Ultrasonic-Assisted pulse electrodeposition of Ni-P/Graphene oxide composite Coatings: Effect of acoustic energy on Microstructure, Wear, and corrosion.

NiP-graphene oxide (GO) composite coatings were fabricated by ultrasonic-assisted pulse electrodeposition using a horn-type ultrasonic processor operating at 20 kHz and equipped with an 8 mm-diameter titanium probe. The non-sonicated condition was designated as 0 W, while nominal generator power readings of approximately 50 and 100 W were obtained under the selected sonication conditions; the corresponding calorimetric power dissipated in 400 mL of electrolyte was determined experimentally. The calorimetric powers measured at nominal settings of 50 and 100 W were 34.67 and 49.64 W, corresponding to volumetric power densities of 0.0867 and 0.1241 W mL⁻1, respectively. The effects of acoustic energy input and GO concentration on coating morphology, crystallographic structure, hardness, tribological behavior, and corrosion resistance were systematically evaluated using FESEM, EDS, Raman spectroscopy, XRD, microhardness testing, ball-on-disc wear testing, potentiodynamic polarization, and electrochemical impedance spectroscopy. Increasing the calorimetric power density promoted cavitation-assisted mass transport, GO deagglomeration, heterogeneous nucleation, and hydrogen-bubble removal from the cathode surface. Consequently, the crystallite size decreased from 33.8 to 24.5 nm, while the hardness increased from 623 to 679 HV. Further optimization of the GO concentration revealed that the coating produced with 300 mg L⁻1 GO at a nominal ultrasonic power of 100 W exhibited the highest hardness of approximately 704 HV, together with the lowest coefficient of friction, wear rate, and corrosion current density. The optimized coating was subsequently tested under different normal loads and sliding speeds, and a wear-mechanism map was constructed to identify transitions among mild abrasive wear, abrasive-fatigue wear, and oxidation-assisted delamination. These findings establish a quantitative acoustic energy-microstructure-property relationship and demonstrate the potential of ultrasonic-assisted pulse electrodeposition for producing NiP-GO composite coatings with enhanced wear and corrosion resistance.