Influence of low energy–high flux nitrogen implantation on the oxidation behavior of AISI 304L austenitic stainless steel

Abstract

Low energy–high flux (1.2 keV, 1 mA/cm2) nitriding of an austenitic AISI 304L stainless steel has been carried out by implanting a dose of 3.5×1019 ions cm−2 at 400 °C for 1 h. An important increase in surface hardness has been found to occur as a result of the formation of the so-called expanded austenite γN phase. Transmission electron microscopy studies have also shown the existence of hexagonal Cr2N precipitates at the nitrided layer/matrix interfacial region. The oxidation behavior has been then studied in the temperature range between 400 and 550 °C for 24 h under synthetic air. It is shown that nitridation slightly modifies the oxidation kinetics as a result of the progressive transformation of the γN phase towards CrN precipitation and α-FeNi matrix formation. More chromium enriched scales are, anyhow, developed on the nitrided steel than in the untreated one. These results are discussed on the basis of the chromium diffusion in the nitrided layer and its preferential chemical bonding with nitrogen atoms.