Hole-like surface morphologies on the stainless steel surface through laser surface texturing underwater

Laser-matter interaction in the liquid environment can produce some special structures on the target surface under certain conditions. In this paper, group micro holes have been fabricated on 304 stainless steel surfaces through laser surface texturing underwater with nanosecond laser. The effects of pulse duration, scanning speed, laser fluence and scanning times on the surface morphologies have been investigated. The surface morphologies have been characterized through scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM). Energy dispersive spectrometer (EDS) has been used to analyze the chemical compositions within the holes. For further clarifying the forming mechanisms of micro holes, high-speed camera was used to monitor the texturing process. The main conclusions are as follows. The group micro holes were fabricated through the water jet interaction due to laser-induced bubble collapsing. The sizes of these micro holes can reach below 2 μm. Increasing laser pulse width, the sizes of holes will increase accordingly due to laser-induced bigger bubbles. Before the target surface is full of the micro holes, lower laser scanning speed, higher laser fluence and more scanning times produce more micro holes on the target surface. While after the hole number is saturated, further increasing laser fluence and scanning times, or decreasing laser scanning speed tend to deepen the holes or make their inner surfaces smoother due to the multiple impingement of water jet, rather than increase the number of the micro holes. With this method, group through holes with a diameter of a few microns have been successfully prepared on the 304 stainless steel foil. So besides surface texturing, this method also demonstrate another great potential application in the field of drilling ultra-small through holes.