The effect of Ta addition on the glass forming ability and mechanical properties of Ni-Zr-Nb-Al metallic glass alloys

The effect of Ta substitution for Zr in the Ni-Zr-Nb-Al metallic glass alloys has investigated by using thermal analysis, X-ray diffractometry and transmission electron microscopy. Small additions of Ta improve the glass forming ability (GFA) of the alloys Ni₆₁Zr_28-xNb₇Al₄Ta _x (x = 0, 2, 4, 6, 8). The glass transition and crystallization temperatures increase with increasing Ta content up to 8 at.%. The liquidus temperature also increases, but less rapidly, resulting in the increase of T_rg and γ values compared with the quaternary Ni-Zr-Nb-Al alloy. Fully glassy rods with the diameter of up to 2 mm can be fabricated by a copper mold casting method. The addition of Ta remarkably improves the plasticity under compression. The compressive strength and macroscopic plastic strain of the bulk metallic glass Ni₆₁Zr₂₄Nb₇Al₄Ta₆ alloy are 3080 MPa and 5%, respectively. The enhanced plasticity can be ascribed to local chemical inhomogeneity resulting from the existence of atom pair with positive enthalpy of mixing in the liquid state.