Preparation And Properties Of Enhancing Friction Type Ni-P/Diamond Composite Coating Deposited By Electrochemical Technique

In this thesis, enhancing friction type Ni-P/diamond composite coatings were fabricatedon45#steel surface by electrochemical technique. The mechanical properties of Ni-P bondinglayer with different levels of P were studied. Effects of diamond content and diamond particlesize on enhancing friction of Ni-P/diamond composite coatings with middle P content wereinvestigated. Effect of enhancing friction under conditions of dry friction, oil lubrication andgrease lubrication conditions were also studied. Moreover, the enhancing friction mechanismwere analysed. The main conclusions are listed as follows:（1）The Ni-P/diamond composite coatings with different P and diamond micro-particlescontent were electrochemically deposited by changing hypophosphite and diamond content inbath. The effect of deposition time on the composite coating thickness was also studied. Apart of the diamond particles were uniformly embedded in the matrix of phosphorus Ni-Palloy coating, and the rest of diamond particles protruded from the coating surface.（2）The investigation on the microstructure and mechanical properties of theNi-P/diamond composite coatings shown that a strong bonding between the deposit and steelsubstrate was achieved. Ni-P bonding layer generated a hard phase Ni3P after heat treatment.The hardness of the adhesive layer achieved the maximum of893Hv at the P content of7at.%, when the Ni-P bonding layer possessed the most excellent grip strength to diamondparticles.（3）Under dry friction conditions, the friction coefficient of Ni-P/diamond compositecoatings firstly increased and then decreased with the diamond particle content in thecomposite coatings increasing. The composite coefficient of static friction coatings achieved0.72when the Ni-P diamond area of content was22±5%.（4）The friction coefficient of Ni-P/diamond composite coatings increased withdiamond particle size increasing under dry friction conditions. Under dry friction, oillubrication and grease lubrication conditions, Ni-P/diamond composite coating frictioncoefficient were all around0.5. Compared with the traditional steel/steel with vice, Ni-P/diamond composite coatings with special surface design dramatically improved strength andmechanical interlock with the opposite, increasing friction by as much as200to300%.(5) As shown by tafel curves and corrosion morphologies, Ni-P/diamond compositecoating performed more excellent resistant corrosion than Ni-P ally coating in acid, saline andalkaline solution.