Composite and Real Hardnesses of Thin Coatings

Abstract

The paper presents the results of an analysis of the mechanics of contact between a rigid sphere and an elastic rigidly plastic two-layer half-space that imitates a surface covered with a hard strengthening coating. Analytical dependences are derived which relate the surface hardness to the base and coating hard¬nesses within the whole possible range of the coating thickness. A new physical interpretation of the mechanism of the deformation of a layered solid is proposed for the range of the indentation depth that commonly characterizes the domain of the existence of the composite hardness. The obtained theoretical solutions are used to determine the ranges of the thicknesses within which the composite and real hardnesses of a hardened surface exist.

Modelling Kinetic Indentation in Topocomposite Surface of Elastic Rigid-plastic Solid Bodies

“…In the work [1] the mechanics of indentation of a rigid sphere of rad ius Rin elastic rigid-p lastic two-layered halfspace(single-layered topocomposite) is considered. The topocompositeconsists of a top layer with thickness h coherently boundedwith a substrate, which is essentially thicker than a top layer, i.e.H>>h. The material of the top layer has elastic characteristics -the modulus ofnormal elasticity E 1 , Poisson' s ratio μ 1 and yield point (init ial tensile yield stress) 1 T  , for thesubstrate material these characteristics are 0…”

“…The development of the methods of parts surfaces hardening by concentrated flows of energy and matter allows obtaining high-quality coatings with the thickness of a fraction of micron. Mechanical properties of such coatings may d iffer markedly fro m that of substrates [1].…”

Elastic Characteristics Calculation for Thin Coatings and Bodies with a Topocomposite Structure Considering Specific Deformation of Layered Bodies during Instrumented Indentation

“…, H 0 , H 1 is the hardness of the substrate material and the coating, respectively; sc is the penetration depth of the pyramidal indenter corresponding to the load Pc (more details on the derivation of the dependences and the notation of the parameters are provided in [3]). …”

“…, where с  is the spherical indenter penetration into a perfectly elastic single-layer topocomposite; 0  is the spherical indenter penetration into a homogeneous half-space having an elastic characteristic of the substrate material of the topocomposite; Ф is the elastic-geometric parameter: The study in [3] illustrates the possibility of transforming analytic expressions describing the mechanics of the contact interaction of a sphere with a two-layer solid body (a singlelayer topocomposite) into a dependence of the loading forces and hardness on the pyramidal indenter penetration, which is typical for the standard instrumented indentation procedure [4]. The analysis of the obtained theoretical dependences has shown that the hardness at indentation of the topocomposite surface over the entire depth of the surface layer with increasing penetration depth is characterized by three regions of existence of the parameters under study.…”

“…The objective set in this work is achieved by applying the basic principles of the developed in [1][2][3] model of contact interaction of a spherical indenter with the elastic-plastic layered system surface simulating a solid surface hardened by a thin protective coating. The model is based on the modified Hertz problem, which takes into account the true diagram of the contact pressure in the sphere interaction with the hardened surface.…”