Atomic structure evolution related to the Invar effect in Fe-based bulk metallic glasses

The Invar effect is universally observed in Fe-based bulk metallic glasses. However, there is limited understanding on how this effect manifests at the atomic scale. Here, we use in-situ synchrotron-based high-energy X-ray diffraction to study the structural transformations of (Fe71.2B24Y4.8)(96)Nb-4 and (Fe73.2B22Y4.8)(95)Mo-5 bulk metallic glasses around the Curie temperature to understand the Invar effect they exhibit. The first two diffraction peaks shift in accordance with the macroscopically measured thermal expansion, which reveals the Invar effect. Additionally, the nearest-neighbor Fe-Fe pair distance correlates well with the macroscopic thermal expansion. In-situ X-ray diffraction is thus able to elucidate the Invar effect in Fe-based metallic glasses at the atomic scale. Here, we find that the Invar effect is not just a macroscopic effect but has a clear atomistic equivalent in the average Fe-Fe pair distance and also shows itself in higher-order atomic shells composed of multiple atom species. There is limited understanding of the Invar effect at atomic scale. Here the authors show that the Invar effect is not only a macroscopic effect, but also has a clear atomistic equivalent in the average distance of Fe-Fe pair as well as higher-order atomic shells composed of multiple atom species.

Automated summary

The Invar effect in Fe-based bulk metallic glasses is widely observed, but its manifestation at the atomic scale is not well understood. In this study, in-situ X-ray diffraction was used to investigate the structural transformations of two bulk metallic glasses, revealing that the Invar effect is consistent with macroscopic thermal expansion and correlated with Fe-Fe pair distance.