Al-Pd-Mn icosahedral quasicrystal prepared by floating zone melting technique

We tried to grow Al-Pd-Mn icosahedral quasicrystal (IQC) by floating zone melting technique. Molten block of Al_73.2Pd_19.3Mn_7.0 at around 1140 K was travelled through a bar of Al_69.4Pd_20.3Mn_10.3 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_69.6Pd_20.3Mn_10.1 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_69.8Pd_21.4Mn_8.8, and a small amount of decagonal quasicrystal (DQC) of Al_68.6Pd_13.3Mn_18.1 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 Fl type of Ishimasa and Mori (1992). Micro-Vickers hardness (H_V) was about 950 at 25 g, irrespective of annealed or as-solidified and of the presence or absence of DQC lamellae. H_V decreased with increasing load, as reported formerly. The fracture toughness (K_IC) of annealed sample with lamellae (2.1 MPam^1/2) was about 1.5 tunes as large as that of annealed one without lamellae (1.3 MPam^1/2) and as-solidified one with lamellae (1.4 MPam^1/2).