Plasma-driven strategies for advanced composite coatings

Spanning ceramics to organics, composite coatings combine multiple phases to deliver tailored hardness, chemical stability, thermal resistance, and multifunctional performance beyond single-phase materials.Achieving these properties requires precise deposition methods, and plasma-assisted techniques have proven especially effective because of their ability to penetrate into intricate areas and complicated geometries.These include plasma spraying (Atmospheric, Vaccum and Solution Plasma Spraying -APS, VPS, SPS), plasma-enhanced chemical vapor deposition (PECVD), plasma-assisted PVD, plasma electrolytic oxidation (PEO), and plasma polymerization.By generating highly energetic reactive environments and enhancing precursor ionization, plasma processes improve coating density, microstructure, and interfacial bonding, enabling next-generation composite coatings for a wide range of engineering applications.Composite coatings can be applied to a variety of substrates, including metals, alloys, ceramics, polymers, and hybrid composites.Ensuring strong adhesion, uniform deposition, and optimal performance requires proper substrate preparation and plasma activation prior to coating. Carbon composite coatingsAmong the many types of composite coatings, carbon-based systems have attracted particular attention due to their combination of chemical inertness, high hardness, low friction, and large specific surface area.These characteristics make carbon composite coatings especially suitable for tribological applications and energy storage devices, making them an important focus in plasma-assisted coating research.Plasma spraying has been studied for the deposition of carbon-based composites, enabling the incorporation of diverse powders, including high-melting-point materials such as graphite, tungsten, silicon carbide, and titanium oxide, to produce coatings with tailored microstructure, enhanced surface performance, and functional properties for advanced industrial applications.For example, carbon-silicon-sulfur composite coatings have been deposited via APS from flake-like graphite powders at varying torch powers.Higher plasma temperatures reduced large surface particles, decreased roughness, and lowered oxidation, while increasing specific surface area, pore volume, and crystalline graphite content.Microhardness rose from 120 to 314 HV as power increased, attributed to enhanced crystallinity and splat bonding.Maximum elasticity was observed at 19.4 kW.These coatings are suitable for high-performance energy storage and tribological applications, where hardness, conductivity, and durability are critical.Similarly, the wear resistance of Ti6Al4V alloy has been improved via plasma-sprayed coatings of 70% Al mixed with varying Si and MWCNTs.MWCNTs enhance hightemperature performance, wear, and corrosion resistance.Optimized Al-Si-15% MWCNT coatings increase tensile strength (29.7%), hardness (8.2%), impact strength (41.7%), reduce wear (25.4%), and boost corrosion resistance (63.6%). 1 APS is used to produce composite coatings combining metal or cermet matrices with carbon-based solid lubricants.Incorporating carbon nanotubes (CNTs) as nano-additives enhances the overall coating performance by reducing wear, lowering friction, and improving lubrication in tribological systems like piston ring-cylinder liners.Pin-on-disk tests reveal that CNTs increase bonding strength by up to 33%, reduce wear rates by up to 80%, and decrease friction coefficients, demonstrating the effectiveness of CNT-reinforced composite coatings for high-performance, load-bearing applications.2 Another low-cost thermal plasma dissociation method enables in situ deposition of multiphase carbon coatings, including graphite, diamond-like carbon, lonsdaleite, and diamond, on SiC.Using a carbon-arc plasma in an argon medium, silicon is selectively removed through high temperatures and the chlorine-like corrosive effect of Ar ions.Fast plasma reaction kinetics, driven by ions, excited atoms, and molecules, promote simultaneous formation of carbon phases.The resulting coatings enhance hardness, reduce friction and improve sinterability.