The effect of NH3 plasma pre-treatment on the adhesion property of (Ti1-xAlx)N coatings deposited by plasma-enhanced chemical vapor deposition

Abstract (Ti 1− X Al X )N has been coated on high speed steel (HSS) substrate by a plasma-enhanced chemical vapor deposition (PECVD) process from a gas mixture of TiCl 4 , AlCl 3 , NH 3 , H 2 , and Ar. Prior to deposition, the substrate was treated by NH 3 plasma in the same deposition chamber. It has been found that CrN was formed on the substrate surface after the NH 3 treatment. Iron compounds which are known to degrade the adhesion property of the coating, however, were not observed. The lattice parameters of the HSS and the coatings increased after the NH 3 treatment by the incorporation of nitrogen atoms. The microhardness of (Ti 1− X Al X )N, however, was not changed by the pre-treatment. The adhesion strength of the coatings without the NH 3 treatment decreased considerably when X Al in (Ti 1− X Al X )N was greater than 0.15, which could be increased markedly by the substrate pre-treatment with NH 3 plasma. The improvement of the adhesion was achieved by the decrease of the stress gradient at the interface of the substrate and the coating resulted from the formation of TiN prior to (Ti 1− X Al X )N as well as by the different lattice parameter change between the substrate and the coating after the plasma treatment. Oxide removal on the substrate surface also contributed to the adhesion improvement.