Microstructure and cutting performance of V-C based coatings deposited by HIPIMS/UBM

The poisoning of different target materials under Direct Current Magnetron Sputtering (DCMS) and DCMS/ High Power Impulse Magnetron Sputtering (HIPIMS) discharges, using two reactive gases, were analysed. For both discharges, in mixed Ar+CH4+N2 atmosphere, low flow processes were influenced by methane; conversely, at high flow they were dominated by nitrogen. In DC discharges, vanadium targets were poisoned at 55% of reactive gas flow. Poisoning resulted in a 2-fold increase in total pressure and a 50 % increase in discharge voltage/current ratio. TiAl targets poisoned at lower reactive gas flows exhibited narrower hysteresis than V targets. For DCMS/HIPIMS discharges, both targets poisoned earlier and the hysteresis was narrower than in DC discharge. It is confirmed by trends in the partial pressure, the voltage/current ratio and ion fluxes of metals and reactive gasses. These effects are due to higher reactivity of the plasma; this is evidenced by higher fluxes of N+ and N2+ and radicals containing H, C and N. The voltage/current ratio reduced by 50% as the target is poisoned; this is a contrast to operation in DC mode where it increased. This could be attributed to efficient ionization and drop in plasma impedance. The effect of target poisoning using two reactive gases was utilised to deposit a series of TiAlCN/VCN coatings. As the target was more poisoned, the coating thickness decreases. The microstructure of coatings changed from glassy amorphous to a NaCl-type cubic crystalline phase with columnar structure. The column density decreases with increased flow. Coatings showed an increase in nitrogen and carbon content. Coatings with a high nitrogen and carbon content, show low adhesion to the base layer, and therefore poor wear resistance. Introducing a gas flow ramping between a VN base layer and the TiAlCN/VCN multilayer coating, as well as introducing a metallic layer, improves wear resistance of the coatings. The wear resistance was confirmed during cutting test on the P20 metal bar.