Tetrahedral amorphous carbon (ta-C) coatings are attractive for improving the tribological performance of austenitic stainless steels because of their high hardness, low friction coefficient, and chemical inertness. A duplex coating system consisting of an HVOF-sprayed WC-10Co4Cr interlayer and a PVD-deposited ta-C coating was used to improve the load-bearing capacity and wear resistance of ta-C-coated 316 stainless steel. Scratch responses and dry reciprocating sliding wear behavior of the duplex coating were compared with those of a single PVD ta-C coating deposited directly on 316 stainless steel. The ta-C coatings in both systems had similar thicknesses and comparable hardness values. The HVOF-sprayed WC-10Co4Cr interlayer, with a thickness of 0.27 mm, hardness of 1315 HV0.3, porosity of 0.55
Laser cladding technology plays an important role in improving the wear resistance and corrosion resistance of drilling equipment. This paper investigates the effects of different sliding frequencies on the tribocorrosion and electrochemical properties of Ni625-WC laser-clad coatings. The results indicate that as the sliding frequency increases, the open circuit potential of the coating shifts negatively, the impedance decreases, and the corrosion resistance declines. Meanwhile, the coefficient of friction decreases, whereas the wear volume loss increases. The dominant wear mechanisms transition from abrasive wear and adhesive wear at lower sliding frequencies to intensified oxidative wear and microcrack formation at higher sliding frequencies. Quantitative analysis reveals that the total volume loss is primarily contributed by mechanical wear, and the corrosion-accelerated wear shows an increasing trend with increasing sliding frequency. Microcracks induced by high sliding frequency provide channels for the ingress of corrosive Cl−, further aggravating coating damage. The downhole operating environment for drilling tools is variable, and the differences in sliding frequency between drilling equipment and various working conditions directly affect their wear and corrosion behavior. The application of laser cladding technology to prepare Ni625-WC laser-clad coatings holds great potential for protecting drilling tools, but it significantly alters the coating microstructure. This paper systematically investigates the electrochemical behavior and wear-corrosion mechanisms of Ni625-WC laser-clad coatings from the perspectives of microstructure and sliding frequency, and also elucidates failure mechanism. This research has important theoretical value and engineering application significance for optimizing drilling parameters and extending the service life of tools.
Thermal barrier coatings (TBCs) are used in internal combustion engines to protect metallic components from high temperature. However, the thermally grown oxide (TGO) layer affects the service life of TBCs. In this study, finite element models incorporating non-uniform TGO layers with different thicknesses are developed to investigate the effects of TGO presence and thickness on the thermomechanical behavior of atmospheric plasma-sprayed (APS) TBCs under thermal shock. The results show that the presence of a thin TGO layer has a negligible influence on the overall thermal insulation performance under the investigated conditions, while it significantly affects the stress distribution within the ceramic top coat (TC). Compared with the TBC without TGO, the 5-μm-thick TGO reduces the maximum Y-direction tensile stress in the TC layer from 466.57 to 348.6 MPa and the maximum positive shear stress from 282.47 to 168.65 MPa. Within the investigated TGO thickness range of 2-6 μm, increasing TGO thickness further reduces the peak thermal mismatch stresses, with the maximum tensile stress and positive shear stress decreasing by approximately 25 and 26
AISI 4140 steel, known for its strength, toughness, and fatigue resistance, is ideal for various applications. Considering the widespread use of this material, there is a continual need to develop cost-effective and rapid repair methods. This study examined the effect of powder heat treatment and in situ peening (using Praxair 410CrC powders) on the cold spray characteristics of 4140 powder and also evaluated the resulting microstructure and mechanical properties. 4140 powders were annealed at 650 °C for 1 and 3 h, which resulted in 35 and 50
Herein, flame-sprayed TPU/MWCNTs coatings were employed to investigate how self-organized fractal MWCNTs clusters regulate electromagnetic loss mechanisms and stabilize microwave absorption. As the MWCNTs content increased from 3 to 6 wt.
CoCrFeNiMn high-entropy alloys generally suffer from limited hardness and tribological performance due to the dominance of a ductile FCC solid solution structure. To tailor the solidification microstructure and surface properties of FCC-dominated CoCrFeNiMn high-entropy alloy coatings, Ti and B4C were introduced as reactive elements during plasma cladding. The effects of Ti content on phase composition, microstructure evolution, mechanical properties, wear resistance, and corrosion behavior were systematically investigated using SEM, EDS, EPMA, EBSD, AFM, KPFM, and electrochemical tests. During plasma cladding, Ti/B4C reactions coupled with rapid solidification promoted the formation of TiC, TiB2, and Cr-rich borides, which evolved from isolated particles into a semi-continuous intergranular network. With increasing Ti content, the microstructure evolved from columnar grains to refined equiaxed grains, and the reinforcing phases transformed from isolated particles into a semi-continuous network. The CoCrFeNiMnTi0.5(B4C)0.19 coating exhibited the optimal comprehensive performance, achieving a hardness of 470 HV0.2, a friction coefficient of 0.47, and a wear rate of 1.25 × 10-6 mm3·N-1·m-1. Corrosion tests indicated that the semi-continuous network promoted the formation of a stable passive film and inhibited corrosive medium penetration. AFM and KPFM analyses further revealed a relatively uniform surface potential distribution and reduced electrochemical heterogeneity, contributing to enhance corrosion resistance. This work develops a novel plasma cladding approach to fabricate high-performance CoCrFeNiMn high-entropy alloy composite coatings via Ti/B4C-triggered in-situ reactions under rapid solidification conditions. The unique plasma cladding-induced reaction–solidification coupling mechanism is revealed, demonstrating the evolution of TiC, TiB2, and Cr-rich borides from isolated particles into a semi-continuous carbide–boride network. This interconnected reinforcement architecture enables synergistic enhancement of hardness, wear resistance, and corrosion protection through grain refinement, load transfer, and electrochemical homogenization. The findings provide new insights into designing advanced HEA composite coatings by plasma cladding technology.
Thermal barrier coatings (TBCs) protect turbine engine components allowing them to operate at high temperatures, significantly improving turbine power and fuel efficiency. Suspension plasma spraying (SPS), allows the creation of columnar microstructures with controlled porosity, thermal stresses, and lower thermal conductivity. However, the major challenge for the columnar structure is that it facilitates the penetration of calcium–magnesium–alumino-silicates (CMAS), which leads to TBC deterioration. To mitigate this, a laser post-treatment process has been proposed to re-melt the top layer of TBCs. In this study, columnar yttria-stabilized zirconia (8YSZ) topcoats were deposited by axial SPS. A CO2 laser treatment was used to create a re-melted layer at the surface of the SPS coatings. The influence of key laser parameters, such as scanning speed and laser power, on the microstructure of the re-melted top layer of the columns in the SPS coatings was investigated. Also, the micro-hardness, crack network and phase analysis of the laser re-melted layer were studied. The study showed that increasing the scanning speed increased the width of cracks of re-melted zone of TBC. Additionally, the laser glazing decreased surface roughness, sealed open porosity, produced a dense microstructure, and increased micro-hardness. The phase composition remained stable (metastable tetragonal (t′) phase) for both as-sprayed and laser-glazed samples. The primary objective of this study is to investigate the refinement of suspension plasma-sprayed (SPS) 8YSZ coatings through COâ‚‚ laser surface re-melting. Unlike traditional studies focused on sealing lamellar APS coatings, this work specifically targets the unique columnar microstructure inherent to SPS. The effects of laser power and scanning speed were optimized in relation to the re-melted layer thickness, crack width, and crack length. Furthermore, phase composition and microhardness analyses were conducted to evaluate the influence of laser glazing on the as-sprayed 8YSZ coatings.
Laser cladding layers and diamond-like carbon (DLC) films are widely employed to improve the corrosion resistance of marine steels. However, defects such as pores and cracks in these coatings can act as initiation sites for localized corrosion during prolonged exposure to marine environments, thereby accelerating substrate failure. In this study, 304 stainless steel (304 SS) was first treated by laser cladding and subsequently coated with various nitrogen-doped DLC films deposited by plasma-enhanced chemical vapor deposition to form composite coatings. The localized failure mechanisms of these composite coatings under long-term exposure to sodium chloride solutions were investigated through electrochemical measurements, microstructural characterization, thermodynamic analysis, and numerical simulation. The results demonstrate that the DLC layer effectively seals surface defects in the laser-cladded layer and enhances barrier performance owing to its high chemical inertness. Nitrogen incorporated significantly alters the corrosion behavior by consuming locally generated H+ ions to form NH4+, thereby mitigating acidification within defect microzones. This shift in local pH promotes the formation of compact spinel-type oxides (e.g., Fe3O4, FeCr2O4, and NiFe2O4) instead of porous hematite, effectively suppressing autocatalytic localized corrosion. Increasing nitrogen content enhances the density of active sites in the DLC matrix, accelerates spinel nucleation, and facilitates earlier passivation. In situ electrochemical noise analysis reveals a transition from stable pitting in undoped coatings to uniform corrosion and eventual passivation in N-doped coatings. A reaction–diffusion model based on the Nernst–Planck framework further clarifies the relationship between microzone pH evolution and oxide stability. These findings elucidate the synergistic mechanism between laser-induced microstructural heterogeneity and nitrogen-regulated local chemistry, providing a mechanistic basis for durability prediction and optimized design of laser cladding/DLC composite coatings for marine applications. This work develops a nitrogen-doped DLC/laser-cladded 304 stainless steel composite coating with enhanced corrosion resistance in chloride-containing environments. Unlike conventional laser-cladding studies mainly focused on microstructural refinement or hardness improvement, this study systematically reveals the synergistic interaction between laser-induced defect structures and nitrogen-regulated localized corrosion behavior. Cross-sectional SEM, electrochemical noise analysis, pH evolution simulations, and XPS characterization demonstrate that nitrogen incorporation suppresses defect-channel propagation and regulates the local hydrochemical environment, thereby promoting the formation of stable spinel oxides. The work provides new insight into corrosion control mechanisms in laser-modified composite coating systems.
The service life of hot-rolling descaling rollers is severely limited by premature failure under synergistic high-temperature friction, wear, and alternating loads. Herein, non-spherical WC particles replaced conventional spherical WC to fabricate Ni-based composite coatings via plasma arc surfacing, so as to reveal the regulation mechanism of WC dosage on multicarbide evolution and high-temperature failure mechanisms. With WC contents of 30-65 wt.
In this study, WC-10Co-4Cr composite coatings with various TiC contents (0, 5, and 10 wt.
Thermal spray coatings often require a substrate pre-treatment for adequate adhesion, such as roughening which facilitates mechanical anchoring of the coating material on the surface asperities. This is commonly accomplished by grit blasting with hard ceramic particles, achieving roughness of the order of microns. For some materials combinations, this roughness may not be sufficient, while grit remnants at the interface may undermine the adhesion. Besides, repeated use of the grit leads to its degradation and adverse impacts on the reproducibility. Laser texturing presents an advanced alternative technology which offers the advantages of achieving significantly higher roughness values, regular structures, and elimination of grit contamination. In this study, various laser textures were developed on steel substrates as a pre-treatment for plasma sprayed tungsten coatings, which may find applications in plasma-facing components of future fusion devices. The laser texturing was optimized in several stages to achieve high processing rates without compromising the desired interface properties. Tungsten coatings were applied by radio frequency/inductively coupled plasma (RF/ICP) spraying. The relevant characteristics of the coating–substrate pairs, such as substrate morphology, coating structure, adhesion, and thermal diffusivity were investigated. Finally, performance of the coatings under fusion-relevant heat fluxes was tested. The obtained results demonstrate the suitability of laser texturing for pre-treatment of steel substrates before the deposition of plasma sprayed tungsten coatings, and the achievement of high processing rates, comparable to the traditional grit blasting, while providing superior control of the textured interface. The adhesion to the substrate is higher than coating cohesion for both treatments. The coatings showed high durability under thermal cycling conditions relevant for fusion reactor environments. The novelty of this work lies in the development of laser texturing as a substrate treatment with high processing rate, comparable to conventional grit blasting, without any adverse effects on coating adhesion. Additionally, tungsten coating characteristics, including thermal cycling performance at conditions relevant for nuclear fusion applications, are demonstrated.
Cold spray deposition was investigated as a candidate technology for producing corrosion- and abrasion-resistant coatings for deep borehole nuclear waste disposal canisters. Commercially pure grade 2 Ti, Cu, Cu-1 wt.
Steam turbine valve stems are subjected to the coupled effects of high-temperature oxidation, thermal fatigue stress, and high-temperature wear during start-stop cycles and long-term service, which severely restricts their service reliability and service life. To achieve efficient surface strengthening and performance improvement of valve stems, in this study, nano-TiO2-reinforced cobalt-based alloy composite coatings were fabricated on GH901 high-temperature superalloy substrates via laser cladding, and the influence laws of the modified coatings on microstructural evolution, microhardness, and high-temperature tribological properties were systematically investigated. The results show that the introduction of nano-TiO2 can effectively regulate the microstructure and mechanical properties of the coatings and significantly refine the coating grains. The maximum microhardness of the coatings is increased by 39.1
To address the thermal decomposition of WS2 during thermal spraying and enhance the solid lubrication performance of WS2-containing coatings, this study prepared WS2@(Cu2O/Cu) core–shell powders via a facile chemical replacement method. These powders were then blended with Cu powder to fabricate Cu/WS2/Cu2O composite coatings using atmospheric plasma spraying. Quantitative XRD analysis showed that compared with the directly mixed Cu/WS2 powder, the core–shell powder effectively reduced both the loss and decomposition rates of WS2 during plasma spraying. At 15 wt.
La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) has been widely employed as a cathode and current collector material for tubular segmented-in-series solid oxide fuel cells (Tubular-SIS-SOFCs), yet plasma-sprayed LSCF current collector layers (CCLs) often suffer from insufficient gas permeability and performance degradation caused by B-site element evaporation in high-temperature plasma jets, while conventional noble-metal current collectors increase cost and compromise long-term stability. In this work, a composite strategy was developed by incorporating transition-metal particles into LSCF feedstock via atmospheric plasma spraying (APS) to construct a noble-metal-free ceramic CCL. Due to poor wettability between overheated metal droplets and LSCF splats, metallic particles solidified in a dispersed morphology within the coating. During subsequent heat treatment, in situ oxidation-induced volumetric expansion of metal particles promoted controlled crack propagation, enhancing gas diffusion pathways, while thermally driven metal-ion diffusion partially compensated B-site depletion and restored lattice conductivity. Systematic investigation revealed that the LSCF-5Fe coating fabricated at 25 kW achieved an optimal balance between gas permeability, mechanical integrity, and electrical conductivity. Among different metals, LSCF-5Cu exhibited the highest post-treatment conductivity of 100.5 S cm−1. Tubular-SIS-SOFCs employing metal-particle-modified LSCF CCLs delivered over 50
Ultrasonic vibration-assisted laser cladding of Inconel 625 coatings shows great application potential; however, the quality and performance of the resulting coatings are highly dependent on specific process parameters. This study aims to fabricate high-performance Inconel 625 coatings by ultrasonic vibration-assisted laser cladding, with laser power, scanning speed, powder feeding rate, and ultrasonic amplitude optimized to achieve low dilution, an appropriate aspect ratio, and high microhardness. Orthogonal experiments were conducted to analyze the effects of process parameters. On this basis, a Tent-SSA-BP prediction model was established to describe the relationship between process parameters and coating performance, and the NSGA-II algorithm was combined for multi-objective optimization, with the optimization results experimentally validated. Finally, Inconel 625 coatings were fabricated by ultrasonic vibration-assisted laser cladding using the optimized parameters and an appropriate overlap rate, and their microstructure, microhardness, and wear performance were characterized. The results show that scanning speed mainly affects dilution rate and microhardness, while laser power predominantly influences the aspect ratio. The Tent-SSA-BP model demonstrated high prediction accuracy for all three outputs. NSGA-II optimization determined the optimal parameters as a laser power of 868.29 W, scanning speed of 3.30 mm/s, powder feeding rate of 8.01 g/min, and ultrasonic amplitude of 17.83 μm, with predicted dilution rate, aspect ratio, and microhardness of 43.02
Corrosion failure induced by molten CaO-MgO-Al2O3-SiO2 (CMAS) infiltration critically limits thermal barrier coatings (TBCs) durability. This study develops a finite element model incorporating CMAS penetration into the ceramic layer to investigate how the morphology and size of CMAS-filled pores affect thermomechanical behavior. The results show that larger aspect ratios promote smoother heat conduction and reduce peak heat flux from 3 to 2.4 W/mm2, while stress concentration at pore tips intensifies with Smax reaching 155 MPa. Under smaller aspect ratios, the shear stress exhibits significant fluctuations, with peak values approaching 120 MPa. Enlarged circular pores induce localized heat flux concentration, whereas elliptical pores cause stronger Smax fluctuations, increasing by 35.4
Fe-based amorphous coatings are widely used in petrochemical, mining, and power generation industries due to their excellent wear and corrosion resistance derived from the unique amorphous structure. Therefore, wide-beam laser cladding was employed to investigate the role of powder feed rate on microstructure and wear performance. The coatings exhibited amorphous–crystalline composite structure, with the amorphous phase content increasing then decreasing as the feed rate increased, peaking at about 72
In aerosol deposition, fine ceramic powders in sizes of less than typically 5 μm are deposited as a coating at room temperature. Aerosol deposition must be performed under a vacuum to apply such fine powders and avoid bow shock effects. According to experimental results, coating formation by aerosol deposition only occurs if particle velocities exceed a material-specific threshold velocity. Thus, knowledge of attained particle velocities over acceleration in the nozzle and under the expansion into a vacuum is essential for deriving conditions for successful deposition. In the present study, 3D CFD simulations were used to investigate the key geometric variables in particle acceleration. Three different nozzle geometries were investigated: a converging nozzle, a converging–diverging nozzle, and a converging nozzle followed by a constant cross section toward the exit. In addition, these three nozzle geometries were optimized to maximize the particle impact velocity. The results show that the converging–diverging nozzle supplies the highest particle velocities within this comparison. By the design of optimization, the particle velocities can be improved for all the geometry types. The most promising geometry from the CFD optimization was manufactured and compared to the original one, providing a gain in experimentally measured particle velocity of 24
The present study introduces and validates a comprehensive numerical model for hydrogen-fueled high-velocity oxygen-fuel (HVOF) spraying of tungsten carbide-cobalt-chromium (WC-Co-Cr) powder. We conduct three-dimensional (3D), two-way coupled simulations of the reactive, particle-laden flow within the DJ2600 thermal spray gun and its supersonic exhaust jet. The model incorporates the real nozzle geometry, applies the eddy-dissipation concept (EDC) as a finite-rate chemistry approach for hydrogen combustion, and uses an explicit algebraic Reynolds stress model (EARSM) for turbulent scales. Consequently, our simulations enable a precise analysis of flame dynamics by revealing unprecedented levels of flow field detail in the nozzle’s convergent section. We find that the interaction of fuel, oxidizer, and cooling air streams produces diverse, three-dimensional flame shapes. Furthermore, we compare the standard particle modeling approach from literature with an enhanced approach that accounts for rarefied flow at the particle scale, viscous heating in the boundary layers around particles, and temperature-dependent particle heat capacities. Our results demonstrate that including these phenomena is critical for correctly predicting particle impact properties. Finally, we analyze particle states both in flight and upon impact on the target surface.
