Physical Design Principles of Thermally Stable Multicomponent Nanocomposite Coatings

This paper discusses the use of multicomponent composites as advanced nanostructured coatings. Their composition and synthesis conditions allow a simultaneous nucleation of islands of different mutually insoluble phases, which limit the island growth. Components for the coatings are chosen so that, firstly, to form nitrides, carbides, oxides, and more complex compounds with a high enthalpy of formation. Secondly, to form insoluble copper and nickel in order to reduce differences in the elastic moduli of the substrate and coating, eliminate stress concentrators, and increase the fracture toughness of the surface layers. The phase-structural state and the elastic stress distribution in the coatings are investigated to assess the torsional lattice curvature and local internal stresses as one of the most important factors in increasing the coating microhardness to HV = 40 GPa. Two types of substructures were distinguished in the nanocoatings depending on the composition: a nanocomposite one with less than 20-nm crystals in the amorphous matrix, and a two-level substructure with grains of hundreds of nanometers fragmented into 10- to 20-nm crystals. High elastic and elastoplastic bending-torsion was observed in coatings of various types. Using Ti-Al-Si-Ni-Cr-Cu-C-O-N coatings as an example, we confirm the effectiveness of the proposed multicomponent coating design principles that provide high hardness, fracture toughness, and thermal stability.