2004 Volume 45 Issue 9 Pages 2936-2940
A glassy phase containing high volume fractions (Vf) of bcc Ta-based phase was formed in as-cast (Cu0.6Hf0.25Ti0.15)94Ta6 alloy rods with diameters up to 2 mm. Its Vf increased from 9.5 to 11% with increasing rod diameter from 1 to 2 mm. The in-situ bcc phase has a dendritic morphology with a size of about 10 μm and its size tends to increase with increasing Vf. The bcc phase has analytical compositions of 1.4 at% Cu, 7.6 at% Ti and 91.0 at% Ta. The lattice parameter of the bcc phase is 3.306 nm which approximates to that of Ta metal. The thermal stability of the remaining glassy matrix remains unchanged in coexistence with the bcc phase. The mixed structure is presumed to be formed by the primary precipitation of ductile dendritic bcc phase, followed by the solidification of the remaining liquid to glassy phase. The Young's modulus (E), yield strength (σy), true compressive fracture strength (σt,f) and true plastic strain (εp) were 104 GPa, 2125 MPa, 2100 MPa and 0.34, respectively, for the φ2 mm rod with 11% Vf. The σy and σt,f are higher than those (2010 MPa and 2005 MPa) for the Cu60Hf25Ti15 glassy alloy rod with a diameter of 2 mm. Especially, the εp for the (Cu0.6Hf0.25Ti0.15)94Ta6 mixed structure alloy is dramatically enhanced in comparison with that (εp = 0.016) for Cu60Hf25Ti15 single phase alloy. The enhancement of σy, σt,f and εp in the mixed structure of glassy and bcc phase for the new Cu-based system is promising for future uses as a new type of high-strength bulk glassy alloy.