The equilibrium phase diagram in a pseudo-binary Al 8d-1 Pd 20 Mn 1 (x=3 to 15 at%) system was examined with the aim of searching an alloy composition at which the icosahedral (l) phase precipitates directly from liquid as a primary phase. The l-phase precipitated as the primary phase in the range of 3 to 9%Mn and as the second phase through the peritectic reaction in the range of 9 to 15%Mn. From further detailed examinations of Pd and Mn contents, an optimum composition to obtain the primary l-phase is concluded to be Al 71.3 Pd 20.3 Mn 8.2 . Subsequently, the preparation of the I-ingor with a large single domain size was tried at the optimum composition in various melting conditions. As a result, the inoculation and drawing-up treatment with a polycrystalline BN needle in an arc melting with a hemishere copper mold was found to be effective in controlling the nucleation and growth of the l-phase and the largest domain size reached as large as 8 mm. The formation of the large single domain was also confirmed from the evidence that the X-ray Laue patterns taken from the inoculated ingor reveal the five-, three-, and two-fold symmetries.
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