Study On Electrodeposition And Property Of Ni-P/BN(h) Composite Coating

Ni-P alloy coating have been widely applied in industries, such as mechanical,electronics and economy. However, with the development of technology and the needsof complex work environment, Ni-P composite coatings have received increasingattention with their multifunction. The hexagonal boron nitride [BN（h）] particles haveexcellent lubrication performance, high thermal stability and corrosion resistance, sopreparation Ni-P/BN（h） composite coating with BN（h） particles, can further improvethe corrosion resistant wear resisting performance of Ni-P alloy coating.Ni-P/BN（h） composite coating were prepared by electroplating, evaluated by theorganization structure of the coating, microhardness and deposition rate of the coating,the optimal operating condition as follows:pulse frequency1500Hz, occupies emptiescompared0.2, pH4.0, electroplating temperature50℃, current density5A/dm2, thecontent of BN（h） particle in plating solution20g/L, surface active agent poval.The effect of technology for heating processing on organization structure andmicrohardness of Ni-P/BN（h） composite coating was studied. The results show that:as-deposited Ni-P/BN（h） composite coating was amorphous structure; a small amountof Ni₅P₄and Ni₁₂P₅etc. metastable phases were precipitated from coating and thecoating was still amorphous structure after200℃heat treatment; but heat treatment of300℃,the precipitated phases are a lot of unsteady phases and a small amount of Ni3Pstable state phase, the composite coating was amorphous structure and crystallinestate mix organize; after heat treatment of400℃, the composite coating wascrystallized in great degree, compared to Ni-P alloy coating, BN（h） particles lead toreduce the precipitated speed of the second phase and extend crystallization time. thecrystallized temperature of the coating. At given heat treatment temperature, themicrohardness of Ni-P/BN（h） composite coatings increase at beginning, then decreasewith the extension of heat treatment time, have a maximum microhardness; The timeof reached the maximum microhardness of composite coating was short with the heattreatment temperature rises. Friction factor of Ni-P/BN（h） composite coating reduced with the suspensionquantity of BN（h） increased; when suspension quantity of BN（h） was20g/L, thefriction factor was minimum, about0.08, wear loss was just as a quarter of Ni-P alloyplating, Ni-P/BN（h） composite coating showed excellent tribological properties. Thefriction factor of composite coating increased with loads and rotation speed increased,the wear mechanism of composite coating was slight particle attrition when low loadand low rotation speed, however, the wear mechanism of composite coating wasfatigue wear and particle attrition synergy when high load and high rotation speed.The corrosion resistance performance of Ni-P/BN（h） composite coating wasresearched by SEM, tafel polarization curves and electrochemical impedancespectroscopy. The experimental results show that: the corrosion resistant performanceof Ni-P/BN（h） was superior to Ni-P alloy plating when immersed in3.5%NaCl and10%H₂SO₄solution for240h; corrosion resistance performance of Ni-P/BN（h）composite coating which after heat treatment in3.5%NaCl solution were changed,The best corrosion resistance performance is300℃heat treatment, and after400℃heat treatment of corrosion resistant performance was reduce, appear a little corrosion,the polarization resistance was least; And, the corrosion resistance of Ni-P/BN （h）composite coating were first increases, then decreased as for the extension ofimmersed time.