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In addition to metal coatings, the high temperature resistance of nickel alloy tubes can be improved by optimizing the alloy composition, carrying out surface modification treatments, improving the manufacturing process, and adopting suitable thermal insulation measures, as described below:
Optimize alloy composition
Adding high melting point elements: Adding tungsten (W), molybdenum (Mo), rhenium (Re) and other high melting point elements can improve the melting point and high temperature strength of nickel alloy. These elements form a solid solution in the alloy, increasing the interatomic bonding force and improving the alloy's ability to resist high-temperature deformation. For example, in some aircraft engines with nickel-based alloys, tungsten and molybdenum content is higher, so that the alloy in the high temperature of more than 1000 ℃ still maintain good mechanical properties.
Add rare earth elements: rare earth elements such as cerium (Ce), lanthanum (La), etc. added to the nickel alloy, can improve the oxidation resistance of the alloy. Rare earth elements can refine the grain, improve the denseness and adhesion of the oxide film, slow down the oxidation rate, thus improving the high temperature resistance of the alloy.
Surface modification treatment
Laser surface treatment: the use of laser beams on the surface of nickel alloy tubes can make the surface form a fine grain organization, improve surface hardness and strength. At the same time, laser treatment can also introduce compressive stress on the surface to improve fatigue resistance, which helps to improve the comprehensive performance of the tube at high temperature.
Ion injection: specific ions are injected into the surface of nickel alloy tubes, which can change the chemical composition and organizational structure of the surface and form a layer of modified layer with special properties. For example, the injection of carbon, nitrogen and other elements can improve the hardness and wear resistance of the surface, reducing material failure due to abrasion in high temperature environments, thus improving high temperature resistance.
Improvement of manufacturing process
Powder metallurgy process: The use of powder metallurgy methods to prepare nickel alloy tubes can obtain a more uniform organizational structure and higher densities. The high temperature performance of the alloy can be improved by precisely controlling the particle size, composition and sintering process of the powder. Powder metallurgy nickel alloys have better strength and creep resistance at elevated temperatures compared to conventional casting or forging processes.
Hot Isostatic Pressing Process: A hot isostatic pressing process is applied to nickel alloy tubes during the manufacturing process. This process can eliminate the pores and defects within the material and improve the density and homogeneity of the material, thus enhancing the mechanical properties and corrosion resistance of the alloy at high temperatures.
Adoption of thermal insulation measures
Installation of heat-insulating materials: Wrap heat-insulating materials, such as ceramic fiber, rock wool, etc., around the exterior of nickel alloy tubes. These heat-insulating materials have low thermal conductivity and good high-temperature resistance, which can reduce the heat exchange between the tubes and the external high-temperature environment and lower the surface temperature of the tubes, thus alleviating the impact of high temperature on the tube material and improving its high-temperature resistance.
Design of air-cooling structure: design air-cooling channels around the tube, so that the cold air flows in the channel and takes away the heat from the surface of the tube. This method can effectively reduce the working temperature of the tube and improve its reliability and service life in high temperature environment. For example, in the nickel alloy piping system of some industrial furnaces, the use of air-cooled structure can reduce the surface temperature of the tube by 100 - 200℃.