Anomalous thermal expansion in the deep super-cooled liquid region of a ZrCuAlAg bulk metallic glass

Bulk metallic glasses (BMGs), like other glasses, soften in the super-cooled liquid region (SCLR). Here in this work, surprisingly, a large expansion is reported occurring in the deep SCLR of a Zr47Cu37Al8Ag8 BMG. Nano-crystals (NCs) are found precipitated during the anomalous expansion of Zr47Cu37Al8Ag8, but also in the SCLR of Zr43Cu41Al8Ag8 that exhibits a conventional softening. It is found that there is a steep composition and density change at the NCs/amorphous matrix transition region in the former alloy, and this transition region exerts a thermal stress of about 0.15 MPa to the surrounding super-cooled liquid (SCL) and drives the soft SCL to expand severely.