A colourimetric and microstructural study of the tarnishing of gold-based bulk metallic glasses

Eisenbart, Miriam; Klotz, Ulrich; Busch, Ralf; Gallino, Isabella

doi:10.1016/j.corsci.2014.04.024

Cited by 21 publications

(9 citation statements)

References 39 publications

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“…For each composition, plates of dimensions 3 × 13 × 35 mm were produced by casting the master alloys into a water-cooled Cu-mold using a tilt-casting apparatus (MC15, Indutherm GmbH, Walzbachtal, Germany). The preparation of the master alloys required a variety of processing methods that are described in [19,21,22,33,[42][43][44][45]. The P-containing master alloys were purified in a flux of B 2 O 3 prior to casting.…”

Section: Methodsmentioning

confidence: 99%

On the Fragility of Bulk Metallic Glass Forming Liquids

Gallino

2017

Entropy

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Abstract:In contrast to pure metals and most non-glass forming alloys, metallic glass-formers are moderately strong liquids in terms of fragility. The notion of fragility of an undercooling liquid reflects the sensitivity of the viscosity of the liquid to temperature changes and describes the degree of departure of the liquid kinetics from the Arrhenius equation. In general, the fragility of metallic glass-formers increases with the complexity of the alloy with differences between the alloy families, e.g., Pd-based alloys being more fragile than Zr-based alloys, which are more fragile than Mg-based alloys. Here, experimental data are assessed for 15 bulk metallic glasses-formers including the novel and technologically important systems based on Ni-Cr-Nb-P-B, Fe-Mo-Ni-Cr-P-C-B, and Au-Ag-Pd-Cu-Si. The data for the equilibrium viscosity are analyzed using the Vogel-Fulcher-Tammann (VFT) equation, the Mauro-Yue-Ellison-Gupta-Allan (MYEGA) equation, and the Adam-Gibbs approach based on specific heat capacity data. An overall larger trend of the excess specific heat for the more fragile supercooled liquids is experimentally observed than for the stronger liquids. Moreover, the stronger the glass, the higher the free enthalpy barrier to cooperative rearrangements is, suggesting the same microscopic origin and rigorously connecting the kinetic and thermodynamic aspects of fragility.

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Section: Methodsmentioning

confidence: 99%

On the Fragility of Bulk Metallic Glass Forming Liquids

Gallino

2017

Entropy

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“…For example, Eisenbart et al [68,69] have recently reported that the large amount of Cu in this particular composition, in combination with the presence of Si, is the main contributor to the fast tarnishing kinetics observed at room temperature. Furthermore, Yu et al [38] investigated the chemical influence on slow β relaxations in a number of BMG systems and have shown that the presence of Cu leads to the formation of a pronounced DMA loss peak in Pd-based BMGs.…”

Section: B Atomic-scale Structural Changes During β Relaxationmentioning

confidence: 99%

βrelaxation and low-temperature aging in a Au-based bulk metallic glass: From elastic properties to atomic-scale structure

et al. 2014

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The slow β relaxation is understood to be a universal feature of glassy dynamics. Its presence in bulk metallic glasses (BMGs) is evidence of a broad relaxation time spectrum that extends to deep within the glassy state. Despite the breadth of research devoted to this phenomenon, its microscopic origin is still not fully understood. The low-temperature aging behavior and atomic structural rearrangements of a Au 49 Cu 26.9 Si 16.3 Ag 5.5 Pd 2.3 BMG are investigated in the regime of the slow β relaxation by employing an ensemble of experimental techniques such as high-intensity synchrotron x-ray scattering, modulated differential scanning calorimetry (MDSC), dynamic mechanical analysis (DMA), impulse excitation, and dilatometry. Evidence of a distinct slow β-relaxation regime is seen in the form of (1) an excess wing of the DMA loss modulus beginning at ∼50• C, (2) a crossover effect of elastic modulus with isothermal aging at 50• C, and (3) a broad, nonreversing and largely irreversible sub-T g endotherm in the MDSC results. Atomic rearrangements occurring at the onset of the measured slow β-relaxation temperature regime were found to be confined mainly to the short-range order length scale while no significant atomic rearrangements occur on the length scale of the medium-range order. Furthermore, evidence is presented that suggests the crossover effect in Young's modulus is due to the evolution of chemical short-range order. These results support the emergent picture of a dynamically heterogeneous glassy structure, in which low-temperature relaxation occurs through atomic rearrangements confined mostly to the short-range order length scale.

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“…T m, re-sol is higher than the melting temperature T m = 618 K on first heating the MG; this difference is discussed in §4. 4.…”

Section: Differential Scanning Calorimetrymentioning

confidence: 99%

In-Situ TEM Study of the Crystallization Sequence in a Gold-Based Metallic Glass

et al. 2020

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The composition Au 49 Ag 5.5 Pd 2.3 Cu 26.9 Si 16.3 (at.%) is of interest as the basis for the development of goldbased bulk metallic glasses for application in jewellery. In-situ heating in transmission electron microscopy (TEM) and differential scanning calorimetry (DSC, both conventional and fast) are used to obtain a comprehensive characterization of the decomposition on heating a melt-spun glass of this composition. Linking TEM with DSC over a range of heating rates 0.083-20 0 0 K s -1 , allows the sample temperature in the TEM heating stage to be calibrated. On heating up to melting, the glass decomposes in up to four stages: (1) complete transformation to single-phase nanocrystalline (Au,Cu) 7 Si; (2) grain growth of this phase; (3) precipitation of (Pd,Ag)Si, reducing the supersaturation of silicon in the (Au,Cu) 7 Si matrix; (4) with the precipitate phase remaining stable, decomposition of the matrix to a mixture of (Au,Ag) 8 Cu 2 , AuCu and Cu 3 Au phases. At all stages, grain diameters remain sub-micrometre; some of the stable nanocrystalline microstructures may themselves be of interest for applications. The characterization of the decomposition can assist in the optimization of the glass composition to improve tarnishresistance, while retaining adequate glass-forming ability, formability in thermoplastic processing, and resistance to crystallization. For materials in general, the close correlation of in-situ TEM and DSC results should find wide use in characterizing complex transformation sequences.

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A colourimetric and microstructural study of the tarnishing of gold-based bulk metallic glasses

Cited by 21 publications

References 39 publications

On the Fragility of Bulk Metallic Glass Forming Liquids

On the Fragility of Bulk Metallic Glass Forming Liquids

βrelaxation and low-temperature aging in a Au-based bulk metallic glass: From elastic properties to atomic-scale structure

In-Situ TEM Study of the Crystallization Sequence in a Gold-Based Metallic Glass

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