## 2 Materials and Methods  
Cylindrical samples made of CrWMn steel (Table 1) with a diameter of 10 mm and a height of 15 mm with a roughness \(R_{a}\) of 1.0 \(\pm\) 0.1 \(\upmu\)m were used for the study.  
The setup shown in Figure 1 was used to process the steel samples. PEN and PEP were performed on this setup using different electrolytes and electrophysical processing parameters. An aqueous solution containing ammonium chloride NH\({}_{4}\)Cl (10%) and ammonium nitrate NH\({}_{4}\)NO\({}_{3}\) (10%) was used for nitriding. Diffusion saturation (nitriding) was carried out at a temperature of 700 \({}^{\circ}\)C for 5 min. After saturation, the sample temperature was increased to 850 \({}^{\circ}\)C, and quenching was carried out by disconnecting the voltage. Then, the nitridted samples underwent PEP. For this purpose, an aqueous solution of ammonium chloride NH\({}_{4}\)Cl (3%) with the addition of glycerol C\({}_{3}\)H\({}_{8}\)O\({}_{3}\) (5%), as well as an aqueous solution of ammonium sulfate (NH\({}_{4}\))\({}_{2}\)SO\({}_{4}\) (5%) were used. The polishing process was carried out at a voltage of 325 V for 1 and 2 min. During PEN and PEP, electrolytes circulated through a heat exchanger to maintain a constant temperature: 30 \({}^{\circ}\)C during nitriding and 70 \({}^{\circ}\)C during polishing.  
To determine the phase composition of the treated surface, a PANalytical Empyrean X-ray diffractometer (Malvern Panalytical, Malvern, UK) with PANalytical High Score Plus software (v.2.0.0) [40] and ICCD PDF-2 and COD databases [41] was used.  
The cross-sectional structure of the treated samples and their elemental composition were analyzed using a Tescan Vega 3 scanning electron microscope (SEM) (Tescan,  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline
**Element** & **C** & **Cr** & **W** & **Mn** & **Si** & **Ni** & **S** & **P** & **Cu** & **Fe** \\ \hline wt.\% & 0.9–1.05 & 0.9–1.2 & 1.2–1.6 & 0.8–1.1 & 0.1–0.4 & \(\leq\)0.4 & \(\leq\)0.03 & \(\leq\)0.03 & balance \\ \hline \end{tabular}
\end{table}
Table 1: Composition of CrWMn steel samples.  
Brno, Czech Republic) and an X-Act energy dispersive analysis (EDX) detector (Oxford Instruments, Abingdon, UK).  
The structure of the modified layer, as well as the morphology of the surface and friction tracks after tribological tests, were analyzed using a Micromed MET optical metallographic microscope (Micromed, St. Petersburg, Russia).  
The distribution of microhardness in the surface layer of the treated samples was determined using a Vickers microhardness tester (Falcon 503, Innovatest Europe BV, Maastricht, The Netherlands) under a 10 g load.  
A TR-200 profilometer (Beijing TIME High Technology Ltd., Beijing, China) was used to measure the surface roughness and microgeometry parameters of the friction track.  
Tribological tests were performed on the side surface of the samples according to the shaft-bushing scheme (Figure 2). In this scheme, the sample was a rotating shaft, and the counter body made of hardened tool steel was a bushing. The sliding speed over a path of 1000 m was 1.555 m/s at a constant load of 10 N.  
Figure 1: PEN and PEP installation scheme: 1—ventilation duct; 2—protective screen of the working chamber; 3—linear drive; 4—workpiece-electrode (anode); 5—cylindrical cell-electrode (cathode); 6—working chamber; 7—valve with electric drive; 8—flow meter; 9—heat exchanger; 10—pump; 11—water filter.  
Figure 2: Friction scheme and unit: 1—cylindrical sample; 2—counter body; 3, 4—shaft; 5—crank; 6—pneumatic cylinder; 7—guides; 8—table; 9—strain gauges.