Rotational Fretting Wear of Ion Nitrided Medium Carbon Steel

Abstract

The nitrided layer on the surface of LZ50 (0.50% C) carbon steel was prepared by ion nitriding technique and its characterizations were detected by using Vickers hardness tester, profilometer, scanning electric microscope (SEM), optical microscope (OM) and X-ray diffraction (XRD). Rotational fretting is one of basic running modes in contact configuration of ball-on-flat, to which was paid little attention. The rotational fretting wear behaviors of the nitrided layer and its substrate steel were comparatively studied in dry condition under varied angular displacement amplitudes (θ) in range of 0.125º-1º, imposed normal load (Fn) of 20 N and a constant rotational speed of 0.2º/s. The experimental results showed that the nitrided layer presented rough and porous surface and high hardness was mainly consist of ε-Fe2-3N and γ׳-Fe4N phases. Compared with the substrate steel, the nitrided layer had a significant effect on reducing the friction coefficient and improving the fretting wear resistance, though the nitrided layer almost didn’t change the fretting running regimes of the substrate steel. In the partial slip regime, lower friction coefficients and slight damage appeared for the nitrided layer due to the coordination of elastic deformation of contact zones. In the slip regime, the friction coefficient of the nitrided layer was lower than that of the substrate in the initial stage as a result of the preventing plastic deformation by its high hardness surface. The rotational fretting wear mechanism of the nitrided layer in the slip regime was mainly identified as abrasive wear, oxidative wear and delamination. As a result, the nitrided layer presented a better capability for alleviating rotational fretting wear.