Carbon nitride based hard multilayer films prepared by closed field unbalanced magnetron sputtering

Single layer a-CN_x films as well as CN/HN multilayer films were deposited onto Si (100) and M42 high speed steel substrates by closed field unbalanced magnetron sputtering. In CN_x/TiN multilayers, different bilayer (CN_x+TiN layer) thickness could be attained in two ways: by changing the substrate rotation speed (1·3-20 rev min^-1) and by varying the C target current only with substrate rotation speed fixed at 4 rev min^-1 during the deposition process. The films were characterised by employing atomic force microscopy (AFM), nano/microindentation measurements, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), pin on disc wear test, scratch tester and Rockwell C tester. The XPS results of CN_x films suggest the formation of a major fraction of N-C sp² bonds and a few N-C sp³ bonds. The nanohardness of CN_x film about 11·7-20·8 GPa depends on the N/C ratio. In CN_x/TiN multilayers, TIN, TiO₂, TiC, C - N and C=N chemical and bonding states exist, The mechanical and tribological properties are influenced by different bilayer periods (about 10-1 nm). The root mean square (RMS) surface roughness measured by AFM was between 0·7 and 1·9 nm. High microhardness (∼50 GPa) of the multilayered structure depends on the bilayer thickness. The internal compressive stress is associated with the hardness of the multilayer which falls to about 3·3-7·7 GPa. The pin on disc tests under dry condition show a low friction coefficient between 0·11 and 0·15. Rockwell C and scratch tests show excellent adhesion results for the coating prepared at C target current of 0·5 A.