The nanostructured phase transition and thermal stability of superhard f-TiN/h-AlSiN films

The superhard Ti–Al–Si–N films were synthesized by multi-arc ion plating technology and the influence of vacuum annealing on the structures and properties of the films was investigated. Transmission electron microscopy observation confirmed that the as-deposited Ti–Al–Si–N films were consisted of fcc-TiN/hcp-AlSiN multilayers with a period of 8 nm. The result also showed that a minute layer of cubic structure was observed in hcp-AlSiN layer at the interface between TiN layers and AlSiN layers, which resulted in an epitaxial growth between TiN layers and AlSiN layers. The annealing experiment of the Ti–Al–Si–N films was performed in vacuum furnace for 2 h at temperatures ranging from 700 to 1100 °C. With increasing annealing temperatures, no novel phases were observed indicating that the film retained the sharp interfaces. The grains of the film coarsened and showed mixed orientations at 1100 °C. The transformation of h-AlSiN into h-AlN and Al-depleted AlSiNx and partial crystalline SiNx was speculated during the annealing process by the XPS and DSC results. The film retained super hardness of above 47 GPa even at 1100 °C due to the formation of crystalline SiNx and the minute c-(Al, Si)N layer between c-TiN layers and h-AlSiN layers which delayed the transformation of (Al, Si)N from cubic phase to hexagonal phase. The adhesion strength of the film was also discussed and that vacuum annealing could improve the adhesion strength.