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

Abstract

Fe 100− x Ni x alloys (10< x<90 at%) were prepared by mechanical alloying (MA) of elemental powders in a high-energy planetary ball mill and studied by X-ray diffractometry and Mössbauer 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 100 at% Ni. Block size was 10–15 nm. Consequent annealing of MA samples resulted in further extension of FCC single-phase concentration range to the relatively low Ni content (20 at%). 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 Mössbauer 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 properties.