Effect of Structure and Surface Roughness on Wetting Angle of a Hypoeutectic Cast Iron

Preliminary results of a research on the effects of microstructure and surface roughness of a hypoeutectic cast iron on its wetting angle are presented in this article. For this purpose, molten cast iron was solidified at different cooling rates to produce two samples of the same composition, i.e. a gray cast iron with A type flake graphite and a white cast iron. Two samples were then prepared in polished, electroetched (four different stages) and mechanically abraded (four different stages) conditions and their wetting angles were measured after evaluating their roughness profile. Maximum and minimum wetting angles were observed on white cast iron surfaces roughened with 80 and 800 sand papers which were equal to 42 and 13 degrees, respectively.Wetting angles of electroetched white cast iron surfaces varied between 25 and 31 degrees by varying surface roughness. Maximum and minimum wetting angles on the surface of gray cast iron were obtained in stage one (40 degree) and stage three (25 degree) of electroetching, respectively. Wetting angles on mechanically abraded surfaces of this sample varied between 27 and 31 degrees. Then, the surface roughness factor and the solid fraction in contact with water were calculated using Wenzel equation and Cassie Baxter equation, respectively, and Wenzel and Cassie-Baxter wetting angles of the surfaces were calculated and were compared with their corresponding measured wetting angles. The results indicated that the surface microstructure and the type of constituents present at the surface, surface-roughening method and surface-roughness value influence the cast iron surface wettability, and it is possible to modify metal wetting angle by modification of its structure, surface-roughness method and surface-roughness value. It was also shown that in gray cast iron, the wetting behavior of the electroetched surfaces followed Cassie-Baxter equation in the first and second stages of electroetching and followed Wenzel equation at higher surface roughness (third and fourth stages of electroetching). In all stages of mechanically abrading, the surface of this sample followed Wenzel equation. The wetting behavior of the white cast iron followed Wenzel equation in all electroetching stages. In mechanically abraded conditions, the white cast iron wettability was variable and depended on the surface roughness.