Mechanisms of segregation induced strengthening and toughening of ultrafine-grained tungsten alloys at elevated temperatures

• Applicant: Dr. Nicolas Peter
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544676970

Brittle failure along cleavage planes or interfaces is a common issue in nanostructured materials, particularly for metals with low ductility such as tungsten (W). Efforts to enhance strength and ductility through improved grain boundary cohesion via grain boundary segregation engineering have proven to be potential strategies to address these challenges. However, it is not entirely clear how segregating elements influence the interface configuration, their impact on ductility and fracture toughness, and especially how their influence manifests at elevated temperatures. Hypotheses / research questions / objectives: Determining the conditions under which grain boundary segregation causes specific configurations and assessing its influence on strength and plasticity should, hypothetically, allow for a targeted adjustment of interfacial plasticity. In the proposed project, a combination of micro-/nanomechanical tests and atomically resolved structural and chemical characterizations will shed light on the influence of different doping elements on grain boundary segregation in W interfaces. Approach / methods: To uncover the fundamental processes of plastic deformation at interfaces and crack tips, a multi-scale approach is employed. In this context, defined interfaces are utilized in micro- and nanoscale fracture experiments in SEM and TEM, as well as deformation experiments at atomic resolution in TEM. The influences of interface structure and temperature on processes during fracture are examined across all relevant length scales, from room temperature to application-relevant elevated temperatures. The identified influences are compared with molecular dynamics simulations of digital twins. For example, simulated strains for dislocation emission ahead of a crack tip or from an interface can be validated using TEM and correlated with bulk-like SEM experiments. Level of originality / innovation: The combination of highly advanced in-situ investigations at the micro-, nano-, and atomic scales with correlative, large-scale, atomistic simulations forms an innovative approach to assess the fracture behavior of interface-engineered, nanostructured materials. Understanding which grain boundary motifs favor plasticity and prevent crack growth ultimately allows for knowledge-based adjustments of interfacial microstates. This enables us to improve these materials in terms of their currently limited fracture properties and thermal stability. Accordingly, this work paves the way for novel materials for extreme environments and is highly resource-efficient and recycling-friendly.

• DFG Programme: Research Grants
• International Connection: Austria
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Cooperation Partner: Professor Dr. Daniel Kiener