Inst. Werkstoffwissenschaften und -technologien

194 Items

Recent Submissions
Hierarchical levels of organization of the Brazil nut mesocarp

Sonego, Marilia ; Fleck, Claudia ; Pessan, Luiz Antonio (2020-04-22)

Aiming to understand Nature´s strategies that inspire new composite materials, the hierarchical levels of organization of the Brazil nut (Bertholletia excelsa) mesocarp were investigated. Optical microscopy, scanning electron microscopy (SEM), microtomography (MicroCT) and small-angle X-ray scattering (SAXS) were used to deeply describe the cellular and fibrillary levels of organization. The me...

Freeze Casting: From Low‐Dimensional Building Blocks to Aligned Porous Structures—A Review of Novel Materials, Methods, and Applications

Shao, Gaofeng ; Hanaor, Dorian A. H. ; Shen, Xiaodong ; Gurlo, Aleksander (2020-03-12)

Freeze casting, also known as ice templating, is a particularly versatile technique that has been applied extensively for the fabrication of well‐controlled biomimetic porous materials based on ceramics, metals, polymers, biomacromolecules, and carbon nanomaterials, endowing them with novel properties and broadening their applicability. The principles of different directional freeze‐casting pro...

Numerical Investigations on Material Flow During Indirect Extrusion of Copper-Clad Aluminum Rods

Kuhnke, Stefan ; Sanabria, Vidal ; Gensch, Felix ; Nitschke, Renè ; Müller, Sören (2020-06-09)

In the extrusion of clad composite materials with different flow stresses are usually used. This causes an inhomogeneous material flow which can induce sleeve or core fracture. In the present study, the material flow during indirect extrusion of copper-clad aluminum (CCA) rods was analyzed by means of experimental and numerical investigations throughout the process. In order to provide material...

Multi-stage ageing in an Al-Mg-Si alloy

Yang, Zi (2020)

Solute clustering and precipitation in Al-Mg-Si alloys have been extensively studied in the past decades oweing to an increasing importance of these alloys in industrial applications. However, many details are still not well understood, especially during multi-stage ageing. In this study, several aspects of multi-stage ageing in a commercial AA6014 alloy were systematically investigated, namely...

Improved oxidation resistance of high emissivity coatings on fibrous ceramic for reusable space systems

Shao, Gaofeng ; Lu, Yucao ; Hanaor, Dorian A. H. ; Cui, Sheng ; Jiao, Jian ; Shen, Xiaodong (2018-11-13)

To develop high emissivity coatings on fibrous ceramic substrates with improved thermal resistance for reusable space systems, WSi2–MoSi2–Si–SiB6-borosilicate glass coatings were prepared on fibrous ZrO2 by slurry dipping and subsequent high temperature rapid sintering. A coating with 20 wt% WSi2 and 50 wt% MoSi2 presents optimal thermal stability with only 10.06 mg/cm2 mass loss and 4.0% emiss...

Röntgenographische Analysen der Umformmechanismen und der Eigenspannungen umgeformter Bleche im Single Point Incremental Forming-Verfahren

Dobecki, Mateus (2020)

Die inkrementelle Blechumformung ist ein flexibles Fertigungsverfahren zur Herstellung komplex geformter Teile durch die kontrollierte Bewegung des Umformwerkzeugs. Die mechanischen Eigenschaften inkrementell umgeformter Bleche im Single Point Incremental Forming (SPIF)-Verfahren werden maßgeblich von den wirkenden Umformmechanismen während der Herstellung beeinflusst. In der vorliegenden Arbei...

Verbesserung der Haltbarkeit von Dokumenten mit Hilfe polymerer Schichten

Scheuerle, Volker (2014-07-18)

Dissertation. Diese Arbeit handelt von der Leistungssteigerung von Lackrezepturen durch Serienkomponenten, deren Potenzial der Schutzwirkungserhöhung nicht ausgeschöpft ist. Sie beginnt mit Voruntersuchungen zur Erfassung von Schädigungsmerkmalen. Eine anschließende Kategorisierung dieser Schädigungen nach Art und Veränderungspotenzial des Dokuments bildet die Ausgangsbasis zur Verbesserung des...

On-chip assembly of 3D graphene-based aerogels for chemiresistive gas sensing

Shao, Gaofeng ; Ovsianytskyi, Oleksandr ; Bekheet, Maged F. ; Gurlo, Aleksander (2019-11-29)

Integration of the material preparation step into the device fabrication process is of prime importance for the development of high performance devices. This study presents an innovative strategy for the in situ assembly of graphene-based aerogels on a chip by polymerization–reduction and annealing processes, which are applied as chemiresistive gas sensors for the detection of NO2.

Verarbeitung und Charakterisierung von Polyamid 6-Polyhydroxybutyrat-Blends

Dill, Svenja (2020)

Aufgrund der deutlich unterschiedlichen Verarbeitungsbereiche von Polyhydroxybutyrat (PHB) und Polyamid 6 (PA 6) ist die gemeinsame Verarbeitung der beiden Polymere eine verfahrenstechnische Herausforderung. Um die Verträglichkeit und Prozessfähigkeit der PA 6-PHB-Blends beurteilen zu können, wurde somit zunächst ein geeigneter Aufbereitungsprozess auf einem Doppelschneckenextruder entwickelt. ...

Extrusion of Aluminum Tubes with Axially Graded Wall Thickness and Mechanical Characterization

Negendank, Maik ; Müller, Sören ; Reimers, Walter (2014-08-25)

In this study the indirect extrusion of seamless aluminum tubes with variable wall thickness was investigated. Therefore, an axially moveable stepped mandrel was applied. Investigations revealed that wall thickness transitions can either be graded over the tube length or very sharp. The microstructures in thin-walled and thick-walled tube sections were investigated. The local variation of the e...

Influence of choked angle of bearing channel on profile grain structure during multi-hole extrusion of aluminum alloy

Müller, Sören ; Sanabria, Vidal (2018-08-11)

Direct extrusion of aluminum alloy EN AW-6060 was carried out applying a four-hole die with pair-wise parallel and choked long channels. Due to the dissimilar friction inside parallel and choked channels profiles with different length were extruded simultaneously. In order to investigate the grain structure evolution along the whole extrusion process, multiple sections from the beginning to the...

Application of Friction Shear Test for Constitutive Modeling Evaluation of Magnesium Alloy AZ31B at high Temperature

Sanabria, Vidal ; Gensch, Felix ; Müller, Sören (2020-04-26)

The experimental determination of the flow stress and its mathematical formulation are essential for the numerical simulation of metal forming processes. The hot compression test is widely used to analyze the flow stress evolution as function of temperature, strain and strain rate. The compression test is limited to a relative low strain (ε≤1) which is acceptable when the stress is minor influe...

Microstructure Evolution of Friction Boundary Layer during Extrusion of AA 6060

Sanabria, Vidal ; Müller, Sören ; Reimers, Walter (2014-10-14)

The tribological behavior between the aluminium alloy AA 6060 and the hot working steel 1.2344 has been recently studied using a new axial friction test for extrusion processes. With this new test, the friction forces as well as the specimens’ plastic deformations generated during sliding tests can be investigated. Selected specimens tested at high temperature (300-500 °C), normalized normal st...

Backward rod extrusion of bimetallic aluminum-copper alloys at room temperature

Sanabria, Vidal ; Gall, Sven ; Gensch, Felix ; Nitschke, René ; Müller, Sören (2019-07-02)

The backward rod extrusion of bimetallic aluminum-copper alloys at room temperature was investigated. The aluminum alloy EN AW-1080A and the copper alloy Cu-ETP were selected to prepare the core and sleeve of the billet respectively. The copper cross section was equivalent to 30% of the billet. Moreover, the billet was extruded applying a conic die angle of 90° and an extrusion ratio of 14:1. E...

Extrusion of magnesium alloy hollow profiles with axial variable wall thickness

Negendank, Maik ; Sanabria, Vidal ; Müller, Sören ; Reimers, Walter (2019-07-02)

Industrially extruded profiles are characterized by a constant cross section along the length since rigid dies are applied in the process. However, if it would be possible to extrude profiles with cross sections that can be locally adapted (tailored) to the acting forces or stresses this would mean a significant potential for weight and material savings. Hence, in this study the extrusion of ma...

Analysis of the flow imbalance on the profile shape during the extrusion of thin magnesium sheets

Gall, Sven ; Müller, Sören ; Reimers, Walter (2013-12-31)

The extrusion process facilitates the production of magnesium sheets featuring a very thin thickness as well as excellent surface properties by using a single process step only. However, the extrusion of the magnesium sheets applying not optimized process parameters, e.g. low billet temperature or/ and poorly deformable magnesium alloy, produce pronounced buckling and waving of the extruded she...

Modification of the anisotropy and strength differential effect of extruded AZ31 by extrusion-shear

Jähnke, Martin ; Gensch, Felix ; Müller, Sören (2018-05-03)

The extrusion of magnesium alloys results in a pronounced fiber texture in which the basal planes are mostly oriented parallel and the c-axes are oriented perpendicular to the extrusion direction. Due to this texture the Strength Differential Effect (SDE), which describes the strength difference between tensile and compression yield strength, and the elastic anisotropy in the sheet plane are ob...

Influence of temperature and sliding speed on the subsurface microstructure evolution of EN AW-6060 under sticking friction conditions

Sanabria, Vidal ; Müller, Sören (2017-10-16)

The microstructure evolution of the friction boundary layer of the aluminum alloy EN AW-6060 was investigated. Sticking friction tests at different temperatures and sliding speeds were carried out. A severe deformation below the friction surface was observed by means of LOM and EBSD mapping. Thus, the thickness variation and the grain structure of the high deformation zone could be described. F...

The Influence of Alloy Composition and Liquid Phase on Foaming of Al−Si−Mg Alloys

García-Moreno, Francisco ; Radtke, Laurenz Alexander ; Neu, Tillmann Robert ; Kamm, Paul Hans ; Klaus, Manuela ; Schlepütz, Christian Matthias ; Banhart, John (2020-01-28)

The foaming behaviour of aluminium alloys processed by the powder compaction technique depends crucially on the exact alloy composition. The AlSi8Mg4 alloy has been in use for a decade now, and it has been claimed that this composition lies in an “island of good foaming”. We investigated the reasons for this by systematically studying alloys around this composition by varying the Mg and Si cont...

Development and Characterization of Mg-SiC Nanocomposite Powders Synthesized by Mechanical Milling

Penther, Daniela ; Fleck, Claudia ; Ghasemi, Alireza ; Riedel, Ralf ; Kamrani, Sepideh (2017-07-03)

Magnesium powder in micron scale and various volume fractions of SiC particles with an average diameter of 50 nm were co-milled by a high energy planetary ball mill for up to 25 h to produce Mg-SiC nanocomposite powders. The milled Mg-SiC nanocomposite powders were characterized by scanning electron microscopy (SEM) and laser particle size analysis (PSA) to study morphological evolutions. Furth...