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Mn-doped CoCuNiTi HEACs were prepared on 45 carbon steel substrate by laser cladding. CoCuNiTi and CoCuMnNiTi HEACs are dual-phase structures composed of FCC and BCC. The addition of Mn causes a decrease in the lattice constant and cell volume of the above two phases, as well as an increase in the density of the two phases and the FCC phase content. The microstructures of the two alloys are the typical dendritic structures. Ti and Co elements are enriched in the dendrite region; Cu element is enriched in the interdendrite region; the distribution of Mn is the most uniform in the dendrite and interdendrite regions. The addition of Mn element causes the microstructure to be significantly refined, and the width of the primary dendrite is reduced from 8.10 μm to 4.11 μm. CoCuNiTi alloy belongs to activation dissolution, and the Mn-containing alloy exhibits an obvious passivation zone. The addition of Mn element increases the capacitive reactance arc radius and the maximum phase angle of the alloy, indicating that the corrosion resistance of the Mn-containing alloy is significantly improved. [ABSTRACT FROM AUTHOR]

To investigate the effect of recovery treatment on the microstructure and tribological properties of ultrasonic impact-treated Al2FeCoNiCrW0.5 high-entropy alloy coatings, laser cladding technology was used to fabricate coatings on a G10450 steel substrate, followed by ultrasonic impact treatment (UIT) and recovery treatment (HR, 300 °C). The results showed that the Al2FeCoNiCrW0.5 high-entropy alloy coating consisted of BCC and FCC phases. Ultrasonic impact treatment slightly broadened the XRD diffraction peaks, while the recovery treatment had minimal effect on them. Ultrasonic impact also refined the coating grains. Ultrasonic impact treatment increased the coating hardness from 738 HV0.5 to 856 HV0.5. Although the subsequent post-annealing slightly reduced the hardness to 806 HV0.5, it significantly improved wear resistance, with wear loss decreasing from 3.273 mm3 to 2.881 mm3, representing a 15% reduction in wear rate. The improvement in wear resistance was attributed to a change in the wear mechanism of the high-entropy alloy coating. Before and after post-annealing, the mechanism transitioned from abrasive wear, adhesive wear, and oxidative wear to primarily abrasive wear and oxidative wear. Additionally, the recovery treatment transformed the surface from hard and brittle to ductile and resilient. [ABSTRACT FROM AUTHOR]

AlxCoCuNiTi (x = 0, 0.4, and 1) high-entropy alloy coatings on 45 steel substrates were prepared by laser cladding, and their phase structure, microstructure, element partition, and wear behavior were investigated. The results show that the AlxCoCuNiTi (x = 0, 0.4, and 1) coatings have a dual-phase structure of FCC and BCC. With the increase of x from 0 to 1, the content of the FCC phase decreases from 66.9 wt.% to 14.3 wt.%, while the content of the BCC phase increases from 33.1 wt.% to 85.7 wt.%. When x = 0.4, the lattice constants of the two phases are the largest, and their densities are the smallest. The microstructure of the AlxCoCuNiTi (x = 0, 0.4, and 1) coatings is composed of BCC-phase dendrites and FCC-phase interdendrite regions. Ti is mainly enriched in the primary phase or BCC dendrites, Cu is enriched in the interdendrite regions, and Al is enriched in the dendrites. The friction coefficients of AlxCoCuNiTi (x = 0, 0.4, and 1) coatings during wear tests are 0.691, 0.691, and 0.627, respectively. The lowering of the wear friction coefficient when increasing the Al content is mainly related to the change in phase structure, microstructure, and wear mechanism. [ABSTRACT FROM AUTHOR]

This study explores the mechanical properties of graphene/aluminum (Gr/Al) nanocomposites through nanoindentation testing performed via molecular dynamics simulations in a large-scale atomic/molecular massively parallel simulator (LAMMPS). The simulation model was initially subjected to energy minimization at 300 K, followed by relaxation for 50 ps under the NPT ensemble, wherein the number of atoms (N), simulation temperature (T), and pressure (P) were conserved. After the model was fully relaxed, loading and unloading simulations were performed. This study focused on the effects of the Gr arrangement with a brick-and-mortar structure and incorporation of high-entropy alloy (HEA) coatings on mechanical properties. The findings revealed that Gr sheets (GSs) significantly impeded dislocation propagation, preventing the dislocation network from penetrating the Gr layer within the plastic zone. However, interactions between dislocations and GSs in the Gr/Al nanocomposites resulted in reduced hardness compared with that of pure aluminum. After modifying the arrangement of GSs and introducing HEA (FeNiCrCoAl) coatings, the elastic modulus and hardness of the Gr/Al nanocomposites were 83 and 9.5 GPa, respectively, representing increases of 21.5% and 17.3% compared with those of pure aluminum. This study demonstrates that vertically oriented GSs in combination with HEA coatings at a mass fraction of 3.4% significantly enhance the mechanical properties of the Gr/Al nanocomposites. [ABSTRACT FROM AUTHOR]

CoCrFeNiSi high entropy alloy coatings doped with different boron (B) contents were prepared on titanium alloy substrate by laser cladding. The microstructure, friction behavior and corrosion resistance of the coatings were investigated, based on which the mechanism of improving the form ability of the laser cladding coatings with doped B element was observed in detail. It was revealed that oxide layer (B2O3) produced on the surface at high temperature had enhanced the form ability of the coating layer by significantly decreasing pores and cracks in the coatings. At the same time, the incorporation of B gave birth to the formation of boride, while the coatings were composed of CoB, CrB, Co2B and amorphous phase. It was worth noting that the high entropy alloy coating exhibited the highest microhardness of up to 1189 HV0.2 and optimum wear resistance as the B content approached 6 wt.%. Furthermore, lower corrosion current density, or better corrosion resistance in other words, was presented by the high entropy alloy coating containing doped B element, which was mainly due to that the improved microstructure of the coatings with fewer pores or cracks had effectively hindered the penetration of chloride ions and formed an effective barrier between the substrate and the corrosion solution. [ABSTRACT FROM AUTHOR]

The microstructure of FeCrNiCoMoBSi high entropy alloy (HEA) laser cladding coating and the effects of laser power on the phase and electrochemical corrosion properties of the coating were investigated. The results show that the HEA coating is composed of columnar crystal band at the bottom, equiaxed crystal band at the top and mixed crystal band in the middle (composed of columnar crystal and equiaxed crystal). The HEA coating prepared at 3000 W exhibits the lowest self-corrosion current density (0.425 µA/cm²), the highest self-corrosion potential (-0.16852 V) and the largest polarization impedance (69 616 Ω). Its impedance modulus is 1 1432 Ω·cm², which is 8.65 times, 4.91 times and 7.14 times of the laser cladding coatings prepared at 1 800 W, 2,500 W and 4 500 W, respectively, as well as its maximum phase angle is 76.23°, which is higher than the other three coatings. The comprehensive evaluation shows that the HEA coating prepared at 3000 W exhibits excellent electrochemical corrosion performance. This is due to its single FCC crystal structure, corrosion-resistant Fe-Ni alloy phase and elemental chromium phase, good crystal crystallinit, fine grain size and excellent passivation effect, making its electrochemical corrosion performance significantly superior to other power prepared coatings. [ABSTRACT FROM AUTHOR]

Mn-doped CoCuNiTi HEACs were prepared on 45 carbon steel substrate by laser cladding. CoCuNiTi and CoCuMnNiTi HEACs are dual-phase structures composed of FCC and BCC. The addition of Mn causes a decrease in the lattice constant and cell volume of the above two phases, as well as an increase in the density of the two phases and the FCC phase content. The microstructures of the two alloys are the typical dendritic structures. Ti and Co elements are enriched in the dendrite region; Cu element is enriched in the interdendrite region; the distribution of Mn is the most uniform in the dendrite and interdendrite regions. The addition of Mn element causes the microstructure to be significantly refined, and the width of the primary dendrite is reduced from 8.10 μm to 4.11 μm. CoCuNiTi alloy belongs to activation dissolution, and the Mn-containing alloy exhibits an obvious passivation zone. The addition of Mn element increases the capacitive reactance arc radius and the maximum phase angle of the alloy, indicating that the corrosion resistance of the Mn-containing alloy is significantly improved.

AlxCoCuNiTi (x = 0, 0.4, and 1) high-entropy alloy coatings on 45 steel substrates were prepared by laser cladding, and their phase structure, microstructure, element partition, and wear behavior were investigated. The results show that the AlxCoCuNiTi (x = 0, 0.4, and 1) coatings have a dual-phase structure of FCC and BCC. With the increase of x from 0 to 1, the content of the FCC phase decreases from 66.9 wt.% to 14.3 wt.%, while the content of the BCC phase increases from 33.1 wt.% to 85.7 wt.%. When x = 0.4, the lattice constants of the two phases are the largest, and their densities are the smallest. The microstructure of the AlxCoCuNiTi (x = 0, 0.4, and 1) coatings is composed of BCC-phase dendrites and FCC-phase interdendrite regions. Ti is mainly enriched in the primary phase or BCC dendrites, Cu is enriched in the interdendrite regions, and Al is enriched in the dendrites. The friction coefficients of AlxCoCuNiTi (x = 0, 0.4, and 1) coatings during wear tests are 0.691, 0.691, and 0.627, respectively. The lowering of the wear friction coefficient when increasing the Al content is mainly related to the change in phase structure, microstructure, and wear mechanism.

We study the graphene (Gr)-strengthened CoCrFeNiMo0.2 high-entropy alloys (HEAs) prepared by laser cladding. The corrosion properties of the alloys under simulated acid rain conditions are studied through rainfall experiments, electrochemical experiments, and immersion experiments. The experimental results show that the microstructure of the Gr-strengthened CoCrFeNiMo0.2 HEAs mainly including three morphologies. Mo element occurs segregation. Gr concentrates on the alloy surface during melting. The alloy has a face centered cubic (FCC) single-phase structure. With increase in the rainfall and immersion period, the corrosion resistance of the Gr-strengthened HEAs decreases. With increase in the pH, the corrosion resistance of the alloys increase. The corrosion current densities of Gr-strengthened CoCrFeNiMo0.2 HEAs are small, indicating that the alloys have excellent corrosion resistance. Electrochemical impedance spectroscopy (EIS) shows that as the pH increases, the capacitance arc radius, impedance modulus, and phase angle show increasing trend. The reason for excellent corrosion resistance are as follows: the Gr enriched on the surface plays a shielding role during alloy melting, Gr reacts with alloy elements to form a passive film on the alloy surface, the lattice distortion and grain refinement are caused by Gr, providing the single-phase structure of the alloy. [ABSTRACT FROM AUTHOR]

High-entropy alloy coatings (HEACs) of Co2CrFeNiMnCux (x = 0, 0.25, 0.5, 0.75, 1.0, 1.25) were fabricated on Q235 steel surfaces by laser cladding. A portion of the HEACs (x = 0, 0.5 and 1.25) displayed a dual-phase FCC structure, while the remaining portion (x = 0.25, 0.75 and 1.0) exhibited a single-phase FCC structure. Furthermore, as the Cu content increased, the grain size of the coatings became finer and elongated. Due to the unique processing technology of laser cladding, the HEACs exhibited a hardness gradient from the top to the substrates. Cu segregated within the crystal and accumulated near the grain boundaries. The primary mechanism for protecting the steel substrate through coatings was passive films protection. Remarkably, the coatings demonstrated better anti-corrosion properties when the Cu content was 0.25, with a charge transfer resistance of 9.528 × 104Ω cm2, corrosion potential of −0.387 V and corrosion current density of 3.125 × 10−7 A/cm2. [ABSTRACT FROM AUTHOR]

Preparing various types of coatings to strengthen the surface of materials is a significant technique to increase the materials' service performance，and the addition of different content of hard phase is conducive to further improve the properties of coatings.The Fe50Mn30Cr10Co10 high-entropy alloy coating with different VC content were prepared through selective laser cladding process，and the effects of VC content on the microstructure，the phase structure，the hardness and the creep properties of the coatings were researched by scanning electron microscope，X-ray diffractometer，nano indentation instrument，etc.Results showed that the coating structure was obviously refined with the increase of VC content.There was no effect on the phase structure of the coating，because of VC being dissolved in FCC lattice.The hardness of the coating increased，owing to the increase of solid solution strengthening effect.Particularly，with the increase of VC content，the creep value of the coating decreased，which was very beneficial to improve the creep performance of the coating material.This provided an important basis for strengthening the properties of the coating of high-entropy alloy by adding VC hard phase.

For studying the effect of nitriding treatment on the microstructure and wear properties of HVOF sprayed Al1-xCoCrFeNiTix(x＝0，0.125，0.250) high-entropy alloy coatings，the HVOF technology was employed to prepare Al1-xCoCrFeNiTix(x＝0，0.125，0.250) highentropy alloy coating on 35CrMo steel substrate，which were further nitrided.The effects of nitriding treatment on the microstructure and wear properties of Al1-xCoCrFeNiTix(x＝0，0.125，0.250) high-entropy alloy coating prepared by HVOF were studied via characterization methods such as SEM，XRD，3D white light interferometer and EDS.Results showed that the high-entropy alloy coating of Al1-xCoCrFeNiTix(x＝0，0.125，0.250) after nitriding treatment had a dense microstructure with a typical thermal spray coating-like structure.The coating thickness was about 300～350 μm，the nitriding layer thickness was about 10 μm，and the nitriding layer phase structure was FCC phase and AlN，CrN and other nitriding phases.Meanwhile，the microhardness of the nitriding layer was 981 HV2N(x＝0)，1 090 HV2N(x＝0.125) and 1 194 HV2N(x＝0.250)，respectively，which was significantly improved compared with the microhardness of 479 HV2N(x＝0)，506 HV2N(x＝0.125) and 548 HV2N(x＝0.250) of the unnitrided high-entropy alloy coating.With the increase of Ti content，the wear resistance of the nitriding layer increased，and Al0.750CoCrFeNiTi0.250nitriding layer possessed the best wear resistance [(2.17×10-6mm3/(N·m)].Besides，the wear failure mechanism of Al1-xCoCrFeNiTix(x＝0，0.125，0.250) nitriding layer was mainly abrasive wear，oxidation wear and adhesive wear.

High-entropy alloys have been widely used in engineering manufacturing due to their hardness, good wear resistance, excellent corrosion resistance, and high-temperature oxidation resistance. However, it is inevitable that metallurgical defects, such as micro cracks and micro pores, are produced when preparing the coating, which affects the overall performance of the alloy to a certain extent. In view of this situation, cavitation water jet peening (CWJP) was used to strengthen the AlCoCrFeNi high-entropy alloy coating. The effect of CWJP impact time on the microstructure and mechanical properties of CWJP were investigated. The results show that CWJP can form an effective hardening layer on the surface layer of the AlCoCrFeNi high-entropy alloy. When the CWJP impact time was 4 h, the microhardness of the surface layer of the specimen was harder than that of 2 h and 6 h, and the CWJP impact time had little effect on the thickness of the hardening layer. Observing the surface of the untreated and CWJP-treated specimens using the EBSD test, it was evident that the microstructure was significantly homogenized, the grains were refined, and the proportion of small-angle grain boundaries increased. The system reveals the grain refinement mechanism of the AlCoCrFeNi high-entropy alloy coating during plastic deformation. This study aims to provide a new surface strengthening method for obtaining high-performance AlCoCrFeNi high-entropy alloy coatings. [ABSTRACT FROM AUTHOR]

In order to save the time and cost of friction and wear experiments, the coating composition (different contents of Al, Ti, and Cu elements), ratio of hardness and elastic modulus (H3/E2), vacuum heat treatment (VHT) temperature, and wear form were used as input variables, and the wear rates of high-entropy alloy (HEA) coatings were used as output variables. The dataset was entirely obtained by experiment. Four machine learning algorithms (classification and regression tree (CART), random forest (RF), gradient boosting decision tree (GBDT), and adaptive boosting (AdaBoost)) were used to predict the wear resistance of HEA coatings based on a small amount of data. The results show that except for the GBDT model, the other three models had good performance. Because of the small amount of data, the CART model demonstrated the best prediction performance and can provide guidance for predicting the wear resistance of AlCoCrFeNi-X (Ti, Cu) HEA coatings for drilling equipment. Furthermore, the contribution of different factors to the wear rate of AlCoCrFeNi-X (Ti, Cu) HEA coatings was obtained. Al content had the greatest influence on wear rate, followed by H3/E2, wear form, and VHT temperature. [ABSTRACT FROM AUTHOR]

AlCoCrFeNiTiWC high-entropy alloy (HEA) coatings were prepared using laser cladding technology with continuous laser and air cooling, as well as pulsed laser with water cooling. The phase structures of the coatings were BCC, (Ti,W)C, and μ phase. The carbides and μ phase in the pulsed laser with water-cooled coating were refined, and the proportion of the μ phase decreased. The wear resistance of the pulsed laser with water-cooled coating significantly increased, which can be attributed to the reduction in the proportion of μ phase, the refinement of carbides, and the formation of a wear lubrication layer. The pulsed laser with water cooling enhanced the thickness and uniformity of the passivation film on the coating surface, thereby improving corrosion resistance. [ABSTRACT FROM AUTHOR]

In the marine atmosphere, the corrosion rate of ship components is 4–5 times higher than that of the inland atmosphere. To solve the serious corrosion problem arising from long-term service in the marine environment of naval aircraft and ships, etc., this paper takes Al0.7FeCoCrNiCux system high-entropy alloy coating prepared by laser melting technology with 5083 aluminum alloys as the base material and analyzes the aging and failure mode of equipment coating under a marine atmospheric environment. XRD and SEM were utilized to study the microscopic morphological structure of the coatings. The laws of influence of Cu elements on the electrochemical corrosion behavior of the Al0.7FeCoCrNiCux system high-entropy alloy in 3.5 wt.% NaCl neutral solution was investigated by using dynamic potential polarization and electrochemical impedance spectroscopy, and neutral salt spray acceleration tests and outdoor atmospheric exposure tests were carried out. The results show that the Al0.7FeCoCrNiCux (x = 0) high-entropy alloy coating has a single BCC phase structure and the Al0.7FeCoCrNiCux (x = 0.30, 0.60, 0.80, 1.00) high-entropy alloy coating consists of both BCC and FCC phases with a typical dendrite morphology. With the increase in Cu content, the self-corrosion potential of Al0.7FeCoCrNiCux gradually increases and the current density gradually decreases, which with the results of the electrochemical impedance spectrum analysis, indicating that the corrosion resistance of Al0.7FeCoCrNiCu1.00 is optimal. The results of the neutral salt spray acceleration test and the outdoor atmospheric exposure test were integrated to conduct a comprehensive evaluation of the corrosion resistance of the coating. The corrosion resistance of Al0.7FeCoCrNiCux coating increases with the increase in Cu content, and the impressive strength and plastic deformation are best when x = 0.80. Neutral salt spray accelerated the test with no corrosion at 5040 h, and even if the coating is broken, it can last up to 4320 h. In the outdoor atmospheric exposure test, which was conducted 12 months after the coating surface test, no corrosion occurred. [ABSTRACT FROM AUTHOR]

• The WC powder core spiral AlCuNiCrTi-CWW was produced. • The WC reinforced HEA coating was synthesized in situ via vibration assistance TIG-cladding. • The HEA coating via VA-TIG-cladding has the maximum microhardness (725HV). • The HEA coating via VA-TIG-cladding has lowest friction coefficient (0.42). • The HEA coating via VA-TIG-cladding has the smallest volume wear rate (0.1397 × 10−4 mm3/N·m). Aiming at the difficulty preparing high-entropy alloy (HEA) coating by adding carbide powder using TIG-cladding, the WC core spiral CWW prefabricated vibration assisted TIG-cladding method is proposed in this work. The HEA coating (S1-coating) was prepared on the EA4T steel using AlCuNiCrTi cable-type welding wire (CWW) via TIG-cladding, then the WC reinforced HEA coating (S2-coating) was produced using spiral AlCuNiCrTi-CWW with WC powder core by TIG-cladding. Finally, another WC reinforced HEA coating (S3-coating) via vibration assistance TIG-cladding using the same material as S2-coating. The S1-coating is composed of BCC and FCC solid solutions. Except for the same phases as S1-coating, TiC appeared in the S2-coating and the S3-coating. Due to the grain refinement effect caused by vibration, the S3-coating has the maximum microhardness (725HV), lowest friction coefficient (0.42) and the smallest volume wear rate (0.1397 × 10−4 mm3/N·m). The addition of vibration assistance effectively improves the microhardness and wear resistance of the coating without changing CWW composition. [ABSTRACT FROM AUTHOR]

High entropy alloy (HEA) coatings of equimolar AlCoCrFeNi typically exhibit a lower oxidation rate at high temperatures by forming a protective passivation film. However, the metal elements consumption during long-term oxidation limitted the application. In this work, AlCoCrFeNi HEA coatings doped by AlSi as a supplement to passivation elements were prepared by atmospheric plasma spraying (APS), and AlSi capsules were diffused uniformly into the coating through annealing treatment to offset the element consumption during high-temperature oxidation. Results showed that annealing promoted Al and Si atoms diffusing into the solid solution, which stabilized BCC and inhibited FCC formation. During the oxidation at 900 °C, a protective Al 2 O 3 film was formed on the coating surface, and AlSi capsules continuously transported Al ions to the consumption zone and reduced oxidation rate to 0.0015 g/cm2. The HEA coating doped by passivation element capsules provided a new approach for the design of novel antioxidant coatings. [Display omitted] • AlSi as a supplement for AlCoCrFeNi coatings counteracted the element consumption and softening at high-temperature oxidation. • AlCoCrFeNi coatings doped with uniform AlSi were fabricated through plasma spraying+annealing, maintaining a biphasic BCC + FCC. • At annealing, the BCC → FCC transition was suppressed with AlSi atoms filled the Al consumption region. • AlSi promotes the hard BCC phase at 600–1200 °C annealing, improving the microhardness (470 HV → 602 HV). • At 900 °C oxidation, AlSi inhibited the spinel oxides and promote the protective Al 2 O 3. [ABSTRACT FROM AUTHOR]

Infrared-blue composite laser cladding technology is used to prepare highly conductive and wear-resistant CoCrFeNi-(Mo, Ti, W) HEA coatings on the surface of the copper alloy to overcome the problem of high reflectivity of copper alloy aiming to enhance the surface performance of copper alloy current-carrying friction part. The microstructure and electrical properties of the high-entropy alloy coating were investigated. The wear resistance of the coatings was tested under high-speed and high-current conditions using a self-made current-carrying friction and wear testing machine. The results show that fine-grain and second-phase strengthening significantly enhances the hardness of the high-entropy alloy coating. The high-entropy alloy coating maintains the excellent electrical conductivity of the copper alloy, with an overall conductivity remaining above 60 % IACS. During the current-carrying friction process, the CoCrFeNi-(Mo, Ti, W) HEA coatings exhibited good wear resistance, with wear rates of 0.84 g/h, 1.08 g/h, and 1.32 g/h, respectively. The wear mechanisms observed included varying degrees of adhesive wear, abrasive wear, fatigue wear, and arc erosion. [Display omitted] • Successful high-entropy alloy coatings on copper alloys using laser cladding • Friction experiments were conducted at high currents (108 A/m2). • CoCrFeNi-(Mo, Ti, W) HEA coatings show excellent electrical conductivity and wear resistance. • Studied how doping with different elements affects the electrical and tribological properties of coatings. [ABSTRACT FROM AUTHOR]

In this study, spark plasma sintering (SPS) was used for the thermoelectric composite treatment of CrMnFeCoNi/WC plasma transfer arc welding (PTA) coating to explore the difference compared with common heat treatment (HT). X-ray diffraction (XRD) was used to detect the phase composition, and a combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to characterize the microstructure. The performance of nano-indentation was tested. The results show that the coating after PTA has a large dislocation density due to internal stress, while HT and SPS treatment significantly reduce the internal stress and dislocation density of the coating. Nano-indentation test shows that the hardness of the coating after PTA is 4.24 GPa, and after HT, the hardness decreases to 4.05 GPa. However, the coating after SPS treatment has significant precipitation-strengthening effect due to the wide existence of the precipitated phase, and the hardness rises to 4.78 GPa. [ABSTRACT FROM AUTHOR]

This study investigated the effect of potential change on the microstructure and corrosion properties of CoCrFeMnNi HEA coatings synthesized by the electrochemical deposition method. The films were precipitated in an electrolyte based on a DMF-CH3CN organic system comprising Co, Cr, Fe, Mn, and Ni cations. GIXRD pattern in all samples showed a single face-centered-cubic structure. SEM-EDS results show that the coating morphology and the elements value in alloy composition vary at different coating potentials. Coatings were uniform and crack-free surfaces. The results of the wettability test showed all coatings were super-hydrophilic. All the alloys exhibited similar passivation and negative hysteresis processes in the CPP test. However, the 5 V sample exhibited a lower Epit value than the 6 V, and none of the samples were sensitive to pitting corrosion. The CPP test result showed that the corrosion current density of the 5 V sample was 0.0525 μA/cm2, the minimum corrosion rate for the coated samples, and has improved the corrosion resistance of the substrate by about 44 times. The EIS test results showed the excellent performance of the coatings in enhancing the corrosion resistance compared to Cu substrate and similar alloy samples in a 3.5 wt% NaCl solution, as the protection efficiency was about 90%. These High entropy alloy coatings are suitable for engineering applications in which higher corrosion protection is needed.

In order to save the time and cost of friction and wear experiments, the coating composition (different contents of Al, Ti, and Cu elements), ratio of hardness and elastic modulus (H3/E2), vacuum heat treatment (VHT) temperature, and wear form were used as input variables, and the wear rates of high-entropy alloy (HEA) coatings were used as output variables. The dataset was entirely obtained by experiment. Four machine learning algorithms (classification and regression tree (CART), random forest (RF), gradient boosting decision tree (GBDT), and adaptive boosting (AdaBoost)) were used to predict the wear resistance of HEA coatings based on a small amount of data. The results show that except for the GBDT model, the other three models had good performance. Because of the small amount of data, the CART model demonstrated the best prediction performance and can provide guidance for predicting the wear resistance of AlCoCrFeNi-X (Ti, Cu) HEA coatings for drilling equipment. Furthermore, the contribution of different factors to the wear rate of AlCoCrFeNi-X (Ti, Cu) HEA coatings was obtained. Al content had the greatest influence on wear rate, followed by H3/E2, wear form, and VHT temperature.

FeCoCrNiMnAl high-entropy alloy cladding was fabricated on the surface of 4Cr5MoSiV1 substrate by laser cladding technology. The microstructure, hardness and wear resistance of the cladding layer were systematically investigated using electron back scattered diffraction, transmission electron microscope, microhardness and wear tests. The was no obvious change in the grain size, type and proportion of phases (dual-phases of face centred cubic and body centred cubic) in the FeCoCrNiMnAl coating after heat treatment at 600°C for 100 h. The recrystallization induced by the heat treatment decreased the density of dislocations. Finally, the microhardness and wear resistance of the FeCoCrNiMnAl cladding layer decreased by 9.2% and 11.7%, respectively, after the heat treatment. Nevertheless, it still fulfils the application requirements. [ABSTRACT FROM AUTHOR]

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A series of novel (AlCrFeTiV) 100-x Ni x (x = 0, 10, 20, and 30) high-entropy alloy (HEA) coatings were prepared via laser cladding on Ti6Al4V. The microstructure evolution, hardness, wear behavior, and high-temperature oxidation resistance were systematically studied. The results indicate that the microstructure of the (AlCrFeTiV) 100-x Ni x HEA coatings gradually transition from BCC1 (enriched Ti, Al) + BCC2 (enriched V, Cr) + Laves phases to BCC + NiAl-type B2 + Laves phases with increasing x content. Ni addition gradually increased the hardness and wear resistance of the HEA; however, the formation of the B2 phase led to a slight decrease in hardness. Among the studied compositions, the Ni 30 HEA coating exhibited the best wear resistance, with a wear mass loss of 8 mg·mm−2 and a wear mass loss of only 13.6 % for Ti6Al4V. The wear mechanism of the (AlCrFeTiV) 70 Ni 30 HEA coating is a comprehensive effect of abrasive wear, oxidative wear, and adhesive wear. Compared with those of Ti6Al4V, the oxidation rates of the AlCrFeTiV, Ni 0 , Ni 10 , Ni 20 , and Ni 30 HEA coatings decreased by 65 %, 62 %, 55 %, and 61 %, respectively. The improved oxidation resistance is attributed to the formation of a dense NiXO 4 spinel oxide layer. The Ni 20 HEA coating exhibited excellent oxidation resistance at 800 °C, and the oxidation mechanism was further investigated via first-principle calculations. The results indicate that there is strong charge transfer between O atoms and Ni and Al, which tends to form NiAlO 4 -type spinel oxides. • Ni addition improves hardness and wear resistance of AlCrFeTiV HEA coating. • Dense NiXO 4 -type spinel oxide increases high-temperature oxidation resistance. • DFT shows strong charge transfer between O atoms and Ni, Al to form NiAlO 4 oxide. [ABSTRACT FROM AUTHOR]

High-entropy alloy powders synthesized by mechanical alloying were used as feedstock to prepare FeCoNiCrAl and FeCoNiCrMn coatings by atmospheric plasma spraying. The microstructure and phase composition of the coatings were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, x-ray diffraction, and transmission electron microscopy. The microhardness and wear behavior of the coatings were measured by a microhardness tester and a pin disk-type wear tester, respectively. Polarization curves were plotted to compare the corrosion resistance of the coatings in 3.5 wt.% NaCl solution. It was observed that the FeCoNiCrAl coating was composed of micro-nano face-centered cubic and body-centered cubic solid solutions and a small amount of band-like micro-nano alumina formed during plasma spraying and the FeCoNiCrMn coating was composed of only face-centered cubic solid solution and dispersed nanocrystalline oxide (Mn1.5Cr1.5O4). The average microhardness values of the FeCoNiCrAl and FeCoNiCrMn coatings were determined as 550.1 HV100gf and 440.9 HV100gf, respectively. The FeCoNiCrAl coating had better wear resistance than the FeCoNiCrMn coating. The main wear mechanisms of the FeCoNiCrAl and FeCoNiCrMn coatings were fatigue wear. The FeCoNiCrAl coating had higher corrosion potential, lower corrosion current density, and better corrosion resistance than the FeCoNiCrMn coating. [ABSTRACT FROM AUTHOR]

A high-entropy alloy coating of AlCoCrFeNi was prepared by plasma spraying and then remelted via laser remelting. The effect of laser remelting on the microstructure, mechanical properties and wear resistance of the AlCoCrFeNi coating was investigated. Particularly, the effect of surface free energy on the wear resistance of the coatings before and after remelting was explored. The results showed that the remelted AlCoCrFeNi coating retained the same single BCC solid solution structure as the as-sprayed AlCoCrFeNi coating. Besides, the defects in the coating were basically eliminated by laser remelting, leading to the porosity of the coating decreased from 4.8 to only 0.3%. Consequently, the hardness, elastic modulus and fracture toughness of the coating were enhanced by 38%, and the wear loss of the remelted AlCoCrFeNi coating was only 22% of that of the as-sprayed one. Therefore, laser remelting is a feasible method to improve the microstructure and enhance the wear resistance of the AlCoCrFeNi high-entropy alloy coating. [ABSTRACT FROM AUTHOR]

In this article, the synergistic effect of the addition of V and Nb on CoCrFeMnNi high-entropy alloy (HEA) coating prepared by plasma cladding was studied. The results showed that the addition of V and Nb promoted the precipitation of intermetallics in the HEA coating and had no effect on the face-centered cubic (FCC) structure of the matrix. The CoCrFeMnNiVNb composite coating presented a complex phase structure including an FCC phase, FeNb intermetallic (Laves) phase, and CoFeV intermetallic (sigma) phase. Compared with the CoCrFeMnNi coating, the microhardness of the CoCrFeMnNiV, CoCrFeMnNiNb, and CoCrFeMnNiVNb coatings increased by 4.3, 4.2, and 6.5 times, respectively. The exceptional hardness was primarily attributed to the formation of hard intermetallics and solution strengthening of V and Nb. The synergistic reinforcement effect of V and Nb on the wear properties was better than that of a sole addition. The wear resistance of the CoCrFeMnNiVNb coating was the best, corresponding to the lowest wear rate of 1.85 × 10−5 mm3·N−1·m−1. The addition of V and Nb restrained abrasive wear and adhesive wear and promoted the formation of oxide layers on the worn surface of the HEA coatings during sliding. [ABSTRACT FROM AUTHOR]

This study deals with Al2O3-13wt.%TiO2-reinforced CoCrFeMnNi high-entropy alloy (HEA) composite coatings prepared by plasma spraying. The effect of the Al2O3-TiO2 ceramic phase on the microstructure, mechanical properties and high-temperature tribological performance of the as-sprayed composite coatings was investigated. The results showed that the composite coatings consisted of a HEA phase with a FCC (face-centered cubic) structure and an Al2O3-TiO2 ceramic phase with a three-dimensional network structure. The coatings presented a typical layered structure with less porosity than pure HEA coatings. The three-dimensional network structure was mainly due to partially melted Al2O3-13wt.%TiO2 particles during the spraying process. The composite coating with Al2O3-TiO2 ceramic phase had an improved plastic deformation resistance and a reduced elastic recovery resistance. Its wear rate was lower than that of the pure HEA coating. The main wear mechanisms included oxidation, wear and adhesive wear. The Al2O3-TiO2 ceramic phase reduced the adhesive wear and promoted the tribological behavior of the HEA composite coating at low temperature. The excellent wear resistance of the as-sprayed coating at high temperatures was mainly due to the formation of an oxide layer on the worn surface. [ABSTRACT FROM AUTHOR]

The effects of substrate temperature and deposition time on the morphology and corrosion resistance of FeCoCrNiMo0.3 coating fabricated by magnetron sputtering were investigated by scanning electron microscopy and electrochemical tests. The FeCoCrNiMo0.3 coating was mainly composed of the face-centered cubic phase. High substrate temperature promoted the densification of the coating, and the pitting resistance and protective ability of the coating in 3.5wt% NaCl solution was thus improved. When the deposition time was prolonged at 500°C, the thickness of the coating remarkably increased. Meanwhile, the pitting resistance improved as the deposition time increased from 1 to 3 h; however, further improvement could not be obtained for the coating sputtered for 5 h. Overall, the pitting resistance of the FeCoCrNiMo0.3 coating sputtered at 500°C for 3 h exceeds those of most of the reported high-entropy alloy coatings. [ABSTRACT FROM AUTHOR]

FeNiCoCrTi0.5Nb0.5 high-entropy alloy coating is prepared on AISI 1045 steel by laser cladding. The cross-sectional macroscopic morphology, phase, microstructure, microhardness and wear resistance are studied systematically. The results show that FeNiCoCrTi0.5Nb0.5 coating has no porosities, cracks or other defects and is well metallurgically bonded to the substrate. The coating is composed of body-centred cubic (BCC) solid solution, face-centred cubic (FCC) solid solution and hard Laves phase. The solid solution phase and Laves phase distribute uniformly and closely in a lamellar shape to form a fine and dense eutectic structure. The microhardness of FeNiCoCrTi0.5Nb0.5 coating is about three times that of the substrate. Compared with the substrate, the coating has superior wear resistance. [ABSTRACT FROM AUTHOR]

FeNiCoCrTi0.5 coatings with different process parameters were fabricated by laser cladding. The macro-morphology, phase, micro-structure, hardness, and wear resistance of each coating were studied. The smoothness and dilution rate of the FeNiCoCrTi0.5 coating generally increased with the increase of specific energy (Es), which is the laser irradiation energy received by a unit area. FeNiCoCrTi0.5 coatings at different parameters had bcc, fcc, and Ti-rich phases as well as equiaxed, dendritic, and columnar structures. When Es increased, the size of each structure increased and the distribution area of the columnar and dendritic structures changed. The prepared FeNiCoCrTi0.5 coating with the Es of 72.22 J·mm−2 had the highest hardness and the best wear resistance, the highest hardness of the coating reached HV 498.37, which is twice the substrate hardness. The average hardness of the FeNiCoCrTi0.5 coating with the Es of 72.22 J·mm−2 was 15.8% higher than the lowest average hardness of the coating with the Es of 108.33 J·mm−2. The worn surface morphologies indicate that the FeNiCoCrTi0.5 coatings exhibited abrasive wear. [ABSTRACT FROM AUTHOR]

Based on the two-way diffusion behavior of FeCoCrNi and W elements and the lattice distortion principle during alloy solidification, a new type of HEA wear-resistant coating with Laves phase and hardness gradient was prepared in this work. Analysis results show that the Laves phase has higher hardness and resistance to deformation, while the FCC phase exhibits higher plastic deformation ability. The tribological properties of the coating material under both room- and high-temperature wear conditions are improved by the synergistic effect of the hard Laves phase and the ductile FCC phase. Moreover, the transition effect of the intermediate eutectic layer alleviates the stress concentration during the friction process, and the oxide film shows a strong wear resistant under the room-temperature wear condition. [Display omitted] • The HEA wear-resistant coating with Laves phase and hardness gradient distribution was prepared in situ. • The FCC-Laves dual-phase structure with soft and hard cross has good strength and toughness. • The wear mechanism of W-CC at room temperature is three-body wear with slight oxidation. • The high hardness of Laves phase and the oxidation of FCC phase improve the high temperature anti-friction performance. • When the oxide film is worn at room temperature, it shows a strong wear protection effect. [ABSTRACT FROM AUTHOR]

High entropy alloy attracts great attention for its high thermal stability and corrosion resistance. A CoCrFeNiMn high-entropy alloy coating was deposited on grey cast iron through plasma transfer arc cladding. It formed fine acicular martensite near the grey cast iron, with columnar grains perpendicular to the interface between the grey cast iron substrate and the cladding layer as well as dendrite in the middle part of the coatings. Simple FCC solid solutions present in the coatings which were similar to the powder’s structure. The coating had a microhardness of 300 ± 21.5 HV0.2 when the cladding current was 80 A for the solid solution strengthening. The HEA coating had the highest corrosion potential of −0.253 V when the plasma current was 60 A, which was much higher than the grey cast iron’s corrosion potential of −0.708 V. Meanwhile, the coating had a much lower corrosion current density of 9.075 × 10−7 mA/cm2 than the grey cast iron’s 2.4825 × 10−6 mA/cm2, which reflected that the CoCrFeNiMn HEA coating had much better corrosion resistance and lower corrosion rate than the grey cast iron for single FCC solid solution phase and a relatively higher concentration of Cr in the grain boundaries than in the grains and this could lead to corrosion protection effects.

The AlCrFeNi2W0.2Nbx high-entropy alloy (HEA) coatings were synthesized on the 304 stainless steel by laser cladding. The microstructure, microhardness and wear resistance of HEA coatings were investigated. The HEA coatings show a good metallurgical bonding to the substrate, and they consist of the cladding zone, bonding zone and heat-affected zone. The phase structures of the HEA coatings are the BCC solid solution phase and the Fe2Nb-type Laves phase. The Nb0.5 composition shows a hypo-eutectic microstructure; the primary phase is the BCC solid solution phase. While Nb1.0, Nb1.5 and Nb2.0 coatings show hyper-eutectic microstructures, the primary dendrites show the Laves phase. The microhardness of AlCrFeNi2W0.2Nbx coatings increases with increasing Nb content and that of the Nb2.0 coating is up to 890.7 HV, about 4.5 times as the 304 stainless steel. Dry sliding model wear testing has been performed. The AlCrFeNi2W0.2Nbx (x = 1.5, 2.0) high-entropy alloy coatings exhibit an order of magnitude lower wear than 304 stainless steel under the same loading conditions. It is attributed to the larger volume fraction of hard Laves phase and the anti-attrition of newly formed oxidation films during friction process. [ABSTRACT FROM AUTHOR]

Corrosion caused by salt-spray and fatigue failure resulting from cyclic sea wave and strong storm are common degradation problem in offshore structural steels, and their interaction would accelerate service failure of these steels. In this work, therefore, FeCoNiCrMn high-entropy alloy (HEA) coatings were first prepared on 321 steels to simultaneously improve their corrosion and fatigue resistance. Then the pre-corrosion in salt-spray environment and subsequent high-cycle fatigue (HCF) tests were conducted on both coated and uncoated steel. The same HCF tests were also performed on the uncorroded steel specimens to reveal the influence of pre-corrosion on their fatigue resistance. The results showed that the corrosion and fatigue resistance of coated steel were both improved, which should be attributed to the higher strength, dislocation motivity and formation rate of corrosion film of the HEA coating. Moreover, pre-corrosion would decrease the mechanical properties and depth of the HEA coating, leading to significant damage to the fatigue resistance of coated steel. However, after pre-corrosion, the fatigue life of uncoated and coated steel was decreased by 18.2 %–38.8 % and 34.4 %–42.6 % at different stress amplitudes, respectively, showing the significant protective effect of HEA coatings against the pre-corrosion damage to fatigue life of offshore 321 steel. • FeCoNiCrMn high-entropy alloy coating was prepared on offshore AISI 321 steels by selective laser melting. • The grain microstructures of the coating from inside to outside were respectively characterized by fine and coarse columnar dendrites. • The effects of the coating on the corrosion and fatigue resistance of 321 steel were revealed. • The influence of pre-corrosion on the fatigue resistance of both uncoated and coated steels were discussed. [ABSTRACT FROM AUTHOR]

A major drawback in the application of AlCoCrFeNiCu high-entropy alloy (HEA) coatings is a susceptibility to hot-cracking, which is closely related to a grain boundary segregation due to the low melting point Cu component. Reducing or eliminating the grain boundary segregation of Cu is an effective means of reducing cracking in the HEA coating. In this study, blended and partial pre-alloyed powders were used as feedstock to fabricate the AlCoCrFeNiCu coating. The application of electron beam (EB) cladding to partial pre-alloyed powders, prepared by resistance seam welding (RSEW), resulted in an appreciable reduction of crack density in the coating. This response is attributed to the formation of Ni 3 Al and Al 4 Cu 9 promoted by the relatively low heat generated during the RSEW process. In subsequent EB cladding, nanoscale Me 3 Al (Me = Cu, Ni) replaced the Cu-rich phase at grain boundaries. The hardness and wear resistance of coatings using partially pre-alloyed powders were 17.2 % and 15.8 % higher, respectively, than blended powders. The findings of this study indicate that the use of partial pre-alloyed powders can offer a new effective approach to reducing the hot cracks in EB cladding AlCoCrFeNiCu HEA coatings. [Display omitted] • AlCoCrFeNiCu coatings were fabricated by blended and partial pre-alloyed powders. • Cracks were reduced using partial pre-alloyed powders by electron beam cladding. • Ni 3 Al and Al 4 Cu 9 phases reduced the interdendritic segregation of Cu in RE coatings. • Wear resistance of RE coating was optimal 20.4 % higher than EB coating. [ABSTRACT FROM AUTHOR]

The influence of temperature on the corrosion and cavitation erosion-corrosion (CE-C) behavior of Al 10 Cr 28 Co 28 Ni 34 high-entropy alloy (HEA) coating in seawater was investigated. Interestingly, the corrosion resistance of the coating progressively diminished with an increase in seawater temperature, but the CE-C resistance demonstrated a trend of initial increase followed by a decrease. At higher seawater temperature, the resistance of the coating surface and the destructive force of the bubbles were respectively enhanced and weakened due to the increase in oxide film thickness, maximum bubble size, and collapse time, together leading to a reduction in the damage degree to the coating. • The hardening index and corrosion resistance of HEA coating are higher. • The seawater temperature changes the maximum radius of bubbles and collapse time. • The cumulative mass loss of HEA coating in seawater at 60 °C is instead reduced. • The oxide film formed on coating surface thickens at higher seawater temperature. • The designed HEA coating has excellent application prospects in offshore equipment. [ABSTRACT FROM AUTHOR]