Wear and Corrosion Properties of Cold-Sprayed AISI 316L Coatings Treated by Combined Plasma Carburizing and Nitriding at Low Temperature

Cold-sprayed AISI 316L stainless steel coatings are treated to form an austenite phase with excessive dissolved nitrogen (known as the S-phase) by plasma nitriding at temperatures below 450 °C. The S-phase is a hard and wear-resistant layer with high corrosion resistance. However, the S-phase layer formed after only nitriding is thin and the hardness abruptly decreases at a certain depth; it lacks mechanical reliability. We examined two types of combined low-temperature plasma treatment to enhance the mechanical reliability of the S-phase layer: (i) sequential and (ii) simultaneous. In the sequential plasma treatment, the carburizing step was followed by nitriding. In the simultaneous treatment, the nitriding and carburizing steps were conducted at the same time. Both combined plasma treatments succeeded in thickening the S-phase layers and changed the hardness depth profiles to decrease smoothly. In addition, anodic polarization measurements indicated that sequential treatment involving carburizing followed by nitriding for 2 h each resulted in high corrosion resistance.