Growth characteristics of multilayered physical vapour deposited TiN/TaNx on high speed steel substrate

During the last years multilayer technology has covered a larger volume of the thin film research area of hard coatings. In the present work, multilayered TiN/TaNx coatings deposited using a hybrid technique combining reactive electron beam evaporation (TiN) and reactive de magnetron sputtering (TaN) were investigated. Ten coatings with different multilayer periods (i.e. one lamella of TIN together with one TaN), deposited on high speed steel substrates, were investigated with respect to chemical and phase composition as well as microstructure and morphology. The results indicate that by just changing the lamella thickness, the growth characteristics of multilayered TiN/TaNx could be varied in a controlled manner. It was found that the cubic TaN phase was grown if the lamellae were kept thin (< 6 nm) as a result of pseudomorphic stabilization by the underlying cubic TSI lamellae and intermixed Ti atoms in the TaN, lamellae. If TaN was grown thicker than this, hexagonal TaN0.8 and, over 15 nn also hexagonal Ta2N, appeared. The Ta2N phase is found to become less textured with thickness. Furthermore, it was found that the morphology of the coating could be changed by just varying the multilayer period. For periods thinner than 42 nm the coating obtained a columnar structure. typical for single layered TiN. A period thicker than 42 nm (corresponding to a TaN lamella thickness of 15 nm) allowed TaN, to grow in a more fine grained structure, typical for single layered TaN and hence resulting in a less columnar coating. This fine-grained structure corresponds to the untextured Ta2N phase. <(c)> 2001 Elsevier Science B.V. All rights reserved.