Ultrafine Grained Iron, Which is Fabricated by Severe Plastic Deformation Stimulated by Diffusion Flow of Dopant Element: Structural Features and Mechanical Behaviour

摘要

Sections of nanograined (grain size-d < 100 nm) and submicrograined (100 nm < d < 1 mu m) structures followed by the fine micrograined (d < 10 mu rn) regime are recognised in the surface of alpha-Fe samples subjected to the friction treatment in a gas atmosphere, i.e. with air (FT) or with ammonia-gas (FN). Using a nanoin-dentation technique, the relationships between microstructure and mechanical parameters such as hardness (H_h), plasticity characteristic (delta_A), and Young's modulus (E) are found to be actually dependent on the grain scale. Scale effect of grain structure on the response to deformation of nanograined iron subjected to FT or FN routes are shown to be influenced by nanocrystalline particles of precipitation phases (Fe_3O_4 oxide or Fe_4N nitride), which are much expected either due to negligible solubility of dopant element (in particular, oxygen) or due to decomposition process resulted from natural ageing of alpha-Fe[N].