Tribocorrosion behavior of boronized AISI 4140 steel

In this study, AISI 4140 steel was boronized using powder-pack-boronizing process, seeking to produce a monophasic iron boride (Fe2B) layer. The microstructural and chemical characteristics were evaluated by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), respectively and Grazing incidence X-ray diffraction (GIXRD). Mechanical behavior was probed by instrumented indentation while tribological behavior was determined through pin-on-disc tests. For the pin-on-disc tests, two condition were evaluated, dry condition and also immersed in 3.5% NaCl solution, which was connected to a potentiostat, monitoring the open circuit potential (OCP). The single Fe2B layer was indeed obtained with a thickness around 42 mu m. The iron boride layer showed significantly lower wear rate and also lower coefficient of friction (COF) during tribocorrosion tests, in comparison with unboronized specimens. An opposite behavior was verified during dry tribological tests, where unboronized samples presented lower COF behavior.