Search Results (1,972)

Al₂O₃:Cr³⁺ coatings were synthesized on tungsten substrates by plasma electrolytic oxidation in a phosphate-aluminate electrolyte containing dispersed Cr₂O₃ nanoparticles, and their structural, photoluminescent, and temperature-sensing properties were investigated. The coatings exhibited a typical porous PEO morphology with a uniform thickness of approximately 31 μm, and EDS analysis confirmed the incorporation of Cr species from the electrolyte, with Cr content increasing with the concentration of Cr₂O₃ particles. XRD analysis showed that the coatings were composed predominantly of α-Al₂O₃, with minor contributions from metastable γ-Al₂O₃, confirming that our previously established process for forming the thermodynamically stable α-Al₂O₃ phase directly on a non-aluminum substrate remains robust upon the introduction of dopant nanoparticles. The Al₂O₃:Cr³⁺ coatings displayed characteristic ruby-like photoluminescence, including broad excitation bands associated with the ⁴A₂⟶⁴T₁ and ⁴A₂⟶⁴T₂ transitions and sharp R-line emission arising from the spin-forbidden ²E⟶⁴A₂ transition. The strongest emission was obtained for coatings prepared with 0.05 g/L Cr₂O₃, while higher concentrations resulted in concentration quenching. Temperature-dependent photoluminescence revealed two complementary thermometric mechanisms: R-line spectral shifting and thermally induced redistribution between the ²E and ⁴T₂ emissions. The deconvolution-based intensity-ratio approach provided a stronger temperature response than simple spectral partitioning, demonstrating the potential of PEO-derived Al₂O₃:Cr³⁺ coatings on tungsten as robust luminescent temperature-sensing layers. Full article

Graphene-reinforced CrCoNiFeMo high-entropy alloy composite coatings were fabricated on 17-4PH stainless steel by laser cladding for the surface protection of industrial robotic end-effector grippers. The effects of graphene content on microstructure, hardness, wear behavior and corrosion resistance were investigated. Graphene-derived carbon suppressed Laves and σ phases and promoted the in situ formation of M23C6, M7C3 and Co2C carbides, transforming the coating into a carbide-reinforced FCC/BCC composite structure. The average hardness increased from 462 HV0.2 to 676 HV0.2 with increasing graphene content. The 0.4 wt.% graphene coating showed the best wear resistance, with the lowest friction coefficient of 0.42 and minimum wear scar width and depth of 546 μm and 5.72 μm, which was attributed to carbide strengthening and the possible formation of a carbonaceous lubricating tribo-layer. The 0.2 wt.% graphene coating exhibited the best corrosion resistance, with the lowest corrosion current density of 5.81 μA/cm² and the highest impedance response. Excessive graphene caused carbon-rich agglomeration, excessive carbide precipitation and weakened passivation. This work provides a feasible surface strengthening strategy for 17-4PH stainless steel robotic gripper components. Full article

CoCrFeMnNi high-entropy alloy (HEA) coatings were fabricated on an S41500 stainless steel substrate by laser cladding and subsequently strengthened using machine hammer peening (MHP) at three hammering energies of 1.7 J, 3.5 J, and 5.0 J. The effects of MHP treatment on the phase structure, surface morphology, microhardness, and tribological properties of the coatings were systematically investigated. The results showed that all coatings retained a single-phase face-centered cubic (FCC) structure after MHP treatment, indicating excellent microstructural stability during impact-induced strengthening. With increasing hammering energy, the surface morphology gradually evolved from discrete hammering indentations to a more continuous orange-peel-like texture, while the surface roughness initially increased and then decreased. MHP significantly enhanced the surface hardness of the coatings. In particular, the MHP3.5 sample exhibited the highest surface hardness of approximately 420 HV, representing an increase of about 120% compared with the untreated coating. Under dry sliding conditions at a load of 30 N, the MHP3.5 sample exhibited the lowest and most stable friction coefficient, maintaining a steady-state value of approximately 0.40–0.45. Its specific wear rate decreased by nearly 45% compared with that of the untreated coating. The improved wear resistance was mainly attributed to the combined effects of strain hardening, grain refinement, and dislocation strengthening induced by machine hammer peening. Considering the hardness, friction coefficient, and specific wear rate results together, a hammering energy of 3.5 J was identified as the most suitable MHP parameter under the low-load wear conditions investigated in this study. Full article

The article presents the results of research concerning the laser cladding process of the Inconel 625 coatings reinforced with Cr₃C₂ particles. Nickel-based superalloys find widespread application in aggressive corrosive environments because of their many favorable properties, such as high tensile and fatigue strength and excellent resistance to high-temperature corrosion. The current research aimed to improve the surface wear resistance of Inconel 625 coatings by the addition of 20–40 vol.% of Cr₃C₂ particles. The research focused on determining the impact of the laser beam power and Cr₃C₂ particle content on the quality, structure and properties (microhardness and solid particle erosion wear resistance) of coatings. The investigation included the macrostructure and microstructure analyses, Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), Vickers microhardness and solid particle erosion tests (according to the ASTM G76-18 standard). The main results showed that the homogenous composite Inconel 625 + Cr₃C₂ coatings can be produced using the laser cladding process to improve the hardness and erosive wear resistance in comparison to pure metallic Inconel 625 coatings. Full article

TiN/TiAlN coatings were deposited on 40Cr steel substrates by DC magnetron sputtering to improve the surface tribological performance of the steel. The influence of sputtering power (80, 100, 120, 140, 160 and 180 W) on coating morphology, phase structure, adhesion strength and wear behavior was evaluated using SEM, EDS, XRD, Vickers microhardness testing, scratch testing and ball-on-disk tribological testing. The coatings were dense and relatively smooth, with only a small number of submicron particles. Increasing sputtering power increased the coating thickness, and the EDS results suggested an increase in Al content of up to 160 W, whereas the crystallite size of the TiAlN (200) phase first decreased and then increased. XRD analysis showed that the coatings were dominated by face-centered cubic TiAlN, accompanied by weak TiN and AlN diffraction peaks. Among the tested samples, the coating deposited at 140 W showed the most favorable measured combination of adhesion and tribological properties within the tested series, with a thickness of 1.76 μm, a Vickers microhardness of 906.35 HV0.25, an adhesion strength of 45.6 N, an average friction coefficient of 0.322 and a specific wear rate of 28.37 × 10⁻⁷ mm³ N⁻¹ m⁻¹. These measured trends are consistent with the dense morphology, refined crystallites, high microhardness and higher measured adhesion observed at moderate sputtering power. In contrast, excessive sputtering power was associated with particle coarsening and coating defects, accompanied by higher measured friction and wear. Full article

This study presents a comparative investigation of the microstructure, phase composition, microhardness, tribological behavior, and corrosion resistance of heterogeneous coatings deposited on St3 steel by twin-wire electric arc spraying (TWEAS). Three wire combinations were examined: ER309LSi + Steel 70, Sv-08G2S + Steel 70, and 30KhGSA + ER309LSi. The coatings were characterized using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), Vickers microhardness testing, ball-on-disc tribological measurements, and potentiodynamic polarization in 3.5 wt.% NaCl solution. All coatings exhibited a characteristic lamellar structure with a thickness of 340–360 μm and hardness values significantly higher than those of the steel substrate. The 30KhGSA + ER309LSi coating demonstrated the highest cross-sectional microhardness (532 ± 13 HV) and the lowest specific wear rate (0.411 × 10⁻⁴ mm³/(N·m)), which was more than five times lower than that of the substrate. The enhanced wear resistance was associated with the formation of the Cr₇C₃ and Cr₂₃C₆ carbide phases, as identified by XRD. The Sv-08G2S + Steel 70 coating exhibited the lowest corrosion rate among the investigated coatings due to its more homogeneous ferritic structure and reduced electrochemical contrast between lamellae. The results demonstrate that the phase composition and distribution of alloying elements play a decisive role in determining the functional properties of heterogeneous TWEAS coatings. Full article

High-entropy alloy (HEA) coatings exhibit enhanced chemical stability when doped with carbon, primarily due to the strong bonding between carbon and transition metals. Typical transition metals used in these coatings include Cr, Fe, Co, Ni, Cu, Ti, V, W, Nb, Ta, and Zr. Owing to their excellent chemical stability, HEA coatings are widely employed to protect component surfaces operating in highly corrosive environments. Against this backdrop, the present study investigates the effect of carbon doping introduced via methane gas flow during the physical vapor deposition of TiAlTaZrNb HEA coatings on corrosion resistance. The morphology and structure of the coatings were analyzed by field emission scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. Corrosion protection and coating resistance were assessed through potentiodynamic polarization and electrochemical impedance spectroscopy. While increasing the methane flow resulted in an approximately 34% reduction in coating thickness, the overall coating resistance increased by one order of magnitude, reaching a maximum at a methane flow rate of 9 sccm, corresponding to the carbon solubility limit. This improvement was evidenced by a decrease in the corrosion rate from 8.02 × 10⁻² mm y⁻¹ for the uncoated H13 steel to 8.00 × 10⁻⁴ mm y⁻¹ for the HEA-coated samples. However, at higher methane flow rates, carbon precipitation and the formation of parallel microcracks contributed to an increase in corrosion rate. Full article

Next-generation wastewater treatment and recycling rely on membrane-based processes, but they face a trade-off among permeability, selectivity, and fouling resistance. In the present study, thin-film nanocomposite (TFN) membranes were fabricated by incorporating a ternary TiO₂-SiO₂-biochar nanofiller into a polysulfone (PSf) support using nonsolvent-induced phase separation, after which m-phenylenediamine and trimesoyl chloride were used via interfacial polymerization to produce a selective polyamide layer. The membrane compositions were M1 (22 wt.% PSf), M2 (22 wt.% PSf/0.5 wt.% TiO₂/0.5 wt.% SiO₂/0.5 wt.% biochar), and M3 (polyamide-coated M2). FTIR, XRD, SEM, contact-angle, porosity, and mechanical analyses supported successful membrane formation and changes in morphology, wettability, and structural strength after nanofiller incorporation and TFC coating. The addition of a nanofiller increased the hydrophilicity of the membranes by decreasing the water contact angle from 98.6 ± 0.8° for pristine PSf to 35.6 ± 1.5° for the nanocomposite membrane. Consequently, the pure-water permeability increased from 21 to 37 L m⁻² h⁻¹ bar⁻¹. After polyamide layer formation, the optimized TFN membrane maintained a contact angle of 55.4 ± 3.8° and achieved a high Congo red rejection of 98% with permeate flux of 7–9 L m⁻² h⁻¹ bar⁻¹. The membrane also showed good antifouling performance, with flux recovery ratios exceeding 90%. For heavy-metal-containing solutions, the optimized membrane showed apparent removal efficiencies of 78–98% for multivalent heavy metals (Pb²⁺, Hg²⁺, Cd²⁺, Mn²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Fe³⁺, As³⁺, and Cr⁶⁺). Static adsorption tests showed the order M2 > M3 > M1, confirming that exposed TiO₂-SiO₂-biochar sites contribute to pollutant uptake, while the superior filtration performance of M3 is attributed to the combined effect of the polyamide selective layer and adsorption-assisted interactions. Overall, the TiO₂-SiO₂-biochar-based TFN membrane provides a promising platform for dye removal and preliminary heavy-metal attenuation from contaminated water. Full article

This study presents a novel in situ reinforcement strategy for 17-4PH stainless steel by using Nb and Cr₃C₂ powders as precursors, addressing the challenge of poor particle dispersion and interfacial bonding in conventional ex situ ceramic additions. The coatings were systematically compared with 17-4PH coatings without the addition of a reinforcing phase. The results show that the coating without Nb addition is dominated by α-Fe martensite, exhibiting a coarse columnar/dendritic microstructure. After adding Nb and Cr₃C₂, the coating successfully forms in situ face-centered cubic NbC, with a significantly refined and uniformly distributed microstructure. The 10 wt.% Nb+Cr₃C₂ coating exhibits a refined microstructure with an average grain size reduced from 1.12 μm to 0.85 μm and a microhardness of 495.5 HV, representing an 86% increase over the substrate and a 34% improvement compared to the unreinforced coating. Friction–wear tests demonstrate that the composite coating reduces wear track width and depth by approximately 50% and 45%, respectively, compared to the substrate, with the wear mechanism transitioning from severe adhesive and fatigue wear to mild abrasive wear and localized micro-delamination. In situ synthesized NbC effectively optimizes the coating microstructure, enhances interfacial bonding, and markedly improves the hardness and wear resistance of 17-4PH coatings, providing theoretical and technical support for their engineering application under severe service conditions. Full article

Advanced thermal barrier coatings (TBCs) are essential for improving the efficiency and performance of gas turbine engines. Increasing engine operating temperatures and harsh service environments are pushing the current industry-standard 8 wt% yttria-stabilized zirconia (8YSZ) to its performance limits. High-rare-earth-oxide zirconates, such as Gd₂Zr₂O₇, have emerged as promising materials for next-generation engines due to their excellent high-temperature phase stability, lower thermal conductivity, and enhanced resistance to CMAS attack. In this work, dense vertically cracked (DVC) Gd₂Zr₂O₇/8YSZ bilayer coatings were developed using the air plasma spray (APS) process. Two approaches were employed for deposition of the NiCrAlYHfSi bond coat: (i) high-velocity oxygen fuel (HVOF), and (ii) APS flash-coated HVOF NiCrAlYHfSi bond coat. The durability of DVC TBC systems with the two bond coat types was evaluated by furnace cycling test (FCT) at 1125 °C. The TBC system with an APS flash-coated HVOF bond coat exhibited an FCT lifetime approximately twice that of the system with the HVOF bond coat alone. The improvement is primarily attributed to the higher surface roughness of the APS flash-coated bond coat, which enhances resistance to crack initiation, propagation, and linkage, thereby extending thermal cycling life. Full article

In this work, a non-standardized hypereutectic aluminum–silicon alloy AlSi21Cu5MgCr intended for the automotive industry is presented. The modification of the alloy is performed with the conventional modifier phosphorus in an amount of 0.04 wt%. The applied metallurgical treatment is the basis for the obtained modified structure. It has been established that after conducting the T6 heat treatment, the free silicon crystals are reduced to 26.9 µm, and the eutectic silicon crystals are spherical in shape and have dimensions not exceeding 8 µm. The macrohardness of the studied alloy is 168.5HV_10/10, a value significantly higher than that required for this type of alloy, which is in the range of 95 ÷ 137 HV (90 ÷ 130 HB). The microhardness of the α-phase in the composition of the eutectic is 154 µHV_50/10, which indicates that after quenching a saturated solid solution was fixed, and during the artificial aging process secondary strengthening phases were formed and separated. A CrAlN hard coating was deposited on the alloy surface. The mechanical properties of the coating were characterized by a hardness of 14 GPa, whereas the AlSi21Cu5MgCr substrate had a hardness of 2 GPa. The results showed considerable improvement of the hardness of the new alloy and well-tuned elastic–plastic properties. The obtained adhesive properties are compatible with this class of materials. The composition of the CrAlN hard coating is homogeneously distributed on the alloy surface and the morphology is improved. The investigations showed that CrAlN hard coatings could successfully be applied for the modification of the surface of AlSIMgCu alloys. Full article

AlCoCrFeNi high-entropy alloy coatings reinforced with different TiN contents (2 wt.%, 4 wt.%, and 6 wt.%) were fabricated on 304 stainless steel by laser cladding. The effects of TiN addition on the microstructure, hardness, friction behavior, and wear resistance of the coatings were investigated. Dry reciprocating sliding tests were conducted under a load of 10 N, a frequency of 5 Hz, a stroke length of 5 mm, and a duration of 20 min using GCr15 bearing steel balls as the counterpart. The results showed that the 2 wt.% TiN coating exhibited the best tribological performance within the investigated composition range, with a microhardness of 579.6 HV_0.5, a relatively low and stable friction coefficient of approximately 0.30–0.35, and a wear rate of 2.9 × 10⁻⁴ mm³/(N·m). When the TiN content increased to 4 wt.% and 6 wt.%, the wear resistance decreased, which was mainly associated with particle agglomeration, local stress concentration, and brittle spalling. These results indicate that appropriate TiN addition can improve the load-bearing capacity and wear resistance of laser-cladded AlCoCrFeNi coatings, providing a potential surface-strengthening strategy for 304 stainless steel components under dry sliding conditions. Full article

The surface treatment of inner walls in large-aspect-ratio tubes plays a pivotal role in ensuring long-term stable operation of equipment. Although traditional methods like electroplating are widely used, they often suffer from limited protection, poor adhesion, and environmental drawbacks. Magnetron sputtering (MS) represents a promising alternative; however, few studies have successfully developed coatings that balance high hardness with strong adhesion on the inner walls of tubes featuring large length-to-diameter ratios. In this study, we deposited Cr coating on the inner wall of a tube with an aspect ratio of 13.3 using MS technology, and regulated the process to enhance the hardness and adhesion strength of the coating. By systematically varying the bias voltage, the microstructure and properties of the coating were effectively tailored. Results show that a bias voltage of −200 V promotes pronounced (110) preferred orientation in the Cr coating, yielding an optimal combination of high hardness (~11.54 GPa) and a low coefficient of friction (~0.4). Furthermore, scratch testing revealed robust coating–substrate adhesion strength, with initial failure loads exceeding 50 N under various bias conditions. These findings demonstrate that optimizing the bias voltage during MS deposition is an effective approach for fabricating high-performance Cr coatings, providing a viable strategy to improve the durability and reliability of high-end equipment. Full article

Worn roller mill roll shafts made of Steel 45 require cost-effective surface restoration; plasma transferred arc (PTA) deposition of Ni–Cr–B–Si + WC composite coatings is a promising approach, yet the effect of arc current on coating quality remains insufficiently characterised for this substrate. Six coatings were deposited from PS-12NVK-01 powder (65 wt.% PG-10N-01 + 35 wt.% WC) at arc currents of 50–100 A on Steel 45 substrates using a ZTW3501DC PTA system; coatings were characterised by SEM, EDS mapping, XRD (HighScore Plus, PDF-2), Vickers microhardness profiling, and ball-on-flat tribological testing. EDS analysis revealed that compositional dilution increases from 18.1% at 60 A to 46.6% at 100 A; XRD identified WC + Cr₃C₂ + Ni₃B + Ni₂B + (Fe,Ni)γ at 50 A, transitioning through Cr₇C₃ + W₂C dominance at 80 A to an Fe₀.₆₄Ni₀.₃₆ matrix at 100 A; and coating thickness peaked at 2.70 mm at 80 A. The 60 A coating yielded the highest surface hardness (887 ± 76 HV, >4× the substrate), the lowest specific wear rate (4.00 × 10⁻⁶ mm³/(N·m), ~22× lower than uncoated Steel 45), and minimum dilution (18.1%), identifying 60 A as the most favourable deposition current for the restoration of roller mill roll shafts under the process parameters employed. Full article

High-entropy alloys exhibit a broad light-responsive spectrum, spanning the ultraviolet to visible range, and their light absorption coefficient is significantly higher than that of traditional binary oxides. Cr/AlCrNbSiTiN/AlCrNbSiTiO gradient nano-multilayer coatings with excellent solar selective absorption properties are prepared using ion source enhanced magnetron sputtering. The effects of thickness of the absorption layer of AlCrNbSiTiN (3/4/5 min, denoted as S-3/4/5) are systematically investigated. It is worth noting that nano-multilayer coatings of S-3, S-4, and S-5 exhibit nearly perfect absorption rates of 0.9847, 0.9888, and 0.9879, respectively. The TEM images shows clear interfaces between the various coating layers, exhibiting a gradient structure that combines nanocrystalline and amorphous characteristics. From the substrate to the surface, there is an increase in the content of nanocrystalline phases, coarsening of grain sizes, and a decrease in the amount of amorphous phases. The primary absorption layer of AlCrNbSiTiN displays a typical face-centered cubic nitride structure. The XPS analysis reveals that the high-valent oxides (Nb⁵⁺, Cr⁶⁺) ensure thermal stability, whereas mixed valence states of Cr³⁺/Cr⁶⁺ may enhance visible light absorption through multi-electron transitions. This study analyzes how both the thickness of absorbing layers and high-temperature annealing affect the optical properties and photothermal conversion performance of AlCrNbSiTiN-based high-entropy coatings, which provides valuable insights for developing high-performance selective absorbers. Full article