Conventional Bulk Metallic Glasses Research Articles

Identifying the high entropy effect on plastic dynamics in bulk metallic glasses: A nanoindentation study at room and elevated temperatures

In this study, the spatiotemporal dynamic analyses of intermittent plastic flow in the nanoindentation of different Bulk metallic glasses (BMGs), at various temperatures, were carefully performed to provide insight into the amorphous structural-property relationship. Based on the displacement-time series and largest Lyapunov exponent during serrated flow, two distinct types of dynamic behaviors were identified at room temperature, i.e., the serrated flow dynamics transforms form a self-organized critical state in traditional BMGs to a more chaotic state in high entropy BMGs (HE-BMGs). This may originate from their local structural difference that the solvent-solute architecture in conventional BMGs is broken in HE-BMGs. Furthermore, sluggish diffusion in HE-BMG can effectively retard relaxation kinetics, which leads to the deviation of HE-BMGs from the conventional BMGs in terms of the relationship between the chaotic behavior and temperature. Indeed, the insignificant change in dynamic complexity of HE-BMG conforms to its increased structural stability at elevated temperatures, which was soundly elucidated from both topological and kinetic factors. This study is of significance in understanding the configuration complexity and structure stability in HE-BMGs and helpful for designing BMGs with promising properties against external mechanical and thermal agitations.

High thermal stability and sluggish crystallization kinetics of high-entropy bulk metallic glasses

Metallic glasses are metastable and their thermal stability is critical for practical applications, particularly at elevated temperatures. The conventional bulk metallic glasses (BMGs), though exhibiting high glass-forming ability (GFA), crystallize quickly when being heated to a temperature higher than their glass transition temperature. This problem may potentially be alleviated due to the recent developments of high-entropy (or multi-principle-element) bulk metallic glasses (HE-BMGs). In this work, we demonstrate that typical HE-BMGs, i.e., ZrTiHfCuNiBe and ZrTiCuNiBe, have higher kinetic stability, as compared with the benchmark glass Vitreoy1 (Zr41.2Ti13.8Cu12.5Ni10Be22.5) with a similar chemical composition. The measured activation energy for glass transition and crystallization of the HE-BMGs is nearly twice that of Vitreloy 1. Moreover, the sluggish crystallization region ΔTpl-pf, defined as the temperature span between the last exothermic crystallization peak temperature Tpl and the first crystallization exothermic peak temperature Tpf, of all the HE-BMGs is much wider than that of Vitreloy 1. In addition, high-resolution transmission electron microscopy characterization of the crystallized products at different temperatures and the continuous heating transformation diagram which is proposed to estimate the lifetime at any temperature below the melting point further confirm high thermal stability of the HE-BMGs. Surprisingly, all the HE-BMGs show a small fragility value, which contradicts with their low GFA, suggesting that the underlying diffusion mechanism in the liquid and the solid of HE-BMGs is different.

High mixing entropy bulk metallic glasses

Bulk metallic glasses (BMGs) are usually based on a single principal element such as Zr, Cu, Mg and Fe. In this work, we report the formation of a series of high mixing entropy BMGs based on multiple major elements, which have unique characteristics of excellent glass-forming ability and mechanical properties compared with conventional BMGs. The high mixing entropy BMGs based on multiple major elements might be of significance in scientific studies, potential applications, and providing a novel approach in search for new metallic glass-forming systems.

On calorimetric study of the fragility in bulk metallic glasses with low glass transition temperature: (Ce0.72Cu0.28)90−x Al10Fex (x = 0, 5 or 10) and Zn38Mg12Ca32Yb18

Compared with conventional bulk metallic glasses, Ce-based and Zn-based bulk metallic glasses have received considerable attention because of their possible application as structural and functional materials. Kinetic fragility parameter m in amorphous material presents degree of deviations from the Arrhenius law above the glass transition temperature (Tg) of the material. Kinetic fragility parameter (m) and Kauzmann temperature (TK) in (Ce0.72Cu0.28)90−x Al10Fex (x = 0, 5 or 10) and Zn38Mg12Ca32Yb18 bulk metallic glasses have been determined by differential scanning calorimetry (DSC). Results show that Zn38Mg12Ca32Yb18 presents a higher m than (Ce0.72Cu0.28)90−x Al10Fex (x = 0, 5 or 10). The activation energies Eg for glass transition are 1.51 eV (x = 0), 1.59 eV (x = 5) and 1.83 eV (x = 10) in (Ce0.72Cu0.28)90−x Al10Fex (x = 0, 5 or 10), and 3.59 eV in Zn38Mg12Ca32Yb18, respectively. The values of Eg increase with increasing the Fe content in (Ce0.72Cu0.28)90−x Al10Fex (x = 0, 5 or 10) bulk metallic glasses. Kinetic fragility parameter m of bulk metallic glasses increases with the glass transition temperature Tg of bulk metallic glasses, in agreement with previous investigations.

Unconventional elastic properties, deformation behavior and fracture characteristics of newly developed rare earth bulk metallic glasses

Significant differences in the thermal, elastic and mechanical behavior of bulk metallic glasses (BMGs) based on rare earth (RE) elements (i.e., Pr-based, Ce-based and Nd-based) have been found when comparing them with archetypical Zr-based and Ti-based amorphous metallic alloys. Our results show that RE-BMG exhibits a large supercooled liquid region, low elastic constants and concomitant elastic softening, low hardness, complete lack of macroscopic plasticity and compressive fracture angles, ψ C,F, larger than 45° (as opposed to polycrystalline materials, where ψ C,F = 45°, and conventional BMGs, where ψ C,F ≤ 45°). Most of these features stem from the rather low glass transition temperature displayed by these alloys, which is relatively close to room temperature. However, contrary to some previous studies, our observations reveal that the lack of plasticity of these materials cannot be simply rationalized in terms of their Poisson’s ratio but is also due to some tensile features (i.e., dilatational effects) accompanying compressive fracture behavior.