Mechanical properties of bulk amorphous Zr-Al-Cu-Ni-Ag alloys containing nanoscale quasicrystalline particles

Nanoscale icosahedral quasicrystalline particles were found to precipitate at high volume fractions of nearly 100% as a metastable phase in the crystallization process of bulk amorphous Zr₆₅Al_7.5Cu_17.5-xNi₁₀Ag_x (x=5 and 10 at%) alloys. The icosahedral particles precipitate from the supercooled liquid and have a spherical morphology. The average particle size is in the range of 30 to 40 nm and tends to decrease with increasing Ag content. The maximum volume fraction (V_f) of the icosahedral phase is about 85% for the 5%Ag alloy and nearly 100% for the 10%Ag alloy. The mixed amorphous plus icosahedral phases change into an equilibrium structure of Zr₂Cu+Zr₂Ni+Zr₂Al₃ phases with a further increase in temperature. Tensile fracture strength (σ_f) of the bulk amorphous rod is 1650 MPa at V_f=0%, increases to 1900 MPa at V_f=45% and then decreases with further increasing V_f. The increase in σ_f is due to the suppression effect of the nanoscale icosahedral particles on the shear deformation of the amorphous matrix. The finding that the tensile strength of the bulk amorphous alloys is improved by the precipitation of high volume fraction of nanoscale icosahedral particles points to the future development of bulk nanoquasicrystalline amorphous alloys for applications.