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31APPLICATION OF SHS-ELECTRODE MATERIALS IN PULSED ELECTROSPARK DEPOSITION TECHNOLOGY
A. E. Kudryashov*" and E. A. Levashov"
aNational University of Science and Technology MISiS, Moscow, 119049 Russia
*e-mail: aekudr@yandex.ru
DOI: 10.24411/9999-0014A-2019-10072
The pulsed electrospark deposition (ESD) technology is widely used in different industries due to high adhesive properties of the deposited coatings and the fact that this technology allows local treatment of large-size items and is a relatively simple procedure that can be automated. Coating application is an environmentally friendly process characterized by low energy-output ratio, high profitability, and quick achievement of the breakeven point.
The range of practical application of the ESD technology can be broadened by developing novel compositions of electrode materials.
Metals and their alloys, graphite, and hard alloys (mainly those based on tungsten carbides of grades VK (WC-Co), TK (TiC-WC-Co), and TTK (TiC-WC-TaC-Co) that are produced using the traditional powder metallurgy technology) are conventionally used as electrode materials. Tungsten-free hard alloys of grades TN (TiC-Ni-Mo), KNT (Ti(CN)-Ni-Mo), LKTs (TiZr(CN)-Ni-Mo), etc. are less common [1, 2].
However, the conventional microcrystalline hard alloys do not always meet the requirements posed to electrode materials as they are characterized by high erosion resistance, low transfer efficiency, low hardness of coatings formed by these alloys, low heat and oxidation resistance of tungsten carbide, as well as the high coefficient of friction of the deposited coatings.
In this connection, there exists a demand for designing advanced electrode materials, including nanostructured hard alloys. Mastering the technology of self-propagating high-temperature synthesis (SHS) has opened up a fundamentally new approach to fabrication of electrodes for electrospark deposition.
Electrode materials forming multifunctional coatings (wear-, heat- and corrosion-resistant coatings, anti-friction coatings, coatings with enhanced hardness, etc.) on the surface of treated items are selected depending on a specific scientific-and-technological problem. By varying the frequency-energy modes of treatment, as well as the type of electrode materials (hard alloys, metals and their alloys), the ESD technology is successfully used for strengthening and repairing tools and machine components.
The objective of this study was to demonstrate application of SHS-electrode materials for the pulsed electrospark deposition technology.
The designed electrode materials can be subdivided into several groups. However, electrode materials modified with high-melting-point nanodispersed components are the most widely used ones [3].
Application of modified electrode materials becomes especially topical, since these materials improve properties of the deposited coatings (increase their thickness, continuity, microhardness, heat and wear resistance, as well as reduce their coefficient of friction) [3].
The Korona, Impuls, and Elitron equipment, as well as advanced high-frequency Alier-Metal setups, has been successfully employed for solving technical problems. The use of novel Alier-Metal high-frequency setups (with the pulse frequency ranging from 3000-3200 Hz to 50000 Hz) has significantly reduced roughness of the deposited coatings, making it possible to treat critical parts of specialized equipment. It is most reasonable to subject expensive small-batch
XV International Symposium on Self-Propagating High-Temperature Synthesis
items (such as critical parts of aerospace and specialized equipment, large-sized dies for hot forging, and forming rollers) to electrospark treatment.
Electrospark strengthening of a pilot batch of flanges (made of VT 20 titanium alloy) with STIM-3BVn (TiC-Cr3C2-Ni-Wnano) electrode materials was carried out to increase their service life (Fig. 1a). Bench tests conducted at the A. Lyulka Scientific and Technical Center of the Research and Production Association "Saturn" revealed that parts strengthened with SHS electrodes had undergone minimal wear. Tests of the parts strengthened with T15K6 alloy were stopped because of significant wear. STIM-3BVn electrode materials have been introduced into manufacturing of flanges employed in 117C aircraft engines and are supplied to a number of enterprises (PAO "Ufa Engine Industrial Association", Lytkarino Machine-Building Plant, and AO "Salyut Machine-Building Production Association.")
Technological recommendations for electrospark deposition of coatings using SHS electrodes onto pilot batches of advanced aircraft equipment parts made of titanium alloys have been developed in cooperation with the All-Russian Scientific Research Institute of Aviation Materials for OAO "Production Design Corporation Teploobmennik". The technology of electrospark treatment of dies was intended primarily for strengthening dies for hot-die forging as this is the most complex and expensive type of dies. The technology is successfully used for strengthening other types of dies: blanking, forming, drawing, bending, isothermal, as well as cold-forging dies.
Application of advanced modified hard-alloy electrodes and modern Alier-Metal equipment ensures that durability of die tooling is enhanced over twofold. In order to improve performance, solid lubricants (WSe2, MoS2, graphite) were applied onto coatings deposited by electrospark treatment. Durability of the drawing matrix used at the cold die-forging shop at the Likhachev Moscow Automotive Plant (AMO ZiL) treated using this technology increased more than 12-fold. The developed technology of electrospark strengthening of die tooling has undergone appraisal at such enterprises as PAO "Ufa Engine Industrial Association", S. Ordzhonikidze Plant (Podolsk, Russia), AO "Salyut Machine-Building Production Association", AMO ZiL, Turbine Blades Plant, a branch of OAO "Powder Machines" (St. Petersburg, Russia), Aircraft Production Association (Nizhny Novgorod, Russia), Plant of the Research Institute of Automation and Instrument-Building (NIIAP) (Moscow, Russia), AOOT "Kontur" (Novgorod, Russia), AO "Stupino Metallurgical Company", etc. At a number of enterprises, the developed technologies for die strengthening and SHS-electrode materials have been introduced into the technological process.
A hardening unit manufactured by Cobra company is used at ZAO "Sprint-RIM" (Moscow, Russia) to produce metal strap. The temperature of metal strap exposed to hardening is 960°C at the inlet and 20°C at the outlet of water-cooled plate. While in service, the plate surface undergoes severe wear. In order to increase the service life, the plate surface was subjected to ESD treatment with STIM-40NA (TiC-NiAl), STIM-40NAKNn (TiC-NiAl-NbCnano), and VK8 electrodes. ESD treatment enhanced plate durability more than tenfold.
Application of high-energy modes of ESD made it possible not only to strengthen the surface of forming rollers for copper wire production (up to fourfold) but also to restore their size after roller re-machining (ELKAT Enterprise, Moscow, Russia). Electrospark retreatment of the deposited coatings with carbon-containing materials was proposed to further enhance performance of the coatings. Retreatment reduces roughness of the surface layer and the size of structural components of the coating, increases the volume fraction of carbide phases, reduces and stabilizes the coefficient of friction at elevated loads and temperatures [4, 5].
SHS-electrode materials have been successfully used to treat cutting tools, parts of railway equipment, brick-making molds, drill bit casings and milling cutters for the construction industry, to strengthen valve ends of internal combustion engines for sport cars manufactured from titanium alloys, casings of sensors for oil wells (Fig. 1b), and to restore the size of various items.
(a) (b)
Fig. 1. Strengthened items. A flange (a) and a sensor housing (b).
1. A.E. Gitlevich, V.V. Mikhailov, N.Y. Parkanskii, et al., Electrospark Alloying of Metal Surfaces, Chisinau: Shtiintsa, 1985, 195 p.
2. S.V. Nikolenko, A.D. Verkhoturov, New Electrode Materials for Electrospark Alloying, Vladivostok: Dal'nauka, 2005, 219 p.
3. E.A. Levashov, A.S. Rogachev, V.V. Kurbatkina, Yu.M. Maksimov, et al., Advanced Materials and Technologies of Self-Propagating High-Temperature Synthesis, Moscow: Mosk. Inst. Stali Splavov, 2011, 377 р.
4. A.E. Kudryashov, Zh.V. Eremeeva, E.A. Levashov, V.Yu. Lopatin, et al., On application of carbon-containing electrode materials in technology of electrospark alloying: Part 1. Peculiarities of coating formation using electrospark treatment of titanium alloy OT4-1, Surf. Eng. Appl. Electrochem., 2018, vol. 54, no 5, pp. 437-445.
5. A.E. Kudryashov, Zh.V. Eremeeva, E.A. Levashov, V.Yu. Lopatin, et al., On the application of carbon-containing electrode materials in electrospark alloying technology. Part 2. Structure and properties of two-layer coatings. Surf. Eng. Appl. Electrochem., vol. 54, no 6, pp.535-545.
