Combined process of vibratory processing and oxidation with the use of polymeric environments

. Studies were carried out to combine vibration processing and oxidation in polymer working media, which allowed to combine three technological stages. Characteristic traces of direct and oblique impact of the polymer working medium, along the surface of the metal with oxide film, are determined. Studies of the structure of the nanorelief of the vibrational chemical-mechanical oxide coating and the main parameters of the process are . 10 and 1 μm). The study of the coating surface at the micro / nanoscale was carried out on a Zeiss SUPRA25 analytical field emission electron microscope. Longitudinal lines are visible on the surface after machining with a thickness of up to 1 micron.


Introduction
Vibration processing makes it possible to provide the effect of the combined action of the energy resulting from the mechanical and chemical components of the coating formation process. Vibration processing provides a change in the physical and chemical properties of the surface layer of the part, as well as its activation. Given the versatility of vibration equipment, it can be used not only for coating formation processes, but also for finishing and stripping and hardening operations, which is important because reduces the cost of production [1][2][3][4][5][6][7].

Materials and research methods
The study of the mechanism of formation of an oxide film is based on the methodology for determining the nature of the location, size, depth and shape of processing traces when working in an environment of polymer working media (polyethylene balls) during oxidation and without an oxidizing solution and for establishing the quality of the film, the general appearance of the surface using optical electron microscopic research methods.
In previously published works [8][9][10][11][12][13] there is information about the formation of the surface layer in the process of vibration processing in the environment of metallic working media. These processes are accompanied by plastic deformation of the surface layers of the metal under conditions of multiple dynamic contact of particles of the working medium with the part.
When combining the method of vibration processing and oxidation, the interaction of the polymer working medium and the surface layer of the material being processed is carried out through the interlayer of the formed oxide film and the solution located in the contact zone. According to the theory of chemical oxidation, the formation of an oxide film, its growth is the result of the interaction of the metal with the working solution, which is carried out through the pores of the film formed during the oxidation process.
The working medium must not interact with the process fluid (oxidizing solution). Considering that finishing and oxidation is the final operation in the technological process, the working environment should be light, elastic, and not allow scratches and nicks. Therefore, as a working medium, we used polymeric working mediums ø 2-3 mm (Fig. 1). Non-metallic bodies ensure the uniformity of the oxide coating over the entire surface of the workpiece, serve as suppliers of the oxidizing solution to the reaction zone, as well as smoothing irregularities. Table 1 shows some of the characteristics of polyethylene.  The vibrating polymer balls, in contact with the surface growing under the action of the chemical component of the combined oxide film process, loosens it, which facilitates the access of the oxidizing chemical solution to the metal surface. The reactivity of the solution is enhanced by the activation of its constituent components.
The intensity of the ongoing processes is noted not only in the reaction zone, but also in the zone of direct contact. Under the influence of normal and tangential forces, the surface layer of the oxide film changes due to the vibrational mechanical action of the system. Shear processes of elastoplastic deformation include the sliding mechanism, which manifests itself in the movement of one part of the grain in relation to another. Outwardly, the manifestation of this movement is expressed by the formation of slip bands on the metal surface [21][22][23][24][25]. Figure 1 shows the structure of the AD1 aluminum alloy before and after processing. Analysis of the photographs shows that when evaluating the roughness, which determines the operational properties of the product, on the surface under study there is a large number of randomly located processing traces -protrusions and depressions. They come in a variety of shapes, depths and sizes. Shallow depressions and longitudinal multidirectional marks of various shapes and sizes are visible, which is a consequence of direct and oblique impacts of the polymer working medium. The contours of the tracks are uneven, which indicates the variable nature of the movement of the polymer ball relative to the treated surface. [30][31].
When examining photographs of the surface of the samples processed for 15 minutes, the heterogeneity of the surface layer of the treated surface is noted. There are polished areas of the surface and areas with signs of destruction. With a longer treatment (35 min), contact and the overlap of many single traces on the metal surface are observed. When examining the processed traces, it can be seen that individual polymer balls, when interacting with the treated surface, leave on it an intermittent trace, consisting of smaller traces due to the nature of the movement of the balls. With such a cross pattern of the arrangement of the considered traces of processing, a kind of microrelief is formed, which affects the quality of the vibration chemical-mechanical coating. Analyzing the results obtained, it can be noted that when applying a vibrational chemical-mechanical oxide coating, elongated traces are formed on the coating surface, resulting from the sliding of the ball relative to the treated surface, and mixed-type traces, which are the result of both sliding and direct impact.
The large number of traces covering almost the entire surface of the sample indicates the occurrence of processes of elastoplastic deformation at the micro/nanoscale and loosening of surface layer of the natural oxide film. These phenomena are of great importance in the formation of an oxide film and surface microrelief, since direct contact of the ball occurs along the oxide film [5][6][7][8].
Numerous studies have established the presence of plastic flow of the material in a thin surface layer of the sample in the direction of movement of an individual granule, therefore, with a direct impact of a polyethylene ball, the deformation is directed deep into the sample. Most of the marks are inherent to the impact of balls directed at an angle to the surface, which cause brittle destruction of the oxide and shear of individual particles. Such interaction with the surface allows loosening of the oxide layer with the formation of fine particles, which accelerates chemical processes [26][27][28][29][30]. Some of the particles are seized by their juvenile surfaces with oxide, sometimes getting into the pores and reducing their volume, partially carried away by the oxidizing solution, and partially compacted by subsequent blows of polyethylene balls. Consequently, as a result of vibration wave action, the oxide film is loosened and smoothed during its growth. [32][33][34].
In the contact zone, due to the sliding impacts of the polyethylene balls, there is some displacement of the growing coating towards the rotation of the working medium (Fig. 3). In fig. 6a and 6b it can be seen that the traces after polishing of the samples do not overlap before coating. The formation of a vibrational chemical-mechanical oxide coating at the micro level occurs on the metal surface in such a way that the coating copies the relief of the original surface, as evidenced by contrasting stripes. In fig. 6c,d (scale 200 nm), shape and size of the oxide coating nucleus is clearly visible, it is found that not all cells have oval shape, sizes range from 10 to 50 nm. The conducted studies allow us to conclude that the use of polyethylene working media is advisable to use for the formation of vibrating chemical-mechanical oxide coatings. Which by the protective ability is 1.5 times higher than the oxide film obtained by the standard method.

Conclusions
1. It was found that the optimal modes of formation of a vibrational chemical-mechanical oxide coating (vibration amplitude -2.5 mm, vibration frequency -16-35 Hz, processing time -15 min, working medium -polyethylene balls D 2-2.5 mm) make it possible to obtain a coating with a thickness of 5 μm with no hydrogenated surface coating layer. 2. A relationship was established between the state of the original surface and the performance of parts after applying a vibrational chemical-mechanical oxide coating, which made it possible to adjust the technological modes and the technological process of manufacturing high-resource parts with coatings.