To improve Superni-718's oxidation resistance at high temperatures, a nanostructured Cr/CoAlTa/YSZ multilayer coating was deposited by magnetron sputtering. The effects of substrate deposition temperatures (100°C, 150°C, and 200°C) on the coating microstructure, phase stability, and oxidation kinetics were systematically evaluated under cyclic oxidation for 100 cycles at 900°C in air. Post-exposure characterization examined the development of thermally grown oxide (TGO), phase constitution, and microstructural degradation mechanisms. Oxidation behavior was governed by the formation of an adherent, continuous Cr 2 O 3 scale, which was strengthened by spinel oxides that effectively prevented oxygen infiltration and metal-ion transport. Yttria-stabilized zirconia (YSZ) helped preserve microstructural integrity by limiting phase change and crack development during heat cycling. In coatings deposited at 200°C, a finer nanostructure, lower defect density, and better oxidation resistance were associated with a dense, slow-growing TGO layer with improved adhesion. Increased adatom mobility during deposition likely contributed to improved coating densification and reduced defect density. The observed oxidation behavior is consistent with reduced oxygen transport through the coating and the beneficial influence of reactive elements reported in previous studies.
GH4169 Ni-based superalloy is widely used in high-end equipment, and as to improve the quality of its laser-cladded layer, GH4169 laser-cladded coatings require simultaneous control of clad macromorphology and microstructure. However, previous parameter optimizations have generally treated microstructural features as post-process observations rather than direct optimization objectives. In the present study, the equiaxed grain diameter, columnar dendrite spacing and Laves phase content were incorporated, together with cladding width, cladding height and dilution ratio, as six direct responses in an L16 Taguchi-grey relational framework. The results establish a relationship among process parameters and microstructural evolution. Within the investigated parameter range, increasing specific energy reduced the cooling rate and prolonged molten-pool solidification, resulting in coarser equiaxed grains, wider columnar dendrite spacing and a higher Laves phase content. Increasing the powder feeding rate reduced the effective energy delivered to the molten pool and refined these microstructural features. The optimized parameters of 500 W, 10 mm/s and 9.2 g/min increased the width-to-height ratio by 15.37%, while decreasing the Laves phase content from 3.11% to 2.94%, the equiaxed grain diameter from 4.71 μm to 4.61 μm and the columnar dendrite spacing from 5.17 μm to 4.99 μm. The relative error between the predicted and experimental grey relational grades was 2.17%. The novelty of this work lies in the direct, coupled optimization of coating geometry and quantitative solidification microstructure rather than geometry alone.
In response to the escalating demand for functional surfaces in marine applications and aerospace, this study investigates the precision fabrication of microstructured surfaces on TC6 using structured diamond grit tools. A novel kinematic model is developed to reveal the formation mechanisms of microstructures, integrating numerical simulations and experimental validation to optimize critical cutting parameters. The simulations reveal that increasing the tool-workpiece speed ratio enhances periodicity and reduces the overlapping effects of microstructures. Controlled feed speeds (20–100 rpm) ensure uniform separation distances between microstructures. Experimental results demonstrate that the distribution of microstructures is determined by the interplay between speed ratio ( v s / v w ) and feed speed ( f ). And their topographies are dominated by the dynamic morphology of the diamond grit. Notably, the proposed methodology contributed to the fabrication of microstructured arrays with controlled depths (7–15 μm) and good consistency. This work deepens the understanding of the distribution of microstructures and provides a scalable solution for fabricating arrayed structured surfaces.
Hot corrosion caused by vanadium- and sulfate-containing molten deposits is a major degradation mechanism of yttria-stabilized zirconia thermal barrier coatings (YSZ-TBCs) in gas-turbine environments. In this study, water-based nitrate precursor treatments were applied to YSZ-TBC-coated Inconel 738LC substrates using a flame-assisted spray process under burner-rig conditions. An Al-based precursor system (Water AN2) was evaluated under both static V 2 O 5 exposure and cyclic simulated hot-corrosion environments. Exposure to molten V 2 O 5 at 1000 °C for 10 h caused severe delamination of the as-received YSZ-TBC specimen, whereas the Water AN2-treated specimen maintained coating integrity. During cyclic hot-corrosion testing using a V 2 O 5 –Na 2 SO 4 –NiSO 4 corrosive solution, the precursor-treated specimen exhibited delayed degradation, smaller mass variation, and reduced growth of needle-like corrosion products. SEM observations revealed substantially reduced corrosion-product density and crystal growth on the precursor-treated surface, while EDS analysis confirmed the formation of vanadate-related corrosion products under the test conditions. In addition, stable spray operation was maintained throughout the treatment process without nozzle clogging. The results demonstrate that water-based nitrate precursor treatment delays degradation and suppresses corrosion-product growth in YSZ-TBC systems exposed to severe vanadate hot-corrosion environments. The approach requires no modification of the underlying coating architecture and provides a practical route for improving coating durability in gas-turbine applications.
Friction surfacing as a promising coating technology in solid-state method enables the development of defect-free, metallurgically bonded coatings for dissimilar material combinations. This study investigates the influence of engineered knurled surface topographies (L10, S10, R12, R20, L22, S24) on the interfacial bonding, microstructural evolution, and performance of AA6061 T6 coatings deposited on IS2062 steel. Push-off testing revealed a maximum bonding strength of similar to 15.4 kN for the R20 pattern, indicating optimal mechanical interlocking and heat generation, whereas coarse and fine patterns exhibited comparatively lower strengths of 10.8-13.3 kN. Microstructural characterization using SEM and FESEM confirmed dense, defect-free coatings with refined grains due to dynamic recrystallization, while EDX analysis indicated similar to 63 wt.% Al and similar to 32 wt.% Fe with a thin diffusion layer. XRD confirms stable FCC-Al and BCC-Fe phases with suppressed brittle intermetallics, ensuring a structurally sound coating. AFM analysis revealed a uniform nanoscale morphology with similar to 86 nm height variation. A graded microhardness profile with peak strengthening at the interface was observed. Corrosion studies demonstrated enhanced performance with higher polarization resistance (42.21 k Omega) and protective passive behavior. Overall, optimized knurled topography significantly enhances coating integrity and functional performance.
Thermal spray coatings have been identified as a potential method for improving the electrochemical performance of energy storage devices, such as batteries, supercapacitors, and fuel cells. This survey presents a synthesis of recent investigations into the use of thermal spray coating in such devices, and also points out the development of coating materials, deposition methods, and microstructural manipulation. Metal alloys with nickel-cobalt-chromium have been used as electrode materials with very high specific capacitances, cycling stabilities, and energy/power density values having been recorded. The dielectric properties, chemical stability, and capacity maintenance of ceramics, such as Al 2 O 3 , TiO 2 , and ZrO 2 , have also shown better results when used in batteries. Carbon-based electrodes in spray-coated form, such as multiwalled carbon nanotubes and graphene aerogels, have demonstrated high power and long-term durability in supercapacitors. The rationalization of the thickness of the coating, porosity, and interfacial adhesion process plays an instrumental role in determining the desired electrochemical properties. Nevertheless, it is not without its difficulties in terms of managing microstructural defects, the uniformity of coatings, and their industrial scaling up. Future plans include developing advanced coating materials, novel spray technologies, and modeling systems to circumvent present-day constraints and explore the potential of thermal spray coatings in next-generation energy storage devices. Further investigation of thermal spray coatings presents possibilities for energy-saving, high-performance, durable, and sustainable energy storage applications in the future.
Copper plating technology is of great importance in the electronics industry, especially in printed circuit board (PCB) and integrated circuit manufacturing. As the market demand for high-performance, highly integrated electronic devices continues to grow, electroplating copper processes are confronted with a series of technical challenges. This paper systematically reviews the classification, functional characteristics and action mechanisms of inhibitors, accelerators and levelers during the electrodeposition process. It focuses on analyzing the individual mechanisms of key additives such as polyethylene glycol (PEG), bis(3-sulfopropyl) disulfide (SPS) and chloride ions (Cl − ) in optimizing the coating structure by regulating interfacial adsorption configuration, inducing preferred crystal orientation and refining grain size. On this basis, the synergistic interaction mechanisms of additives in the PEG-Cl − -SPS ternary system and other multi-component systems are discussed in depth, revealing how dynamic competitive adsorption and alternating “inhibition-acceleration” structures synergistically regulate the microstructural evolution of copper deposition. Finally, from the perspective of structural optimization, the breakthrough directions of superfilling technology, the design strategies of novel polymeric additives and the future development trends of intelligent regulation of process parameters are summarized, aiming to provide theoretical basis and technical support for the further optimization of copper electroplating technology.
Bioinspired wettability surfaces have attracted significant attention for applications in directional droplet transport, condensation-water harvesting, and thermal management. In this study, a simple and low-cost sticker-assisted masking technique was developed to fabricate dual-wettability patterned copper surfaces through selective stearic acid (SA) functionalization. This lithography-free approach enabled the formation of patterned hydrophobic and hydrophilic regions on a single copper substrate. FE-SEM analysis revealed clear morphological differences between the functionalized and non-functionalized regions; while image-based surface roughness analysis performed using Gwyddion software (version 2.71) demonstrated that the hydrophobic region possessed approximately two-fold higher roughness than hydrophilic region, confirming the formation of a hierarchical surface morphology. EDS and ATR-FTIR analyses verified successful SA functionalization through increased carbon content and characteristic CH 2 , C=O, and C–O absorption bands. Static water contact angle measurements yielded contact angles of 85°, 99°, and 72° for the hydrophilic, hydrophobic, and dual-patterned surfaces, respectively, confirming the successful development of a wettability contrast. The observed wettability behavior was attributed to the combined effects of surface-energy chemistry, copper oxide formation, and hierarchical surface morphology. The fabricated dual-wettability surfaces exhibited favorable droplet interaction characteristics, demonstrating their potential for condensation water enhancement, and heat transfer applications. Overall, the proposed fabrication strategy offers a facile, scalable, and cost-effective route for developing bioinspired, dual-wettability copper surfaces for advanced surface engineering applications.
The CoCrFeMnNi multi-principal element alloy (MPEA), renowned for exceptional mechanical, thermal and corrosion properties, presents challenges in cost-effective deposition. This work demonstrates a dilution-engineered Gas Tungsten Arc Welding (GTAW) in-situ alloying approach using commercially available feedstock (SS304 filler tube + elemental powders). A two-stage strategy was employed includes (1) full-factorial experimental design identifying critical heat input (H.I.(c) approximate to 784 J/mm) and critical dilution (D-c approximate to 23 at% Fe) and (2) powder volume (P-v) variation (20-60%) to achieve equiatomic composition. Results reveal equiatomic CoCrFeMnNi (20 at% each) achieved at optimized condition of 120 A, 100 mm/min, 30% P-v, with dominant single-phase FCC microstructure, grain refinement (30.6 +/- 9.1 & micro;m), and enhanced corrosion resistance (E-corr = -0.34 V vs. -0.51 V for vacuum arc-melted reference). The absence of intermetallic compounds in the micro-hardness survey across interface and superior metallurgical bonding (ASTM-E290 bend test >90 degrees without de-lamination) demonstrate the viability of commercially feasible in-situ alloying for GTAW-based MPEA coatings.
Cold spray is a solid-state coating and repair technology that limits melting-related oxidation and grain coarsening; however, as-sprayed deposits can contain residual porosity, high residual stresses, and weak interparticle interfaces that restrict mechanical reliability. This review surveys post-spray heat treatment (PSHT) routes reported for cold-sprayed coatings, with primary emphasis on annealing/ageing and induction-based heating, while more limited HIP-related evidence is discussed where relevant. PSHT strengthens deposits primarily through diffusion-assisted consolidation, pore closure, and recovery/recrystallization that convert mechanically interlocked contacts into more continuous metallurgical bonds. Reported outcomes include higher interparticle/adhesive strength, improved tensile strength–ductility balance, tailored hardness (system-dependent), and enhanced fatigue and wear resistance; in some alloys, atmosphere control during PSHT plays an important role in governing interfacial stability and overall coating integrity. The evidence shows strong material dependence: precipitation-hardenable aluminum alloys benefit from moderate ageing schedules, whereas titanium alloys require higher-temperature treatments to maximize strength–ductility synergy but may soften due to loss of cold-work. Excessive temperatures or air exposure can trigger oxidation, intermetallic formation, and grain coarsening, underscoring the need for system-specific process windows. Key gaps include standardized reporting and long-term durability data under combined corrosion–thermal cycling–fatigue loading, and multivariate optimization linking spray conditions with PSHT.
Titanium alloys are extensively utilised in orthopaedic and dental implants; however, concerns related to corrosion-induced ion release and implant-associated infections necessitate advanced surface engineering strategies. In this investigation, micro-arc oxidation (MAO) was employed to fabricate bioactive oxide coatings on Ti6Al7Nb alloy, followed by addition of silver nanoparticles (AgNPs) to impart antibacterial functionality. The performance of MAO-coated Ti6Al7Nb was systematically compared with Ti6Al4V ELI under identical processing conditions. Surface characterization revealed a porous TiO 2 -based coating composed of anatase and rutile phases with uniformly incorporated Ca and P. Electrochemical impedance spectroscopy demonstrated a bilayer coating structure, having porous outside layer and a dense inside barrier layer responsible for superior corrosion resistance. The inner layer resistance of Ti–6Al–7Nb (97,980 Ω.cm 2 ) exceeded that of Ti–6Al–4V ELI, indicating enhanced electrochemical stability, likely associated with the presence of niobium oxide. Biocompatibility assessment using MTT assay showed that MAO-coated Ti–6Al–7Nb achieved the highest average cell viability (94.53%), significantly exceeding the ISO 10993-5 threshold of 70% and outperforming uncoated counterparts. Incorporation of AgNPs resulted in stronger antibacterial performance verses S. aureus and E. coli, having a maximum inhibition zone of 16.5 millimetre at 1.5 g/L silver nanoparticles concentration. The antibacterial effect was concentration-dependent and attributed to membrane disruption and sustained Ag + ion release. Overall, the combined improvements in corrosion resistance, cytocompatibility, and antibacterial performance demonstrate that AgNP-incorporated MAO-coated Ti6Al7Nb is a highly promising candidate for next-generation implants requiring long-term stability and infection resistance.
In recent decades, there has been considerable interest in the production of biodegradable biomaterials derived from magnesium (Mg). Although Mg is prone to corrosion, its favorable properties—such as less density and excellent biocompatibility—have driven substantial research in this area. To enhance both the resistance to corrosion and biocompatibility, electrophoretic deposition (EPD) has been studied as an effective surface modification technique. This review offers a comprehensive examination of EPD coatings applied to alloys of Mg, incorporating various bioactive reinforcements. Additionally, it addresses the challenges faced by Mg-based alloys and explores potential directions for future research.
M50 steel is a critical material in aerospace bearing systems owing to its high strength and fatigue resistance. Nevertheless, it remains highly susceptible to surface degradation under extreme operational conditions involving flash temperatures above 800°C and contact stresses exceeding 4 GPa. Conventional surface treatments are frequently limited by inadequate modification depth and low thermal stability. Plasma immersion ion implantation (PIII) has recently arisen as a promising technology to overcome these challenges. High-dose nitrogen implantation promotes the formation of nitride layers through CrN precipitation and dislocation pinning, resulting in achieving a remarkable nanohardness increase to 16.3 GPa. Similarly, gradient carbon implantation fosters architectured carbide coatings that reduce abrasive wear rates. Recent advances in process control, particularly through machine learning-assisted regulation and Langmuir probe diagnostics, have further enhanced implantation uniformity to over 98.7%, thereby extending full-scale bearing fatigue life. Despite these promising developments, critical challenges remain in understanding the multiphysics interactions during extreme surface damage and in optimizing the mechanical performance under combined thermo-mechanical loads. This review provides a systematic assessment of recent progress in PIII technologies for M50 steel and identifies the major scientific and technical gaps that remain unresolved. By summarizing current limitations and emerging research directions, it outlines potential pathways for advancing surface engineering strategies that could facilitate the transition from laboratory studies to practical application.
Marine biofouling remains a persistent challenge affecting the durability, efficiency and operational cost of marine structures and vessels. Conventional antifouling coatings, although effective, they are limited due to several factors, including toxicity, environmental persistence and regulatory restrictions. In this context, chitosan (CHT) and CHT-based nanocomposites have now intruded into various applications, satisfying multi-faceted requisites. What started from a humble beginning of marine shell waste transformed to chitin, transpired to CHT and diversified to multiple CHT derivatives and nanocomposites. The CHT-based coatings hold promise as eco-friendly alternatives due to their biodegradability, biocompatibility and inherent antimicrobial properties. Hence, the present review aimed to consolidate the various existing CHT based nanocomposites, and evaluated their antifouling and antibacterial efficiencies. Among the CHT-based nanocomposites, ZnO-CHT systems have demonstrated efficient antifouling with relatively lower toxicity, making them one of the most efficient and sustainable antifouling systems. In addition to the antifouling performance, the mechanisms behind the antifouling activity of the CHT-based nanocomposites were also discussed. The future recommendations based on the current challenges faced have been summarised. By consolidating the current knowledge on antifouling application of CHT-based nanocomposites, this review addresses existing knowledge gaps and provides comprehensive information and insights for future research and developments.
