Influence of severe plastic deformation (SPD) under high pressure on martensitic phase transformations and hardening of Fe-Mn alloys has been studied. The named alloys with wide concentration content of manganese (from 0 to 55 wt.%), having in initial state bcc, hcp and fcc (stable and metastable austenite) phases after thermoplastic treatment and quenching from 1370 K in water were as the objects under investigation. SPD under high and ultra-high pressure was performed by the means of hydroextrusion techniques, torsional shear under pressure and usage of diamond anvil cell (DAC). The ranges of pressure varies from 0 to 60 GPa and the deformation degree does not exceed 10 units of true deformation, accordingly.
The influence of manganese contents (8-20-26-40 wt.%) and hydroextrusion parameters on γ\-ε\ and γ\,ε\ - \alfa\ phase transformations and work-hardening intensity is highlighted. The correlation between the rate of strain-induced martensitic transformations and the values of stressed state parameters is stated. It is pointed out that microstructural evolution due to deformation under high pressure gives a fear combination of strength, plasticity and static and delayed fracture resistance of metastable Fe-Mn alloys.
The complex study of properties and structures of Fe-Mn-alloys, deformed in DAC, including the nanocrystalline structures, by methods of microhardness measurements, transmission electron microscopy, X-ray diffraction analysis), Moessbauer effect and metallography has been carried out. The obtained results of complex investigation of studied alloys at nanocrystalline state have revealed the strong dependence of phase solid transformations on parameters of SPD under pressure and initial phase, structure state and concentration of Mn at alloys.