Study Of Wear Resistant Coating Technology Applied On Large Thin-Wall Parts By Plasma Spraying Process

As one of the key parts which are widely used in paper industry, ceramic coating blades are easy to be worn out and have large markets in our country. Now these kinds of high-tech products all rely on imports with expensive prices. Two major difficult problems in the preparation technology of ceramic coating blade were studied in this paper:One is the wear resistant ceramic coating preparation process on large thin-wall parts. The other is the precision grinding process of ceramic coating on blade. Main initial results are shown as follows:Nano ceramic composite coating blades were prepared successfully for the first time in domestic. The preparing process parameters were designed and optimized according to structural featuresBy means of two factors orthogonal test and the variance analysis, the influences of sandblasting distance, air pressure and their interaction on sandblasting quality of coating blade was studied and the sandblasting process factor for thin wall parts were optimized. The influence rule of spraying current, voltage, spraying distance and powder feed rate on porosity of the ceramic coating and flatness of the blade was studied and the plasma spraying parameters of wear resistant ceramic coating on large thin-wall parts was optimized by adopting orthogonal experimentation. Special fixture was designed for plasma spraying on blade steel belt. By the aiding of this apparatus, the difficulties for spraying on thin wall parts such as excessive temperature rise and easy yielding were overcome.According to ultra-long and ultra-thin structure features of ceramic coating blade which is difficult for precision finishing, special fixtureand the grinding process were designed firstly in home. By the aid of this fixture, each side of the blade can be grinded with a small precision grinding machine to get the necessary geometry and dimensional precision without the restriction of the coatmg bade length. Material removal mechanism and the effect of grinding parameters on coating surface finish were discussed. The key performance indexes of the coating blade such as straightness, parallelism and surface roughness all reach to the accuracy requirementThe preparation technology of high-performance nano and micron ceramic composite coatings on large, long and thin parts was realized successfully in this subject. Micron and nano-AT13 ceramic coating samples were prepared with optimized plasma spraying parameters. Microstructure, phases and components distribution of the two coatings were analyzed with the aid of modern analytical means such as scanning electron microscope, energy spectrum analysis, transmission electron microscope and X-ray diffraction. Residual stress and its distribution in the coatings, mechanical properties and abrasive wear resistance of the coatings were studied by experimental methods. The results showed:①Both of the nano and micron coatings prepared by plasma spraying process have dense and even microstructure, low porosity and higher bond strength. The two coatings all meet the application requirements of coating blade.②Main phases of the two coatings areα-Al2O3,Υ-Al2O3 and TiO2. More TiO2 phase was detected in nano AT13 coating. However, more Al2O3 phase was found in micron AT13 coating, mainly because the ceramic powders melt more fully and elements diffusion is more remarkable than that in nano AT13 coating. In rich Al2O3 region of the two coatings, amorphous and nanocrystalline structures were found. Nano AT 13 coating presents typical duplex microstructure and grain refinement phenomenon.③Both nano and micron AT13 coatings prepared by plasma spraying process are in residual compressive stress state. Because of the higher porosity and growing up phenomenon of nanocrystalline, the residual compressive stress in nano ceramic coating is released and lowers apparently than that of micron AT13 ceramic coating.④Both of the two coating have excellent abrasive wear resistant properties. Main failure pattern of micro AT13 coating is the tiny grains spalling along crystal boundary and the flake layer fragmenting caused by micro cracks expansion at the action of grinding stress. Main failure pattern of nano AT13 coating is the tiny grains spalling along crystal boundary. Because the grain size of nano AT13 coating is tinier and the grain boundary area is larger, more energy is needed for micro cracks expansion. So the abrasive wear resistance of nano AT 13 coating is superior to that of micron coating,has an important theoretical and practical significance onnationalization of the key parts in paper industry-ceramic coating blade, breaking the international monopoly in this field and realizing the independent intellectual property rights.