Obrabotka Metallov 2018 Vol. 20 No. 4

OBRABOTKAMETALLOV Vol. 20 No. 4 2018 32 TECHNOLOGY Formation of Hardening Coatings based on Fe-Cr-Si-B-C Alloys with High Glass-Forming Ability by Laser-Plasma Methods Maksim Khomyakov a,* , Pavel Pinaev b , Pavel Statsenko c , Ilya Miroshnichenko d , Gennadiy Grachev e Institute of Laser Physics of the Siberian Branch of the RAS, 15B Ac. Lavrentieva ave., Novosibirsk, 630090, Russian Federation a http://orcid.org/0000-0001-8095-2092, mnkhomy@laser.nsc.ru, b http://orcid.org/0000-0003-1232-4945, pavel_academ@mail.ru , c http://orcid.org/0000-0002-5396-7990, statsenkopa@laser.nsc.ru , d http://orcid.org/0000-0001-6911-4207 , mib383@gmail.com, e http://orcid.org/0000-0001-8853-3079, grachev@laser.nsc.ru Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2018 vol. 20 no. 4 pp. 21–34 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2018-20.4-21-34 Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov ARTICLE INFO Article history : Received: 14 September 2018 Revised: 01 October 2018 Accepted: 31 October 2018 Available online: 15 December 2018 Keywords : Laser plasma Laser technology Surface hardening Amorphous metal coatings Hardness Fe-Cr-Si-B-C. Acknowledgements The authors would like to express their gratitude to Vladimir A. Bataev and Lyubov V. Chuchkova of the Materials Research Center of the Novosibirsk State Technical University for their assistance in the structural study of the obtained coatings. Funding The reported research was funded by Russian Foundation for Basic Research and the government of the region of the Russian Federation, grant № 17-48-543315. ABSTRACT Introduction. In recent years, the fundamentals of the laser-plasma methods for surface modification and micropowder coating application have been developed in the Institute of Laser Physics. The methods are based on the use of optical pulsed discharge plasma. The discharge is ignited by the repetitive laser pulses focused on the surface of the workpiece in a gas or a gas-powder stream. The high pulse repetition frequency of 10-120 kHz is achieved using the generator-amplifier CO 2 -laser system with the half-height pulse duration set τ = 150-200 ns. The search for other timely applications of these methods is currently ongoing. An interest in the obtaining of amorphous metallic coatings on the surface of structural materials is yet to wane after the decades of intense research done by scientists all over the world due to the outstanding physical, chemical and mechanical properties of such coatings. The purpose of this work is to obtain the hardening coatings based on the Fe-Cr-Si-B-C alloys with high glass-forming ability and to investigate the possibility of obtaining a coating with an amorphous structure using laser-plasma methods. Theory. As the surface of the metallic alloys was under the intense thermal influence of the pulsed laser plasma, the numerical modeling was applied to determine the dependence of amorphized layer’s thickness on the material properties, as well as in relation to the parameters of the laser irradiation and the laser plasma. Experimental methods. The experiments are carried out in two stages using the installation designed at the Institute: (1) at first, the uniform coatings were prepared on the surface of steel substrates using the laser-plasma application method incorporating the powders of the AP-FeCr4Mn2Si2B4V1 (Fe 71.75 Cr 3.33 Si 3.54 B 14.10 C 4.81 Mn 1.7 4 V 0.73 ) and AP-FeCr11Mn4SiB (Fe 66.8 Cr 10.79 Si 5.3 B 11.42 C 2.85 Mn 2.84 ) grades; (2) then, the surface coatings underwent the rapid laser-plasma modification to ensure the remelting of the thin surface layer. Results and discussion. The numerical methods applied have proven the theoretical possibility of obtaining an amorphous layer of about 3-5 μm thick, based on the Fe-Si-B alloys. As a result, the parameter range required for the successful laser-plasma modification is determined. The hardness of the obtained coatings is measured and its thickness has been determined in dependence on the application parameters. The hardness is measured using the nanoindentation method and equals 12 ± 1 GPa in regards to the coating incorporating the powder AP-FeCr4Mn2Si2B4V1 and 8.5 ± 0.7 GPa in case of the powder AP-FeCr11Mn4SiB; the thickness of the coatings is up to 0.1-0.4 mm. Using optical microscopy, SEM and X-ray diffraction the structure of the coatings is investigated. It is demonstrated that the laser-plasma modification of the coatings on the surface leads to the structure refinement of the surface layer. The characteristic size of the crystallites is 0.5-1 μm. In addition, the hardness of the remelted layer is increased up to 13.8 ± 0.7 GPa for the AP-FeCr4Mn2Si2B4V1 alloy and up to 10.5 ± 0.5 GPa for the AP-FeCr11Mn4SiB alloy. Using SEM and X-ray diffraction the structure of the coatings is investigated. The amorphous phase in the remelted coating layer is not detected, which might be due to an increase in the critical cooling rate during the laser amorphization as compared to the traditional methods of melt quenching. For citation: Khomyakov M.N., Pinaev P.A., Statsenko P.A., Miroshnichenko I.B., Grachev G.N. Formation of hardening coatings based on Fe-Cr-Si-B-C alloys with high glass-forming ability by laser-plasma methods. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science , 2018, vol. 20, no. 4, pp. 21–34. doi: 10.17212/1994-6309-2018-20.4-21–34. (In Russian). ______ * Corresponding author Khomyakov Maksim N. , Junior researcher Institute of Laser Physics of the Siberian Branch of the RAS, 15B Ac. Lavrentieva ave., 630090, Novosibirsk, Russian Federation Tel.: +7 (383) 330-47-36, e-mail: mnkhomy@laser.nsc.ru