Resubmission: High-strength, low-stress cemented carbide-steel brazed joints due to dispersed gamma-Fe-Co-Cu precipitates in the copper-rich fillet

• Applicant: Professor Dr.-Ing. Wolfgang Tillmann
• Subject Area: Joining and Separation Technology ; Synthesis and Properties of Functional Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 527885000

The overall objective of this research project is to maximize the joint quality of the cemented carbide-maraging-steel brazed joint by consistently using all strength-increasing measures permitted by the metallurgy of the material joint system to be brazed. From the point of view of possible applications in the field of machining technology, this is done against the background of increasing the service life as well as increasing the feed forces of tools such as brazed hammer drills, cemented carbide-tipped saw blades or tool holders with large-area joining surfaces. In addition to the application of an adequate temperature-time regime and the selection of a suitable brazing material, the focus of this research project is increasingly on the introduction of a wetting-promoting Ni layer into the existing joint material system as well as on the resulting material mechanisms within the brazed seam which increase the brazed joint quality. A Ni layer applied by arc PVD to the otherwise difficult-to-wet maraging steel dissolves in the brazing melt during the brazing process and alloys the brazing zone in such a way that, after solidification, both finely dispersed gamma-Fe-Co precipitates are present in the brazing material structure and fine-seamed, brittle-phase-reduced interfacial transitions with a defect-free bond to the base materials. Two elementary material-technological factors, which are of scientific importance for this research project, are the precipitation hardenability typical for Cu-Ni-Fe alloys and the complete solubility of the elements Cu and Ni in each other. Thus, not only the morphology of the described gamma-Fe-Co phases is influenced by an adapted temperature-time profile as well as the change of the chemical composition of the brazing zone by the variation of the Ni layer work, but also the ductility of the Cu-rich matrix phase is adjusted in a targeted manner, so that a positive influence on the global composite properties is brought about. The research project is also of high technical relevance, since the choice of the high-melting solder Cu, which is commonly used for brazing carbide-steel, brings the time-temperature profile of the brazing process into line with the time-temperature transformation behavior of the maraging steel, so that the downstream tempering process results in simultaneous precipitation hardening in both the steel and the brazing material. In this process, the holistic heat transfer modes of thermal radiation and, if necessary, fabrication prevailing in the vacuum furnace are utilized, so that, in contrast to brazing processes with a local heat input (e.g. induction brazing), there is a holistic positive influence on the mechanical steel properties.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Lukas Wojarski