Investigation On Electroless Plating Ni-P Alloys On Nanocrystalline Copper

As a material surface treatment technology, electroless plating has developed very rapidly in recent years. Many relevant research has been did, and platings with various functions such as composite Coatings, multiple alloy coatings has emerged. However, the traditional electroless Ni-P coating operates simply and costs less, and by the change of the process, we can also get Ni-P coating with various special performance. So electroless Ni-P coating is still widely used, and the study on Ni-P coating is still significant. Now, study on Ni-P coating has many, but the research on the effect of the organizational structure of substrate material on the deposition process and performance of Ni-P coating is still not enough.In this paper, electroless plating Ni-P alloy coating was deposited on coarse-grained and nanocrystalline copper respectively. Surface morphologies, microstructures and properties of Ni-P coatings on two different samples were compared, and the effect of heat treatment on the microstructures and properties of Ni-P coatings on two different samples was also studied.Based on the studies, the main conclusion can be drown as follows:1. By orthogonal experiment, the optimal scheme of electroless plating Ni-P coating on nanocrystalline copper is obtained: NiSO4·6H2O 30g/L NaH2PO2·H2O 35g/L Na3C6H5O7·2H2O 30g/L CH3CH(OH)COOH 16ml/L NH4Cl 1mol/L pH:7 Temperature:80℃2. The nanocrystalline copper does not need to be polished before the electroless plating. Electroless Ni-P coating can deposit on the surface directly, and the deposition rate on nanocrystalline copper is faster than on coarse-grained copper. During the deposition of the plating, concentration of NaH2PO2, temperature and pH value of the plating bath can affect the performance of the coating. And the temperature of plating bath affects more, followed by the concentration of NaH2PO2, and pH value is less affected.3. Silvery white, brightness and uniform electroless Ni-P coating is obtained on nanocrystalline and coarse-grained copper respectively. And by the metallographic microscope, we can observe that electroless Ni-P coating is composed of compact cellular structure, and the size of the cellular structure is uniform. Surface morphology of the Ni-P coating does not change significantiy after heat treatment under lower temperature. While Ni-P coating recrystallizes and the cellular structure grows up after heat treatment under 500 ℃. In addition, compared with coarse-grained copper, the cellular structure on nanocrystalline copper is larger.4. After the same deposition time, the Ni-P coating on nanocrystalline copper is thicker, and it suggests the deposition rate on nanocrystalline copper is faster. This mainly because nanocrystalline copper has finer grain and greater catalytic activity on per unit area, so the deposition rate on nanocrystalline copper under the same conditions is faster.5. The Ni-P coating is amorphous before heat treatment, and gradually transforms into crystalline structure after different heat treatment. Electroless plating Ni-P coating on nanocrystalline copper has high hardness, and the hardness can become higher after heat treatment under lower temperature. The coating on nanocrystalline copper has highest hardness after heat treatment under 300℃, and then the hardness value declines with the increase of the heat treatment temperature.6. Electroless plating Ni-P coating on nanocrystalline copper has better adhension strength, this mainly because the size of the grain of nanorystalline copper is smaller, and the mechanical bite on nanocrystalline copper is more. And also the surface of nanocrystalline copper is rough, which contributes to the mechanical bite. The adhension strength of Ni-P coatings on two different samples increases after heat treatment. And compared with coarse-grained copper, the adhension strength of Ni-P coating on nanorystalline copper is better. 7. Ni-P coating got in the study has small friction coefficient. Wear resistance of the coating deposited on nanocrystalline and coarse-grained copper shows different changes, and the Ni-P coating on nanorystalline copper has lower friction coefficient and shows better Wear resistance. This because, on the one hand, the Ni-P coating on nanorystalline copper has higher hardness, and on the other hand, the adhension strength of Ni-P coating on nanorystalline copper is better. And the Ni-P coating on nanorystalline copper shows best Wear resistance after heat treatment under 300℃.