Magnetic monitoring of the hydrogenation-decomposition-desorption-recombination process in SmFe-based alloys

Abstract

A clear understanding of the reactions and phase changes that occur during the processing of a material is vital if we want to be able to achieve the best properties. In this series of experiments we have used a vibrating-sample magnetometer (VSM) to monitor the magnetic state of compacted powder samples of Sm13.7Fe86.3 and Sm13.8Fe82.2Ta4.0 during a standard hydrogenation-disproportionation-desorption-recombination (HDDR) cycle. The samples were mounted in the VSM and heated at 4 °C/min in 1 bar of flowing hydrogen to 750 °C, they were then held for 60 min under hydrogen and approximately 120 min under a vacuum before being cooled to room temperature under a vacuum at 4 °C/min. The results show that the initial absorption of hydrogen by the Sm2Fe17-type phase results in an increase in magnetization as well as TC. At higher temperatures, the disproportionation reactions of the Sm13.7Fe86.3 and Sm13.8Fe82.2Ta4.0 materials were observed to proceed at a faster rate for the second and third cycles of the HDDR procedure than for the first. The results are in agreement with our previous transmission electron microscopy studies, which showed that much of the Ta that was initially dissolved in the Sm2Fe17-type phase of the cast Sm13.8Fe82.2Ta4.0 material was reformed as Ta-based precipitates after a single HDDR cycle leaving the Sm2Fe17-type phase with much less dissolved Ta.