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what is thermal spray?

Thermal Spray Process Diagram

Overview of Thermal Spray Process

Thermal spray is a group of coating processes in which melted (or heated) materials are sprayed onto a prepared surface. The coating material or "feedstock" is heated by electrical (plasma or arc) or chemical means (combustion flame).

Thermal spray coatings can be thick (thickness ranges from twenty microns to several millimeters).

Thermal Spray Coating materials for thermal spray: metals, alloys, ceramics, plastics, fed in powder or wire form, heated to a semi-molten state, and accelerated onto a substrate in the form of micrometer-size particles. Combustion or electrical arc are used as a source of energy for thermal spraying. Coatings are made by the buildup of many sprayed particles.

Thermal Spray Coating quality is assessed by measuring its porosity, oxide content, macro and micro-hardness, bond strength and surface roughness. The coating quality increases with increasing particle velocities.

Types of thermal spray:

  1. Plasma spray (APS)
  2. Detonation Gun
  3. Wire arc spraying
  4. Flame spray
  5. High velocity oxygen fuel (HVOF)
  6. High velocity air fuel (HVAF)
  7. Cold spray 

The original processes: flame spraying and wire arc spraying, the particle velocities are low (< 150 m/s), and raw materials must be molten to be deposited.

Plasma spraying, developed in the 1970s, uses a high-temperature plasma jet generated by arc discharge with typical temperatures >15000 K, which makes it possible to spray refractory materials such as ceramics, oxides, molybdenum, etc. 

HVAF and HVOF have gas velocities greater than the speed of sound and are best for Carbides.

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Definition of Thermal Spray: Thermal Spray is a Group of processes where a material (powder or wire form of carbide, metal, or ceramic) is heated (electric or combustion), atomized, and propelled on to a prepared substrate forming a coating. 

What is Thermal Spray Process Diagram

thermal spray process