High-entropy Alloy Coatings Research Articles

Effect of Mo on microstructure and sliding wear performance of CoCrFeNiMox high entropy alloy coatings by laser cladding

The CoCrFeNiMox (x = 0, 0.5, 1, 1.5 in molar ratio) high-entropy alloys (HEAs) coating were prepared on AISI1045 steel by laser cladding. The microstructure, hardness and tribological properties were investigated through x-ray diffraction, scanning electron microscopy (SEM), microhardness tester and reciprocating tribometer. The result shows that the coating is metallurgically bonded to the substrate and exhibits columnar and equiaxed grains microstructure consisted of main face-centered cubic (FCC) solid solution and few body-centered cubic (BCC) struture when x≤ 1.0. The (Fe, Cr, Mo)-riched σ phase shows up in the CoCrFeNiMo1.5 FCC matrix due to excess Mo addition. CoCrFeNiMox HEA coatings shows an obvious increase of surface hardness from 261 HV0.2 to 793 HV0.2 by increasing the Mo content to 1.5 in the molar ratio, and exhibited the most excellent wear resistance among all the compositions designed in this work. The wear resistance of the CoCrFeNiMo1.5 alloy coating is about 2.2 times higher than that of the coating without Mo. The wear mechanism changes with increasing Mo content, though abrasive wear is a common mechanism, more adhesive wear occurred at low Mo content but few oxidation and fatigue wear occured at high Mo content.

Corrosion and passivation behavior of in-situ TiC reinforced Al0.1CrNbSi0.1TaTiV refractory high entropy alloy coatings via doping C

This work is aimed to explore ways to further improve corrosion properties of single-phase RHEA coating by introducing in-situ TiC phase. Results shown that C/Al0.1CrNbSi0.1TaTiV RHEA coatings exhibited better comprehensive resistance to pitting and general corrosion compared to most of reported HEAs and traditional alloys. The passive film was dominated by a muti-oxide crystalline structure with a thickness of ∼ 11.52 nm. The small-size and evenly distributed TiC phase with most thermodynamically stable could be obtained via doping C and retard the nearby pitting process, improving the pitting behavior and the dense of passive film in 1.0 wt% C coating.

Effect of rare earth La2O3 on the microstructure and corrosion resistance of CoCrFeNiMoSi high entropy alloys

This study systematically investigated the effect of incorporating trace amounts of La2O3 into the CoCrFeNiMoSi high-entropy alloy (HEA) system on its corrosion resistance in neutral chloride ionic salt solutions. The CoCrFeNiMoSi HEA coatings and CoCrFeNiMoSi-0.5 % La2O3 HEA coatings were prepared using the laser melting technique. The microstructure, phase composition, and electrochemical corrosion performance were characterized using X-ray diffraction, scanning electron microscopy, electrochemical workstation, and X-ray photoelectron spectroscopy. The experimental results revealed that the microstructure primarily comprised face-centered cubic structure (FCC), body-centered cubic structure (BCC), and Si-rich intermetallic compounds. Notably, the addition of La2O3 facilitated the formation of the FCC phase. Electrochemical tests demonstrated that the CoCrFeNiMoSi-0.5 % La2O3 HEA coating exhibited an elevated corrosion potential and a reduced self-corrosion current density when compared to the CoCrFeNiMoSi HEA coating. The X-ray photoelectron spectroscopy (XPS) data revealed a notable increase in the Cr content and oxide content of the passive film when La2O3 was present in the HEA. This resulted in the formation of a more protective passivated film. Consequently, the potential utilization of rare earth lanthanum oxide to enhance the corrosion resistance of HEA coatings is promising.

Effect of ZrC on the Microstructure and Properties of CrMnFeCoNi High-Entropy Alloy Coatings Prepared by a Plasma Transferred Arc Process.

The low strength caused by the single FCC structure of the CrMnFeCoNi high entropy alloy (HEA) limits its application in the field of coating. Here, we prepared high-entropy alloy coatings of CrMnFeCoNi with different ZrC contents on Q235 steel by a plasma transferred arc process. The effects of ZrC on the microstructure and properties of the CrMnFeCoNi HEA coating were investigated by optical microscopy, scanning electron microscope, and X-ray diffraction and by employing a potensiostat/galvanostat. The results showed that ZrC mainly existed in the coatings as a second phase, having little influence on the main crystal structure and micromorphology of the CrMnFeCoNi HEA coating. The hardness of the CrMnFeCoNi HEA coating increased with the ZrC content. ZrC can effectively improve the corrosion resistance of the CrMnFeCoNi HEA coating. In a 1 mol/L NaCl solution with 4 wt% ZrC, the annual corrosion rate was only 5.997% of that of the HEA coating. Nevertheless, the improvement in the wear resistance of CrMnFeCoNi high-entropy alloy coatings was not apparent with the addition of ZrC. Consequently, the addition of ZrC to the FeCoCrNiMn high-entropy alloy coating holds promise for applications in corrosion resistance, particularly in oceanic environments.

3D finite element analysis and experimental correlations of laser synthesized AlCrNiTiNb high entropy alloy coating

A 3D Finite Element Analysis (FEA) model of laser cladding process of AlCrNiTiNb high entropy alloy (HEA) coatings on Titanium alloy (Ti6Al4V) substrate has been developed taking into account heat transfer and free surface movement. The use of Ti6Al4V is highly evident in applications such as aerospace, automobile and marine environments due to their outstanding specific strength to weight ratio. Although they have high strength useful for fabrication of engineering components and movable parts in a mechanical system, Ti6Al4V are restricted to non-friction applications as a result of their low hardness. In this work, AlCrNiTiNb HEA hard-coating with equi-atomic ratio was synthesized on Ti6Al4V alloy substrate by laser cladding technique to mitigate the limitations. Prior to experimental method, a 3D computational model was developed to simulate the physical phenomena based on heat transfers involved during laser surface cladding (LSC) of HEA coating on Ti‐6Al‐4V alloy by a laser-assisted direct energy deposition technique. COMSOL Multiphysics 5.3a was used to create a model using heat transfer in solids module incorporating temperature distribution during the layer-wise build-up of 3 layers. The experimental validation showed that the microstructural analysis by scanning electron microscope (SEM) resulted in coating having dendritic and interdendritic structure which resulted in good metallurgical bonding. X-ray diffraction (XRD) analysis displayed that AlCrNiTiNb alloy coating is composed of ordered and disordered solid solution phases (BCC and FCC) with no intermetallic compounds formed. Energy dispersive spectrometer (EDS) confirmed the presence of elements used. The microhardness of AlCrNiTiNb HEA coating reached maximum value around 892 HV which is more than of the substrate. The microhardness increased significantly due to the combination of BCC and FCC solid solution phases.

Effect of Mo content on the microstructure and mechanical properties of CoCrFeNiMox HEA coatings deposited by high power impulse magnetron sputtering

In this work, CoCrFeNiMox high entropy alloy (HEA) films were deposited by High Power Impulse Magnetron Sputtering (HiPIMS) using pure Mo and equiatomic CoCrFeNi targets. The effect of Mo content on the microstructure, residual stress state, and mechanical properties of the films was investigated in the range of 0–20 at.%. All films exhibited a columnar growth morphology and a high density of planar defects. Increasing the Mo content promoted the formation of a fine-grained structure and induced the transformation from a single face-centered cubic (FCC) phase to a mixture of FCC and body-centered cubic (BCC) phases. All produced films displayed a compressive residual stress state regardless of the Mo concentration. In terms of mechanical properties, the hardness of the films increased with increasing Mo content due to solid solution and grain boundary strengthening, along with the formation of a hard BCC phase. On the other hand, the elastic modulus decreased, likely due to the formation of an amorphous phase at higher Mo concentrations.

Review on wear resistance of laser cladding high-entropy alloy coatings

The wear resistance of the part surface has become an important factor affecting its own service life. Laser cladding (LC), as a surface modification technology, can prepare a coating with good metallurgical bonding with the substrate, which can significantly improve the wear resistance of the material surface. High entropy alloys (HEAs) are an emerging coating material with excellent wear resistance. Therefore, this paper reviews the latest development status in wear resistance of laser cladding-high-entropy alloy coatings (LC-HEACs) in terms of the HEAs material system, LC process parameters, strengthening phase, amorphous phase strengthening, assisted cladding, and post-treatment. At the same time, this paper also expounds on the mechanism of LC-HEACs enhancing the surface wear resistance of materials, and the current research status of LC-HEACs in different engineering materials and application environments. Finally, the current research deficiencies, challenges, and future development trends of LC-HEACs in the field of wear resistance are also elaborated, and it is expected to provide some references for their future development and applications.

Tribocorrosion behaviors of VNbMoTaWCr high entropy alloy coatings

In this work, four BCC-structured VNbMoTaW and VNbMoTaWCr high entropy alloy (HEA) coatings with different Cr contents were fabricated on the surface of 304 stainless steel (304SS) plates by a pulsed DC magnetron sputtering system. In addition to the dry pin-on-disk wear test and pure corrosion test, two kinds of tribocorrosion tests were performed. For the tribocorrosion test without applied potential, the HEA coatings were immersed in a 3.5 wt% NaCl aqueous solution at room temperature under 1 N load using a pin-on-disk tribometer. For the tribocorrosion test with applied potentials, the potentiodynamic polarization test was conducted to investigate the effects of external potentials and sliding loads on the corrosion current density, polarization resistance, and wear rates of HEA coatings. The hardness, corrosion resistance, and tribocorrosion (without applied potential) resistance of VNbMoTaWCr HEA coatings increased with increasing Cr content. The VNbMoTaWCr coatings with higher than 24.7 at.% Cr had a high hardness of 16.4 to 16.5 GPa and excellent corrosion resistance in pure corrosion and tribocorrosion without applied potential. On the other hand, as the tribocorrosion was executed with an applied potential higher than the breakdown potential and high current density, the tribocorrosion resistance of HEA coatings was greatly influenced by its protection degradation ratio, Pdr (the polarization resistance ratio between pure corrosion and tribocorrosion setup 2). Finally, the lowest wear rate of 2.55 × 10−5 mm3N−1 m−1, which was 1.4 times better than 304SS, was obtained for the VNbMoTaWCr coating containing 11.65 at.% Cr after the tribocorrosion test with applied high potential because of its lower Pdr value and less decay of corrosion protection ability.

Effect of ultrasonic impact treatment on the microstructure and properties of laser cladded CoCrFeNiMox high entropy alloy coatings

Ultrasonic impact technology was applied to improve the property of laser cladded CoCrFeNiMox (x = 0, 0.25, 0.5, 0.75) high entropy alloy coatings on the surface of low-carbon steel. The phase structures and the microstructural characteristics were studied in detail through X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The microhardness distributions, wear resistance, and corrosion resistance of the samples are illustrated using a microhardness tester, a micro-friction and wear tester, and an electrochemical test system. Single FCC phase solid solution was identified to be the main phase structure, with the interdendritic σ phase precipitating with the increasing Mo content. Although ultrasonic impact treatment did not change the phase composition of the high-entropy alloy (HEA) cladding coatings, evident plastic deformation and broken σ phase appeared near the surface of the impacted layers. Through the combined effects of dislocation, fine-grain, and dispersion strengthening, the microhardness of the CoCrFeNiMox coatings was improved after ultrasonic impact treatment. In addition, ultrasonic impact treatment decreased the surface roughness and increased the wear resistance, and the main wear mechanism of the impacted layers changed from fatigue spalling to abrasive wear. The wear mass of the ultrasonically impacted layers was approximately 92 % of the laser cladded CoCrFeNiMox coatings. Furthermore, ultrasonic impact treatment improved the corrosion resistance of the HEA coatings.

Structure and Phase State of Ceramic High-Entropy Alloy Coatings Formed by Plasma-Assisted Vacuum Arc Deposition

Structure and Phase State of Ceramic High-Entropy Alloy Coatings Formed by Plasma-Assisted Vacuum Arc Deposition

Effect of Cavitation Water Jet Peening on Properties of AlCoCrFeNi High-Entropy Alloy Coating

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.

Effect of Cr content on synergistic effect of Cr-Al during oxidation of high-entropy AlCoCrxNiTi alloys

AlCoCrxNiTi high-entropy alloy coatings, mainly composed of the BCC and B2 phases, were synthesized on Ti-6Al-4V substrates by laser cladding. The incorporation of Cr-refined grains enhanced the hardness of the alloy. Oxidation kinetic curves of the alloys at 800 °C in the air followed the parabolic law, and AlCoCr0.5NiTi alloy exhibited excellent oxidation resistance. The incorporation of an appropriate amount of Cr provided a structural template for the formation of Al2O3 and increased the diffusion rate of Al in the stable oxidation stage, leading to a reduction in the concentration required to form a continuous Al2O3 oxide film.

Effect of niobium content on microstructure and wear and corrosion resistance of laser-clad FeCo0.5CrNi1.5B0.5Nbx coatings on ductile iron

Ductile iron with a high carbon content is highly susceptible to the precipitation of brittle carbides during the cladding process, which makes it challenging to achieve the desired formability of the coating. In this study, FeCo0.5CrNi1.5B0.5Nbx (x = 0.1, 0.2, 0.3, and 0.4) high-entropy alloy coatings were designed using theoretical calculations and prepared on ductile iron through laser cladding. The effect of niobium (Nb) content on the microstructure evolution and phase composition of the coating was explored to determine the alloy component with the highest wear and corrosion resistance. All of the prepared coatings consisted of face-centered cubic (FCC) phases, along with Nb(C, B2) and Laves phases. With the increase in Nb content, the intensity of the diffraction peaks of NbC significantly increased compared to those of the other precipitates due to element diffusion. Nb0.3 coatings, which had the highest hardness, H/E, and H3/E2 values due to the most suitable percentage of FCC and hard phases, presented the lowest average friction coefficients of 0.48, 0.49, and 0.50, as well as the minimum wear volume of 0.64 × 108, 2.06 × 108, and 5.04 × 108 μm3 under loads of 10, 30, and 50 N, respectively. The wear mechanism of all the coatings was dominated by adhesive wear and oxidation wear under loads of 10 N and 30 N, while it changed to abrasive wear under a load of 50 N. Furthermore, Nb0.3 coatings also showed superior corrosion resistance due to the positive influence of the optimal Nb content on the oxide film. The Ecorr values were − 395 mV and − 337 mV, and the Icorr values were 0.21 × 10−6 A/cm2 and 1.10 × 10−6 A/cm2 in NaCl (3.5 wt%) and HCl (0.5 mol/L) solutions, respectively.

Microstructure, mechanical and corrosion properties of FeCrNiCoMnSi0.1 high-entropy alloy coating via TIG arc melting technology and high-frequency ultrasonic impact with welding

With the increase in studies on high-entropy alloys and their impressive structural properties, the preparation processes and applications of high-entropy alloys have become a popular research topic in metallic materials. In this paper, the preparation of FeCrNiCoMnSi0.1 high-entropy alloy coatings was carried out by the follow-welding high-frequency power ultrasonic impact composite TIG arc melting process, the effects of different power ultrasonic impacts on the microstructure and properties of the coatings are investigated. The results showed that the average grain size is reduced by 74 % (from 278 μm to 72 μm), the average microhardness is increased by 41 % from 568 HV1 to 807 HV1, the abrasion resistance is improved by 68 % under the effect of ultrasonic impact. The ultrasonic impact treatment process can effectively refine the microstructure of the coatings and improve the strength of grain boundaries. The corrosion resistance of the coating in 3.5 wt% NaCl solution is enhanced by 65 %, the corrosion type was changed from intergranular corrosion to uniform corrosion. This is mainly caused by the ultrasonic impact treatment which suppresses the elemental segregation of Cr and Mn and improves the grain boundary strength.

Effect of Bias Voltage on Structure, Mechanical Properties, and High-Temperature Water Vapor Corrosion of AlCrNbSiTi High Entropy Alloy Coatings

Fuel cladding tubes are devices used in reactors to encapsulate fuel clots and transmit heat to coolants. However, zirconium alloy materials which are widely used in the fuel cladding pipe of pressurized water reactors have noticeable safety risks in resisting design basis accidents. Therefore, it is very important to improve the corrosion resistance of fuel envelope tubes to high-temperature water vapor oxidation. High-entropy alloys are considered to be a potential protective coating material for cladding tubes. In this study, AlCrNbSiTi high-entropy alloy (HEA) coatings were prepared by magnetron sputtering at different bias voltages. The effect of bias on coating morphologies, structure, mechanical properties, and resistance to high-temperature water vapor corrosion were studied. Experimental results showed that the bias significantly affects the coating surface roughness. In terms of mechanical properties, the sample at 50 V bias exhibited maximum hardness and elastic modulus of 18.2 GPa and 232.4 GPa, respectively. The highest adhesive force of the coating to the substrate of 36 N was obtained at 100 V bias. The optimum water vapor corrosion resistance of the AlCrNbSiTi HEA coating was achieved at 50 V bias, in which sample-point corrosion was the main corrosion failure mechanism.

Study of tribological property of laser-cladded FeCoCrNiMnx high-entropy alloy coatings via experiment and molecular dynamics simulation

Laser cladding was used to fabricate the high entropy alloy (HEA) coating of FeCoCrNiMnx (x = 0, 0.5, 1). Coatings were studied to determine how Mn affected the microstructure, microhardness, and tribological property. Molecular dynamics simulations were used to examine the atomic-scale deformation and wear behavior of FeCoCrNiMn HEA coatings. FeCoCrNiMnx HEA coatings were composed of single FCC-type solid solution. Friction reduction and wear resistance are improved with Mn doping. When compared to the substrate and FeCoCrNi coating, the wear resistance of Mn1 coating is superior by 69.34% and 25.05%, respectively (wear rate is 3.74 ×10−5 mm3/N·m). The findings of molecular dynamics simulations demonstrate that Mn-doping significantly enhances strain hardening by the friction-induced FCC phase transition to the HCP phase. The deformation mechanism of Mn1 coating, as determined by the dislocation evolution pattern, is twinning induced plasticity, which improves the plasticity, strength, and work-hardening rate of coating all at once.

Microstructure and Wear Behavior of AlCoCrFeNiTi0.5 High Entropy Alloy Coating Prepared by Electron Beam Cladding on Ti-6Al-4V Substrate

Microstructure and Wear Behavior of AlCoCrFeNiTi0.5 High Entropy Alloy Coating Prepared by Electron Beam Cladding on Ti-6Al-4V Substrate

Evolution in microstructure and tribological behavior of laser cladded MoxNbTiZr high-entropy refractory alloy coatings with varying Mo content

The effect of the Mo element on the Ni-Ti-Zr refractory high-entropy alloy (RHEA) coatings synthesized by laser cladding were explored in terms of microstructural evolution and tribological behavior assessed by material characterization techniques and drying sliding wear tests. The findings reveal that MoxNbTiZr RHEA coatings, comprising of body center cubic (BCC) matrix phase and several hexagonal close packed (HCP) phases, have a dendrite microstructure with Mo, Nb-rich dendritic region (DR) and Zr-rich interdendritic region (IR), affected by Mo-induced thermodynamic instability. The micro-segregation between DR and IR becomes serious by the synergy effect of melting point difference, diffusion rate, and mixing enthalpy. The microhardness of the RHEA coating has a linear relationship with Mo content, with the highest value of 732.67 HV at x = 1.0. Nanotwins induced by residual stress, high cooling rate, solid-solution strengthening, fine-grain strengthening, and second-phase strengthening, cause microhardness improvement. Due to the generation of the destructive oxide layer and rising coating brittleness, the wear rate rises from 1.66 × 10−4 mm3/(N·m) to 3.75 × 10−4 mm3/(N·m). The wear mechanism of the MoxNbTiZr coatings shifts from oxidation wear to abrasive wear and eventually to three-body abrasion and severe brittle micro-peeling. Among these coatings, Mo0.6NbTiZr exhibits the optimal performance with excellent comprehensive characteristics.

Strengthening mechanisms and high-temperature oxidation properties of laser-clad TaNbZrTi refractory high entropy alloy coatings

Strengthening mechanisms and high-temperature oxidation properties of laser-clad TaNbZrTi refractory high entropy alloy coatings

Effect of nitrogen pressure on the fabrication of AlCrFeCoNiCu0.5 high entropy nitride thin films via cathodic arc deposition

In the past two decades, high entropy alloy (HEA) coatings have attracted great attention due to their superior mechanical properties, outstanding corrosion and oxidation resistance, and exceptionally high thermal stability. In comparison to HEA thin films, high entropy nitrides (HENs) exhibit higher mechanical strength and chemical inertness. In this work, AlCrFeCoNiCu0.5 HEA and HEN thin films were fabricated using a filtered cathodic arc. By regulating the deposition pressure from 0.0005 Pa (HEA thin film) to 0.05 Pa, the nitrogen concentration in each thin film was precisely controlled to tune the mechanical properties. Scanning transmission electron microscopy-energy dispersive spectroscopy revealed that the nitrogen concentration of the films was up to 21.2 at. % at the pressure of 0.05 Pa. The reduced effect of preferential sputtering increased aluminum concentration from 8.3 ± 1.5 to 12.9 ± 2.2 at. % as pressure increased up to 0.05 Pa. X-ray photoelectron spectroscopy further confirmed the formation of AlN and CrN at pressures of 0.01–0.05 Pa. The highest hardness and elastic modulus of the HEN film were 12.4 ± 0.6 and 347.3 ± 17.7 GPa, respectively, which were 84.8% and 131.4% higher than those of the HEA thin film.