The coefficient of thermal expansion (α), Young's and rigid moduli (E and G), Poisson's ratio (ν), compressive yield and fracture strengths (σ y and σ f ), fracture toughness (K), Vickers hardness (H v ) and cleavage fracture mode were examined along two-, three- and five-fold symmetry axes for an Al 70 Pd 20 Mn 10 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. H v at room temperature (RT) increases from 700 to 800 in the order of three->five->two-fold axes. H v 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 σ f along the three-fold axis at RT are 200 GPa, 72 GPa, 0.38 and 520 MPa, respectively. K is 0.3 MPam 1/2 at RT and increases to 3 MPam 1/2 at 600 K. The fracture at RT occurs along the two-fold plane in a cleavage mode. The σ f 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 (0.98 T m ) presumably because of the sliding along the boundary between the approximant and the icosahedral phases.
ASJC Scopus subject areas