Superhard nanocomposite coatings. From basic science toward industrialization
A variety of superhard coatings with Vickers plastic hardness exceeding 40 GPa have been reported by several research groups during the last five years (for recent reviews see refs [1,2]). However, one has to distinguish between superhard nanocomposites, such as nc-TiN/a-Si3N4, nc-TiN/a-Si3N4/a- and nc-TiSi2, nc-(Ti1-xAlx)N/a-Si3N4, nc-TiN/TiB2, nc-TiN/BN, etc. where the high hardness originates from the nanostrucutre and, therefore, remains stable upon annealing to high temperatures [1], and coatings, such as CrN/Ni, ZrN/Ni, and others [2] in which the measured high hardness is due to a high compressive stress that is induced in the coatings due to energetic ion bombardment during their deposition (e.g., by magnetron sputtering). We also summarize the recent progress in the industrial applications of the superhard nanocomposite coatings on machining tools.