Study On The Preparation Of Function Coating By Explosive Compaction-coating Method And Its Mechanism

With the development of surface technology and engineering, it is paid great attention to study functional coatings, which are applied in fields of energy source, petrochemical industry, marine industry, hydraulic engineering, construction industry, machinery, aerospace, transport, and military industry. As an inseparable part of surface technology and engineering, functional coatings have important influence on a national economic construction, national defense, and people living. Although coating based nano-materials have developed rapidly in recent, the manufacture technology of coating is still a challenge, especially in the manufacture of functional coating, which has became a key direction in field of composite material for the researchers.In this dissertation, a new coating manufacturing technology, i.e., explosive compaction coating (ECC) is first proposed, and the related principle is introduced in detail. According to the principle, we design an experiment platform of ECC to explore the technology process of coating and to investigate the bonding mechanism of coating. In addition, the related theory of explosive blast is expected including the explosive detonation driving flying plates, the explosive wave in powder medium, the equation of state for impact on powder materials.Copper coating has been manufactured by ECC. According to the principle of explosive detonation driving the flying plate, the influence of key design parameters on coating manufacture is discussed. Moreover, the metallographic formation, section morphology, surface elementary composition of the coating and microhardness, have been investigated, by optical microscope, SEM, XRD and micro-hardness tester, respectively. Coating porosity is calculated using line transect method.The formation mechanism of ECC has been analyzed, which involves the bonding mechanism between the metal plate and metal powder, and between the metal powder particles. It is obviously found that angular deformation near the boundary is one of the most important factor causing instability boundary and flexuous boundary, which influences the integrating state and intensity of the boundary. Metal jet is created due to shear instability under high-speed deformation of metal, which is deemed to be beneficial to the integration of the metal plate and metal powder. However, as for the metal powder, their integrating mechanism is mainly caused by the plastic deformation of the particles, closed gap under high pressure and melting behavior for the particle surface.In this paper, we calculate the temperature rise of metal powder that is caused by the impact compaction of the metal and the plastic deformation of the particles. The reason of the temperature rise resulting from the shock wave compressing the powder is discussed. The correlated equation with the temperature rise is presented. It is suggested that the temperature rise of powder is also related to the powder plastic deformation resulting from shock wave. The above mentioned temperature rise is a process of instantaneous state, and the retirement of the shock wave belongs to isentropic process. Therefore, the heat can not be transmitted to the interior of particle powder within such short time. It will form heat spots with a very high heat flux in the particle surface and even melt the powder material. The melted contents will re-solidify to combine with the powder particle.SPH method in LS-DYNA was used to simulate the process of the shock wave propagation during the process of ECC under different impact velocities. The stress nephogram drawing, the relation curves of pressure-time and pressure-particle layer are obtained. We can have a better understanding about whether every layer malts or not through calculation the temperature rise of every layer compared with melting point of material. With the attenuation of the pressure of the Shockwave propagating in powder, there will be temperature gradient. Generally, the temperature goes down by layers, so if the temperature of one layer is lower than the melting point, the powder of this layer will not be effectively combined with the powder of the following layer. Therefore, we are able to get the number of effective combining layers. Moreover, it can be calculated through the relating curve of pressure and powder layer.The integration mechanism of ceramics coating, which is manufactured by ECC, has been studied. Simultaneously, the microcosmic mechanism for nanometer ceramics coating has been explored preliminary. The experiment investigation of nano-structure ZrO2 coating shows that the particle of ZrOx does not melt. Moreover, the grain dimension calculation of the powder and coating exhibits that grain size of ZrO2 does not increase. Then, the integration mechanism for nanometer ceramics coating is interpreted by analysis of the breakup mechanism of ceramics particle during explosive coating process.Finally, the researching results have been summed up, and the suggestions for following investigation are given.