Spark plasma sintering of Al-Si-Cu-Fe quasi-crystalline powder
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INTRODUCTION
QUASICRYSTALS are well ordered but nonperiodic structures that can have any of the rotational symmetry axes classically prohibited in crystals (e.g., five-, eight-, ten-, and twelvefold rotation axes).[1] Discovered 20 years ago,[2] quasi-crystalline materials have already found commercial applications such as coatings for cookware and reinforcement in high-strength maraging steel.[3,4] A number of potential applications are under current study, and quasicrystals appeared to be attractive as functional materials in applications requiring specific physical and mechanical properties such as low surface energy, low thermal conduction, high hardness, low friction, and good oxidation resistance.[5,6] Hence, quasicrystals are potential candidates to replace ceramics, which are currently used in thermal protection systems and engine components at temperatures lower than 800 °C, because they also have a coefficient of thermal expansion similar to most structural alloys and have excellent tribological properties.[7,8,9] The structure of quasicrystals can be generated by a threedimensional cut of a six-dimensional periodic object. In a one-dimensional structure, quasicrystals are characterized by an irrational slope, the value of which is the golden mean,
E. FLEURY, Senior Researcher, and D.H. KIM, Professor, Department of Metallurgical Engineering, are with the Center for Non-Crystalline Materials, Yonsei University, Seoul, Korea. Contact e-mail: Fleury@mail. yonsei.ac.kr J.H. LEE, Principal Researcher, is with the Department of Orthopedic Surgery, ASAN Medical Center, Seoul, Korea. S.H. KIM, Associate Professor, is with Kumoh National University of Technology, Kumi, Korea. W.T. KIM, Professor, is with the Department of Physics, Chongju University, Chongju, Korea. J.S. KIM, Professor, is with the Department of Materials Science and Engineering, Ulsan University, Ulsan, Korea. Manuscript submitted February 13, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS A
t (t ⫽ (1 + 15)/2 ⫽ 1.618 . . .). Soon after the announcement of the first quasicrystals, it was found that the icosahedral and decagonal phases (three-dimensional and twodimensional quasicrystals, respectively), have closely related periodic phases called rational approximant structures.[10] According to the cut-and-projection method, approximants are classified by the ratio p/q, where p and q are integers, such as 1/1, 2/1, 3/2, 5/3, 8/5, etc. The closer the ratio is to the golden mean, the higher the degree of relation with quasicrystals. These approximant phases can reproduce the symmetries of quasicrystals, and though periodic, they are believed to have a locally similar atomic structure and properties.[1] Consequently, approximants have recently received much attention, and they are expected to provide useful information about the atomic arrangement of quasicrystals and to give insights about the relationships between structure and property. Since reported by Tsai et al.,[11] the stable icosahedral structure formed in the Al-Cu-Fe alloy system has bee
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