Al-Pd-Mn Icosahedral Quasicrystal Prepared by Floating Zone Melting Technique
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We tried to grow Al–Pd–Mn icosahedral quasicrystal (IQC) by floating zone melting technique. Molten block of Al<SUB>73.2</SUB>Pd<SUB>19.8</SUB>Mn<SUB>7.0</SUB> at around 1140 K was travelled through a bar of Al<SUB>69.4</SUB>Pd<SUB>20.3</SUB>Mn<SUB>10.3</SUB> at the rate of 1.1 to 14 μm/s. The sample obtained (about 1 cm in diameter and about 6 cm in length) was cut in several slices and some of them were annealed at 1073 K for 20 hr in evacuated state. The bulk composition of the sample was Al<SUB>69.6</SUB>Pd<SUB>20.3</SUB>Mn<SUB>10.1</SUB> and almost unchanged along the growth direction. The largest grain was about 5 mm in diameter and several tens of mm along the growth direction. The sample was made mainly of IQC of Al<SUB>69.8</SUB>Pd<SUB>21.4</SUB>Mn<SUB>8.8</SUB>, and a small amount of decagonal quasicrystal (DQC) of Al<SUB>68.6</SUB>Pd<SUB>13.3</SUB>Mn<SUB>18.1</SUB> was seen as fine exsolution lamellae and grain boundary phase. The electron diffraction pattern taken along the two-fold symmetry axis showed that our IQC is F1 type of Ishimasa and Mori (1992). Micro-Vickers hardness (<I>H<SUB>V</SUB></I>) was about 950 at 25 g, irrespective of annealed or as-solidified and of the presence or absence of DQC lamellae. <I>H<SUB>V</SUB></I> decreased with increasing load, as reported formerly. The fracture toughness (<I>K<SUB>IC</SUB></I>) of annealed sample with lamellae (2.1 MPam<SUP>1⁄2</SUP>) was about 1.5 times as large as that of annealed one without lamellae (1.3 MPam<SUP>1⁄2</SUP>) and as-solidified one with lamellae (1.4 MPam<SUP>1⁄2</SUP>).
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MATERIALS TRANSACTIONS 37(3), 448-453, 1996-03
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