A coarse-grained W-25%Cu composite with a tungsten particle size between 2 and 10 pin is subjected to high pressure torsion (HPT) at room temperature to different strains. The evolution of microstructure with increasing strain is studied. At low strains (epsilon(eq) <= 16), an inhomogeneous deformation of the material is found. This inhomogeneity is studied in detail by nanoindentation experiments. At larger strains (epsilon(eq) >= 16), a fragmentation of tungsten particles is observed. The specimen deformed to a strain of 256 exhibits a homogeneous microstructure with a tungsten particle size between 10 and 20 nm. A further increase of strain does not cause a further significant tungsten particle refinement. A possibility of industrial application of HPT to produce nanocomposite materials is discussed.