Studies On Process And Properties Of Pulse Electrodeposited Ni-W-P-SiC Series Composite Coatings

A series new Ni-W-P-SiC, RE-Ni-W-P-SiC, RE-Ni-W-P-SiC-MoS2 and RE-Ni-W-P-PTFE composite coatings with more excellent corrosion-resistance, hardness, oxidation-resistance and wear-resistance by pulse current were studied. The deposited composition, the properties and structure were tested by EPMA-1600 electron probe, 3015 X-ray diffraction patterns, optics microscope, HX-1 micro-hardness instrument, HDV-7 transistor permanent potential apparatus, MM2000 wear machine and YWX-F neutral salt-frog corrosion box, etc.The potential-pH diagram of Ni-P-H2O system at 298K was constructed by use of thermodynamic data. The formation mechanism of Ni-W-P-SiC system composite coatings was explained by means of potential-pH diagram, and the feasibility of pulse composite plating was analyzed by the mechanism and influence factors of pulse plating.The effects of pulse frequency and duty ratio values on the depositing rate and composition of the four composite coatings were studied and the results show that the influences were large. The depositing rate was high at f=20~33Hz, r=0. 4-0.8 in Ni-W-P-SiC and RE-Ni-W-P-SiC pulse electrodeposited processes; The depositing rate was high at f=33Hz, r=0.8 in RE-Ni-W-P-SiC-MoS2 and RE-Ni-W-P-SiC-PTFE electrodeposited processes. Content of Ni was highest in all coatings, Contents of MoS2 and PTFE were litter in RE-Ni-W-P-SiC-MoS2 and RE-Ni-W-P-SiC-PTFE composite coatings.The similarities and differences of the four composite coatings in corrosion-resistance, hardness, oxidation-resistance and wear-resistance and the divergences of properties between pulse deposited coatings and direct deposited coatings were studied. The corrosion-resistance of the four pulse deposited coatings was better than stainless steel(lCr18Ni9Ti) in HCl, H2SO4, H3PO4 and FeCl3 solutions; The deposited coatings by pulse current were better than that of by direct current in corrosion-resistance; The corrosion-resistance of composite coatings after heat-treatment at 400 C was better than plating coatings except RE-Ni-W-P-SiC-PTFE pulse deposited coatings; The corrosion-resistance of all pulse deposited coatings wasthe best in H3PO4 and the worst in FeCl3; Ni-W-P-SiC pulse composite coatings had better corrosion-resistance compared with the other three pulse composite coatings. The hardness of composite coatings was higher than hard chromium except RE-Ni-W-P-SiC-PTFE coatings; The deposited coatings by pulse current were better than that of by direct current in hardness; The hardness of RE-Ni-W-P-SiC composite coatings was the highest in the four pulse composite coatings. The hardness of the pulse composite coatings were much better than hard chromium and direct current coatings; The hardness of RE-Ni-W-P-SiC-MoS2 and RE-Ni-W-P-SiC-PTFE pulse composite coatings were better than the other pulse composite coatings. The oxidation-resistance of the pulse composite coatings were better than that of the direct current deposited coatings; Ni-W-P-SiC and RE-Ni-W-P-SiC pulse composite coatings had more better oxidation-resistance compared with the other composite coatings.The effects of pulse frequent and duty ratio value on corrosion-resistance of Ni-W-P-SiC composite coatings were studied by means of immerse experiments, drawing anodic polarization curves and neutral salt-frog corrosion test. The results indicated that Ni-W-P-SiC composite coatings had excellent corrosion-resistance at the range of f=33~50Hz, r=0.4~0.8. The surface morphologies of Ni-W-P-SiC composite coatings after corrosion indicated that the coating corrosion was dot corrosion in HC1 solution, but the coating corrosion were crack corrosion in H2SO4, H3PO4 and FeCl3 solutions.The studies on the hardness and oxidation-resistance of RE-Ni-W-P-SiC pulse current coatings indicated that pulse frequency and duty ratio value had a large influence on the hardness and oxidation-resistance. The coatings had high hardness at the range of f=50Hz, r=0.6~0.8 and the coatings had good oxidation-resistance at f=33Hz, r=0.4(or 0.6). Both heating temperature and he...