Non-Monotonic Effect of Duty Cycle on the Mechanical, Tribological, and Corrosion Properties of Pulsed DC Plasma-Nitrided 12Cr18Ni10Ti Stainless Steel

Although the duty cycle is an important parameter in pulsed plasma nitriding, its role in simultaneously controlling the microstructure, mechanical performance, tribological behavior, and corrosion resistance of 12Kh18N10T stainless steel remains insufficiently understood. Therefore, this study systematically investigates these relationships under otherwise fixed nitriding conditions. The samples were nitrided at 500 °C, a pressure of 400 Pa, a voltage of 700 V, and a treatment duration of 5 h, with duty cycle (DC) values of 30, 60, and 90%. The surface microstructure and composition were characterized by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. The mechanical properties were evaluated by instrumented nanoindentation, the tribological properties were evaluated using the coefficient of friction and wear rate, and the corrosion resistance was investigated using potentiodynamic polarization. The maximum nitrided layer thickness of 91.29 μm was obtained at DC30, whereas the layer thickness at DC60 and DC90 was approximately 65.07 μm. Fe4N and Cr2N phases were identified in all samples. The DC60 regime provided the highest hardness of 740.6 HV, an elastic modulus of 215.9 GPa, the lowest coefficient of friction of 0.333, and the lowest corrosion current density of 0.000665 mA/cm2. The minimum wear rate of 2.276 × 10−5 mm3/(N·m) was achieved at DC90. These results show that the optimal processing condition depends on the required combination of hardness, wear resistance, coefficient of friction, and corrosion resistance. The obtained results demonstrate that the functional properties of the steel can be effectively tailored by controlling the duty cycle.