Atomic-Scale Structural Evolution and Stability of Supercooled Liquid of a Zr-Based Bulk Metallic Glass

In this Letter, direct experimental evidence is provided for understanding the thermal stability with respect to crystallization in the ${\mathrm{Zr}}_{41.2}{\mathrm{Ti}}_{13.8}{\mathrm{Cu}}_{12.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{22.5}$ glass-forming liquid. Through high-resolution transmission electron microscopy, the atomic-structure evolution in the glass-forming liquid during the isothermal annealing process is clearly revealed. In contrast with the existing theoretical models, our results reveal that, prior to nanocrystallization, there exists a metastable state prone to forming icosahedralike atomic clusters, which impede the subsequent crystallization and hence stabilize the supercooled liquid. The outcome of the current research underpins the topological origin for the excellent thermal stability displayed by the Zr-based bulk metallic glass.

Figure 1

The HRTEM images with the corresponding selected area diffraction patterns in the insets for the samples (a) in the as-prepared state and isothermally annealed at 646 K for (c) 1850 s, (d) 3600 s, and (e) 7200 s, respectively.

Figure 2

The typical icosahedralike atomic ordering in the ${\mathrm{Zr}}_{41.2}{\mathrm{Ti}}_{13.8}{\mathrm{Cu}}_{12.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{22.5}$ BMG after isothermally annealing at 646 K. (a–c) are the IFT-filtered images of the selected areas in Fig. 2 (a–c), respectively.

Figure 3

The typical localized atomic ordering observed during nanocrystallization of the ${\mathrm{Zr}}_{41.2}{\mathrm{Ti}}_{13.8}{\mathrm{Cu}}_{12.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{22.5}$ supercooled liquid at 646 K for 7200 s. (a–d) are the atomic configurations for an amorphous region with ordered clusters. The enclose areas in (a) show the icosahedralike clusters, and (b–c) and (d) the ordering clusters in the imperfect 1D and 2D type order packing, respectively. (e–h) are the corresponding FT diffraction patterns ($\mathrm{\text{scale bar}}=1\mathrm{nm}$). Note that the solid (white) and dashed (yellow) circles mark the positions of the atomic clusters close to the boundaries of and within the 1D or 2D type order packing regions, respectively.

Figure 4

The schematics of the potential energy profiles for the ${\mathrm{Zr}}_{41.2}{\mathrm{Ti}}_{13.8}{\mathrm{Cu}}_{12.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{22.5}$ supercooled liquid showing the effect of short-range ordering on subsequent crystallization.