Investigation of Laser-Material Interactions of Functionalized Diamond-Impregnated Metal Matrix Composite Formulations During Laser Powder Bed Fusion

• Applicants: Professor Dr.-Ing. Wolfgang Tillmann; Professor Dr.-Ing. Gerd Witt
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 445942492

The purpose of this research project is to develop a fundamental understanding of interactions that occur during melting and solidification of diamond-reinforced metal matrix composites (DMMC) during the Laser Powder Bed Fusion (LPBF) process. DMMCs are produced from a mixture of diamonds and steel powder (1.4404). Since diamonds graphitize at approx. 720°C, arc-PVD coatings are applied to the diamond particles and the influence of the laser exposure on the graphitization is investigated. The metallic coatings are also used to induce carbide interfacial reactions between the diamonds and the metallic matrix, producing strong bonds on the one hand and a diffusion barrier on the other. The application of highmelting Mo and W layers protects the diamond particles from direct contact with the melt, assuming the process is properly adapted, and the layer thickness is suitable. Matrix material-related layers such as Ni, Cr or Ti serve as diffusion-promoting melting phases supporting the embedding of diamond particles in the matrix. In order to take advantage of both effects, multilayers are synthesized which combineboth the high-melting metal and the melting phase. Thus, the scientific question arises how the layer thickness correlates with the two desired mechanisms during laser irradiation. In addition, the steel matrix powder (d50 ≤ 63 μm) is added with CuSn powder of different particle sizes (0.035 - 44 μm) by mechanical alloying. In addition to anincreased ductility of the component, this approach lowers the melting point of the powder mixture, enabling liquid phase sintering at reduced laser power and exposing the diamonds to lower temperatures. Another central aspect of this project addresses thepowder-laser interaction and to what extent the functionalization of particle surfaces influences the binding mechanisms in the LPBF process. The systematic analysis of the process parameters and strategies is carried out experimentally by melting tests of lines and primitive geometries. Pyrometry is used to perform in-situ temperature measurements which document the thermal history in the heataffected zone (HAZ). The superordinate objective is to systematically determine the tolerable temperature peak values and gradients and thus to understand the fundamental relationships of graphitization in rapid solidification processes. In addition to the measurement of thetemperature cycles, the melt dynamics and dwell time as well as the particle migration caused by this are characterized by an additional imaging and temporally high time resolution analysis of the melting process. The results are used to draw conclusions about the interaction between material, resulting process behavior and microstructural characteristics and to derive a process strategy for the production of microstructurally graded DMMC components.

• DFG Programme: Research Grants