Microstructure and hardness of copper–carbon nanotube composites consolidated by High Pressure Torsion

Blends of Cu powders and 3 vol.% carbon nanotubes (CNTs) were consolidated by High Pressure Torsion (HPT) at room temperature (RT) and 373 K. The grain size, the lattice defect densities as well as the hardness of the composite samples were determined. It was found that the Cu–CNT composite processed at RT exhibited a half as large mean grain size and a three times higher dislocation density than those observed in the specimens either consolidated from pure Cu powder or processed from bulk Cu by HPT. The small grain size and the pinning effect of CNT fragments on dislocations led to significant twin boundary formation during HPT. The increase of the temperature of HPT-processing to 373 K resulted in a slight increase of the grain size, and a strong decrease of the dislocation density and the twin boundary frequency in the composite. The correlation between the microstructural parameters and the flow stress calculated from the hardness was discussed.

► Composites were consolidated from blends of Cu powders and carbon nanotubes.
► Nanotubes yielded extremely high dislocation density and small grain size in Cu.
► Increase of processing temperature resulted in reduction of defect densities.
► The high flow stress is resulted mainly by the large dislocation density.