Compositional analysis of the icosahedral phase in rapidly quenched Al-Mn and Al-V alloys
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INTRODUCTION
QUASICRYSTALS with icosahedral point-group symmetry and long-range orientational order have recently been found to form in rapidly quenched A1-X (X = Mn, Cr, Fe, V, Pd, Pt, or Ru) 1-6 binary and AI-Mn-X (X = Fe or Si) 7 ternary alloys. Furthermore, it has been proposed 8-H that the new class of crystals can be interpreted as having a nonperiodic structure which retains simple point-group symmetries with long-range correlations. In the subsequent investigations, the formation and stability of the threedimensional icosahedral quasicrystal have been reported to be understood from a simple Landau theory of two- or three-component systems. 12'~3 Additionally, theories for elasticity and dislocation defect in the icosahedral quasicrystals have been presented. 14The present authors 3'~5have also demonstrated for the first time with high-resolution transmission electron micrographs that the melt-quenched A185.7Mn143 (at. pct) alloy was composed of a threedimensional aggregation of icosahedra over a long-range scale. In addition, the electrical 16and magnetic ~7properties and the thermal stability 16'18'~9including the decomposition temperature from the icosahedral to stable phase and the activation energy for the decomposition reaction have been determined. However, little experimental evidence has been provided on the solute concentration of the icosahedral quasicrystals in rapidly quenched AI-X alloys. The question of whether the nonequilibrium phase is a quasicrystal with a fixed stoichiometry or with widely varied solute concentrations is still unsolved. The solution of this problem is expected to give a fundamental knowledge for the construction of the structural model for the icosahedral quasicrystal including the atomic configuration of the constituent elements. This work was undertaken in an effort to obtain the solute concentration of the icosahedral phase in rapidly quenched A1-Mn and A1-V alloys by analytical scanning transmission and A. INOUE, Associate Professor, and 1". MASUMOTO, Professor, are with The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai 980, Japan. L. ARNBERG and B. LEHTINEN are Members, Research Staff, Swedish Institute for Metals Research, Drottning Kristinas vag 48, S-114 28 Stockholm, Sweden. M. OGUCHI is Member, Research Staff, Teikoku Pistonring Ltd., Okaya 394, Japan. Manuscript submitted October 16, 1985. METALLURGICALTRANSACTIONS A
conventional transmission electron microscopy (ASTEM and TEM) and X-ray diffractometry. Since the icosahedral phase reported to this date has always coexisted with other phases, the use of ASTEM or ATEM is, among the possible analytical techniques, particularly suited for pursuing the present research object. The A1-Mn and AI-V systems were chosen since in the systems where icosahedral quasicrystals have been found, 1-6 the solid solubility extension of solute elements into aluminum by rapid solidification is greatest (-~9 at. pct Mn) for A1-Mn and least (22 at. pct V) for A1-Vfl° II.
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