Preparation and Corrosion Behavior of Ni-Co-Si3N4-Al2O3 Nanocomposite Coatings Using Jet Electrodeposition with Varying Jet Voltages and Pulse Parameters
摘要
Ni-Co-Si3N4-Al2O3 composite coatings were successfully fabricated on a C1045 steel substrate by varying the jet voltage (6, 8, 10, and 12 V), pulse frequency (2, 4, 6, and 8 kHz), and duty cycle (50, 60, 70, 80, and 90%). The microstructure, chemical composition, grain size, microhardness, wettability, and corrosion resistance of the Ni-Co-Si3N4-Al2O3 coatings were comprehensively analyzed. The results revealed that pinholes, precipitate structures, and cracks were observed at a low jet voltage, whereas microcracks reappeared at a high jet voltage. The Ni-Co-Si3N4-Al2O3 composite coatings at 4 kHz and 70% exhibited excellent uniformity, compactness, and fine structures. All the Ni-Co-Si3N4-Al2O3 composite coatings displayed Ni face-centered-cubic diffraction peaks, with an average grain size of 18.82 nm. Microhardness and wettability test results indicated that the microhardness and water contact angle of the Ni-Co-Si3N4-Al2O3 composite coatings initially increased and then decreased with an increase in the jet voltage, pulse frequency, and duty cycle. At 8 V, 4 kHz, and 70%, the microhardness and contact angle of the composite coatings were 666.5 HV0.1 and 118.8°, respectively. Furthermore, the corrosion resistance test results demonstrated that the Ni-Co-Si3N4-Al2O3 composite coatings exhibited a more positive Ecorr, lower Icorr, and larger Rp and Rct at an optimal pulse frequency and duty cycle with a constant jet voltage. The impedance semicircle diameter of the coatings was the largest at 8 V, 4 kHz, and 70%. Additionally, Ecorr, Icorr, Rp, and Rct of the Ni-Co-Si3N4-Al2O3 binary nanocomposite coatings reached − 358 mV, 2.18 µA·cm−2, 13.22 kΩ·cm−2, and 8.12 × 104 Ω·cm−2, respectively.