Isothermal Heat-Treatment and Phase Transformation of Fe-Pd Permanent Magnet Alloys

Abstract

Iron and palladium alloys containing about 20–45 at% palladium showed a high coercive force and a large maximum energy product by a prolonged isothermal heat-treatment at relatively low temperatures.The present work was carried out to investigate the relation between the heat-treatment and the phase transformations so as to obtain a better understanding of the phase components and the process of the transformation. For this purpose, the isothermal transformation (TTT) curves of the representative four kinds alloys were determined by means of X-ray diffraction.It becomes clear that the γ phase obtained by water-quenching changes to γ+α by the heat-treatment at high temperature, and that by the heat-treatment at low temperature, the γ phase changes to γ+α+γ1→α+γ1 or γ+α→α+γ1. According to the TTT curves, a relatively long tempering time is needed to form the γ1 phase which is essential for obtaining excellent permanent magnet properties. Furthermore, it has been found that there is an almost similar behavior in the transformation by the same tempering-treatment regardless of whether the alloys has been slowly cooled at the rates of 0.11–0.055 K/s or water-quenched from the homogenizing temperature.