Formation of nanocrystalline structure in tantalum by sliding friction treatment

•A new technique for fabricating nano-structural surface layer was proposed.•Nanocrystalline structure was obtained in the surface layer of a pure Ta plate.•The formation of graded microstructure Ta was dominated by dislocation activities.

We have investigated the microstructural evolution as a function of depth from the surface of a pure tantalum plate subjected to sliding friction treatment (SFT), which is suggested to be a low-cost, simple and efficient severe plastic deformation technique to produce nanocrystalline structure on the surface of metals. A differential scanning calorimetry was used to examine the thermal stability of the microstructure. A transmission electron microscope was used to analyze the different microstructure features as a function of the depth from the surface. Details of the microstructural evolution were discussed and mechanisms were suggested. With an increasing depth from the treated surface, a progressive change in the microstructure from nano-grains to micro-grains was found, which is proposed to be dominated by dislocation activities.