Quasicrystals, which differ from ordinary crystals, have long-range order, but their structures are not periodic and have no translational symmetry. Their rotational symmetries are determined by the aperiodic arrangement of atoms in two or three dimensions, with symmetries forbidden in ordinary crystals. Among metallic quasicrystals, icosahedral (IQC) and decagonal (DQC) forms are distinguished. DQCs are often found in aluminum-based alloys and are characterized by quasiperiodicity in two dimensions and periodicity in the third.
Their structure is described using decagonal columnar clusters and Gummelt and Lucas arrays. The metastability of nonequivalent atomic configurations in sublattices with irrational segmentation, especially in aluminum alloys, is a problem of DQC systems, limiting their application. In this study, a rational approximating structure is proposed that mimics the atomic arrangement in DQC, but is part of the Bravais lattice with a periodic structure and translational symmetry that are absent in quasicrystals, potentially providing increased stability and opening new possibilities for the transition from quasicrystalline to crystalline materials.
Quasicrystals, which are more common in binary and ternary systems, are less frequently observed in more complex systems with four or five elements. In this study, a rational approximating structure based on a three-element system is presented, expanding the known rational quasi-crystalline approximations and offering advantages in improving material properties. The preparation of complex quasi-crystalline structures by traditional methods is difficult due to differences in melting temperatures and chemical properties, which affects their practical applications and scalability. Quasicrystals are known for their high hardness, wear resistance, low thermal and electrical conductivity, high mechanical strength, optical properties, and hydrogen storage capacity. Rational approximating structures, with their more stable sublattice arrangement, can be a promising alternative for mass production. The use of laser powder bed fusion (LPBF), an additive manufacturing (AM) technology, provides a rapid and reproducible solution for creating materials with quasi-crystalline structure.
The paper presents a study of the possibility of forming a decagonal quasicrystalline structure approximated by a rational crystal in an aluminum alloy using additive manufacturing. Thermodynamic and kinetic conditions that facilitate the formation of this phase during a controlled crystallization process are considered.
Decagonal quasicrystals with unique physical and mechanical properties are of considerable interest for materials science. Additive manufacturing opens up new possibilities for creating complex alloys and structures with controlled phase composition. The aim of this work is to study the possibility of synthesizing a decagonal phase in the Al–Ni–Cu–Fe–Mn–Cr system implanted in an aluminum matrix using selective laser melting (SLM).
The starting material was aluminum alloy powder with the addition of Ni, Cu, Fe, Mn and Cr. SLM parameters such as laser power, scanning speed and layer thickness were varied to optimize the crystallization process and achieve the desired phase composition. The structural analysis of the obtained samples was carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM).
XRD analysis showed the presence of peaks corresponding to the decagonal phase, as well as other intermetallic compounds. Microstructural analysis revealed the formation of regions with different phase compositions, depending on the SLM parameters. A tendency for the decagonal phase to form in regions with increased cooling rates was detected.
Additive manufacturing is a promising method for creating complex-alloyed aluminum alloys with the formation of a decagonal quasicrystalline structure approximated by a rational crystal. Optimization of SLM parameters and alloy composition will allow controlling the phase composition and improving the properties of the obtained materials. Further research is aimed at studying the effect of heat treatment on the stability and properties of the decagonal phase.
Author: Kai-Chieh Chang, Fei-Yi Hung, Jun-Ren Zhao
Institute: Department of Materials Science and Engineering, National Cheng Kung University, Tainan, 701, Taiwan