Obrabotka Metallov 2018 Vol. 20 No. 2

OBRABOTKAMETALLOV Vol. 20 No. 2 2018 97 MATERIAL SCIENCE Formation of Coatings Based on Boron and Aluminum on the Surface of Carbon Steels by Electron Beam Alloying Undrakh Mishigdorzhiyn a, * , Igor Sizov b , Ivan Polyansky c East Siberia State University of Technology and Management, 40V Kluchevskaya st., Ulan-Ude, 670013, Russian Federation a http://orcid.org/0000-0002-7863-9045, druh@mail.ru , b http://orcid.org/0000-0002-4468-784X , sigperlit@mail.ru , c http://orcid.org/0000-0002-7350-8791 , i.polyansky@mail.ru ARTICLE INFO Article history : Received: 24 January 2018 Revised: 02 March 2018 Accepted: 05 April 2018 Available online: 15 June 2018 Keywords : Electron beam alloying Iron borides Iron aluminides Microstructure Microhardness Acknowledgements : The authors are grateful to Dr. B.V. Dampilon , the researcher of the Institute of Strength Physics and Materials Science (Siberian Branch of Russian Academy of Science, Tomsk) for his assistance in experiments. Funding : The present work was supported by the grant of the President of the Russian Federation for the state support of young Russian scientists – PhD holders Grant number MK- 2641.2018.8 and State support (Grant No: 11.9999.2017/5.2) for conducting research. ABSTRACT Introduction. Boronizing and boroaluminizing are effective methods used to improve the surface properties of machine parts and tools. However, its application in industrial production is often restricted. High brittleness of boronized and boroaluminized layers is one of the restraining factors. Conventional methods of boronizing and boroaluminizing with furnace heating are aimed at the formation of needle and layered structured layers respectively. As a rule, the hardest and most brittle phases are formed on top of these layers, such as FeB and Fe 2 Al 5 . The purpose of the work: to study the phase formation sequence in boronized and boroaluminized layers obtained after electron beam treatment in vacuum on the surface of carbon steels. The methods of investigation. Alloying with either boron carbide (electron beam boronizing) or boron carbide and aluminum (electron beam boroaluminizing) is applied. Different modes of electron beam processing are tested: accelerating voltage, beam current and irradiation time. Microstructure, microhardness, element and phase composition of obtained layers are investigated. Results and Discussion . It is established that the phase formation at electron beam alloying with boron carbide occurs according to diagram Fe-B, where iron monoboride FeB is the nucleate phase. FeB iron monoboride crystallizes in the form of rhombic and prismatic crystals and Fe 2 B appears in the form of rounded dendrites. Thus, FeB crystals come out as being enclosed into Fe 2 B shells. The remaining liquid crystallizes as a eutectic system during cooling. This pattern formation of layer is also valid for the electron beam boroaluminizing. The only difference is the eutectic’s composition, which consists of Fe 2 B phase and solid solutions of aluminum and boron in α-Fe. Generally, the microstructure of obtained layer after electron beam treatment is more preferable than the ones after conventional treatment with furnace heating. The layer structure with hard and brittle FeB surrounded by Fe 2 B and eutectic lead to an increase in its mechanical properties. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2018 vol. 20 no. 2 pp. 87–99 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2018-20.2-87-99 For citation: Mishigdorzhiyn U.L., Sizov I.G., Polaynsky I.P. Formation of coatings based on boron and aluminum on the surface of carbon steels by electron beam alloying. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science , 2018, vol. 20, no. 2, pp. 87–99. doi: 10.17212/1994-6309-2018-20.2-87-99. (In Russian). ______ * Corresponding author Mishigdorzhiyn Undrakh L. , Ph.D. (Engineering), Senior Researcher East Siberia State University of Technology and Management, 40V Kluchevskaya st., 670013, Ulan-Ude, Russian Federation Tel.: 8 (3012) 43-14-17, e-mail: druh@mail.ru Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov