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Cyclic degradation of Co49Ni21Ga30 high-temperature shape memory alloy - On the roles of dislocation activity and chemical order
(2015)
Conventional shape memory alloys (SMAs), such as binary Ni-Ti, are typically limited to service temperatures below 100 °C. Recent studies on Co-Ni-Ga high temperature (HT) SMAs revealed the potential that these alloys can be used up to temperatures of about 400 °C. Analysis of the cyclic functional properties showed that degradation in these alloys is mainly triggered by intensive dislocation motion. However, data on the cyclic stress-strain response and the mechanisms leading to functional degradation of Co-Ni-Ga ...
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Cyclic Deformation Response of Ultra-fine Grained Titanium at Elevated Temperatures
(2019)
This study focuses on the high-temperature cyclic deformation response (CDR) of ultra-fine grained (UFG) titanium of commercial purity (grade 4) processed via equal channel angular extrusion as a severe plastic deformation method. Low-cycle fatigue experiments were conducted at elevated temperatures up to 600 °C and at strain amplitudes ranging from 0.2% to 0.6%. Besides temperature and strain amplitude, the influence of two processing routes (8BC and 8E) on the fatigue characteristics of UFG Ti was examined. It is ...
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Energy Resolved Residual Stress Analysis with Laboratory X-Ray Sources
(2017-04-17)
It is well known that existing residual stress fields play an important role for strength and lifetime of components. Consequently there is a great interest in the availability of fast, reliable and possibly nondestructive methods for their determination. In this context, X-ray diffraction methods play an important role in technical practice as well as in scientific research. They are based on the determination of lattice strains from which residual stresses are determined applying Hooke's law with appropriate elastic ...
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Prozessintegration von induktiver Wärmebehandlung und Festwalzen – sichere und zuverlässige Komponenten mit hoher Schwingfestigkeit
(2017-02-08)
Mechanische Oberflächenbehandlungen, beispielsweise das Festwalzen, spielen in der technischen Praxis eine bedeutende Rolle und tragen wesentlich zur Steigerung der Zuverlässigkeit hochbeanspruchter Komponenten bei. In einer Reihe von Fällen wurde gezeigt, dass eine Erhöhung der Prozesstemperatur die Wirksamkeit der Verfahren noch steigert, weil dies zu einer besseren Stabilisierung der eingebrachten Druckeigenspannungen führt. Eine wesentliche Voraussetzung zur Einführung dieser Verfahren in die Praxis ist allerdings, ...
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Bend Straightening of a Carbonitrided Gear Shaft – Consequences on Residual Stresses and Retained Austenite near the Surface
(2017-06-20)
Carbonitriding of shafts in drive technology is strongly connected with distortion. Bend straightening is an important process step in order to eliminate distortion without removing the hardened surface layer. As shown in several investigations, even for simple part geometries, bending induced stresses and plastic deformations have a strong impact not only on the residual stress state but also on the microstructure after straightening. As gear shafts become increasingly filigree and complex in their geometry, the ...
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Climatic Ageing of Components of Polymer Based Electrochromic Devices
(2013-09-09)
Combining a shading function and a polycarbonate window displays an attractive alternative to the currently employed glass roof in vehicles. However, the ageing of such a device must be investigated before any application. Therefore, our investigations focus on the ageing of the components of a polycarbonate based electrochromic device. The optical, electrical, mechanical and electrochemical properties of the ion storage layer as well as the substrate will be assessed after storage in a climate with a high humidity ...
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Characterization of Anisotropic Properties of Hot Compacted Self-Reinforced Composites (SRCs) via Thermal Diffusivity Measurement
(2019-11-01)
The mechanical properties of self-reinforced composites (SRCs) produced in a hot compaction process significantly depend on the process parameters. Only a little deviation of the process temperature or pressure causes the component to act differently under mechanical load. This is a chance and a challenge at the same time, since this process is difficult to handle but by properly controlling the process parameters, the mechanical properties can be adjusted, even locally for one component. In this research SRC are ...
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A Closer Look at the Bonding Capacity of Thick Metal-Plastic Hybrids
(2019-03-01)
Metal-plastic hybrids have a lot of advantages compared to purely metal or purely plastic parts. A good design for metal-plastic hybrids can help to save weight, for example in automotive applications. Therefore, it is important to understand the joining mechanisms between both materials. Aluminum AlSi9Cu3(Fe) and polyamide 6.6 with 35 % glass fibers were used as joining partners. The materials were joined by enclosing the metal part at least partially with plastic right inside the injection molding tool. Afterwards, ...
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UV Pre-Treatment for Polycarbonate for Bonding LSR in a Multi-Component Injection Molding Process
(2019-03-01)
In this study, the influence of UVC radiation and the influence of ozone on the surface energy of specimens made of polycarbonate were investigated. In an additional step, the peeling resistance of silicone flaps, which were overmolded, onto pre-treated PC plates of multicomponent specimens were analyzed. For this purpose, the samples were exposed to UVC radiation for different lengths of time, ranging from 5 s to 3 600 s. To further evaluate the influence of the ozone created by the UVC in the presence of oxygen, ...
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Additive manufacturing of Co-Ni-Ga high-temperature shape memory alloy - Processability 3 and phase transformation behavior
(2019)
Co-Ni-Ga high-temperature shape memory alloy is additively processed by selective laser melting for the first time. Reversiblemartensitic transformation of the as-built material is proven by differential scanning calorimetry. Microstructural analysis reveals a columnar-grained microstructure due to epitaxial solidification. Columnar-grained microstructures are characterized by a very low degree of constraints being beneficial for superior functional performance in numerous shape memory alloys. However, process-induced ...