Papers by Author: Tatiana Liapina

Abstract: α-Iron foils were exposed to various gas atmospheres containing all or a number of the components NH3, CO, H2 and N2 for different periods of time at 550°C. In this way surficial compound layers were generated which contain different iron nitrides (ε, γ’), iron carbonitride (ε) and/or iron carbide (cementite, Fe3C). These compound layers were used to study phase transformations associated with N- and/or Cdiffusion processes in the corresponding phases. These studies involved (a) the layer-growth kinetics of cementite and (b) various solid-state phase transformations occurring in compound layers upon annealing in vacuum.

Abstract: ε/γ'-iron nitride (ε-Fe3N1+x, γ'-Fe4N) compound layers with thicknesses of about 10 µm were grown on pure α-Fe by gas nitriding at 823 K followed by quenching and were annealed at different temperatures in the range of 613 K – 693 K for different periods of time. These heat treatments led to a redistribution of nitrogen within the compound layer as well as between the compound layer and the adjacent ferrite, inducing thickness changes of the ε- and γ'-layers. The changes were analysed by light microscopy, electron probe microanalysis and X-ray diffraction. Models to describe and interpret the phase transformations in the ε/γ'-iron nitride compound layers as a function of time and temperature are discussed.