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

Abstract 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 (ΔTx (>50 K), Trg (>0.539), γ (>0.373), ΔHchem ( S σ k B (>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)99.5B0.5 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)99.5B0.5 alloy exhibits an outstanding superelastic property among the alloys investigated in the present study.