Thermal Spray Coating Technologies
Thermal Spray Coatings are produced by projecting a molten stream of particles onto the base material. On impact these particles deform and solidify to form splats, and these splats mechanically lock onto the surface. There are numerous ways of generating the stream of molten particles using an electric-arc, plasma or a combustion process.
Depending on the process it is possible to procuce coatings of pure metals, alloys, ceramics and ceramic metal composites (cermets), and coating thickness generally varies between 0.1 and 2.0 mm. The adhesion and cohesion of a thermal spray coating is purely mechanical, which has certain advantages and disadvantages.
The main advantage is that there is no metallurgical compatability issue between the substrate and the coating, and it is therefore possible to apply a wide variety of coating materials onto essentially any substrate (e.g. bronze and cast-iron). The heat input into the base materials is also limited, and it is therefore possible to apply a thermal spray coating to a heat-sensitive substrate (e.g. heat-treated HSLA steels like 4140 and martensitic stainless steel) with no risk of softening or distortion. The main disadvantage is that the adhesive and cohesive strength of a thermal spray coating is relatively low, making coatings susceptible to damage from high mechanical loads (such as point or impact loads), cyclical loads or thermal stresses.
High Velocity oxy-fuel (HVOF) uses high-pressure combustion as the heat source to create a high-velocity gas stream that both melts and propels a powder feedstock material to the substrate. HVOF coatings generally exhibit fine homogeneous microstructures, low in oxide and porosity content, that are tenaciously bonded to the substrate.
Plasma spray uses an electric-arc ionised process gases containing argon and/or helium/hydrogen to produce a very hot gas stream to melt a very wide range of powder feedstock materials to apply high-quality coatings of metals, metallic alloys, carbides, cermets and oxide ceramics.
Combustion Powder and Wire
Combustion spray uses the combustion of a fuel gas and oxy gen to create a heat source, but at lower pressures than HVOF. Combustion spray is an economical choice for the application of quality coatings.
Combustion Powder Spray uses metals, metallic alloys or fine ceramics as the feed stock material in powder form.
Combustion Wire Spray uses metals or metallic alloys as the feedstock material in wire form. It is often used for the application of hard coatings for salvage and restoration and is well-known for the application of corrosion coatings, even on very large structures.
Electric arc wire spray uses two electrically charged feedstock wires, of opposite polarity, that are brought together at a controlled rate to form an arc. This arc melts the wire feedstock and an air stream propels the molten material to the substrate. Electric arc wire is commonly used to apply bond coat materials, salvage and restoration coatings and a wide range of corrosion coatings on large structures. As the coolest of all thermal spray processes, it can be used to coat many substrates, including metals and plastics.