Probing the growth and melting pathways of a decagonal quasicrystal in real-time

Abstract

How does a quasicrystal grow? Despite the decades of research that have been dedicated to this area of study, it remains one of the fundamental puzzles in the field of crystal growth. Although there has been no lack of theoretical studies on quasicrystal growth, there have been very few experimental investigations with which to test their various hypotheses. In particular, evidence of the in situ and three-dimensional (3D) growth of a quasicrystal from a parent liquid phase is lacking. To fill-in-the-gaps in our understanding of the solidification and melting pathways of quasicrystals, we performed synchrotron-based X-ray imaging experiments on a decagonal phase with composition of Al-15at%Ni-15at%Co. High-flux X-ray tomography enabled us to observe both growth and melting morphologies of the 3D quasicrystal at temperature. We determined that there is no time-reversal symmetry upon growth and melting of the decagonal quasicrystal. While quasicrystal growth is predominantly dominated by the attachment kinetics of atomic clusters in the liquid phase, melting is instead barrier-less and limited by buoyancy-driven convection. These experimental results provide the much-needed benchmark data that can be used to validate simulations of phase transformations involving this unique phase of matter.

Processing metallic materials far from equilibrium

“…Even so, further advances in the field are needed to describe (1) the solidification of multicomponent, multiphase systems of industrial significance (e.g., high entropy alloys), in which convective fluid flow may play a dominant role; (2) the growth of complex intermetallics, which make up 94% of known compounds 35 and may exhibit a relatively strong anisotropy in interfacial energy and interfacial mobility; 36,37 (3) nonclassical or multistep nucleation pathways, which are typically associated with the presence of several free-energy minima; 9,38 (4) the relationship between eutectic growth and glass formation, and the competition between the two seen at high solidification rates; and (5) the relationship between high Pe growth in solidification and in solid-state transformation. 39 Answers to these questions depend not only on the integration of experiments and modeling/ simulations, but also the availability of databases for thermophysical properties (e.g., composition-dependent interdiffusivities).…”

Now showing in 4D: Quasicrystal growth and dissolution

“…The calculated kinetic coefficient of the Al-Co-Ni decagonal quasicrystal is significantly smaller than that of periodic crystals (both simple and intermetallic) by over three orders-of-magnitude ( Fig. 1(c)) [1]. The smaller kinetic coefficient points to the presence of large attaching clusters or "building blocks" that contribute to a more sluggish growth rate.…”

“…Although there has been no lack of theoretical studies on quasicrystal growth, there have been very few experimental investigations with which to test their various hypotheses. To this end, we have recently performed synchrotron-based experiments on a decagonal (i.e., two-dimensional or 2D) quasicrystal of composition Al-8wt%Co-8wt%Ni [1]. High flux X-ray tomography enabled us to capture projections at temperature during continuous cooling.…”

“…1(b)). Therefore, the growth and dissolution processes of the decagonal quasicrystal lack time-reversal symmetry, and quasicrystal dissolution is not locally-controlled [1]. Instead, dissolution is limited by buoyancy-driven convection in the surrounding melt, leading to highly anisotropic growth rates of the bounding aperiodic facets.…”

“…Quasicrystals of both decagonal d and icosahedral i variants possess kinetic coefficients that are at least three orders-of-magnitude smaller than that of other known periodic crystals. Adapted from Ref [1]…”