In the wire arc spray method—also called the electric arc process—two consumable metal wires, connected to a high-current direct current (DC) power source, are fed into a spray gun. These wires meet inside the gun, forming an electric arc that melts their tips. The wires are driven by either an electric motor or an air motor. Once melted, the metal is broken into droplets and directed toward the surface to be coated using a stream of compressed air. Since the wires are melted directly by the arc itself, this process has significantly higher thermal efficiency than other thermal spray techniques.

The spray rate depends mainly on the electrical current used and is influenced by the material’s melting point and electrical conductivity. As the molten metal detaches from the wire tips, it breaks into small droplets, forming a fine spray. The same airflow used to atomize the molten metal also accelerates it toward the surface, where the particles flatten and solidify, gradually forming a coating.

Unlike flame or plasma spraying, where particles melt within a gas jet, in electric arc spraying the metal is already molten when it enters the air stream. The droplets begin cooling immediately after they leave the arc. To reduce oxidation, it’s essential to keep the spray distance short and use high air velocities for atomizing.

This process transfers the least amount of heat to the substrate among conventional thermal spray methods because there is no flame or plasma involved. Materials like copper- and iron-based alloys typically spray at a rate of 4.5 kg (10 lb) per 100 amps per hour, while zinc sprays at about 11 kg (25 lb) per 100 amps per hour. The substrate remains relatively cool since there’s no hot gas flow directed at it.

Electric arc spraying is limited to conductive materials that can be formed into wire. However, the development of cored wires—metal tubes filled with powdered material—has broadened the usable material range to include cermets and amorphous alloys. These core powders typically contain carbides or glassy (amorphous) metallic compounds.