Characteristics And Co-Deposition Mechanism Of Automatic Brush Electroplated Ni-Ptfe Composite Coatings

A high polytetrafluoroethylene (PTFE) content, smooth, dense, Ni-PTFE composite coating with uniform PTFE particles distribution was developed by automatic brush electroplating (BEP), increasing the coating manufacturing efficiency and enlarging the application range of brush electroplating. The relationships among automatic BEP parameters, microstructure and properties were explored, and the key parameters were optimized. A three-step co-deposition model, including transmission of PTFE particles by bath, desorption of CTAB from PTFE particles and deposition of PTFE particles by reduction of Ni2+ was proposed, with which the co-deposition mechanism of automatic BEP Ni-PTFE composite coating was revealed. It provides a theoretic and engineering basis for future use.The distribution of composite coating quality, such as surface morphology, PTFE content in coating, coating thickness, deposition rate and micro-hardness was discussed. Two functions were established, revealing the variation of anode movement speed and accumulated deposition time at any site with coating length, anode length and anode movement frequency. The key parameters of automatic BEP Ni-PTFE composite coatings were optimized and determined. The phase, grain size of Ni matrix, surface morphology, cross-sectioned microstructure and PTFE existence in coating were analyzed. The results showed that, PTFE content in coating is controlled by bath temperature, PTFE concentration in plating bath, working voltage and anode movement speed commonly, in which the bath temperature is the most important parameter. PTFE particles are tightly bonded with Ni matrix and there is no porosity at the interface.A co-deposition model was proposed. First, PTFE particles with adsorbed Ni2+ and CTAB ions reach the vicinity of the cathode surface by plating bath. Second, CTAB ions are desorbed from PTFE particles surface and adsorbed on cathode surface. Last, PTFE particles attach on the cathode surface by reduction of Ni2+ adsorbed on the surface of PTFE particles and are embedded by growing Ni matrix. The co-deposition of PTFE particles with Ni matrix is controlled by mechanical and electrochemical mechanisms commonly.The relationships among automatic BEP parameters, microstructure and properties were explored. The effect of PTFE content in coating on friction and wear properties was discussed. The results show that, with the increase of the bath temperature and PTFE concentration in plating bath, the PTFE content in coating increases and the friction coefficient decreases. With a higher PTFE concentration in plating bath, PTFE particles agglomerate in coating, resulting in poor wear resistance. For higher bath temperature, PTFE particles distribute uniformly in coating, resulting in good wear resistance. The anode movement speed has little effect on PTFE content in coating, coating roughness and density, friction and wear properties. The microstructure of Ni-PTFE composite coatings is refined by increased anode movement speed. The rough and loose microstructure obtained with high working voltage, leads to low friction coefficient and high wear rate.