**5. Conclusions**

(a) The paper shows the possibility of increasing the hardness and wear resistance of an austenitic stainless steel surface using anodic plasma electrolytic treatment. The positive effect of anodic dissolution on the reduction in surface roughness, as well as the complex effect of high-temperature oxidation and anodic dissolution on the morphology of the surface, has been confirmed. The structural features and phase composition of the modified surfaces are revealed, which determine the hardness of the surface layers and, together with the morphology of the surface, the tribological properties of the processed products.

(b) The hardness of the nitrided layers increases to 1450 HV with a thickness of up to 20–25 μm due to the formation of iron nitrides and iron-chromium carbides with a decrease in roughness of 3.7 times after PEN. This leads to an increase in wear resistance by two orders of magnitude.

(c) The PEC of the steel surface leads to an increase in hardness up to 800 HV and a thickness of the hardened layer up to 80 μm due to the formation of chromium carbides and a solid solution of carbon. The roughness and wear resistance of the treated surface change by approximately the same values as after PEN.

(d) It was revealed that when PEB is conducted on austenitic stainless steel, there is no hardening of the surface, but, at the same time, there is a decrease in roughness and an increase in the wear resistance of the surface.

(e) The frictional bonds in the friction process of each type of treatment are broken because of the plastic displacement of the counterbody material. The type of wear can be characterized as fatigue wear with boundary friction and plastic contact. The correlation of the friction coefficient and the Kragelsky–Kombalov criterion, a generalized dimensionless criterion of surface roughness, is shown.

**Author Contributions:** Conceptualization, S.K. and A.N.; methodology, T.M. and I.T.; validation, S.K., I.T. and T.M.; formal analysis, A.N.; investigation, T.M., I.T., R.B., E.S. and I.K.; resources, S.K.; writing—original draft preparation, S.K.; writing—review and editing, A.N. and I.K.; visualization, T.M. and I.T.; supervision, S.K.; project administration, S.K.; funding acquisition, S.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Russian Science Foundation, grant number 18-79-10094.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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