A two-step periodic micro-nano patterning process via ultrasonic impact treatment on a rough SUS301 stainless steel surface

- Current ultrasonic impact treatment produced micro-nano dimples and an enhanced surface.
- A two-step process on a rough material work surface was proposed and studied.
- The surface roughness and hardness were respectively reduced and increased after Step 1.
- The micro-nano dimple array was successfully fabricated with good repeatability and clear structure after two steps.

The micro-nano dimple array has generally been considered as a valuable surface texture in rolling and sliding applications. It can improve tribological behaviors by providing reservoirs for lubricants and wear debris. The purpose of this study was to demonstrate a two-step process for creating micro-nano dimples with an enhanced surface by ultrasonic impact treatment (UIT) on a rough SUS301 stainless steel surface. Surface morphology, microhardness, phase transformation, microstructures of the micro-nano dimples and wear behavior were investigated using scanning electron microscopy, microhardness testing, X-ray diffraction, atomic force microscopy and ball-on-flat test. It was found that micro-nano dimples of different sizes were successfully established under the same vibration frequency and different machining speeds. Surface smoothing and hardening effects were also obtained. The two-step treated sample showed excellent wear resistance under low load. The developed technique is facile and efficient, and can potentially be employed to fabricate micro- and nanostructures with simplistic procedural advantage for improvement in wear behavior.