| Based on the ordinary electroplating, composite electro-deposition is a composite treatment surface technology, which is developed by adding infusible high-hardness, high wear-resistant particles into the bath。And composite plating is also a new technique of preparing composite materials, which is developing rapidly in recent years. Reserving the advantages of ordinary plating, the composite plating owns more excellent performance, such as high-hardness, selflubricit, wear-resisting, high temperature oxidation resistance and so on. The technique of composite plating shows wide applicable prospect in the industries of machinery, motorcars, energy sources and chemical engineering, et al.In this thesis, micron-diamond is used as composite particles, Ni-W-P-diamond composite coatings are successfully prepared by the way of electrodeposition. The micro-morphology and micro-structure of Ni-W-P-diamond composite coatings were studied by SEM,XRD, HVS-1000 micro-hardness instrument, UMT-3 friction and wear tester. Respectively, the effects of micro-structure on the properties were also discussed. In this paper, the detailed research work was as follows:1. In this thesis, the technological conditions of Ni-W-P-diamond composite coatings were studied by the numbers. The effect of some conditions (such as current density of cathode, content of diamond in bath, stirring rate,electrolyte temperature and pH value ,etal)on the diamond content in the composite coatings and their micro-hardness were discussed. On the basis, the optimal process conditions have been made sure for electrodepositing Ni-W-P-diamond composite coating as following: current density is 7A/dm2, the diamond concentration in solution is 10g/L, electrolyte temperature is 70℃, pH=6.5,stirring rate is 200rpm.On the condition, the composite coatings obtained in our experiments are hoar and half bright, the dispersion of diamond particles is homogeneous, and the deposition rate is about 18μm/h. The diamond content in composite coatings is about 10wt.%. The Ni-W-P-diamond composite coating obtained under optimal process conditions has a microhardness above 900Hv,Which was 1.5 times Ni-W-P coating.2. Furthermore, the effect of heat treatment on the micro-hardness,the structure and corrosion resistance of Ni-W-P-diamond composite coatings and the resistance to oxidation at high temperature were discussed. The experimental results show that when heat treatment temperature is below 500℃for 1h, the amorphous structure of deposit was still a mixture of amorphous and nanocrystalline; The composite coatings start to crystallize when heat-treated at 500℃for 1h, and Ni3P phase was formed. When heat treatment is above 600℃for 1h , the crystallization has been finished by and large. And the composite plating heat-treated at 500℃for 1h exhibits the highest micro-hardness (1424Hv) and the best corrosion resistance. Ni-W-P-diamond composite coating has better resistance to high temperature oxidation than Ni-W-P coating.3. The wear-resistant of the composite coatings was studied in the first time, The effect of some factors (such as the temperature of heat treatment, content of diamond in bath, the abrasion loading)on wear-resistant were discussed Ni-W-P-diamond composite coating has the best wear resistance when heat treatment is 500℃for 1h and the diamond content in composite coatings is about 7 wt.%. Ni-W-P-diamond composite coating has better wear-resistant than Ni-W-P alloy plating and Cr plating. |
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