CROSS-SECTIONAL TRANSMISSION ELECTRON-MICROSCOPY CHARACTERIZATION OF PLASMA IMMERSION ION-IMPLANTED AUSTENITIC STAINLESS-STEEL

Cross-sectional transmission electron microscopy (XTEM), selected area diffraction (SAD) and nano;beam diffraction (NBD) techniques were use d to investigate the surface microstructure of 316 stainless steel, im planted with high doses of nitrogen ions at 150, 250, 350, 450 and 520 degrees C using plasma immersion ion implantation. It has been found that the treatment temperature has a strong influence on the evolution of the microstructure. An amorphous layer of about 1 mu m thick with a heavily stressed substrate underneath was observed on the 150 degree s C implanted sample. Both the 250 and 350 degrees C implanted samples showed a thin nanocrystalline sublayer at the outermost surface and a n amorphous sublayer between the nanocrystalline sublayer and the subs trate. A thick amorphous layer up to 3 mu m thick was formed on the 45 0 degrees C implanted sample whereas at 520 degrees C, cellular precip itation of CrN and alpha-ferrite dominated the system. It is suggested that a solid state chemical reaction and the poor mobility of the rea ctant atoms are the key factors for the solid state amorphisation by n itrogen ion implantation into austenite.