Structural properties and evaluation of crystal fraction by cryogenic heat capacity measurements of Fe-based nanocrystalline alloy

An amorphous Fe73.5Cu1Nb3Si13.5B9 alloy was prepared by the rapid solidification technique. The rapidly quenched alloys have been annealed in the temperature range from 490 to 550 °C for 90 min and their structure was investigated by using X-ray diffraction (XRD). After annealing, at crystallization temperature, the microstructure of the samples composed of nanocrystalline Fe3Si grains surrounded by the residual amorphous phase. The crystal fractions of the annealed samples were evaluated by heat capacity measurements. Heat capacities of the as-quenched and annealed samples were measured at different temperatures between 15 and 40 K. This method is useful for evaluating small changes in the amount of crystalline phase and provides a new tool for finding the nanocrystalline fraction. The volume fraction of the crystalline phase increased from 15.92 to 94.21% as annealing temperature increased from 490 to 550 °C.