## 1 Introduction  
The serviceability of a machine partly depends critically on the stability of the constituent metal during loading. The loading could be cyclic, continuous or impact loading [1, 2]. Failure under the influence of different types of loads mainly starts from the part's surface layer [3]. Treatment of the part's working surfaces significantly affects damage initiation and growth and accordingly the product operability as a whole [4]. The formation of a thin surface layer of the part (using methods related to surface engineering) can extend the overall machine life and reliability as a whole [5, 6]. One of the most important issues in the reliability of machine parts is to improve their performance properties by forming strengthened layers with a nanocrystalline structure on the working surfaces of massive parts. The working surfaces of parts can be strengthened by applying various types of coatings [7, 8, 9], saturating the surface layers with various chemical elements [10, 11, 12], and modifying the surface layers [13, 14, 15, 16]. During modification, the phase and structural state,grain size, chemical composition, and physical, mechanical and electrochemical properties of the surface layers change [17; 18]. The crystal lattice of the modified metal in the surface layer is the same as that of the base metal, and its dimensions change. There is no clear interface between the strengthened layer and the base metal [19; 20]. Methods that use highly concentrated energy sources (laser [21; 22], plasma [23] and other treatments [24; 25; 26]) are currently used to strengthen the working surfaces of machine parts [27; 28; 29]. The essence of these surface strengthening methods is that small volumes of metal are influenced by concentrated energy streams of high intensity at high velocities (the high-rate heating of the metal of the surface layer to temperatures of polymorphic transformations), followed by rapid cooling. The structure of the metal surface layer is ground down to the size of nanocrystals by heating, cooling and deforming it at a high rate. Such treatment conditions produce strengthened surface layers with specific mechanical, electrochemical, corrosion and operational characteristics. Such methods also include friction treatment [30; 31]. In the process of strengthening by using highly concentrated energy source methods to increase the thickness and microhardness of the layer on the working surfaces of machine parts, various types of coatings, pastes, etc., are applied. Chemical elements diffuse from coatings and pastes into the surface layers of the treated surfaces under heat flow. Due to this, the characteristics of the strengthened surface layers are improved. Thermo-deformation treatment (TDT) refers to strengthening methods using highly concentrated sources of thermal energy. Heat flow occurs due to the friction of the tool at high speed on the processed surface in the zone of their contact. The contact zone is heated to high temperatures (above the polymorphic transformation temperature). To prevent metal adhesion of the contacting surfaces and improve the quality parameters of the treated surfaces, a process fluid is introduced into the processing zone. These process liquids can also help to form strengthened layers with improved properties. The process liquid is decomposed into chemical components under the influence of high temperatures and pressures in the contact zone of the tool's working surface with the surface to be processed, diffusing into the surface layer's metal. The composition of mineral oil includes the C-H group (C--carbon and H--hydrogen), that is, carbon and hydrogen are released during decomposition, which diffuse into the surface layer of the metal. Strengthened layers with a nanocrystalline structure significantly improve the performance characteristics of machine parts, especially the wear resistance of friction pairs under various wear conditions [29; 30].