Coated

Coated refers to a material or object to which a layer, typically thin, of another substance has been applied to its surface. The purpose of a coating is to alter surface properties such as hardness, wear resistance, corrosion resistance, appearance, or biocompatibility without changing the bulk of the substrate.

Coatings can be protective, functional, or decorative. Protective coatings reduce environmental damage; functional coatings impart electrical conductivity, hydrophobicity, or anti-reflective properties; decorative coatings improve color and gloss while providing some protection. Common coating classes include metallic coatings (nickel, chromium, zinc), ceramic coatings (alumina, zirconia), polymer coatings (epoxy, polyurethane, fluoropolymer), and composite/multilayer systems.

Coatings are applied by various methods depending on substrate and required properties. Techniques include electroplating and electrodeposition, galvanizing, anodizing; deposition methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and atomic layer deposition (ALD); and liquid-based processes like spray coating, dip coating, and brush coating. Thickness ranges from a few nanometers to several millimeters.

Performance depends on adhesion between coating and substrate, coating thickness, and environmental exposure. Key properties include hardness, wear and corrosion resistance, thermal stability, optical or electrical characteristics, and biocompatibility. Testing often involves adhesion tests, scratch tests, corrosion tests (salt spray), and non-destructive thickness measurements. Standards such as ASTM and ISO provide methods for qualification and quality control.

Coating challenges include poor adhesion, cracking, porosity, or delamination. Substrate shape, temperature limits, and chemical compatibility influence selection. Environmental concerns focus on solvents and worker exposure, driving preference for waterborne or powder coatings in some sectors.

Coatings are integral to industries ranging from automotive and aerospace to electronics, medical devices, energy, and consumer goods, where they extend service life, enhance performance, and enable new functionalities.