Method of depositing composite metal coatings containing low friction oxides
Reference Number: N 01-02
Inventors: Rao, V. Durga Nageswar
It is an object of this invention to provide an effective method of thermally spraying light weight metal substrates with a metal or metal alloy powder by use of controlled plasma gases and powder aspirant gases that ensure formation and/or retention of the metal's lower oxygen form of oxide which can function as a self-lubricating phase. It is further an object to control and use such gases to additionally form hard wear resistant particles during the spraying process (nitrides and carbides) that become commingled in the coating with the self-lubricating phase.
The invention herein, meeting such objects, has the following steps: (a) preparing at least one metal substrate surface to be essentially oxide free and in a condition to adherently receive the coating, (b) plasma spraying a supply of metal (M) powder particles onto the substrate surface to produce a coating of such metal (M) and an oxide (MO.sub.x) of such metal that has the lowest oxygen content of any of such metal's oxide forms, the plasma being formed by introduction of a primary plasma gas to an electromagnetic field to ionize the gas as a plasma stream which stream envelopes each particle of the introduced powder, the powder particles being introduced to the plasma stream by an aspirating gas and being melted or plasticized substantially only at a surface region of each particle by the heat of the plasma, (i) the primary plasma gas being essentially constituted of a reactively oxide-neutral gas but including a reducing gas component when the oxide of the powder is less than 90% MO, (ii) the aspirating gas being essentially constituted of a reactively oxide-neutral gas but including an oxidizing component when the volume content of the oxide form (Mo) of the powder is less than 5% by volume or it is desired to increase the volume of the oxide form (MO) of the powder to substantially over 5% in the coating.