Nucleation of Al2 O 3 Layers on Cemented Carbide Tools

Abstract

Aluminum oxide was deposited with a CVD technique onto polished and uncoated cemented carbide substrates. Experiments of short duration were performed with varying process parameters. The density of nuclei on the phase in cemented carbide and on the coating was measured for each experiment. The corresponding chemical equilibria of the gas phase were calculated. The supersaturations of reactants were compared with the nuclei densities. It was found that the densities of nuclei vary with the supersaturation of the oxygen donors ( and ). In these experiments there was a relative shortage of oxygen donors. The early stage of the deposition is supposed to influence the adhesion of the coating in two ways. First, voids that form in the cemented carbide substrate surface during heating up may cause pores, which decrease the strength of the interface. Second, too sparse a nucleation weakens the bond between the coating and the substrate. By using cemented carbide as the substrate it is possible to avoid the void formation and to obtain an evenly distributed nucleation.