Effect of heat treatment on the microstructure and corrosion properties of electroless Ni-P coating on AISI 1010 steel in a simulated seawater

Abstract The effect of heat treatment on surface topography and corrosion behavior of an electroless nanocrystalline Ni-P coating on AISI 1010 low-carbon steel was investigated. Detailed characterizations using secondary electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX), atomic force microscopy (AFM), and x-ray diffractometry (XRD) were employed to examine the coating morphology and microstructure. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were applied to examine the corrosion behavior of the Ni-P coating in simulated seawater. Results demonstrate that heat treatment at 300 °C (HT–300) significantly improved corrosion resistance, reducing the corrosion rate from 142.10 ± 2 mmpy in the non-heat-treated coating to 22.26 ± 0.72 mmpy. The coating heat-treated at 300 °C promotes the crystallization of the deposited Ni-P layer with the formation of Ni 3 P phase, which acts as a protective barrier against corrosion. The formation of the intermetallic Ni 3 P phase upon heat treatment also enhances the hardness of the Ni-P coating as high as 978.3 ± 4.5 HV. Heat treatment at 500 °C results in the formation of Fe 3 O 4 and Fe 2 O 3 phases, indicating that the optimal HT temperature has been exceeded. EIS analysis confirmed enhanced coating stability due to increased charge transfer resistance, while x-ray photoelectron spectroscopy (XPS) identified NiO, Ni(OH) 2 , Fe 3 O 4 , and Ni 3 P phases as corrosion products. These findings highlight the effectiveness of heat treatment in enhancing the protective properties of Ni-P coatings for marine applications.