Superlattice effect for enhanced fracture toughness of hard coatings

Coherently grown nanolayered TiN/CrN thin films exhibit a superlattice effect in fracture toughness, similar to the reported effect in indentation hardness. We found-by employing in-situ micromechanical cantilever bending tests on free-standing TiN/CrN superlattice films- that the fracture toughness increases with decreasing bilayer period (A), reaching a maximum at Lambda similar to 6 nm. For ultrathin layers (Lambda similar to 2 nm), the fracture toughness drops to the lowest value due to intermixing and loss of superlattice structure. Both, fracture toughness and hardness peak for similar bilayer periods of TiN/CrN superlattices. (C) 2016 Elsevier Ltd.