Micromechanical Characteristics of the Surface Layer of 45 Steel After Electric-Spark Treatment
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MICROMECHANICAL CHARACTERISTICS OF THE SURFACE LAYER OF 45 STEEL AFTER ELECTRIC-SPARK TREATMENT V. М. Holubets’,1, 2 М. І. Pashechko,3 J. Borc,3 and М. Barszcz3
UDC 620.198
We analyze the principal micromechanical characteristics of the surface layers of 45 steel with electricspark coatings, namely, their microhardness, microplasticity (creep), Young’s modulus, elastic and relaxation properties, elasticity of microstrains, and the changes in the contact stiffness. Keywords: electric-spark coating, nanoindentation, nanoscratching, micromechanical characteristics.
Introduction As a major task of mechanical engineering, we can mention the necessity of increasing the reliability and durability of machine components, mechanisms, and cutting tools. In this case, an important applied problem is to guarantee the realization of conditions of steady-state friction and wear in elements of tribojoints and the stability of their operation. The technology of electric-spark alloying (ESA) is now extensively used in the industry due to the possibility of transfer of any conducting materials onto the hardened surface, high strength and adhesion of the hardened surface layer of the metal, local deposition of electric-spark coatings (ESC) without noticeable deformation, the absence of heating of the treated surface, and low energy consumption. For the efficient application of ESA, it is important to develop and master new electrode materials (today, these are mainly titanium–cobalt and tungsten–cobalt hard alloys, and graphite; in some cases, also chromium, white cast iron, etc.). The restoration of the sizes of components is also performed by the ESA method, as a rule, with the help of electrodes made of materials similar in their physicomechanical properties to the material of the product. In the process of friction, the contacting surfaces are subjected to various mechanical and thermal actions, which strongly affects both the structural changes in the surface layer and the tribotechnical parameters of friction couples. The tribological behaviors of the components are determined by the physicomechanical properties of the surface layers with a thickness of up to 0.1 mm. Note that the contact processes are localized in these layers [1]. Under the conditions of friction, the surface microasperities suffer the action of stresses in different directions. These stresses vary from compression to tension and damage the surface [2]. The fracture resistance and the character of damages are determined, first of all, by the mechanical characteristics of the surface layers and the works of elastic and plastic deformation of the microasperities. These quantities may undergo significant changes under the influence of the components of the medium [3, 4]. The micromechanical characteristics of thin surface layers in micro- and submicrovolumes can be evaluated either by the dynamic nanoindentation with recording of the kinetic diagrams of indentation [5, 6] or by using 1 2 3
Ukrainian National Forestry University, Lviv, Ukraine.
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