Mechanical properties and oxidation resistance of chemically vapor deposited TiSiN nanocomposite coating with thermodynamically designed compositions

Abstract

TiSiN coating with nanocrystallite surrounded by amorphous phase has attracted a broad interest because of its high hardness and excellent oxidation resistance desired for cutting tools. In the present work, TiSiN coatings were designed and prepared from a gaseous mixture of TiCl4, SiCl4, NH3 and H2 by low pressure chemical vapor deposition (CVD) process under the guidance of calculated CVD phase diagrams. The calculated compositions and phases in the deposited coatings agree well with the experimental ones. The deposited TiSiN coatings consist of nano-crystalline TiN and amorphous Si3N4 (a-Si3N4). A maximum hardness of about 2800 HV0.02 was obtained, corresponding to a minimum crystallite size of 17.7 nm and a-Si3N4 volume fraction of 13.3% for TiSiN coating deposited at 1123 K under 3.0 kPa. After oxidation at 973 K for 1 h, TiSiN coating kept intact while TiN was completely oxidized. TiSiN nanocomposite coating formed by Si incorporation to TiN displayed superior hardness and oxidation resistance in comparison with those of TiN. The correlation of TiSiN coating hardness with volume fraction of a-Si3N4 and TiN grain size was discussed. The present work demonstrates a novel strategy of thermodynamic calculations and key experiments to deposit CVD TiSiN coatings highly efficiently, which is equally valid for the design of other CVD hard coatings.