OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 Ta b l e 1 Composition of anode mixtures, designations and characteristics of coatings Designation of samples Composition of powder mixture, vol.% Charge content in the anode mixture, vol.% The content of ERTi-1 granules, vol.% Thickness, μm Si Ti Si2.6 31.6 68.4 2.633 97.367 24.8 ± 7.9 Si6.0 6.048 93.952 21.7 ± 11.2 Ta b l e 2 Chemical composition of AISI304 steel Element Fe Cr Ni Mn Cu P C S Concentration, wt. % 66.374 18 8 ≤ 2 ≤ 1 ≤ 0.045 ≤ 0.03 ≤ 0.03 generated discharge rectangular current pulses with an amplitude of 110 A, at a voltage of 30 V, with a duration of 100 μs and a period of 1,000 μs. Argon was filled into the working volume of the container at a rate of 10 L/min to prevent titanium nitriding. The setup for electrospark deposition of coatings with a non-localized electrode is described in detail in [14, 15]. The structure of the coatings was studied using a Vega 3 LMH (Tescan, Czech Republic) and an X-max 80 energy dispersive spectrometer (EDS) (Oxford Instruments, UK). The phase composition of the coatings was determined using a DRON-7 X-ray diffractometer in Cu-Kα radiation. The microhardness of the coatings was measured on a PMT-3M hardness tester at a load of 0.5 N according to the Vickers method. The wear resistance and coefficient of friction of the coatings were studied according to the ASTM G99 – 17 using “pin-on-disk” scheme. The tests were carried out in dry sliding mode using a counterbody in the form of a disk made of high-speed steel M45 at speed 0.47 ms– at a load of 10 N for 600 s. Polarization tests were carried out in a three-electrode cell after 30 minutes of holding samples in a 3.5% NaCl solution under natural aeration conditions at room temperature until a stationary value of the corrosion potential was established. Scanning was performed using a P-2X potentiostat (Elins, Russia) at a rate of 10 mV∙s–1 in the range of –1.5 – 0.5 V. The contact area of the samples with the electrolyte solution was 1 cm2. The counter electrode was a paired ETP-02 platinum electrode, the reference electrode was a standard silver chloride electrode, and the coated samples and AISI304 steel served as the working electrode. The test for cyclic high-temperature resistance was carried out in a furnace at a temperature of 900 °C. The total testing time was 100 hours. The samples were kept at a given temperature and after some time intervals (~6 hours) were removed and cooled in a desiccator to room temperature. During the test, all samples were placed in a corundum crucible to account for the mass of exfoliated oxides. The weight change of all samples was measured using a laboratory balance with an accuracy of 0.1 mg. Results and discussion The coatings were deposited within 180 s, since the mass of the substrate began to decrease during further processing due to the accumulation of defects and the onset of the threshold of brittle fracture of the coating, which is characteristic of ESD [16]. The X-ray analysis of the coatings showed the presence of ferrochrome (Fe-Cr) and hexagonal titanium (αTi) phases forming the coating matrix (Fig. 1). Titanium silicide Ti5Si3 and silicon act as a reinforcing ceramic. The Ti5Si3 phase is formed during the interaction of silicon with titanium melt on the granule’s surface, which is accompanied by heat release (ΔHo 298 = = –581.2 kJ/mol), according to reaction 1: 5Ti + 3Si = Ti5Si3. (1)
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