Microstructure And Mechanical Properties Of NbN/AlN Multilayer Films And AlCN, TiAlCN Composite Films

A series of NbN thin films, NbN/AlN multilayer films, Al-C-N composite films and Ti-Al-C-N composite films were prepared by reactive magnetron sputtering method. The relationship between the microstructure and mechanical properties of NbN coatings were studied. The effect of modulation period and modulation ratio on the microstructure and mechanical properties of NbN/AlN multilayers coatings were studied. The hardening mechanisms of multilayer films had also been investigated. The effect of C target power on the microstructure, mechanical properties and wear behavior of Al-C-N composite films. The effect of C target power on the microstructure and mechanical properties of Ti-Al-C-N composite films. The hardening mechanisms of composite films have also been investigated.The results are showed as follows: The flow of N2 has significant influence on the structure of NbN thin film, The NbN thin films showed (200) preferential orientation with increase of nitrogen gas flow. All the NbN thin films showed cubic structure under our experiment condition. The change of sputtering power has no significant influence on the structure of NbN thin film. The hardness of the NbN thin film increased along with the rise of sputtering power within a certain range.The crystal structure of AlN layers in the multilayers and the hardness of NbN/AlN multilayers depend on the thickness of AlN layers. When the thickness of NbN is 5.0 nm and AlN layer is less than 0.8 nm. The results show that AlN exists as a metastable cubic phase in multilayers at small modulation periods due to the"template effect"of NbN layer and could forms superlattice with NbN layer. Correspondingly, multilayers show the superhardness effect with the enhancement of hardness at small modulation periods. The maximum hardness of the multilayers is 33.3GPa. With the increase of the thickness of AlN layers, AlN layer grows as its stable hexagonal structure (h-AlN) in multilayers, the lattice plane｛111｝of NbN was likely to coherent with the｛002｝of AlN, Then the hardness of the multilayers dropped.As increase the sputtering power of C target. The hardness of Al-C-N composite films increased firstly, and then dropped. The maximum hardness of the composite films is 41.84GPa when the sputtering power of C target is 50W. Solid solution strengthening, lattice strain of coordinated interface resulted in the increase of hardness of Al-C-N composite films. While the grain size of composite films decreased as the sputtering power of C target increased. With further increasing the sputtering power of C target, crystalline Al-C-N composite films turned into amorphous and the hardness of films decreased. The Friction coefficient of films decreased as the increase of the sputtering power of C target.As increase the sputtering power of C target, a distinct change of the microstructure of Ti-Al-C-N composite films could be seen from the XRD pattern, the (111) preferential orientation of TiN crystal disappeared, showed (200) preferential orientation, the peak of diffraction turn to low angel. The lattice constants of NbN reduce with increase the sputtering power of C target, the XRD patterns became more and more smooth. The maximum hardness of the composite films is 41.82GPa when the sputtering power of C target is 180W, a-CNx could existed in the film when farther increase the C target power, the microhardness of films dropped obviously. Solid solution strengthening, grain refinement and lattice strain of interface may resulted in the increase of hardness of Ti-Al-C-N composite films.