ON THE PROGRESS OF THE HDDR PROCESS AS THE MICROSTRUCTURE CONTROL METHOD

摘要

In this work, the progress of the HDDR process is discussed mainly on the Nd-Fe-B magnet system. There are three technologies being used for he Nd-Fe-B permanent magnet production; the sintering technique, the rapid quenching-annealing and the HDDR process. The HDDR process utilizes the HDDR phenomenon, in which hydrogen absorbing intermetallic compounds go through as they are heated in hydrogen atmosphere, Hydrogenation -Decomposition-Desorption-Recombination. In the HDDR process, these four steps in the HDDR phenomenon are processed by choosing suitable reaction conditions regarding to hydrogen gas pressure, temperature, rate of desorption and etc., and we can produce permanent magnet powders of good magnetic properties with microstructures consisting with sub-micron size crystalline grains. In the anisotropic magnet powders, the sub-micron size crystals are being mostly aligned in the crystallographic c-axis direction. Possible applications of the HDDR process to other systems are also discussed.