Efficient fabrication of gradient nanostructure layer on surface of commercial pure copper by coupling electric pulse and ultrasonics treatment

Severe plastic deformation can be easily produced on metal surfaces by coupling the micro thermal shock from high peak pulse current and the micro mechanical shock from ultrasonics. Moreover, an efficient method for preparing a gradient nanostructured metal surface by coupling electric pulse and ultrasonics treatment (CEPUT) is developed in this study. The variation in microstructure and hardness of the specimen are investigated by electron backscatter diffraction, transmission electron microscope, X-ray diffraction, and nano-indentation measurement. Results showed that on the treated copper surface with CEPUT, the original grain boundaries are no longer recognized, the average grain size decreases from 48.77 μm to 39.22 nm, and the thickness of severe plastic deformation layer reaches to approximately 500 μm. Moreover, the hardness reaches to 2.105 GPa, and CEPUT also reduces the texture in the sample surface. A computational model is developed and the grain refinement mechanism is proposed to describe the electrical-thermal-mechanical phenomena during CEPUT. The proposed simple and cost-effective method of grain refinement and to produce the graded materials is effective, especially in the materials of high thermal and electrical conductivity.