Fracture toughness and crack-resistance curve behavior in metallic glass-matrix composites

Nonlinear-elastic fracture mechanics methods are used to assess the fracture toughness of bulk metallic glass (BMG) composites; results are compared with similar measurements for other monolithic and composite BMG alloys. Mechanistically, plastic shielding gives rise to characteristic resistance-curve behavior where the fracture resistance increases with crack extension. Specifically, confinement of damage by second-phase dendrites is shown to result in enhancement of the toughness by nearly an order of magnitude relative to unreinforced glass

Genesis Mission Bulk Metallic Glass Solar Wind Collector: Characterization of Return Samples Available for Re-Allocation

The Genesis mission collected solar wind atoms for 28 months with a variety of collectors mounted on a spacecraft. A total of fifteen pure materials were selected as collectors based on engineering and science requirements. One of the materials was the bulk metallic glass (BMG). It was intended for collecting noble gases and solar energetic particles (SEP). This material is an amorphous metal which was custom made by C.C. Hays at the California Institute of Technology. The final glass composition is Zr58.5Nb2.8Cu15.6Ni12.8Al10.3 (in atom percent). The BMG was located on top of the wafer array mechanism and was exposed for the entire time the science canister was open (~28 months). Fortunately, the BMG did not suffer any serious damage and was intact after the Genesis canisters hard-landing into the Utah desert (Fig. 1)

Oxidation Behavior of a Pd_(43)Cu_(27)Ni_(10)P_(20) Bulk Metallic Glass and Foam in Dry Air

The oxidation behavior of both Pd_(43)Cu_(27)Ni_(10)P_(20) bulk metallic glass (Pd4-BMG) and its amorphous foam containing 45 pct porosity (Pd4-AF) was investigated over the temperature range of 343 K (70 °C) to 623 K (350 °C) in dry air. The results showed that virtually no oxidation occurred in the Pd4-BMG at T < 523 K (250 °C), revealing the alloy’s favorable oxidation resistance in this temperature range. In addition, the oxidation kinetics at T ≥ 523 K (250 °C) followed a parabolic-rate law, and the parabolic-rate constants (k_p values) generally increased with temperature. It was found that the oxidation k_p values of the Pd4-AF are slightly lower than those of the Pd4-BMG, indicating that the porous structure contributes to improving the overall oxidation resistance. The scale formed on the alloys was composed exclusively of CuO at T ≥ 548 K (275 °C), whose thickness gradually increased with increasing temperature. In addition, the amorphous structure remained unchanged at T ≤ 548 K (275 °C), while a triplex-phase structure developed after the oxidation at higher temperatures, consisting of Pd_2Ni_2P, Cu_3P, and Pd_3P

Thermophysical and elastic properties of Cu50Zr50 and (Cu50Zr50)95Al5 bulk-metallic-glass-forming alloys

By employing a containerless high-temperature high-vacuum electrostatic levitation technique, the thermophysical properties, including the ratio between the specific heat capacity and the hemispherical total emissivity, the specific volume, and the viscosity, of Cu50Zr50 and (Cu50Zr50)95Al5 bulk-metallic-glass (BMG)-forming liquids have been measured. Compared with Cu50Zr50, the improved glass-forming ability of (Cu50Zr50)95Al5 can be attributed to its dense liquid structure and its high value of viscosity. Additionally, the relationship between the viscosity of various BMG forming liquids at the melting temperature and the elastic properties of the corresponding glasses at room temperature will be compared

Labour supply and skills demands in fashion retailing

If, as Adam Smith once famously suggested, Britain was a nation of shopkeepers then it is now a nation of shopworkers. Retail is now a significant part of the UK economy, accounting for £256 billion in sales and one-third of all consumer spending (Skillsmart, 2007). It is the largest private sector employer in the UK, employing 3m workers, or 1 in 10 of the working population. For future job creation in the UK economy retail is also similarly prominent and the sector is expected to create a further 250,000 jobs to 2014 (Skillsmart, 2007). The centrality of retail to economic success and job creation is apparent in other advanced economies. For example, within the US, retail sales is the occupation with the largest projected job growth in the period 2004-2014 (Gatta et al., 2009) and in Australia retail accounts for 1 in 6 workers (Buchanan et al., 2003). Within the UK these workers are employed in approximately 290,000 businesses, encompassing large and small organizations and also a number of sub-sectors. This variance suggests that retail should not be regarded as homogenous in its labour demands. Hart et al. (2007) note how skill requirements and the types of workers employed may differ across the sector. This chapter further opens up this point, providing an analysis of the labour supply and skills demands for the sub-sectors of clothing, footwear and leather goods, which are described by Skillsmart (2007: 48) as being 'significant categories in UK retailing'

Bio mit Gesicht - Erfolgschancen einer kundennahen und innovativen Marketingstrategie

Mangelndes Vertrauen in Bio-Produkte wirkt als eine zentrale Kaufbarriere. Mit der Marketingstrategie Bio mit Gesicht (BMG) soll die Anonymität von Produkten aufgehoben und Vertrauen geschaffen werden, indem die Erzeuger und Verarbeiter im Internet vorgestellt werden. Ziel des Projekts "Bio mit Gesicht – Erfolgschancen einer kundennahen und innovativen Marketingstrategie“ war es, die Markteinführung der Produktlinie BMG wissenschaftlich zu begleiten und praxisrelevante Aussagen über die Konzeption zukünftiger Marketingstrategien zu treffen. Dabei wurde im Rahmen einer quantitativen und einer qualitativen Studie untersucht, worauf das Vertrauen in Bio-Produkte grundsätzlich beruht und ob BMG geeignet ist, das Vertrauen in Bio-Produkte zu steigern. Die Studien zeigen, dass die Kennzeichnung von Bio-Lebensmitteln mit Bio-Labels eine zentrale Rolle dabei spielt, wie Konsumenten deren Vertrauenswürdigkeit beurteilen. Bio-Produkte, die ein Verbandslabel aufweisen, genießen das höchste Vertrauen, gefolgt von staatlichen Labels. Trotz seines geringen Bekanntheitsgrads wirkt auch das BMG-Logo vertrauensbildend. Offenbar erweckt bereits allein das signalgebende Wort „bio“ im Label Vertrauen. Auch schaffen Einkaufsstätten Vertrauen, die aus Sicht der Konsumenten Bio-Produkte aus Überzeugung verkaufen. Regionalität erhöht ebenfalls die Vertrauenswürdigkeit eines Bio-Produkts signifikant. Am höchsten ist das Vertrauen in Bio-Lebensmittel unter Konsumenten, die Bio-Lebensmittel überwiegend in Bio-Läden kaufen. Im Gegensatz zum BMG-Label steigert BMG als Rückverfolgbarkeitssystem via Internet das Vertrauen in Bio-Produkte derzeit kaum. Doch insbesondere durch die zunehmende Verbreitung von Smartphones und den damit verbundenen Vorteil, Produktinformationen noch vor dem Einkauf abrufen zu können, könnte die Bedeutung von BMG zukünftig steigern. Auch die wachsende Bedeutung von elektronischen Lesegeräten, mit denen sich Artikeldaten bereits während des Lebensmitteleinkaufs abrufen lassen, steigert das Potenzial von Rückverfolgbarkeitssystemen. Die Analyse der Zugriffszahlen zeigte zudem, dass in Zeiten eines Lebensmittelskandals (z.B. Dioxin in Eiern, EHEC) die Besucherzahlen auf der Internetseite von BMG deutlich steigen

Near-threshold fatigue crack growth in bulk metallic glass composites

A major drawback in using bulk metallic glasses (BMGs) as structural materials is their extremely poor fatigue performance. One way to alleviate this problem is through the composite route, in which second phases are introduced into the glass to arrest crack growth. In this paper, the fatigue crack growth behavior of in situ reinforced BMGs with crystalline dendrites, which are tailored to impart significant ductility and toughness to the BMG, was investigated. Three composites, all with equal volume fraction of dendrite phases, were examined to assess the influence of chemical composition on the near-threshold fatigue crack growth characteristics. While the ductility is enhanced at the cost of yield strength vis-à-vis that of the fully amorphous BMG, the threshold stress intensity factor range for fatigue crack initiation in composites was found to be enhanced by more than 100%. Crack blunting and trapping by the dendritic phases and constraining of the shear bands within the interdendritic regions are the micromechanisms responsible for this enhanced fatigue crack growth resistance

Decomposition and primary crystallization in undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 melts

Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glasses were prepared by cooling the melt with a rate of about 10 K/s and investigated with respect to their chemical and structural homogeneity by atom probe field ion microscopy and transmission electron microscopy. The measurements on these slowly cooled samples reveal that the alloy exhibits phase separation in the undercooled liquid state. Significant composition fluctuations are found in the Be and Zr concentration but not in the Ti, Cu, and Ni concentration. The decomposed microstructure is compared with the microstructure obtained upon primary crystallization, suggesting that the nucleation during primary crystallization of this bulk glass former is triggered by the preceding diffusion controlled decomposition in the undercooled liquid state