The possibilities for modifying product surfaces are greater today than ever before but for precisely that reason manufacturers and artisans often need help choosing the best option. One of the most versatile methods is thermal plasma spraying, but even under this heading there are numerous methods and a multitude of possible materials that can be used. Choosing the best combination can help you reduce material costs while improving the durability, versatility and features of your product.
It is always sensible to talk to your plasma spray specialist for help in choosing the best method and coating. Some popular choices include tungsten carbide, molybdenum/alumina, chrome oxide and abradable coatings like aluminium/graphite and boron nitride. However, plasma spray specialists often develop their own coating ranges (such as Apticote 800) or will formulate a bespoke coating honed to your precise specifications. The following paragraphs broadly outline your options.
Useful metal coatings include blends and alloys of copper, nickel, aluminium, tin and molybdenum. The aim is often corrosion resistance or to achieve a dry low friction surface for things like piston rods, moving valves and shifter forks. It is important to remember that not all metals are compatible with each other (mostly because of galvanic reactions, see https://www.engineersedge.com/galvanic_capatability.htm.
Abradable materials are designed to be less abrasion resistant than surfaces which they might come into contact with – insuring against wear or damage to the latter. They are therefore used for things like seals and gaskets close to critical components like turbine blades. Common options include aluminium/graphite and aluminium/polyester composites and the nitrides of nickel, chromium and boron. Some (like Apticote 800-89) also provide excellent corrosion protection from sea water or chemicals.
Ceramic combinations with metals such as titanium dioxide, chromium oxide or zirconium dioxide provide hard surfaces with excellent wear resistance and thermal insulation. They are often the ideal choice for piston caps, crankshafts, pumps, piston rods, exhausts and valve fittings.
Cermets are based on ceramics with a metal binder that improves shock resistance (both physical and thermal). Most are based on carbides, nitrides, borides, silicides or oxides. An example is a TiC-Co-Ni cermet coating that is often applied to cutting tools to improve wear resistance. Tungsten carbide/Co is a common choice for brake discs, capstans, seals and compressor blades, while chrome carbide/Ni/Cr provides additional corrosion resistance for things like ship doors and lock gates.