## 1 Introduction  
Surface modification and protective coating deposition are widely spread technologies used to improve the exploitation durability of machine parts and tools [1; 2; 3]. Electric-arc spraying (EAS) (metallization) belongs to the family of spraying technologies aimed at the formation of a coating through transferring molten metal to the target surface [4; 5; 6]. EAS procedure uses airflow to atomize and transfer the electrode's material melted in a weld arc [7; 8]. With that, an intense chemical interaction of the atomizing airflow with the electrode material occurs, leading to substantial burnout of alloying elements and deterioration of the deposited coating [9]. The oxidation negatively affects the microstructure leading to a decrease in exploitation behavior (wear resistance [10; 11], corrosion resistance [12], pull-off strength [13], mechanical properties [14], etc.) of the coatings and bulk metal parts. The oxidizing intensity grows with an increase in air pressure and the distance between the apparatus nozzle and the processed part [15]. Therefore, the influence of an atomizing gas flow upon the quality of the deposited coatings was always in the focus of the researchers [16]. Particular attention was paid to spraying distance as a key EAS parameter, determining atomizing gas dynamics. The work [17] presents the evaluation method for the spraying distance where the molten drops retain their spherical shape before their collision with the surface. Based on the analysis of the dynamics of the drops' flight, the maximal critical size of the spraying area was determined on the example of carbide material [17]. Much attention has been paid to the investigation of the influence of nozzle geometry and dynamics of atomizing gas flows on the properties of steel coatings [18; 19; 20]. [PERSON] et al. [21] developed the nozzles of different designs based on the simulation of the airflowgeometry and atomizing velocity. By comparing these nozzles, the authors [21] revealed the presence of non-uniformity of a gas flow density and velocity depending on the type and length of the nozzle. Similar results were obtained in [22], which was devoted to investigating the process of twin-wire spraying with the application of front and axial nozzles. In [23], the flow inside and outside the spray gun and gas-particle interactions were simulated based on a three-dimensional model. The numerical hydro-dynamic analysis performed in [24; 25] with the application of equations of continuity and momentums for different inclination angles of the front spraying nozzle revealed a high-velocity area inside the airflow. Experimental determination of the molten particle velocity and the porosity of the deposited coating showed that the density and the temperature of the flow grow with an increase in the electrode inclination angle. The influence of electrodes on airflow dynamics was investigated in [24], where with the application of hydro-dynamical calculations and the help of a high-speed camera shooting, the character of wave expansion and its influence on the dimensions of the sprayed particles were studied. This work testifies the prospects of the application of pulsating and mixed flows. [PERSON] et al. [26] investigated the effect of impulse parameters of arc current upon the molten metal behavior and heat transfer under EAS. On the basis of the gas flow simulation using the magnet hydrodynamics equations, the authors [26] analyzed five sets of current variations, which are of interest from the point of view of the formation of the molten metal droplets. Gas dynamics of thermal spraying have been largely investigated in regard to the plasma method of atomizing. [PERSON] et al. [27] presented the results of investigations of the arc dynamics and its influence on temperature distribution and flow fields inside and outside the heat source. This work confirmed the importance of control over airflows at different types of atomizing.