Effects of different Al2O3 additions on the properties of thermally sprayed alumina ceramic coatings

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Effect of Al2O3 Addition on Properties of Thermal Sprayed Alumina Ceramic Coatings











Objective To study the effect of Al2O3 addition on the properties of Cr2O3/TiO2/Al2O3/SiO2 quaternary composite ceramic coatings. Methods Quaternary composite ceramic coatings with different Al2O3 contents were prepared on the surface of X80 pipeline steel substrate of oil and gas pipelines by thermal spraying technology. In addition, in order to explore the effect of substrate temperature on coating properties, all coatings were prepared on two substrates preheated by plasma torch and at room temperature. The porosity, hardness, bonding force and electrochemical corrosion properties of the prepared coatings were detected by boiling weighing method, Vickers hardness tester, scratch tester, and electrochemical workstation, and X-ray diffractometer (XRD), scanning electron microscope (SEM) analysis of the phase composition and morphological characteristics of coatings with different Al2O3 content, to study the effect of Al2O3 content on the properties of coatings. Results With the increase of Al2O3 content, the porosity of the Cr2O3/TiO2/Al2O3/SiO2 quaternary composite ceramic coating first decreased and then increased, and the corresponding binding force and Vickers hardness of the quaternary composite ceramic coating increased first. Decrease after increase.











When the mass fraction of Al2O3 is 60%, the performance of the quaternary composite ceramic coating is the best, the porosity is 3.6%, the hardness is 824.6HV, and the bonding force is 53.8N. The electrochemical corrosion test shows that Al2O3 can enhance the corrosion resistance of the coating. When the mass fraction of Al2O3 is 60%, the self-corrosion potential of the coating is the highest, which is -0.28 V. In addition, under the preheating and non-preheating conditions of the substrate, the properties of the prepared coating are consistent with the change of Al2O3 content, but the preheating of the substrate is more conducive to the improvement of the coating properties than the non-preheating. Conclusion The addition of Al2O3 can not only effectively reduce the Cr content of the coating, but also significantly improve the properties of the quaternary composite ceramic coating, especially the corrosion resistance. In addition, preheating the substrate before thermal spraying is beneficial to the improvement of coating performance.







Petroleum and its related products play an important role in industrial development, and petroleum is therefore called "the blood of industry". Oil transportation relies on transportation methods such as roads, railways, aviation and oil pipelines. Among them, oil and gas transportation pipelines can pass through various areas due to their short construction period, low transportation cost, high safety factor, continuous high efficiency and no pollution. Due to the small amount of land and few transshipment links, it has become one of the most widely used transportation methods for petroleum and related industrial products. Excellent pipeline quality is the premise to ensure safe and reliable oil and gas transportation. At present, the commonly used transportation pipelines are mostly metal pipes. In order to improve the corrosion resistance and wear resistance of the pipeline, organic coating protection, electrochemical protection technology, addition of corrosion inhibitors and reasonable anti-corrosion and anti-wear technology are often used. Organic coating (such as two/three layers of polyethylene PE, two/three layers of polypropylene PP, epoxy powder, polyurethane) + corrosion inhibitor (such as imidazoline) is the most economical, direct and universal method of pipeline anticorrosion. However, the organic coating is prone to deterioration and aging, and more current base stations need to be established for electrochemical protection, and the corrosion inhibitor is difficult to remove. Based on the above problems, it is a research work with important theoretical and practical significance to further explore to improve or change the protection technology and measures of oil and gas pipelines, and to provide simple, environmentally friendly, low-cost, reliable, and easy-to-maintain protection methods.



Thermal spraying technology is a surface modification method that sprays the molten or semi-molten state of the spray material to the surface of the part by atomizing it through a high-speed airflow.











The thermal spraying technology can prepare a surface functional coating that is superior to the performance of the substrate, which can endow the surface of the material with excellent properties such as corrosion resistance, wear resistance, high temperature oxidation resistance, and fatigue resistance.











As a kind of thermal spraying technology, thermal spraying technology has the advantages of high flame temperature, small thermal influence of substrate, smooth coating, controllable thickness, low porosity, low impurity content, optimized spraying parameters, and wide variety of spraying materials. , has become the most commonly used process for the preparation of high melting point coating materials.







High-performance ceramics are used as spraying materials, and thermal spraying technology is used to combine the toughness of metal materials with the advantages of ceramic materials such as corrosion resistance, wear resistance, high hardness, strong thermal insulation, low linear expansion coefficient, and no pollution, which can meet the Use of equipment and its components under harsh conditions.











In recent years, this technology has been gradually applied in the field of petroleum engineering, and has achieved good results in the repair, strengthening and protection of mechanical equipment and equipment.



At present, single, two-component or three-component ceramic coatings with high content of Cr2O3 as the main component are mainly used for surface modification of pipelines, such as Cr2O3/TiO2, Al2O3/Cr2O3 and Cr2O3/TiO2/SiO2 composite ceramic coating materials, etc. .











The composite design of Cr2O3 and TiO2, Al2O3, SiO2 and other ceramic coating materials effectively improves the density, mechanical properties and application stability of single-component ceramic coating materials.











However, Cr2O3 ceramic materials are relatively expensive and cause pollution to the ecological environment. At present, how to reduce the coating cost and chromium content has become an urgent problem to be solved.







In addition, studies have shown that adding SiO2 to Al2O3 ceramic coating materials can make the crystal grains of the material more uniform, and form continuous vitreous between the grains, inhibit the formation of cracks, and hinder the propagation of cracks.











Combined with the research results of the literature, it can be seen that the combination of Cr2O3, TiO2, SiO2 and Al2O3 in two or three combinations can prepare composite ceramic coatings with more excellent properties.











Therefore, this thesis attempts to prepare Cr2O3/TiO2/Al2O3/SiO2 four-component composite ceramic coating material to further reduce the Cr2O3 content and cost in the coating.







Based on this, and considering the excellent performance of Al2O3 material and its low cost, this thesis studies the four-component composite ceramic coatings of Cr2O3/TiO2/Al2O3/SiO2 with different Al2O3 contents while keeping the TiO2 and SiO2 contents constant. The microstructure, mechanical properties and electrochemical corrosion properties of the materials and their influencing mechanisms have explored the possibility of partially replacing Cr2O3 by Al2O3, which has laid a certain experimental foundation for the diversification of protective coatings for oil and gas pipelines.