OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 4 2023 Ta b l e 2 Modes of electric discharge alloying Specimen designation МС50 МС150 МС450 S 50 150 450 T, ms 2.5 7.5 22.5 τ, µs 50 50 50 Number of pulses 144,000 48,000 16,000 ASTM G99-17 standard under dry sliding friction with the use of a disk counterbody made of M45 highspeed steel (65 HRC) at a speed of 0.47 m/s at a load of 25 N. Cyclic high-temperature resistance tests were carried out in a muffle furnace at 700 °C in air. The specimens in the form of a cube with an edge of 6 mm, with a coating on each face, were held at a given temperature for ~6 h, then cooled in an desiccator to room temperature. The total testing time was 100 h. During the oxidation resistance test, the specimens were placed in ceramic crucibles to account in the mass of formed oxides. The wetting edge angle was determined by the “sessile drop” method [23]. Free surface energy was determined by wetting with distilled water, ethanol (C2H5OH), sodium chloride solution (6M NaCl), formic acid (CH2O2). The free surface energy was calculated using the theoretical model [24]: 2 1 2 1 ( ) SL S L S L L S Y Y Y Y Y Y Y = + - - β - (1) which in combination with Young’s equation gives: [ ]2 1 (1 cos ) 2 1 ( ) , S L S L L Y Y Y Y Y + Θ = - β - (2) where β1 is equal to 0.0001057 (m/mN) 2. Then equation (2) allows, with some assumption, to estimate the free surface energy (Ys) from the measurement of the contact angle of a liquid with known surface tension YL. Results and its discussion The study of mass transfer in the EDA process is important for establishing the fact of cathode weight increase and the value of specific cathode weight gain, especially when using new anode-cathode electrode pairs, since the coating thickness can be considered as a function of cathode weight gain over time [25]. Fig. 1 shows the dependences of anode erosion, the value of specific cathode weight gain and total mass-transfer coefficient on the EDA time. The anode electrical erosion curves increased linearly over the EDA time (fig. 1, a), the greatest anode erosion was observed at the highest duty cycle. With increasing the duty cycle by 3 and 9 times, the erosion values decreased in 1.2 and 5 times, respectively. Thus, the anode erosion depends nonlinearly on the number of pulses sent by the generator. With an increase in the duty cycle due to a reduction in the number of discharge pulses, the values of summarized cathode weight gain decreased by 1.5 and 2.2 times, respectively (fig. 1, b). The cathode weight gain monotonically increased during the first 4 minutes of EDA, and in the following 5–6 minutes a slowdown in the weight gain was observed due to the approaching the brittle fracture threshold [21]. In accordance with this, the mass-transfer coefficient (Сt.c) gradually decreased with increasing EDA time for all modes. At minimum duty cycle, Сt.c was twice as large compared to the other modes (fig. 1, c). This is explained by the decrease in the number of discharges per unit of the surface being treated per unit of time, at which the electrodes cool down to lowest temperatures. When the initial temperature of the anode decreases, the volume of melt microbath decreases and, accordingly, erosion at a single discharge decreases.
RkJQdWJsaXNoZXIy MTk0ODM1