Nanoscale precipitates and phase transformations in a rapidly-solidified Fe-Pt-B amorphous alloy

The phase transformations in a rapidly solidified (Fe0.75Pt0.25)75B25 alloy on heating were studied by X-ray diffractometry, differential scanning and isothermal calorimetries. An as-solidified structure was examined by transmission electron microscopy (TEM). The results of TEM, including nano-beam diffraction and high-resolution imaging, clearly indicate the existence of nano-scale cubic cF4 Fe(Pt) solid solution particles within the as-solidified amorphous matrix. The particles of the cF4 Fe(Pt) phase start growing at elevated temperature and undergo ordering forming a tP4 FePt compound followed by the precipitation of a tI12 Fe2B phase from the residual amorphous matrix. The ordering of the cubic phase takes place after an incubation period which allows to anticipate a nucleation and growth mechanism. This process is followed by further growth of the particles. The transformation behavior on heating is studied in detail.