Effect of Al and Si additions on microstructure and mechanical properties of TiN coatings

Abstract

Ti-X-N (X=Al, Si or Al+Si) coatings were grown onto cemented carbide substrates by cathodic arc evaporation. The hardness of the coatings was obtained by nanoindentation and the microstructure was investigated by XRD, XPS and SEM. Solid solution hardening results in a hardness increase from 24 GPa for TiN to 31.2 GPa for TiAlN. The higher hardness values of 36.7 GPa for TiSiN and 42.4 GPa for TiAlSiN are obtained by the incorporation of Si into TiN (TiAlN) coatings due to the formation of special three-dimensional net structure consisting of nanocrystalline (nc) TiN (TiAlN) encapsulated in an amorphous (a) Si₃N₄ matrix phase. Furthermore, the nc-TiAlN/a-Si₃N₄ coating shows the best machining performance.

Keywords

TiN coating / alloying element / hardness / cutting test