Structural model for bulk amorphous alloys

Abstract

A structural model is proposed for bulk amorphous alloys based on the pair distribution functions (PDFs) measured using neutron scattering at ambient and cryogenic temperatures and different structural states. Reverse Monte Carlo (RMC) simulations were performed, in which icosahedral and cubic structures were used as the initial structures for the PDF refinement. The combined PDF and RMC studies show that strongly bonded clusters, with atomic-bond lengths shorter than their crystalline counterpart structures, are randomly distributed and strongly connected in the amorphous matrix. An attempt has also been made to identify the relationship between amorphous structures and their mechanical properties.

Atomic migration and bonding characteristics during a glass transition investigated using as-cast Zr-Cu-Al

“…The most recent studies [ [19][20][21][22] ] from PDFs of BMGs have pointed out that free volumes are resulted from these atom pairs that have longer bond lengths than that in the solid solution but normally not long enough to fill in an atom, this making the free volume concept being more clear. …”

“…However, the authors of the theory warned against its use in metallic systems, because the critical size of the free volume, γv*/v 0 , where v 0 is the atomic volume, is only about 0.1, whereas it is about 0.8 for hard-sphere systems for which the theory was designed [ 18 ]. Indeed metallic atoms are not hard-sphere-like, and is easily deformable, making it difficult to apply the free-volume theory in its original form [19][20][21][22].…”

The Development of Structure Model in Metallic Glasses

“…The lack of unit cells makes the amorphous structures much more complex at the atomic level and thus one of the important In addition, Figure 14 shows a schematic illustration to further understand vividly the mutual relation among the three parts of the model proposed by Fan. The black-color parts represent the clusters, and the interconnecting zone between the clusters and the free volume region are shown in Figure 14 Based on a systematic study on PDF and RDF at different temperatures and phase states for ternary bulk metallic glasses 37,126,[127][128][129][130] , in 2015, they finally defined the free-volume, i-zone and cluster in metallic glasses for quantitatively understanding these concepts 129 . That is, (1) cluster: natural communities consist of strongly connected atoms, in which the bond distances of the nearest atoms interests to conduct further studies on their local atomic structures, which might be able to help scientists finally wipe the remaining mystery away.…”

“…Taking this advantage, Fan et al collected total-scattering for PDF on the as-cast and its crystallized counterpart of a Zr-Cu-Al ternary BMG at room temperature and cryogenic 15 K. They constructed an atomic model based on the peak spallation, atomic compression and tension appeared on the PDF data for the nearest atom pairs, in which strongly bonded clusters act as units or "hard spheres" instead of the individual atoms acting as hard spheres, and these clusters are randomly distributed, strongly connected, and result in free volume between the clusters 126 . They further developed the atomic model in 2009, and described it as the tight-bond cluster model.…”

Structure relaxation of Mg65Cu25Gd10 metallic glass and its effect on strength

“…So Mg 65 Cu 25 Gd 10 has become the foundation for studying other Mg-based metallic glasses, however, the understanding of Mg 65 Cu 25 Gd 10 is very limited. In the present work, we endeavored to study the structural changes in Mg 65 Cu 25 Gd 10 metallic glass resulted from low temperature annealing through extended X-ray absorption fine structure (EXAFS) and evaluate their effects on strength that was in favor of the understanding of the relationship between local atomic structures and properties [15] .…”