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Thermal spray coatings are a group of industrial processes used to apply metallic or non-metallic coatings to a substrate. These coatings improve the surface properties of a component, such as wear resistance, corrosion protection, or electrical insulation. The general principle involves heating coating materials to a molten or semi-molten state and then accelerating them towards the substrate using a high-velocity gas stream. Upon impact, the particles flatten, cool, and solidify, building up a cohesive coating layer by layer.

Several distinct thermal spray techniques exist, each differing in the method of heating and accelerating the coating material. Flame spraying uses a combustion flame to melt and propel the coating material, often in powder or wire form. Arc spraying utilizes an electric arc between two consumable electrodes made of the coating material to melt it, with compressed air then atomizing and accelerating the molten droplets. Plasma spraying employs an electric arc through a gas (plasma) to generate extremely high temperatures, capable of melting and propelling a wide range of materials, including ceramics. High-velocity oxygen fuel (HVOF) spraying uses the combustion of fuel and oxygen to generate a high-velocity, high-temperature gas stream that propels molten or semi-molten particles. Detonation gun spraying (also known as D-gun spraying) uses controlled explosions to accelerate molten particles at very high velocities.

The choice of technique depends on factors such as the material to be sprayed, the desired coating properties, the substrate material, and economic considerations. Each method offers unique advantages in terms of particle velocity, temperature, deposit efficiency, and the types of materials that can be applied.