Size-dependent vitrification in metallic glasses.

Reducing the sample size can profoundly impact properties of bulk metallic glasses. Here, we systematically reduce the length scale of Au and Pt-based metallic glasses and study their vitrification behavior and atomic mobility. For this purpose, we exploit fast scanning calorimetry (FSC) allowing to study glassy dynamics in an exceptionally wide range of cooling rates and frequencies.

Model Metallic Glasses for Superior Electrocatalytic Performance in a Hydrogen Oxidation Reaction.

Metallic glasses or amorphous alloys, with their excellent chemical stability, disordered atomic arrangement, and ability for thermoplastic nanostructuring, show promising performance toward a range of electrocatalytic reactions in proton-exchange membrane fuel cells. However, there are knowledge gaps and a distinct lack of understanding of the role of amorphous alloy chemistry in determining their catalytic activity. Here, we demonstrate the influence of alloy chemistry and the associated electronic structure on the hydrogen oxidation reaction (HOR) activity of a systematic series of PtPdCuNiP bulk metallic glasses (BMGs) with = 0 to 42.

Solid State Joining of a Cold Rolled Zr-Based Bulk Metallic Glass to a Wrought Aluminum Alloy by Power Ultrasonics.

Ultrasonic metal welding (UMW) enables joining in the solid state at relative low temperatures with short cycle times. This technique is of particular interest for joining metallic glasses to each other or to other materials, because crystallization of the amorphous structure can be prevented due to the low thermal loading and the rapidity of the process. In this work, UMW is applied to join one 1 mm thick sheet of a commercial wrought aluminum alloy (AA5754) and one 0.

Effect of composition and thermal history on deformation behavior and cluster connections in model bulk metallic glasses.

The compositional dependence and influence of relaxation state on the deformation behavior of a Pt-Pd-based bulk metallic glasses model system was investigated, where platinum is systematically replaced by topologically equivalent palladium atoms. The hardness and modulus increased with rising Pd content as well as by annealing below the glass transition temperature. Decreasing strain-rate sensitivity and increasing serration length are observed in nano indentation with increase in Pd content as well as thermal relaxation.

Influence of Initial Temperature and Convective Heat Loss on the Self-Propagating Reaction in Al/Ni Multilayer Foils.

A two-dimensional numerical model for self-propagating reactions in Al/Ni multilayer foils was developed. It was used to study thermal properties, convective heat loss, and the effect of initial temperature on the self-propagating reaction in Al/Ni multilayer foils. For model adjustments by experimental results, these Al/Ni multilayer foils were fabricated by the magnetron sputtering technique with a 1:1 atomic ratio.

The effect of shear on the liquid-liquid transition and crystallization of the undercooled ZrTiCuNiBe(Vit1) bulk metallic glass forming alloy.

An entropy driven liquid-liquid transition (LLT) from a fragile (less ordered) to a strong (highly ordered) liquid occurs in the phase during undercooling. In this work, we show that this ordering transition as well as the applied shear rate affect the onset of crystallization. By recording simultaneously melt viscosity and temperature profiles, we quantitatively determine the shift in the upper part of the time-temperature-transformation diagram of Vit1 to shorter times with increasing shear rate.

Vitrification decoupling from α-relaxation in a metallic glass.

Understanding how glasses form, the so-called vitrification, remains a major challenge in materials science. Here, we study vitrification kinetics, in terms of the limiting fictive temperature, and atomic mobility related to the α-relaxation of an Au-based bulk metallic glass former by fast scanning calorimetry. We show that the time scale of the α-relaxation exhibits super-Arrhenius temperature dependence typical of fragile liquids.

Ultrafast scanning calorimetry of newly developed Au-Ga bulk metallic glasses.

The isothermal crystallization times and critical cooling rates of the liquid phase are determined for the two bulk metallic glass forming alloys AuAgPdCuSiand AuAgPdCuGaSiby using fast differential scanning calorimetry, covering the whole timescale of the crystallization event of the metallic melt. In the case of AuAgPdCuSi, a typical crystallization nose was observed, whereas for the AuAgPdCuGaSi, a more complex crystallization behavior with two distinct crystallization noses was found. Even for the complex crystallization behavior of the AuAgPdCuGaSialloy it is shown that the minimal isothermal nose timeτx*does allow for a quantification of the macroscopic critical thickness.

X-Ray Photon Correlation Spectroscopy Reveals Intermittent Aging Dynamics in a Metallic Glass.

We use coherent x rays to probe the aging dynamics of a metallic glass directly on the atomic level. Contrary to the common assumption of a steady slowing down of the dynamics usually observed in macroscopic studies, we show that the structural relaxation processes underlying aging in this metallic glass are intermittent and highly heterogeneous at the atomic scale. Moreover, physical aging is triggered by cooperative atomic rearrangements, driven by the relaxation of internal stresses.