Insight into Structural Changes and Electrochemical Properties of Spark Plasma Sintered Nanostructured Ferritic and Austenitic Stainless Steels

Nanostructured ferritic (Fe(82-x)-Cr-18-Si-x, x = 0-3 wt %) and austenitic (Fe(73-x)-Cr-18-Ni-9-Six, x = 0-3 wt %) stainless steel (SS) alloys were developed by mechanical alloying (MA) and spark plasma sintering (SPS). The unit cell parameter estimated from X-ray diffraction spectra exhibited a decreasing trend with an increase in wt % of Si content in both alloy systems. The particle size of powders estimated using bright field transmission electron microscopy images for ferritic (3 wt % Si) and austenitic (3 wt % Si) SS powders was found to be 65 +/- 5 nm and 18 +/- 3 nm, respectively. In case of the ferritic system, 3 wt % Si exhibited the highest densification (similar to 98%) and micro-hardness of about 350.6 +/- 11.2 HV, respectively. Similarly, for the austenitic system (3 wt % Si), maximum densification and micro-hardness values were about 99% and 476.6 +/- 15.2 HV, respectively. Comparative analysis of potentiodynamic polarization, linear polarization, and electrochemical impedance spectroscopy results indicates an increase in electrochemical performance of both alloy systems as the wt % Si was increased. The increase in electrochemical performance is directly related to the increase in densification owing to Si addition in these alloys.