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

Abstract

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 Zr 47 Cu 37 Al 8 Ag 8 BMG. Nano-crystals (NCs) are found precipitated during the anomalous expansion of Zr 47 Cu 37 Al 8 Ag 8 , but also in the SCLR of Zr 43 Cu 41 Al 8 Ag 8 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. IMPACT STATEMENT An anomalous expansion, and particularly a large expansion instead of softening, is reported occurring in the deep SCLR of a Zr-based bulk metallic glass for the first time.

Unveiling a new type of ultradense anomalous metallic glass with improved strength and ductility through a high-pressure heat treatment

“…Isothermal annealing of the as-cast sample at 740 K for 5,10,17,18,20,22, and 23 min and successive isochronal DSC scans were conducted to evaluate the thermal properties/structural differences between the heat-treated sample under ambient pressure and the high-pressure heat-treated samples by comparing the crystallization temperature (T x ) and crystallization enthalpy (ΔH cry ). The microstructures of the samples that were isothermally heat-treated at 740 K for 17, 20 and 23 min were examined using TEM.…”

“…Therefore, the total density of the high-pressure heat-treated sample should be higher than that of the partially crystallized sample. Although a few studies have been reported 21,22 , it has been infrequently observed that a fully amorphous sample is denser than the already crystallized sample. The electrical resistivity measurement of the partially crystallized sample was also conducted, as shown in Fig.…”