Microstructure and antibacterial properties of microwave plasma nitrided layers on biomedical stainless steels

► During nitriding treatment between 350 °C and 550 °C, the phase transformation sequence on the nitrided layers of the alloys was found to be γ → (γ + γN) → (γ + α + CrN). ► The nitrogen penetrated deeper into the substrate as treated temperature increases. ► The surface hardness of AISI 303 stainless steel could be enhanced with the formation of γN phase in nitriding process. ► The antibacterial metallic ions (Fe+ and Cr+) can be dissolution from the γN and CrN phases on the nitrided layers of the nitrided samples and thus come into the bacterial suspension to kill bacteria.