## 4 Conclusions and Future Research Perspectives  
* Of the three components of SE (Figure 10), the least amount of research has been devoted to the physical nature of the SB process (Figure 11). There is a lack of research on the tribological behaviour of the pair of deforming element-machined surfaces, and, in particular, the wear (service life) of the deforming element, the material of which can be a type of diamond, hardened steel, or a type of hard alloy (Table 1). Such information is necessary to evaluate the cost/quality ratio when choosing finishing according to set criteria. All other aspects being equal, the different materials of a deforming element will result in different friction coefficients, and, consequently, different SI characteristics will be obtained, and thus the component will have a different OB. Such comparative studies are lacking for both simple correlations SB-SI and SB-OB. In addition to the above, the development of new diamonds and other structures as materials for deforming elements in SB processes is also a relevant, justified direction for future research. * Figure 11 shows that four times less research has been devoted to the OB of SBed components compared to the SI, which explains the significantly less studied SB-OB correlation and especially the SI-OB correlation (Figure 14). Therefore, deepening the  
\begin{table}
\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline \hline \multicolumn{1}{c}{Characteristics of SI} & \multicolumn{1}{c}{Method of Research} & \multicolumn{1}{c}{One-} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \\ \hline Ra (Sa) & Surface & HV & Res. & Micro- & One- & Panned Experiment & Objective & Refex. \\  & Topog. & HV & Stress & Struct. & Factor-at- & Regression & ANOVA & & \\ \hline \(\bullet\) & \(\bullet\) & \(\bullet\) & & & \(\bullet\) & & & & [45] \\ \(\bullet\) & \(\bullet\) & \(  
research on these two simple correlations is a necessary condition to obtain a complete and balanced picture along the axis SB-SI-OB. * The majority of studies (Table 5) are devoted to individual characteristics of SI and do not give a complete picture of its condition for a given processed material, resulting from a specific SB process. At the same time, very little attention has been paid to the SB of promising structural materials such as titanium-, magnesium-, and nickel-based alloys (see Figure 5). No information was found on the SB of cast iron. Therefore, the study of the SB-SI-OB correlation for these materials is a promising direction. * Only 9% of research was devoted to SB of complex surfaces and cylindrical holes (Figure 6). The development of suitable mixed SB processes will significantly improve the tribological behaviour of holes in austenitic stainless steel 'cylinder'-type structural elements widely used in various industrial applications. In general, a promising direction for future research is the SB of holes in structural elements, the service life of which is limited by the wear of these holes. A challenge is to develop methods, devices, and deforming elements for the SB of small holes. * The SB-OB correlation has been studied the least in terms of corrosion behaviour. Only two publications [90; 93] are dedicated to individual aspects of this problem. Future research can be aimed at distinguishing and evaluating the influence of individual main characteristics of SI resulting from DB on the corrosion resistance of austenitic stainless steels. Thus, by having information on the SI of a given component, its corrosion behaviour can be predicted. * A particularly promising direction is the development of combined finishing processes, in which the application of SB before or after another type of impact provides a synergistic effect for modifying SL. The literature survey shows that the possibilities for the development of combined processes with the application of SB are insufficiently explored.