Microstructural Features and Tribological Behaviour of Low-Alloyed Steel Modified by High-Energy Plasma Pulse

Authors Yu.G. Chabak

Priazovskyi State Technical University, 7, Universitetskaia St., 87555 Mariupol, Ukraine

Е-mail julia.chabak25@gmail.com
Issue Volume 11, Year 2019, Number 4
Dates Received 08 April 2019; revised manuscript received 05 August 2019; published online 22 August 2019
Citation Yu.G. Chabak, J. Nano- Electron. Phys. 11 No 4, 04010 (2019)
DOI https://doi.org/10.21272/jnep.11(4).04010
PACS Number(s) 52.77. – j, 62.20.Qp, 61.66.Dk, 64.70.Kb
Keywords Pulsed-plasma treatment, Modification (7) , Microstructure (21) , Wear resistance (2) , Friction coefficient.

The purpose of the work is to study the microstructure and tribological properties of modified layers obtained on the surface of low-alloyed structural steel 75Mn by the use of high-energy plasma pulse. Sub-surface layers were modified using an electrothermal axial plasma accelerator with arc discharge voltage up to 4 kV and discharge current up to 4 kA producing the plasma flux with the power density in the range of (1.4-1.75)(109 W/m2. The microstructure and properties of the layers were investigated using scanning electron microscopy, XRD, microhardness measurement, and “Ball-on-Disk” wear test. The results showed that a single plasma impulse with power density of 1.4(109 W/m2 forms on the surface a modified layer of 13-15 (m thick with average microhardness of 985 HV consisting of ultrafine-grained martensite and 15.9 vol. % of retained austenite. Increasing power density to 1.75(109 W/m2 led to the formation of modified layer of bigger width (22-26 (m) comprising two martensite-austenite sublayers divided by thin (0.3-0.5 (m) austenitic layer. The average microhardness of inner and outer sublayers is 963 HV and 670 HV respectively. The outer sublayer contains higher volume fraction of retained austenite (32 vol. %). It was found that plasma treatment leads to enrichment of the modified layer with plasma-transferred carbon which up to 1.4 wt. %. Plasma modification improves the tribological properties of 75Mn steel, that manifests in increasing wear resistance by 18-90 % and stabilizing the coefficient of friction during the wear testing. The wear process of modified surfaces takes place according to abrasive mechanism with groove formation without intense surface oxidation. The surface deterioration occurs due to multiple deformation of relief elements with detachment of highly deformed microchips.

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