Using electrical discharge surface preparation for thermal coatings
Reference Number: N 01-02
Inventors: Rao, V. Durga Nageswar; Rose, Robert Alan; Parsons, Robert S.; Yeager, David Alan
A method of preparing the surface of a conductive metal to be non-smooth and non-passivated for reception of thermal sprayed coatings. The method comprises melting and rapidly solidifying globules of the surface by electrical discharge by bring an electrode (anode) in close gap-sparking proximity to the surface, filling the gap with an electrolyte containing a halogenated hydrocarbon fluid present in an amount of 2-5% of the electrolyte, and imposing a pulsed DC voltage (i.e. 20-100 volts at 40-200 amps) on the electrode to provide cyclical sparking between the electrode and the surface through the electrolyte resulting in a breakdown of the hydrocarbon to release nascent halogen atoms which attack the surface to prevent passivation during melting and solidification of the globules. The electrolyte is preferably cooled to a temperature below 65.degree. F. during the sparking, and the halogenated hydrocarbon is preferably present in a sufficient amount to attack silicon and aluminum, if such surface is an aluminum alloy containing silicon.