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 Mossbauer spectroscopy were used to investigate structure and phase constitution of the samples. Thermornagnetic measurements were used to study phase transformations at heating and cooling. The gamma -> alpha(2) 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 gamma-phase alloys were subjected to mechanical deformation, which was accompanied by the appearance of ferromagnetic properties due to partial transformation of gamma-phase to alpha(2)-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. (c) 2007 Elsevier B.V. All rights reserved.