Tungsten has outstanding material properties such as a high melting point, high intrinsic strength and a low degradation rate by neutrons. Hence, it is frequently considered a candidate material for fusion reactor shielding. Despite these outstanding properties, tungsten lacks ductility, leading to low damage as well as fracture tolerance, and is therefore hardly appropriate for safety-relevant applications. To improve ductility, strategies such as alloying or composing are commonly used. The former requires expensive alloying elements such as hafnium or rhenium to circumvent brittle intermetallic phases, while composing reduces the strength compared to pure tungsten.
In this work, copper is added to tungsten as a ductile phase. To counter the strength reduction, the composite is subjected to grain refinement by high-pressure torsion, thereby shifting the grain size into the nano-crystalline regime. To tailor the grain size of the microstructure the deformation temperature was increased up to 400°C during the HPT process. The microstructural saturation after the HPT process was verified by Vickers hardness measurements and SEM investigations. Additionally, the matrix grain size was determined via TEM analysis, showing a clear relation between deformation temperature and saturation matrix grain size. Further, to investigate the material’s fracture characteristics, microcantilevers were fabricated employing FIB milling. To examine the sample size effect, cantilevers with different cross-sections were fabricated. All cantilevers were tested in situ in an SEM utilizing quasi-static loading. The fracture analysis confirmed that the fracture process is dominated by intercrystalline fracture and that the achievable fracture toughness of ~9±1 MPa√m is primarily governed by inhomogeneities present in the matrix. Besides that, the analysis confirmed a sample size effect on fracture toughness for the smallest cantilever dimensions.