Thermal stability and mechanical properties of bulk glassy Cu-Zr-Ti-(Nb, Ta) alloys

Bulk glassy Cu-Zr-Ti base alloys containing a small amount of Nb or Ta were found to exhibit high strength combined with significant plastic elongation. The glass transition temperature (T_g), crystallization temperature (T_x) and ΔT_x(= T_x - T_g) of the Cu-based bulk glassy alloys are in the range of 719 to 731 K, 765 to 769 K and 46 to 44 K, respectively, for the Nb-containing alloy and 716 to 741 K, 752 to 780 K and 44 to 34 K, respectively, for the Ta-containing alloy. With increasing Nb or Ta content to 3 at% for the (Cu_0.6Zr_0.3Ti_0.1)_100-xM_x alloys, the Young's modulus, yield strength and compressive fracture strength increase from 114 to 121 GPa, 1785 to 2010 MPa and 2150 to 2250 MPa, respectively, and the plastic elongation shows a maximum of 1.8% at l%Nb and 3.4% at 1%Ta. The 1%Ta alloy exhibited good combination of high fracture strength of 2250 MPa and large total elongation of 5.4%. The effectiveness of additional Nb or Ta on the increase in elongation and fracture strength is presumably due to the mixed state of atomic pairs with attractive and repulsive bonding natures among the constituent elements with significantly different atomic size mismatches. The success of forming the bulk glassy alloys with high strength and significant elongation is encouraging for future applications as high-strength type materials.