The Al-Cu-Fe phase diagram: 0 to 25 At. pct Fe and 50
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I.
INTRODUCTION
RECENTLY, a stable icosahedral phase, q/-A16Cu2Fe, with remarkable structural perfection was discovered in the AI-Cu-Fe system, l~] The class of phases A16Cu2X, where X = Fe, Ru, or Os, has much narrower diffraction peaks than previously reported icosahedral phases: t2j with appropriate annealing, phason strain, indicative of structural disorder, appears to be zero. tzl Furthermore, the diffraction patterns can be indexed to a body-centered icosahedral reciprocal lattice, t4] The six-dimensional (6-D) lattice is thus face-centered cubic, whereas other known icosahedral phases have a primitive 6-D hypercube lattice. Despite widespread interest in this new class of quasicrystal, the AI-Cu-Fe phase diagram in the region of the icosahedral phase has not been well defined. The present work constitutes a determination of the equilibrium phase diagram in this region. The region of study encompasses 50 to 75 at. pct A1 and 0 to 25 at. pct Fe at temperatures between 680 ~ and 800 ~ The objectives were to establish tie lines between the icosahedral phase and all other stable phases and to determine composition ranges for the relevant phases. II. PREVIOUS STUDIES OF THE PHASE DIAGRAM
The first comprehensive study of the AI-Cu-Fe system was published by Bradley and Goldschmidt in 1939;151 these investigators discovered several ternary phases, including the icosahedral phase, but did not establish the structures in any detail. They reported a subsolidus projection in the region of the icosahedral phase using X-ray diffraction techniques. Their samples were prepared by isothermal annealing at various temperatures from 550 ~ to 1000 ~ followed by cooling to room temperature at 10 ~ Relevant binary and ternary phases F R A N K W. GAYLE, A L E X A N D E R J. SHAPIRO, FRANCIS S. BIANCANIELLO, and W I L L I A M J. BOETTINGER, Metallurgists, are with the Metallurgy Division, National Institute of Standards and Technology, Gaithersburg, M D 20899. Manuscript submitted March 19, 1991. METALLURGICAL TRANSACTIONS A
identified by Bradley and Goldschmidt are included in Table I, and their phase designations as given in Table I have been adopted for the present study. Prevarskiy [6] examined 600 ~ and 800 ~ isothermal sections of the ternary system and confirmed the existence of the ternary compounds ~, to-Al7Cu2Fe, and ~b-Al~0CUloFe (but not x-AI~aCu~0Fe). The composition ranges for the temary phases varied somewhat from those of Bradley and Goldschmidt. Details of other regions of the A1-Cu-Fe system have also been reported. Extensive studies have been made of the A1-A13Fe-A12Cu subsystem tS-'] including liquidus projections and isothermal and isoplethal sections. Several reviews have also been given, t~2'~3,14JSimilar studies have been conducted in the 0 to 50 at. pct A1 range, t~5'j6j III.
EXPERIMENTAL PROCEDURE
Sixteen alloy compositions (Figure 1) were prepared by arc-melting mixtures of AI, Cu, and Fe (->99.99 pct purity) and then solidifying on a water-chilled copper hearth. Arc-melted specimens often exhibited
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