Structure and properties of ZrN coatings deposited by high power impulse magnetron sputtering technology

Monolayer ZrN coatings were deposited exclusively by the novel High Power Impulse Magnetron Sputtering (HIPIMS) technology in an industrial scale PVD machine (HTC-1000-4 target system). Coatings were deposited on 1 micron polished M2 High speed steel, 304 L Stainless steel and on Si (100) specimens. Prior to deposition, HIPIMS plasma sustained on a Zirconium (Zr) target was utilised to pretreat the specimens. Coatings were deposited at 400°C in a mixed N2 and Ar atmosphere using 2 magnetrons in HIPIMS mode and at three different substrate bias voltages (UBIAS) keeping all other process parameters constant. The thicknesses of the coatings measured by the ball cratering technique were in the range of 1.84 µm, 1.96 µm and 2.13 µm at bias voltages of -95 V, -75 V and -65 volts respectively, where the difference in thickness can be attributed to the re-sputtering effect. X-ray diffraction experiments on SS specimens revealed a dominating 111 texture for all three coatings irrespective of the bias voltage. Cross-sectional transmission electron microscopy revealed extremely dense coating structures at all bias voltages, similar to the transition zone structure (Zone T) reported by Thornton. The -95 bias voltage coatings appeared extremely smooth on the top and with no dome shaped structures often associated with low ion bombardment during deposition. HIPIMS pretreatment lead to high adhesion (LC) of the coatings to the substrate. A continuous ductile perforation of the coating was observed at progressive loads greater than 65 N however no spallation of the coating was observed up to loads of 100 N. High values of hardness (40.4 GPa), Young's Modulus (424 GPa) and compressive stress (10 GPa) were recorded for coatings deposited at -95 BV. Hardness and internal stress of the coating was found increasing with more negative bias voltages. All the coatings exhibited high dry sliding wear resistance (KC) in the range of 6 x 10-15 m3N-1m-1. Cross-sectional Transmission Electron Microscopy and Atomic Force Microscopy analysis has been used to study the effect of ion bombardment obtained from HIPIMS on the structure of the coatings.