Influence of Pulse Times on the Characteristics of Ni-W-P-CeO2-SiO2 Nano-composite Coatings

Square-wave pulse current was used to electrodeposit Ni-W-P alloy coating containing nano-CeO2 and nano-SiO2 particles. At constant pulse peak current density (30 A/dm(2)), the influence of pulse on-times and pulse off-times on the characteristics was researched, the characteristics were assessed by chemical compositions, microhardness and microstructures. The results showed that pulse co-deposition of Ni, W, P, nano-CeO2 and nano-SiO2 particles led to Ni-W-P-CeO2-SiO2 nano-composite coatings in fine-grained structure on common carbon steel. When the pulse on-time and pulse off-time were both controlled at 100 mu s, the highest microhardness of 6890 MPa was obtained. At constant pulse off-time (1000 mu s), the crystal size of the nano-composite coating decreased with increasing the pulse on-time of 100 similar to 400 mu s before it started to increase with further increasing the pulse on-time of 400 similar to 1000 mu s. At constant pulse on-time (100 mu s), increasing the pulse off-time of 100 similar to 4000 mu s resulted in a progressive increase of the crystal size of the nano-composite coatings.