The effect of hydrogen pressure and temperature on kinetics of hydrogen-induced direct phase transformation in hard magnetic alloy

Abstract

The kinetics of hydrogen-induced direct phase transformations in the Nd 15Fe 77B 8 hard magnetic alloy has been investigated. It has been determined that, as the temperature and the hydrogen pressure increase, a phase transformation significantly accelerates. According to the Johnson–Mehl–Avrami model the equations describing the isothermal kinetic diagrams for these transformations have been deduced. It has been shown that the kinetics of the phase transformation is controlled by the Fe-atoms diffusion. An increase of hydrogen pressure results in an increase in the free energy of the NdH 2 hydride formation and this is the main factor in accelerating a hydrogen-induced direct phase transformation evolution in the Nd 2Fe 14B type alloys.