Studies on the Properties and Structure of Pulse Electrodeposited Ni-W-P Series Multi-Composite Coatings

Abstract

The hardness, wear rates, phase structure and morphologies of DC(direct current) and PC(pulse current )electrodeposited Ni-W-P-SiC, RE-Ni-W-P-SiC, RE-Ni-W-P-SiC-MoS2 and RENi- W-P-SiC-PTFE composite coatings are studied. The results indicate that the hardness of pulse composite coatings is higher than that of DC composite coatings, but the hardness of RE-Ni-W-PSiC- PTFE composite coating is lower. The hardness of the four kinds of composite coatings increases with the rise of heat treatment temperature and reaches the highest value at 400°C, thereafter, the hardness begins to decrease. The hardness of RE-Ni-W-P-SiC composite coating is the highest when duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz and the hardness of RE-Ni-W-P-SiC composite coatings at 0.8 is higher than that at 0.6; the wear rates of Ni-W-P-SiC, RE-Ni-W-P-SiC, and RE-Ni-W-P-SiC-PTFE pulse composite coatings are lower than that of DC composite coatings and the wear rates of RE-Ni-W-P-SiC-MoS2 and RE-Ni-W-P-SiC-PTFE composite coatings are the lowest. Ni-W-P-SiC and RE-Ni-W-P-SiC pulse composite coatings are amorphous, and RE-Ni-W-P-SiC-MoS2 pulse composite coating is mixture, but the RE-Ni-W-PSiC- PTFE composite coating is crystal as–deposited. The crystalline grain size of PC composite coatings is smaller than that of DC composite coatings, and the addition of rare earth into the coatings can make crystalline grains become fine, all kinds of grains in the coatings distribute equably and there are not cracks on the surface and in the sections.