Abstract
In this paper, the possibility of applying the electrospark alloying (ESA) method to obtain boron-containing coatings characterised by increased hardness and wear resistance is considered. A new method for producing such coatings is proposed. The method consists in applying grease containing aluminium powder and amorphous boron to the surface to be treated and subsequently processing the obtained surface using the ESA method by a graphite electrode. The microstructural analysis of the Al-C-B coatings on steel C40 showed that the surface layer consists of several zones, the number and parameters of which are determined by the energy conditions of the ESA process. Durametric studies showed that with an increase in the discharge energy influence, the microhardness values of both the upper strengthened layer and the diffusion zone increased to Wp = 0.13 J, Hµ = 6487 MPa, and Wp = 4.9 J, Hµ = 12350 MPa, respectively. The results of X-ray diffraction analysis indicate that at the discharge energies of 0.13 and 0.55 J, the phase composition of the coating is represented by solid solutions of body-centred cubic lattice (BCC) and face-centred cubic lattice (FCC). The coatings obtained at Wp = 4.9 J were characterised by the presence of intermetallics Fe4Al13 and borocementite Fe3 (CB) in addition to the solid solutions. The X-ray spectral analysis of the obtained coatings indicated that during the electrospark alloying process, the surface layers were saturated with aluminium, boron, and carbon. With increasing discharge energy, the diffusion zone increases; during the ESA process with the use of the discharge energy of 0.13 J for steel C40, the diffusion zone is 10–15 μm. When replacing a substrate made of steel C40 with the same one material but of steel C22, an increase in the thickness of the surface layer accompanied by a slight decrease in microhardness is observed as a result of processing with the use of the ESA method. There were simulated phase portraits of the Al-C-B coatings. It is shown that near the stationary points in the phase portraits, one can see either a slowing down of the evolution or a spiral twisting of the diffusion-process particle.
Highlights
Most critical parts of compressors, pumps, gas transfer apparatuses, and other dynamic equipment (DE) operate at high speeds, pressures, and temperatures, and under abrasive and corrosive conditions, or exposure to other types of working environments.Usually, the problems associated with improving the reliability and durability of those parts are solved through the use of expensive and high-hardness materials
We have shown that the alloying procedure performed by the elements during the electrospark alloying (ESA) process can be accomplished by creating a special technological environment (STE) without the use of expensive electrode materials and with a reduction in the time for obtaining a coating, thereby increasing productivity and cutting production costs
The research results indicate that the microstructure of the Al-C-B coatings consists of several zones, the number and parameters of which are determined by the energy conditions of the ESA process (Figure 1)
Summary
Most critical parts of compressors, pumps, gas transfer apparatuses, and other dynamic equipment (DE) operate at high speeds, pressures, and temperatures, and under abrasive and corrosive conditions, or exposure to other types of working environments.Usually, the problems associated with improving the reliability and durability of those parts are solved through the use of expensive and high-hardness materials. Most critical parts of compressors, pumps, gas transfer apparatuses, and other dynamic equipment (DE) operate at high speeds, pressures, and temperatures, and under abrasive and corrosive conditions, or exposure to other types of working environments. In [1], it was shown that in high-speed pumps and high-pressure compressors, non-contact type mechanical seals are widely used, whose sealing rings are made entirely of wear-resistant materials such as tungsten carbide, silicon carbide, and various types of graphite. Being accompanied by an increase in operating parameters of the DE, the development of technology entails the need for the appearance of new and cheaper but no less reliable composite materials that combine the protective properties of the coatings with the mechanical strength of the substrate.
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