| To make the equipments meet the severe service requirement, the eletroless or eletro-brush plating technology has been developed from the single coating, to the composite coating, and to the nano-particle composite coating. The nano-particle composite plating technology is used for preparing the composite coating with the distinctive anti-wear performance.Nano-particles were dispersed into the plating electrolyte by using ultrasonic,mechanical and surfactant. The experimental project was confirmed through optimizing the technics. Microstructure of nano-particle composite coatings was studied through SEM and XRD, and deposition mechanism of the composite coating was investigated as well as their reinforcement mechanism. Annealing the coating, the microstructure and properties was studied and compared before and after annealing. The main results gained are as follows:The preparation process of the composite coatings was optimized. When the bath compositions and conditions for the electroless coatings were: WC nanoparticles 1g/L, stirring rate 200 rad/min, pH=4.5 and deposition time 3 h, it was found that the nanocomposite coating was able to significantly obtain a high rate of deposition, and improve the quality of the composite coatings.Micro-structure of nano-particles composite coatings was analyzed by means of SEM and XRD. Reinforcement mechanisms of composite coatings were as follows: fine crystals and second phase particles. The distribution of nano-particles was uniform, and also the nano-particles adhered to nickel compactly.The nano-structured coatings was annealed at 200℃, 400℃and 600℃in vacuum It was found that for all the samples annealed at different temperature, the thermal stability of WC particles in the coatings is evident, since there are no changes in the shape and intensity of the diffraction profile of the WC phase. And the microhardness and wear resistance of the 400℃annealed sample increased to the maximum value.By the observation of SEM to the abrasion morphology of nanocomposite coating, it reveals that in the process of abrasion, nano-particles restrained the plastic deformation through blocking the slippage of dislocations and so hindered the initiation and propagation of cracks, together with high mico-hardness of nano-particles, which provided the excellent contact fatigue resistance to the nano-particles composite coatings.Study on micro-strcture and anti-fretting wear of the coating showed the mechanism that nano-particle composite coatings and higher anti-fretting were property. Uniform compact morphology and fine microstructure of the coatings, and high hardness and dispersed nano-particles in the coatings, together with the reinforcement nano-particles provided to the debris film, increased the resistance of plastic deformation on the worn surface and so reduced the materials adhesion and transfer, which restrained the initiation and propagation of cracks and gave high anti-fretting wear properties to the nano-particle composite coatings. |
