Improvement of the thermoplastic formability of Zr65Cu17.5Ni10Al7.5 bulk metallic glass by minor addition of Erbium

The softness of Zr65Cu17.5Ni10Al7.5 bulk metallic glass (BMG) in the super-cooled liquid range (SCLR) is obviously improved by minor addition of 2% Er, which makes (Zr65Cu17.5Ni10Al7.5)98Er2 (Zr65Er2) to be a very formable Be-free Zr-based BMG. It is found the lower glass transition temperature of Zr65Er2 has an important contribution to the improvement of formability, which is contrary to the general understanding that the larger fragility and wider super-cooled liquid region (SCLR) are the major reasons for better thermoplastic formability. This finding is well explained by using the linear simplification of the SCLR in Angell plot. Zr65Er2 also has lower crystallization temperature and melting temperature, which is believed to be related to the formation of short-range ordering with lower transition energy rather than the composition shift to near eutectic. The above results help understand the effect of minor addition of rare-earth to the formability of Zr-based bulk metallic glasses.