Collaborative Research Center 1368 - Oxygen-free production

Sub-project B04 "Adhesive-based assembly processes in an XHV-adequate atmosphere with deoxidized and oxidized joining partners"

Project leader: Prof. Dr. rer. nat. Wolfgang Maus-Friedrichs, Prof. Dr. Ing. Annika Raatz

Funding phase 1: 01/2020 - 12/2023

Funding phase 2: 01/2024 - 12/2027

Funding body: DFG

Researchers: M. Sc. Philipp Moritz, Dr. rer. nat. Lienhard Wegewitz

The joining technology of adhesive bonding is playing an increasingly important role in assembly technology. In contrast to other joining processes, such as welding or soldering, adhesive bonding enables the creation of hybrid structures, i.e. the joining of dissimilar materials. In an XHV-adequate atmosphere, metals can theoretically be bonded without intermediate oxide layers. This direct bonding offers potential for higher bond strength, new joining partner/adhesive combinations and thinner layer thicknesses. The aim of the sub-project is to gain insights into the technical properties of bonded joints produced in an XHV-adequate atmosphere and with deoxidized joining partners, and to explore the possibilities for new process design derived from this. The challenge with oxygen-free bonding is that, on the one hand, the adhesion mechanisms are influenced by oxide layers and, on the other hand, the setting reaction of special adhesives is slowed down or favored by oxygen or water. The absence of oxygen and moisture in an XHV-adequate environment therefore has a fundamental effect on the properties of an adhesive bond and the bonding process.

Sub-project C01 "Clarification of mechanisms and processes for the deoxidation of material surfaces and their implementation on a laboratory and pilot plant scale"

Project leader: Prof. Dr. rer. nat. Wolfgang Maus-Friedrichs, Dr. rer. nat. Sebastian Dahle

Funding phase 1: 01/2020 - 12/2023

Funding phase 2: 01/2024 - 12/2027

Funding body: DFG

Supervisor: B.Sc. Maria Argurusi

The deoxidation of the surfaces of semi-finished products is an essential part of oxygen-free production. The elucidation of the mechanisms that mediate deoxidation is also an important basis in project areas A and B and when working with oxide-containing semi-finished products. The project is therefore investigating the mechanisms that can be used to deoxidize semi-finished products. Both the thermal and the plasma-chemical reduction of oxides of the construction materials iron, copper, aluminum and titanium, which are essential for the SFB, are addressed. Based on fundamental investigations of the mechanisms, reaction kinetics and the processes involved, a description of thermal and plasma-chemical deoxidation will be formulated. In the next step, this knowledge will be transferred to the pilot plant scale, where it will be validated and the description suitably extended. This should enable the results to be used in the other sub-projects, particularly in project areas A and B. In addition, joint questions will be addressed there by simulating the observations of the other sub-projects in model experiments. Only through close cooperation within the CRC can further effects from the observations be clarified and fundamentally described.

Sub-project C02 " Powder deoxidation"

Project leader: Prof. Dr. rer. nat. Alfred Weber

Funding phase 1: 01/2020 - 12/2023

Funding phase 2: 01/2024 - 12/2027

Funding body: DFG

Metallic powders are used in numerous manufacturing processes (e.g. joining processes, additive manufacturing, coating) as additive and base materials whose oxygen-free processing planned in this CRC requires prior deoxidation. In this project, gas-borne particles are to be freed from their oxide layers by plasma-induced chemical processes in reducing gases (hydrogen and silane in inert gas). In order to realize an easily scalable process, the deoxidation is to be carried out in a fluidized bed. In contrast to entrained-flow reactors, the fluidized bed allows higher concentrations and residence times while maintaining controlled conditions. Deoxidation is carried out in a circulating fluidized bed in order to repeatedly pass the particles to be deoxidized to and or through the reactive plasma zones. After successful deoxidation, the particles are discharged from the fluidized bed via a cyclone separator and prepared for dispatch or fed directly into a corresponding further processing step.

Subproject S01 "Central Analytics"

Project leader: Prof. Dr. rer. nat. Wolfgang Maus-Friedrichs, Dr. rer. nat. René Gustus

Funding phase 1: 01/2020 - 12/2023

Funding phase 2: 01/2024 - 12/2027

Funding body: DFG

Supervisor: M. Sc. Maik Szafarska

The subproject Central Analytics serves the uniform analysis and description of the surfaces and interfaces of the various subprojects in the CRC. The aim of the subproject is to establish and provide a central analytical infrastructure with the task of supporting the other subprojects of the SFB1368 in the elucidation of project-relevant surface and interface processes. The scientific core interest lies in particular in the elucidation of the fundamental mechanisms of the interaction of the joining partners, the processes during mechanical treatments under oxygen-free conditions and the investigation of the diffusion of metals into other metals in oxide-free contact. The establishment of a central infrastructure for the analysis of surfaces and interfaces is intended in particular to ensure the reproducibility and comparability of measurements required for the discussion of results and the creation of models. The Central Analytics sub-project is responsible for the planning, execution and evaluation of the measurements and also organizes the transport of samples between the sub-projects. In all process steps, from planning to documentation of results, Central Analytics is in close contact with the commissioning sub-projects. In order to ensure the oxygen-free transport between the XHV-adequate laboratory chambers and the respective measuring equipment of Central Analytics, which is urgently required for the cooperating sub-projects, a suitable sample transport system is to be set up. Sample transportation is divided into two phases. In phase 1, the samples to be analyzed are transported to the Central Analytical Unit in an XHV-adequate atmosphere using suitable transport containers and transferred to a transfer chamber on site. In phase 2, the samples are then transferred to the respective measuring equipment using special transfer systems. Before the start of regular measurement operations, a detailed validation of the planned sample transport is carried out. For this purpose, well-defined oxide-free control samples are prepared, which pass through each phase of the sample transport. As soon as it is ensured that no oxygen contamination occurs during sample transport, the sample transport system is used in regular operation.

Subproject T01 "Use of Dielectric Barrier Discharge (DBD) plasmas in longitudinal seam high-frequency welding to realize oxygen-free production conditions"

Project leader: Dr.-Ing. Henning Wiche

Funding period: 01/2024 - 12/2026

Funding body: DFG

Researcher: M.Sc. Viktor Udachin

Weld seam defects in the form of oxide inclusions are a major production problem in longitudinal high-frequency welding. This is the focus of the present research project. A plasma treatment unit, designed as a plasma jet, is to be integrated in the heating section with the additional introduction of reducing shielding gas mixtures such as argon/silane or argon/hydrogen to deoxidize the strip edges. The plasma activates the gases and thus enables effective deoxidation. The working gas flow provides a local XHV-adequate atmosphere during the welding process. The design of the plasma as a dielectric barrier discharge (DBD) prevents the additional introduction of thermal energy into the process. The basic principles for the use of DBDs for metal deoxidation in an oxygen-free atmosphere were successfully developed on a laboratory scale in sub-project C01 during the first funding period and are used there and in other sub-projects of the CRC for deoxidation. In addition to this objective, the effects on the welding process are also to be analyzed in detail. In high-frequency welding, for example, there are three characteristic welding gap shapes depending on the energy input, whereby a spatial separation can occur between the strip edge convergence point and the welding point. The processes in the resulting welding gap are complex. In particular, the stochastically occurring arc bridge formation at the convergence point and the molten pool ejection in the welding gap due to the electromagnetic fields acting as a function of the arc frequency at the strip edge convergence point pose challenges for process control. Any positive or negative influences of the plasma must be fully investigated. By implementing an oxygen-free production process, the application partner aims to improve the weld seam quality (characterized by the achievable notched impact strength), increase the process yield and expand the product portfolio. In addition, the findings on targeted process-integrated deoxidation using plasma jets, together with the experience from sub-project C01, can be used as a knowledge base for other sub-projects of the CRC.