Grain boundary analysis and design of powders, green bodies and component parts as a function of sintering conditions

• Applicant: Professor Dr.-Ing. Martin Heilmaier, since 5/2024
• Subject Area: Glass, Ceramics and Derived Composites
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 416817512

The investigated refractory composites of metals (Ta or Nb) with ceramics (Al2O3) exhibit the advantages of both material classes in terms of better creep and thermal shock resistance, corrosion and erosion resistance, as well as electrical conductivity. A potential application is the spider brick, which directs the melt in, e.g., steel production. The presented subproject 5 (SP5) is embedded in a research unit consisting of 7 subprojects (SPs) and contributes specifically with atom probe tomography (APT) to a nanoscale investigation.Similar to the first period of the grant, we also plan for the second to analyze the reaction at the interface above 1500°C with a near-atomic resolution to obtain a better understanding of the diffusion and phase transition at the metal-ceramic interface. For this, we continue to compare sputtered refractory metal films on an alumina substrate as a model system with the technical grade materials from SP1, SP2, SP3, and SP7. In the investigation of both Transmission electron microscopy (TEM), among other techniques, supports APT in identifying the influence of different additives separately. The influence of cyclic cold isostatic pressing, sequential pressure slip casting, and various sintering regimes on the phase boundaries in the technical materials will be studied. Furthermore, we will investigate the effect of the planned 3D printing in SP1 on the nanostructure. The adhesion of the refractory metal on the alumina is decisive for the material properties. Thus, we will quantify this adhesion by loading the metal film with hydrogen and measuring the resulting buckling. Another essential property of the materials is their oxidation and corrosion resistance, which will be investigated together with SP2. In this context, flame spraying yields an Al2O3 coating surrounding and protecting the base material. This produces new interfaces of metal and alumina with the new alumina, which will be analyzed. Refractory metal silicides can further improve the oxidation resistance, but also cause a reaction between these silicides and the alumina, which will be studied with film samples. Finally, the corrosive effect during direct exposure to the melt on the composite is highly relevant and will be modeled by molten Fe on the film samples.In the frame of the proposed project, we are planning to answer the following scientific questions:1. Can we change the fracture behavior with additives, i.e., modification of the interface segregation?2. What is the influence of additives at the interface on the adhesion of the refractory metal on the alumina?3. How do 3D printing processes affect the interface and the nanostructure and how can this be controlled?4. How effective is thermal spraying and the use of silicide phases in preventing corrosion and oxidation?5. How will the composite material behave if the coating fails and the composite is directly exposed to the melt?

• DFG Programme: Research Units
• Subproject of: FOR 3010: Multifunctional, coarse grain Refractory Composite Materials for Key-Components in High temperature applications
• Ehemaliger Antragsteller: Dr. Torben Boll, until 4/2024