Control of hydrophobic and hydrophilic characteristics of metallic materials using shot blasting

In this study, changes in surface texture and surface wettability caused by shot blasting were analysed quantitatively by measuring the contact angle. Shot blasting was performed on stainless steel (AISI 304). Six types of particles with different shapes and mechanical properties were used, and the processing pressure and time were varied. It was observed that the shape and mechanical properties of the particles affected the surface wettability more than the processing pressure and time. In particular, the wettability improved when using polygonal particles than on an untreated surface, and it decreased slightly when using spherical particles. A correlation was observed between arithmetic mean roughness (Ra) and wettability. In other words, a parameter describing the height direction in the surface roughness can be used as a guideline to control wettability. In addition, we performed theoretical calculations based on Wenzel's theory and compared the theoretical and the measured values. The increase of the surface roughness by the shot blasting was found to have little influence on the wettability in the Wenzel theory method. A correlation between the arithmetic mean roughness Ra and the wettability was observed. However, a comparison with Wenzel's theory showed that there are other parameters that affect the wettability rather than the roughness.