Microstructure and mechanical properties of arc evaporated Ti(Al,Si)N coatings

Ti(Al)SiN protective hard coatings are promising candidates for the metal cutting industry, due to their favorable properties such as a high hardness and good oxidation resistance. Within the scope of this work, the microstructure of cathodic arc evaporated TiN, Ti84Si16N, Ti81Al3S16N and Ti70Al14Si16N was correlated with their mechanical properties. X-ray diffraction (XRD) as well as scanning electron microscopy investigations of the cross-sections revealed a pronounced grain refinement for Ti(Al)SiN compared to TiN. The texture of the coatings was analyzed by XRD pole-figures, showing a change in the preferred orientation in growth direction from (111) for TiN to (200) for Ti(Al)SiN. Hardness values were found to strongly increase from 29 GPa to 40 GPa upon Si addition, but remained constant for further alloying with Al. Micromechanical bending tests allowed to gain a detailed insight into the fracture properties of the investigated coatings and revealed an enhanced fracture stress and fracture toughness (K-IC) for Ti(Al)SiN compared to TiN. Hereby, the K-IC value of 2.4 +/- 0.3 MPa m(1/2) for TiN could be increased to a maximum of 3.3 +/- 0.2 MPa m(1/2) for Ti70Al14Si16N. The present findings provide a systematic overview of the microstructure and mechanical properties of arc evaporated Ti(Al,Si)N coatings, thus allowing to select the most suitable coatings for different applications in the cutting industry.