Ti-Zr-Ni-Cu-B metallic glass as a precursor for superelastic alloy after crystallization

In this study, 0.25, 0.5, and 1 at% boron is added to increase glass forming ability and thermal stability of Ti₃₅Zr₁₅Ni₄₀Cu₁₀ metallic glass, exhibiting outstanding superelasticity after crystallization. In order to confirm the improvement of thermal stability in supercooled liquid region, crystallization behavior and activation energy were investigated according to the amount of boron added. When more than 0.5 at% boron is added, a stable supercooled liquid is maintained, showing high values in glass forming ability parameters (ΔT_x (>50 K), T_rg (>0.539), γ (>0.373), ΔH^chem (<−33.8 kJ/mol), and [Formula-presented] (>0.2709)). On the other hand, boron has a significant effect on grain refinement in Ti₃₅Zr₁₅Ni₄₀Cu₁₀ alloy. As a result, the average grain size when fully crystallized decreases from ~250 ㎚ in Ti₃₅Zr₁₅Ni₄₀Cu₁₀ to ~70 ㎚ in (Ti₃₅Zr₁₅Ni₄₀Cu₁₀)₉₉B₁. At room temperature, the crystallized ribbon samples show superelasticity, verifying the possibility of utilizing metallic glass as a precursor. (Ti₃₅Zr₁₅Ni₄₀Cu₁₀)_99.5B_0.5 alloy shows the best superelasticity with remnant depth ratio of 8.0%. In addition, superelastic temperature range becomes wider from 59 K to 310 K with increasing boron content up to 0.5 at% but decreases afterward. Therefore, (Ti₃₅Zr₁₅Ni₄₀Cu₁₀)_99.5B_0.5 alloy exhibits an outstanding superelastic property among the alloys investigated in the present study.