Ternary and quarternary TiSiN and TiSiCN nanocomposite coatings obtained by Chemical Vapor Deposition

Abstract TiN and TiC x N y are commercial CVD coatings widely used for cutting tools. A promising route for improving their performance is the addition of silicon. Therefore the main objective of this work is the preparation of TiSiN and TiSiCN coatings with a nanocomposite structure offering a higher hardness as well as an improved oxidation and wear resistance. New low pressure CVD processes in the range 800 °C–900 °C were developed for the successful deposition of nanocomposite coatings of TiSiN and TiSiCN on hard metal substrates. TiSiN nanocomposites are obtained with a mixture of the precursors TiCl 4 , SiCl 4 and NH 3 whereas for TiSiCN coatings acetonitrile is added instead of NH 3 . In this work microstructure, composition, properties and oxidation behavior of the nanocomposite coatings were investigated. TiSiN coatings consist of the crystalline phases TiN, Ti 5 Si 3 and amorphous silicon nitride. The hardness correlates well with silicon content and crystallite size. A maximum hardness of about 3700 HV[0.01] was observed at a silicon content between 6 at.% and 8 at.% and a TiN crystallite size about 15 nm. TiSiCN coatings prepared with the acetonitrile process exhibit a nanocomposite structure of nanocrystalline TiC x N y and amorphous SiC x N y . Compared to TiSiN a still higher hardness up to 4100 HV[0.01] was measured for a silicon content of 11.7 at.%. TiSiN coatings with a silicon content between 5.5 and 7.7 at.% offer an oxidation resistance up to 700 °C. But TiSiCN with 2.2 at.%–11.7 at.% silicon is even more stable up to 900 °C. At these temperatures TiO 2 is formed at the surface. The examination of the adherence showed that a diffusion barrier is necessary for suppressing the cobalt diffusion from cemented carbide substrate into the layers. If interlayers of TiN or TiC x N y were applied critical loads of 80 N for TiSiN and 43 N for TiSiCN coatings were obtained by scratch tests.