▎ 摘　　要

NOVELTY - Boiler tail heating surface gradient coating comprises a first coating, a second coating and a third coating. The first coating, the second coating and the third coating are arranged in order from close to the substrate to away from the substrate. The substrate is the heating surface at the tail of the boiler. The raw materials of each coating include niobium carbide powder, modified graphene powder and zirconium-nickel-based amorphous alloy powder. In the first coating, the mass percentage of niobium carbide powder is 5-7%, the mass percentage of the modified graphene powder is 5-7%, and the mass percentage of zirconium-nickel-based amorphous alloy powder is 86-90%. In the second coating, the mass percentage of niobium carbide powder is 9-11%, the mass percentage of the modified graphene powder is 9-11%, and the mass percentage of zirconium-nickel-based amorphous alloy powder is 78-82%. In the third coating, the mass percentage of niobium carbide powder is 13-15%. USE - Used as boiler tail heating surface gradient coating. ADVANTAGE - The coating increases as the distance from the heating surface of the boiler tail as the substrate increases, the content of modified graphene, niobium carbide and zirconium-nickel-based amorphous alloy content in a single coating layer all present a gradient change, optimally matches the overall coating's flue gas corrosion resistance and soot erosion resistance performance, makes the gradient coating fully play the role of protecting the heating surface of the boiler tail, effectively reduces the stress concentration caused by the large difference between the thermal expansion coefficient of the coating and the substrate, effectively improves the bonding strength between the coating and the substrate of the heating surface of the boiler tail, and reduces the risk of coating cracking and peeling. DETAILED DESCRIPTION - Boiler tail heating surface gradient coating comprises a first coating, a second coating and a third coating. The first coating, the second coating and the third coating are arranged in order from close to the substrate to away from the substrate. The substrate is the heating surface at the tail of the boiler. The raw materials of each coating include niobium carbide powder, modified graphene powder and zirconium-nickel-based amorphous alloy powder. In the first coating, the mass percentage of niobium carbide powder is 5-7%, the mass percentage of the modified graphene powder is 5-7%, and the mass percentage of zirconium-nickel-based amorphous alloy powder is 86-90%. In the second coating, the mass percentage of niobium carbide powder is 9-11%, the mass percentage of the modified graphene powder is 9-11%, and the mass percentage of zirconium-nickel-based amorphous alloy powder is 78-82%. In the third coating, the mass percentage of niobium carbide powder is 13-15%, the mass percentage of the modified graphene powder is 13-15%, and the mass percentage of zirconium-nickel-based amorphous alloy powder is 70-74%. An INDEPENDENT CLAIM is also included for preparing the boiler tail heating surface gradient coating, comprising (i) using anhydrous ethanol as medium, ball milling the niobium pentoxide powder and graphene powder with silicon carbide grinding ball for 6-8 hours, where the mass ratio of the niobium pentoxide powder and graphene powder is 84-88:12-16; (ii) placing the system after ball milling in an oven at 120-160 degrees C for 4-8 hours to obtain dried powder; (iii) programming the temperature of the dried powder to 1800-1900 degrees C under vacuum condition, keeping it for 4-8 hours and sintering to obtain niobium carbide powder, where the vacuum degree of the vacuum condition is 100-200 Pa and the heating rate of programmed heating is 5-15 degrees C/minute; (iv) adding the graphene powder into a container, adding absolute ethanol into the container, stirring and mixing, adding deionized water, stirring and mixing, placing in an ultrasonic disperser with frequency of 50-80 Hz for ultrasonic treatment for 4-6 hours to obtain post-ultrasound system, where the quality of the absolute ethanol is 300 to 500 times the quality of the graphene powder and the mass of the deionized water is 90-110 times the mass of the graphene powder; (v) adding niobium precursor into the ultrasonic system, stirring and mixing for 4-6 hours, performing suction filtration, drying the retentate obtained from suction filtration in an oven at 100-120 degrees C for 40-80 minutes and obtaining dry powder, where the niobium precursor is a mixture of niobium oxalate and sodium niobate, the ratio of the mass of the niobium oxalate to the mass of the system after ultrasound is 1:400-600 and the ratio of the quality of the sodium niobate to the quality of the system after ultrasound is 1: (200-400); (vi) programming the temperature of the dry powder to 1800-1900 degrees C under vacuum condition, keeping it for 4-8 hours for sintering, obtaining modified graphene powder, where the vacuum degree of the vacuum condition is 60-120 Pa and the rate of programmed heating is 5-10 degrees C/minute; (vii) smelting the raw materials for preparing zirconium-nickel-based amorphous alloy powder in a high vacuum arc melting furnace to obtain master alloy ingot under argon condition, where the raw material of the zirconium-nickel-based amorphous alloy powder includes 35-42% zirconium, 35-42 wt.% nickel, 4-6 wt.% aluminum, 6-10 wt.% iron, 2-6 wt.% tungsten, 2-4 wt.% chromium, 1-2 wt.% yttrium and 1-2 wt.% carbon, the smelting temperature is 1800-2200 degrees C, and the smelting time is 2-4 hours; (viii) placing the master alloy ingot in a graphite crucible in a tightly coupled atomizer, pouring argon gas into the tightly coupled atomizer, turning on the tightly coupled atomizer, and controlling the pressure to be 8-12 MPa, induction heating to 2073-2473 K to atomize the master alloy ingot in the graphite crucible, obtaining zirconium-nickel-based amorphous alloy powder with particle size of 12-16 mu m, where the induction heating is electromagnetic induction heating, and the frequency of the induction heating is 20-40 KHz, and the diameter of the flow guide tube of the tightly coupled atomizer is 6-8 mm; (ix) ball milling the niobium carbide powder, the modified graphene powder and the zirconium-nickel-based amorphous alloy powder with silicon carbide milling balls for 4-8 hours using absolute ethanol as medium, and obtaining the mixed system after ball milling.