Improvement of the cavitation erosion resistance for low-temperature plasma nitrided Ca-6NM martensitic stainless steel

The present work reports increase of the cavitation erosion resistance for low-temperature plasma nitrided CA-6NM martensitic stainless steel, which was investigated by means of a 20 kHz ultrasonic vibrator at peak-to-peak amplitude of 50 μm. The study was emphasized for the three first cavitation stages, usually presented at the cumulative material mass loss-time curve, for surfaces treated in dc pulsed plasma at 350 °C, in 5% N2+95% H2 gas mixture, for different nitriding times of 6, 12, and 24 h. The changes on nitrided surfaces were evaluated by XRD and nanoindentation technique. The modification of the treated surface morphology as a function of the testing time in the incubation, acceleration, and maximum erosion rate stages was also verified by SEM analysis. The improvement of the cavitation erosion resistance for nitrided surfaces is believed to be due to the nitrogen-expanded austenite (γN-Fe) formation from a tempered martensite matrix.