CORRELATION BETWEEN PROCESSING PARAMETERS AND MECHANICAL-PROPERTIES AS A FUNCTION OF SUBSTRATE POLARIZATION AND DEPTH IN A NITRIDED 316L STAINLESS-STEEL USING NANOINDENTATION AND SCANNING FORCE MICROSCOPY

The effects of substrate polarisation in a nitrided 316L stainless ste el have been investigated in an attempt to accurately correlate proces sing parameters with surface mechanical properties. Nanoindentation al lows the Vickers hardness to be measured at precise depths, meaning th at the variation in properties with nitriding depth can be evaluated a nd correlated with the process parameters. By combining such measureme nts with surface imaging techniques (scanning force microscopy and sca nning electron microscopy) and electron probe micro-analysis, if is po ssible to explain both the mechanical property and microstructural var iations of such layers, having been produced in a low pressure are pla sma discharge at 680 K with a mixed Ar-N-2 gas. In this study the nano indentation technique is presented as a new and valid method for the c haracterisation of nitrided layers, shown by hardness measurements on four nitrided layers produced with different substrate polarisation po tentials. The net advantages of such an approach over conventional met hods (e.g. microhardness testing) and the possibility of analysing mic rostructural phases previously not well detected by X-ray diffraction, make nanoindentation an attractive tool for a more complete understan ding of the nitriding process. (C) 1997 Elsevier Science Ltd. All righ ts reserved.