Hydrophobic durability and anti-corrosion of plasma nitriding layer: Evolution mechanisms of corrosion behavior under variations in local hydrochemistry

Mechanisms for the effects of nitrogen on the durability of hydrophobic and corrosion resistance of modified layers prepared on the surface of AH32 steel by plasma nitriding have been investigated. It was found that plasma nitriding can significantly improve the hydrophobicity of AH32 steel. All the contact angles (CAs) of the AH32 steel with 1 h, 3 h and 5 h nitriding were higher than 120 degrees, which had excellent hydrophobicity. The acidification degree of the solution within the nitriding layer's micro-zone was effectively reduced due to the dissolution of nitrogen. The micro-nano structures of the nitriding layers corroded severely after 15 days of exposure to NaCl solution. When the nitriding time is extended to 5 h, the acidification degree of the solution was intensified due to the enhanced blocking effect, and the nitrogen in the nitriding layer saturated that cannot provide enough nitrogen ions to offset the acidification of the solution, so the durability decreased instead. In comparison, the modified layer with 3 h nitriding in this study had the best durability and long-term service protective effect on AH32 steel.