Search Results (281)

Tribological processes in extreme environments pose serious material challenges, requiring coatings that resist both wear and corrosion. This review summarizes recent advances in protective coatings engineered for extreme environments such as high temperatures, chemically aggressive media, and high-pressure and abrasive domains, as well as cryogenic and space applications. A comprehensive overview of promising coating materials is provided, including ceramic-based coatings, metallic and alloy coatings, and polymer and composite systems, as well as nanostructured and multilayered architectures. These materials are deployed using advanced coating technologies such as thermal spraying (plasma spray, high-velocity oxygen fuel (HVOF), and cold spray), chemical and physical vapor deposition (CVD and PVD), electrochemical methods (electrodeposition), additive manufacturing, and in situ coating approaches. Key degradation mechanisms such as adhesive and abrasive wear, oxidation, hot corrosion, stress corrosion cracking, and tribocorrosion are examined with coating performance. The review also explores application-specific needs in aerospace, marine, energy, biomedical, and mining sectors operating in aggressive physiological environments. Emerging trends in the field are highlighted, including self-healing and smart coatings, environmentally friendly coating technologies, functionally graded and nanostructured coatings, and the integration of machine learning in coating design and optimization. Finally, the review addresses broader considerations such as scalability, cost-effectiveness, long-term durability, maintenance requirements, and environmental regulations. This comprehensive analysis aims to synthesize current knowledge while identifying future directions for innovation in protective coatings for extreme environments. Full article

Arsenic (As) and cadmium (Cd) in rice grains are major global food safety concerns. Iron (Fe) can help reduce both, but current Fe treatments suffer from poor stability, low leaf absorption, and fast soil immobilization, with unclear underlying mechanisms. To address these issues, an Fe-based metal–organic framework (MIL-88) was modified with sodium alginate (SA) to form MIL-88@SA. Its stability as a foliar inhibitor and its leaf absorption were tested, and its effects on As and Cd accumulation in rice were compared with those of soluble Fe (FeCl₃) and chelating Fe (HA + FeCl₃) in a field study on As–Cd co-contaminated rice paddies. Compared with the control, MIL-88@SA outperformed or matched the other Fe treatments. A single foliar spray during the tillering stage increased the rice yield by 19% and reduced the inorganic As and Cd content in the grains by 22.8% and 67.8%, respectively, while the other Fe treatments required two sprays. Its superior performance was attributed to better leaf affinity and thermal stability. Laser ablation inductively coupled plasma–mass spectrometry (LA–ICP–MS) and confocal laser scanning microscopy (CLSM) analyses revealed that Fe improved photosynthesis and alleviated As–Cd stress in leaves, MIL-88@SA promoted As and Cd redistribution, and Fe–Cd co-accumulation in leaf veins enhanced Cd retention in leaves. Full article

Thickness inspection of thermal barrier coatings is crucial to safeguard the reliability of high-temperature components of aero-engines, but traditional destructive inspection methods are difficult to meet the demand for rapid assessment in the field. In this study, a new non-destructive testing method integrating terahertz time-domain spectroscopy and machine learning algorithms is proposed to systematically study the thickness inspection of 8YSZ coatings prepared by two processes, namely atmospheric plasma spraying (APS) and electron beam physical vapor deposition (EB-PVD). By optimizing the preparation process parameters, 620 sets of specimens with thicknesses of 100–400 μm are prepared, and three types of characteristic parameters, namely, time delay Δt, frequency shift Δf, and energy decay η, are extracted by combining wavelet threshold denoising and time-frequency joint analysis. A CNN-RF cascade model is constructed to realize coating process classification, and an attention-LSTM and SVR weighted fusion model is developed for thickness regression prediction. The results show that the multimodal feature fusion reduces the root-mean-square error of thickness prediction to 8.9 μm, which further improves the accuracy over the single feature model. The classification accuracy reaches 96.8%, of which the feature importance of time delay Δt accounts for 62%. The hierarchical modeling strategy reduces the detection mean absolute error from 6.2 μm to 4.1 μm. the method provides a high-precision solution for intelligent quality assessment of thermal barrier coatings, which is of great significance in promoting the progress of intelligent manufacturing technology for high-end equipment. Full article

This work presents an exhaustive parametric study of the multi-scale residual stress analysis on arbitrary substrate geometry based on a one-way-coupled thermo-mechanical model in an Atmospheric Plasma Spray process. It was carried out by modifying key process parameters, such as substrate surface geometry, substrate pre-heating temperature, and coating thickness, in an Al₂O₃ coating process on an aluminium substrate. The relationship of these parameters to the generation of quenching stress, thermal stress and residual stress was analysed at three different sub-modelling scales, from the macroscopic dimension of the substrate to the microscopic dimension of the splats. The thermo-mechanical phenomena occurring during the deposition process at the microscopic level were discussed in the proposed cases. Understanding these phenomena helps to optimise the parameters of the coating process by identifying the underlying mechanisms responsible for the generation of residual stresses. The simulated residual stresses of the 200 μm Al₂O₃ outer coated aluminium cylinder were experimental validated using the incremental high-speed micro-hole drilling and milling method. Full article

Green soybeans, or edamame (Glycine max L. Merril), serve as a superior source of phytochemicals and other nutritive substances and are commonly used as ingredients and additives in food products due to their polyphenols’ functional properties and antioxidant activity. Hence, it is very important to use a process to extract compounds with functional roles from plants as efficiently as possible. In this study, we sought to identify the optimal conditions for extracting genistein, belonging to the aglycone subgroup of isoflavones, from edamame using the cold plasma (CP) and enzyme method. Additionally, the impact of various drying techniques (spray-drying and freeze-drying) and storage conditions on the crude genistein extract powder was evaluated. The findings showed that the maximum values for the total phenolic content (TPC), total flavonoid content (TFC), and genistein (22.5 ± 0.23 mg of gallic acid equivalents (GAE)/100 g; 15.3 ± 0.13 mg of catechin equivalents (CAE)/100 g; and 12.6 ± 0.10 mg/100 g, respectively) were achieved under optimal pretreatment conditions using a CP gas flow rate of 5 L/min for 30 min, followed by enzymatic treatment at a specific enzyme concentration of 2.0% (v/v) for 240 min of incubation. Moreover, a scanning electron microscopy (SEM) analysis demonstrated that the CP and enzyme treatment induced significant structural changes, as evidenced by the presence of deeper pores on the surface of the powder granules. Spray-drying demonstrated a superior efficacy compared to freeze-drying for encapsulating the crude isoflavone extract. This study’s results also demonstrated that storage at 4 °C significantly stabilized the TPC, TFC, and genistein content and the antioxidant activity while preserving the physical properties (solubility and color) of the crude extract powder for up to 45 days. In summary, cold plasma pretreatment and enzymatic treatments offer practical solutions by enhancing the efficiency of non-thermal extraction processes, thereby increasing the yield of bioactive compounds, maintaining quality, and diminishing reliance on traditional, harsh methods. The elevated genistein content in the crude extract powder indicates its prospective application as a functional ingredient in various food and nutraceutical contexts. Full article

Thermal spraying technique has potential in manufacturing economic, profitable thermoelectric coatings. In order to characterize the electrical performance of thermoelectric coatings more conveniently, a simple setup for thermoelectric power factor of thermoelectric coatings is designed and developed. The indigenously designed setup is simple and low-cost. The compact structure makes it easy to cooperate with existing heating furnace, allowing a fast measurement in a variable temperature range. The differential method and the off-axis four-point geometry are used in Seebeck coefficient and electrical resistivity measurement, respectively. The Spring-load unit and other details of construction of the setup are described specifically. The Seebeck coefficient of the plasma-sprayed higher manganese silicide (HMS) coating was measured to be approximately 132.35 μV/K at 150 °C, with measurements showing high linearity (R² > 0.99). The setup demonstrated reliable electrical resistivity results for Cr20Ni80 alloy, closely matching published values (1.16 × 10⁻⁶ Ω·m vs. 1.10 × 10⁻⁶ Ω·m). HMS coating was also characterized from 50 °C to 500 °C to validate the setup on thermoelectric performance characterization across a wide temperature range. These results confirm the reliability of the developed setup. Full article

The success of orthopedic implants critically depends on achieving mechanical and biological compatibility with bone tissue. Traditional titanium implants often suffer from high stiffness, which induces stress shielding, a phenomenon that compromises implant integration and accelerates prosthetic loosening. This study introduces an innovative approach to mitigate these limitations by engineering a porous titanium substrate with a controlled microstructure. Utilizing sodium chloride as a spacer holder, an elution and sintering process was applied at 1250 °C under high vacuum conditions to reduce the material’s elastic modulus. By manipulating NaCl volume fractions (20%, 25%, 30%, and 35%), porous titanium samples were created with elastic moduli between 16.37 and 22.56 GPa, closely matching cortical bone properties (4 to 20 GPa). A hydroxyapatite coating applied via plasma thermal spraying further enhanced osseointegration of the material. Comprehensive characterization through X-ray diffraction, scanning electron microscopy, and compression testing validated the material’s structural integrity. In vitro cytotoxicity assessments using osteoblast cells demonstrated exceptional cell viability exceeding 70%, confirming the material’s biocompatibility. These findings represent a significant advancement in biomaterial design, offering a promising strategy for developing next-generation joint prostheses with superior mechanical and biological adaptation to bone tissue. Full article

This paper presents a comprehensive analysis of recent advancements in the application of thermal spraying techniques to enhance the durability and wear resistance of agricultural machinery components, with a particular focus on disc harrow assemblies. Given the harsh conditions under which tillage tools operate—characterized by abrasive wear, impact stresses, and chemical exposure from various soil types—thermal sprayed coatings have emerged as a viable solution to extend the service life of these components. The study discusses various deposition methods, particularly Atmospheric Plasma Spraying (APS), and evaluates their effectiveness in creating high-performance surface layers that resist wear, corrosion, and mechanical degradation. The review also summarizes experimental and field test results for coatings based on materials such as NiCrBSi, WC-Co-Cr, TiO₂, Al₂O₃, Cr₂O_3, and ceramic–metal composites, highlighting their significant improvements in hardness, friction reduction, and resistance to delamination and oxidation. The paper highlights research using thermal spraying techniques, especially APS for agricultural applications, with emphasis mostly on components intended for soil processing and requiring good resistance to abrasive wear. Full article

The ongoing development of maritime powers has driven markedly growing requirements for novel naval and civilian vessel categories in recent years. The import temperature of gas turbines is rising, and the issue of corrosion can no longer be ignored, creating an urgent need to develop coatings with high-temperature resistance, corrosion resistance, and good toughness. This study utilized plasma spraying technology to prepare composite AT13 ceramic coatings with 0 wt.%, 5 wt.%, 10 wt.%, and 15 wt.% GO/Cu (GO:Cu = 1:10) content. It systematically investigated the effects of GO/Cu doping on the porosity, Vickers hardness, fracture toughness, thermal shock resistance, and corrosion resistance of the AT13 coatings while exploring the corrosion behavior of the composite coatings. The experimental results indicate that doping with GO/Cu can effectively fill the pores of the coatings, leading to an overall improvement in coating performance. The coating with 10 wt.% doping (G2) exhibited the best comprehensive performance, with a 72% reduction in porosity compared to the original coating, a 23.2% increase in Vickers hardness, a 31.4% enhancement in fracture toughness, and an 83% decrease in corrosion rate. It also demonstrated the best thermal shock resistance, maintaining a relatively intact surface after 31 days of immersion in artificial seawater, with only a few pitting and cracking defects observed in the areas of corrosion. Full article

Modern industrial systems and biomass-fired furnaces require surface treatments that can withstand aggressive chemical, thermal, and corrosive environments. This study investigates the corrosion and thermal resistance of plasma-sprayed Al₂O₃-TiO₂ coatings produced using a DC air–hydrogen plasma spray process. Coatings of compositions of Al₂O₃, Al₂O₃-3 wt.% TiO₂, Al₂O₃-13 wt.% TiO₂, and Al₂O₃-40 wt.% TiO₂ were deposited on steel substrates with a Ni/Cr bond layer by plasma spraying. The coatings were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) to evaluate their morphology, elemental composition, and crystalline phases. Electrochemical tests were performed in a naturally aerated 0.5 mol/L NaCl solution and cyclic thermal–chemical exposure tests (500 °C using 35% KCl) to assess their corrosion kinetics and thermal stability. The results indicate that pure Al₂O₃ and low TiO₂ (3 wt.%) coatings exhibit fine barrier properties, while coatings with a higher TiO₂ content develop additional phases (e.g., Ti₃O₅, Al₂TiO₅) that improve thermal resistance but reduce chemical durability. Full article

The Co-CuCoMnO_x coatings with varying proportions were prepared and investigated to develop a novel metal–ceramic solar selective absorption coating employed at high temperature. The CuCoMnO_x powders were synthesized using the solid-phase reaction method. Subsequently, Co-CuCoMnO_x coatings were deposited on the surface of 316L steels utilizing the atmospheric plasma spraying (APS) technique. The results showed that the synthesized CuCoMnO_x powders were mainly composed of two phases, which were Cu_1.5Mn_1.5O₄ and MnCo₂O₄. The CuCoMnO_x powders had a solar absorptance of 0.929 and an infrared emittance of 0.862, which was considered a good solar absorbent. The synthesized Co-CuCoMnO_x coating had a typical thermal spray layered stacking structure. The chemical phases of the coatings were mainly Co, CoO, and CoCuMnO_x. Due to the addition of CuCoMnO_x inhibiting the oxidation of Co during the thermal spraying process, the 95Co-5CuCoMnO_x (wt%) coating exhibited the optimal quality factor (α/ε) of 2.184, with a solar absorptance α of 0.808 and an infrared emittance ε of 0.370, respectively. Moreover, this specific coating demonstrated a good thermal stability for up to 3 h when exposed to an atmospheric environment at 450 °C. The results indicate its significant potential for high-temperature solar selective absorption coating. Full article

The selection of a suitable plasma-facing material (PFM) that must protect the divertor, cooling systems, and structural components is an important challenge in the design of advanced fusion reactors and requires careful consideration. Material degradation due to melting and evaporation may lead to plasma contamination, which must be strictly avoided. Among the candidate materials, tungsten (W) is the most promising because of its thermo-mechanical and physical properties, which allow it to endure repeated exposure to extremely harsh conditions within the reactor. The plasma spraying (PS) technique is gaining increasing interest for the deposition of tungsten (W) coatings to protect heat sink materials, due to its relatively low cost, high deposition rates, and capability to coat complex-shaped surfaces and fix damaged coatings in situ. This review aims to provide a systematic assessment of tungsten (W) coatings produced by PS techniques, evaluating their suitability as PFMs. It discusses W-based materials, plasma spraying technologies, the role of the interface in joining W coating and metallic substrates such as copper alloys and steels, and the main issues related to coating surface erosion under steady-state and transient heat loads associated with advanced fusion reactor operation modes and off-normal events. Quantitative data available in the literature, such as porosity, oxygen content, thermal conductivity of the coatings, residual stresses accumulated in the coating–substrate interface, surface temperature, and material loss following heat load events, were summarized and compared to bulk W ones. The results demonstrate that, following optimization of the fabrication process, PS-W coatings exhibit excellent performance. In addition, previously mentioned advantages of PS technology make PS-W coatings an attractive alternative for PFM fabrication. Full article

This work presents a new approach for the fabrication of 316L/Al₂O₃ composites, based on a combination of spray granulation, radio frequency (RF) plasma spheroidization and spark plasma sintering (SPS). Initially, a suspension containing 316L and alumina powders is formulated by precisely adjusting the pH and selecting an appropriate dispersant, thereby ensuring homogeneous dispersion of the constituents. The spray granulation process then produces granules with controlled size and morphology. RF plasma spheroidization, carried out using a TekSphero-40 system, is investigated by varying parameters such as the power, gas flow rates, injection position and feed rate, in order to optimize the formation of spherical and dense particles. The analysis reveals a marked sensitivity to heat transfer from the plasma to the particles, with a tendency for fine particles to segregate, which underscores the necessity for precise control of the processing conditions. Finally, SPS densification, performed under a constant pressure and a rigorously controlled thermal cycle, yields composites with excellent density and hardness characteristics. This study thus demonstrates that the proposed hybrid process offers an optimal synergy between a uniform distribution of alumina and a controlled microstructure, opening up promising avenues for the design of high-performance composite materials for demanding applications. Full article

The main purpose of this work is to suppress the rate of thermal and oxidative corrosion of copper substrates using double-ceramic-layer thermal barrier coatings (TBCs). Herein, the orthogonal spray experiment was employed to optimize the spraying parameters for TBCs consisting of Cu/NiCoCrAlY/8YSZ/(Y_0.5Gd_0.5)TaO₄. The thermal cycling and average mass loss rate of TBCs prepared by atmospheric plasma spraying (APS) with optimum spraying parameters correspond to 20 cycles and 0.56‰, respectively. The thermal conductivity (0.39 W·m⁻¹·K⁻¹ at 900 °C) of (Y_0.5Gd_0.5)TaO₄ is 71.68% and 52.7% lower than that of (Y_0.5Gd_0.5)TaO₄ bulk and 8YSZ, respectively. Meanwhile, the bond strength increased from 8.86 MPa to 14.03 MPa as the heat treatment time increased from 0 h to 24 h, benefiting from the heat treatment to release the residual stresses inside the coating. Additionally, the hardness increased from 5.88 ± 0.56 GPa to 7.9 ± 0.64 GPa as the heat treatment temperature increased from room temperature to 1000 °C, resulting from the healing of pores and increased densification. Lastly, crack growth driven by thermal stress mismatch accumulated during thermal cycling is the main cause of coating failure. The above results demonstrated that 8YSZ/(Y_0.5Gd_0.5)TaO₄ can increase the service span of copper substrate. Full article

Plasma spray coating employs a high-temperature plasma jet to melt and deposit powdered materials onto substrates and plays a critical role in aerospace and manufacturing. Despite its importance, the influence of torch behavior, particularly the thermal response of plasma to gas composition changes, remains inadequately characterized. In this study, a three-dimensional MHD simulation using OpenFOAM (v2112) was performed on a Metco 9MB plasma torch operating in an Ar–H₂–N₂ environment under the LTE assumption to investigate the effect of nitrogen addition. The simulation revealed that increasing nitrogen levels results in a dual effect on the temperature distribution: temperatures rise near the cathode tip and decrease downstream, likely due to variations in the net emission coefficient and enthalpy characteristics of nitrogen. Furthermore, although the outlet velocity remained largely unaffected, the Mach number increased as the nitrogen reduced the speed of sound. These findings provide essential insights for optimizing ternary gas mixtures to enhance coating efficiency in thermal spray applications. Full article