Surface nanocrystallization and enhanced surface mechanical properties of nickel-based superalloy by coupled electric pulse and ultrasonic treatment

Abstract

Coupled electric pulse and ultrasonic treatment (CEPUT) is easy to cause severe plastic deformation on Inconel 718 nickel-based superalloy surface with high strength and high hardness. Moreover, the top surface grain with the average size of 25.8 nm and the nanocrystalline layer with the thickness of more than 40 μm are prepared on processed Inconel 718 surface. In CEPUT, the electric pulse can increase the material plasticity, accelerate the dislocation migration, decrease the work hardening, promote the recrystallization rate, so the nanocrystalline layer can be easily produced. The wear resistance of the nanocrystalline layer has also been investigated. Results indicate that compared with the unprocessed sample, the maximum wear track depth is decreased by 19.4%, the wear weight is reduced by 32.5%, and the average friction coefficient is lowered by 15.8% with the processed sample using the peak current of 1000 A during CEPUT. Moreover, the dominant wear mechanism transforms from the compound actions of abrasive wear and adhesive wear to abrasive wear after CEPUT. Such wear resistance enhancements may be owing to the improvement of the hardness and the surface topography caused by the grain refinement, the high density dislocation, and the low surface roughness on the processed sample surface.