Electrochemical dissolution behavior and characterisation of passivation films of PH13-8Mo in NaNO3

Abstract

PH13-8Mo stainless steel, renowned for its superior physical and mechanical properties due to advanced smelting processes, is widely employed in high-stakes aerospace applications, including nuclear energy systems, rocketry, and critical aerospace components. However, its high strength and hardness present challenges in machining, especially for intricate structural shapes. This study investigates the electrochemical machining (ECM) of PH13-8Mo, emphasizing its dissolution characteristics and the behavior of key constituent elements—iron (Fe), chromium (Cr), nickel (Ni), molybdenum (Mo), and aluminum (Al)—in corrosion processes. Techniques such as open circuit potential (OCP), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) were employed to characterize each element’s contribution to passivation. Morphological analysis indicated that residual surface austenite dissolves progressively with increased current density, exposing the underlying martensitic phase. Post-dissolution EIS analysis revealed that Fe and Ni facilitate secondary passivation, whereas Mo significantly enhances passivation film density. A mechanistic dissolution model is proposed to elucidate the progressive dissolution behavior of PH13-8Mo.