Chimney Formation in Solidifying Ga-25wt pct In Alloys Under the Influence of Thermosolutal Melt Convection

The directional solidification of Ga-25wt pct In alloys within a Hele-Shaw cell under the influence of thermosolutal convection was observed by means of X-ray radioscopy. The unstable density stratification at the solidification front causes the formation of rising plumes containing solute-rich liquids. The development of the chimneys and the probability of their surviving depend sensitively on the spatial and temporal properties of the flow field. Variations of the vertical temperature gradient along the solidification cell lead to the observation of different mechanisms for chimney formation. Perturbations of the dendritic structure are the origin of development of segregation freckles in case of low temperature gradients. The long-term stabilities of these segregation channels are strongly influenced by the transient nature of the melt convection. The situation at higher temperature gradients is characterized by two dominating convection rolls in the liquid phase which are driven by a lateral temperature gradient and the convex shape of the solidification front. The penetration of this flow pattern into the mushy zone results in continuous accumulation of solute in the central part of the mushy zone followed by a remelting of the solid fraction and the occurrence of a stable chimney.     

Predicting glass-forming compositions in the Al–La and Al–La–Ni systems

In this work, a criterion considering the topological instability (λ) and the differences in the electronegativity of the constituent elements (Δe) was applied to the Al–La and Al–Ni–La systems in order to predict the best glass-forming compositions. The results were compared with literature data and with our own experimental data for the Al–La–Ni system. The alloy described in the literature as the best glass former in the Al–La system is located near the point with local maximum for the λ·Δe criterion. A good agreement was found between the predictions of the λ·Δe criterion and literature data in the Al–La–Ni system, with the region of the best glass-forming ability (GFA) and largest supercooled liquid region (ΔT_x) coinciding with the best compositional region for amorphization indicated by the λ·Δe criterion. Four new glassy compositions were found in the Al–La–Ni system, with the best predicted composition presenting the best glass-forming ability observed so far for this system. Although the λ·Δe criterion needs further refinements for completely describe the glass-forming ability in the Al–La and Al–La–Ni systems, the results demonstrated that this criterion is a good tool to predict new glass-forming compositions.     

Effect of cold rolling on compressive and tensile mechanical properties of Zr52.5Ti5Cu18Ni14.5Al10 bulk metallic glass

The effect of cold-rolling on structure, thermal stability, and compressive and tensile mechanical properties of the Zr_52.5Ti₅Cu₁₈Ni_14.5Al₁₀ bulk metallic glass has been investigated. The results reveal that cold-rolling does not influence the thermal stability of the material. However, the small plastic deformation induced by cold-rolling is very effective for improving the room temperature plastic strain of the glass: the compressive plastic strain increases from 1.1% for the as-cast material to 2.6% for the cold-rolled sample and the tensile ductility increases from 0% for the as-cast glass to 0.8% for the cold-rolled sample. Hardness measurements indicate that cold rolling creates a heterogeneous microstructure consisting of hard and soft regions. Most likely, the soft regions are preferred locations for shear band formation and propagation, whereas the hard regions may act as obstacles for shear band propagation, effectively limiting shear bands from propagating catastrophically and, consequently, enhancing the room temperature plastic deformation of the glass.     

Sicherheit im Smart Grid

Ein Smart Grid ist eine besonders schützenswerte, kritische Infrastruktur, die vielf?ltige Angriffsfl?chen bietet. Mit der zunehmenden Abh?ngigkeit von einem zuverl?ssigen und robusten Smart Grid für die Versorgungssicherheit steigen Verletzlichkeit und Verwundbarkeit durch gezielte Angriffe (Terroranschl?ge, Hackeraktivit?ten, Manipulationsversuche). Informations- und Telekommunikationstechnik dient dabei als Tatwaffe und ist zugleich das Ziel von Angriffen. Der Beitrag zeigt, welche Schutzma?nahmen für die Konzeption zukunftssicherer Smart Grids unerl?sslich sind.     

Form follows performance: Entwicklung des modularen,weitgespannten Tragwerks für ein neues Montagewerk

Form follows performance: Developing of a modular and low‐spaned structure for an automotive factory. Present global markets demand for increasing effectivity concerning qualitiy, budget and time issues. ‘Zero tolerance’ consequently aims to avoid a multitude of interfaces in planning process of complex factory projects. State of the art CAD/CAM database technology allows for integral 3 dimensional data workflow, authors develop programming and performance of a modular steel structure for an automotive factory project in design phase, shop drawings and site organisation by means of synergetic 3D‐workflow.