ORIGINAL PAPER Low Friction CrNMPP/TiNDCMS Multilayer Coatings

widely used in automotive applications due to their high hardness and wear resistance. Recently, we showed that a multilayer architecture of CrN and TiN, deposited using the hybrid—high power impulse magnetron sputtering (HIP-IMS) and direct current magnetron sputtering (DCMS)— HIPIMS/DCMS deposition technique, results in coatings which indicate not only increased mechanical and tribo-logical properties but also friction coefficients in the range of diamond-like-carbon coatings when tested at RT and ambient air conditions. The modulated pulsed power (MPP) deposition technique was used to replace the HIP-IMS powered cathode within this study to allow for a higher deposition rate, which is based on the complex MPP pulse configuration. Our results on MPP/DCMS deposited CrN/TiN multilayer coatings indicate excellent mechanical and tribological properties, comparable to those obtained for HIPIMS/DCMS. Hardness values are around 25 GPa with wear rates in the range of 2 9 10-16 Nm/m3 and a coefficient of friction around 0.05 when preparing a su-perlattice structure. The low friction values can directly be correlated to the relative humidity in the ambient air during dry sliding testing. A minimum relative humidity of 13 % is necessary to guarantee such low friction values, as con-firmed by repeated tests, which are even obtained after vacuum annealing to 700 C. Our results demonstrate that the co-sputtering of high metal ion sputtering techniques and conventional DC sputtering opens a new field of applications for CrN/TiN coatings as high wear resistance and low friction coatings