Surface wettability control on zircaloy-4 by nanosecond Nd:YAG laser with beam homogenizer

Abstract

We introduce the laser-induced surface processing (LISP) method that imparts hydrophilicity and hydrophobicity using a Nd:YAG nanosecond laser, especially the high-fluence (HF) condition for fast processing and the low-fluence (LF) condition to control the surface wettability. A prime example of HF processing is laser shock peening, where we show the potential to achieve both strength enhancement and wettability in materials. This could be a new advantageous feature in areas such as reactor maintenance. We combined a beam homogenizer with LISP to increase processing efficiency. The beam homogenizer realizes a uniform fluorescence distribution in the beam area and, at the same time, makes the beam rectangular to increase work efficiency. The maximum contact angle was 123.8° for the zircaloy-4 specimen through HF processing with the beam homogenizer. We also showed that nanosecond laser-induced periodic surface structures could be generated by combining LF processing with specific conditions of a beam homogenizer. This could produce a superhydrophobic surface with contact angles up to 166° on zircaloy-4 or achieve a near superhydrophilic surface with a contact angle of 17.9° depending on the processing conditions.