Effect of Saccharin on the Structure and Properties of Electrodeposition NiWP Alloy Coatings

NiWP alloy coatings electrodeposited on pure copper substrates with additive saccharin (C₇H₅NO₃S) contents of 0-6 g/L were investigated via scanning electron microscope (SEM), x-ray diffractometer, microhardness, polarization curves, deposition rate, and wear resistance. Results show that the corrosion resistance, microhardness, and wear resistance of the NiWP alloy coatings have been optimized with the increase in saccharin contents changing from 2 to 4 g/L. The morphology of the NiWP alloy coatings observed via SEM exhibits a typical spherical nodular structure. The increase in saccharin content will decrease crack formation. The phases of NiWP alloy coatings are mainly the mixture of amorphous and microcrystalline nickel. Moreover, the quality of the coating can be improved through a slight change in the deposition rate. The hardness of the NiWP alloy coating continues to increase from 530.5 to 630.5 HV with the increase in saccharin content from 0 to 6 g/L. In addition, the P and W contents in the alloy coating are increased from 8.29 to 8.66 wt.% and from 28.68 to 30.45 wt.%, respectively. The corrosion potential is varied from −0.332 to −0.247 V, and the current density is varied from 23.81 to 3.282 µA/cm² when the saccharin content is in the range of 0-4 g/L. With the increase in saccharin content from 0 to 4 g/L, the wear loss decreases gradually. Subsequently, a plateau is reached when the saccharin content is higher than 4 g/L. NiWP coatings show better tribological performances under high rotational speed than those under low rotational speed. Several possible reasons have been discussed.