Diagnostic and modeling of N₂-H₂discharges for iron nitriding

Abstract

The production of N and H atoms has been studied in DC and HF N2-H2 flowing discharges and post-discharges in connection with nitriding of iron substrates. Experimentally, the N and H atoms have been detected by emission spectroscopy and Laser Induced Fluorescence (LIF). A strong increase of the Mayn gas atom density (N or H) was found when a small amount of a second gas (H2 or N2) was added. This increase in N or H atom densities is interpreted by a model describing the kinetics in the reactive gas volume and on the surface of the reactor walls (pyrex tube). In particular, it is shown that the destruction probabilities of N and H atoms on the tube wall are reduced by a factor of about 2 as a few % of H2 or N2 is introduced into N2 or H2. Correlations are established between the density of N and H atoms and the thickness and quality of iron nitride layers growing on iron substrates located within a reactor and placed in the post-discharge of a N2−H2 HF flowing discharge. Under the conditions of maximum N and H atom density, thick ϵ−Fe2N1−x layers without iron oxide superficial sublayer have been found on the iron surface.