| Electrodepositing RE-Ni-W-P-B4C composite coating on mould of continuous casting was studied in this paper. Coatings with high hardness, better wear-resistance and oxidation-resistance properties were obtained in the study. The main contents of this article are as follows:The potential-pH diagrams of W-H2O, P-H2O and Ni-P-H2O systems at 298K were constructed by use of thermodynamic data. The electrodeposition mechanism of RE-Ni-W-P- B4C composite coating on copper was explained by analyzing potential-pH diagram and the principle of particulate electrodepositing. It showed that W and P went into the coating both by "induced co-deposition effect" and forming alloy, in which P was electrodeposited with the intermetallic compound Ni3P form. And CeO2 and B4C went into the coating by codepositing. The effect of experimental condition on hardness, thickness, and microstructure of the coatings was studied by orthogonal experiments. The hardness was tested by HM-114 rigidity tester. The surface and section morphology, thickness and microstructure were observed by ASM-SX SEM. The hardness of RE-Ni-W-P-B4C composite coatings as-deposited was in the range of 825.1HV and 1097.5HV, and the thickness value was 20.5μm to 150μm. The optimal electrodeposition conditions determined by analysis were: NiSO4·6H2O:70g·L-1, NaH2PO2·H2O:10g·L-1, Na2WO4·2H2O:150g·L-1, C6H8O7·H2O:140g·L-1, B4C:90110g·L-1, CeO2 :11g·L-1, pH= 67, Dk= 10A·dm-2, T= 60℃, t=4h, persisting agitating anterior 3 hours and stopping agitating latter 1 hour.The coating with better properties, microstructure and appearance was obtained in optimized condition. The phases of the coating examined by Philip XRD, it shows that the composit coating as-deposited was amorphous form. The composite coatings was crystallized form at 500℃for 3 hours which were: CeO2,Ni,W,P,Ni3P,Ni3B. The content of the component analyzed by ICP was: Ni:78.41%,W:3.64%,P:3.53%,B4C:12.84%,Ce2O:1.32%. The combination state assessed by filing showed that the combination of coating and copper base was well. The coating attained the highest hardness value when heat treated at 500℃for 3 hours, and the value was 1236.4HV. Compared with the resistance to high temperature oxidation of Cu, Ni-W-P, RE-Ni-W-P-SiC and RE-Ni-W-P-B4C coatings, the oxidation rate order of Cu and coatings was in the order of Cu>Ni-W-P>RE-Ni-W-P-B4C>RE-Ni-W-P-SiC. The thickness of the coating electrodeposited in optimized condition for 96 hours was 2219.5μm. Compared with current mould coatings used in China, RE-Ni-W-P-B4C coating has better hardness value, wear resistance and resistance to high temperature oxidation and it is hopeful to become a new-type mould coating.
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