【作者】 李卫红；

【导师】 徐洲； 周细应；

【作者基本信息】 上海交通大学 ， 材料学， 2008， 博士

【摘要】 本文采用自动电刷镀技术制备了高复合量、平整致密、颗粒分布均匀的Ni-PTFE复合镀层,明显提高了复合镀层的制备效率,扩大了电刷镀技术的应用范围。通过系统的试验研究揭示了复合镀层自动电刷镀工艺参量、镀层组织与性能间的关系及作用规律,优化并确定了复合镀层制备的关键工艺参量。构建了包括液相传输、CTAB阳离子脱附和PTFE复合的复合镀层沉积模型,从理论上揭示了自动电刷镀Ni-PTFE复合镀层的共沉积机理,为今后将该技术应用于其它复合镀层提供了理论与工程应用基础。在复合镀层的制备与组织方面,探讨了复合镀层的质量,如镀层微观形貌,PTFE复合量、厚度、沉积速率和显微硬度等因素的分布规律,建立了镀层每一处阳极运动速率、沉积累计时间与被镀平面长度、阳极长度和阳极运动频率的关系式,给出了改善镀层质量分布均匀性的措施,优化并确定了自动电刷镀Ni-PTFE复合镀层的关键工艺参量。分析了复合镀层的相组成、基质金属晶粒尺寸、镀层的微观形貌和断面组织以及PTFE在镀层中的存在形式。结果表明,控制复合镀层PTFE复合量的关键参量包括温度、PTFE加入量、工作电压和阳极运动速率等,其中温度的作用最为明显。在PTFE颗粒与基质金属相结合的界面处,不存在孔隙等缺陷,PTFE颗粒与基质金属结合紧密。在复合镀层的沉积机制研究方面,提出了包括液相传输、CTAB阳离子脱附和PTFE复合的复合镀层沉积模型。首先,PTFE颗粒连同其表面吸附的Ni2+和CTAB阳离子在液流作用下,到达阴极表面附近;然后,CTAB阳离子从PTFE颗粒表面上脱附;最后,PTFE颗粒表面吸附的Ni2+发生电化学还原反应与阴极表面相结合,并被不断生长的Ni基包埋。PTFE颗粒沉积过程是力学机理与电化学机理共同作用的结果。最后,结合复合镀层的摩擦磨损性能研究,建立了复合镀层电刷镀工艺参量、镀层组织特性与复合镀层摩擦磨损性能间的关系,探讨了PTFE复合量等参数对摩擦磨损性能的作用规律。结果表明,随镀液温度的升高,PTFE颗粒在镀层中弥散分布,复合量显著增加,镀层组织越来越平整致密,摩擦系数明显减小,耐磨性增加。随PTFE加入量的增加,PTFE发生团聚,镀层组织越来越粗糙,摩擦系数明显减小,耐磨性下降。而阳极运动速率对PTFE复合量和镀层的粗糙度、致密性和摩擦磨损性能影响不大,但可细化镀层组织。工作电压对PTFE复合量影响不大,但随着工作电压的增加,镀层明显趋向粗糙疏松,减小摩擦系数,耐磨性下降。更多还原

【Abstract】 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.更多还原