Wear of cobalt-based alloys sliding in molten zinc

Abstract

Wear of cobalt-based alloys coupled with different materials was evaluated in molten zinc. A highly deformed worn surface was formed on a cobalt-based alloy running against itself, evidenced by the wide and deep wear grooves. Wear behaviour of the cobalt-based alloys improved in terms of severity of the wear grooves when paired with dissimilar materials. The alloys had relatively even wear against a cermet coating of WC–Co and SiC with inclusion of graphite. There was negligible wear on a cobalt-based alloy when it was tested against 316L stainless steel (SS). Thorough analyses on the tested samples revealed that cobalt-based alloys readily reacted with molten zinc to form intermetallic compounds. Abrasion is identified as the major wear mechanism that causes wear on cobalt-based alloys when the same materials are running against each other. Cobalt-based aluminides, transformed from wear particles and then built up on contact surfaces, can easily plough the test materials and result in highly grooved worn surfaces. Surface fatigue wear is believed to contribute to the wear processes involving dissimilar material pairs. The synergistic aggravation of wear by reactive products of the test material with molten zinc indicates the involvement of corrosive wear.