Materials and concept of plasma spraying

In order to extend service life of equipment and machine parts, or to increase resistance of mechanical parts exposed to severe conditions, different coatings are applied. There are numerous options in the process of providing a coating to mechanical components in order to protect them. Being versatile, and providing for an array of different materials makes plasma spraying a very popular process, although it is not the best choice for others. Materials in the form of powder commonly used in the process are oxides (TiO2, ZrO2, ZrSiO4, Cr2O3, Y2O3, their mixtures, etc.), carbides, borides, nitrides and cermets (WC–Co and Cr3C2–NiCr is the most widely applied one). In the process of plasma spraying, plasma is generated within the plasma torch via an electric arc. Depending on the material being coated or substrates and their different properties, a large number of different process parameters can be adapted to suit the specific need. The plasma spraying process can be implemented as: 1) atmospheric plasma spraying, where the plasma jet exits the torch into the atmospheric environment; 2) controlled atmosphere plasma spraying, where the jet is exiting into a chamber providing the controlled atmosphere (Ar); 3) low pressure plasma spraying or vacuum plasma spraying, where the jet is exiting the torch into a low pressure chamber at vacuum conditions; 4) plasma spraying physical vapor deposition as hybrid process