Brazeability of similar hybrid joint compounds consisting of additively manufactured and conventional material grades

• Applicant: Professor Dr.-Ing. Wolfgang Tillmann
• Subject Area: Production Automation and Assembly Technology
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 407147480

Selective-Laser-Melting (SLM) is a metal-powder-based manufacturing process that offers the best possible design options for the production of highly complex components. Until today, generating a SLM part on a simple geometrical, conventionally produced component requires such components to be segmented, brazed and tempered prior to realizing a hybrid joint compound. The disadvantages of this procedure are mainly based on the fact that the SLM part contains high residual stresses and has a completely different material structure in the generated state. Therefore, these compounds offer wholly dissimilar mechanical-technological properties. Furthermore, technically efficient SLM components require a subsequent heat treatment which extends the already complex production chain by another process step.Selective laser melting as well as a combined brazing/heat treatment processes offer a great potential to combine the respective advantages into an efficient production chain. As proven in preliminary tests, the residual porosity and oxide inclusions affect the brazing quality and the joint strength significantly, although the SLM materials had a density higher than 99.8 vol.-%. This research project will systematically generate fundamental knowledge to braze similar composite and hybrid composites of conventional and SLM material grades for austenitic stainless steel 316L (X2CrNiMo17-12-2) and nickel maraging tool steel 18Ni300 (X3NiCoMoTi18-9-5). Furthermore, the brazed joints will be benchmarked to appropriate composites which are only manufactured by selective laser melting. Additionally, the joints will be heat-treated to equalize the microstructure and minimize residual stresses. The overall objective is to establish a suitable process chain to produce similar hybrid composites of SLM and conventional materials, which is based on characteristic values of the mechanical joint properties. In detail, the focus of the research project is mainly the investigation of the brazing process using these material grades. The established brazing processes for conventional composites are transferred to these composites and analyzed with respect to the wetting and flow behavior, the joint strength, with a strong focus on the influence of pores and oxides within the SLM material to the brazing quality. In addition, gas phase etching followed by nickel plating of the joining surfaces will be examined for the brazing samples. These processes will remove the oxides and close the open porosity, thus enhancing the brazing quality and the joint strength significantly.

• DFG Programme: Research Grants