Abstract
The coefficient of thermal expansion (α), Young’s and rigid moduli (E and G), Poisson’s ratio (ν), compressive yield and fracture strengths (σy and σf), fracture toughness (K), Vickers hardness (Hv) and cleavage fracture mode were examined along two-, three- and five-fold symmetry axes for an Al70Pd20Mn10 single-quasicrystal prepared by the Czochralski method. In the temperature range below 600 K, α is 1.3×10−5 K−1 which is about 50% as high as that for conventional Al-based alloys. Hv at room temperature (RT) increases from 700 to 800 in the order of three- > five- > two-fold axes. Hv decreases gradually with increasing temperature and rapidly in the range above 600 K corresponding to a half of the melting temperature. E, G, ν and σf along the three-fold axis at RT are 200 GPa, 72 GPa, 0.38 and 520 MPa, respectively. K is 0.3 MPam1⁄2 at RT and increases to 3 MPam1⁄2 at 600 K. The fracture at RT occurs along the two-fold plane in a cleavage mode. The σf value increases gradually to 570 MPa in the range below 973 K and significantly to 630 MPa at 1023 K accompanying the appearance of significant plastic elongation. The distinct plastic deformation is presumably due to the high deformability of the phason-induced periodic approximants with an Al-rich composition which were preferentially formed along the five-fold planes. Furthermore, the superplasticity was also found to occur at 1123 K (0.98Tm) presumably because of the sliding along the boundary between the approximant and the icosahedral phases.
