The Temperature Effect on Properties of Fe-Co-Ni Nanostructured System

Abstract

The influence of heating process (up to 200, 400 and 600 °C) on the phase transformation of non-equilibrium biphase Fe-Co-Ni systems was studied. The system was not changed at 200 °C, it remained nanostructured, and there were no phase transformations. At higher temperatures phase transformation BCC- into FCC-phase (high-temperature phase modification) was observed. The degree of phase transformation depended on the system composition. At 400–600 °C there was coarsening of the crystallites. In addition, there was the phenomenon of system oxidizing attended by iron outflow from phase; as a result, the lattice parameters were decreased. According to the measurements of the lattice parameters at coolingdown, parameters dependences on temperature and coefficients of thermal expansion were obtained. Changing of the system composition (due to metal oxidation) had low impact on the coefficients. The phases with different compositions and close lattice parameters had different coefficients of expansion. It was supposed that the expansion coefficients dependence from the composition was not additive. Magnetic characteristics of the samples were measured. It was found that heating changed it essentially. The main reasons of it was coarsening of grains (crystallites) and changes of the phase composition. The dependence of the magnetic properties of systems on phase composition and size of the crystallites (particles), as well as changes occurring under the temperature effect were required a more detailed study.