Microstructure, mechanical properties and cutting performances of TiSiCN super-hard nanocomposite coatings deposited using CVD method under the guidance of thermodynamic calculations

Abstract

A general strategy for the development of TiSiCN super-hard nanocomposite coatings was proposed in the present work. Subsequently, TiSiCN coatings with promising industrial applications for cutting tools were prepared from gaseous mixtures of TiCl4, SiCl4, CH3CN, NH3/N2 and H2 by a low pressure chemical vapor deposition (CVD) process under the guidance of established phase diagrams. The chemical compositions, microstructure, mechanical properties and cutting performances of TiSiCN coatings were investigated. No Si was doped into MT (moderate temperature)-Ti(C,N) with N2 addition while higher Si contents (2.87–6.43 at.%) were obtained by using NH3. The measured compositions and phase assemblages of TiSiCN coatings were reasonably described by thermodynamic calculations. TiSiCN coatings showed nanocomposite structures consisting of nanocrystalline TiCxNy and amorphous SiCxNy. A maximum hardness (44.9 ± 0.9 GPa), ratios of H/E⁎ and H3/E⁎2 (H-hardness, E*-effective elastic modulus) were obtained for TiSiCN coating with a Si content of 2.87 at.% and a grain size of 37.7 nm, indicating enhanced mechanical properties to those of the previous works. TiSiCN displayed a superior cutting performance compared to MT-Ti(C,N) during continuous wet turning of nodular cast iron (DIN GGG40). It also exhibits a better wear resistance than state-of-the-art thicker MT-Ti(C,N) + Al2O3 multilayer coating during dry milling of the same material. TiSiCN coatings with better performances could be designed with the aid of the CVD phase diagrams in this work.