Corrosion and tribocorrosion behaviours of AISI 321, AISI 431 and FDMA borided and non-borided steels

Abstract

Corrosion and tribocorrosion behaviours of non-borided and borided steel materials were evaluated under sliding contact in a 3.5 wt% NaCl solution, using an alternative tribometer integrated with a potentiostat for electrochemical control. Alloy-steel samples were borided by a powder-pack boriding process during 1 h at 950 °C. Microstructural examinations and phase analysis were performed employing Scanning Electron Microscopy (SEM) and x-ray diffraction. The surface profiles of wear tracks were obtained using a high resolution surface profilometer. Under corrosion conditions, it was found that a negative effect of boriding treatment was observed in the corrosion resistance of the investigated steels due to the presence of porosity and microcracks within FeB and Fe2B coating layers. On the other hand, the tribocorrosion tests indicated the positive effect of boride coating which induced a shift of the polarization curves of the borided steels to higher corrosion potentials contrary to the Tafel polarization curves of the non-borided steel materials which shifted to lower corrosion potentials. Moreover, even though the borided steels presented lower corrosion performances, the synergistic effect between corrosion and wear acting together resulted in a decrease of their coefficient of friction (COF) values and material losses with respect to the non-borided steel materials. In addition, the line profile of their surfaces exhibited less pronounced wear behaviour showing shallowed wear depth leading subsequently to a lower wear volume and loss compared to the non-borided steel materials. Microscopic observations revealed that wear-induced corrosion was more dominant in the corrosion-wear synergism.