MECHANICAL CHARACTERIZATION OF KAPPA-ALUMINA AND ALPHA-ALUMINA FILMS ON HARDMETALS USING INDENTATION METHODS

The mechanical properties of thin films of two allotropic modifications of alumina have been examined. These coatings were chemically vapour deposited onto cemented carbide substrates and the film thickness was 6 and 4 mu m respectively for the alpha and kappa alumina. Indentations on the films and substrate were conducted with an ultra microindentation system using diamond Berkovich and small, spherical-tipped indenters. Analysis of the data showed differences between the two different allotropes. The kappa alumina was slightly harder than the alpha phase, although the modulus showed the opposite response. The resultant spherical indentation-induced stress-strain curves for the films are also compared with those of the cemented carbide substrate. SEM pictures of the indentations revealed evidence for both brittle and plastic behaviour of the alumina films.