Advanced hard coatings with enhanced toughness and resistance to cracking

Nanocomposite coatings represent a new generation of materials [1-41] and references therein. They are composed of at least two separated phases with nanocrystalline (nc-) and/or amorphous (a-) structure or their combinations. The nanocomposite materials, due to very small (≤10 nm) grains and a significant role of boundary regions surrounding individual grains, exhibit enhanced or even completely new unique properties compared with the conventional materials composed of larger (≥100 nm) grains. New properties of the nanocomposite materials are caused by the increase of the ratio of the grain surface S and its volume V, and occur when the ratio S/V > 0.1. The high ratio S/V (> 0.1) results in the dominance of the grain boundary regions increasing with decreasing grain size d, reduced action of the grain volume, stopping of the generation of dislocations, and the promotion of new processes such as the grain boundary sliding or the grain boundary enhancement due to an interatomic interaction between the atoms of neighboring grains. It means that dramatic changes in properties and behavior of the nanocomposite materials compared with that of the conventional materials are the result of (1) the strong change of the geometrical structure of material, particularly the size d and the shape of grain and the separation distance w between grains, and (2) the enhanced chemical and electronic bonding between atoms of neighboring phases or grains. These are main reasons why the nanocomposite coatings can exhibit enhanced and new unique properties.