Thermostability and thermoplastic formability of (Zr65Cu17.5Ni10Al7.5)100−xREx (x = 0.25–3.25, RE: Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) bulk metallic glasses

• 9 Rare-earth elements are added into Zr65Cu17.5Ni10Al7.5 BMG.
• Thermostability and softness in super-cooled liquid region are investigated.
• The best addition amount is determined by mixing enthalpy.
• The shear modulus of the RE elements has great influence on the softness.
• (Zr65Cu17.5Ni10Al7.5)98Er2 has the largest softness and thus the best formability.

The width ΔT of super-cooled liquid region (SCLR) and the softness (ΔL/L0)s of (Zr65Cu17.5Ni10Al7.5)100−xREx (x = 0.25–3.25, rare-earth RE: Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) bulk metallic glasses (BMGs) in SCLR are systemically investigated by thermoanalysis tests, where ΔT and (ΔL/L0)s are used to evaluate their thermostability and thermoplastic formability in SCLR, respectively. It is found that only a small amount of Yb can be added into the matrix alloy, and the addition of each RE increases ΔT. With the addition of the same RE, (ΔL/L0)s depends on ΔT, but with the addition of different RE elements, (ΔL/L0)s and ΔT have not a clear correlation and the best addition amount is different. These phenomena and regularities are well explained based on the properties of RE elements, including boiling point, mixing enthalpy, oxides formation enthalpy and shear modulus. The improvement in the formability of (Zr65Cu17.5Ni10Al7.5)98.00Er2.00, which has the largest (ΔL/L0)s, is also verified by thermoplastic forming experiment. This composition has the best formability in the Be-free Zr-based BMGs. The researches provide a basis for development of new BMGs with better thermostability and thermoplastic formability via minor addition of RE elements.