W-Cu composites are commonly used as heat-sinks or high-performance switches in power electronics. To enhance their mechanical properties and mutually their usability, grain refinement of the initially coarse-grained microstructure was realized using high–pressure torsion. This leads to different microstructural conditions, exhibiting fine-, ultrafine-grained or nanocrystalline microstructures. Scanning as well as transmission electron microscopy was performed to analyze the respective grain size and microstructures. The hardness and Young’s modulus of the deformed specimens were quantified by nanoindentation testing. Furthermore, X–ray diffraction indicated a decreased grain size and changed lattice spacings upon increasing the deformation ratio. The deformed specimens were tested for their fracture behaviour by continuous stiffness measurements during in-situ microcantilever bending experiments. Here, mean J–integral values of 288 ± 38 J/m2 and 402 ± 89 J/m2 were determined for the 5 and 50 times turned specimens, respectively. The combination of different characterization methods applied on a W–Cu composite allows to identify both, beneficial and unfavourable microstructural components regarding the fracture properties.