Uhlenwinkel, Volker
Lade...
Preferred name
Uhlenwinkel, Volker
Official Name
Uhlenwinkel, Volker
Alternative Name
Uhlenwinkel, V.
ORCID
GND
7 Ergebnisse
Gerade angezeigt 1 - 7 von 7
- Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Processing soft ferromagnetic metallic glasses: on novel cooling strategies in gas atomization, hydrogen enhancement, and consolidationProcessing soft ferromagnetic glass-forming alloys through gas atomization and consolidation is the most effective technique to produce bulk samples. The commercial viability of these materials depends on commercial purity feedstock. However, crystallization in commercial purity feedstock is several orders of magnitude faster than in high purity materials. The production of amorphous powders with commercial purity requires high cooling rates, which can only be achieved by extending the common process window in conventional gas atomization. The development of novel cooling strategies during molten metal gas atomization on two model alloys ({(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 and Fe76B10Si9P5) is reported. Hydrogen inducement during liquid quenching significantly improved the glass-forming ability and soft magnetic properties of {(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 powders. Spark plasma sintering experiments verified that amorphous rings could be produced regardless of the cooling strategies used. While the saturation magnetization was almost unaffected by consolidation, the coercivity increased slightly and permeability decreased significantly. The magnetic properties of the final bulk samples were independent of feedstock quality. The developed cooling strategies provide a great opportunity for the commercialization of soft ferromagnetic glass-forming alloys with commercial purity.Wissenschaftlicher ArtikelBand:5926 24 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Effect of hot gas atomization on spray forming of steel tubes using a close-coupled atomizer (CCA)Hot gas atomization in spray forming has been used for the first time to improve the quality of spray-formed tubular deposits. This technique reduces gas consumption and produces smaller droplets than cold gas atomization. The flight velocity and cooling rate of the atomized droplets increase with increasing gas temperature. These features can further influence the quality of the spray-formed deposits. Until now, spray-formed tubes have not been used on industrial scale due to insufficient deposit quality in terms of porosity and bonding to the substrate. Using a close-coupled atomizer (CCA), qualitative improvements of the as-sprayed deposits have been previously studied. In the present study, a comparative investigation is done to find the influence of hot gas atomization on the spray forming of the bearing steel AISI 52100 (100Cr6) using a close-coupled atomizer. The spray-formed deposit with hot gas atomization (gas temperature about 300 °C) shows lower deposit surface temperature and smaller grain size in comparison to the deposit produced under cold gas atomization condition due to smaller droplet diameter and higher cooling rate of the droplets. Moreover, the as-sprayed deposits under hot gas atomization show a higher relative density at a lower deposit surface temperature, which extends the process window for the flexible production of spray-formed tubes.Wissenschaftlicher ArtikelBand:28228 22 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Formulation of blast-furnace slag for use in hydraulically bound construction materialsDry powder granulation of slag melts by gas atomization offers a means of reducing the resource expenditure associated with the conventional wet processing of blast furnace slags (BFS). Slags are a by-product of the iron production process and are subsequently processed to create a fine powder, which is then used in the manufacture of building materials. The melt atomization process, which is widely used in metal powder production, was adapted to process the slag into fine, amorphous and spherical particles. Therefore, this study investigates the development of an adapted high-temperature atomization process utilizing a new developed atomizer, the resulting properties of the slag particles, and the suitability of atomized blast furnace slag powders (ABFS) for use in building materials. It is demonstrated that BFS can be properly atomized to form spherical, amorphous particles that exhibit excellent flowability and a low Carr-Index. The utilization of heated atomization gas and high atomizing gas pressure increases the content of small particles below 200 μm in diameter with up to 60 % of the powder mass. The atomized slag powder exhibits comparable latent hydraulic properties as ground slag powders. The utilization of the atomized slag powder fraction below 90 μm in concrete approaches the results of formulations containing conventionally processed slag. In this way, the requisite water content in concrete formulations can be diminished, and the concrete formulation's CO2 footprint may be reduced. Consequently, liquid BFS can be directly processed into spherical and amorphous particles through hot gas atomization and the resulting slag powder can be utilized in building materials.Wissenschaftlicher ArtikelBand:45163 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Additive manufacturing of high modulus steels: New possibilities for lightweight designThis work demonstrates the feasibility of fabricating bulk nanostructured high modulus steels in-situ by additive manufacturing. This ideal match of novel processes and alloy concepts opens up new pathways for lightweight design by producing light, stiff, strong and ductile components with minimal geometric restraints. On the example of an Fe – Ti – B alloy, a conventional processing sequence of melting and casting pre-alloys, gas-atomisation and laser powder bed fusion (selective laser melting) led to finely dispersed metastable particle and matrix phases. A simple annealing step transformed them into the desired equilibrium constituents of ductile ferrite (matrix) and light and stiff TiB2 (particles), with only minimal changes in particle size (about 20–150 nm in diameter) and distribution (mainly on the matrix grain boundaries). This nano-scaled composite structure promises an extremely attractive property profile, i.e. an increased stiffness/ratio at elevated strength and without deteriorated ductility. However, the not yet optimized parameters of the laser fusion process led to the formation of few pores and cracks, which prevented the complete assessment of the property profile of the manufactured samples. Material and processing strategies for the further development of this promising lightweight design approach – including the suitability of other powder metallurgy processing routes – are outlined and discussed.Wissenschaftlicher ArtikelBand:3218 33 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Impact of process flow conditions on particle morphology in metal powder production via gas atomizationAdditive manufacturing processes as for instance selective laser melting or electron beam melting are becoming more common and just turning into standard manufacturing processes for metal components. Nevertheless, these processes are still new compared to classic powder metallurgy manufacturing routes such as pressing and sintering. Hence not all necessary requirements for the powders in use are fully known yet. This makes an increase in control of the powder properties a crucial task to achieve. To reach this goal one must understand the different influences on the powder production process from the beginning of the whole production route. In this work, the influence of the spray chamber flow on the particle morphology is examined. The nozzle system used to produce the metal powders is a close-coupled atomization system with a convergent-divergent gas nozzle configuration. The particle morphology as well as the particle size distribution have been analyzed to examine the influence of the atomization gas flow compared to an additional use of a coaxial gas flow. To review the changes of the flow patterns, computational fluid dynamic simulations have been performed. The particle trajectories were calculated to assess the change in particle behavior as well. Atomization experiments have been conducted with an AISI 52100 (1.3505) steel in a small batch atomization plant to evaluate the influence of the change in flow on the particle size distribution and circularity. The experimental results show that a use of additional coaxial gas leads to an increase in particle circularity up to 10% for relevant particle sizes. An approach for the quantification of satellite occurrence is given by examination of the shift of the particle size distribution to smaller diameters.Wissenschaftlicher ArtikelBand:31Heft:182 119 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Porosity and microstructure of steel tubes spray-formed by close-coupled atomizer(Elsevier, 2020-02); ; ; ; Close-coupled atomizers (CCA) can be used to reduce the porosity of spray-formed deposits compared to free fall atomizers (FFA), possibly due to smaller size and higher velocity of the atomized droplets. Previous studies on spray-formed AISI 52100 (100Cr6) tubular deposits show that CCA leads to less porosity in the inner and outer surface regions of the tubular deposits. However, there are very few investigations on the thermal profiles of the spray-formed deposits and on the influences of process conditions during spray forming via CCA. To provide insight into the thermal profile of the deposits, in this study in-situ measurement of the deposit surface temperature is performed by a two color pyrometer and the substrate temperature is measured by means of thermocouples. The porosity and microstructure of the spray-formed deposits under various process conditions are investigated by means of optical microscopy and image analysis. This investigation shows that the deposit thickness has a higher influence on the deposit surface temperature than the gas to melt flow rate ratio (GMR). Higher deposit temperature results in lower porosity and larger grain size. Moreover, the deposition positions on the deposit length has an influence on the porosity. The porosity in the vicinity of the substrate is higher at the deposit end position than the deposit start position. Finally, the present study suggests an optimal deposit surface temperature range for spray forming of highly dense tubular deposit by CCA.Wissenschaftlicher ArtikelBand:27618 12 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Reducing cohesion of metal powders for additive manufacturing by nanoparticle dry-coating(Elsevier Science, 2021-02); ; ; ; Additive manufacturing processes, such as laser powder bed fusion, require steady powder processing but often exhibit poor flowability and low powder bed densities. Reducing the attractive Van-der-Waals force through nanoparticle coating can enhance initially poor flowability. We investigated the effect of dry-coating nanosized SiO2 on gas-atomized CoCrFeNi powders containing different amounts of particles < 20 μm with respect to nanoparticle concentration and mixing time. The dynamic angle of repose of a 0–90 μm powder reduced 50% and bulk powder density increased 30% with nanoparticle concentrations up to 0.153 wt.-%. The granular Bond-number was correlated with the powder flowability and porosity. The effect of mixing time was investigated with mixing two fractions 20–90 μm and 0–90 μm at a constant nominal nanoparticle surface area coverage of 128% for 2 to 1440 min. Short mixing times improved the flowability, while extensive mixing resulted in nanoparticle reagglomeration and deteriorated flow.Wissenschaftlicher ArtikelBand:379100 160