Influence of plasma conditions and surface finish on wear and corrosion behaviour of nitrocarburized AISI 316 L

The study examines wear and corrosion resistance of expanded austenite layers on AISI 316 L, produced through a modified plasma nitrocarburizing (PNC) process utilizing a solid carbon precursor. Thereby, the generated reactive HCN allows for two adjustable PNC modes: direct glow and afterglow. The work investigates the effects of these PNC modes on polished and ground surfaces subjected to identical treatments (430 °C, 4 h, N 2 -H 2 plasma) using scanning electron microscopy, glow discharge optical emission spectroscopy , X-ray diffraction, hardness measurements, pin-on-disc tests against Al 2 O 3 , salt spray tests, and electrochemical polarization in 3.5 wt% NaCl solution. Significant differences were observed between the two PNC modes regarding layer modification and service behaviour. The direct glow PNC mode, involving both HCN gas-phase reactions and N ions (N 2 + , N + ) from the plasma-activated surface, resulted in a higher nitrogen diffusion depth and a higher nitrogen content, leading to increased surface hardness and reduced wear volume loss three times lower than that of the afterglow mode. However, the high nitrogen input caused surface cracks, negatively impacting corrosion resistance for both surface finish types. In contrast, the afterglow PNC mode, which relies solely on HCN gas-phase reactions, resulted in lower N content and N diffusion depth, still exhibiting wear loss ten times lower than the untreated steel, and, however, an undisturbed morphology without cracks. Electrochemical tests revealed that only polished samples showed a quasi-passive zone and superior corrosion resistance, highlighting the significant influence of surface conditions prior to PNC treatment, particularly in the afterglow mode. • Solid C precursor enables short-term processes in different PNC modes. • High N uptake in direct glow PNC mode causes defects for polished and ground surfaces. • Direct glow PNC mode increases hardness and wear but impairs corrosion resistance. • Afterglow PNC mode results in surface layers with less or even without defects. • Polished surfaces treated in afterglow PNC mode have superior passive behaviour.