Structure and mechanical properties of CrN/TiN multilayer coatings prepared by a combined HIPIMS/UBMS deposition technique

CrN and TiN coatings are known for their high hardness and good wear resistance. The structure and the mechanical properties of such coatings can be improved by increasing the ion bombardment during film growth. As high power impulse magnetron sputtering (HIPIMS) is known to allow high ion densities in the plasma, with a small deposition rate, we study the structure and mechanical properties of CrN/TiN multilayer coatings deposited by combining HIPIMS with conventional unbalanced magnetron sputtering (UBMS).Our results demonstrate that the microstructure of TiN coatings prepared by UBMS changes from dense columnar to open voided if a one fold substrate rotation is used where the films periodically leave and enter the plasma region in front of the target. Hence, also the hardness decreases from ~ 28 to 12 GPa if a one fold substrate rotation is used. This drawback can be overcome if the coatings are prepared by HIPIMS, resulting in hardness values of ~ 39 and 34 GPa without and with a one fold substrate rotation, respectively. Recently, we reported a corresponding behaviour of CrN coatings. In a multilayer arrangement of TiN and CrN, where the TiN layers are prepared by UBMS and the CrN layers are prepared by HIPIMS the hardness with around 26 GPa is also much higher as compared to 11 GPa of the TiN single layer deposited by UBMS. Hence, HIPIMS also influences the plasma conditions in front of the cathode operated by UBMS.