Preparation And Properties Of Ni-based Tribological Composite Coatings

It was showed by early researches that nearly 70% failure of the components wascaused by friction and wear, which led great loss to the civil economy. Therefore, it isof great importance to improve the components' properties to friction and wear.Composite plating techniques have the advantages of less investment, easier operationas well as the properties adjustment with the different desired requirements, so thathave a very prosperous application in surface science and engineering. In recent years,with the development of nano-technology, nano-composite plating techniques havebeen gradually formed. Compared with the common layer with micron particles, thenano-composite coatings have higher hardness, better self-lubricating performanceand higher wear resistance.A great deal of selective experiments has been done to explore the optimalpreparation parameters of the Ni-based coatings. The best parameters for Ni-PTFEcoating are as follows: pH3.5, cathodic current density 7A/cm2, 60 min, 60℃ and48mol/L PTFE content. Whereas for Ni-P-Si3N4 coatings, the optimal parameters arepH4.8, cathodic current density of 3A/dm2, 60 min, 75℃ and 0.5g/L Si3N4 content.Accompanied with the increasing of factors listed above, the plating rate ofNi-P-Si3N4 coating exhibited a trend of firstly increase and then decrease. In addition,when the Si3N4 concentration increased further, the deposition rate reduced graduallyand reached a certain value at last.The morphology, microstructure, hardness as well as friction and wear behaviorsof Ni-based composite coatings were observed and determined by using XRD, SEM,MH-6 microhardness tester and friction and wear tester. Ni-P-Si3N4 coating obtainedwas compact and smooth. After a heat treatment at 400℃, the hardness of the coatingcan reach a value up to 995.8HV which is much higher than that of Ni-P coating.Ni-PTFE coating is also compact, smooth and uniform. Under the same load and testduration, the coefficient of friction and the wear loss of Ni-PTFE coating are less thanthat of Ni-P-Si3N4 coating.Ni-PTFE-Si3N4 composite coating was designed and developed based on theoptimal preparation parameters for Ni-P-Si3N4 and Ni-PTFE coatings. Compared withNi-P-Si3N4 and Ni-PTFE coatings, Ni-PTFE-Si3N4 composite coating has a higherhardness, better lubrication and higher wear resistance.