Invar effect of Fe-based bulk metallic glasses

Invar alloys have a wide application owing to its low expansion characteristics. Recently, it is revealed that some Fe-based bulk metallic glasses (BMGs), which have much higher strength than that of traditional Fe-Ni Invar alloys, also have the Invar effect. Combining the low expansion of the Invar effect and the good mechanical properties of Fe-based BMGs has an attractive potential for applications, for which firstly systematic study on the Invar effect of Fe-based BMGs is needed. In this work, the thermal expansion of 14 FeSiPCBM, (Fe,Co)BSiNb, FeNiPC and FeMoPCB BMGs are investigated. The results show all the alloys have the Invar effect, but can be categorized in two types, depending on whether the low expansion occurs in a wide temperature range below the Curie temperature T-c, or in a narrow temperature range near T-c. It is found the former type of alloys have lower T-c and saturation magnetic induction density, i.e., weaker magnetic properties. The substitution of Fe by Co and Ni weakens the Invar effect. These findings are explained based on the characteristics of the amorphous structure and the Bethe-Slater curve. The findings in this paper help to further develop low expansion Fe-based BMGs.