Revealing a structural transition in typical Fe-based glass-forming alloy melts

The viscosity-temperature relation of three typical Fe-based glass-forming alloys was investigated by rotational vibration-type high-temperature melt viscometry and ab initio molecular dynamics simulation. It was shown that during the first heating process until 1500 degrees C, the viscosity decreased suddenly at approximately 1400 degrees C, demonstrating a structural transition which was confirmed by the thermoanalysis. However, if the heating temperature was below 1400 degrees C or during the following second thermal cycle, such structural transition cannot be observed. The viscosity curves of all samples during cooling processes can be well described by the Arrhenius equation, in which the activation energy was inversely proportional to the Fe content. The Fe2B-like clusters have higher total energy, higher melting point and larger size than that of Fe3B-like clusters. Thus, we suggested that the structural transition may be related to the transformation from Fe2B-like clusters to Fe3B-like clusters. The structural transition in liquid was eliminated and a homogeneous Fe-based alloy melt was obtained after a rather long relaxation time at a temperature higher than the melting point of infusible clusters. This study could offer some helpful reference for understanding the nature of alloy melt and the quality control of Fe-based amorphous alloys.