Influence of current density on phase formation and tribological behavior of plasma nitrided AISI H13 steel

The effects of plasma current density on phase formation of plasma nitrided H13 steel, and on the consequent tribological properties were investigated. The combination of plasma current density and sample temperature formed several different phases, whose relative abundance influenced the friction and wear behaviors. The phases were identified using conversion electron Mössbauer spectroscopy and grazing incidence X-ray diffraction. Elemental depth profiles were determined with glow discharge optical emission spectroscopy and nuclear reaction analysis. The coefficients of friction and the dimensional specific wear rates were evaluated in pin-on-disk tests. Reduction of the coefficient of friction in the initial stages of the tests was attributed to the presence of cementite, formed in certain conditions of plasma processing. Specific wear rates were quantified with profilometry of the wear scars and indicated ten times lower values, when compared to the non-nitrided samples.