Nanoscale texture analysis of d-HDDR processed Nd-Fe-B powder particles

A strong texture in polycrystalline Nd-Fe-B powder particles processed by dynamic hydrogenation disproportionation desorption and recombination (d-HDDR) method is of importance for enhanced macroscopic magnetic properties [1]. This heavily depends on the processing parameters such as the hydrogen partial pressure [2]. The initial and the final step of the HDDR process has already been extensively studied by electron backscatter diffraction (EBSD) technique in the scanning electron microscope (SEM) [3]. However, for SEM-EBSD analyses, e.g. after the early and full disproportionation step, the spatial resolution as well as the signal of the Kikuchi patterns was not sufficient for a thorough local texture analysis. Therefore, analyses on the nanometer scale have been carried out in a transmission electron microscope (TEM) using orientation and phase mapping via ASTAR/DigiSTAR (""EBSD inside the TEM""). In this case, a spatial resolution of up to one nanometer can be achieved. Data evaluation was carried out using the Matlab® MTEX toolbox yielding, for example, pole figures. Using this technique it is possible to map the phase distribution of a-Fe, NdH2, and Fe2B as well as their texture in order to reveal an inter-phase textural relation during the different HDDR process steps. The current understanding is that solely the Fe2B phase is responsible for the texture transfer. The obtained results for the different process steps and parameters will be interpreted with respect to the existing models and the texture analysis results on a-Fe and NdH2 from ASTAR/DigiSTAR and EBSD will be compared to evaluate the statistical reliability.