Fractal atomic-level percolation in metallic glasses

Abstract

Percolating cluster, factal structure Metallic glasses are appealing materials because they are strong and can bend without breaking. These materials are disordered but possess none of the defects seen in crystalline counterparts. Chen et al. developed a model for metallic glasses in which clusters of atoms float free in the liquid, begin to jam, and finally organize into a short-range fractal structure below the glass transition temperature. This model also accounted for the density and high strength characteristics of bulk samples. Science , this issue p. 1306

Constant real-space fractal dimensionality and structure evolution in Ti62Cu38 metallic glass under high pressure

“…2,3 Furthermore, the fractal dimensionality of metallic glasses in real space was found to remain as about 2.5 as well, which was calculated from the atomic nearest-neighbor distance in pair distribution function (PDF) in two typical binary metallic glasses of Cu-Zr and Ni-Al systems up to 20 GPa from classical molecular dynamics (MD) simulations. 1 More interestingly, the pressure dependence of crossover feature on the power law exponent shifting from 2.5 to 3 with increasing atomic separation distance was proposed, which related to that pressure tune the correlation length change based on continuum percolation model. 1 However, no experimental PDF data was reported to exam the real space fractal dimensionality for any metallic glass system so far, and the validity of these fractal features in real space for metallic glass under high pressure conditions need to be checked by measured data in addition to the MD simulations.…”

“…1 More interestingly, the pressure dependence of crossover feature on the power law exponent shifting from 2.5 to 3 with increasing atomic separation distance was proposed, which related to that pressure tune the correlation length change based on continuum percolation model. 1 However, no experimental PDF data was reported to exam the real space fractal dimensionality for any metallic glass system so far, and the validity of these fractal features in real space for metallic glass under high pressure conditions need to be checked by measured data in addition to the MD simulations. Based on this motivation, a typical binary metallic glass Ti-Cu system, which has been studied at ambient conditions for many years, [4][5][6] was selected as model for the study of structure and real space fractal dimensionality under pressure conditions in this paper.…”

“…This is different from the result in previous MD simulations, which suggested power law exponent cross-over phenomenon could be common in metallic glass systems. 1 It is well-known the limitation of classical MD simulation which is strongly depend on quality of potential. As pointed out in the supplementary materials in previous report, 1 the embedded-atomic method (EAM) type potentials used in its MD simulations, normally are not tested at high pressure conditions, which may result in errors.…”

“…1,2 From real space PDF curves at various pressure conditions, fractal dimensionalities were determined by normalized positions of the second peak r 2 , the third peak r 3 , and the fourth peak r 4 as 2.44 (0.05), 2.59 (0.02), and 2.48 (0.02), respectively, as shown in Fig. 3 (b).…”

“…For example, the limited range of Q in previous high pressure X-ray scattering measurement restricted the accuracy of Fourier transforms to real space PDF, therefore the MD 3 simulations instead of measured PDF was used to study the structure evolution of metallic glass upon compression. 1 The PDF method is able to provide valuable insights into the local atomic structure, and recently became advanced structure analysis technique combined with synchrotron high energy X-ray scattering measurement with high Q range. 7,8 Since the PDF method provides real space structural information in one dimension, simulations of the total scattering data using modeling techniques, such as reverse Monte Carlo (RMC), are extremely useful for visualizing the three-dimensional atomic arrangement of liquid and amorphous materials.…”