γ_N-shift as a function of N₂ content in AISI 304 nitriding

We present in this work some experimental results obtained from nitriding AISI 304 stainless steel at different temperatures by means of RF/DC generated 10¹⁵ m^-3 density plasmas in the 1-4 eV electron temperature range. The samples were biased up to -400 V. Substrate temperatures have proved to be an influential factor in the diffusion of the ions impinging onto the material under treatment. In turn, the γ_N shift expansion observed by XRD during this temperature increase is a function of the amount of nitrogen introduced to the sample and is related to the bias, the nitrided layer depth and the plasma characteristics. Thus, we have identified the substrate temperature as a global control variable in order to analyse the evolution of the nitrogen enrichment process through its influence on the X-ray diffraction imaging of the γ_N shift in the samples. The optimization of the temperature is explored along with its limits in terms of the Cr precipitation threshold.