An abnormal meta-stable nanoscale eutectic reaction revealed by in-situ observations

Abstract

Phase selection and growth of materials far from equilibrium provides fertile ground for novel phases and morphologies since a multitude of different pathways may be energetically accessible. In this study, a complex metastable devitrification of Al60Sm11 (ε-phase) from its amorphous precursor is discovered using a combination of in-situ high-energy X-ray diffraction (HEXRD), providing insight into the average bulk behavior, and in-situ aberration corrected scanning transmission electron microscopy, revealing the atomic scale mechanisms of growth and their dynamics. We have found that non-equilibrium chemical partitioning disrupts the nominal planer growth by formation of nanoscale Al enriched regions inhomogeneously segregated at the ε/glass interface, to locally balance the compositionally dependent driving force and the associated diffusional burden imposed on its grain growth. These Al-rich regions form fcc-Al-rich nanocrystallites epitaxially with the ε-phase, modifying ε/glass interface mobility and creating a crenulated growth front. This new mechanism offers a pathway for fabricating alloy structures with nanoprecipitate dispersions through a meta-stable phase transition.

Monitoring eutectoid decomposition process of metastable phases in Al-Sm alloy via in-situ X-ray scattering and ex-situ transmission electron microscopy

“…Since SAXS reflects the electronic density fluctuation and enables to provide insight of chemical separation in the materials, minimal SAXS change at first exothermic event suggests the transformation from amorphous to -Al60Sm11 is nearly chemically partitionless, which has been confirmed by TEM observation in our previous studies [9,14].…”

“…A prerequisite to understand the underlying dynamics and kinetics requires the determination of actual size, shape, and distribution of each phase with certain spatial and temporal resolution. Synchrotron-based X-ray scattering methods, featured with high X-ray flux, brilliance and coherence, are widely available in most synchrotron facilities and enable in-situ, time-resolved X-ray experiments over hierarchically ordered length scales [14,15]. Synchrotron wide-angle x-ray diffraction (WAXD) coupled with small-angle x-ray scattering (SAXS) enables to investigate the phase and structure evolution at different length scales in temporal resolution, which facilitates the kinetics study of phase transformation [16].…”

“…The pathway selection is dependent on the chemical composition as well as the time/temperature profile. The high-precision, WAXD results unveiled many metastable phase structures along the pathway, which have been the basis for modeling to better design and predict vitrification/devitrification processes [14,19]. In this study, we provide a systematic study on devitrification process on melt-spun Al87.6Sm12.4, combining dynamic scanning calorimetry (DSC), WAXD/SAXS, and TEM to gain more insight into the morphological as well as the relevant chemical partition or phase separation.…”

Self-Supported Ni/NiSPx Microdendrite Structure for Highly Efficient and Stable Overall Water Splitting in Simulated Industrial Environment

“…In comparison with the crystal database, we found that these two lattices correspond to the (111) and (200) crystal planes of metal Ni (JCPDS 87-0712), respectively. In addition, many disordered structures can be observed in the field of vision (shown in the small yellow circles in the Figures f and S1), indicating that there are a lot of defects in the original sample, which is conducive to reducing surface energy and promoting the stability of the dendritic structure. − In addition to the crystalline phase corresponding to the metal Ni, there are a large number of amorphous structures in the field of vision, as shown by the red circle. In contrast, it can be observed that the NiSP x catalytic electrode is composed entirely of amorphous components without the presence of crystalline nickel (Figure S2).…”

Recent Progress of Amorphous Nanomaterials

“…Most amorphous catalysts are unable to withstand a hot environment with high temperature. 348,481 Amorphous structures may also convert to crystals under illumination. During mechanical testing, amorphous materials have also been frequently reported to transform to crystal.…”