Phase transformations in Fe-Ni system at mechanical alloying and consequent annealing of elemental powder mixtures

Fe100-x Ni-x alloys (10 < 90at%) were prepared by mechanical alloying (MA) of elemental powders in a high-energy planetary ball mill and studied by X-ray diffractometry and Mossbauer spectroscopy. It is shown that the concentration ranges of single-phase solid solutions of MA samples extend significantly as compared with those obtained by conventional techniques. In our case, the BCC phase exists in the range from 0 to 20 at% Ni and FCC phase from 30 to 100at% Ni. Block sire was 10-15nm. Consequent annealing of MA samples resulted in further extension of FCC single-phase concentration range to the relatively low Ni content (20at%). This was caused by considerable retardation of austenite-martensite transformation in MA alloys. The FCC alloys with 20-28 at% Ni were found to be non-ferromagnetic at room temperature: only the paramagnetic component was observed in the corresponding Mossbauer spectra. However, the treatments of low-nickel austenite alloys like cooling in liquid nitrogen or mechanical deformation provoked austenite-martensite transformation and led to the rise of ferromagnetic prpoerties. (C) 2001 Elsevier Science B.V. All rights reserved.