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Aufsatz
Damage Tolerance Evaluation of E-PBF-Manufactured Inconel 718 Strut Geometries by Advanced Characterization Techniques
(2020-01-06)
By means of electron beam powder bed fusion (E-PBF), highly complex lightweight structures can be manufactured within short process times. Due to the increasing complexity of producible components and the entangled interplay of damage mechanisms, common bulk material properties such as ultimate tensile or fatigue strength are not sufficient to guarantee safe and reliable use in demanding applications. Within this work, the damage tolerance of E-PBF-manufactured Ni-based alloy Inconel 718 (IN 718) strut geometries ...
Aufsatz
Tribological Performance of Additively Manufactured AISI H13 Steel in Different Surface Conditions
(2021-02-16)
Additive manufacturing of metallic tribological components offers unprecedented degrees of freedom, but the surface roughness of most as-printed surfaces impedes the direct applicability of such structures, and postprocessing is necessary. Here, the tribological performance of AISI H13 steel samples was studied. These were additively manufactured through laser powder bed fusion (L-PBF), also referred to as selective laser melting (SLM). Samples were tested in four different surface conditions: as-printed, polished, ...
Aufsatz
Overmoulding of Additively Manufactured Titanium Inserts Using Polyoxymethylene (POM)—Evaluation of Bond Quality as a Function of Process Parameters
(2021-06-15)
Due to their process-induced porous surfaces, additively manufactured structures are not optimized for applications in which friction is a key factor. To improve the frictional properties of additively manufactured titanium inserts of various thicknesses, two tribologically optimized POM materials, which differ in terms of filler composition and contents, were used to overmould the inserts. The titanium inserts were manufactured in two different building directions, resulting in a variation in surface roughness. The ...
Aufsatz
Determination and Validation of Residual Stresses in CFRP/Metal Hybrid Components Using the Incremental Hole Drilling Method
(2020-09-21)
Lightweight materials contribute to an efficient decrease in fuel consumption in the automotive and aircraft industries. Hybrid components made of metal and carbon fiber-reinforced plastics (CFRP) have a high potential in lightweight applications due to their high strength-to-weight ratio. For cost-effective processing of hybrid materials, advanced manufacturing processes such as the prepreg-press-technology have been developed, in which the bonding between a metallic component and a fiber compound is exclusively ...
Dissertation
Oberflächennahe Schädigung von Superlegierungen unter Hochtemperatur
(2020-02)
In der vorliegenden Arbeit wird die Alterung von Nickelbasislegierungen in Oberflächennähe betrachtet. Dabei wird der Einfluss von Temperatur und Zeit in Zusammenhang mit der Oberflächenrauheit, Deformation und der Konzentration von Natriumsulfat an der Probenoberfläche untersucht. Zur Quantifizierung der Schädigung kommen rasterelektronenmikroskopische Methoden wie EBSD und EDX zum Einsatz.
Es wird gezeigt, dass die analysierten Verarmungs- und Vergröberungsprozesse der Gamma'-Ausscheidungen eine deutliche ...
Aufsatz
Effect of Compositional Variation Induced by EBM Processing on Deformation Behavior and Phase Stability of Austenitic Cr-Mn-Ni TRIP Steel
(2020-01-24)
Electron beam melting (EBM) is an established powder bed-based additive manufacturing process for the fabrication of complex-shaped metallic components. For metastable austenitic Cr-Mn-Ni TRIP steel, the formation of a homogeneous fine-grained microstructure and outstanding damage tolerance have been reported. However, depending on the process parameters, a certain fraction of Mn evaporates. This can have a significant impact on deformation mechanisms as well as kinetics, as was previously shown for as-cast material. ...
Aufsatz
On the Impact of Texture and Grain Size on the Pseudoelastic Properties of Polycrystalline Fe–Ni–Co–Al–Ti Alloy
(2020-05-08)
The effects of thermomechanical treatments on crystallographic texture and grain size evolution and their impact on the pseudoelastic properties in Fe41–Ni28–Co17–Al11.5–Ti2.5 (at.%) were studied in the present paper. The results show that cold rolling leads to brass-type texture in this alloy, which is typical for low stacking fault energy materials. Thermal treatments up to 1300 °C were conducted and it is shown that the presence of β-phase helps to control grain growth. After the dissolution of the secondary phase ...
Aufsatz
A Novel Approach to Robustly Determine Residual Stress in Additively Manufactured Microstructures Using Synchrotron Radiation
(2021-07-29)
In recent decades additive manufacturing (AM) for years has been in focus of academia and industry as its underlying production principle allows for the realization of designs of unprecedented geometrical complexity. However, often such structures are not realized due to the lack of understanding of structural and mechanical properties, this fact amongst others related to the unique microstructures established by the related processes. In this context, residual stresses, highly affected by the scan strategy and process ...
Aufsatz
Effect of Crystallographic Orientation and Grain Boundaries on Martensitic Transformation and Superelastic Response of Oligocrystalline Fe–Mn–Al–Ni Shape Memory Alloys
(2021-07-26)
In situ tensile tests employing digital image correlation were conducted to study the martensitic transformation of oligocrystalline Fe–Mn–Al–Ni shape memory alloys in depth. The influence of different grain orientations, i.e., near-〈001〉 and near-〈101〉, as well as the influence of different grain boundary misorientations are in focus of the present work. The results reveal that the reversibility of the martensite strongly depends on the type of martensitic evolving, i.e., twinned or detwinned. Furthermore, it is ...
Aufsatz
Simultaneous impact modified and chain extended glass fiber reinforced poly(lactic acid) composites: Mechanical, thermal, crystallization, and dynamic mechanical performance
(2021-02-05)
Herein, glass fiber (GF) reinforced binary, ternary, and quaternary poly(lactic acid) (PLA) composites were prepared. Toughening, and chain extension of PLA was achieved through the incorporation of impact modifier and chain extender and their concurrent effects on the spectroscopic, crystallization, mechanical, thermal, and thermomechanical properties of the composites were investigated. High mechanical properties of GF influenced the mechanical performance of the composites. However, GF alone could not restrict the ...