Hard yet tough ceramic coating : not a dream any more—I. via nanostructured multilayering

This paper describes how hard yet touch ceramic coating is achieved: hard and brittle nanocomposite layers (nanocrystalline CrAlN imbedded in amorphous SiNx or nc-CrAlN/a-SiNx are intimately combined with soft and tough CrAlN polycrystalline layers (pc-CrAlN) to build multilayer coatings of different period thickness with a constant total coating thickness of one micron. At the period thickness of 20 nm, an improved hardness of 33 GPa was achieved with a scratch toughness 5 times as much as that of the nanocomposite monolayer. At the period thickness of 40 nm, drastic scratch toughness was increased 7 folds at a slightly reduction of hardness (from 30 to 27.9 GPa)