Alloy Coatings Research Articles

Improving the mechanical and wear properties of AZ91 magnesium alloy via laser cladded (AlCu)3.5CoCrNiSnx (x = 0 and 1) high entropy alloy coatings

(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.

Comparative analysis of microstructure and corrosion resistance in laser-clad austenitic and martensitic stainless-steel coatings

Post-casting austenite often possesses better corrosion resistance than martensite. In order to compare the difference of corrosion resistance between austenitic stainless steel coating (ASSC) and martensitic stainless steel coating (MSSC) in the powder metallurgical state, two stainless steel Fe-based alloy coatings of the same process parameter were prepared on the surface of 40Cr steel by using laser cladding technology. Through SEM, EBSD, XRD and electrochemical tests, the microstructure, phase and cross-section metallurgical bonding condition of the coating were studied, and the difference in corrosion resistance between the two was comprehensively analyzed. The results showed that the main phase structure of ASSC was the FCC phase, and the main phase structure of MSSC was the BCC phase. The average self-corrosion current (9.92 × 10−8 A/cm2) and average self-corrosion rate (1.04 × 10−3 g/m2·h) of MSSC were 4.77 % and 5.62 % of ASSC, respectively. In addition, the polarization resistance, impedance value, and passivation film density of MSSC are higher than ASSC, MSSC has less damage from corrosion. The combination of factors, such as fabric refinement and passivation film density, makes the corrosion resistance of MSSC better than ASSC.

Cavitation erosion performance and phase transformation strengthening behavior of laser clad iron-based shape memory alloy coatings

In order to avoid cavitation damage on the surface of overcurrent components after long-term service, the surface is reinforced with a coating to improve its cavitation resistance, thus prolonging service life. The present study employed analytical techniques, such as X-ray diffractometry (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), to investigate the cavitation erosion performance of laser clad Fe-Mn-Si-Cr-Ni shape memory alloy (SMA) coatings with focus on the enhancing mechanism of their martensitic phase transformation. The results indicated that laser cladding could produce high-quality SMA coatings, free of defects such as pores and cracks, resulting in a significant improvement in the cavitation erosion performance. After 5 h of the cavitation, the coated samples remained in the cavitation erosion incubation stage, demonstrating an accumulated mass loss rate of approximately 0.12 mg/h, merely 13 % of that observed in the matrix samples. Extensive microstructural delamination occurred in the matrix samples after 5 h of the cavitation, whereas the coated samples exhibited only "shear bands" formed by plastic deformation on the surface. The martensitic phase transformation from γ-austenite to ε-martensite served to dissipate the stress induced by cavitation bubble collapse on one hand, and, on the other hand, the robust nature of martensite produced a hardening effect, significantly enhancing the cavitation resistance of the coating.

Construction of hard BCC phases FeCrVMnTix wear-resistant high-entropy alloy coatings enhanced by solid solution of Ti elements

To address the complex working conditions encountered by 1Cr13 ferritic/martensitic steel during operation, it is imperative to develop high-entropy alloys (HEAs) protective coatings with enhanced friction resistance. In this work, guided by the valence electron concentration criterion, we constructed a single-phase body-centered cubic (BCC) structure with high hardness. This was achieved through the introduction of titanium (Ti), which has a significantly different atomic radius compared to other elements. FeCrVMnTix (x = 0, 0.5, 1.0, 1.5, and 2.0) coatings were fabricated on 1Cr13 steel surfaces using laser cladding techniques, and the microstructure, mechanical properties, and wear-resistance properties of Ti-doped HEA coatings were investigated. The results reveal that the FeCrVMnTix coatings are comprised of a BCC solid solution. Increasing Ti content refined the dendritic structure of the coatings, enhancing the Vickers hardness from 4.35 GPa to 8.27 GPa and the Young's modulus from 232.6 GPa to 273.2 GPa. Additionally, the wear rate decreased from 3.07 × 10−5 mm3·N−1·m−1 to 4.94 × 10−6 mm3·N−1·m−1. Notably, the FeCrVMnTi2.0 coating demonstrated excellent wear resistance that can be attributed to the solid solution strengthening effect of Ti. These findings underscore the pivotal role of Ti in enhancing the wear resistance of the coatings.

Dilution induced variation of microstructure and mechanical properties on Co-Cr-Fe-Ni high entropy alloy coatings prepared by laser cladding

The remarkable properties of some series of high entropy alloys (HEAs) have garnered extensive interest in the development of HEA coatings. In this study, we prepared non-equiatomic Co-Cr-Fe-Ni HEA coatings using laser cladding method with Co-Cr-Fe-Ni cable-type welding wire (CTWW) as the filling material and investigated the effect of dilution rate on the microstructure evolution of coatings. By changing the wire feeding speed, a large dilution rate range was obtained which is from over 80 % to below 20 % and a variation of the coating's microstructure and mechanical properties was discovered within this large dilution rate range. All of the coatings are dense and uniform, with good metallurgical bonding. A pivotal discovery was made when the dilution rate decreased from approximately 35 %–40 % to below this threshold. The coating transitions from face centered cubic (FCC) and body centered cubic (BCC) dual-phase to FCC single-phase, accompanied by a precipitous drop in hardness from approximately 425 HV to below 175 HV. The interlaced distribution and dislocation pile-up of the layered BCC eutectic structure within the FCC phase are the main reasons for this dramatic change. Therefore, controlling the dilution rate is an effective way to regulate the performance of Co-Cr-Fe-Ni HEA coatings.

Determination of the significance of atomic concentration on surface properties of Ba x Mg1-x F2 alloy coatings via microscopic and spectroscopic techniques.

Both BaF2 and MgF2 compounds and Ba x Mg1-x F2 alloy thin films were deposited on glass and silicon (Si) substrates in nanometric sizes (100 ± 10 nm) in a high vacuum environment by radio frequency (rf) magnetron sputtering. Using BaF2 (99% purity) and MgF2 (99% purity) target materials and adjusting the power levels applied to these targets, Ba x Mg1-x F2 alloy coatings at different atomic concentrations were formed under the same vacuum conditions. The microstructure and surface characteristics of the samples were analysed with the help of spectroscopic and microscopic methods. For the surface characterization, with scanning acoustic microscopy (SAM), 2-dimensional surface acoustic images of the samples were mapped, the surface acoustic impedance values were determined, and information about the micro hardness of the materials was obtained. Surface roughness values and grain sizes were obtained by taking 3-dimensional surface images of investigated materials using atomic force microscopy (AFM). Average nanometric particle sizes were determined for each sample with scanning electron microscopy (SEM), therefore, information about surface homogeneity was obtained. For the microstructural characterization, quantitative elemental analysis was performed using scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS), and stoichiometric ratios of atomic compositions were identified. By evaluating the data obtained from the microscopic and spectroscopic measurements, the effect of the atomic concentration parameter on the morphological properties of the material was determined. The usability of the produced binary fluoride alloy thin film coatings is promising for emerging optoelectronic, ceramic industry, biomedical and surface acoustic wave applications.

Influence of casein on the degradation process of polylactide-casein coatings for resorbable alloys

This study used the dip-coating method to develop a new biocompatible coating composed of polylactide (PLA) and casein for ZnMg1.2 wt% alloy implants. It evaluated its impact on the alloy's degradation in a simulated body fluid. After 168 h of immersion in Ringer's solution, surface morphology analysis showed that the PLA-casein coatings demonstrated uniform degradation, with the corrosion current density measured at 48 µA/cm2. Contact angle measurements indicated that the average contact angles for the PLA-casein-coated samples were below 80°, signifying a hydrophilic nature that promotes cell adhesion. Fourier-transform infrared spectroscopy (FTIR) revealed no presence of lactic acid on PLA-casein coatings after immersion, in contrast to pure PLA coatings. Pull-off adhesion tests showed tensile strength values of 7.6 MPa for pure PLA coatings and 5 MPa for PLA-casein coatings. Electrochemical tests further supported the favorable corrosion resistance of the PLA-casein coatings, highlighting their potential to reduce tissue inflammation and improve the biocompatibility of ZnMg1.2 wt% alloy implants.

Design, microstructure, wear and corrosion behaviors of laser clad FeNiCoCrMo0.3Nbx hypoeutectic high entropy alloys coatings

FeNiCoCrMo0.3Nbx (x = 0.15, 0.40 and 0.55 in molar ratio) hypoeutectic high entropy alloys (HEAs) coatings are prepared by laser cladding (LC) designed by binary eutectic composition strategy. Nbx HEAs coatings present FCC + Laves duplex. Under the joint action of various strengthening mechanisms, the average microhardness of Nb0.15, Nb0.40 and Nb0.55 coatings is as high as 480.5 ± 7, 510.2 ± 6 and 540.6 ± 5 HV0.2, respectively. The unique fluctuating oxide film of the HEAs coatings plays a role in reducing wear, with the specific wear rates of 0.37 × 10−4, 0.22 × 10−4 and 0.18 × 10−4 mm3/Nm for Nb0.15, Nb0.40, and Nb0.55 cladding layers, respectively. The Nbx HEAs coatings displayed excellent corrosion resistance in 0.5 M H2SO4 solution. For Nb0.15 and Nb0.40 HEAs coatings, the increase of Nb promotes the formation of passivation film and improves corrosion resistance. However, the higher dislocation density intensifies the chemical inhomogeneity of the alloy due to excessive addition of Nb, which is not conducive to the corrosion resistance of Nb0.55 HEAs coating. The Nb0.40 cladding layer exhibits better corrosion resistance, and the Icorr is only 1.24 ± 0.6 μA/cm2. Combined with Mott-Schottky (M-S) test, the carrier densities (ND) of three HEAs coatings are increased in the order of Nb0.40 (1.09 × 1021 cm−3) < Nb0.15 (1.83 × 1021 cm−3) < Nb0.55 (3.57 × 1021 cm−3), indicating that the strong protective passivation film is also a key factor to achieve better corrosion resistance.

Wear and Corrosion Resistances of Arc-Sprayed FeCr Alloy and Fe-Based Coatings for Boiler Heat Exchanger Pipelines

Wear and Corrosion Resistances of Arc-Sprayed FeCr Alloy and Fe-Based Coatings for Boiler Heat Exchanger Pipelines

Improved wear and corrosion protection of Ni–P alloy coating by an electrodeposited Ni–Co–P alloy coating

To improve the comprehensive protection performances of steel C1045 surface, the Ni–Co–P alloy coatings with varying CoSO4·7 H2O concentration (0, 10, 20, 30, 40, 50, 60 and 70 g·L–1) were successfully prepared by an electrodeposition technique on a steel C1045 surface. The effect of the addition of CoSO4·7 H2O in the plating solution on the surface microstructure, elemental composition, crystallite size, microhardness, wear and corrosion resistance of the Ni–Co–P alloy coatings were analyzed by using a scanning electron microscope, an energy dispersive spectroscopy, an X-ray diffraction, a microhardness tester, a friction wear tester and an electrochemical workstation, respectively. The results indicated that the Ni–Co–P alloy coating exhibited a flatter morphology, compact microstructure and more excellent properties compared with Ni–P alloy coating, and the addition and variation of CoSO4·7 H2O in the plating solution had significant effects on the surface microstructure and comprehensive protection performances Ni–Co–P alloy coating. Notably, when the mass concentration of CoSO4·7 H2O in the plating solution was 50 g·L–1, the Ni–Co–P alloy coating had the highest content of Co element (22.67 wt·%), smallest crystallite size (20.41 nm) and highest microhardness (716.2 HV0.1). Furthermore, its wear resistance and corrosion resistance were considerably improved compared to that of the Ni–P alloy coating. The minimum average dynamic friction coefficient, wear scar width and depth of Ni–Co–P alloy coating at 50 g·L–1 were 0.47±0.02, 450.9 µm and 14.1 µm, respectively. The corrosion current density (Icorr) of Ni–Co–P alloy coating was the smallest (0.68 µA·cm–2), the corrosion rate (Rcorr) was slowest (8.25 µm·year–1), and the polarization resistance (Rp) of the Ni–Co–P alloy coating was highest (29.83 kΩ·cm2). The corrosion resistance of Ni–Co–P alloy coating was best.

Study on corrosion resistance of arc sprayed Zn–xAl (x = 19, 27, and 37) pseudo alloy coatings in salt spray environment

AbstractTo study the corrosion behavior of Zn–Al pseudo alloy coatings with different Al contents, Zn–xAl (x = 19, 27, and 37) pseudo alloy coatings were prepared by the wire arc spraying technique using Zn and Al wires with different diameters. This study investigated the microstructure, electrochemical corrosion behavior, and corrosion morphology and products of the as‐sprayed coatings after the salt spray test in 5 wt% NaCl solution. The results exhibited that the Zn–Al pseudo alloy coatings with higher Al content form denser corrosion products (Zn5(OH)8Cl2·H2O and Zn–Al layered double hydroxide) with stronger self‐shielding effect against corrosive media, thus provide better long‐term corrosion protection. Besides, electrochemical reactions are controlled by mass transfer until corrosion for 24 h, and then by a combination of mass transfer and diffusion for 96 h. Overall, it can be concluded that the Zn–37Al pseudo alloy coating in this study shows great potential to protect steel substrates from corrosion.

Optimizing substrate bias voltage to improve mechanical and tribological properties of ductile FeCoNiCu high entropy alloy coatings with FCC structure

Conventional hard coatings are limited in their tribological applications due to their high brittleness. High-entropy alloy (HEA) coatings, which combine high toughness and hardness, represent a new class of tribological coatings with great potential. The microstructure and stress state of HEA coatings can be significantly affected by the deposition parameters of magnetron sputtering, which can regulate their mechanical and tribological properties. In this study, DC magnetron sputtering with varying substrate bias voltages was used to deposit FeCoNiCu HEA coatings with an FCC single phase structure on 316 stainless steel. The microstructure, mechanical, and tribological properties of these coatings were studied in detail. The residual tensile stress of the coatings decreases, while toughness and hardness increase as the bias voltage increases. The coatings exhibited optimal toughness, highest hardness (11.3 GPa), and the lowest wear rate (as low as 6.01 × 10−5 mm3/N·m) when the bias voltage was set to −200 V. The formation of a metal oxide adhesion layer during friction improved the tribological properties of the coatings. This study demonstrates that optimizing the deposition bias voltage is an effective way to improve the mechanical and tribological properties of high-entropy, face-centered cubic alloy coatings, which are intrinsically tough and ductile.

Effect of Laser Multiple Remelting on the Geometric Parameters and Component Distribution of CrMnFeCoNi High-Entropy Alloys Coatings Fabricated on Al Alloy by Laser Cladding

Effect of Laser Multiple Remelting on the Geometric Parameters and Component Distribution of CrMnFeCoNi High-Entropy Alloys Coatings Fabricated on Al Alloy by Laser Cladding

Microstructure and Corrosion Study on Friction Surfaced Aluminum Alloy Coatings over Mild Steel

In this study, the low-carbon steel (AISI 1018 mild steel) substrate is coated with the aluminum alloys AA6082-T6, Al-20Zn, and Al-2Si-15SiC to improve its corrosion resistance by the friction surfacing (FS) technique. To produce a high-quality coating, friction surfacing process variables including spin speed, speed of travel, and the rate of feed are crucial. This experiment examines twelve friction-surfaced plates with different parameter combinations. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) examinations were carried out in order to comprehend the microstructure and chemical composition of the coating deposits and the area in contact between the coated surface and the substrate. Microstructure investigation reveals that the intermetallic combination of Fe-Al at the coating interface region is an effect of the elemental diffusion of Fe to aluminum at the contact interface. Then a uniform and fine-grained coating deposit is observed as a result of the continuous recrystallization of the consumable rod under frictional stress and heat generation. According to the outcomes of the microhardness test, the coated surface is roughly 15–16% harder than the consumable rod. The coating bond strength was measured using a ram tensile test, and it ranged from 102 MPa to 135 MPa. Finally, evaluation of corrosion behavior through immersion testing and pitting corrosion testing reveals that the coatings made of Al-20Zn and Al-2Si-15SiC exhibit good corrosive resistance in an alkaline environment.

Microstructure, multi-scale mechanical and tribological performance of HVAF sprayed AlCoCrFeNi high-entropy alloy coating

Thermal spray high-entropy alloy (HEA) coatings have demonstrated potential for improving the wear resistance of conventional materials used in extreme engineering environments. In the present work, an equiatomic AlCoCrFeNi HEA coating was manufactured using the high velocity air fuel (HVAF) process. The phase and microstructural transformations in gas-atomized (GA) powder during HVAF spraying were analyzed using SEM, EDS and EBSD techniques. The tribological properties of this HEA coating sliding against an Al2O3 ball at both room temperature (RT) and 600 °C were also evaluated. The GA powder was composed of Body Centred Cubic (BCC) + ordered BCC (B2) phases, which transformed to BCC + B2 + minor Face Centred Cubic (FCC) phases during the HVAF coating process, validating the thermodynamic phase prediction projected by the Scheil simulation for non-equilibrium processing conditions. The rapid solidification and high velocity impact-assisted deformation of GA powder resulted in significant grain refinement in the HVAF coating, which ultimately improved the mechanical properties at both micro and nanoscale levels. The wear resistance of the HEA coating at RT was severely impacted by the relatively brittle BCC/B2 phase structure, leading to susceptibility to abrasive wear and surface fatigue. The wear resistance at 600 °C was slightly lower at RT due to the formation of a brittle oxide layer on the worn surface, which induced surface fatigue and aggravated mass loss of the coating.

Current-carrying tribological properties and wear mechanisms of Mo-containing Cu alloy coatings produced by laser cladding

Copper alloy-molybdenum coatings were prepared on the surface of Cu-Cr-Zr alloys by laser cladding. The phase and microstructure were observed, and the hardness, conductivity, friction and wear properties under current-carrying conditions were tested. The results indicate that the prepared coatings exhibit good metallurgical bonding with the substrate. The Brinell hardness of the coatings ranges from 60 to 105 HB, and the electrical conductivity ranges from 17 % to 27 % IACS. The primary wear mechanism is abrasive wear and adhesive wear without current, resulting in the detachment of the Mo phase and transfer of the Cu phase during the sliding process. And it shifts to severe adhesive wear under current-carrying conditions, leading to the formation of aluminum deposit on the coatings.

Irradiation response of microstructure and mechanical properties of NbMoVCr multi-principal element alloy coatings

In this study, NbMoVCr multi-principal element alloy (MPEA) coatings with near-equal atomic ratios were deposited onto the ferritic/martensitic (F/M) steel substrate by magnetron sputtering and then irradiated using 6 MeV Au2+ at room temperature (RT) and 550 °C, respectively. The results demonstrate that the NbMoVCr coatings have excellent irradiation resistance in terms of phase stability. RT-irradiation introduces both interstitial- and vacancy-type dislocation loops, and the dislocation loop density increases with the increase of irradiation damage dose. Meanwhile, RT-irradiation could also induce grain growth of the coating. However, under high-temperature irradiation, more recombination and annihilation of irradiation-induced defects, and recrystallization occur in the coating. In addition, irradiation also promotes the desegregation of V and Cr elements at the grain boundaries and enhances the uniformity of the distribution of coating elements. Irradiation softening and hardening in NbMoVCr coatings are also found to depend strongly on both irradiation damage dose and irradiation temperature. The creep deformation mechanism of the coating is dominated by diffusion; thus, the irradiation-enhanced diffusion reduces the creep resistance of the coating.

Enhancing corrosion and wear resistance of a 7075 aluminum alloy via depositing TC4 coating

Aluminum alloys have been widely used in engineering due to their high strength and low density. However, their poor corrosion and wear resistance have largely limited their application in marine equipment. This study successfully improved the corrosion and wear resistance of a typical 7075 Al alloy by depositing a high-performance TC4 titanium alloy coating using in-house annular laser cladding equipment. Microstructural investigations revealed that the defect-free TC4 coating is metallurgically bonded to the 7075 Al alloy substrate along with excellent bond strength. Electrochemical test results showed that compared to the hot-forged 7075 Al alloy and hot-forged double-phase TC4 bulk alloy, the TC4 coating exhibits superior corrosion resistance due to its net-basket α-single-phase microstructure. Further, wear testing results showed that the coefficient of friction and wear volume of the TC4 coating are far lower than that of 7075 Al alloy. The enhanced wear resistance is closely related to the high hardness of the TC4 coating and its excellent fatigue-wear resistance. Therefore, this work can serve as a reference to improve Aluminum alloys' corrosion and wear resistance by depositing Titanium alloy coatings using the annular laser cladding process, which shall widen the potential applications of Aluminum alloys in marine equipment.

Microstructure and wear properties of carbide reinforced high-entropy alloy coatings on EA4T steel via vibration assisted TIG-cladding using WC core spiral AlCuNiCrTi-CWW

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.

Molecular Dynamics Study on Wear Resistance of High Entropy Alloy Coatings Considering the Effect of Temperature.

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.