Completed Research

Title: Development of a production solution for novel coated welding consumables and integration into an existing welding process Funding: ZIM Duration: 07/17 - 09/19 Abstract: The project investigated PVD coatings of welding wire electrodes and their influence on weld seam properties and processing properties in the welding process. By a systematic analysis of the influence of monoelement coatings of different layer thicknesses, multi-component and multilayer coatings could be developed in the further course of the project. In the weld metal an average yield strength of up to 1100 MPa at an impact energy of 37 J was achieved. Effects on the arc length could be documented with the aid of a high-speed camera. In order to achieve scientifically reproducible results, the welding wire electrodes for the welding tests carried out were coated with a PVD system that meets the industrial standard. In addition to the development of various coating systems, a prototype of a plant for continuous coating of wire electrodes was developed and built. The speed of the industrial wire drawing process cannot be reached with the coating plant, so the idea was pursued to coat the wire as a pre-product with a larger diameter and to manufacture the final product from it. The serving of niche markets with extraordinary demands on the metallurgy of a weld metal is conceivable due to the developed continuous wire coating and the associated flexibility.

Title: Hybrid Composite Forging as a Joining Process for Solid Aluminium Parts and Steel Sheets Funding: DFG Duration: 04/17 - 08/19

Abstract: The aim of the proposed research project was the development of a hybrid composite forging process for the material combination steel/aluminum. In a first process step, a solid aluminium part was to be formed on a steel sheet and a material-closed connection of the two elements was to be created by the forming process. The material connection was to be achieved by using zinc as the brazing material, which is melted in the process and then solidifies again. In a further step, the hybrid element was further formed in order to analyse the suitability of the connection for further processing. The process was mapped in a model which shows the joint quality of the elements as a function of the process parameters of the forming.

For this purpose, the ISAF determined the optimum joining parameters for the combination of sheet steel/solid aluminium part with the aid of zinc filler metal. For this purpose, a test set-up was developed by means of pressure tests in the furnace. Within the scope of these tests, various process parameters were varied in order to characterise their influence on the joining joint. These included the temperature, pressure, time and the surface quality of the materials used. Based on these test results, the adhesion processes as well as the behaviour of the materials were analysed in order to take the findings into account when designing the combined forming and joining process. It was possible to produce a joint which only shows isolated brittle Fe-Al phases. Strengths of 2.1 kN were achieved.

The second step was the implementation of the determined process field into the forging process and was pursued by IPH. Subsequently, a possible parameter field was determined, supported by FEM simulations. In particular, the setting of the desired process parameters from the model tests in the joining zone was to be achieved by specific variation of the forming parameters in the FEM simulations. Following the FEM simulations, experimental forging tests were carried out with the simulated forming parameters. In order to investigate the possibility of further processing of the hybrid components produced, they were further formed by a sheet metal forming process under load on the joint. The results showed on the one hand a defined process window in which the production of composite hybrid components appears possible, and on the other hand the presence of composite hybrid forged and sheet metal formed components.

In addition to the tests, the correlations between the joining quality and the forming parameters were determined. For this purpose, the manufactured components were examined with regard to their mechanical and metallographic properties, both after joining and after sheet metal forming. On the basis of these results and the analysis of the measurement and simulation results, an overall model was then created that relates the input parameters to the quality of the joint.

Title: Load-bearing arc brazed joint of high-strength steel sheets under metallurgical and geometrical aspects Funding: DFG (joint proposal) Duration: 12/13 - 11/16 Abstract: According to the current state of research, there is a high divergence between the application possibilities and the real use of arc brazed joints. This is due to the fact that at present the understanding of the failure of arc brazed thin sheet metal joints, under static and cyclical load, is not yet sufficiently available to allow a load-compatible design of the joined components. This fundamental understanding of the interrelationships between the geometric design of the brazed seam, especially at the lap joint, and its local metallurgical composition on the joint properties is to be developed within the framework of the research project. The locations where an arc brazed lap joint usually fails are known for both static and cyclical loads. However, the exact local processes and failure mechanisms could not be described sufficiently so far. Therefore, the aim of the planned research project is to investigate the main factors influencing the static and cyclical strength of the joint in detail in order to draw conclusions about the underlying failure mechanisms. This will enable a more reliable statement about the causes of failure. The aim of the research project is therefore divided into two subgoals. Subgoal 1 is to realize a brazed joint which is characterized by a high static strength at the base material level and at the same time still good cyclic strength. Subgoal 2 is to create a joint which has a very good strength under cyclic loading, significantly higher than the 25 % of the tolerable load of the base material that has been possible up to now, while still having good static strength. High reliability and reproducibility of the results with low scatter is an integrative target requirement for both mentioned subgoals. In this way, a more reliable and stronger connection is achieved with regard to the predominant load.

Title: VentiWear: Tailor-made wear protection systems for the lightweight structural design of industrial fans Grant: ZIM Duration: 03/13-03/15 Abstract: Industrial fans are subject to massive wear and tear during their operation, making it necessary to carry out regular technical inspections and maintenance and repair work One possibility to reduce the occurring wear is the use of prefabricated wear plates, which are provided by specialized suppliers. This conventional solution, however, allows few material variants for high-speed large fans, which means that certain required properties of the armouring are not available. Furthermore, the hard phase morphology cannot be realized by the coating processes used so far, as it is required for erosion wear caused by fine particles. Further disadvantages are that the structural materials are often not directly coated in the initial armouring, as they are thermally stressed to such an extent by the available conventional coating processes such as plasma powder cladding, open-arc processes and metal shielding gas processes that their original mechanical-technological properties are irreversibly lost and therefore cannot be considered as a load-bearing cross-section in the computational design.

Within the framework of the research project, wear protection systems suitable for the stress and coating process were therefore developed for the build-up welding of highly stressed structural components made of high-strength and ultra-high-strength fine-grained structural steels using modern, controlled (low-energy) welding coating processes for lightweight fans. In addition to a massive increase in the service life (> 340%) of the coatings compared to the uncoated base materials, a considerable reduction in the fan weight, i.e. the weight of the coated individual parts by > 20% was achieved.

Title: Development and characterisation of a SOFC stack with single cells electrically connected in parallel 'El PaSO' Funding: AiF/DECHEMA Duration: 12/2012 - 02/2015

Abstract: Due to their high efficiency and fuel flexibility, SOFC fuel cells are considered to be the hope for future energy supply in stationary and mobile applications. Besides the high costs, problems of lifetime and degradation are currently a major obstacle for a rapid market entry. Some parameters influencing stack degradation are directly related to the standard series connection of individual cells. For example, electrically insulating seals must be used, for which glass solders are usually used. However, these are usually not able to meet the demanding requirements during operation (temperature range, thermal cycles) for the required operating time. Furthermore, the series connection means that a gentle operating point is defined by the weakest individual cell. Monitoring of all individual cell voltages is not provided for in practical systems due to the high effort involved. As a consequence, the stack operating point is only controlled via the total voltage. The operator is therefore virtually "blind" with regard to the state of the individual cells. This creates the danger that the weakest cells are operated below their limit voltage and thus degrade further. This self-amplifying mechanism is inherently connected to the serial connection as long as no single cell monitoring is performed. The stack concept proposed here with parallel connection of the individual cells promises advantages. Since all cells are operated at the same voltage, the operating status of all cells can be determined and monitored by simple and cost-effective measurement of a single voltage. Critical operating states can thus be reliably detected and suitable countermeasures (e.g. lowering the load current) can be taken at an early stage. At the same time, the individual levels no longer have to be sealed electrically insulated, so that soldering and welding processes with metallic sealing materials can be used for sealing. The parallel concept is also advantageous in terms of reliability: While in the case of series connection, the failure of one cell leads to the total failure of the stack ("fairy lights effect"), only the available power is reduced in the case of parallel connection. Two different design variants for SOFC high-temperature fuel cells were developed in the project: An all-ceramic concept with a cell housing made of 3YSZ, which was joined using Reactive Air Brazing (RAB), and a metallic housing made of Crofer 22 APU, which was laser-welded.

By taking into account the respective component tolerances, their different coefficients of thermal expansion and chemical aspects of the material pairings used, it was shown that the concept of the parallel-connected double cell with two electrically connected single cells is viable and promising as a repeating unit. The connection of ceramic-ceramic and ceramic-metal pairings by means of RAB could replace the glass solders which tend to become brittle. This would also increase the lifetime of such stacks.

The performance and robustness of the ceramic stack design was confirmed in several setups and a 1200-hour long-term test. Analyses after the end of the tests showed that the RAB connection is suitable as a gas-tight connection between metal and ceramic components, but still show further potential for improvement of this new stack concept.

Title: Development of welding elements for stud welding with rotating arc for the substitution of weld nuts Funding: ZIM Duration: 03/13-02/15 Abstract: The aim of the joint project was the systematic further development of the MARC (Magnetic-Rotating-Arc) welding process developed by the joint partner HBS in the direction of an application for processing weld nuts, comparable to DIN 929 and DIN 934, which are used millions of times in medium-sized industry, for example in switch cabinet and housing construction. In its previous form, the MARC process already offered numerous advantages and unique selling points in the stud welding sector, but always had to be adapted to the respective welding element. However, this procedure, which was largely based on empirical experience, was not sufficient to adapt the process to a spectrum (M6 - M12) of non-rotationally symmetrical parts for sheet thicknesses of 1-5 mm which is necessary for a successful market positioning. The project served to develop this knowledge with the aim of

1. development of welding elements of suitable geometry 2. further development of equipment technology and qualification of the welding process

In a program accompanied by statistical test planning, element geometry and parameter fields for the safe welding of nuts in accordance with the requirements were developed and are made available to the users by the alliance partner.

Title: Development of a NT-PEM-FC with twisted membrane plate plane (ProPa-FC) Grant: ERDF Duration: 01/13- 08/14 Abstract: The objective is the development of a parallel low-temperature PEM fuel cell (NT-PEM-FC) with vertically arranged membranes and horizontally arranged gas distribution plates in the temperature range 60°C - 80°C based on a novel multi-component polymer plate. Using a small stack, the feasibility of the concept and the production technology will be tested, the operating behaviour of the fuel cell will be investigated and compared with fuel cells which can be described as state of the art. The multi-component plastics are characterized by the fact that they consist of an electrically conductive core and an insulating frame, which makes new concepts and improved fuel cells possible. For this reason, a NT-PEM-FC with a conventional structure is being developed for comparison, in which this new multi-component plastic is also used.

Title: Investigation of liquid metal embrittlement by zinc during welding of novel high-manganese steels Funding: DFG Duration: 01/12 - 12/14 Abstract: The development of innovative materials is being consistently pursued by steel manufacturers in order to meet the demands of the metal processing industry with regard to diverging properties. In this context, high-manganese steels have been developed which are characterized by very high strength and ductility. During the joining processing of these materials in the surface-treated state, the phenomenon of solder crack formation has been observed, especially when producing mixed joints in combination with ferritic steels. Within the framework of the project, the factors influencing the formation of brazing cracks during the welding of steels with a high manganese content are to be fundamentally analysed. Based on these findings, a joining concept for resistance spot welding will be developed, which should enable the production of joints with reduced soldering cracks.

Title: Development of coatings for aluminium bipolar plates for high temperature PEM fuel cells with flow-optimised channel structures (AlBB) Funding: ZIM Duration: 02/12- 01/14

Abstract: The aim of the joint project is the utilization of so far not usable aluminium bipolar plates in the high temperature PEM range by suitable coatings. While the previous expensive and very brittle graphite compound materials are able to withstand the demanding conditions of high temperatures, phosphoric acid and high current, the material is now to be replaced by cheaper aluminium in order to make use of the better material properties such as conductivity. The resulting higher efficiency combined with the use of more favourable production methods is the reason for this novel approach. The aim is to develop a coating material that is extremely corrosion-resistant on the one hand and has a low electrical contact resistance on the other. The greatest challenge is the high coefficient of thermal expansion of aluminium compared to coatings, which nevertheless must not show any damage. Among other things, the adhesion of coatings can be improved by design, which is why the bipolar plates are optimized simulatively.

Title: Grain refinement of aluminium casting alloys by powder metallurgically produced master alloys Funding: ZIM, Berlin Duration: 12/2009 - 10/2011 Abstract: The aim of the joint project is to make AlCu alloys usable for an application in complex and thermomechanically highly stressed components through improved castability by means of new grain refiners. Within the scope of the project, a system is to be developed to adapt grain refiners specifically to the respective aluminium alloy systems in order to achieve improved effectiveness. These particles are to be supplied via powder metallurgically produced master alloys, which are produced by mechanically alloying the particles with a carrier material and subsequent consolidation. After the master alloy is added to the aluminium melt, it dissolves, whereby the higher-melting particles contained therein are dispersed in the melt and serve as heterogeneous nuclei for solidifying phases. The effectiveness of the master alloys should be reflected not only in improved castability but also in the mechanical properties. Alternative manufacturing processes for the grain refiners are also to be investigated, which have the potential for series production. Finally, a process chain for production is to be defined which will enable efficient and cost-minimal production. In addition to the TU Clausthal, an industrial company is also involved in this research project.

Titles: Nano- or quasi nanostructured coatings for abrasive and erosive loads - technology consisting of filler material, energy supply and burner system SUNA; technology of coating, execution and evaluation of tribological tests, determination of process parameters Funding: ZIM, Berlin Duration: 12/2009 - 11/2011 Abstract: According to estimates of the Gesellschaft für Tribologie (Society for Tribology), wear and tear causes annual damage with a total volume of about 35 billion euros in the German economy alone. If signs of wear are unavoidable due to process conditions, appropriate wear protection layers have to be provided or applied to the functional surfaces of the respective plants, machines and devices in order to increase the economic efficiency. Hard alloys based on nickel and cobalt, for example, are available for this purpose, but they are not competitive with iron-based alloys in terms of the ratio between service life and costs, so that their use for cost-effective wear protection is considered particularly promising. The main factors influencing the wear behaviour of materials, apart from the tribological system involved, are, in addition to the type and arrangement, the size and distribution of the wear-retarding hard phases in the metal matrices. These properties are dependent on the alloy composition on the one hand, and on the other hand also on the coating process-specific characteristics, such as energy input, solidification cross section, cooling rate and mixing of the base material, and can be manipulated in a targeted manner with modern alloying and process technology measures. Particularly in the case of abrasive-erosive stress caused by fine and ultra-fine particles, finely structured microstructures are decisive carriers of wear protection, so that nanostructures in iron-based alloys meet the requirements for low-cost and effective wear protection, especially in this field of application. Alloying costs can be further reduced by alternative hard phase formers, whereby the claim is to have at least an equivalent property profile to the conventional hard phases. The provision of usable and tribologically evaluated, novel, highly wear-resistant (quasi-) nanostructured hard alloys based on iron for thermal spraying and selected build-up welding processes, combined with a novel burner system for PTA processes and an adapted energy supply system are the main objectives of this research project. This strongly practice-oriented task has a fundamental character, since the theoretical bases known up to now for microstructure formation in the area of the desired alloy composition are still insufficient, so that the path to the finished component necessarily leads through an extensive test phase. In addition to Clausthal Technical University, another university and two industrial partners are involved in this research project.

Title: Investigations on the production of partial claddings from Ni-based alloys using the Cold-Metal-Transfer-Process (CMT) Funding: AiF/DECHEMA Duration: 01/2010 - 12/2011 Abstract: The aim of this project is the investigation of claddings produced with the CMT process from the material group of corrosion-resistant nickel-based alloys. The aim is to develop process parameters that allow a reliable and reproducible deposition welding of different nickel base materials, such as alloy 59 (2.4607) and alloy 686 (2.4606) as well as alloy 625 (2.4831) as reference material. First of all, the influence of different process parameters dependent on the welding consumables, including the variation of the shielding gas, layer thickness, deposition rate on bead shape, fusion penetration, mixing and microstructure morphology is investigated. By determining the mechanical-technical properties, e.g. the bending strength and the course of hardness, the generated material composites are to be qualified in detail. Based on the results obtained, the process control of the different materials in defined parameter ranges will then be optimised to produce single-layer coatings with low dilution. The influence of these welding process parameters on the corrosion properties of the produced claddings will be investigated. In addition to the known test methods, in which immersion tests are usually applied, electrochemical test methods for the application for weld claddings of nickel-based alloys on high-alloy steels are modified and further developed within the research project.

title:Production, property analysis and wear behaviour of technical surfaces made of microstructured metallic materials and coatings Funding: DFG/ Bonn Duration: 01/2010 - 12/2011 Abstract: Wear represents a not insignificant damage in the economic balance. For technical surfaces which are subject to high material removal due to non-lubricated abrasive, adhesive or erosive wear, the adjustment of specific material properties is the only possibility to minimize the wear-related removal. The combination of hard and soft structural components with a fine-grained structure and finely dispersed precipitates together with defined manufacturing processes and conditions results in materials and layer structures that are adapted to the wear stresses. Thus the material removal can be limited to a minimum. The application includes the modification of modern coating technologies for the targeted microstructuring of the materials, the qualification of the materials and coating layers with regard to their wear resistance, and the investigation of light metals in order to improve the wear resistance of this group of materials. In addition, the alloys and coating composites are subjected to a metallurgical and mechanical-technical property analysis. Powder-based thermal coating processes such as PTA welding and plasma spraying are used, which are particularly characterised by their high flexibility in terms of powder composition and thermal management. In addition, the process-related advantages of hot isostatic pressing are used to develop wear-resistant coatings for extreme loads. TP 3: Welding generation of wear protection layers with finely dispersed, directed hard phase intercalation For the wear resistance of a wear protection layer made of hard alloys, the statistical distribution of the hard material phases according to size, shape and arrangement has a significant influence. In case of attacks of granular materials, it is necessary that the distance from hard phase to hard phase is smaller than the average diameter of the abrasive particles. In addition to the line spacing, a directional arrangement of elongated hard phases can also improve the wear resistance. The generation of these defined microstructure morphologies by specific interventions of the temperature-time cycles during the generation by PTA-welding of the coating layers is investigated. TP 4: Model wear investigations on different coating systems as a function of the production-related characteristics Wear is a system parameter that depends on the overall mechanical-physical behaviour of all components involved and their mutual influence, as well as on the effective wear mechanism. On the basis of selected model tests, the correlation between microstructure structure and wear behaviour will be investigated qualitatively and quantitatively. Of special interest are the expected differences in the abrasion behaviour between the different model tests simulating different wear mechanisms. Involved partners: TP 1: Production and properties of novel coatings with Fe-based pseudo alloys by hot isostatic pressing LWT, RUB Bochum TP 2: Analysis of the fatigue behaviour of coated materials with high wear resistance IWW, TU-Clausthal TP 5: Thermal spraying of PTA material systems IWW, TU Chemnitz TP 6: Plasma anodizing of thermally sprayed aluminium layers to produce wear resistant edge layers IWW, TU Chemnitz

Title:Generation and joining of SLM-generated components made of hard metal Funding: AiF/DVS Duration: 01.05.2010 - 30.04.2012 Abstract: In tool mould making and mechanical engineering wear and tear of tools and moulds occurs and leads to considerable financial disadvantages due to repair as well as downtimes of the components. Currently, two main methods are used to counteract the wear. The first possibility is to apply a wear protection layer to the corresponding components. Depending on the process, this has a negative effect on the base material and requires considerable reworking. A second possibility is to design the components completely from wear-resistant materials. However, this is very cost-intensive, since the hard machining required for this is very complex. A third possibility, which was examined more closely in the project, is the production of wear parts made of hard metal by a generative SLM (Selective Laser Melting) process in order to join them to inexpensive metallic basic bodies. The advantage of the SLM technology is the possibility to create a functional component via a generative process. Even slight variations of the process parameters can lead to very different properties during the production of SLM components. For joining laser-generated hard metal products with each other or with substrates, brazing and high-temperature brazing (e.g. furnace brazing, plasma brazing (Plasmatron)) of these material combinations is considered a useful joining process. At the end of the research project, a demonstrator component produced with the knowledge gained and matched in the PbA will be joined and tested under real conditions. The approach pursued by the BIAS and ISAF of the material-closed connection of wear bodies and easily machinable basic bodies offers not only a technologically innovative approach but also an economic potential, especially for the kmU strongly represented in the field of tool and mould making.

Title: Investigations into the production of partial claddings of Ni-based alloys using the Cold-Metal-Transfer-Process (CMT) Funding: AiF/DECHEMA Duration: 01/2010 - 03/2012

Abstract: The aim of this project is the investigation of claddings produced with the CMT process from the material group of corrosion-resistant nickel-based alloys. The aim is to develop process parameters that allow a reliable and reproducible deposition welding of different nickel base materials, such as alloy 59 (2.4607) and alloy 686 (2.4606) as well as alloy 625 (2.4831) as reference material. First of all, the influence of different process parameters dependent on the welding consumables, including the variation of the shielding gas, layer thickness, deposition rate on bead shape, fusion penetration, mixing and microstructure morphology is investigated. By determining the mechanical-technical properties, e.g. the bending strength and the course of hardness, the generated material composites are to be qualified in detail. Based on the results obtained, the process control of the different materials in defined parameter ranges will then be optimised to produce single-layer coatings with low dilution. The influence of these welding process parameters on the corrosion properties of the produced claddings will be investigated. In addition to the known test methods, in which immersion tests are usually applied, electrochemical test methods for the application for weld claddings of nickel-based alloys on high-alloy steels are modified and further developed within the research project.

Title: Prototype development of a novel high-temperature fuel cell (H2-HTFC) Funding: N-Bank Duration: 01/2008 - 12/2010 Abstract: The aim of this project is the production of a functional fuel cell stack based on simple and inexpensive components, which has the potential for mass production The novel membranes used in these fuel cells shall be composites with polymer electrolyte membranes, which can be used without complex humidification regimes in the temperature range of 100 to 160 °C at high efficiency. The fuel cell is based constructively on a graphite polymer, symmetrical base plate. The flow channels are developed and optimized at ISAF with the help of flow simulation. The aim here is to realistically reproduce the electrochemical processes in a HT-PEM. Due to their geometries, the assembling of stacks will ensure a safe gas flow and gas tightness of the system in equal measure, while at the same time providing high power density. Furthermore, the use of thermally stable membranes with sufficient to good conductivity and high thermal load capacity leads to increased efficiency due to higher operating temperature and less effort by humidifying the fuel gases. If necessary, the polymer membrane should simultaneously act as a gas seal, which would result in further potential savings.

Title: Process and Material Investigations for the Welding Production and Qualification of Components made of Multiphase Steels Funding: DFG / SFB 362 T6 Duration: 10/2007 - 09/2010 Abstract: The consideration of the entire process chain in sheet metal processing is an essential prerequisite for the improvement of the strength assessment of sheet metal components. Especially when using multiphase steels, the strength adjustment also plays an important role with respect to the utilization of the bake hardening potential. Within the framework of the subproject applied for, the welding process simulation on the basis of the thermal effect of the process is to be tested and evaluated both experimentally and numerically with commercially available programs on thin sheet structures made of multiphase steels and made assessable.

Title: Design systematics for the development of high-strength, locally adapted structures with the help of Finite Element Design (FED) Funding: DFG / SFB 675 TP C7 Duration: 07/2008 - 06/2010 Abstract: The potential of locally modified structures can be used most effectively in practice if the designer has access to this knowledge already in the concept phase of the product development process. Therefore, the aim of subproject C7 is the development of a design system that is based on the finite component element as the smallest design unit (FED-Finite Element Design). Thereby the potentials of local property optimization are considered and the interactions between material, manufacturing and design are shown. This methodology represents a novel approach to solving complex design tasks in a way that has not been used before. In the first phase of the project, the development of the new design system (FED) with multi material design components by joining will be started and validated.

Title: Material-adapted process control in the welding processing of locally consolidated materials for the production of nodes and structures Funding: DFG / SFB 675 TP B5 Duration: 07/2008 - 06/2010 Abstract: The importance of welding production for product manufacturing has in the past led to a constant new and further development of welding and joining processes. This tendency has continued in the last decades. This is due to the challenges associated with the processing of modern steels (e.g. dual-phase steels, TRIP steels, martensite-phase steels) and light metal alloys. With the planned provision of new material potentials in the Collaborative Research Centre 675 through the targeted adjustment of local properties on modern lightweight materials, new challenges are again being posed to welding technology production. In the simplest case, the thermally unstable local properties of the starting semi-finished products must be maintained. At the same time it is possible to use the joining process itself to improve the structural and component properties. High-frequency welding offers excellent potential for achieving the desired transfer of local property adjustments to the finished component by initiating suitable material reactions. On the one hand, the HF welding process has a strong local limitation of the thermal load on the base material due to the skin and proximity effect. On the other hand, the process-specific coupling of heating and forming (upsetting process) offers the possibility of significantly improving the properties of the weld seam. Conceivable here is the grain refinement of the weld seam structure to increase strength and ductility, comparable to a thermomechanical treatment during the final forming process when rolling steel strips, or the deliberate introduction of plastic deformation. A systematic investigation of the qualitative and quantitative possibilities for the generation of defined material reactions in HF-welds is therefore the aim of the process- and plant-related subproject B5.

Titles: Low-heat joining - Fabrication and fatigue strength of brazed locally strengthened structures Funding: DFG / SFB 675 TP C3 Duration: 07/2006 - 06/2010 Abstract: In order to use locally adapted materials for various applications even under cyclic loading, a fatigue life calculation concept is required for dimensioning and material adapted processing for process-safe manufacturing. For this purpose, the interaction of brazing parameters, brazing systems and pre- and post-treatment is investigated and a manufacturing concept is developed. In addition, a service life calculation concept for cyclically stressed brazing seams on locally property-adapted materials is being developed and adapted to brazed component-like structures.

Title:Investigations into MSG flat-wire welding of aluminium materials Promotion: AIF 13.141 B Duration: 03/02 - 02/04

Abstract: The aim of the research project was the development of process engineering prerequisites for the welding joining of aluminium materials with flat wire electrodes. Detailed investigations were carried out on process stability and material transition in the pulsed and spray arc as a function of geometry and position of the joint. Furthermore, the weldability of different alloys, the application possibilities of special shielding gas compositions and the corrosion resistance of the joints were determined by varying the process parameters. Furthermore, the properties of the welded joints were checked by metallographic methods and by means of mechanical-technological tests depending on the base materials, additives and welding process conditions used. The results of the investigations complemented each other to form a production technology suitable for industrial use and should thus contribute to a rapid introduction into operation.

Title:Metallurgical studies on the development of Cu- and Ni-based additives for the plasma powder soldering process Promotion: AiF Duration: 02/02- 01/04

Abstract: In addition to new materials, lightweight construction requires innovative joining techniques, since improved material properties can only become effective if the joining technology allows the transfer of material properties to the entire structure. At the same time, the importance of corrosion protection increases due to decreasing sheet thicknesses. Therefore, techniques are required with which it is possible to produce joints that are safe to manufacture, economical, low in heat, distortion and stress, and with sufficient strength. Especially for this purpose, brazing processes offer enormous potential for many design tasks. Due to the achievable mechanical properties of the existing filler materials, however, the areas of application are limited to the joining of deep-drawing steels in low strength ranges. The aim of the research project is to create metallurgical conditions for the plasma powder brazing of surface-refined thin sheets of higher and high-strength steel materials. A further focus of this application is the investigation of the interaction of process energy, powder used and the coating properties of the sheet metal on the diffusion and alloying processes as well as structural changes in the seam and in the base material and the resulting seam properties.

Title:Investigations into the welding processing of silicon-based hard materials to increase wear resistance Funding: AiF Duration: 03/02- 02/04

Abstract: Silicon is of great importance in materials engineering. It is used for deoxidation, alloying and hard phase formation. The application of silicon carbide as a hard material has so far mainly taken place outside of melt metallurgical processes. Silicon carbide is used as an abrasive for high-strength materials. But silicon carbide is also used for high-temperature ceramics in combination with various matrix materials. The first approaches to melt metallurgical processing of silicon carbide have been made with particle-reinforced aluminium. Silicon carbide is also partly used in thermal spray coatings. Due to its covalent bond and its special high-temperature properties (decomposition above 2500°C), silicon carbide could not be processed metallurgically by welding until now. The reactivity of silicon in metallic melts also has a disturbing effect, as the carbide often dissolves in favour of other phases. Due to its high hardness and low density compared to the carbides usually used in welding technology, silicon carbide is particularly suitable for wear protection coatings on light metals. From an economic point of view, the low production costs of silicon carbide compared to other carbides speak in favour of using silicon carbide also in heavy metal coatings. If silicon carbide can be successfully embedded in welding metallurgical coatings without defects, there is a high potential for improving the properties of wear protection coatings and reducing costs. The aim of the project is to investigate the metallurgical behaviour of silicon carbide during welding processing via build-up welding or build-up brazing processes in different matrix materials and to develop suitable coating materials or material systems that are suitable for different substrate materials. Due to the specific properties of silicon carbide - high hardness, low density - light metals are particularly suitable as substrate materials, whereby it makes sense to adjust the melting points between substrate and coating material. Al matrix materials with different alloy contents are therefore used. However, the low production costs of SiC also make it interesting to use SiC in other matrix materials and for other substrate materials. In order to exclude decomposition phenomena of the carbide above 2500 °C as far as possible, self-flowing (low-melting) NiCrBSi or NiBSi matrix materials are therefore included in the investigations, which are widely used for coatings on steel substrates. As welding processes, the plasma-powder process, which guarantees a concentrated heat input with low mixing due to the high energy density in the plasma beam, and the MSG flux cored wire process, which can be used advantageously as a low-cost and uncomplicated coating process, especially under construction site conditions, will be investigated. The application of silicon carbide as a hard material in wear-resistant coatings is expected to lead to specifically lighter coatings which, due to the low manufacturing costs of silicon carbide, are more cost-effective than the tungsten carbide-reinforced coatings used so far.

Title: Seam design and material reactions during electron beam welding of aluminium materials in the atmosphere Promotion: AiF Duration: 03/01- 02/03

Abstract: The aim of the research project was to gain new knowledge about the weld seam design and the material reactions occurring during high-performance welding of aluminium materials with the electron beam to atmosphere (NV-EBW) by means of constructive and metallurgical investigations. The aim was to investigate the extent to which the quality of aluminium welded joints can be improved by seam design and process-related measures. The influence of high welding speeds on the microstructure, the precipitation behaviour and the mechanical-technological properties of the welded joints should be taken into account, since industrial users in particular must use rationalisation potential in the welding cycle times due to international cost pressure. In addition to the determination of realistic ranges for the high welding speeds to be taken as a basis, the metallurgical and materials science processes during the joining process should be investigated and, based on this, concrete specifications and instructions for the design, layout and execution of high-quality joints on these materials should be derived. In the foreground was the task of determining a joining technology adapted to the treatment condition of the base material by means of targeted thermal influencing. Tolerance ranges and process limits were to be obtained. Temperature, dwell time and cooling rate decisively determine the character of metallurgical processes. One focus of the investigations was therefore the clarification of the thermal processes in the area of the weld seam or in the HAZ as a function of the material condition and the process parameters as well as their effect on the mechanical-technological properties of the seam (static strength, hardness, deep-drawing ability). The aim was to gain knowledge about the structure of the microstructure and the precipitation behaviour by correlation of the variables influencing the process. The causes leading to the deterioration of the material properties after welding were to be identified and measures to improve the quality of the welded joints were to be worked out. In addition, the requirements for the components to be welded with regard to design and preparation were to be recorded. In this context, the aim was to record the relationships between joint shape, component thickness and outgassing processes of the melt and thus the formation of pores.

Title:Metallurgical and corrosion-chemical investigations into the production of plasma powder post-cladding from Ni-based alloys Funding: AiF Duration: 03/01- 02/03

Abstract: The aim of the research project is to produce corrosion-resistant post-claddings of Ni-based materials of low layer thickness using the high performance plasma powder welding process on connection-welded clad plates, to investigate and to optimize them with regard to quality and application performance. The necessary layer properties are to be achieved using the insert technique with a layer thickness of 2 to 4 mm. In this case, due to the required layer quality (high corrosion resistance), a small amount of mixing is required. For economic reasons, at least a weld deposition rate of 12 to 15 kg/h is required. Within the framework of the research project, reliable findings on the performance and possible applications of post-cladding with high-performance plasma powder cladding are to be developed. Compared to the processes used so far, the process is expected to offer considerable advantages in the area of highly stressed, thin and high-alloy corrosion protection layers, which will result in a significant increase in efficiency. Furthermore, the high layer quality and material savings as well as the modification of the existing high-performance torch for processing nominal pipe diameters of 200 mm could open up new areas for the production of components made of clad plates. The substitution of the conventional processes (RES / TIG) is particularly suitable in those industrial sectors where high-alloy coating materials such as Ni-based alloys are processed with very high corrosion requirements and relatively small component diameters. Summary

Title: Investigations into the qualification of plasma powder joint welding of alumimium for industrial use Funding: AiF Duration: 03/01- 02/03

Abstract: The favourable properties of aluminium and its alloys, such as low specific weight, low tendency to corrosion, relatively good formability and workability as well as good to very good mechanical-technological properties, open up more and more fields of application for aluminium materials. Just as with steels, processability is one of the essential properties of aluminium materials, which is the prerequisite for a wide range of applications for this group of materials. In this context, joinability, especially weldability, plays a decisive role. Gas-shielded arc welding has become established for the welding of aluminium materials. Depending on the welding task, both processes with non-consumable electrodes (TIG) and processes with consumable electrodes (MIG) are used. In the TIG / plasma processes, too, a filler wire is used in the majority of cases. In addition, certain aluminium alloys cannot be welded without an additive due to their hot cracking tendency. Due to the external wire feed, welding with a wire-shaped filler metal leads to the known disadvantages such as wire slip, limited accessibility and freedom of movement, especially with narrow and small component contours and complexly structured workpieces. A new process variant that does not even allow the above-mentioned problems to arise is plasma powder joint welding. The powdered filler material is fed into the weld pool via the torch centrally and without current. This allows the seam geometry to be influenced independently of the set line energy. Furthermore, the process has an additional degree of freedom due to the directional independence of the filler metal addition. The aim of the project was to qualify plasma powder welding for joining aluminium materials. The parameters for a safe and reproducible joint welding of different materials from the group of non-age-hardenable aluminium alloys were to be worked out. For the safe destruction of the thermally stable oxide skin, it is necessary to include newly developed plasma process variants in the investigations. Summary

Title:Investigations into the development of precipitation hardenable layers of nickel-based superalloys Funding: AiF Duration: 12/00 - 11/02

Abstract: The aim of the research project was the application-oriented alloy development of precipitation hardenable nickel base superalloys. The alloys to be developed should form precipitates already during welding, so that optimum mechanical properties for high-temperature applications can be achieved by a relatively simple heat treatment, i.e. short and at relatively low temperatures. Special emphasis was placed on the determination of the precipitation mechanisms in order to provide the user with concrete information for specific problem solutions, which would enable the alloys to be used successfully in the high-temperature range, both in repair and in the production of new parts. Summary

Title: Investigations into resistance spot welding of thin sheets made of newly developed higher and ultra-high strength steels Grant: AiF Duration: 10/00 - 12/02

Abstract: Multiphase steels (DP, TRIP, CP) represent an innovative material that is expected to have a wide range of applications in the future. Due to their combined structural properties, these alloys can be used in a wide range of applications in many branches of industry. Although their use offers advantages, many aspects must be taken into account for lightweight steel construction. In addition to the question of the material, aspects such as material-compatible design and safe production technology play an important role here. Up to now, there has been insufficient knowledge about welding technology and the associated weldability of high-strength steels. Inquiries from industry showed that there are some reservations about the use of these materials in series production, especially in connection with resistance spot welding. While there are numerous recommendations for parameterization for conventional steel materials, these are naturally still largely lacking for the newly developed materials. Within the framework of the research project AiF-FV No. 12.618N "Investigations on resistance spot welding of thin sheets made of newly developed higher and ultra-high strength steel materials", higher strength steel materials of the types DP, RA, CP and MS were investigated in different strength levels and coating variants. To characterise the welding behaviour, weld areas were recorded in identical and mixed combinations. An adjustment of the welding parameters towards increased electrode forces usually leads to wider current ranges and to macroscopically faultless welding lens formation. A reheating phase has a positive effect on the hardness of the welded joint. Cold forming prior to the welding process leads to higher forces in the shear tensile test due to an increase in the strength of the base material. A material-related influence on the fatigue strength properties could not be proven in the tests carried out.

Title:Comparative studies on the influence of high-power beam welding on the metallurgical properties of Al and MG alloys Funding: AiF Duration: 10/00 - 9/02

Abstract: The aim of the project was to develop technical and design specifications for welding of aluminium and magnesium alloys using high-energy beam processes (high-power Nd-YAG laser and electron beam in atmosphere). In particular, the influence of high welding speeds of 10 m/min and more on the microstructure, the precipitation behaviour and the mechanical-technological properties of the welded joints was to be investigated, since industrial users in particular must exploit rationalisation potentials for welding times due to international cost pressure. The base materials were commercially available die casting and wrought alloys with low wall thickness. Within the framework of the investigations, the metallurgical and material processes during joining were to be determined and, based on this, concrete specifications and instructions for the design, layout and manufacture of high-quality joints on the materials were to be derived. One focus of the investigations carried out was the clarification of the thermal processes in the heat-affected zone as a function of material condition and process parameters and their effect on the weld properties with regard to corrosion resistance and mechanical-technological properties (static and dynamic strength, hardness). In the foreground was the task of creating a joining technology adapted to the treatment condition of the base material by means of targeted thermal influencing. Tolerance ranges and process limits were to be determined. Summary

Title:Investigations into the weldability of precipitation hardenable stainless steel alloys Grant: AiF Duration: 5/99 - 4/01

Abstract: The aim of the project is to develop welding and design specifications for MSG and laser beam welding of precipitation hardenable stainless steels also in the treated state. For this purpose, the metallurgical and materials science processes during the joining process are to be investigated and, based on this, constructive principles and criteria for the design, layout and execution of high-quality welded joints on these materials are to be derived. In the foreground is the task of creating a welded joint technology adapted to the treatment condition of the base material by means of targeted thermal influencing. One focus of the planned investigations is the clarification of the thermal processes in the area of the weld seam, i.e. in the HAZ, as a function of material condition and process parameters as well as their effect on the seam properties with regard to corrosion resistance and mechanical-technological properties (toughness, strength, hardness). The aim here is to gain knowledge of the structure of the microstructure in the HAZ area and the precipitation behaviour by correlation of the variables influencing the process. The causes leading to deterioration of the material properties after welding shall be recorded and measures shall be worked out to improve the quality of the welded joints. Temperature, dwell time and the cooling rate decisively determine the character of the metallurgical processes. The establishment of criteria for assessing the critical cooling conditions as a function of the material condition is thus a further sub-goal of the project. Based on these findings, a model for the quantitative description of the interaction between heat conduction in the process, the starting material and the properties of the welded components to be achieved is to be developed. Summary

Title:Process control and design concepts for the joining of complex components Funding: DFG / SFB 390 TP B3 Duration: 98/01

Title:Superplastic properties and diffusion welding of magnesium-based alloys Funding: DFG / SFB 390 TP C1 Duration: 98/01

Abstract: There are only few basic findings available on the superplastic behaviour of magnesium alloys, which can make a further decisive contribution to weight reduction in lightweight construction due to their density which is about 40% lower than that of aluminium materials. As experiences from the field of aluminium and titanium alloys show, the use of superplastic properties is especially useful for the material group of magnesium alloys due to their limited cold formability. Superplasticity is understood to be the ability of a material to withstand degrees of deformation without necking and practically no work hardening when only very low flow stresses are applied, which exceed the limits of about 10 to 40% that are usual for "normal plastic" materials by some 100 to over 1000%. Within the last 5 years of the current SFB390, extensive investigations have been carried out on possibilities to improve the superplastic properties of magnesium-based alloys. One of the main objectives was to reduce the grain size in the microstructure to d<10µm. For this purpose, two simple processes have been developed in subproject C1, with the help of which the superplastic properties of ZRE1 and AM20 magnesium casting alloys can be greatly improved by preforming by extrusion. The results confirm the assumption that the grain size has the main influence on the superplastic deformation properties. For example, it was possible to achieve a breaking elongation of 1050% for a conventional ZRE1 magnesium alloy at a constant strain rate of 1.6x10-4 s-1 and a breaking elongation of 550% for a conventional AM20 magnesium alloy at a constant strain rate of 10-3 s-1. The greatly reduced grain size also resulted in the modified alloys not only improving their superplastic properties but also their general properties such as hardness and tensile strength.

Title:Welding under extreme conditions Grant: DFG / SFB 264 TP B3 Duration: 98/01

Abstract: Within the scope of this research project, extensive basic investigations are carried out to develop a concept for an underwater welding system in terms of automated production and to increase the quality of underwater welded seams. In particular, correlations between the boundary conditions of pressure and moisture-afflicted welds and the resulting process and material behaviour have to be worked out.

Title:Alternative materials for wire bonding in the narrowest grid Support: AiF Duration: 12/98 - 11/00

Title:Metallurgical investigations into the coating of thin substrates with sheets >2 mm Funding: AiF Duration: 12/98 - 11/00

Abstract: The aim of the project is to use the plasma powder process to produce single-layer coatings of Fe- and Ni-based alloys on thin substrates with wall thicknesses of 2 - 6 mm. Furthermore, their properties and the economic efficiency are to be determined. By a specific combination of alloy composition and powder addition optimal coating properties can be adjusted. These process-influencing parameters will be successfully determined during the project. In order to be able to classify the determined results, investigations are also carried out on commercially available open-arc (OA) welds. The investigations carried out will provide knowledge about the achievable properties of the material composite, which will enable the industrial application of this coating process and thus lead to a weight reduction in component production. Summary

Title:Development of a consulting system for surface protection by thermal spraying Promotion: AiF Duration: 11/98 - 10/00

Abstract: The planned system (working title "SPRIWARE") shall show exemplarily on plasma spraying that a suitable selection or output of spray materials is possible on the basis of tribological systems (wear parts with counter body, ambient and frictional conditions) as well as spraying process and spraying system parameters.

Title:Investigations to determine process interactions and to influence seam properties in combined plasma-arc laser welding Promotion: AiF Duration: 11/98 - 10/00

Abstract: The aim of the planned research project is to develop a joining technique based on combined plasma-arc laser welding using the example of work pieces sensitive to hardening as well as the joining of aluminium alloys in practical investigations. This technique allows high productivity even at low beam power. Another important focus of the process investigations is the improvement of gap bridging, whereby the use of filler wire is also planned. In order to achieve the research objective, a developed hybrid welding system is to be adapted to the above-mentioned problems based on the results of the applicant's preliminary investigations. Summary

Title:Investigation and optimisation of the mechanical and corrosion properties of welded joints of wrought aluminium alloys in combination with aluminium casting alloys Funding: AiF Duration: 9/98 - 12/00

Abstract: Within the scope of the planned work, the welding technology and material fundamentals are to be worked out in order to improve the load-bearing capacity and especially the corrosion properties of welded components of the combination Al-wrought alloy with Al-cast alloy and to determine their component properties. By means of plasma welding with variable polarity in different positions, materials relevant for apparatus and vessel construction are joined. The aim is to reduce the number of pores and, above all, to improve or adjust the corrosion properties of the base materials and the weld metal. Electrochemical investigations are to provide information about the pitting behaviour and potential deviations of the weld areas. Stress corrosion cracking and ageing tests in various media are also planned. Accompanying metallographic, analytical and X-ray investigations will be carried out to characterize the microstructure and seam properties. Summary

title:Use of nitrogen-containing high-temperature plasmas for reactive coating by means of plasma deposition welding Funding: AiF Duration: 8/98 - 7/00

Abstract: By the targeted addition of nitrogen to the plasma and powder feed gas during plasma cladding, a nitriding of iron-based hard alloys during cladding and a solid solution strengthening by nitrogen embedded in the matrix shall be achieved. The reactive generation of hard materials in the molten state is expected to result in fine-grained precipitation of the hard materials and, due to the process-related strong turbulence of the melt, a homogeneous distribution over the cross-section of the coating. Starting from a high base wear resistance of Fe-Cr-V alloys, an increase in the abrasive wear resistance is to be achieved by increasing the hard material content without coarsening the hard materials. Fine-grained precipitates are the prerequisite for using highly wear-resistant coatings for cutting machine knives or similar tools and wearing parts. Within the framework of the research project, different process variants of plasma powder cladding (plasma arc process, plasma jet plasma arc process) are to be investigated. The influence of the nitrogen content of the working gases on the hard material content and the proportion of dissolved nitrogen in the matrix material will be investigated by varying the addition of nitrogen to the plasma and feed gas and the use of different shielding gases. Parameter investigations are used to determine optimum process conditions. By means of metallographic, GDOS and TEM investigations, the resulting nitrides or the dissolved nitrogen content shall be detected. The increased wear resistance as well as the applicability of the coatings for machine knives will be proven by wear tests (grinding paper test, friction wheel tribometer) and field tests of sample tools.

Title:Investigations into the welding of high-alloy Cr-Ni steels with self-protecting cored wire electrodes under water Funding: AiF Duration: 8/98 - 12/00

Abstract: The aim of the research project applied for is to carry out investigations on the design and use of self-protecting flux-cored wire electrodes for mechanized underwater welding of high-alloy Cr-Ni steels and to obtain information on the influence of the flux-cored wire composition and design on metallurgy and thus on the properties of the joint. From this, requirements for corresponding electrodes are to be derived and a concept for a suitable flux-cored wire is to be developed. Summary

Title:Gas shielded metal arc welding of light metal materials using magnesium alloys as an example Funding: AiF Duration: 8/98 - 12/00

Abstract: The aim of the research project is to carry out fundamental investigations on the influence of power source characteristics and welding parameters on process safety during gas shielded arc welding of magnesium alloys. Furthermore, the suitability for gas shielded metal arc welding of different alloys of wrought and die cast materials is to be investigated. The tendency to hot cracking and the formation of the weld seam including HAZ, e.g. precipitation occurring therein, are the focus of interest. As a third objective, the static strength and the fatigue strength shall be determined to such an extent that reliable numerical values can be given for the design of structures. Finally, it is planned to develop reliable statements on corrosion using the salt spray test in accordance with DIN 50 021.

Title:Investigations into the corrosion and wear behaviour of hard material-reinforced magnesium alloys Funding: AiF Duration: 7/98 - 6/00

Abstract: The aim of the research project is to create corrosion and wear resistant surfaces on magnesium alloys with the plasma welding process by melting the surface with the targeted addition of hard material particles (SiC, TiC, TiB2, ZrB2). The aim is to investigate how the wear resistance and possibly also the corrosion resistance of magnesium surfaces can be improved by the incorporation of hard materials while adapting the parameters influencing the process. In addition, it is to be investigated what influence the incorporation of the hard materials has on the formation of the microstructure and on the temperature and composition dependent precipitation behaviour.

Title:Diffusion welding of metals with ultra-fine-grained ceramics Funding: VW-Vorab Duration: 4/98 - 12/99

Title:Investigations into arc welding with sintered strip electrodes containing hard materials Grant: AiF Duration: 1/98 - 12/99

Abstract: The aim of the planned research project is to produce hard material-reinforced build-up weld coatings by means of the arc welding processes UP, RES and MSG and subsequently to investigate them. This is to be achieved by the use of sintered strip electrodes containing hard material. By using the sintering technology, hard material particles, tungsten melting carbides (WSC), are to be bound in ferritic and austenitic matrix materials and processed as strip electrodes with the above mentioned methods.

Title:Influence of solidification and transformation conditions on the ferrite content and ferrite morphology of metastable austenitic weld metal Funding: DFG Duration: 98/99

Title:SPP "Mechanism oriented life time prediction for cyclically loaded metallic tools" Improvement of the life time prediction for multi-axial vibrational stress by consideration of micro-crack formation and micro-crack propagation Funding: DFG Duration: 98/99

Title:Determination of quality-relevant material and process parameters for the combined forming and joining of thin sheet metal Funding: DFG / SFB 362 TP A3 Duration: 98/99

Abstract: On the way to shortening the process chain and thus further reducing production costs, the use of tailored blanks with linear seams has already achieved great success. This has made it possible to avoid overdimensioning and also save forming and assembly steps. However, the use of Tailored Blanks also has disadvantages, mainly due to the cost-intensive adaptation of forming tools by e.g. segmentation or incorporation of recesses for the seam displacement occurring during the forming process. The design of the forming tools must also be adapted to the different sheet thicknesses of the processed blanks in order to avoid wrinkling if the surface pressure is too low or tearing if the surface pressure is too high. For production reasons, it is also rarely possible to lay the seam on a contour that does not change (trajectory). This can be remedied by using tailored components with non-linear seams and contour welds. The term Tailored Components covers not only components produced in the welding/forming sequence, but also the reverse sequence, whereby blanks, for example, are formed with the existing conventional machines and tools and then joined by contour welding. This procedure offers the following advantages: By using non-linear seams and contours, cost-optimized components can be produced which could not be manufactured using previous production methods; the expensive conversion of forming tools including a lengthy try-out phase due to the use of tailored blanks is no longer necessary with contour welding and, in addition, the strong trend in the industry towards modular design is taken into account. High-frequency welding is particularly suitable for the production of non-linear seams and contour welds due to the simple seam preparation, the low equipment requirements and the very high welding speed of up to 1m per 1s. Thus the process can be integrated into the running cycle of modern press lines.

Title:Mash seam welding of thin sheet metal - Material and process related simulation and interactions with the forming process Funding: DFG / SFB 362 TP B6 Duration: 98/99

Abstract: The concept of process-integrated post-treatment of pinch-off seams developed in subproject B6 has proven to be very effective. The utilization of the welding heat during post-straightening results in a significantly better formability than with cold post-straightening. The downstream heat treatment of the weld seam only proves to be useful if the mash-seam has been re-rolled. Without levelling of the weld superelevation, the strength and deformation properties of the mash-seam are so good that heat treatment is not necessary. The inductive process for heat treatment has proven to be very effective. By suitably matching the inductor geometry, distance to the workpiece and working frequency, it is possible to heat the seam area in a targeted manner without thermally affecting the base material. Despite the extremely short holding times of only a maximum of three seconds, a significant improvement in hardness values, tensile strength and formability has been demonstrated. Using three different steels as examples, it was shown that rolled, reheated seams have a formability at least equivalent to that of the base material. The fatigue strength is not affected or even improved by the post-treatment of the seams.

Title:Fundamentals of reaction engineering, design and construction of ultrasonic reactors Funding: DFG / SFB 180 TP B14 Duration: 98/99

Abstract: Within the scope of the project, the Institute of Welding and Cutting Fabrication Processes analyses the wear mechanisms prevailing in cavitation with the aim of selecting and optimising materials for use as sonotrode and reactor material in ultrasonic reactors. By testing according to ASTM G32-85, different materials for the reactor core as well as the influence of different surface treatments - PVD and CVD thin films, laser treatments - on the titanium alloy TiAl6V4, which is often used as sonotrode material in ultrasonic technology, are investigated with regard to the cavitation resistance against direct and indirect cavitation. A further focus is the investigation of the local cavitation behaviour of weld seams on the reactor materials and the influence of the manufacturing parameters on the wear behaviour. Distilled water and the fluids used in a phase transfer catalysis in a US reactor serve as test media. The aim is to significantly increase the service life of ultrasonic reactors by minimizing wear due to cavitation through targeted surface modification or process control during welding production.

Title:Electron beam welding of thin sheet materials in the atmosphere - Fundamental investigations on material and process behaviour Funding: DFG / SFB 362 TP B9 Duration: 98/99

Abstract: Electron beam welding in free atmosphere (NV-EBW) is a key technology that is beginning to establish itself in large-scale production for some applications. This process not only substitutes conventional processing techniques, but also offers excellent approaches for the production of economical and high-quality welded joints on thin sheet materials. Due to the high power density, the heat conduction can be specifically influenced. Due to the lower thermal load, the melt pool remains small and the heat-affected zone narrow, which promises good weld properties. The method is also characterised by a high process speed, good integration into production lines and easier handling than electron beam welding in a vacuum, as the non-productive times for vacuum generation are eliminated. Furthermore, the use of filler materials for the avoidance of edge notches and seam collapse in thin components or for joining dissimilar metals is practically easier to realize. From an economic point of view, the decisive advantage of the NV-EBW compared to current high-power lasers is mainly due to the lower operating costs and the higher efficiency in beam generation.

Title:Investigations into the influence of process behaviour and seam properties by the use of metered filler metals in metal active gas (MAG) high-performance welding Funding: DFG Duration: 98/99

Abstract: In the research project applied for, fundamental investigations on the influence of the wire electrode under consideration of the shielding gas composition on the seam formation and the pore formation are to be carried out, especially in high-performance MAG welding for higher wire feed speeds. The fundamental research into the specific influence of the processes in the weld pool through the use of basic-doped welding consumables is in the foreground. For this purpose, the effects of the basic elements in the filler metal on the weld pool formation are to be investigated in more detail, whereby particular importance is attached to the processes on the surface. These are to be made accessible, among other things, by high-speed recordings. For welding and metallurgical reasons, it makes sense to optimise the efficiency of the doping so that the desired phenomena can be achieved with minimum proportions of basic additives. Based on these basic investigations, it should be examined to what extent the use of special cored wire electrodes with a low basic content is possible and reasonable. In addition, the possibility of incorporating basic slag formers into a solid wire is to be investigated more intensively on the basis of the preliminary investigations. In addition to the fundamental investigations into the material-specific properties of the doped wire electrode and the influences on the welding parameters, further problems determining quality are to be considered. These concern process and filler material specific aspects such as wire structure, stiffness and deformation influence, wire feeding behaviour, requirements on current transmission and contact tube spacing in order to achieve reproducible penetration profiles and corresponding seam qualities. The systematic, scientific investigations are intended to clarify the determining parameter dependencies, whereby still existing knowledge gaps in the area of basic-doped weld filler metals must be closed. In addition to the scientific findings, the investigations are also expected to provide an impulse for broad areas of welding technology. On the one hand, this concerns a better understanding of the processes in the weld pool and the resulting developments. In the concrete case, implementation of the results at a later date could lead to an expansion of the field of application of MAG high-performance welding processes and thus to an improvement of the market opportunities of German companies. The results of these investigations should make it possible to increase the efficiency and/or the quality of MAG high-performance welded joints and thus enhance the economic efficiency of the MAG high-performance welding processes as well as the competitiveness. At deposition rates of over 23 m/min with 1.2 mm wires - comparable to SG2 quality - it should be possible to produce pore-free, high-quality seams in order to increase the performance of the welding process with assured seam quality and thus the overall production efficiency, even in areas where X-ray-safe welded joints are required.

Title:Surface modification by vacuum coating of gold fine wires to improve ultrasonic weldability at low process temperatures Funding: DFG Duration: 98

title:Material-related numerical simulation of thermal processes in production engineering Funding: DFG Duration: 1/97 - 12/99

Abstract: The aim of this subproject is to realize the numerical simulation of the material and process behavior during fusion welding. The methodical, integrated approach of the joining process in its entirety is the focus of this project. This means that a holistic approach and solution methodology for the system material/welding process is aimed at in order to create a basis for a prediction of the suitable process parameters as well as the seam properties.

Title:Mechanism oriented life time prediction of edge layer nitrided titanium alloys under consideration of fracture mechanical modelling of the short crack behaviour Funding: DFG Duration: 7/97 - 7/99

Abstract: The task of the mechanism oriented life time prediction is to model the microstructural fatigue processes occurring in the material during cyclic loading and to link them directly to life time predictions. Surface-nitrided titanium alloys are suitable model materials for this task. Such materials have a high innovation potential for the use in combined dynamic and tribological loads. At the same time, the surface layer treatments influence the fatigue behaviour, whereby there is a considerable knowledge deficit with regard to both fatigue mechanisms and life expectancy prediction. The aim of the project is to develop the basis for a mechanism-oriented life time prediction of surface layer nitrided titanium alloys. For this purpose, plasma nitriding and laser nitriding processes are to be used to set surface layer states with clearly different edge zone and core properties, so that microstructural fatigue processes deviating from one another occur under cyclic loading. Their respective predominant mechanisms are to be analysed with the aid of analytical and experimental methods under single-stage tensile-compression alternating stress with variable stress ratios and to be represented in a short-crack progress model. Based on these investigations, a concept is to be developed which makes it possible to transfer the fracture-mechanical approaches into the life prediction for a single-stage, medium stress load. It is expected that within the framework of the project applied for, fundamental findings on the fatigue behaviour of surface layer composites, on the application potential of surface layer nitrided titanium alloys and on the qualification of the surface layer processes used can be developed.