Search Results (2,529)

A Ti-Al-Si composite coating was prepared on Ti65 titanium alloy using a two-step hot-dipping + pre-oxidation method to improve its tribological performance and high-temperature oxidation resistance. The second-step dipping time strongly affected the coating microstructure and wear behavior. The optimal coating, prepared with a dipping time of 5 min in each step, exhibited negligible wear after oxidation at 800 °C for 1000 h and 2500 h, with slight adhesive wear and oxidative wear as the dominant mechanisms. Longer dipping times led to mixed wear modes and reduced wear resistance. Under high-temperature corrosion conditions, the coating showed good long-term stability in water vapor, with its mass gain following a sub-parabolic law, Δm = 0.39·t^0.47, because the internal multilayered structure effectively blocked inward oxygen diffusion. However, in environments containing NaCl or 75 wt.% Na₂SO₄ + 25 wt.% NaCl, catastrophic hot corrosion occurred, regardless of the presence of water vapor, through a chlorine-driven oxidation–chlorination–reoxidation autocatalytic cycle. In the mixed salt environment, Na₂SO₄ decomposition supplied additional oxygen and alkaline species, accelerating the degradation and spallation of the Al₂O₃ and TiO₂ scales. Water vapor further intensified this cycle by generating HCl, which promoted rapid consumption of Al and Ti in the coating. This study reveals the wear behavior and hot corrosion failure mechanisms of Ti-Al-Si coatings under complex conditions, providing guidance for process optimization and applications in marine atmospheres. Full article

The three-phase region of Mo₃Si-Mo₅Si₃-Mo₅SiB₂(MoSiB) exhibits excellent high-temperature oxidation resistance and is considered a highly promising high-temperature structural material. However, the presence of porous structures significantly increases the surface area exposed to oxidation. Metallic porous materials often suffer from inadequate corrosion resistance and insufficient high-temperature oxidation resistance, whereas ceramic porous materials are plagued by high brittleness. Intermetallic compounds offer a combination of the advantages of both metals and ceramics. Nevertheless, the high-temperature oxidation behavior of porous MoSiB has not yet been systematically elucidated. The study systematically investigates the effect of pore structure on the high-temperature oxidation behavior of porous MoSiB at 1000 °C and 1300 °C, with a focus on oxidation kinetics, phase evolution, surface and cross-sectional morphology and underlying oxidation mechanisms. The effects of porosity and temperature on the oxidation process are also analyzed. The results indicate that at 1000 °C, the material exhibits uniform oxidation, with lower porosity contributing to better oxidation resistance. At 1300 °C, oxidation is limited to the surface layer, where low-viscosity SiO₂(B) rapidly seals the pores to form a dense protective layer. This research reveals the high-temperature oxidation mechanism and phase evolution of porous MoSiB, providing a theoretical foundation for its application in high-temperature structural fields. Full article

The structural stability of high-temperature-formed oxide films (HTOFs) on SAC305 solder plays a critical role in determining corrosion reliability during long-term thermal exposure, yet the coupled effects of oxide evolution and substrate microstructure changes remain unclear. In this work, SAC305 solder was thermally aged at 150 °C for 10–60 days, and the evolution of the oxide film structure and substrate microstructure was systematically investigated using SEM, XRD, XPS, and electrochemical techniques. The results reveal that HTOF mainly consists of a SnO/SnO₂-layered structure with thickness increasing slightly from approximately 16.5 nm to 18 nm, while increasing micro-cracks and Ag₃Sn coarsening induced by the Kirkendall effect lead to significant reductions in impedance parameters and corrosion resistance. These findings demonstrate that the degradation of HTOF is governed by the coupled effects of oxide defect accumulation and intermetallic phase coarsening, providing a mechanistic insight into the corrosion failure of SAC305 solder under long-term thermal aging conditions. Full article

In this study, C/N-containing Fe₃O₄ oxide films over an inner nitride layer were fabricated on 45# steel by oxynitriding to improve corrosion resistance in chloride-containing environments. The films exhibited a dense polyhedral structure, with nanoscale Fe₃O₄ precipitates at grain boundaries. Nitrogen and carbon were uniformly distributed within the oxide grains, inducing lattice expansion and modifying the Fe-O bonding environment. First-principles calculations based on C/N substitution models suggested that C/N incorporation may increase the unit cell volume, strengthen lattice bonding, and enhance the theoretical hardness of Fe₃O₄. The optimally doped films exhibited outstanding corrosion resistance, with a corrosion potential of 0.115 V_SCE, a corrosion current density of 3.16 × 10⁻¹⁰ A/cm² in 3.5 wt.% NaCl solution, and a corrosion-free lifetime of up to 3600 h in neutral salt spray testing. This superior performance is attributed to the synergistic effects of the compact single-phase magnetite layer, grain boundary precipitates, and modified electronic structure, which collectively inhibit chloride ingress and convert localized electrochemical attack into uniform corrosion. The experimental results are consistent with first-principles predictions, which clarified the mechanism of nitrogen doping in material corrosion protection from a mechanistic perspective. Full article

This study investigates the corrosion behaviour of a WC–6Co cemented carbide (94 wt% WC, 6 wt% Co) in acidic (pH 2) and alkaline (pH 13) electrolytes used for industrial PVD coating removal. The removal of the coating was not investigated, since no coatings were applied or analysed in this study. The objective was exclusively to simulate the corrosion response of the exposed substrate after the coating had been removed during electrochemical stripping. Potentiodynamic polarisation measurements were performed from OCP −0.2 V to +3 V at a scan rate of 1 mV·s⁻¹, followed by surface characterisation using SEM/EDS and laser profilometry to identify corrosion mechanisms and quantify material degradation. In an acidic solution, corrosion was dominated by cobalt dissolution, followed by the formation of a W–O-rich corrosion-product layer, as indicated by increased tungsten and oxygen contents in SEM/EDS analyses. The layer became increasingly porous and mechanically unstable at higher potentials. Progressive thickening of the corrosion-product layer and subsequent breakdown resulted in significant material loss, including surface abrasion up to ~8 µm. In alkaline electrolytes, SEM/EDS analyses revealed a Co–O-rich surface layer, suggesting cobalt-containing hydroxide/oxide corrosion products. These results suggest that surface-layer formation on WC–Co does not necessarily provide reliable corrosion protection, as stability and morphology strongly depend on pH. These findings provide valuable guidance for the use of cemented carbides in electrochemical stripping processes for PVD coating removal. Full article

The Iulia Felix is a 2nd-century AD Roman shipwreck that was discovered off the coast of Grado in 1986. Following its recovery, the hull was dismantled and treated with high concentrations of PEG 4000 at elevated temperatures. This process was completed in 2003. The elements were then stored for over 20 years. During this prolonged storage period, salt efflorescence developed on some surfaces, raising concerns about ongoing degradation and prompting an investigation into the composition of the wood and how environmental conditions influence it. The efflorescence was analysed using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), X-ray powder diffraction (XRPD) and Fourier transform infrared spectroscopy (FTIR). To evaluate the impact of environmental factors, samples were exposed to controlled humidity levels of 35% and 85% until equilibrium was achieved. The analyses identified iron- and sulphur-based compounds, including hydrated ferrous sulphates, calcium sulphate and hydrated iron oxides. These findings suggest a corrosion-related degradation process that originates in a marine burial environment and progresses in humid, oxygen-rich conditions after recovery. The presence of PEG within the efflorescence indicates that environmental conditions after treatment promoted its gradual migration to the surface. Climate testing revealed that PEG 4000 significantly reduced hygroscopic exchange with the environment. Under dry conditions, dimensional changes were minimal, with less than 1% variation in mass and surface area. In contrast, prolonged exposure to high humidity resulted in a 11% increase in mass due to moisture uptake, as well as a roughly 5% increase in surface area. This was accompanied by minor cracking and, in some cases, structural failure. This study highlights the long-term conservation challenges posed by waterlogged archaeological wood treated with high-molecular-weight PEG. It emphasises the importance of continuous environmental monitoring to mitigate degradation processes and preserve structural integrity, providing valuable insights for future museum conservation strategies. Full article

The acetic acid corrosion resistance of silver electrodes is critical for ensuring photovoltaic (PV) module reliability. Ethylene-vinyl acetate (EVA) is the most widely used encapsulant material in photovoltaic modules. Under exposure to light, heat, and moisture, EVA decomposes to generate acetic acid, which corrodes the silver electrodes, leading to energy conversion efficiency degradation of the module. To address this problem, the lead-free paste was formulated and evaluated in this paper to improve the anti-acetic acid performance. The contact resistivity of the front and the rear side of the solar cells have been measured before and after acetic acid exposure, and greater degradation is shown in the front electrode than in the rear side. Furthermore, the lead-free paste demonstrates lower efficiency degradation compared to the lead-containing paste after acetic acid exposure. In addition, top-view and cross-sectional scanning electron microscopy was performed to analyze the mechanism of the acetic acid corrosion resistance, in which the silver acetate particles were observed. Our experimental results demonstrate that the lead-free paste exhibits superior acetic acid corrosion resistance, which is due to its higher glass acidity and the absence of lead oxide that causes enhanced chemical reactivity with acetic acid. Based on these findings, the acetic acid corrosion model is proposed to attribute the conversion efficiency degradation of reactions between acetic acid and silver, as well as the glass of the silver electrodes. Full article

Yttrium doping has been reported to be an effective approach to enhance the mechanical and protective properties of ZrN coatings by magnetron sputtering. Nitrogen (N₂) flow ratio during reactive magnetron sputtering is known to critically influence the stoichiometry, defect structure, and microstructure of nitride coatings. However, its systematic effect on Y-doped ZrN (ZrYN) coatings has remained unexplored. In this work, ZrYN coatings with a fixed Y content were deposited by reactive magnetron sputtering under varying N₂ flow ratios (0–10%). Their microstructure, mechanical properties, corrosion resistance in 3.5 wt% NaCl solution, and oxidation behavior at 650 °C were systematically investigated. Below 5% N₂ flow ratio, the coatings are metallic ZrY, showing very low hardness, poor corrosion resistance, and catastrophic oxidation failure. At N₂ flow ratio ≥ 5%, cubic ZrYN forms, with stoichiometry varying from sub-stoichiometric (5%) to near-stoichiometric (7.5%) to over-stoichiometric (10%). The near-stoichiometric coating at 7.5% exhibits the finest columnar grains and densest microstructure, leading to the highest hardness (32.2 ± 1.4 GPa) and an elastic modulus of (469.6 ± 24.5 GPa), as well as the best corrosion resistance (two orders of magnitude lower than bare 316 stainless steel). Upon oxidation, it forms a thin and dense epitaxial t-ZrO₂ scale stabilized by Y₂O₃, suppressing the destructive tetragonal to monoclinic transformation. Off-stoichiometric coatings at 5% and 10% develop thicker, cracked oxide scales and show inferior properties. Precise control of N₂ flow ratio is therefore essential to achieve a near-stoichiometric ZrYN coating with superior mechanical, anti-corrosion, and anti-oxidation performance. Full article

Optical fiber sensors deployed in harsh industrial fields, e.g., high-temperature wet-oxygen, face severe challenges in signal attenuation and mechanical degradation. While amorphous silicon oxycarbide (a-SiOC) coatings offer a promising solution due to their adjustable thermo-mechanical properties, balancing their structural density with environmental stability remains a critical technical bottleneck. In this study, a-SiOC coatings were deposited on optical fibers using hexamethyldisilane (HMDS) and trace oxygen via radio-frequency capacitively coupled plasma-enhanced chemical vapor deposition (PECVD). A systematic investigation was conducted to determine the impact of deposition temperature (70–420 °C) on the precursor dissociation kinetics, microstructural evolution, and corrosion resistance of the coatings. An elevation in temperature promotes the elimination of organic terminal groups (–CH₃, –H) and enhances surface diffusion, driving the coating from a loose, carbon-rich “polymer-like” structure (dominated by Si–C bonds) to a dense, inorganic “silica-like” skeleton (dominated by Si–O–Si bonds). High-temperature corrosion tests in a wet-oxygen environment (500–900 °C) demonstrate that the failure mechanism is highly dependent on deposition temperature. Coatings deposited at low temperatures suffer catastrophic cracking due to pronounced oxidative shrinkage and the release of volatile species, whereas coatings deposited at 420 °C exhibit microcracking caused by severe carbon phase separation and stress concentration within the rigid inorganic network. In the present system, 350 °C is identified as the optimal deposition temperature, as it achieves the best balance of network densification and structural flexibility, while exhibiting the best mechanical performance. Full article

Hot-press forming (HPF) steel is a promising lightweight material for automotive applications but suffers from oxidation and reduced corrosion due to high-temperature processing. Aluminized coatings, particularly Al-10Si, are widely used to mitigate this issue. However, HPF heat treatment can create brittle alloy layers with cracks, compromising retention and increasing corrosion risk. This study investigated the effects of Sr addition on the microstructure and corrosion resistance of Al-Si-coated HPF steel. Al-Si and Al-Si-Sr coatings were applied to steel substrates and subjected to heat treatment to produce heat-treated (HT) Al-Si and HT Al-Si-Sr samples. Sr addition refined and spheroidized eutectic Si particles, improved coating homogeneity, and mitigated vertical crack formation in the Al-Fe-Si intermetallic layer. The resulting dense, crack-free alloy layer effectively shielded the Fe substrate from corrosion. After heat treatment, Sr facilitated the formation of a fine lamellar microstructure and a dense, continuous oxide film, enhancing coating retention and sustaining barrier protection. These improvements significantly delayed corrosion propagation into the Fe substrate. Corrosion resistance was evaluated using salt-spray tests (ASTM B117), potentiodynamic polarization, and electrochemical impedance spectroscopy in 3.5 wt.% NaCl solutions. Microstructural analyses revealed that even minimal Sr content (0.05%) considerably enhanced the performance of Al-Si coatings, demonstrating industrial applicability. This study highlights the potential of Sr-added Al-Si coatings in addressing the demand for lightweight and corrosion-resistant materials in the automotive industry, offering a viable solution for high-performance and environmentally sustainable applications. Full article

The objective of this study was to further improve the wear and corrosion resistance of biomedical Ti6Al4V alloy micro-arc oxidation coating, so as to improve its comprehensive service performance. In this study, the effects of pulsed laser power (20–100 W) on the structure, composition, tribological properties and corrosion resistance of the composite coating were systematically studied by using pulsed laser remelting pretreatment technology. The results show that when the power is 100 W, the microwave stripe and fine grain structure formed by pulsed laser remelting can improve the discharge uniformity during the micro-arc oxidation process. The porosity of the composite coating decreases from 21.32% to 10.94%, and the thickness increases from 8.14 μm to 19.49 μm, which is beneficial to improve the compactness and uniformity of the micro-arc oxidation coating. In addition, the pulse laser remelting pretreatment increased the surface hardness of the composite coating to 745.5 HV, and the friction coefficient decreased from 0.76 to 0.51, thereby improving the wear resistance of the composite coating. The electrochemical test results show that the corrosion current density of the composite coating is reduced from 7.28 × 10⁻⁸ A·cm⁻² to 1.91 × 10⁻⁸ A·cm⁻² due to the optimization of the composite coating structure, and the corrosion resistance is significantly enhanced. This study provides an effective pretreatment strategy for the construction of high-performance MAO composite coatings. Full article

The article is devoted to the study of the properties of the obtained heat-insulating refractory materials, based on fireclay scrap of various fractions (2.5 mm, 1.0 mm, 0.5 mm, and 0.1 mm) using a complex of mineral and oxide additives. The fillers used were titanium dioxide powder and silicon production wastes, which included microsilica powder, aluminum oxide, zinc oxide, zirconium oxide, chromium oxide, iron oxide, cement, lime, and baking soda. The choice of these fillers was due to the fact that they initially have corrosion resistance. Liquid glass acted as a binder. The resulting thermal barrier material was tested to determine its physical and mechanical properties, namely, thermal conductivity, porosity, compressive strength, and microstructure. According to the obtained results for the physical and mechanical properties, the secondary refractory material had properties close to GOST. So, according to GOST 12170-2021, the thermal conductivity values of the obtained materials were included in the 0.03–15.0 W/(m·K) range. The porosity values of the obtained samples complied with GOST 2409-2014 and were not more than 30%. The maximum compressive strength was 171.31 kgf/mm². The microstructure of the material of the obtained samples was very porous, and the pores were evenly distributed throughout the volume, which is extremely important for heat-insulating materials. A distinctive feature of the technology was the absence of a high-temperature firing stage: the required physical and mechanical properties of the material were achieved when heated to 180–300 °C with subsequent slow cooling in the furnace, which significantly reduces energy consumption compared to traditional refractory technologies. The use of waste from the production of chamotte scrap and microsilica will help to reduce negative impacts on the environment, save natural resources, and expand the raw material base. Full article

This study examined the stress corrosion of Alloy 625 in Cl⁻ + S₂O₃²⁻ solutions using digital holography in combination with electrochemical methods. Without elastic tensile stress, intergranular corrosion (IGC) occurred, due to the higher activity of grain boundaries compared to the grain interior and to preferential adsorption of sulfur (produced by S₂O₃²⁻ decomposition) at these boundaries. Digital holography observations showed that IGC initiated at certain grain boundaries and propagated to adjacent boundaries, even in the absence of elastic tensile deformation. Applying elastic tensile stress (260 MPa, ~46% σy) increased the defect density within the oxide film, thereby enhancing corrosion and anodic currents, and inducing river-like cracks. Although elastic tensile stress suppressed IGC, it simultaneously promoted stress corrosion cracking (SCC), as the stress exerted a stronger accelerating effect on corrosion than the grain-boundary did. Digital holography allowed in situ monitoring of the stress corrosion process in Alloy 625, demonstrating that cracks initiated via localized corrosion/IGC and subsequently propagated along the direction of the applied stress. Full article

Thermal spray technologies are widely used in aerospace, gas turbine, and automotive industries, where nickel-based superalloys are valued for their mechanical strength and resistance to oxidation and corrosion at elevated temperatures. This study investigates the microstructure and tribological performance of Ni–5Al/Inconel 625 composite coatings deposited on AISI 1025 steel using wire arc spraying, aiming to provide a cost-effective alternative to bulk superalloys and more advanced thermal spray techniques. Microstructural characterization was performed using optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, while surface roughness, microhardness, and dry sliding wear behavior were evaluated using ball-on-disk tests against Al₂O₃ counter-bodies. Confocal microscopy and three-dimensional triboscopic imaging were employed to analyze wear-track morphology and friction behavior. X-ray diffraction (XRD) analysis confirmed the presence of a predominantly intermetallic Ni₃Al (γ′) phase with secondary NiAl in the bond coat, indicating significant interdiffusion between the NiAl bond coat and the Inconel 625 top coat. The top coat exhibited a face-centered cubic (FCC) γ Ni-based solid solution. The coatings exhibited a typical lamellar structure with low porosity (2%–3%) and oxide content of 12%–15%, primarily chromium and niobium oxides located at splat boundaries. Abrasion, combined with interlamellar decohesion, was identified as the dominant wear mechanism. Post-deposition polishing reduced surface roughness from 11.9 µm to 2.12 µm, leading to a 2.5-fold reduction in wear volume and a significant decrease in debris pile-up. The corresponding specific wear rates were approximately 9.3 × 10⁻⁵ mm³/Nm and 3 × 10⁻⁵ mm³/Nm for the as-prepared and polished conditions, respectively, which are within the range reported in the literature for similar coatings. These findings demonstrate that wire arc-sprayed Ni–5Al/Inconel 625 coatings, particularly after polishing, offer improved wear resistance while maintaining cost-effectiveness, making them a promising alternative for tribological applications. Full article

Perfluorosulfonic acid (PFSA) membranes are a key component in many applications, but their low dimensional stability and mechanical strength can result in unsatisfactory device performance and a short life span. To effectively and economically mitigate these limitations with the lowest possible sacrifice of desirable properties, we report herein a PFSA membrane reinforced with a low-cost and easily available polyethylene (PE) mesh fabricated using a simple solution casting method. The high-strength and non-swellable mesh embedded in the PFSA matrix restricts its free swelling. As a result, the reinforced membrane shows a remarkably enhanced dimensional stability, lowering the areal swelling ratio to ~8% in water at 100 °C, in contrast to the ~58% of the unreinforced solution-cast membrane and ~44% of the melt-extruded commercial N117 membrane. Although the non-conductive PE mesh poses certain hindrances to proton transport, the reinforced membranes maintain ~94% of the proton conductivity of the pure PFSA membrane. Moreover, the mechanical strength of the reinforced membrane is enhanced to nearly three times that of the unreinforced one, reaching ~44 MPa. The incorporation of the PE mesh also leads to an enhanced resistance to oxidative corrosion and H₂ gas crossover of the membrane. This research demonstrates a promising technological pathway for developing high-performance and cost-competitive PFSA membranes. Full article