Preparation and toughening of a-CuZr/c-ZrN nano-multilayer hard coatings

Abstract

Hard coatings are prone to crack and failure when subjected to large external impact loads due to poor toughness. In this paper, a-CuZr/c-ZrN nanomultilayers were designed to improve the toughness of ZrN coatings. Two groups of a-CuZr/c-ZrN nanomultilayers were prepared: CuZr (10 nm)/ZrN (34, 51, 85 nm) as Group 1 and CuZr (4, 8, 16, 25 nm)/ZrN (46 nm) as Group 2. The microstructures were analyzed by Grazing incident X-ray diffraction (GIXRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). Hardness, elastic modulus were tested by nanoindentation; scratch tests and Vickers indentation methods were adopted to characteristic the toughness. The relationship between parameters of layer structure and mechanical properties were analyzed, the toughening effect and related mechanism were investigated. The conclusions were: In Group 1, both of the hardness and fracture toughness of multilayer coatings increase with the decrease of ZrN layer thickness. In Group 2, the hardness decreases first and then increases with the CuZr thickness increases. The toughness increased with the CuZr thickness increases, especially the a-CuZr/c-ZrN = 25/46 nm has the significant toughening effect, which toughness reached 0.5468 MPa·m0.5 (about 43% higher than the ZrN single-layer film). This is mainly affected by the a-CuZr layer thickness of the multilayer film which alter the deformation mechanism.