Influence of melt temperature on the Invar effect in (Fe71.2B24Y4.8)(96)Nb-4 bulk metallic glass

Abstract

The influence of melt temperature on the glass formation, physical properties and local structure of (Fe71.2B24Y4.8)(96)Nb-4 bulk metallic glass (BMG) was investigated through X-ray diffractometry, differential scanning calorimetry, thermal dilatation, and Mossbauer spectra tests. Amorphous alloys were formed by fast cooling of the melt from the temperature range of 1573-1773 K. BMG cast from 1623 K has lower Curie temperature and larger spontaneous volume magnetostriction, i.e., stronger Invar effect. The abnormality, which can not be eliminated by annealing, is attributed to the higher amount of Fe-Fe pairs indicated by the hyperfine field distribution. This special local structure is inherited from the melt, which has a liquid-liquid change manifested by an exothermic step region at the temperature range of 1615-1650 K. Through a slow-cooling process, the melt in the liquid-liquid change is frozen to a crystalline structure contained Y2Fe17 phase with a high intensity signal. These findings help explain the correlation between the liquid-liquid change and the structure of cooling products.