Excellent Mechanical Properties of Cu-Hf-Ti-Ta Bulk Glassy Alloys Containing In-Situ Dendrite Ta-based BCC Phase

抄録

A glassy phase containing high volume fractions (V_f) of bcc Ta-based phase was formed in as-cast (Cu_0.6Hf_0.25Ti_0.15)₉₄Ta₆ alloy rods with diameters up to 2 mm. Its V_f 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 V_f. 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 (σ_y), true compressive fracture strength (σ_t,f) and true plastic strain (ε_p) were 104 GPa, 2125 MPa, 2100 MPa and 0.34, respectively, for the φ2 mm rod with 11% V_f. The σ_y and σ_t,f are higher than those (2010 MPa and 2005 MPa) for the Cu₆₀Hf₂₅Ti₁₅ glassy alloy rod with a diameter of 2 mm. Especially, the ε_p for the (Cu_0.6Hf_0.25Ti_0.15)₉₄Ta₆ mixed structure alloy is dramatically enhanced in comparison with that (ε_p = 0.016) for Cu₆₀Hf₂₅Ti₁₅ single phase alloy. The enhancement of σ_y, σ_t,f and ε_p 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.