Modification of Cr/CrN composite structure by Fe addition and its effect on decorative performance and corrosion resistance

A CrN ceramic coating is a promising substitution for electroplated Cr (Ⅵ) hard coatings; however, it has not yet replaced a decorative Cr (Ⅵ) layer owing to its low reflectivity of visible light and relatively poor corrosion resistance. A Cr/CrN composite structure can address these shortcomings. Our recent work demonstrated that an addition of Fe can facilitate the densification of hot-pressed Cr sputtering targets and enhance the mechanical properties of Cr/CrN composite coatings. In this work, we focus on reporting optical properties and corrosion resistance of the Fe-modified Cr/CrN layers for decorative applications, and clarifying the effect of Fe on these performances. The results show that Fe can increase the amount of metallic phase in the Cr/CrN composite structure and helps enhance its reflectance in the visible region. The composite coating deposited by Cr₉₀Fe₁₀ (at.%) target/alloy exhibits a greater reflectivity of visible light and a better corrosion resistance than those of a single-phase CrN coating. This is attributed to its fine microstructure, which is beneficial for a dense and smooth surface. The color of the coating can be controlled by both the partial pressure ratio of N₂ during deposition and the Fe content in the Cr-Fe sputtering target. The present results show that the addition of Fe can lead to the reduction in the processing cost of Cr targets, enhance the mechanical properties of the composite coatings, and broaden the deposition window. Such cost-effective Fe-modified Cr/CrN composite coatings are expected to be used in various decorative applications.     

Tribocorrosion characteristics of CrMoSiCN/Ag coatings on Ti6Al4V alloys in seawater

CrMoSiCN/Ag coatings were deposited on Ti6Al4V alloys at the trimethylsilane flow of 15 sccm using closed-field unbalanced magnetron sputtering, and their microstructures were observed and analyzed using SEM, XRD, XPS and TEM, respectively. The coatings’ mechanical properties were measured using nano-indenter. The tribocorrosion characteristics of Ti6Al4V and CrMoSiCN/Ag coatings were investigated in seawater using tribocorrosion tester. The results revealed that the nanocomposite coatings consisted of (Cr, Mo)N solid solution, Ag nanocrystal and amorphous SiCN_x matrix. As the Ag target current increased to 1.0 A, a large amount of Ag nanoparticles were observed on the coating surface. The coating hardness initially increased to 21.0 ± 0.7 GPa at the Ag target current of 0.4 A and then declined. After the Ag element was added into coatings, their tribocorrosion characteristics were improved. The tribocorrosion characteristics of coatings were much better than those of Ti6Al4V. The tribocorrosion characteristics of CrMoSiCN/Ag coating at the Ag target current of 1.0 A were the best in seawater.     

Effect of nitrogen pressure on the microstructure,mechanical and electrochemical properties of CrAlN coatings deposited by filter cathode vacuum arc

CrAlN coatings were prepared on Al–Si alloys using filter cathode vacuum arc deposition technique with nitrogen as the reactive gas and Cr₂₅Al₇₅ alloy target as the arc source. The effect of nitrogen pressure on the microstructure, mechanical properties and electrochemical properties of the coatings had been systematically studied. The results showed that the composition, structure and performance of the CrAlN coating depended on the nitrogen pressure. As the nitrogen pressure increased, the Al and Cr content decreased while the N content increased slowly in the coating. Meanwhile, the phase structure gradually changed from AlN phase to CrN phase. The hardness of the CrAlN coating increased significantly with the increase of nitrogen pressure from 0.04 to 0.06 Pa due to the formation of CrN phase and grain refinement. However, further increasing the nitrogen pressure to 0.07 Pa, the hardness was reduced owing to the deterioration of the surface quality caused by target poisoning. Moreover, the adhesion strength of the coating gradually decreases, and the corrosion resistance of the CrAlN coating first increased and then decreased with increasing the nitrogen pressure. The CrAlN coating deposited at a nitrogen pressure of 0.05 Pa had the best corrosion resistance, with the highest polarization resistance, charge transfer resistance and pore resistance, which was related to the combined effect of great compactness and AlN-dominant phase structure in the coating.     

Structure,mechanical, and thermal properties of Ti1‐xAlxN/CrAlN (x = 0.48, 0.58, and 0.66) multilayered coatings

Nano‐multilayered TiAlN/CrAlN coatings combining advantages of Ti‐Al‐N and Cr‐Al‐N are considered to be promising candidates for advanced machining processes. Here, the structure and thermal properties of Ti_1‐xAl_xN/CrAlN (x = 0.48, 0.58, and 0.66) multilayered coatings as well as referential Ti_1‐xAl_xN and Cr_0.32Al_0.68N monolithic coatings were investigated. Ti_1‐xAl_xN coatings show a structural transformation from cubic structure for x = 0.48 to mixed cubic and wurtzite structure for x = 0.58 and 0.66, and Cr_0.32Al_0.68N coating exhibits a single cubic structure. Through a multilayer arrangement with Cr_0.32Al_0.68N layers, the Ti_0.52Al_0.48N and Ti_0.42Al_0.58N layers can be stabilized in their metastable cubic structure, but the Ti_0.34Al_0.66N layer still tends to crystallize in the mixed cubic and wurtzite structure. The hardness of Ti_0.52Al_0.48N/CrAlN and Ti_0.42Al_0.58N/CrAlN coatings is higher than that of corresponding monolithic coatings regardless of as‐deposited and annealed states. Especially, after annealing at 800°C, the Ti_0.52Al_0.48N/CrAlN and Ti_0.42Al_0.58N/CrAlN coatings reach their peak hardness of ~34.2 and 32.8 GPa due to the spinodal decomposition of Ti_1‐xAl_xN layers. However, the oxidation resistance of Ti_1‐xAl_xN/CrAlN coatings is mainly up to the Al content of Ti_1‐xAl_xN layers, where only the Ti_0.34Al_0.66N/CrAlN coating can survive the 10 h exposure to air at 1000°C.     

Effects of surface pretreatments on the deposition of adherent diamond coatings on cemented tungsten carbide substrates

Well-adhered microcrystalline diamond (MCD) coatings have been deposited on WC–Co substrates by the microwave plasma enhanced chemical vapor deposition (MPECVD) method. A multi-interlayer system Cr/CrN/Cr was deposited on the cemented carbide substrate before diamond deposition to act as a diffusion barrier. The interlayer-coated substrate was shortly peened by friable diamond powders with an average size of 150 μm to roughen the surface. Diamond coatings deposited on short peened substrates show higher nucleation density and stronger adhesion properties. The X-ray diffraction (XRD) pattern showed that an additional carbide compound layer (Cr₃C₂ and Cr₇C₃) was formed during the CVD diamond deposition to work as an intermediate bonding layer for better adhesion. Rockwell indentation tests with a load of 1470 N were conducted to investigate the coating's adhesion. No delamination outside of the indentation zone was observed for the diamond coating deposited on the roughened sample. Electron probe microanalysis (EPMA) results showed that the delamination in the indentation zone occurred mainly at the diamond/Cr interface and very little Co (less than 1 wt.%) was detected on the Cr failure surface. This suggests that during the CVD process Co/C inter-diffusion was successfully prevented by the Cr/CrN/Cr buffer layers.     

Corrosion properties and cell performance of CrN/Cr-coated stainless steel 316L as a metal bipolar plate for a direct methanol fuel cell

CrN/Cr-coated stainless steel (STS) 316L is investigated as the material for a metal bipolar plate for a direct methanol fuel cell (DMFC) under actual operating circumstances. Protective coating layers of CrN/Cr are formed on STS 316L using an unbalanced magnetron (UBM) DC sputter via Cr target in an effort to improve the corrosion resistance and long-term stability of the STS 316L. In a corrosion resistance test, the CrN/Cr-coated STS 316L shows much better corrosion resistance than bare STS 316L in simulated electrolytic environments under anodic and cathodic potentials relevant to DMFCs. The interfacial contact resistance (ICR) between CrN/Cr-coated 316L and carbon paper decrease to 4 mΩ cm² at a compaction force of 150 N cm⁻² compared to bare STS 316L (570 mΩ cm²). The CrN/Cr-coated STS 316L cell has better cell performance compared to the bare STS 316L cell. Furthermore, the CrN/Cr-coated STS 316L cell exhibit low voltage losses of 38.2 μV h⁻¹ under long-term operation of 760 h. These results show that the CrN/Cr-coated STS 316L, demonstrating its feasibility for use as a metal bipolar plate in a DMFC under actual operating circumstances.     

First-principles study of the stability,electronic and mechanical properties of Cr2N and CrN with the variation of Ni doping concentration

First-principles approach was applied to investigate the stability, electronic and mechanical properties of Cr_2-xNi_xN (x = 0, 0.083, 0.167,0.250, 0.333) and Cr_1-xNi_xN (x = 0,0.125,0.25,0.375, 0.5). The calculated formation enthalpy and mechanical stability results show that Cr_2-xNi_xN and Cr_1-xNi_xN are all stable. The bulk, shear and Young's modulus results indicate that different variation trend is observed in Cr_2-xNi_xN and Cr_1-xNi_xN with the increase of x. Base on Pugh and Pettifor criteria, Cr₂N belongs to the brittle area and the ductility of Cr_2-xNi_xN increases with the increment of x, obtain the maximum results when x = 0.333. However, CrN, which belongs to the ductile area, alloying with Ni decreases its ductility and increases its brittleness, reach the maximum brittleness when x = 0.5. The charge density difference study reveals that the doped Ni atom affects the interaction between Cr and N in Cr_2-xNi_xN and Cr_1-xNi_xN differently. Furthermore, the stress-strain curve of Cr₂N, Cr_1.833Ni_0.167N, and Cr_1.667Ni_0.333N under shear and tensile deformation shows that the ultimate stress of Cr₂N is decreased and its ductility increased. Nevertheless, the stress-strain curve of CrN, Cr_0.75Ni_0.25N, and Cr_0.5Ni_0.5N under shear and tensile deformation indicates that the strength of CrN can be enhanced and its deformation process is significantly changed when x = 0.25.     

Investigation of the tribological and biomechanical properties of CrAlTiN and CrN/NbN coatings on SST 304

This study examines the influence of thin layer coatings of CrAlTiN and CrN/NbN, deposited via physical vapor, on the biocompatibility, mechanical, tribological, and corrosion properties of stainless steel 304. The microstructure and morphology of the thin CrAlTiN and CrN/NbN layers were characterized by scanning electron microscopy (SEM), EDX, and X-ray diffraction. The pin on disc wear test was performed on bare and metal-nitride coated SST 304 under a 15 N load at 60 rpm and showed that the wear rates of the thin CrAlTiN and CrN/NbN film coatings were lower than the bare substrate wear ratio. The coefficients of friction (COFs) attained were 0.64, 0.5, and 0.55 for the bare substrate, CrN/NbN coating, and CrAlTiN coating, respectively. Nano indentation tests were also performed on CrAlTiN-coated and CrN/NbN-coated SST 304. The nanohardnesses and Young's moduli of the coated substrates were 28 GPa and 390 GPa (CrN/NbN-coated) and 33 GPa and 450 GPa (CrA1TiN-coated), respectively. For comparison, the nanohardness and Young's modulus of the uncoated substrate were 4.8 GPa and 185 GPa, respectively. Corrosion tests were conducted, and the behaviors of the bare and metal nitride-deposited substrates were studied in CaCl₂ for seven days. The corrosion Tafel test results showed that the metal-nitride coatings offer proper corrosion resistance and can protect the substrate against penetration of CaCl₂ electrolyte. The CrN/NbN-coated substrates showed better corrosion resistance compared to the CrAlTiN-coated ones. In evaluating the biocompatibility of the CrAlTiN and CrN/NbN coatings, the human cell line MDA-MB-231 was found to attach and proliferate well on the surfaces of the two coatings.     

Corrosion Investigation of Chromium Nitride and Chromium Carbide Coatings for PEM Fuel Cell Bipolar Plates in Simulated Cathode Condition

Transition metals nitrides and carbides are used as coatings on bipolar plates for proton exchange membrane fuel cells (PEMFCs) due to their suitable electrical conductivity and corrosion resistance. Chromium electroplated AISI 316L stainless steel bipolar plates were treated by plasma nitriding and solid carburizing to form chromium nitride and chromium carbide, respectively. The presence of CrN/Cr₂N and Cr₇C₃/Cr₂₃C₆ was verified by X‐ray diffractometry (XRD) in chromium nitride and chromium carbide coatings, respectively. The corrosion behavior of coatings was investigated by potentiodynamic polarization, potentiostatic polarization and electrochemical impedance spectroscopy (EIS) in simulated cathode condition. Coated samples showed better corrosion behavior than untreated bare sample. EIS results indicated decrease in corrosion current density after 500 hours, however coatings acted as barrier against solution access to substrate. Corrosion current densities of coatings were close to targets of United Stated department of energy (DOE).     

Comparison of electrochemical behavior of CrN single-layer coating and Cr/CrN nanolayered coating produced by cathodic arc evaporation physical vapor deposition

The aim of the present work is to study the CrN single-layer coating and the Cr/CrN nanolayered coating by cathodic arc evaporation physical vapor deposition (CAE-PVD) on AISI 304 stainless steel and to assess the electrochemical behavior of the coatings. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were utilized to study the morphology and microstructure of the coatings. The mechanical behavior of the coatings was studied by the nanoindentation technique. The electrochemical behavior of the formed coatings in 3.5 wt.% NaCl solution was investigated via electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests. Based on the microscopic images, it was realized that both CrN and Cr/CrN coatings were formed having a dense structure on the substrate. The results of EIS measurements showed gradual changes in the polarization resistance of the Cr/CrN nanolayered coating during the immersion time. However, significant changes in the polarization resistance of the CrN single-layer coating were seen by increasing immersion time comparing with the Cr/CrN coating. The higher polarization resistance of the Cr/CrN coating can be attributed to the effects of the interface between the layers in comparison to the CrN coating.     

Corrosive wear behavior of HVOF-sprayed micro-nano-structured Cr3C2–NiCr cermet coatings under aqueous media

A novel micro-nano-structured Cr₃C₂–NiCr cermet coating was prepared on 316L stainless steel by high-velocity oxygen fuel spraying technology (HVOF). Cermet coatings with different contents of micro-and nano-sized Cr₃C₂ particles as the hard phase and a NiCr alloy matrix as the bonding phase were prepared and characterized in terms of porosity, microhardness, and corrosive wear resistance in a 3.5% NaCl solution and artificial seawater. Compared to nanostructured coatings, micro-nano-structured coatings avoid decarburization and reduce nanoparticle agglomeration during the spray process, and mechanical and electrochemical properties were improved in comparison with those of conventional coatings. The micro-nano-structured Cr₃C₂–NiCr coating rendered low porosity (≤0.34%) and high microhardness (≥1105.0HV_0.3). The coating comprising 50% nano-sized Cr₃C₂ grains exhibited the best corrosive wear resistance owing to its densest microstructure and highest microhardness. Furthermore, compared to static corrosion, the dynamic corrosion of the coatings led to more severe mechanical wear, because corrosion destroyed the coating surface and ions promoted corrosion to invade coatings through the pores during corrosion wear.     

Phase formation and microstructure evolution of plasma sprayed Cr2AlC MAX phase coatings under post annealing

In this study, thick Cr₂AlC coatings were first synthesized via plasma spraying of Cr₃C₂–Al–Cr agglomerated powders and post annealing. The microstructure evolution and mechanical properties of the Cr₂AlC coatings annealed at 500–1000 °C were investigated. The as-sprayed coatings exhibited a lamellar structure, primarily consisting of Cr₂AlC, Cr₇C₃, Cr₂₃C₆, and (Cr, Al)C_x solid solutions. The short residence time during spraying led to incomplete reactions in the Cr₃C₂@Al–Cr agglomerates, resulting in the formation of (Cr, Al)C_x. Post annealing provided sufficient energy for the transition of (Cr, Al)C_x → Cr₂AlC. With an increase in the annealing temperature (<900 °C), gradual transition of the (Cr, Al)C_x phase led to a slight increase in the Cr₂AlC content, and thus, the as-annealed coatings maintained high hardness (>1000 HV_0.2) with improved fracture toughness. Higher annealing temperatures (>900 °C) promoted clear enhancement of the Cr₂AlC content, thus reducing the coating hardness. The transition phase (Cr, Al)C_x and high temperature annealing were the primary factors to promoting the formation of the Cr₂AlC phase in sprayed coatings. This study indicates that the Cr₃C₂@Al–Cr agglomerates can be effective alternatives to expensive MAX phase powders as feedstock for plasma spraying of Cr₂AlC coatings.     

Fabrication of Cr‐Cr23C6/Cr2N Composite Coatings: Change in the Phase Structure and Effect on the Corrosion Properties

Cr‐C composite coatings were electro‐codeposited in sulfuric acid‐based solutions containing submicrometer‐sized carbon black particles. The effect of heat‐treatment conditions on the carbide phase formation in the composite coatings and their corrosion behaviors were investigated. The obtained results showed that the Cr‐C composite coatings can be fabricated successfully and with an additional heat treatment, it is possible to obtain a Cr‐Cr₂₃C₆/Cr₂N composite structure. Therefore, the increase in corrosion potential suggests improvement in corrosion resistance due to the formation of Cr₂₃C₆/Cr₂N. This implies that Cr‐Cr₂₃C₆ and/or Cr₂N composite coatings have potential application to industrial fields in many respects.     

Influence of Al content and post-annealing on synthesis and mechanical properties of plasma sprayed Cr–Al–C composite coatings

Due to ultra-high temperature and short reaction time, it was very challenging to produce high purity MAX phase by plasma spraying. In this study, Cr–Al-graphite agglomerated powders with different Al additions (x = 0.2–1.5) was used to prepare Cr–Al–C composite coatings by atmospheric plasma spraying followed with annealing. Results showed that the as-sprayed coatings displayed typical lamellar structure, mainly composed of Cr–C binary carbides (Cr₇C₃ and Cr₂₃C₆) and residual Al. After annealing at 700 °C, the newly formed Cr₂AlC phase increased significantly in the coatings. The higher addition of Al, the more Cr₂AlC phase formed after annealing. The enhanced atomic diffusion, sufficient Al source and existence of (Cr, Al)C_x contributed to the formation of Cr₂AlC under annealing. Annealing treatment improved the hardness of the coating, but with the increase of Cr₂AlC phase content, the hardness decreased slightly. The Al content and post-annealing had a synergistic effect on the formation of Cr₂AlC phase in the sprayed coatings. This provided an effective route to control the Cr₂AlC content in sprayed Cr–Al–C composite coatings.     

Influence of N2 flow rate on microstructure and properties of CrNx ceramic films prepared by MPP technique at low temperature

In this study, CrN_x ceramic films were prepared utilizing modulated pulsed power magnetron sputtering (MPP) technique at low deposition temperature, with varying flow rates of the reactive gas, i.e. N₂. The influences of N₂ flow rate on the density of the plasma surrounding the target sheath, microstructure evolution, mechanical/tribological and anti-corrosion properties of the as-deposited CrN_x ceramic films were investigated systematically. Results indicated that the plasma density increased sharply with increasing N₂ flow rate in the range of 75 sccm to 175 sccm. Nevertheless, with further increase of N₂ flow rate to 200 sccm, the growing trend of ionization slowed down probably due to the insufficiency of the power density. With increasing N₂ flow rate, the Cr elemental concentration decreased from 69.7 at.% to 57.5 at.%, and that of N increased from 23.2 at.% to 36.6 at.%. The sub-stoichiometric ratio of the CrN films could be attributed to the relative lower reactive kinetic energy at low deposition temperature. The analyses on the microstructure evolution of CrN_x films revealed that with insufficient introduced nitrogen, competitive growth between Cr₂N(110), Cr₂N(111), Cr(110) phases (note that all crystalline planes indexed here are parallel to the coating surface) were found; and with relative sufficient nitrogen, fcc-CrN phase took over, with preferred orientation of (111). Due to the improvement of density and the fine-grain strengthening mechanism, with 100 sccm N₂ flow rate, the hardness of the CrN_x films obtained the maximum value of 21.4 GPa. The films deposited at 75 sccm nitrogen showed the highest friction coefficient (i.e. ~0.75), which could be partially attributed to the presence of impurity particles on the film surface. And for the remaining films, the friction coefficient maintained in the range of 0.38–0.52. As for the anti-corrosion properties, the CrN_x film deposited at 100 sccm nitrogen showed the lowest corrosion current (i.e. 44.2 nA/cm²), indicating excellent anti-corrosion property.     

Corrosion resistance of AlN and Fe3Al reinforced Fe-based plasma cladding layer in 3.5 wt% NaCl solution

Fe-based cladding layers were prepared via the plasma cladding method using nitrogen as protective and reactant gas. The effects of Al on the phase structure, morphology, composition, and corrosion resistance of the cladding layers were investigated. The based cladding layer consisted of α-Fe, Cr, and small amounts of CrN and Fe_xN, whereas Fe₃Al, Cr₅Al₈ and AlN occurred in the cladding layer with Al. Many AlN particles less than 4 μm in diameter were uniformly distributed in the cladding layer. The nitrides in the cladding layer could accelerate the formation of a passive film and increase the corrosion resistance of the cladding layer. A compact and stable passive film composed of Al₂O₃, Cr₂O₃, α-FeOOH, and Fe₃O₄ formed on the surface of the cladding layer with Al, which is beneficial in protecting the substrate and significantly improving the cladding layer's corrosion resistance.     

Positive modification on the mechanical,tribological and oxidation properties of AlCrNbSiN coatings by regulating the Nb/Si-doping ratio

The precise control of Nb/Si-doping ratio is the critical factor to tailor AlCrNbSiN coatings with superior comprehensive properties. In this study, the effect of Nb/Si-doping ratio on the microstructure, mechanical, tribological and oxidation properties of AlCrNbSiN coatings was systematically researched. With the increase of Nb/Si-doping ratio, coatings’ microstructures changed from a featureless dense structure to a columnar and equiaxed mixed microstructure gradually. The main phase was transformed from the solid solution phase of h-Al(Cr)N for Nb-free coating (Nb/Si = 0:1) to c-Al(Cr)N solid solution for three Nb-containing coatings (Nb/Si = 1:2, 1:1 and 2:1). When Nb/Si ratio is 1:1, the formation of harmful h-NbN phase was found in the coating. The performance results indicated that, (1) The AlCrNbSiN coating with the Nb/Si ratio of 2:1 achieved optimal hardness (~34.9 GPa), toughness (CPRs ~569.3) and the minimum wear rate of 2.34 × 10⁻⁶ mm³/(N·m); (2) When the Nb/Si-doping ratio is 1:2, the coating exhibited the best oxidation resistance, attributing to the sufficient (Al, Si)O_x oxidation protective layer and only a small amount of AlNbO₄ and CrNbO₄ formed at 1200 °C.     

Effect of MoS2 content on friction and wear properties of Mo and S co-doped CrN coatings at 25–600 °C

With increasingly harsh working environments for mechanical systems and the rapid development of various high-tech industries, requirements for the stable operation of mechanical systems are increasing in a wide temperature range. Mo and S co-doped CrN coatings with different MoS₂ contents were prepared via unbalanced magnetron sputtering to provide better friction properties to the coatings at high temperatures. Scanning electron microscopy and nanoindentation were adopted to analyze the microstructure and mechanical performance. The mechanical performance of the coatings was enhanced by increasing the MoS₂ content, however, excessive MoS₂ reduced the mechanical properties of the coatings. Besides, the adhesion of the coatings first increased and then decreased rapidly with the increase of the MoS₂ content. In addition, the residual stress of the coating first decreased and then increased upon increasing the MoS₂ content. The high-temperature tribological behavior of the coatings was measured from room temperature (25 °C) to 600 °C. The CrN/MoS₂-0.6A coating was found to exhibit low friction and wear coefficient at room temperature and relatively good comprehensive properties at high temperature. This study provides a feasible design for engineering applications and lays the foundations for the preparation of coatings with superior high-temperature friction properties.     

Complex study of protective Cr3C2–NiAl coatings deposited by vacuum electro-spark alloying,pulsed cathodic arc evaporation,magnetron sputtering,and hybrid technology

Coatings were obtained by vacuum electro-spark alloying (VESA), pulsed cathodic arc evaporation (PCAE), magnetron sputtering (MS) techniques and VESA-PCAE-MS hybrid technology using Cr₃C₂–NiAl electrodes. The structure of the coatings was analyzed using scanning and transmission electron microscopy, X-ray diffraction and energy-dispersive spectroscopy. Mechanical properties were determined by nanoindentation, while tribological properties were assessed using pin-on-disk tribometer. Corrosion resistance was estimated by voltammetry in 1 N H₂SO₄ and 3.5%NaCl solutions. Oxidation resistance tests were performed at 800°С in air. The VESA coating had the highest thickness, low friction coefficient and high wear resistance. PCAE coating demonstrated the highest hardness (24 GPa) and elastic recovery (59%), oxidation resistance and superior corrosion resistance both in 1 N H₂SO₄ (i_corr = 70 μА/cm²) and 3.5%NaCl (i_corr = 0.74 μА/cm²) solutions. The MS coating had average mechanical properties and low corrosion current density (71 μА/cm²) in 1 N H₂SO₄. Deposition of coatings using VESA-PCAE-MS hybrid technology led to an increase in corrosion and oxidation resistance at least by 1.5 times in comparison with the VESA coating.     

Influence of Cr2O3 particles on corrosion,mechanical and thermal control properties of green PEO coatings on Mg alloy

The influence of micro-sized Cr₂O₃ particles on the corrosion, mechanical and thermal control performance of plasma electrolytic oxidation coated Mg was studied. More contents of Cr₂O₃ particles were embedded into phosphate containing PEO coatings compared with coatings produced from silicate based electrolytes, resulting in green coatings with enhanced thermal control and mechanical property. The existence of particles has slightly improved the corrosion resistance and hardness of the coating. It was found that the absorptance of the coating was increased if higher concentration of Cr₂O₃ particles is incorporated into the layer, which is probably ascribed to low band gap of Cr₂O₃.