Institute of Fundamental Technological Research

This paper presents an analysis of various technologies, including such as aluminization, cementation, nitriding, and nitrocementation, to increase the quality parameters of surface layers of parts, performed by electrospark alloying (ESA) and by additional saturation of surfaces with alloying elements from special technological environments (STE). During aluminization, the thickness of the "white" layer and the diffusion zone, as well as the microhardness, coating continuity and roughness of the surface increased as the discharge energy (Wp) increased. The layer consists of iron-aluminium intermetallics and free aluminium. It has been proposed to perform the ESA process with the same electrode (aluminium), but at lower energies, in order to reduce the surface roughness and obtain continuous coatings. The comparative study of the parameters of the quality of the layers after the traditional cementation - ESA with carbon electrode (CESA) and after the proposed one has shown that after the treatment of the surface with the use of the proposed technology, the roughness of the surface decreases. Simultaneously, the continuity of the doped layer increases up to 100%, the depth of the carbon diffusion zone increases up to 80 µm, and the microhardness and "white" layer thickness increase to 9932 MPa and 230 µm, respectively. The analysis of the structure-forming characteristics of the surface layers of carbon steel after ESA nitriding and nitrocarburising using STE has shown that the layer structures obtained consist of the following three areas, such as the non-etchable "white" layer, the modified diffusion zone and the substrate. Thickness, microhardness of the coating zones, integrity of the "white" layer, and surface roughness also increase as the discharge energy increases.

Electrodes, Hardness, Metallurgy, Surface hardening

The paper analyzes the works devoted to solving problems affecting the bearing life of rolling bearings (RB) and to revealing reserves for its increase. There proposed a new technology for forming a protective coating on the shaft bearing journal or on the surface of a sleeve pressed thereon, which consists in the use of a combined technology comprising a process for stage-by-stage aluminizing by the method of electrospark alloying (A ESA ) followed by a process of ion nitriding (IN). Such a coating has a 100% continuity, the greatest thickness of the increased hardness zone of 300 µm, the surface microhardness of 7700 MPa, and the roughness (Ra) after non-abrasive ultrasonic finishing (NAUF) of 0.5 µm, The results of the X-ray microanalysis indicate that an increased content of aluminum is observed in the surface layer at the distance of up to 40 µm after the stage-by-stage AESA process. The research results have shown that in order to restore the shaft bearing journal neck surface layer hardness, which had been lost because of the repair work, the step-by-step AESA technology is more preferable. Thus, when removing the surface layer to a depth of 0.15 mm and subsequently carburizing by the method of electrospark alloying (C ESA ), the maximum microhardness of the surface layer is 7250 MPa, and the thickness of the zone of the increased hardness is 150 µm, At subsequently processing by the AESA method, these quality parameters of the surface layer are, respectively, 7350 MPa and 210 µm. The use of the NAUF method, both after C ESA and AESA processes, makes it possible to reduce the surface roughness up to Ra = 0.5 µm. To decrease the surface roughness of the RB housing seat, it is advisably to practice burnishing with a diamond tool (DB) after the A ESA process