UDC 621.9.048The use of focused solar radiation to improve the mechanical properties of spark-deposited TiN, TiB 2 , and Mo coatings is studied. It is shown that the tribotechnical characteristics of sparkdeposited coatings improve after exposure to focused solar radiation over steel coatings after thermal treatment. Solar treatment of 30KhGSA steel leads to its strengthening-hardening with fine-grained annealed martensite being formed.The improvement in the tribotechnical properties of structural steel parts is important technically and economically. In aviation, the tribotechnical properties of 30KhGSA steel are improved mainly by placing a galvanic chromium coating over it. This method is advantageous as it provides high wear resistance, low friction coefficient, and corrosion resistance of the coating [1]. However, it is disadvantageous as the coating process is environmentally harmful, decreases fatigue characteristics, takes much time, and is expensive.Hence, electrospark alloying (ESA) needs to be used to improve the surface behavior of 30KhGSA steel. It is mainly intended to make an alloyed layer to be strongly bonded to the substrate. Equipment for ESA is simple and easy to operate. However, nonuniform rough coatings are one of its drawbacks (because of discrete discharge pulses) [2]. To improve the physical and technical properties of spark-deposited coatings (roughness, porosity), focused solar radiation (FSR) should be used [3]. For obtaining wear-resistant coatings, TiN and TiB 2 are promising materials. To decrease the brittleness of electrodes from these materials, Cr, Ni, Mo, and Al 2 O 3 additions are introduced [3].The objective of this paper is to study the use of FSR to improve the mechanical properties of sparkdeposited coatings.We examined the structure and properties of spark-deposited TiN-(Cr, Ni), TiN-(Ni, Mo), and TiB 2 -(Ni, Mo) coatings on 30KhGSA steel. All materials contained Al 2 O 3 . An EFI-46A unit was used for ESA at I = 1.5 A and C = 300 μF; the tribotechnical characteristics were determined using an MT-68 friction test machine in air at a sliding speed of V = 10 m/sec and a load of P = 0.5 MPa. We used 65G steel (HRC 50) as a counterface. An SGU-2
The composition of iron-based electrode material for the spark restoration of steel parts is optimized. The material permits depositing coatings twice as thick as those made of sormite. Varying the content of chromium carbide, one can change coating hardness from 3.9 to 6.8 GPa. The wear resistance of coatings is increased by 20 to 35%.Austenitic chromium-nickel steels, stellite, and sormite are used to restore machinery parts with spark deposition. Chromium-nickel steel promotes good deposition resulting in coatings up to 1 mm thick. The steel is austenitic and does not harden (rapid quenching takes place in spark deposition) and thus plastic deformation may occur when a coating is formed. Such coatings have insignificant hardness but are usually used in friction conditions intended for hard, tempered steel.Stellite coatings have good hardness (40-46 HRC) and thickness (to 1 mm), but the base metal for these alloys is cobalt, which is very expensive. The most acceptable material for depositing restoration coatings is sormite (stellite-like material). Its base metal is iron, which contains (wt.%) 1.5-5.5 C, 27-32 Cr, 1-4 Si, 1-2 Mn, 1-5 Ni, 0.1-1 Mo, and 0.2-0.4 W [1]. Sormite is cheaper than stellite, also ensures good deposition (coating thickness to 1 mm), and has high hardness (44-52 HRC).This material has been developed for arc or oxyacetylene deposit welding with flux or gas protection against oxidation. Spark deposition differs from deposit welding by discreteness, large temperature gradients, and no need for oxidation protection in air. Therefore, the composition of electrode material should be adjusted to such conditions. Mangan as an alloy deoxidizer in spark deposition does not give good results (steel G13 is also austenitic and should seemingly promote proper deposition, but this is not actually so and the coating surface is dark because of extensive oxidation). Hence, only silicon should be used as a deoxidizer since it forms protective glassy films [2].Tempering at high temperatures makes steels containing chromium, nickel, and silicon brittle. Sormite is also among such materials. Temper brittleness may be avoided by either rapid quenching or addition of a small amount of Mo (0.2-0.4%) or W (0.5-0.7%). Steel cannot be rapidly quenched in deposit welding since heat is generated continuously and the electrode moves slowly over the surface. Hence, molybdenum or tungsten is introduced into sormite. In spark discharge, heat is generated during 0.2-0.4 µsec, which is only 2-4% of the total treatment time at a pulse frequency of 100 Hz. The rest of the time goes for rapid quenching as metals have high heat conductivity. Temper brittleness is prevented by rapid quenching, and Mo or W is not required in electrode material.
The paper examines how the porosity of electrode materials used to restore parts influences the electrospark deposition process. A higher porosity decreases the heat conductivity of the electrode material. A smaller amount of heat spreads along the electrode and, hence, a greater amount of heat remains for melting. Erosion and deposition of the material increase accordingly.
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