Face-centered cubic phase stability and martensitic transformation under deformation in Fe–Ni and Fe–Mn alloys nanostructured by mechanical alloying and high-pressure torsion

Binary Fe100−xMnx (6 ≤ x ≤ 30) and Fe100−yNiy (10 ≤ y ≤ 30) alloys, where x and y are given in at.%, were prepared by mechanical alloying from elemental powders in a high-energy planetary ball mill. X-ray diffraction and Mössbauer spectroscopy were used to investigate structure and phase constitution of the samples. Thermomagnetic measurements were used to study phase transformations at heating and cooling. The γ → α2 martensitic transformation temperature was decreased in the mechanically alloyed specimens by about 300–350 K compared with that of ordinary cast alloys. Powder and consolidated γ-phase alloys were subjected to mechanical deformation, which was accompanied by the appearance of ferromagnetic properties due to partial transformation of γ-phase to α2-phase. Mechanically alloyed Fe80Ni20 and Fe78Ni22 alloys were also subjected to severe plastic deformation by high-pressure torsion. Differences in the phase composition of alloys after various treatments were discussed using the thermodynamic data.