Study of α1 and α2 Phases in Ticonal 600 Alloy

Abstract

The changes in the magnetic properties of Ticonal 600 (Fe-24% Co-14% Ni-8% Al-3% Cu) and the evolution of the microstructures, as observed on thin foils by transmission electron microscopy, both resulting from the interruption of the magnetic cooling by a water quench from temperatures in the range 850°–600°C, were studied at room temperature before and after double tempering. These data were used in connection with a system of approximated relations to estimate the saturation magnetization, σs1 and σs2, and the compositions of α1 and α2 phases, respectively. During the magnetic cooling, σs1 first decreased slightly, between 850°–800°C, and then increased, while σs2 decreased continuously over the entire temperature range. Tempering induced a decrease in σs1; and an increase in σs1; however, the latter effect become less important as the prior magnetic treatment progressed to lower temperatures. Cooling down to 600°C followed by tempering resulted in a σs2 value of the order of 93–100 emu/g, while σs1 was found between 184–195 emu/g. After the same cycle of heat treatments, the chemical compositions of the phases were calculated as being (in wt.%): Fe (50–57)-Co (37–45)-Ni≤5-Al≤0.3-Cu≤5 (α1 phase) and Fe (42–52)-Co≤7-Ni (26–36)-Al (18–19)-Cu≤7 (α2 phase).