SURFACE HARDENING AND DEPOSITION OF COATINGS ON METALS BY A MOBILE SOURCE OF LOCALIZED ELECTRICAL RESISTIVE HEATING

A method of surface hardening, coating deposition and surface alloying based on electrical resistive heating localized at the surface of a m etal substrate has been developed. Localization of resistive hearing w as obtained by passing electric current through the contact between a moving roller and the substrate. The small size of the contact imposed a severe constriction on the electric current causing intense resisti ve heating close ro the contact. Simultaneous motion of the roller and substrate provided surface coverage by the heating process. Tests wit h steel on steel showed that this technique can generate a surface lay er with a martensitic or quenched microstructure, whilst a lest with z inc on copper revealed that surface alloyed layer of copper and zinc c an be generated. Tests where tile roller has a lower melting point tha n the substrate, e.g. tests with zinc on steel substrates, revealed th at a strongly adhering coating can be deposited by the roller.