Effect of pulsed current coupled ultrasonic rolling on surface fretting friction and wear properties of Ti-6Al-4V alloy

Abstract

Surface friction properties of Ti-6Al-4V alloy after pulsed current coupled ultrasonic rolling (PCUR) treatment were studied in this paper. The research results showed that the process of PCUR treatment effectively improved the microstructure of material surface layer relative to the only ultrasonic rolling (UR) treatment. The maximum thickness of the deformation layer was about 40μm and accompanied by the fine grain and dense dislocation. Moreover, there were no significant micro defects in material surface layer after PUSR treatment. It was attributed to the effective material plastic deformation and grain refinement effects promoted by pulsed current assisted high-frequency ultrasonic vibration. Meanwhile, it significantly reduced surface roughness of the material to a minimum of 0.18μm. The specimen showed the large hardening depth (300 μm) and high surface microhardness (530 HV) after PCUR processing. Meanwhile, the influence depth of residual stress was extended to 0.53 mm. Surface friction properties of the specimens after PCUR and UR treatment were tested with GCr 15 and Si₃N₄, and the specific wear mechanism was analyzed. It was found that the specimen after PCUR treatment had the lower coefficient of friction (CoF) and smaller wear scar compared with the sample treated by UR treatment and showed a lower wear rate. The main reason was that pulsed current coupled ultrasonic rolling effectively promoted material surface layer to produce good plastic deformation, reduce the microscopic defects and refine the grain size.