TiBCN:CNx multilayer coatings deposited by pulsed closed field unbalanced magnetron sputtering

In this study, a combination of nanocomposite and multilayer coating design was investigated in an effort to reduce the coefficient of friction (COF) while maintaining good mechanical properties of the TiBCN coatings. The TiBCN:CNx coatings consist of TiBCN and CNx nanolayers which were deposited alternately by reactive sputtering a TiBC composite target (80 mol% TiB2 + 20 mol% TiC) and a graphite target in an Ar:N2 mixture using a pulsed closed field unbalanced magnetron sputtering system. Low angle X-ray diffraction and transmission electron microscopy characterizations confirmed that the coatings consist of different bilayer periods in a range of 3.5 to 7.0 nm. The TiBCN layers exhibited a nanocomposite structure, whereas the CNx layers were in an amorphous state. The mechanical properties and wear resistance of the TiBCN:CNx multilayer coatings were investigated using nanoindentation and ball-on-disk wear test. The TiBCN:CNx coatings exhibited high hardness in a range of 20-30 GPa. The highest hardness of 30 GPa was achieved in the coating with a bilayer period of 4.5 nm. A low COF of 0.17 sliding against a WC-Co ball was obtained at a bilayer period of 4.5 nm, which is much lower than those of the single layer TiBCN and TiBC nanocomposite coatings (0.55-0.7).