ TiC reinforced CoCrFeNi high-entropy alloy coating was prepared on a 45 steel substrate by laser cladding. The synergistic effect of W and ex/in-situ TiC on the microstructure and wear properties of the coating was studied. The results showed that the ex/in-situ TiC promoted the selection of the FCC phase with a preferred orientation to the (111) crystal plane, and the increasing of in-situ TiC and W+ex-situ TiC/in-situ TiC resulted in the transformation of the FCC phase to the BCC phase. The microstructure of W+in-situ TiC coating was more uniform and two heterogeneous nucleation points Cr 3 C 2 and TiC appeared in the coatings during the solidification process. The wear width, depth, and volume were minimized. The wear rate (2.54×10−6 mm3/(N·m)) was an order of magnitude lower than that of CoCrFeNi (4.97×10−5 mm3/(N·m)). The W+in-situ TiC coating shows the best wear resistance. There were a small amount of wear debris and shallow furrow-like grooves, and the wear mechanism was abrasive wear. The synergistic effect of W and in-situ TiC on wear resistance was significant. • The addition of W and in-situ TiC significantly improves the quality of the coating. • Phase compositions were predicted by Thermo-Calc software and thermodynamic calculations. • Discussion on the evolution mechanisms of microstructure and wear mechanisms. • Wear resistance explained in terms of microstructure. [ABSTRACT FROM AUTHOR]

[Display omitted] • TiAl second phase inhibiting elemental diffusion at grain boundaries to resist LBE corrosion. • AlTi 0.75 CrFe shows the best performance with the thinnest OL after LBE corrosion. • Increased Ti in HEA coating leads to finer grains and better corrosion resistance. High-entropy alloy (HEA), when used as coating materials for structural steel in lead–bismuth eutectic (LBE) nuclear reactor, faces severe dissolution corrosion due to the diffusion of their constituents along grain boundaries. In order to mitigate dissolution corrosion, a method to enhance the LBE corrosion resistance of HEA is proposed by utilizing a second phase to inhibit elemental diffusion at grain boundaries. Herein, we used the laser cladding technique to prepare a series of biphase AlTi x CrFe HEA coating with a body-centered cubic primary phase and a TiAl second phase. During the LBE corrosion process, a single-layer oxide layer (OL) formed on the HEA coating surface, and meanwhile there existed an internal oxidation zone (IOZ) formed beneath the single-layer OL at AlTi x CrFe HEA coating interface, which gradually converted into the single-layer OL as the corrosion time prolonged. After 2000 h of corrosion, AlTi 0.75 CrFe HEA coating exhibited the lowest OL thickness (8.1 μm) and oxidation rate (0.065 μm2/h) because Al, Ti, and Cr acted as protective elements, rapidly forming a protective OL on the surface. Meanwhile, the presence of TiAl second phase at the grain boundaries impeded the mobility of elements, which improved the dissolution corrosion resistance and diminished its destructive impact on the protective OL. [ABSTRACT FROM AUTHOR]

Nowadays, high-entropy alloys (HEAs) have become a hot research topic in the field of coating materials. However, HEAs have a large wide range of compositional systems, and the differences in their composition inevitably lead to the significant variations in the matching process parameters of laser cladding and post-treatment methods, which in turn give the coatings a broad range of microstructures and protective properties. Therefore, it is crucial to review and summarize the research progresses on laser cladding HEA coatings to provide a reference for obtaining high-performance HEA coatings and further expand the application of HEA coatings. This work describes the working mechanism of laser cladding and illustrates the advantages and drawbacks of laser cladding in detail. The effects of the addition of alloying elements, process parameters and post-treatment techniques on the microstructures and properties of the coatings are thoroughly reviewed and analyzed. In addition, the correlations between the chemical compositions of HEAs, process parameters of laser cladding, post-treatment techniques and the microstructure and protective properties of the coatings are investigated and summarized. On this basis, the future development direction of HEA coatings is outlined. [ABSTRACT FROM AUTHOR]

FeNiCoCrNbx (x: molar ratio, x = 0, 0.1, 0.2, 0.3) high entropy alloy coatings (HEACs) were fabricated on 316 stainless steel (SS) by laser cladding (LC). Experimental results showed that the addition of Nb increased the lattice constant of FeNiCoCrNb high entropy alloy system. HEAC exhibited the transformation from columnar crystal at the interface to equiaxed crystal at the surface on the cross-sectional plane because of the change in the temperature gradient (G) and solidification rate (R). When x = 0.3, lamellar Laves phases appeared in ID. The microhardness of the four HEACs was 1.78, 2.19, 2.30 and 2.37 times that of 316 SS. The HEAC with x = 0.3 as well as 316 SS exhibited typical p-type semiconductor characteristics, which showed excellent corrosion resistance as indicated by the lowest I corr of 2.46 × 10−9 A cm−2 and a larger passivation region with 2 times that of 316 SS. [ABSTRACT FROM AUTHOR]

Synchronous ultrasonic impact treatment (UIT) is proposed to enhance the microstructure and wear property of laser cladded CoCrFeNiMo high entropy alloy (HEA) coatings on 45 steel. FCC phase with minor tetragonal σ phase and rhombic η phase are form in both conventional and UIT treated coatings. Due to the plastic deformation and high-frequency vibrations induced by UIT, dislocation interactions lead to recrystallization process at the top region coating. With the application of UIT, the columnar grains at top region of the coating transform into fine equiaxed grains owing to recrystallization. The fragmentation of dendrites occurs in the middle region of the coating, resulting in reduced dendrite arm spacing. The results also show the defects, such as pores and microcracks, are effectively eliminated within the coating. Microhardness and wear property of the coating are remarkably enhanced owing to fine-grain strengthening and second-phase strengthening. The average friction coefficient decreases from 0.56 for the conventional sample to 0.49 for the UIT treated sample, and the wear mechanism evolved from a combination of abrasive, fatigue, and oxidized wear to predominantly fatigue and oxidized wear. It indicates that synchronous ultrasonic impact assisted laser cladding is a potential method to fabricate high-performance HEA coatings. • Synchronous ultrasonic impact treatment (UIT) assisted laser cladding was proposed to prepare coating. • Effect of synchronous UIT on microstructure, microhardness and wear property of HEA coating was studied. • The microhardness and wear property of laser cladded HEA coating assisted by UIT are remarkable enhanced. [ABSTRACT FROM AUTHOR]

The incorporation of Laves phase into HEAs coating represents a novel approach to enhance wear resistance, building upon the innovative background of titanium alloy surface protection. The TiAlZrVNi X (X = 1, 1.5, 2) HEAs coatings were prepared in this study using laser cladding advantages to achieve dependable wear-resistant coatings. The microstructure, phase composition, microhardness, and tribological properties of the HEA coatings were simultaneously investigated. TiAlZrVNi X coatings were composed of V-rich HCP solid solution phases, C14-Laves phases, and NiTi 2 phases. The microhardness of the 1.5Ni coating measured 708.75HV 0.3 and wear rate of 1.12 × 10−13m3N−1 m−1. The primary wear mechanism was abrasive wear, and it had been confirmed that the 1.5Ni coating exhibited best wear resistance. The Laves phase with high space utilization would produce precipitation strengthening and dispersion strengthening, effectively reducing the stress-induced microcrack diffusion. Additionally, the introduction of Ni elements induced the growth of the NiTi 2 phase in order to enhance the strength while mitigating brittleness, thereby enhancing the wear resistance of the coatings. • The TiAlZrVNi X (X = 1, 1.5, 2) HEAs coatings were prepared by laser cladding. • Laves phase was introduced by adding Ni element to improve the properties of the coating. • The Laves phase content was modulated by the NiTi 2 phase. • The wear mechanisms of TiAlZrVNi X coatings displayed with varying Ni content were investigated. [ABSTRACT FROM AUTHOR]

To enhance the wear resistance of high entropy alloy (HEA) coatings and broaden their applications under extreme conditions, this study proposed an in-situ synthesis process of a dual-phase strengthened nitrides layer on laser cladded HEA coating. The microstructural evolution and mechanical properties of FeCoCrNiAl 0.5 HEA coating by plasma nitriding were systematically investigated, revealing formation and strengthening mechanisms of nitrides. In comparison to the traditional nitrided substrate 38CrMoAl, the results showed that the nitrided HEA coating exhibited high hardness and wear resistance, characterized by dual-phase nitrides AlN+CrN due to the negative Gibbs free energy, negative nitride formation enthalpy and higher atomic specific surface areas. While only a single-phase iron nitride with lower hardness was obtained on the nitrided 38CrMoAl. The microhardness and wear mass loss of the nitrided HEA coating were 1167 HV and 0.435×10−6 mg/mm, respectively, which were 33.4% higher and 63.3% lower than those of the nitrided 38CrMoAl. The strengthening effects attributed to the refinement of dual-phase nitrides, interstitial solid solution by N atoms, dispersion strengthening by higher proportion of nitrides. • Dual-phase AlN and CrN nitrides formed in the high entropy alloy coating by plasma nitriding. • Negative free energy and formation enthalpy drived the dual-phase nitrides. • The multiple strengthening mechanisms improved the performance of the coating. [ABSTRACT FROM AUTHOR]

Wear is one of the primary challenges for high-temperature working components. In this paper, FeCoCrNi 2 MoSi eutectic high-entropy alloy coatings were successfully prepared by introducing MoNiSi ternary silicides with Laves structure into FeCoCrNi high-entropy alloys using laser cladding technology. The alloy achieves a balance of strength and toughness through the nanoscale eutectic structure with alternating FCC and Laves phases. Tribological experiments conducted over a wide temperature range from 25 °C to 800 °C show that the synergistic effect of the nano-lamellar structure and the alternating soft and hard structure makes the coating have excellent wear resistance at room temperature. The improvement of wear resistance at high temperatures (800 °C) is mainly due to the formation of the oxide film on the coatings. • Eutectic high-entropy alloys with nano-lamellar structure prepared by laser cladding technique. • The formation of a flake structure of the oxide film has a protective effect on the wear surface. • The synergistic effect of the lamellar structure and the nano-scale layer results in excellent wear resistance. [ABSTRACT FROM AUTHOR]

In this work, a novel lightweight AlCrTiNbMo refractory high-entropy alloy (RHEA) coating has been developed to overcome the surface damage defects in Ti-6Al-4V alloys under wear and erosion conditions. A crack-free in-situ nitride (AlCrTiNbMo)N x RHEA coating were successfully prepared by the gas assisted laser nitriding. According to XRD, SEM and TEM analysis, AlCrTiNbMo coating was composed of single BCC phase, while (AlCrTiNbMo)N x coating was constituted by BCC and TiN phases. The average microhardness of AlCrTiNbMo and (AlCrTiNbMo)N x RHEA coatings were 591.2 HV 0.3 and 1070.1 HV 0.3 respectively. (AlCrTiNbMo)N x RHEA coating has lower friction coefficient and wear rate than AlCrTiNbMo RHEA coating and the substrate from room temperature to 600 °C. At 600 °C, (AlCrTiNbMo)N x RHEA coating showed a rare self-lubricating behavior, the friction coefficient decreased to 0.275 (61.9 % of the substrate), and the wear rate was 0.06 mm3/N m× 10−4 (1.24 % of the substrate). The erosion rates of (AlCrTiNbMo)N x RHEA coating at erosion angle of 30°, 60° and 90° were 11.0 %, 22.3 %, and 36.8 % of those of the substrate, respectively. The homogeneous and hard TiN array-BCC structure generated by in-situ self-reaction was the main factor for the excellent wear and erosion resistance of (AlCrTiNbMo)N x RHEA coating. Thus, (AlCrTiNbMo)N x RHEA coating and corresponding laser nitride technique were expected to be applied in the severe working environment of high temperature, wear, and erosion. • In-situ nitride (AlCrTiNbMo)N x refractory high-entropy alloy coating by gas assisted laser nitriding was first proposed. • The wear and erosion performance of Ti-6Al-4V alloy was improved significantly and the effect mechanism was investigated. • The homogeneous and hard TiN array-BCC structure generated was the main factor for the excellent performance. [ABSTRACT FROM AUTHOR]

(CoCrFeNi)95Nb5 high entropy alloy (HEA) coatings were successfully fabricated on a substrate of Q235 steel by laser cladding technology. These (CoCrFeNi)95Nb5 HEA coatings possess excellent properties, particularly corrosion resistance, which is clearly superior to that of some typical bulk HEA and common engineering alloys. In order to obtain appropriate laser cladding preparation process parameters, the effects of laser energy density on the microstructure, microhardness, and corrosion resistance of (CoCrFeNi)95Nb5 HEA coating were closely studied. Results showed that as the laser energy density increases, precipitation of the Laves phase in (CoCrFeNi)95Nb5 HEA coating gradually decreases, and diffusion of the Fe element in the substrate intensifies, affecting the integrity of the (CoCrFeNi)95Nb5 HEA. This decreases the microhardness of (CoCrFeNi)95Nb5 HEA coatings. Moreover, the relative content of Cr2O3, Cr(OH)3, and Nb2O5 in the surface passive film of the coating decreases with increasing energy density, causing corrosion resistance to decrease. This study demonstrates the controllability of a high-performance HEA coating using laser cladding technology, which has significance for the laser cladding preparation of other CoCrFeNi-system HEA coatings. [ABSTRACT FROM AUTHOR]

The high entropy alloy (HEA) coatings are potential candidates for advanced application in the protection of steel and other traditional alloys due to their excellent physical and mechanical performance. The AlCoCrFeNi alloy series were favorably studied due to comparably low cost and stable performance. In this research, the AlCoCrFeNi coatings were prepared through surface mechanical abrasion treatment (SMAT). The process implied the comprehensive effect of cold welding and friction. The submicron-size SiC particles were added into the raw materials in different amounts. For SMAT, a high-energy ball milling method was adopted to promote the alloying of metals, disperse SiCp, and combine the powder to the carbon steel substrate. Afterward, the phase composition, microstructure of coatings, and distribution of reinforcement were detected through XRD and SEM analysis, separately, and the effect of SiC particles content on the properties of the coatings was analyzed. The results show that the addition of submicron-sized SiC significantly improved the density and stiffness of the HEA coating and diminished defects and surface roughness. Сoatings containing SiC display enhanced adhesion force and wear resistance. The proposed mechanism is that the submicron SiC particles promoted mechanical alloying of pure metal and intensified the adherence and cold welding of the coating. Especially, herein, the addition of 15 wt.% SiC granted the best comprehensive properties of the coating. Excessive SiC content led to the deterioration of coating plasticity and the growth of cracks. [ABSTRACT FROM AUTHOR]

By laser cladding, a FeCrAlMoSi x high entropy alloy (HEA) coating (x = 0, 0.05, and 0.10) was produced on Ti6Al4V titanium alloy surface to improve its resistance to the influence of high-temperature fretting wear on Ti6Al4V. The mechanical characteristics, phase composition, and fretting wear resistance of the coating were examined at RT and 400 °C. The findings show that the FeCrAlMoSi x coating is made up of a B2 phase and an intermetallic compound μ phase. At RT and 400 °C, increasing the Si concentration significantly enhanced the coating's microhardness. At x = 0.10, the average microhardness of the coated surface was 805 HV, and grain refinement and increase in μ phase were the reasons for the improvement of microhardness. The fretting wear experiment shows that the coating system can reduce wear loss and COF. In addition, at RT and high temperature, increasing the Si element can considerably improve the coating's resistance to fretting wear. However, due to stress concentration, too much μ phase may increase the risk of microcracking in the coating. This work provides a potential method for improving the protection against fretting wear damage on the titanium alloys' surface. • Using laser cladding technique, a FeCrAlMoSi x HEA coating was successfully applied on titanium alloy surface. • The high-temperature fretting wear volume of the coating is reduced about 7 times compared to the substrate. • The Si content has a greater impact on the microstructure and high-temperature fretting wear resistance of the coating. [ABSTRACT FROM AUTHOR]

In this paper, the single target power adjustable characteristics of multi target magnetron co-sputte-ring technology were adopted. (AlCrMoNbZr)１－x－yNyOx high entropy alloy coatings were deposited on Zr-4 substrates by adjusting O2 flow rate. X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), nano-indentation and electrochemical workstation were used to characterize the microstructure 9 morphology, nano-hardness and corrosion resistance of the (AlCrMoNbZr)１－x－yNyOx high entropy alloy coating with different O2 flow. The results showed that the phase structure of the coating was completely transformed from fee to bcc and maintained a stable bcc structure with the increase of O2 flow from 0 to 15 mL/min. The coating nano-hardness decreased from 22 to 7 GPa with the increase of O2 flow. The (AlCrMoNbZr)１－x－yNyOx high entropy alloy coating with O2 flow of 10 mL/min exhibited excellent corrosion resistance, and its corrosion current density was about 6 times lower than that of the (AlCrMoNbZr) N coating with O2 flow rate of 0 mL/min. [ABSTRACT FROM AUTHOR]

By using laser cladding (LC), high entropy alloy coatings (HEACs) with FeNiCoCr as the base material and TiC added directly (D-TiC) and in-situ (I-TiC) were created. The phase composition, microstructure, mechanical characteristics, electrochemical corrosion, and cavitation erosion behavior of HEACs were examined in relation to two TiC addition methods, and a thorough investigation of the effects of mechanical characteristics and corrosion resistance on cavitation erosion behavior was conducted. Large clusters of TiC were visible in the D-TiC HEAC, in contrast to the sparse and scattered distribution of them in the I-TiC HEAC. The average grain size of the composite coating substantially fell from 25.7 μm for FeNiCoCr coating to 11.8 μm for D-TiC coating and 9.4 μm for I-TiC coating when TiC were included in the skeleton. The I-TiC composite coating precipitated by nucleation and growth with the maximum average microhardness of 440 ± 6 HV under the combined action of solid solution strengthening, fine crystal strengthening, and second phase strengthening. In 3.5 wt% NaCl solution, the galvanic corrosion between TiC particles and the FCC matrix significantly weakened the corrosion resistance of the D-TiC HEAC, with the I corr reaching 3.47 × 10−2 ± 0.8 μA/cm2. The I-TiC HEAC exhibited approximately equal corrosion resistance to FeNiCoCr with an I corr of merely 5.92 × 10−3 ± 0.3 μA/cm2. Varying cavitation incubation periods (IPs) existed in 316 SS and HEACs at the beginning of the cavitation experiment. The mean depth of erosion rate (MDER) of FeNiCoCr, D-TiC and I-TiC coatings was 0.19 ± 0.09, 0.42 ± 0.04, and 0.15 ± 0.02 μm h−1, respectively, which was only 1/5, 1/2, and 1/6 of that of substrate (0.90 ± 0.13 μm h−1). The cavitation surface of 316 SS was full of craters and cracks without any original surface. Meanwhile, due to the weak interfacial bonding strength between TiC/HEA, the cavitation erosion morphologies of D-TiC HEAC contained spallation of large TiC particles. Attributed to its ideal mechanical and corrosion resistance, the I-TiC composite coating demonstrated the best resistance to cavitation erosion. • Different types of TiC reinforced FeNiCoCr HEAC • The synergistic effect of corrosion and cavitation erosion • The precipitation mechanism of in-situ TiC • Galvanic corrosion between TiC and HEA matrix [ABSTRACT FROM AUTHOR]

Oil-spill remediation requires low-cost, high-efficiency, and operationally flexible oil-water separators, particularly those with superior corrosion resistance to extend their service life. Superhydrophobic 3D metallic foams are increasingly attracting tremendous attention due to their excellent mechanical stability and promising applications for continuous in-situ separation. Hence, superhydrophobic iron foams were fabricated via cyanide-free electrodeposition of a ZnFeCoNiMn high-entropy alloy (HEA) coating followed by non‑fluorine surface modification with tetradecanoic acid. Fluffy microspheres with hierarchical micro/nanostructure on the superhydrophobic HEA coating contributed to the superhydrophobicity of 3D iron foam. These foams exhibited highly efficient separation of oil and water even under violent stirring (700 rpm). Moreover, they achieved excellent anti-corrosion performance, with a decline in corrosion rate from 14.95 to 0.27 mm·a−1 in a 3.5 wt% NaCl solution, making it perfect for the harsh sea environment. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, CoCrFeNiTix high entropy alloy (HEA) coatings were prepared on the surface of Q235 steel by laser cladding. The microstructure, microhardness, and corrosion resistance of the coatings were studied. The mechanism of their corrosion resistance was elucidated experimentally and by first-principles calculations. The results show that CoCrFeNiTi0.1 adopts a face-centered cubic (FCC) phase, CoCrFeNiTi0.3 exhibits an FCC phase and a tetragonal FeCr phase, and CoCrFeNiTi0.5 adopts an FCC phase, a tetragonal FeCr phase, and a rhombohedral NiTi phase. The FCC phase, tetragonal FeCr phase, rhombohedral NiTi phase, and hexagonal CoTi phase are all observed in the CoCrFeNiTi0.7 HEA. The alloys assume the dendritic structure that is typical of HEAs. Ni and Ti are enriched in the interdendritic regions, whereas Cr and Fe are enriched in the dendrites. With increasing Ti content, the hardness of the cladding layers also increases due to the combined effects of lattice distortion and dispersion strengthening. When exposed to a 3.5 wt.% NaCl solution, pitting corrosion is the main form of corrosion on the CoCrFeNiTix HEA surfaces. The corrosion current densities of CoCrFeNiTix HEAs are much lower than those of other HEAs. As the Ti content increases, the corrosion resistance is improved. Through X-ray photoelectron spectroscopy (XPS) and first-principles calculations, the origin of the higher corrosion resistance of the coatings is connected to the presence of a dense passivation film. In summary, the corrosion resistance and mechanical properties of CoCrFeNiTi0.5 alloy are much better than the other three groups, which promotes the development of HEA systems with high value for industrial application.

In this work, the microstructural evolution and its influence on the wear mechanism with the increasing Ti content are investigated in double-layer Al 0.5 CoCrFeNiSi 0.5 Ti x coatings. The results indicate that FCC solid solution as the matrix phase of first layer changes from cellular structure to columnar dendritic structure due to the addition of Ti. By contrast, BCC solid solution consisting of disordered BCC and ordered B2 are found to be the matrix phase of second layer. Ti promotes the transition of ordered B2 phase from speckle-shape to stripe-shape, and then to square-shape. Besides, Ti facilitates the in-situ synthesis of TiN and TiSi 2 in the Ti-containing coatings. Hardness of the coatings is dramatically improved due to the strengthening effect caused by Ti. The acting wear mechanism changes from abrasive wear of coating Ti0 to oxidational wear and mechanical mixing of Ti-containing coatings. The wear weight loss of the coatings decreases drastically with the increasing Ti content, indicating that the microstructural evolution caused by Ti addition has a positive influence on the wear resistance. • Phase compositions of Al 0.5 CoCrFeNiSi 0.5 Ti x HEA coatings are identified. • The microstructural evolution in response to the Ti addition is explored in detail. • The changes of wear mechanism induced by the increasing Ti content are determined. • The distorted microstructures under the worn surface are characterized. [ABSTRACT FROM AUTHOR]

FeCrCoNiMo 0.5 W x (x = 0,0.25,0.5,0.75,1.0) HEA coatings were prepared on Q235 surfaces by laser cladding technique, the microstructure and phase composition of the coatings were analyzed to investigate the corrosion resistance, frictional wear properties, and wear mechanisms. The results showed that the increase of W caused the coating to produce μ phase, and the FeCrCoNiMo 0.5 W x HEA coating consisted of FCC solid solution and intermetallic compound σ phase and μ phase. The microstructure of the coating possesses a typical dendrite region (DR)-inter-dendrite (ID) structure, and the grain size is significantly refined after the addition of W. With the increase of W content, the microhardness and wear resistance of the coating gradually increased, among which the microhardness of W 1.0 coating was the highest and the wear resistance was the best. The wear mechanism of the coating is mainly oxidation wear, adhesive wear and slight abrasive wear. The addition of a small amount of W promotes the formation of a more stable passivation film. Further increasing the content of W, the phase content of the coating increases, resulting in a highly inhomogeneous passivation film, which reduces the corrosion resistance of the coating. The W 0.25 coating has the best overall corrosion resistance. • Enrichment of intermetallics compounds in the inter-dendrite(ID). • Debris is squeezed onto the wear surface to form an adhesion layer. • The wear mechanism is adhesive wear, oxidation wear and slight abrasive wear. • A small amount of element W promotes the formation of a more stable passivation film. [ABSTRACT FROM AUTHOR]

[AlTiCrNiTa/(AlTiCrNiTa)N] 20 multilayer coatings were prepared by magnetron sputtering on Zr-4 substrate. The mechanical properties, microstructure and wettability of multilayer coatings were systematically studied by SEM, nano indentation instrument, scratch instrument and contact Angle instrument. In addition, after high temperature oxidation corrosion for 45 days, the coating was characterized by SEM and XRD. Al in the coating was wrapped in dense spinel NiCr 2 O 4 , which inhibits layer by layer dissolution of the coating, thus improving the corrosion resistance of the coating. The corrosion mechanism of [AlTiCrNiTa/(AlTiCrNiTa)N] 20 multilayer coatings was evaluated in detail. • The [AlTiCrNiTa/(AlTiCrNiTa)N] 20 multilayer coatings were successfully deposited on the Zr-4 alloy. • The multilayer coating has a high hardness of 52.31 GPa. • The coating showed good resistance under autoclave test. • The main reason for the corrosion resistance of the coating is the in-situ encapsulation of Al in spinel. [ABSTRACT FROM AUTHOR]

CuZrAlTiNi High entropy alloy (HEA) coating was synthesized on T10 substrate using mechanical alloying (MA) and vacuum hot pressing sintering (VHPS) technique. The MA results show that the final product of as-milled powders is amorphous phase. The obtained coating sintered at 950 °C is compact and about 0.9 mm in thickness. It is composed of a couple of face-centered cubic (FCC), one body-centered cubic (BCC) solid solutions and AlNi 2 Zr phase. The interface strength between coating and substrate is 355.5 MPa measured by three point bending test. Compared with T10 substrate, the corrosion resistance of CuZrAlTiNi HEA coating is enhanced greatly in the seawater solution, which is indicated by the higher corrosion potential, wider passivation region, and secondary passivation. The average microhardness of the coating reaches 943 HV 0.2 , and is about 3.5 times higher than the substrate, which is mainly ascribed to the uniformly dispersed nano-size precipitates, phase boundary strengthening and solid solution strengthening. Moreover, the wear resistance of the coating is slightly improved in comparison with the substrate. [ABSTRACT FROM AUTHOR]

The CoCrFeNiW and CoCrFeNiW 0.5 Mo 0.5 high-entropy alloy coatings (HEACs) have been prepared by mechanical alloying and vacuum hot pressing sintering (VHPS) technique on Q235 steel substrate. The microstructures, microhardness, wear resistance and corrosion resistance of HEACs were studied in detail. The final milling products for as-milled CoCrFeNi(W 1 − x Mo x ) (x = 0, 0.5) coating powders are the mixture of body-centered cubic (BCC) and face-centered cubic (FCC) solid solution phases, while order FCC phase exists for CoCrFeNiW. VHPS-ed CoCrFeNiW and CoCrFeNiW 0.5 Mo 0.5 HEACs are 600 and 650 μm in thickness respectively, and bear a good metallurgical bonding to the substrate. Both HEACs comprise two FCC phases with a small amount of δ-NiW and σ-CoCr phases. The average microhardness values of CoCrFeNiW and CoCrFeNiW 0.5 Mo 0.5 HEACs reach 669 and 600 HV respectively, which far exceed the substrate (160 HV). And both coatings exhibit superior wear resistance than substrate under the same wear conditions. The corrosion resistance in 3.5% NaCl solution of the coatings is improved compared with substrate. Especially, Mo addition remarkably enhances corrosion resistance as reflected by the lowest corrosion current density and more positive corrosion potential as well as a reduction in average corrosion rate. [ABSTRACT FROM AUTHOR]

316 stainless steel (SS) was coated with CoCrFeNiNbx (x: atomic ratio, x = 0, 0.1, 0.2, and 0.3) high entropy alloy coatings (HEACs) by laser cladding (LC). The impacts of Nb content on the phase composition, microstructure, microhardness, wear resistance and corrosion properties of CoCrFeNi based HEACs were examined. Different from the canonical dendritic (DR) - interdendritic (ID) microstructure presented by the other three HEACs, the ID of Nb0.3 HEACs also existed nanoscale Nb-rich Laves phase composed of Nb Ni and Nb Co. The inclusion of Nb significantly reduced the average grain size of CoCrFeNi based HEACs from 59.43 μm to 11.38 μm. It also greatly diminished the formation of high angle grain boundaries (HAGBs), increasing the percentage of low angle grain boundaries (LAGBs) from 31 % to 61 %. The microhardness of Nb-containing HEACs was significantly promoted due to the solid solution strengthening and fine grain strengthening caused by large size Nb atoms. Affected by Laves phase with high coordination number and space filling ratio and higher proportion of LAGBs, the microhardness of Nb0.3 HEAC was even as high as 530 HV. The increase in Nb concentration also strengthened the HEACs' resistance to wear. Nb0, Nb0.1, Nb0.2, and Nb0.3 HEACs had corresponding specific wear rates of 0.36, 0.32, 0.23, and 0.20 mm3/Nm. Unlike 316 SS, Nb0 and Nb0.1 HEACs, which had both adhesive wear and abrasive wear, Nb0.2 and Nb0.3 HEACs were mainly wear by abrasive wear. The corrosion behavior of CoCrFeNiNbx HEACs in 0.5 M H 2 SO 4 solution was similar to 316 SS, but the corrosion resistance was stronger than 316 SS. Nb0.3 HEAC with the Ecorr of −164 mV and Icorr of 6.40 × 10−7 A/cm2 showed the best acid corrosion resistance, which could be attributed to the stable and dense passivation film on its surface. Distinct from the intergranular corrosion of other coatings, the corrosion of Nb0.3 HEAC mainly occurred in DR, because the FCC phase acted as the anode site in it when FCC and Laves phase co-existed. • The properties of CoCrFeNi based high entropy alloy coating were investigated. • The wear resistance of FCC + Laves eutectic high entropy alloy coating are analyzed. • Corrosion mechanism of FCC + Laves eutectic high entropy alloy was discussed. [ABSTRACT FROM AUTHOR]

The AlCrNbTiZr high-entropy alloy (HEA) coatings with different deposition temperatures were prepared on Zr-4 substrate by magnetron sputtering. The effects of the deposition temperature on microstructure, mechanical properties, surface wettability, high temperature corrosion and oxidation resistance of coatings were systematically studied. The results show that the thickness of coating decreases first and then increases with the increase of deposition temperature. The coatings deposited at all temperatures is amorphous with BCC nanocrystalline domains, and the coating surface is hydrophobic. The room temperature (RT) deposition coatings have a high hardness of 25.41GPa, a good adhesion of 50 N and corrosion resistance compared with the coating at other deposition temperatures. The coating at RT deposited still has the ability to protect the substrate Zr-4 after the 1200 °C steam oxidation for 30 min. In addition, the corresponding steam oxidation mechanism is discussed in detail. • The coating deposited at RT has a higher hardness of 25.41 GPa. • The coating deposited at RT has excellent steam oxidation resistance at 1200 °C for 30 min. • The coating degradation of is mainly attributed to the codiffusion effect of Cr and Ti. [ABSTRACT FROM AUTHOR]

In this work, the CoCrFeNiNbx (x: molar ratio, x = 0.45, 0.5, 0.75, and 1.0) high entropy alloy coatings were synthesized on a 304 stainless steel substrate by laser cladding to investigate the effect of Nb element on their microstructure, hardness, and wear resistance. The results indicated that in all of the CoCrFeNiNbx alloy coatings, two phases were found: One was a face-centered cubic (FCC) solid solution phase, the other was a Co1.92Nb1.08-type Laves phase. The microstructures of samples varied from hypoeutectic structure (x = 0.45 and 0.5) to hypereutectic structure (x = 0.75 and 1.0). The Vickers hardness of CoCrFeNiNbx alloy coatings was obviously improved compared with the substrate. The hardness value of the CoCrFeNiNb1.0 alloy coating reached to 590 HV, which was 2.8 times higher than that of the substrate. There was also a corresponding variation in wear properties with hardness evolutions. Wherein the hypereutectic CoCrFeNiNb1.0 alloy coating with the highest hardness exhibited the best wear resistance under the same wear condition, the dry wear test showed the wear mass loss of CoCrFeNiNb1.0 alloy coating was less than a third of the substrate. The high hardness and wear resistance properties were considered with the fine lamellar eutectic structure and proper combination of FCC and Laves phases.

• DED with remelting process fabricated CoCrFeNiTi HEA coatings. • Different molten pool thermal characteristics due to the laser remelting process. • The phase and microstructure transform under different remelting laser power. • Extremely increased hardness and wear resistance due to laser remelting process. Owing to their superior mechanical properties of high hardness, wear resistance, and corrosion resistance, CoCrFeNiTi high entropy alloys (HEAs) attracted the attention of researchers to use as coating materials for titanium (Ti) and its alloys. Directed energy deposition (DED) has the potential to combine both the fabrication process and the laser remelting process (implemented by double laser scanning) using the same equipment set-up. With high energy density and rapid cooling rate, combining DED and laser remelting is considered an effective method to enhance solid solution strengthening effects and element segregation of CoCrFeNiTi HEA coatings, thus being able to affect HEA coatings' phase constitutions, microstructure, and mechanical properties. To date, there are no reported publications on the deposition of CoCrFeNiTi HEA coatings via the combination of DED and laser remelting process. In addition, the investigation of the effects of remelting laser power is still lacking. To fill these gaps, the relationships among the levels of remelting laser power, molten pool properties, microstructure, and mechanical properties of CoCrFeNiTi HEA coatings are built by DED with the laser remelting process in this investigation. When the remelting laser power is higher than 225 W (75 % of the laser power in the DED process), the three-phase microstructure changes to a two-phase microstructure. The higher molten pool temperature, lower cooling rate, and secondary solidification induced by a relatively high remelting laser power can enhance the solid solution strengthening effects and promote the precipitation of the high-hardness Χ phase and Laves phase. After the 300 W laser remelting process, the highest average microhardness of the coatings is obtained as 916 HV 1.0 , which is 65 % higher than that of the coatings without laser remelting process. The best wear resistance is observed in the coatings with 225 W remelting laser power instead of 300 W remelting laser power since the high content of brittle phase caused by high remelting laser power could promote the formation of abrasive particles during the dry sliding tests. [ABSTRACT FROM AUTHOR]

High entropy alloy coatings show great potential for improving the wear resistance of the stainless-steel substrate. However, there are few comparative studies on the tribological properties of high entropy alloy coatings with different elements. In the present study, the FeCoCrNiCu x and FeCoCrNiSi x high entropy alloy coatings were designed and prepared by laser cladding. The microstructures of the high entropy coating were analyzed. The tribological properties of the high entropy alloy coatings sliding against Si 3 N 4 balls at room temperature and 600 °C were investigated. The results show that after adding Cu/Si, the tribological properties of the coating change little at room temperature, but increased significantly at high temperature of 600 °C. The FeCoCrNiSi coating has the best tribological performance at 600 °C with an average friction coefficient and wear rate of 0.19 and 0.677 (×10−4 mm3/N·m), respectively. In general, the addition of Cu increases the thermal conduction ability of the coating, improves the toughness and the bonding strength of the coating; the addition of Si refines the grain size, increases the degree of work hardening and improves the wear resistance of the coating. • The effect of Cu/Si on laser cladding FeCoCrNi coatings was investigated. • The addition of Cu/Si in equal molar ratio at room temperature improved wear resistance of FeCoCrNi coating. • At 600 °C, the addition of Cu/Si both improved the tribological properties of FeCoCrNi coating. • The FeCoCrNiSi coating showed the best tribological performance at high temperature (600 °C). [ABSTRACT FROM AUTHOR]

Ni-Cr-Co-Ti-V-Al high-entropy alloy coating on Ti-6Al-4V was synthesized by laser surface alloying. The coating is composed of a B2 matrix and (Co, Ni)Ti 2 compounds with few β-Ti phases. Focused ion beam technique was utilized to prepare TEM sample and TEM observations agree well with XRD and SEM results. The formation of HEA phases is due to high temperature and rapid cooling rate during laser surface alloying. The thermodynamic parameters, ΔH mix , ΔS mix and δ as well as Δχ, should be used to predict the formation of the BCC solid solution, but they are not the strict criteria. Especially when Δχ reaches a high value (≥ 10%), BCC HEA will be partially decomposed, leading to the formation of (Co, Ni)Ti 2 compound phases. [ABSTRACT FROM AUTHOR]

A plasma-deposited CoCrFeMnNi/WC coating was reprocessed by thermoelectric composite treatment via spark plasma sintering (SPS). The microstructure and phase composition of the coating were characterized by a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanical properties were tested by nanoindentation. After SPS treatment, the coating grains changed from columnar to irregular cellular, and a large amount of carbide precipitates appeared in the ingrain and grain boundary areas, which show an FCC structure that is coherent with the matrix. Through the quantitative calculation of the load–displacement curve, it was found that the hardness of the coating increases from 4.24 GPa to 5.02 GPa, and the yield strength increases from 1069.1 MPa to 1270.4 MPa after SPS treatment. Although the grain size of the coating increased slightly and the dislocation density decreased significantly after SPS treatment, the yield strength of the coating was still significantly improved by precipitation strengthening. • SPS thermoelectric composite treatment caused exsolution precipitation of the coating, resulting in nano-size precipitates. • After SPS treatment, the dislocation density of the coating was greatly reduced while the hardness was improved. • The results of nano-indentation test showed that the yield strength of coating reached 1270.4 MPa after SPS treated. • The effect of precipitation strengthening significantly improves the yield strength of the coating. [ABSTRACT FROM AUTHOR]

In this study, CoCrFeNiMo0.2 high entropy alloy coating (average thickness of 990 μm) without defects was successfully prepared on the Inconel 718 substrate by laser cladding. Microstructure and properties were investigated systematically by multiple characterization methods. The EDS and ECC find that the coating has good metallurgical bonding with the substrate. The thermal erosion test indicates that the formation of a passive film with Cr and Mo elements improves the thermal erosion resistance of the coating. According to the results of microhardness tests, the average microhardness in the coating is about 328.9 HV (1.28 times of the substrate). The coating with low wear width (0.454 mm) and depth (7.085 μm) shows outstanding wear resistance due to the formation of the σ phase particles and the fine-grain strengthening. The coating surface's average residual stress is −723.3 MPa (compressive stress), which prevents crack generation. Furthermore, the corrosion resistance of the coating is obviously improved. [ABSTRACT FROM AUTHOR]

Sealing engineering equipment, especially in a harsh environment (e.g. high-pressure), is frequently subjected to tribological impacts during service, leading to an accelerated failure of the seal parts. In this study, an effective strategy was proposed to reduce the wear of the seal part, utilizing high entropy alloy (HEA) coating. A novel wear-resistant MoNiTaTiV HEA coating was designed and prepared on the substrate of GCr15 steel via laser cladding. The microstructure, chemical composition and microhardness of the HEA coating were examed by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and nanoindentation. The wear property of the HEA coating sliding against its QBe2.0 counterpart under dry and oil-lubricated conditions at high-pressure was investigated deeply. As a result, the HEA coating exhibits BCC and TiN ceramic phases and its hardness reaches approximately 1099.7 HV, which is 3.7 times higher than that of the substrate. Additionally, the HEA coating shows superior wear properties to substrate under dry and oil-lubricated conditions, which is closely related to the high hardness of HEA coating reinforced by TiN particles. The adhesion layer and oxide layer were formed on the HEA coating, transferring the two-body to three-body wear. The QBe2.0 counterpart and MoNiTaTiV coating could be a promising anti-wear tribo-pair for seal parts under dry and oil-lubricated conditions. • MoNiTaTiV HEA coating is successfully prepared on GCr15 steel substrate using laser cladding. • HEA coating consists of BCC solid-solution phase and TiN ceramic phase. • Hardness of the HEA coating is 1099 HV, about 3.7 times that of the substrate. • HEA coating exhibits excellent high-pressure wear property sliding against QBe2.0 in dry and oil-lubricated conditions. [ABSTRACT FROM AUTHOR]

The Cu0·9NiAlCoCrFe high entropy alloy coating fabricated on AZ91D magnesium alloys by laser cladding is studied in this paper. Microstructure property of the coating is characterised by optical microscope, scanning electron microscope and X-ray diffraction (XRD). The XRD results show that the coating mainly consists of a simple bcc solid solution phase. Corrosion resistance results of the coating are tested in 3·5 wt-%NaCl solution. Compared to the AZ91D specimen without Cu0·9NiAlCoCrFe coating, the corrosion current density of AZ91D specimen coated with Cu0·9NiAlCoCrFe decreased by four orders of magnitude. [ABSTRACT FROM AUTHOR]