PRODUCTION OF QUASI-CRYSTALLINE AL-PD-MN ALLOYS WITH LARGE SINGLE DOMAIN SIZE

The equilibrium phase diagram in a pseudo-binary Al80-xPd20Mnx(x = 3 to 15 at%) system was examined with the aim of searching an alloy composition at which the icosahedral (I) phase precipitates directly from liquid as a primary Phase. The I-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 I-phase is concluded to be Al71.5Pd20.3Mn8.2. Subsequently, the preparation of the I-ingot 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 I-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 ingot reveal the five-, three- and two-fold symmetries.