Effects of the experimental conditions of chemical vapour deposition on a TiC/TiN double-layer coating

Abstract

Deposits of titanium nitride (TiN) were formed on TiC-coated 94wt.%WC-6wt.%Co substrates by chemical vapour deposition using a TiCl 4, H 2 and N 2 gas mixture. The effects of the deposition temperature, the total flow rate of the reactant gases and the partial pressure of TiCl 4 on the deposition rate, the preferred orientation and the surface morphology of the TiN deposit were investigated. The controlling mechanism of the TiN deposition reaction and its relationship with the deposition temperature and the total flow rate of the reactant gases were also investigated. The deposition rate and the TiN crystal growth along the (220) preferred orientation are increased with an increase in the deposition temperature and an increase in the partial pressure of TiCl 4 at a total flow rate of less than 700 cm 3 min -1. The particle size of the TiN deposit is reduced with an increase in the partial pressure of TiCl 4 and is increased with an increase in the deposition temperature at a total flow rate of less than 700 cm 3 min -1. When the total flow rate is greater than 700 cm 3 min -1, the deposition rate, the TiN crystal growth along the (220) preferred orientation and the particle size of the TiN deposit no longer vary. When the deposition temperature is lower than 1000 °C, the TiN deposition reaction is controlled by the surface reaction; at a temperature above 1000 °C, the reaction is controlled by mass transport. When the total flow rate is less than 700 cm 3 min -1, the deposition reaction is controlled by mass transport; with a total flow rate greater than 700 cm 3 min -1, the reaction is controlled by the surface reaction.