Improved corrosion resistance of SS316L implant materials by nitriding method

Abstract

Nitriding has been carried out on SS316L implant materials by varying nitridation temperature of 400 °C, 420 °C, 440 °C, 460 °C, 480 °C and 500 °C for 3 hours,then followed by varying the nitridation time of 1 hour, 3 hours, 5 hours, 7 hours, 9 hours and 11 hours at optimum temperature of 420 °C. Corrosion test were conducted using potensiodynamic method with 0.9% NaCl intravenous solution as corrosion media of pH 7.4 at 37°C. The phase were characterized by using XRD (X-ray Diffractometer), while microstructure and surface chemical composition were analysed using SEM-EDS (Scanning Electron Microscope – Energy Dispersive Spectrometer). Corrosion test showed the corrosion resistance improvement by 16 times from corrosion rate of 0.1358 mpy for non nitrided SS316L to 0.0082 mpy for nitrided SS316L at 420 °C for 3 hours sample. X-ray diffraction pattern of SS316L implant materials as recieved shows the austenite phase (a), while the nitrided SS316L at 420 °C for 3 hours is a’ phase. There is 2e angle shifting although not significantly, whereas the S phase was not observed. The observation of surface microstructure and chemical composition of non nitrided SS316L sample after corossion test showed the existence of pitting corrosion with 0.42% mass of chlorine. Sample nitrided at temperature of 420 °C for 3 hours showed a flat topography with black spots and from its cross sections, a thick nitride layer of 4 im and nitrogen element up to 31.34% mass were observed. Keywords: Nitriding, SS316L, Implant materials, Corrosion resitantance, Potensiodynamic.