Preparation Of Ni-P-ZrO₂ Electroless Composite Coating On Zr-8Al Alloy

Electroless Ni-P-ZrO₂ composite plating with thickness of 15 μm was prepared on Zr-8Al alloy. The Ni-P-Zr O₂ composite plating was tested and analyzed via X-ray diffractometer, scanning electron microscopy, atomic force microscopy and optical microscope. In this dissertation, the pretreatment phosphating process for Zr-8Al alloy and the effect of the amount of ZrO₂ particles and the type and amount of surfactant on the properties of the composite Ni-P-ZrO₂ plating were studied. The results are as follows.（1） The phosphating solution with Na2HPO₄ is suitable for composite plating on Zr-8Al alloy. The optimum phosphate process is 55℃×4min;The prescription of phosphating solution is: H3PO₄ 15ml/L, ZnSO₄ 3g/L, NaF 1.5g/L, thiourea 0.15g/L, Na2HPO₄ 10g/L;（2） With the increase of ZrO₂ particles, the deposition rate of first increases and then decreases. The deposition rate reaches as high as 10.34×10-2mg/mm2·h when the amount of ZrO₂ particles is 4 g/L;（3） With the increase of ZrO₂ particles, the micro-hardness and wear resistance of Ni-P-ZrO₂ plating increases while the corrosion resistance of that decreases. The wear resistance of Ni-P-ZrO₂ plating was best when the amount of ZrO₂ particles is 4g/L. In order to ensure the best combination of corrosion and wear resistance, 3g/L to 4g/L ZrO₂ particles are favorable;（4） With the increase of OP-10, the deposition rate of electroless Ni-P-ZrO₂ composite plating decreases and the wear resistance of that increases. The optimum amount of OP-10 is among 20²5 ml/L;（5） Smooth Ni-P-ZrO₂ composite plating with uniform cellular is prepared with LAS anionic surfactant and OP-10 nonionic surfactant. Yet the corrosion resistance of Ni-P-ZrO₂ composite plating is decreased with the addition of LAS. So the amount of LAS should be kept below 100 mg/L.