Effect of the volume fraction of nanocrystals on the mechanical properties of (Fe 0·9 Ni 0.1 ) 86 B 14 amorphous/nanocrystalline alloy

The effect of the volume fraction of nanocrystals on the macroscopic mechanical properties and microscopic atomic structure of Fe-based nanocrystalline alloys, as well as the relationship between the two, is an urgent issue to be explored. Seven nanocrystalline alloys with different volume fractions of nanocrystals were formed by annealing treatment of (Fe 0·9 Ni 0.1 ) 86 B 14 amorphous precursor. Through hardness, flat plate bending, and nanoindentation experiments, it is found that when the volume fraction of nanocrystals reaches the range of 45–55 %, there is an abrupt change in the macroscopic mechanical properties. Specifically, when the volume fraction is less than this range, the properties inherit the amorphous matrix, however, larger than this range, the properties are dominated by precipitated nanocrystalline phases. Meanwhile, based on the molecular dynamics simulation method, seven Fe 90 Ni 10 amorphous nanocrystalline models with different volume fractions of body-centered cubic nanocrystals are established, and the deformation mechanism of models and the evolution of their microstructures during the nanoindentation process are obtained intuitively. Moreover, it is further revealed that the significant changes in the Voronoi polyhedral index, which represents the microscopic atomic structure in this range of nanocrystal volume fractions, are the main reason for the abrupt changes in the mechanical properties at the macroscopic level.