Change in atomic coordination in a heavily deformed metallic glass

Abstract

Articles you may be interested inUnderstanding the changes in ductility and Poisson's ratio of metallic glasses during annealing from microscopic dynamics J. Appl. Phys. 118, 034901 (2015); 10.1063/1.4923304The heterogeneous structure of metallic glasses revealed by superconducting transitions A quantitative link between microplastic instability and macroscopic deformation behaviors in metallic glassesThe local structure around Ni and La atoms in Al 85 Ni 10 La 5 amorphous powder after ball milling was investigated by X-ray absorption spectroscopy. A continuous decrease in coordination number of Ni and La as a function of milling time was observed, while the nearest neighbour distance and the mean square atomic displacement did not change, pointing at the creation of free volume around the Ni and La atoms. These structural changes resemble those of a liquid upon temperature increase. The results are described by a shear band model in which the coordination numbers of Ni and La are different within and outside a shear band. V C 2014 AIP Publishing LLC.

Local constriction around minor elements in Al 86 Ni 7 X 1 Y 6 metallic glass (X: Ag, Au, Pt)

“…The experimentally observed reduction in bond length and opposite change in atomic size of Al and TM was supported by the work of Gu et al [13] who calculated the local structure in Al 70 Fe 20 EM 10 (EM: Early transition metals Ti, Zr, Hf, V, Cr) by first-principles method. They found strong interactions between Al and Fe atoms as well as a reduced effective Fe radius and an enlarged effective Al radius, which supports previous conclusions from experimental work [3][4][5][6][7][8][9][10]23]. The low coordination numbers of the X atoms found in the present work may hence be understood on the basis of opposite changes of the effective radii of X atoms and Al atoms as a result of charge transfer.…”

“…4. The strong reduction of bond length found in the present work and in earlier work reported in literature [3][4][5][6][7][8][9][10]23], indicates that the use of metallic radii for calculating the topological instability criterion λ [32] in Al-based metallic glass containing TM and X elements is questionable. The instability criterion λ describes the limiting composition for stability of the amorphous phase of Al-TM-RE alloys calculated from the alloy composition and the metallic radii of the alloying elements.…”

“…The results show that the X-Al cluster compositions deviate from those of the corresponding compounds, see Table 1. This is not in agreement with the exception deduced by the Hume-Rothery rules [7,25], according to which the electronegativity difference between constituting elements reflects the nature of the bonds between atomic pairs in alloys. Elements with sufficiently different electronegativities tend to form compounds, while elements with similar electronegativity tend to form solid solutions.…”

“…Bond-shortening along with very low coordination numbers (N = 6-7) compared to values predicted by the DRPHS model [11] using metallic radii has been reported in several Al-based metallic glasses for TM\ \Al bonds [3][4][5][6][7][8][9][10]23]. In those alloys, shortening of TM\ \Al bonds result in larger effective radii r*(Al) for Al and in smaller values r*(TM) for TM atoms compared with their metallic radii.…”

“…Charge transfer from the first-shell aluminium atoms to the TM atoms leads to s-p hybridization of the Al\ \TM bonds and a concomitant change in the effective atomic radii [3,4]. The size of Al atoms increases, while that of the TM atoms decreases, resulting in Al coordination numbers around TM atoms of about 6 [3,[5][6][7][8][9][10]. Such low numbers are far below the values N DRPHS (TM-Al) ≈ 11 for Al around Ni, Fe and Co obtained for dense random packing of hard spheres (DRPHS) [11] using metallic radii [12].…”