| In recent years, with the development of high and new technology, the working conditions of construction machinery, its equipment and components are becoming more and more rigorous. As a result, pure metal material in some areas are under serious impaction and erosion impact which reduces the length of the service life even to an incompetent point. The ceramic material has been applied in some areas of high technology because of its high melting point, hardness, strong chemical stability, high temperature and corrosion resistance, low thermal expansion coefficient and the coefficient of friction, good wear resistance.Taking the unique excellent performance and obvious weakness of each single material into consideration, researchers attempt to prepare the ceramic coating with special function on the surface of the steel substrate.The proper bonding of the ceramic and the metal can play each other, complement each other’s special performance.This thesis first reviews the present researches on steel based ceramic composite coatings and the thermochemical reaction method, and then states the development and achievement of steel based composite coatings prepared by thermo chemical reaction. At last, it proves the feasibility of using thermochemical reaction method for the preparation of steel based composite coatings. After describing the features of the steel based composite coatings and the analysis of bonding mechanism (chemical action, adsorption, mechanical operation and diffusion), the thesis also makes a conclusion that compared with other methods and means, the preparation of steel based ceramic composite coatings by thermal chemical reaction method has more advantages than other methods.According to the research purpose of this thesis, it states three main tasks of the research:exploring the proportion in the formulation of steel based ceramic composite coatings; exploring the curing process of steel based ceramic composite coatings; detecting the performance of the prepared steel based ceramic composite coatings.The preparation method of a kind of steel matrix surface composite ceramic coating discussed in this paper belongs to the technical field of the steel based protective coating manufacturing, its characteristics are as follows:on the surface of steel base ceramic composite coating layer is composed of silicon carbide, alumina, silica, water glass, aluminum, chromium iron. To determine the percent of coating components and the effect of curing process parameters on the comprehensive performance of coating, the paper uses the orthogonal method and the feeding quantity changing method. Finally, it is concluded that:the main factors that affect the comprehensive properties of the composite coatings are the following proportions configuration, the hybrid filler (alumina and silicon carbide ratio is 1:1) 6.0g, silica (nano powder accounted for 20%～30%) 5.0g, sodium silicate (modulus of 3.2) 7.9g. Using this proportion of formula, more excellent performance of ceramic composite coating can be reached. In order to further improve the comprehensive performance of the ceramic composite coating, the experiment also modifies the ceramic composite coatings, and the method and the modification technical route are also discussed in detail in the paper.Firstly, by adding nano silica, improve the matching degree of expansion coefficient between coating and steel; by adding aluminum powder mass fraction of 20%-25%, improve tissue defects and increase the density and micro-structure of the coatings; by adding about 10% of the chromium iron, greatly improving the coating and the steel substrate metallurgical bonding strength. After mixing it evenly coat it on the steel substrate and coat the mixed rubber material in the same direction evenly on the surface of steel substrate, keeping the coating thickness 0.5～2mm.In order to avoid the emergence of foam and to ensure the great distribution of the structure inside the coating and compact micro-structure during the curing process, first put the coating sample under the room temperature for 16h, then put it in the oven for two stages of heating and solidifying. The first stage is low temperature curing which is around 90 degrees Celsius and it lasts about 1h; the aim is to accelerate the loss of free water and prevent water boiling, but the temperature is not enough to make the coating and the substrate chemical reactions take place which is more complex and better for bond strength, so it requires the second time heating curing. At the next stage, after the lower temperature returns to high one, take the high temperature heating and hardening, high temperature curing. The temperature should be bewteen 450℃ to 600℃ for about 8 hours. The curing process is mainly to shuck off the crystallization of water causing by the silicate products and promote the occurrence of intermolecular dehydration condensation reaction, make the complex chemical reaction occurs between the steel substrate and the interface of ceramic coating.In the thesis, curing process with two times heating is adapted in the preparation of steel based composite coatings and it works out the conflict between the curing time and ceramic composite coating quality reasonablely and helps the formation of transition layer ceramic reinforced phase.This thesis also tests the mechanical properties of the samples, including tensile and shear strength test, abrasion resistance test, thermal shock test, hardness test, acid, alkali and salt corrosion test, bending test and the result is that it has good anti tensile and shear properties, wear resistance, thermal shock, acid, alkali and salt corrosion, anti bending. And then, this thesis also analyzes the elements that affact the thermochemical reaction for the coating preparation. Besides, the particle size distribution and cross section morphology of the coating are analyzed by scanning electron microscope to explain why the performance of the sample is close to the average value from related literature. This paper also points out the shortcomings of this test, and puts forward the suggestions for improvement. Finally, it proves that the thermochemical reaction method successfully guides preparation of the steel based composite coatings, and the comprehensive performance with the method is fine.The significance of this paper is:firstly, combine the advantages of ceramic and steel and then replace the large, expensive material with a very small amount of material: finally reduce the processing cost of the product and also improve the quality of products, extend product life, save resources and energy. The prepared steel based ceramic composite coating has several advantages such as, simple process, convenient construction, low investment and high return. In particular, the Inorganic binder used in the technology not only has the same advantages as general binders, but also has the characteristics of non-toxic, environmental protection, fire resistance, low temperature curing and high temperature use, good performance, and high quality coatings. In addition it possesses pretty good popularization and application value, which will broaden its scope of application in the field of machinery, metallurgy, mining, exploration, petrochemical, chemical, electricity, national defense and military. |
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