Influence of thermal treatment on the adhesion of copper coatings on carbon substrates

Abstract

Sputter deposited copper (Cu) coatings on plane glassy carbon (C) substrates serve as a model for the interface between Cu- and C-fibres in Cu–C metal matrix composites (MMCs). This interface is of crucial importance for the mechanical and thermal properties of copper carbon MMCs. If the Cu-coating is deposited on a nitrogen(N)-radiofrequency (RF)-plasma treated C-substrate at room temperature (RT), the adhesion of Cu to C is excellent. In a further step the Cu-coated C-samples are subjected to a thermal treatment at 800 °C under high vacuum conditions for 1 h to partially mimic the hot pressing step involved in the production of real MMCs. This thermal treatment generates a recrystallization induced dewetting process of the Cu coating from the C substrate, which drastically reduces the adhesion of Cu to C. If a molybdenum-intermediate layer is deposited, no dewetting of the Cu-film takes place, although recrystallization occurs. Additionally the adhesion of the Cu-film is, depending on a minimum thickness of the molybdenum layer, low in the as-deposited state and is strongly increased after the annealing step. SIMS-measurements indicate that this increase is caused by the formation of molybdenum–carbides during the heat treatment.