Limits to the strength of super- and ultrahard nanocomposite coatings

Abstract

Hertzian analysis of the nonlinear elastic response upon unloading provides analytical solutions that were used to verify if the hardness values measured on the super-and ultrahard coatings are self-consistent. The analytical solutions were also used to estimate the tensile strength of the coatings. The highest tensile stress occurs at the periphery of the contact between the coating and the indenter and, in the case of ultrahard coatings, it can reach values in the range of tens of Gpa, thus giving an estimate of their tensile strength. The results show that the tensile strength of the superhard nanocomposites reaches an appreciable fraction of the ideal cohesive strength that is predicted on the basis of the universal binding energy relation. The data are compared with finite element computer modeling in order to obtain a deeper insight into the complex problems. Reliable values of the hardness can be obtained if coatings of a thickness greater than 8 m are used and the load-independent values are measured at sufficiently large indentation depths of greater than 0.3 m.

Real-time control of AlN incorporation in epitaxial Hf1−Al N using high-flux, low-energy (10–40 eV) ion bombardment during reactive magnetron sputter deposition from a Hf0.7Al0.3 alloy target

“…The physical properties of nanocrystalline solids [1] are quite different from those of bulk large grained materials and depend strongly on crystallite size and shape. Multicomponent [2][3][4][5], multiphase [6][7][8][9][10][11], 2-dimensional [12][13][14], and 3-dimensional nanostructured hard coatings [15][16][17] have been synthesized with extreme properties, such as ultrahardness and ultratoughness [5,[7][8][9]18,19], high ductility [20,21], and ultra wear resistance [22].…”

Electronic structure, stability, and mechanism of the decohesion and shear of interfaces in superhard nanocomposites and heterostructures

“…[9][10][11] Thus, the about 1 ML thick Si 3 N 4 -like interface between the TiN nanocrystals 1,3 should be essentially free of flaws, i.e., there had to be an almost perfect binding between the silicon and nitrogen atoms in that interface, giving the same chemical shift of the Si 2p signal in x-ray photoelectron spectra, like in stoichiometric Si 3 N 4 , but with some strain due to mismatch of the sizes of the Si and Ti atoms ͑see Fig. 12b in Ref.…”

Development of novel coating technology by vacuum arc with rotating cathodes for industrial production of nc-(Al1?xTix)N/a-Si3N4 superhard nanocomposite coatings for dry, hard machining

“…9). The extraordinary mechanical properties of these nanocomposites whose tensile strength approaches the ideal one of 10-40 GPa (36) was recently explained in terms of conventional fracture physics scaled to the dimensions of few nm. (37) Because of the generic nature of that design concept, they can be prepared in a variety of chemical composition.…”