Ductile quasicrystalline alloys

Abstract

An icosahedral (I) quasicrystalline phase with a grain size below 40 nm was formed as a metastable phase in crystallization of the bulk glassy ${\mathrm{Zr}}_{\mathrm{65}}{\mathrm{Al}}_{\mathrm{7.5}}{\mathrm{Cu}}_{\text{17.5−x}}{\mathrm{Ni}}_{\mathrm{10}}{\mathrm{M}}_x$ (M=Ag, Pd, Au, or Pt; $\text{x=5}$ and 10 at %) alloys. The volume fraction ${\mathrm{(V}}_f)$ of the I phase is about 85% for the 5% M alloy and nearly 100% for the 10% M alloy. The I phase changes to ${\mathrm{Zr}}_{\mathrm{2}}{\mathrm{Cu+Zr}}_{\mathrm{2}}{\mathrm{Ni+Zr}}_{\mathrm{2}}{\mathrm{Al}}_{\mathrm{3}}$ in a fully annealed state. Compressive fracture strength ${\mathrm{(\sigma }}_{\mathrm{c,f}})$ and fracture elongation ${\mathrm{(\epsilon }}_{\mathrm{c,f}})$ of the 10% Pd cylinder with a diameter of 2 mm are respectively 1640 MPa and 2.2% for the glassy phase and increase to 1830 MPa and 3.1% for the I phase. The increase in ${\sigma }_{\mathrm{c,f}}$ is due to the suppression effect of the I particles against the shear deformation of the intergranular glassy phase, and the increase in ${\epsilon }_{\mathrm{c,f}}$ results from the localization effect of deformation into the glassy layer. The precipitation of the I phase implies that the glassy alloys include randomly oriented I configurations. The present work shows promise for the new class of high-strength nanoquasicrystalline materials.