Crystallization Behavior of Electroless Ni–W–P– n SiO 2 Amorphous/Nanocrystalline Coating

—Electroless Ni–W–P– n SiO 2 coating is successfully deposited on L245 carbon steel by electroless plating technique. The results of X-ray diffraction (XRD) and transmission electron microscope (TEM) show that coating is hybrid structure of amorphous and nanocrystalline. Differential scanning calorimetry (DSC) results indicate that the amorphous structure of coating starts to transform into crystalline structure at approximately 400°C with activation energy of 306.5 kJ/mol. Crystallization reaction rate is K T = 4.11 × 10 20 exp(–306.5 kJ/ RT ). In order to further research the change of coating structure and property during crystallization, heat treatment tests at 300, 350, 400, 450 and 500°C are carried out in chamber electric furnace (SX-4-13). During heat treatment process, the phase composition of different stages can be summarized as: amorphous phase + Ni nanocrystalline (300°C) → amorphous phase + aggregated nanocrystalline (350°C) → remaining amorphous phase + aggregated nanocrystalline + new Ni 3 P phase (400°C)→Ni crystalline phase + growing Ni 3 P phase (450°C) → growing Ni crystalline phase + growing Ni 3 P phase (500°C). The coating has the best corrosion resistance after 350 °C heat treatment.