Abstract
Aluminum-based quasicrystals typically form across narrow composition ranges within binary to quaternary alloys, which makes their fabrication and characterization challenging. Here, we use combinatorial approaches together with fast characterization techniques to study a wide compositional range including known quasicrystal forming compositions. Specifically, we use magnetron co-sputtering to fabricate libraries of ~140 Al-Cu-Fe and ~300 Al-Cu-Fe-Cr alloys. The alloys compositions are measured through automated energy dispersive X-ray spectroscopy. Phase formation and thermal stability are investigated for different thermal processing conditions (as-sputtered and annealed at 400 °C, 520 °C and 600 °C for Al-Cu-Fe libraries; annealed at 600 °C for Al-Cu-Fe-Cr libraries) using automated X-ray diffraction and transmission electron microscopy. In both systems the compositional regions across which the quasicrystalline phase forms are identified. In particular, we demonstrate that the quasicrystalline phase forms across an unusually broad composition range in the Al-Cu-Fe-Cr system. Additionally, some of the considered alloys vitrify during sputtering, which also allows us to study their nucleation behavior. We find that phases with polytetrahedral symmetry, such as the icosahedral quasicrystal and the λ-Al13Fe4 phase, exhibit higher nucleation rates but lower growth rates, as compared to other phases with a lower degree of polytetrahedral order. Altogether, the here used combinatorial approach is powerful to identify compositional regions of quasicrystals.
Highlights
Since the discovery of quasicrystals (QCs) by D
This approach is challenging for multi-component alloys due to its slow rate of exploring new compositions: The potential QC composition space is large, but composition ranges for QC formation are rather narrow and phase transitions can often occur within variations of only 1 at.%
QC phases forming in the Al-Cu-Fe-Cr system have been previously reported[28,29,30,31,32,33,34,35], the complete range of QC formation is unknown to date and will be elucidated by the here presented results
Summary
Since the discovery of quasicrystals (QCs) by D. We use a combinatorial strategy to fabricate and characterize large composition ranges of the quasicrystal-forming systems, Al-Cu-Fe and Al-Cu-Fe-Cr. We use magnetron co-sputtering to fabricate compositional “alloy libraries” and we structurally evaluate such libraries in the as-sputtered state (far away from equilibrium) and in annealed states at different temperatures to approach equilibrium conditions. We use magnetron co-sputtering to fabricate compositional “alloy libraries” and we structurally evaluate such libraries in the as-sputtered state (far away from equilibrium) and in annealed states at different temperatures to approach equilibrium conditions Using this approach, the QC formation range can be identified, suggesting this method as an effective tool for discovering potential QC compositions in large compositional regions. Using the method proposed here we can observe nucleation and growth of complex phases from an amorphous phase, which is structurally similar to the liquid phase across a wide composition range, which contributes to advancing nucleation theory to include both, chemical and topological fluctuations
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