In this paper, we systematically report the preparation of carbon-nanotube (CNT)-reinforced Zr-based bulk metallic glass (BMG) composites. The physical and mechanical properties of the composites were investigated. Compressive testing shows that the composites still display high fracture strength. Investigation also shows that the composites have strong ultrasonic attenuation characteristics and excellent wave absorption ability. The strong wave absorption implies that CNT-reinforced Zr-based BMG composites, besides their excellent mechanical properties, may also have significant potential for applications in shielding acoustic sound or environmental noise.

A new Ca-based bulk glassy alloy with high tensile fracture strength above 2000 MPa was formed in a (Cuo-6Zro.Btio-I)9sY2 alloy by copper mold casting. The maximum sample thickness for glass formation is 4 mrn for Cu6oZrBoTilo and increases to 5 mm for the 2%Y-containing alloy. The addition of 2%Y also causes an increase in the supercooled liquid region (Tx=Tx-Tg) from 36 to 50 K and in the reduced glass transition temperature (Tg/T1) from 0_62 to 0.63. The increase in the glass-forming ability (GFA) is presumably due to the increase in Atx and Tg/T1. The bulk glassy (Cuo.6Zro.BTio.1)98Y2 alloy exhibits good mechanical properties, i.e., 1780MPa for yield strength, 2030 MPa for tensile fracture strength, 2100 MPa for compressive fracture strength, 1.7% for elastic elongation and 1.5% for plastic elongation. The distinct plastic elongation indicates good ductile nature of the Ca-based bulk glassy alloy. The success of synthesizing the new Ca-based bulk glassy alloy with high GFA and good mechanical properties allows us to expect the extension of application fields as a new engineering material. (Received May 29, 2001; Accepted August 1, 2001)

An icosahedral (I) quasicrystalline phase with a grain size below 40 nm was formed as a metastable phase in crystallization of the bulk glassy Zr65Al7.5Cu17.52xNi10Mx ~M5Ag, Pd, Au, or Pt; x55 nd 10 at %! alloys. The volume fraction (Vf) 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 Zr2Cu1Zr2Ni1Zr2Al3 in a fully annealed state. Compressive fracture strength (sc, f) and fracture elongation (e 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 sc, f is due to the suppression effect of the I particles against the shear deformation of the intergranular glassy phase, and the increase in e 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.

Bulk amorphous Zr7o-x-yTixAlyCu20Nilo alloys with a thickness of 2.5 mm were formed in a wide composition range of 0 to 10 at% Ti and 7.5 to 15 at% Al by a squeeze casting process. The bulk amorphous alloys containing 0 to 5%Ti and 12.5 to 15/oAI exhibit good combined properties of high tensiIe fracture strength above 1850 MPa, high specific strength of 28..4 x 105 Nm/kg and high Tg/Tm above 0.60 which have not been obtained for the Zr-based alliorphous alloys reported hitherto. These bulk amorphous alloys have small difference in density of 0.3 to 0.6% between ascast amorphous and crystallized states. The high dense random packing fraction in the multicomponent amorphous structure seems to cause the high glass-for~iiing ability and the high thermal stability of the supercooled liquid region by the decrease in atomic mobility. Furthermore, the crystallized phases change from NiZr2+CuZr+Zr3Al in the range of 5 to 15%A1 and 0 to 2.5%Ti to NiZr I CuZr2 I Zr3A1 in the range of 5 to 15%A1 and 2.5 to 7.5%Ti. The melting temperatures (Tm) of these crystallized compounds increase in the order of ZrNi>ZrENi>ZrECU>ZrCu and hence the crystallized structure of the 5% Ti-containing alloys is composed of ZrNi and Zr2Cu with higher Tm-The change in the auLorphous structure leading to the precipitation of the compounds with higher Tm may be the reason for the higher iLechanical strength in the higher A1 and Zi contents.