Sputter deposited TiAlN/AlTiN and CrAlN/TiAlN: multilayer coatings

Multi-layered coating architectures allow to achieve properties which cannot be obtained by single layers. Thus, the aim of the present thesis was to synthesize TiAlN/AlTiN and CrAlN/TiAlN multilayer coatings and compare their microstructure and mechanical properties to the corresponding Ti1-xAlxN and Cr1-xAlxN single layers. Four single layer coatings with an Al/Ti atomic ratio of 50/50, 70/30 and 80/20 as well as Al/Cr 85/15 were deposited by reactive magnetron sputtering in a laboratory deposition unit. For the nine multilayer coatings, Al/Ti 50/50 layers were combined with the respective other compositions at different sublayer thicknesses. The microstructure and mechanical properties were investigated by X-ray diffraction and nanoindentation. Cross-sections of all single layer coatings and selected multilayers were studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. The application of a multilayered coating architecture allows to stabilize the face-centred cubic (fcc) structure especially in TiAlN/AlTiN coatings. In contrast to the Al0.7Ti0.3N and Al0.8Ti0.2N single layers, which exhibited a dual-phase fcc/wurtzitic (w) and a pure w-structure, respectively, the Ti0.5Al0.5N/Al0.7Ti0.3N multilayers were single-phase fcc and the Ti0.5Al0.5N/Al0.8Ti0.2N multilayers only showed minor w-phase fractions. The stabilization of the fcc-regime of the CrAlN/TiAlN coatings seems to be less pronounced compared to the TiAlN/AlTiN coatings. In general, the CrAlN/TiAlN coatings showed a lower hardness and Young’s modulus compared to the TiAlN/AlTiN coatings. No significant influence of the sublayer thickness on the mechanical properties could be observed.