Effect of Ultrasonic Surface Rolling on Dry Sliding Tribological Behavior of Ductile Iron Under Different Normal Loads

This study emphasizes the effect of ultrasonic surface rolling (USR) on the surface roughness, hardness, and tribological properties of ductile iron under different normal loads. Results revealed that surface roughness was reduced by 96% and surface hardness increased by 37.8% after USR treatment. By increasing normal load, the average friction coefficient of the USR-treated specimens decreased, but the wear rate of both USR-treated and untreated specimens increased, mainly because the dominant wear mechanism changed. The average friction coefficient of the untreated specimen (~ 0.32) was much higher than the USR-treated specimen (~ 0.24) when the normal load was 30 N. However, the wear rate of the USR-treated specimen was larger than that of the untreated specimen when the normal load was greater than 20 N because the higher hardness abrasive particles on the worn surface of the USR-treated specimen not only accelerated abrasive particle wear, but also caused more severe adhesive wear.