Microstructure and mechanical behavior of TiAlCrN multilayer thin films

The effects of bilayer thickness and chromium content on the microstructures and mechanical properties of nanolayered TiAlCrN thin films were studied. The films were deposited onto the WC–Co substrates using cathodic arc method where 4 TiAl alloyed targets and 2 Cr targets were mounted alternately. Complex multilayers were produced by rotation of the sample holder and by controlling deposition conditions. Addition of chromium favors the formation of columnar structures in TiAlCrN layers. In thick bilayer films (Λ=400 nm) the TiAlN layer periodically interrupts the formation of columns in TiAlCrN, while for thinner bilayer films (Λ=10 nm) the columns are not interrupted leading to the formation of perfectly columnar films. Both Cr content and bilayer thickness contribute to hardness enhancement. The addition of Cr favored the formation of the harder cubic (Cr,Al)N phase rather than the softer wurtzite, hcp-(Al,Ti)N phase. The hardness enhancement due to multilayering can be explained by two factors; a grain refinement that leads to an increase in hardness and the formation of columnar structures with a preferred orientation. Indentation induced crack morphology appeared very sensitive to film microstructures, where well organized straight through thickness cracks occurred while indentation of TiAlCrN caused a network of irregular cracks due to the greater contribution of column grain boundary sliding.