Mössbauer characterization of the expanded austenite layer and corrosion products in 316L and nitrided 316L stainless steel

J. PAOLINI, J. GRAU, R. GREGORUTTI, C.I. ELSNER, J. DESIMONI, AND R.C. MERCADER

La Plata

Conferencia; Conferencia Latinoamericana Sobre las Aplicaciones del Efecto Mössbauer; 2008

The stainless steel ASTM 316L stands out because of its high corrosion resistance, which motivates its use in the manufacture of prosthesis and orthopedic implants. In the body environment these are subjected to the action of oxygenated fluids that have in solution chlorine ions, proteins, enzymes, bacteria, and blood serum, which can bring about the chemical disintegration of the material. It has been reported that in electrochemical potentiostatic and potentiodynamic tests the resistance of the nitrided 316L stainless steel is higher than the untreated 316L steel. Its higher resistance might be due to the existence of a surface austenitic layer, saturated in nitrogen, called expanded austenite, whose nature and features are not known in depth. Because the layer is only of a few hundreds of nanometers, conversion electron Mössbauer spectroscopy (CEMS) is an almost ideal technique to investigate the surface layer and the corrosion products that can form after subjecting the samples to corrosion conditions that mimic those prevalent within the human body. In this work we report the first CEMS results of a study designed to better understand the role of this layer in the corrosion resistance of ion nitriding samples of 316L stainless steel.