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 Zr65Al7.5Cu17.5-xNi10Agx (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 (Vf) 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 (σf) of the bulk amorphous rod is 1650 MPa at Vf=0%, increases to 1900 MPa at Vf=45% and then decreases with further increasing Vf. The increase in σf 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.
(Received June 17, 1999; In Final Form October 4, 1999)
Keywords: bulk icosahedral base alloy, zirconium-based alloy, copper mold casting, nanoquasicrystalline particle, mechanical strength, short-range icosahedral configurationPDF (Free) [Editor's Announcement] Table of Contents