EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

High performance applications require materials that combine damage and fracture tolerance with high strength. For such applications tungsten based alloys and composites are frequently considered as candidates. Alloying and composing are both concepts commonly used to improve the ductility of tungsten. However, to exclude brittle inter-metallic phase formation, the former requires use of expensive alloying materials such as rhenium or hafnium while common composites suffer from lower strength compared to pure tungsten. In order to improve the composite’s strength, grain refinement via serve plastic deformation is often conducted. This technique is well-known to increase strength, while preserving ductility down to certain grain sizes.

This work investigates the grain size dependence of the fracture toughness for tungsten-copper composites with 33 wt.% copper. The samples are fabricated from elemental powders and subjected to high pressure torsion for consolidation and grain refinement down to about 20 nm. Subsequently, this nano-composite undergoes different vacuum heat treatments to adjust dislocation densities and grain sizes. In-situ micro mechanical tests are performed at room temperature in a scanning electron microscope to determine the conditional fracture toughness, strength and ductility of the different grain sizes. For a thorough assessment, different sample dimensions will be realized using femtosecond laser and focused ion beam machining to address potential sample size effects and ensure extraction of valid fracture mechanical quantities. Based on this, we will detail the influence of grain size and defect density on the fracture toughness of the tungsten-copper nano-composite, as well as strategies for a further improvement via additional strengthening of the ductile copper phase.