Using an industrial type set-up of pulsed DC plasma chemical vapor deposition the Ti-Si-N
coating on high speed steel (W18Cr4V)
was performed. The effect of N2 flow on microstructure and interfacial bonding strength was investigated. The results show that the deposition rate and contents of Si in Ti-Si-N
coating decrease with increasing N2 flow, and the film structure tends to dense, but the
critical load of scratch method and the microhardness of coating increase obviously when higher N2 flow was used. The Si contents of Ti-Si-N coating decrease with increasing N2 flow, three type phases of nc-TiN/a-Si3N4/Si, nc-TiN/ a-Si3N4/TiSi2/Si, nc-TiN/a-Si3N4/TiSi2 are found in coating orderly. It is known that workpiece is cathode in DC PCVD and low conductivities of Si3N4 and Si during formation of the coating will reduce conductivity of cathode, so quality of coatings is worsened in lower N2 or higher Si content. The results illustrate that there are many differences between pulsed DC PCVD and RF PCVD.