Different Mechanisms Leading to Superhard Coatings: Stable Nanocomposites and High Biaxial Compressive Stress

Abstract

AbstractA strong enhancement of the hardness above 40 GPa in thin coatings can be achieved either by the formation of a suitable nanostructure (heterostructures and nanocomposites) or by a large biaxial compressive stress of ≥ 5 GPa. Superhard and thermally fairly stable nanocomposites, such as nc-TiN/a-Si3N4, nc-TiN/a-Si3N4/a-TiSi2, nc-(Ti1-xAlx)N/a-Si3N4 retain their hardness after annealing to 900-1100°C whereas coatings with a high stress, such as HfB2, CrxN/Ni, ZrN/Ni and others soften to ≤ 20 GPa already after their annealing to 400-500°C due to the relaxation of that stress.