## 2 Methods  
The main physicochemical characteristics of the metals surface includes its macro- and micro relief, as well as the presence of chemical compounds on it. Even after machining, the surface of the vast majority of structural metals is covered with a thin layer of natural oxide. Oxide films are not ideal dielectrics, but they possess a certain conductivity. The resistivity (\(\rho\)) of most oxide films of the processed metals (Fe, Cu, Mo, W, Ti, etc.) is 10\({}^{3}\)-10\({}^{5}\) Ohm m, and the characteristic value of the dielectric constant is \(\varepsilon\approx\) 2-10 [17]. Therefore, from an electro-technical point of view, an oxide film's capacitance and resistance are connected in parallel. The capacitive properties of the film appear at times \(t_{0}\leq\varepsilon\epsilon_{0}\rho\approx\) 3 (10\({}^{-8}\)-10\({}^{-6}\)) sec [18]. The maximum electric field strength due to the accumulation of charge on the oxide film over this time is defined as  
\[E\approx\frac{1}{\varepsilon\epsilon_{0}}\int\limits_{0}^{t_{0}}jdt\approx jp, \tag{1}\]  
where \(j\)--the current density at the cathode of the discharge. In a normal glow discharge, the gas pressure in the working chamber determines the current density in the cathode spot and at the pressures of 1.33-13.3 kPa it can reach 10\({}^{2}\)-10\({}^{3}\) A/m\({}^{2}\). Thus, in a normal DC glow discharges at pressures characteristic of technological processes of metal treatment and welding, the electric field may not reach the values of the electric field strength breakdown for thin oxide films. As it was mentioned in [16], the heating of the oxide films to a 1200 K leads to a rapid decrease of its resistivity (four to six orders of magnitude). Therefore, taking into account the simultaneous heating of the films together with the samples and the noticeable decline in the film resistance with increasing of the temperature, the emergence of arcing breakdown is unlikely. Consequently, the presence of an oxide film on the surface of the cathode (product) can make a massive impact on the discharge's stability but only on the cold cathodes. With the heating of cathode, this factor becomes unimportant. The next parameters characterizing the state of the cathode surface are its macro- and microrelief. In this case, the glow discharge's stability can be affected with the pronounced roughness protrusions obtained after machining, but not with the smoothly changing surface waviness. Figure 3 shows profile curves of the sample's surfaces obtained after treatment with a roughness of 60-80 \(\upmu\)m (Figure 3a) and about 10 \(\upmu\)m (Figure 3b), respectively. For this purpose, a profilometer TR--200 was used. Figure 3: _Cont._The external view of the device and treated samples themselves are shown in Figure 4.  
Figure 4: The view of a profilometer TR-200 (**a**) which is made up of: 1—display; 2—control panel; 3—sensor (pickup) and treated samples (**b**). Figure 3: The profile curves of the samples surfaces obtained after machining by rotational turning with the roughness about 80 μm (**a**) and 10 μm (**b**): 1—single placed; 2—ridge-shaped protrusions. The undergoing intense ions bombardment, the protrusions heat up much more noticeably than the bulk of the electrode (cathode). This inevitably leads to the superheat point's emergence on the cathode surface to temperatures exceeding the melting or boiling point of the metal. In this case, a glow discharge can transit to the local vapor arcs [19; 20]. This can be observed most likely in case when the surface of the protrusions is large enough to provide heating to high temperatures, and the heat transfer to the bulk of the samples is too small. The Analytical Equation of a Glow Discharge Energy Stability while Treatment and Welding of Metals Depending on Cathode Surface State  
Cylinders, cones or hemispheres can be taken as a model of individual micro protrusions [21].