Investigation On The Technology And Performance Of Ni-P Electroless Plating

The cast iron has played an important role in the progress of humansociety, and it also has great influence to the national economy andmanufacturing as an engineering material. With the development of scienceand technology, the quality of cast iron has to meet higher standard. In thepresent, the method to improve cast iron's erosion-resisting andwear-resisting property is surface treating, which can form a kind of coat toprotect its surface. With SEM, GDS, XRD and other electrochemicalmeasuring instrument, the technology and performances of Ni-P electrolessplating on cast iron were systematically studied. Main conclusion is asfollows:1. Through orthogonal experiment, the optimal performance parameterof Ni-P electroless plating is: NiSO₄·6H₂O(10g/l), Na₂HPO₄·H₂O(20g/l),H₃BO₃(5g/l), C₃H₆O₃(10ml/l), KF(1g/l), amber acid(10g/l), at the same time pH=6.0, T=90±2℃, which is depended on the value of the biding force.2. At the optimum performance parameter, the surface of Ni-Pelectroless plating is very compact, and its thickness can reach 51.5μm(2h),at the same the content of phosphorus is between 5%～7%. After scratchexperiment, the result indicates that the binding force between Ni-Pelectroless plating and matrix is 63N, which can satisfy the industrialrequirements.3. Ni-P electroless plating on cast iron belongs to mid class, the surfaceis composed of cystiform substance which has a uniform size, is a littleamorphous phase and some nano-crystal.4. The results of GDS indicate that carbon atoms will be enriched at thesurface of the coat, and Ni, Fe have a gradient distribution.5. After temper at 400℃for 1h, the coating's constitution turns tocrystal from amorphous and nano crystal, which can be indicated by X-Raypattern. At the same time, Ni₅P₂, Ni₁₂P₅, Ni₂P and Ni₃P precipitated fromNi-P solid solution.6. In the process of heat-treatment, the hardness of the coat will alsochange: with increase of heat-treatment temperature, the hardness willdecrease slightly at the first and then largen continuously. Tempered at400℃for 1h, the hardness of the coating can reach a maximum 1140HV,while it will have the tendency to decrease when heat-treatment temperature is higher than 450℃.7. Through electrochemical corrosion experiment at 5%HC1, 5%H₂SO₄and 3.5%NaC1 solution, the corrosion-resistance of the cast iron and Ni-Pelectroless plating had been examined, it is found that free corrosionpotential of the cast iron turns to a higher value after electroless plating ,thecorrosion-resistance has improved greatly. According to the loss of weight at3.5%NaC1 solution, the higher phosphor coating has highercorrosion-resistance than the lower phosphor in 3.5%NaC1 solution.8. The load weight has more obvious influence on the coating'swearing rate: with the load weight increase from 1N to 1.5N, the wearingrate enhances nearly 10 times for Ni-P coating, while after tempered, it willonly enhances 1.3 times.