Abstract
The influence of hydrogen pressure on kinetics of growth of Nd2Fe14B phase during hydrogen-induced reverse phase transformations in the industrial Nd2Fe14B hard magnetic alloy has been studied. It has been determined that, as the temperature and the initial hydrogen pressure increase, a reverse phase transformation significantly accelerates. It has been shown that the kinetics of the reverse phase transformation is controlled by the Fe atoms diffusion and that the rate growth of new Nd2Fe14B phase increase with increase of initial hydrogen pressure. On the base of the Kolmogorov kinetic theory the kinetic equation describing influence of initial hydrogen pressure on the isothermal kinetic diagram for this transformation has been obtained.
Highlights
As well known permanent magnet materials of a RE-TM type are key components of numerous modern devices [1]
The transformation process is based on the formation of a RE-TM hydride which at higher temperatures has a tendency to disproportionate into a mixture of RE-hydride and iron—direct hydrogen induced phase transformation that occurs in case of NdFeB-based alloys by the following scheme [6]
It has been established that, as the temperature and the initial hydrogen pressure increase it lead to considerable acceleration of evolution of reverse phase transformation
Summary
As well known permanent magnet materials of a RE-TM (rare-earth–transition-metal) type are key components of numerous modern devices [1]. There are many processing routes for improving of their magnetic properties [2]. One from perspective technologies for improvement of magnetic properties of RE-TM type alloys is HDDR-process (Hydrogenation–Decomposition– Desorption–Recombination) [3]. Above-mentioned HDDR-process is based on hydrogen-induced reversible phase transformations in the RE-TM type hard magnetic alloys [6]. The transformation process is based on the formation of a RE-TM (rare-earth-transition-metal) hydride which at higher temperatures has a tendency to disproportionate into a mixture of RE-hydride and iron—direct hydrogen induced phase transformation that occurs in case of NdFeB-based alloys by the following scheme [6]
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