La proyección térmica es una técnica utilizada en la fabricación de componentes que consiste en proyectar pequeñas partículas fundidas, semifundidas, calientes e incluso frías (cold spray) que se unen suscesivamente a una superficie. El objetivo es proveer un tratamiento superficial a las piezas que van a estar sometidas a condiciones extremas de rozamiento, desgaste, calor y/o esfuerzos mecánicos. Su uso es muy habitual en diferentes componentes de la industria del automóvil (válvulas), aeronáutica (motores de turbina), turbinas de gas (álabes), imprenta (cilindros) y medicina (implantes). En algunos países de Latinoamérica la proyección térmica es conocida como termorrociado siendo este termino una traducción literal del nombre de la tecnología en inglés thermal spray.

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Thermal spraying techniques are coating processes in which melted (or heated) materials are sprayed onto a surface. The "feedstock" (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame). Thermal spraying can provide thick coatings (approx. thickness range is 20 micrometers to several mm, depending on the process and feedstock), over a large area at high deposition rate as compared to other coating processes such as electroplating, physical and chemical vapor deposition. Coating materials available for thermal spraying include metals, alloys, ceramics, plastics and composites. They are fed in powder or wire form, heated to a molten or semimolten state and accelerated towards substrates in the form of micrometer-size particles. Combustion or electrical arc discharge is usually used as the source of energy for thermal spraying. Resulting coatings are made by the accumulation of numerous sprayed particles. The surface may not heat up significantly, allowing the coating of flammable substances. Coating quality is usually assessed by measuring its porosity, oxide content, macro and micro-hardness, bond strength and surface roughness. Generally, the coating quality increases with increasing particle velocities. Several variations of thermal spraying are distinguished: \n* Plasma spraying \n* Detonation spraying \n* Wire arc spraying \n* Flame spraying \n* High velocity oxy-fuel coating spraying (HVOF) \n* High velocity air fuel (HVAF) \n* Warm spraying \n* Cold spraying In classical (developed between 1910 and 1920) but still widely used processes such as flame spraying and wire arc spraying, the particle velocities are generally low (< 150 m/s), and raw materials must be molten to be deposited. Plasma spraying, developed in the 1970s, usesa high-temperature plasma jet generated by arc dischargewith typical temperatures >15000 K, which makes itpossible to spray refractory materials such as oxides, molybdenum, etc.

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