Ulrich HolländerLeibniz Universität Hannover · Institute of Materials Science
Ulrich Holländer
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Publications (46)
Hot stamping is a process for the production of ultra-high-strength components used in the automotive industry for passenger protection. In this process, cut blanks are heated in a roller hearth furnace, which is operated with gas, to approx. 950 °C in 8 to 10 min and then formed and quenched in a water-cooled tool. This extends the yield strength...
The interaction of silane and water is discussed controversially in literature: some authors suggest monosilane and water react kinetically and sufficiently fast enough to remove water, while others state the reaction occurs only at elevated temperatures. This question is of technological interest for the removal of unavoidable water residues in Ar...
In the hot-stamping process, a sheet blank, usually a manganese boron steel like 22MnB5, is heated up to the austenitising temperature in a roller hearth furnace and then formed in a cooled forming tool. This leads to tensile strengths of about 1500 MPa in the formed parts. The components produced in this process are used in particular in the autom...
The heat-treatable steel 22MnB5 is used in hot stamping processes to produce high-strength body-in-white components. In this process, sheet blanks are conventionally heated in roller hearth furnaces and then hot-stamped, whereby strengths of 1,500 MPa can be achieved. Disadvantages of this process are the low plastic deformation of the material in...
In diesem Beitrag werden die Ergebnisse der sauerstofffreien konduktiven Erwärmung für das Formhärten, welches im Teilbereich A04 des Sonderforschungsbereiches 1368 behandelt wird, vorgestellt. Mit der entwickelten Prozesskammer können unbeschichtete Bleche sauerstofffrei, konduktiv erwärmt und beschichtet werden, die in einem miniaturisierten Stoß...
Stainless steel components, such as heat exchangers for energy and air-conditioning technologies are commonly manufactured using nickel-based brazing fillers in vacuum furnaces or continuous furnaces. In vacuum furnaces, nitrogen is commonly used as cooling gas. In continuous furnaces, nitrogen interacts with the parts during the whole brazing proc...
A process of removal of surface oxides from stainless steels AISI 304 and 446 that involves reduction by residual carbon, followed by formation and desorption of carbon monoxide, is studied by investigation of thermal desorption (with QMS) and SIMS. Carbon monoxide desorption is studied as a function of time and temperature by QMS, carbon diffusion...
Engineering under protective atmospheres or in vacuum allows the production of materials and components, where the absence of oxygen is an essential requirement for a successful processing. Ideally, joining or coating of (and with) metallic materials needs oxide free material surfaces, in order to achieve durable joints or coatings. Using the estab...
Stainless steel components, such as heat exchangers for energy and air-conditioning technologies are commonly manufactured using nickel-based brazing fillers, which provide the highest corrosion and oxidation resistance of the resulting joints. However, the use of nitrogen during the brazing process in shielding gas furnaces or as cooling gas in va...
Berichtet wird über Untersuchungen zur prozessbedingten Stickstoffanreicherung der Fügeteile beim Ofenlöten von Chromnickel(CrNi)-Stählen mit Nickelbasisloten und deren Einfluss auf das Korrosionsverhalten und die Lebensdauer der Lötungen. Im Einzelnen wurde hierbei untersucht, welcher Zusammenhang zwischen dem Grad der Stickstoffanrei-cherung und...
Stainless steel components, such as heat exchangers for energy and air-conditioning technologies are commonly manufactured using nickel-based brazing fillers in continuous furnaces or vacuum furnaces. In the continuous furnace, the brazing process is often supported by a protective gas. As protective gas is commonly used nitrogen or mixtures of nit...
Specimens of austenitic AISI 304 and ferritic 446 (contains 1.7 wt.% Al) underwent heat treatments up to 1200 °C in ultrahigh vacuum (UHV) in an analysis chamber with a base pressure of 10⁻¹⁰ mbar and high vacuum (HV) in an industrial vacuum brazing furnace with a base pressure of 10⁻⁶ mbar. The effect of the two oxygen partial pressure ranges on s...
Brazing of stainless steels is commonly carried out using nickel-based brazing fillers, which provide a high corrosion and oxidation resistance of the resulting joints. These brazed stainless steel joints are mostly used for manufacturing of heat exchangers for energy and air conditioning technologies. The joints of the study were produced at tempe...
Stainless steel components, such as heat exchangers for energy and air-conditioning technologies are brazed using nickel-based fillers, which provide the highest corrosion and oxidation resistance of the resulting joints. The brazing process was carried out for the temperatures 1000 °C, 1125 °C and 1150 °C in vacuum furnaces or continuous furnaces....
Objective of the project presented is the development of a joining process for hot working steel components at low brazing temperatures leading to a bond with a much higher remelting temperature. This basically is achieved by the use of a Cu-Sn melt spinning foil combined with a pure Cu foil. During brazing, the Sn content of the foil is decreased...
The paper presents results of wear investigations of thermally oxidised tool steel specimens with an α-Fe2O3 coating. The friction reducing ability of α-Fe2O3 layers on tool steel was shown in previous studies. Reduced friction and the layer’s stability are prerequistes to realise a dry sheet metal forming process that avoids the use of additional...
Different thermal treatments were performed for the anti-oxidation of steel surfaces, and the processes were investigated ex-situ and in-situ by surface sensitive reflection mode EXAFS experiments at the Cr and Fe K-edges. While the samples for the ex-situ studies were heat-treated in a conveyor belt furnace at temperatures between 600 and 900 °C i...
Beside lithium batteries, PEM fuel cells are the most promising strategy as a power source to achieve the targets for introducing and increasing the usage of electric vehicles. Due to limited space and weight problems, water cooled, metallic bipolar plates in a fuel cell metal stack are preferred in motor vehicles. These plates are stamped metal sh...
This article relates to the development of flux-free brazing processes in the temperature range between 650°C and 850°C using nitrogen doped with monosilane (SiH4) as the process gas. The gaseous SiH4 is an agent which is highly reactive, exerts a strongly reducing effect and, when admixed to the inert gas, quantitatively reacts with the existing r...
Different thermal treatments were performed for the anti-oxidation of steel surfaces, and the processes were investigated ex-situ and in-situ by surface sensitive reflection mode EXAFS experiments at the Cr and Fe K-edges. While the samples for the ex-situ studies were heat-treated in a conveyor belt furnace at temperatures between 600 and 900 °C i...
Beside lithium batteries, PEM fuel cells are the most promising strategy as a power source to achieve the targets for introducing and increasing the usage of electric vehicles. Due to limited space and weight problems, water cooled, metallic bipolar plates in a fuel cell metal stack are preferred in motor vehicles. These plates are stamped metal sh...
Subject of this work is the development of a simple and cost-efficient process for conditioning the surface of forming tools for deep drawing processes in order to minimize friction and wear to a level that dry forming processes without any lubricants will be possible in future. The approach chosen is an oxidative heat treatment of the tool surface...
Im Rahmen des DFG-Vorhabens „Entwicklung und Evaluation von Werkstoffsyste-men für die Herstellung von Reaktionsloten aus Zintl-Phasen-bildenden Legierungen“ wurde eine Radio-Frequenz Magnetron-Sputter Anlage (RF-PVD Anlage) für die alternierende Deposition von Metallen und Erdalkalimetallen (Calcium, Magnesium, etc.) konzipiert und aufgebaut. Dies...
Surface sensitive, reflection mode EXAFS spectroscopy at the Cr and Fe K-edges was used to study the surfaces of stainless steel (EU alloy grade 1.4301 X5CrNi18-10) after different heat treatments. The thermal treatments were performed in a conveyor belt furnace at temperatures between 600 and 900 °C in different gas atmospheres containing inert ca...
A novel method has been developed to process highly filled polymer–particle composites to test samples as braze metal preforms. Polypropylene (PP), low-density polyethylene (LD-PE) and high-density polyethylene (HD-PE) were used as polymer matrices. Two types of nickel-based braze metal microparticles (Ni 102 and EXP 152) were compounded to the pol...
For high volume manufacturing of many stainless steel components, a continuous brazing process using a shielding gas furnace is usually preferred. Regarding the workability of the nickel-based brazes used here, furnace brazing in reducing or inert shielding gas is subject to considerable constraints: On the one hand, the maximum brazing temperature...
Seit den 50er Jahren des 20. Jahrhunderts ist bekannt, dass sich beim Löten mit reinem Kupfer von Stählen unterschiedlichen Kohlenstoffgehalts Stängelkristallite in der Lötnaht bilden. Gelötete Verbindungen mit einem solchen Gefügeaufbau zeichnen sich durch eine grundwerkstoffähnliche Festigkeit aus, wenn die Stängelkristallite die Lötnaht durchdri...
Continuous process brazing in shielding-gas furnaces is tailor-made for manufacturing mass production components by means of brazing technology. Which brazing tasks can actually be carried out by a shielding-gas furnace, depend on many ancillary conditions. In particular these are, besides the component size and joint geometry, the base materials a...
Das Fügen von Aluminiumwerkstoffen ist aufgrund der hohen Sauerstoffaffinität des Aluminiums nach wie vor eine Herausforderung. Insbesondere die Wirtschaftlichkeit des Verfahrens sowie der Verzicht auf Flussmittel beim Schutzgasofenlöten stehen derzeit im Vordergrund aktueller Forschungsvorhaben. Die gezielte Zumischung reaktiver Gase zur inerten P...
In the present work, a new hybrid process is introduced: the gas/solid-transient liquid phase (TLP) bonding. With this process, the filler metal is transported by a gaseous phase to the joining area. The filler metal reacts with the base metal by a metallurgical gas-solid reaction and forms a liquid transition phase, which solidifies isothermally d...
Stängelkristallite werden insbesondere beim Löten von Stählen unterschiedlichen Kohlenstoffgehaltes mit Kupfer beobachtet. Diese aus mit Kupfer durchsetzten Eisen-Kohlenstoff-Mischphasen bestehenden Kristallite wachsen vom kohlenstoffreicheren Fügepartner in das Kupferlötgut. Durchdringen die Stängelkristallite die Lötnaht, so ergibt sich eine grun...
IntroductionBrazing Filler-metal Application by Thermal SprayingElectroplating and Electroless Plating Methods for Brazing Filler-metal ApplicationBrazing Filler-metal Application by PVDSummary and Conclusions
References
This article describes the development of a flux-free aluminium flame brazing process in which the surface is activated for the brazing process by inputting powerful ultrasound into the component. For this purpose, commercially available ultrasonic systems were modified in such a way that they not only withstand the thermal loading in the process b...
Die vorliegende Erfindung betrifft eine Bremsscheibe für ein Fahrzeug, welche mindestens einen Grundkörper (10) aufweist, welcher mindestens partiell im Bereich seiner äußeren Oberfläche eine verschleißfeste Schicht (11) trägt, die als Reibschicht dient, wobei mindestens eine Zwischenschicht (12) zwischen dem Grundkörper und mindestens einer äußere...
Die vorliegende Erfindung betrifft eine Bremsscheibe für ein Fahrzeug, umfassend einen Grundkörper (10), welcher mindestens partiell im Bereich der äußeren Oberfläche eine Beschichtung, umfassend mindestens eine verschleißfeste Schicht (1), trägt, die als Reibschicht dient, wobei die Schichtdicke mindestens einer Schicht der Beschichtung und/oder d...
EinleitungLotapplikation mittels thermischen SpritzensLotapplikation mittels galvanisch/chemischer VerfahrenLotapplikation mittels PVD-VerfahrenZusammenfassung und AusblickLiteratur
Die vorliegende Erfindung betrifft eine Bremsscheibe (9) für ein Fahrzeug, umfassend einen Grundkörper (10), welcher eine mindestens im Bereich der äußeren Oberfläche verschleißfeste Schicht (11) trägt, die als Reibschicht dient sowie einen Bereich aus einem Material zur Haftvermittlung zwischen dem Grundkörper und der mindestens einen verschleißfe...
Brazing-solder systems for the flame and induction brazing of thin titanium components by means of partial heating in air were developed and investigated. In this respect, it was important to protect not only the brazing-solder material but also the substrate from oxygen oxidation and, at the same time, to achieve a good metallurgical bond as well...
The use of modern thermal spraying techniques for filler metal application may offer new solutions for brazing complex metal components without fluxing agents, when the spraying processes are fitted to the requirements of the following brazing process. The necessary coating parameters always depend on the kind of base material, the geometry of the...
The most important factors for the brazing of micromechanical components in MEMS technology (MEMS - micro-electro-mechanical systems) relace to exact positioning of the components, to appropriate surface conditioring, to the heating of a limited legion and to a true-to-contour design of the joints within narnow limits. For this purpose, there is a...
Brazing-solder systems for the flame and induction brazing of thin titanium components by means of partial heating in air were developed and investigated. In this respect, it was important to protect not only the brazing-solder material but also the substrate from oxygen oxidation and, at the same time, to achieve a good metallurgical bond as well...
The effect that metallic molten masses can flow into deep and narrow gaps by capillary action forms the basis of the mould filling mechanism of the micro casting process presented here. Potential applications of "Capillary Action Microcasting" are the minimal invasive surgery (e.g. micromechanical endoscope items, grippers and cutting tools), magne...
