Combined Mössbauer Spectrometry and Atom Probe Tomography Investigation of Mechanically Milled Rare Earth / Transition Metal Powders

Abstract

"The microstructure of mechanically milled Nd2Fe14B, SmCo5/Fe and SmCo3Cu2/-Fe alloys has been investigated by Mössbauer spectrometry and atom probe tomography. The structural changes that occur upon milling and subsequent annealing were characterised at a nanometer scale. Milling promotes intermixing of the elements and the formation of nanograins. In Nd-Fe-B powders, the Nd2Fe14B phase is transformed into -Fe and an amorphous Nd-Fe-B phase. In SmCo5/Fe powders, Fe/Co intermixing occurs, leading to the formation of Sm(Co,Fe)5 and -Fe(Co) phases. In SmCo3Cu2/Fe powders, although Sm is partly oxidised, Fe/Co intermixing occurs as well, leading to the formation of -Fe(Co) nanograins surrounded by Sm(Co,Cu,Fe)5 intergranular regions. The combined Mössbauer and atom probe tomography investigation of rare earth / transition metal powders thus allows revealing the effect of mechanical milling and subsequent annealing on the nanostructure of the powders. These results are helpful for the understanding of the magnetic properties of the powders. Keywords: rare earths-transition metals powders, Mössbauer spectrometry, atom probe tomography "