Power-law scaling and fractal nature of medium-range order in metallic glasses

Abstract

The atomic structure of metallic glasses has been a long-standing scientific problem. Unlike crystalline metals, where long-range ordering is established by periodic stacking of fundamental building blocks known as unit cells, a metallic glass has no long-range translational or orientational order, although some degrees of short- and medium-range order do exist. Previous studies have identified solute- (minority atom)-centred clusters as the fundamental building blocks or short-range order in metallic glasses. Idealized cluster packing schemes, such as efficient cluster packing on a cubic lattice and icosahedral packing as in a quasicrystal, have been proposed and provided first insights on the medium-range order in metallic glasses. However, these packing schemes break down beyond a length scale of a few clusters. Here, on the basis of neutron and X-ray diffraction experiments, we propose a new packing scheme-self-similar packing of atomic clusters. We show that the medium-range order has the characteristics of a fractal network with a dimension of 2.31, and is described by a power-law correlation function over the medium-range length scale. Our finding provides a new perspective of order in disordered materials and has broad implications for understanding their structure-property relationship, particularly those involving a change in length scales.

Hidden topological order and its correlation with glass-forming ability in metallic glasses

“…On the contrary, some studies have demonstrated that plenty of structural information is hidden behind the data of structure factors or PCFs, for example, a global packing containing both spherical-periodic order and local translational symmetry has been revealed by analysing PCFs of many metallic glasses 9 . A fractal nature of medium-range order in metallic glasses was also found by examining the relationship between the first peak position in structure factors and atomic molar volumes in many metallic glasses 7 . In fact, the oscillation in the structure factors or PCFs is an indication that a certain order does exist in amorphous solids 7 .…”

“…Although significant progress has been made and provided insights into the atomic-level structure and short-to-mediumrange order in glasses [3][4][5][6][7][8][9][10][11][12][13][14] , the way of leading to the mediumrange order is still unclear [5][6][7][8][9][10] . Does a universal rule exist that nature follows to construct a glass structure as what has been discovered for crystals?…”

Cryogenic-temperature-induced transition from shear to dilatational failure in metallic glasses

“…Mechanical failure of metallic glasses continues to fascinate researchers [1][2][3][4][5], since dislocations, grain boundaries, crystallographic planes, etc., are not defined in this class of non-crystalline materials [6][7][8][9]. Instead, the shear transformation zone (STZ), i.e.…”

Supercooled liquids with enhanced orientational order

“…Evidence of such structures has been found in metallic glass formers [14][15][16] , where the presence of quasi-crystalline clusters with a few topological defects has been detected by diffraction techniques, such as atomic-scale high-resolution transmission electron microscopy and by X-ray, neutron and electron diffraction. An enhanced degree of topological order may be achieved via structural rearrangements, either by annealing below the glass transition temperature (physical aging) 17 or pressurizing 18 , which permits the nucleation of MRO regions in proximity to the quasi-crystalline clusters and the consecutive propagation of a similarly ordered structure.…”