Nanocomposite TiC/a-C coatings:Structure and properties

This contribution deals with fundamental and applied concepts in nano-structured coatings, in particular focusing on the characterization with high-resolution (transmission) electron microscopy. Both unbalanced and balanced magnetron sputtering systems were used to deposit nc-TiC/a-C nanocomposite coatings with hydrogenated or hydrogen-free amorphous carbon (a-C) matrix, respectively. The contents of Ti and C in the coatings have been varied over a wide range (7 similar to 45 at.% Ti) by changing the flow rate of acetylene gas or the locations of substrates relative to the center of C/TiC targets. Different levels of bias voltage and deposition pressure were used to control the nanostructure. The nanocomposite coatings exhibit hardness of 5 similar to 35 GPa, hardness/E-modulus ratio up to 0.15, wear rate of 4.8 x 10(-17) m(3)/Nm, coefficient of friction of 0.04 under dry sliding and strong self-lubrication effects. The nanostructure and elemental distribution in the coatings have been characterized with cross-sectional and planar high-resolution transmission electron microscopy (HRTEM) and energy filtered TEM. The influences of the volume fraction and size distribution of nanocrystallites TiC (nc-TiC) on the coating properties were examined.