Nanostructured surfaces

Influence of the number of cycles of severe plastic deformation on surface nanostructure formation in low-alloyed steel
Maksymiv O.V.1, Kyryliv V.I.1, Zvirko O.I.1, Gurey V.I.2, Chaikovs’kyi B.P.3
1 Karpenko Physico-Mechanical Institute of the NAS of Ukraine,
5, Naukova St., Lviv 79060, Ukraine.
E-mail: okyryliv@yahoo.com
2 Lviv Polytechnic National University,
12, Bandery St., Lviv 79013, Ukraine.
3 Stepan Gzhytskyi National University of Veterinary Medicine and Biotechnologies,
50, Pekarska St., Lviv 79010, Ukraine.

One of the known methods of formation of surface nanocrystalline structures (NCS) on steels is mechanical-pulse treatment (MPT) which induced surface severe plastic deformation of steel by high-speed friction. Surface NCS provide an increase in strength, hardness, wear resistance, resistance to fatigue and corrosion fatigue, and prevent hydrogen penetration into the substrate being hydrogen permeation barriers [1]. Every point of steel surface under MPT by a tool is treated several times passing through the friction contact (FC) zone, which indicates the number of deformation cycles. Specific pressure in the FC zone, which significantly effects on formation of surface NCS and, consequently, their properties, can be increased by decreasing the effective tool width, which leads to a decrease in the number of cycles.
The present paper aims to study the influence of the number of cycles of MPT on structure refinement, phase composition and physico-mechanical properties of the nanostuctured surface layer of the 65Г steel (0.65C-1Mn). The number of cycles of MPT was changed from 1 to 6. Martensite-austenite-cementite structure with Fe3O4 and FeO oxides was formed on the 65Г steel as a result of MPT. The ratio of the phase composition was depended on the number of cycles: on the first and the second cycle martensite and retained austenite were the basic phases, but, starting from the third cycle, the lines of Fe3O4 and FeO oxides, and cementite phase of Fe3C became clearer on X-Ray diffraction patterns. The phase composition of the surface layer with NCS, its grain sizes and internal stresses defined physical and mechanical properties of the steel. Therefore, obtained results are important for receiving optimal combination of properties of the surface layer and efficiency of MPT.

1.	H. Nykyforchyn, V. Kyryliv, O. Maksymiv, O. Zvirko Mechanical fabrication methods of nanostructured surfaces. In: Handbook of modern coating technologies. Fabrication methods and functional properties. Amsterdam, Elsevie; 2021. p. 25-67.