Effects of Carbon Doping and DC Bias Voltage on Microstructure and Mechanical Properties of AlCrCN Films Synthesized via HiPIMS

This work compares the hardness and adhesion properties of AlCrN and AlCrCN hard coatings synthesized via HiPIMS using Al70Cr30 and Cr targets. The hardness and adhesion properties of AlCrCN films were optimized by performing deposition under various C2H2 flow rates (5, 8, 10, 13, 15, or 20 sccm) and DC bias voltages (−40, −60, −80, −100, or −120 V). EPMA results clearly indicated that the carbon content was increased from 1.9 to 12.2 at.% with increasing C2H2 flow rate from 5 to 20 sccm. XPS results confirmed a various content of chemical bonds (Cr-N, C-N, sp2, and sp3) with various C2H2 flow rate. Grain and columnar refinement in AlCrCN were derived from XRD, TEM, and SAED results. The higher hardness (28.6 GPa) and Young’s modulus (358 GPa) were obtained using an C2H2 flow rate of 5 sccm and a bias voltage of −60 V. Both of which subsequently decreased to 13.5 GPa and 212 GPa, respectively. This can be attributed to the C-N bond inhibiting the development of metal-N bonds. Increasing the bias voltage to −120 V increased the hardness to 32.9 GPa and the Young’s modulus to 372 GPa. Note that the application of bias voltage to enhance hardness should also be applicable to carbon-doped AlCrN films as well. All samples presented good adhesion characteristics (class 1; ISO26443:2008-06).