Selecting the wrong thermal spray feedstock can be a costly mistake leading to premature coating failure. Below is a simple overview of commonly used materials and their applications.
Tungsten Carbide for Wear Resistance
Tungsten carbide, a very hard abrasive feedstock, is typically used for applications suffering from hard wear or sliding. Such an application may be the wear bearing surfaces of the shafts of pumps or the wearing surfaces of the rolls of paper or other materials. Also, the wearing surfaces of tooling can be restored to like new condition. Typically, these coatings are applied by HVOF to produce a dense, low-porosity coating with high hardness. The hardness of such a coating is far in excess of that of any steel and thus is well suited to applications where wear resistance is the primary function of the coating.
Aluminium Oxide for Electrical Isolation
Aluminium oxide is the principal component of a number of different feedstocks designed for wear resistance as well as for electrical isolation. As a hard ceramic it is suitable for applications requiring a wear resistant coating that is non-conductive such as insulating rails and bushings for electrical equipment. It can also be used for components exposed to moderate levels of heat but is not recommended for high thermal cycling applications.
MCrAlY Alloys for Thermal Barriers
The MCrAlY materials are commonly used as bond coats underneath the ceramic thermal barrier coating that is used to protect parts such as the surfaces of turbine blades, exhaust components, and combustion parts which are subjected to prolonged high temperature. Information on the materials selection is given by the Institute of Materials, Minerals and Mining. See also Thermal Sprays.
Copper-Based Materials for Conductivity
Copper and its alloys can be thermally sprayed for applications where it is necessary to restore or enhance a component’s electrical or thermal conductivity. Applications for thermally sprayed copper include the repair of buss bars, and the refurbishment of heat sinks.
Zinc and Aluminium Wire for Corrosion Protection
Spraying with Zinc or Aluminium wire, the coating will act in a sacrificial manner to protect the substrate from corrosion, thus structural steelwork, bridges, and components for offshore use can be coating protected to be maintenance free for long periods.
Matching material to application at the brief stage saves a lot of rework.