Friction surfacing of (i) tool steel, inconel, aluminum and titanium rods onto mild steel substrates and (ii) stainless steel, mild steel and inconel onto aluminum substrates was investigated. It was found that tool steel and inconel were efficiently deposited onto steel to form a dense strong coating while aluminum was only deposited at high contact pressures. Titanium could not be deposited under the tested conditions. Stainless steel, mild steel and inconel could be deposited onto aluminum substrates to form dense coatings, however only SS displayed a lack of intermetallic compound formation with Al. Melting of Al by frictional heat was observed and this led to the formation of brittle and therefore undesirable intermetallic compounds at the interface of the coating. X-ray microscope investigations of the coatings confirmed that the structure of the coating is a continuous series of discrete layers inclined at a shallow angle to the phase of the substrate. Fissures were found between these layers close to the outer surface of the coating, which implies that the uppermost layers should be removed to obtain the best quality of coating. Microscopic observations revealed that there was little mixing between the coating and the steel substrate but some surface roughening and sub-surface deformation of the steel substrate by friction surfacing. The Al-alloy substrate showed similar types of surface alteration but to a far greater extent. Careful control of process parameters such as substrate, speed load and consumable was necessary for coating quality. (C) 1997 Elsevier Science S.A.
