•Spreading of AgCuTi drops on SiC was observed using a large-chamber SEM.•The measured spreading rate was correlated with models for reactive spreading.•A transition between the spreading limiting ...mechanisms is proposed.•Triple line distortions were observed during cooling.
Studies of the spreading kinetics of molten metals on ceramic substrates provide valuable information about the processes determining the interaction between these two materials. Based on experimental and theoretical works, two determining wetting types have been proposed for a variety of high-temperature systems – the reaction limited wetting and the diffusion-limited wetting. In the scope of this contribution an AgCuTi–SiC-system is investigated, which, despite of its high relevance for joining applications, has not yet gained much attention in fundamental works.
The experiments were carried out on a heating stage placed in a large-chamber SEM. This novel method, allows high-resolution imaging and a precise observation of the changes of the liquid drop. Images taken every 5s were used to measure the wetted surface as a function of time at temperatures between 830 and 890°C.
The AgCuTi-melt exhibits different spreading stages during the wetting process. It was shown that, at the beginning of the wetting, the spreading kinetics is determined by the reaction rate at the triple line. After reaching a distinct temperature-dependent angle, the titanium diffusion becomes the main limiting factor.
•X-ray CT reveals voids-distribution in the joint of a brazed sample.•High resolution is possible for materials with similar absorption coefficients.•Image reconstruction techniques offer accurate ...quantitative analysis of voids.•Factors for a successful scan and dataset postprocessing are presented.
Brazing is a relatively fast process that offers sufficient strength in the joint of dissimilar materials. Cemented carbides are often brazed onto steel components in order to improve the wear resistance of engineering tools. In the case of brazing such materials in an ambient atmosphere, a flux is necessary to improve the wetting of the liquid filler alloy on the surfaces. In some cases, the flux cannot be sufficiently removed from the small joint, thus forming voids during solidification. This phenomenon can greatly affect the integrity of the joint. Such voids are not adequately detectable by visual inspection or common nondestructive testing methods, such as ultrasonic scanning, acoustic emission testing, or thermography. In this study, X-ray microscopy is shown to provide adequate visualization and a quantitative analysis of the dispersion of voids within brazed components of cold work steel, 115CrV3, and cemented carbide, K10 (ISO 513). One of the challenging tasks when analyzing the aforementioned brazed materials is achieving a sufficiently high resolution within the joint gap, since the sample materials have similar X-ray absorption coefficients. Such high resolution was successfully achieved in this study by means of multiple scanning and image reconstruction techniques, such as beam filtering, dataset levelling, and noise removal. The voids on the 115CrV3-side are found to expand radially towards the edges of the specimen up to a maximum volume of 1.18E + 07 µm3. The same radial pattern was detected on the side of the K10, where the voids contracted in volume towards the center of the specimen. However, the K10-side was found to exhibit relatively larger voids with a maximum volume of 7.70E + 07 µm3, that is approximately seven times larger than that detected on the 115CrV3-side.
The validation of a brazed work piece requires lot of operating experiences in order to assure a sufficient joint quality for a reliable manufacturing process. In most cases, a quality assurance is ...only performed by destructive methods to measure the strength of the joint. Conventional non-destructive testing methods such as computer tomography, ultrasonic inspection, and magnetic particle inspection as well as other available optical and thermal methods are commonly not suitable for brazing applications in mass production. This is partly due to the fact that these methods are very expensive or even highly limited when it comes to the detection of critical imperfections. Hence, there is a high demand to investigate alternative non-destructive testing methods.
The main focus of this feasibility study is the examination of the electrical resistance behavior of the brazed joint. In this regard, different positions of defects within the filler metal as well as different contact positions for the current supply and voltage measurement of the 4-wire technique are investigated by means of FEM-analyses. A key aspect is the evaluation of the particular voltage distribution within the brazed work pieces as a function of these variations and to generate significant potential differences for the measurement of brazed joints. The results will contribute the design of the resistance measurements on various component geometries to enable a precise quality inspection.
Studies of the spreading kinetics of molten metals on ceramic substrates provide valuable information about the processes determining the interaction between these two materials. Based on ...experimental and theoretical works, two determining wetting types have been proposed for a variety of high-temperature systems - the reaction limited wetting and the diffusion-limited wetting. In the scope of this contribution an AgCuTi-SiC-system is investigated, which, despite of its high relevance for joining applications, has not yet gained much attention in fundamental works. The experiments were carried out on a heating stage placed in a large-chamber SEM. This novel method, allows high-resolution imaging and a precise observation of the changes of the liquid drop. Images taken every 5 s were used to measure the wetted surface as a function of time at temperatures between 830 and 890 degree C. The AgCuTi-melt exhibits different spreading stages during the wetting process. It was shown that, at the beginning of the wetting, the spreading kinetics is determined by the reaction rate at the triple line. After reaching a distinct temperature-dependent angle, the titanium diffusion becomes the main limiting factor.
Der Sonderforschungsbereich (SFB) 696 Forderungsgerechte Auslegung von intralogistischen Systemen – Logistics on Demand wurde im Juli 2006 an der Technischen Universität Dortmund eingerichtet, um ...analytische Methoden und Technologien zur anforderungsgerechten Gestaltung und Organisation intralogistischer Systeme zu entwickeln. In zwölf Teilprojekten ging es darum, die heutigen und zukünftigen Anforderungen der Anwender, darunter auch den produktbegleitenden Service, stärker in den Mittelpunkt der Produktentwicklung intralogistischer Systeme zu rücken. Vision ist es, die methodische und technische Basis für flexible, auf Veränderungen automatisch reagierende, sich selbst kontrollierende und reparierende zuverlässige Intralogistiksysteme zu schaffen.
We present a simple all-solid-state laser source emitting 2.4 W of single-frequency light at 671 nm for laser cooling of lithium atoms. It is based on a diode-pumped solid-state laser, which is ...frequency doubled in a ppZnO:LN ridge waveguide with an internal doubling efficiency of 54%. We develop a simple theory for the thermal effects we observed at elevated fundamental powers, and compare the setup to a more efficient but more complex one with an external resonant frequency doubling cavity providing 5.2 W at 671 nm.
Non-restorative sleep has considerable consequences for daily life. A sleep disorder is recognized by symptoms such as daytime fatigue and performance or concentration disorders. Furthermore, it ...increases the risk of developing cardiovascular, metabolic, and neurologic diseases. The diagnosis and therapy of sleep disorders is not only in the sleep medicine doctor's hands. A multidisciplinary approach reflects the affected patients' choice. Dentists can make an important contribution, especially to the therapy of sleep-related breathing disorder.
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