Magnetron sputtered nc-TiC/a-C nanocomposite coatings:Processing, characterization and properties

Two nanocomposite coatings based on nc-TiC particles in a-C:H matrix were deposited via closed-field unbalanced reactive magnetron sputtering. The composition of the coating was varied by changing the acetylene gas flow during depositions. Electron Probe Micro Analysis (EPMA) analyses show that the Ti content of the coatings is 31.7 and 17.8% at., respectively. From nanoindentations the coatings exhibit a hardness (H) of 20.0 and 15.7 GPa, and a Young's modulus (E) of 229.4 and 136.6 GPa, respectively. Tribological tests determined a friction coefficient as low as 0.046; wear rates in the 10 -16 m3 / N m range and critical loads higher than 30 N. Cube comer indentations were performed to probe the coatings toughness. Transmission electron microscopy (TEM) observations and energy-filtered TEM were employed to characterize the coating nanostructure. The variation in Ti content is accompanied by a variation in TiC particle size and a change in the columnar structure of the coatings. Focus Ion Beam technique (FIB) was employed to prepare cross-sectional samples of cracks propagating from the edges of cube corner indentations. TEM inspection of the FIB samples determined that the most brittle phase in the coating is the Crich column boundary.