Electrodeposition Of Ni/paraffin Composites And Research Of Their Properties

Self-lubricating composites have been widely used in industrial fieldbecause of their excellent tribological properties. In this dissertation,Ni/paraffin composites were designed and fabricated by electrodeposition,and in-situ liquid self-lubrication was achieved as paraffin has low meltingpoint and melts into liquid due to the frictional heat.To prepare paraffin emulsion, a mixture of paraffin and aqueous solutioncontaining CTAB, a cationic surfactant, was first heated to80℃and thencooled down naturally under mechanical stirring and ultrasonication. Theaverage size of the paraffin particles in the emulsion was about1μm, and gotsmaller as the stirring speed increased. SEM images showed sphericalparaffin particles clearly.Ni/paraffin composites were fabricated by DC electrodeposition fromnickel sulfamate electrolyte with an introduction of paraffin emulsion. SEMimages of the composites surface corroded by diluted nitric acid proved that paraffin particles were successfully embedded into the Ni matrix. Paraffincontent in the composites increased with the paraffin concentration in theelectrolyte, reaching12.33vol%from the electrolyte containing1.8g/Lparaffin. Paraffin content decreased as the current density rose up. Theinfluence of stirring pattern to surface quality of the composites was studied.In comparison to magnetic agitation, mechanical stirring could effectivelymake the electrolyte more uniform, resulting in better coating quality. Thepreferred orientation of Ni coating was changed from Ni(200) to Ni(111), andthe grain size was refined as saccharin was introduced into the electrolyte.But the preferred orientation of the composite coatings with saccharin waschanged back to Ni(200), with grain sizes bigger than those of Ni coatingwith saccharin but smaller than those of Ni coating without saccharin. Themicrohardness of the composite coatings dropped down as paraffin contentincreased.The tribological properties of Ni and the composite coatings werestudied by a ball-on-disk friction and wear tester. The friction coefficient of2.38vol%coating was high (higher than0.7), similar to that of Ni coating.The friction coefficients of5.85vol%and7.12vol%coatings were improved,but not very obviously. Compared to Ni coating and those composite coatingswith lower paraffin content, the friction coefficient of9.65vol%coating decreased distinctly, dropping to about0.15。The wear rate of the compositesincreased with the paraffin content. The wear mechanisms of Ni coating and5.85vol%coating were mainly delamination wear and oxidation wear, and amass transfer from the counter-part to the coating also occurred. The mainwear mechanism of9.65vol%coating was plastic smearing. The influence offriction load and friction speed to the tribological properties was alsodiscussed.