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, multilay ered TiN/TaNx coatings deposited using a hybrid technique combining reactiv e electron beam evaporation (TiN) and reactive de magnetron sputtering (TaN ) were investigated. Ten coatings with different multilayer periods (i.e. o ne lamella of TIN together with one TaN), deposited on high speed steel sub strates, were investigated with respect to chemical and phase composition a s 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 cubi c TaN phase was grown if the lamellae were kept thin (< 6 nm) as a result o f pseudomorphic stabilization by the underlying cubic TSI lamellae and inte rmixed Ti atoms in the TaN, lamellae. If TaN was grown thicker than this, h exagonal TaN0.8 and, over 15 nn also hexagonal Ta2N, appeared. The Ta2N pha se is found to become less textured with thickness. Furthermore, it was fou nd 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 co lumnar 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 correspo nds to the untextured Ta2N phase. <(c)> 2001 Elsevier Science B.V. All righ ts reserved.