Nano TiO2 and CeO2 synergistically reinforced Fe-based plasma spray welding layer and application thereof

Abstract

The invention provides a preparation method and application of a nano TiO2 and CeO2 synergistically reinforced Fe-based plasma spray welding layer, and relates to the technical field of material surface engineering, a nano TiO2 and CeO2 synergistically reinforced Fe55 composite powder system is combined with a plasma spray welding process to carry out spray welding repair on a failed valve sealing surface, and the surface quality of a valve is improved. The specific process mainly comprises the steps of pretreatment of a base material, mixing of powder and preparation of a welding layer. The rare earth oxide is added while the ceramic reinforced phase is added, distribution of a hard phase is optimized through the synergistic strengthening effect of nano TiO2 and CeO2, the beneficial effects of being low in cost, stable in process and the like are achieved, and a prepared spray welding layer is compact in structure, free of cracks, good in toughness and hardness matching, excellent in abrasion resistance and corrosion resistance and suitable for large-scale production. The service life of the repaired valve sealing surface under the high-abrasion working condition is prolonged to 18-24 months from original 6-12 months, and better economic benefits and industrial application prospects are achieved.

Description

Technical Field

[0001] This invention relates to the field of surface engineering technology for metallic materials, specifically to a method for preparing a Fe-based plasma spray coating layer synergistically reinforced by nano-TiO2 and CeO2 and its application. Background Technology

[0002] Plasma spraying, as a surface strengthening process with high energy density and high bonding strength, is widely used for the repair and surface strengthening of industrial valve sealing surfaces. Among these, Fe-based alloy powders, due to their low cost and good compatibility with steel substrates, have become a commonly used material for repairing carbon steel and low-alloy steel workpieces (such as valves and molds). However, traditional iron-based sprayed layers still have some significant drawbacks in practical applications, such as insufficient hardness and wear resistance, susceptibility to microcracks and localized flaking, making it difficult to meet the requirements of high-stress wear conditions.

[0003] In the prior art, in order to improve the wear resistance and corrosion resistance of the sprayed weld layer, the method of adding high melting point and high hardness ceramic particles is usually adopted. However, in practical applications, there is a problem of reduced interfacial bonding strength due to the difference in thermal expansion coefficients between the ceramic phase and the metal matrix. In addition, some reinforcing phases are prone to agglomeration, resulting in uneven distribution of hard phase, stress concentration, reduced toughness of the weld layer, and affecting the overall performance of the weld layer.

[0004] This invention, by adding rare earth oxides to a ceramic reinforcing phase, provides a novel spray-welded layer that simultaneously addresses issues such as improved wear resistance, crack suppression, and improved interfacial bonding. This significantly extends the service life of valve sealing surfaces, shortens maintenance cycles, and reduces losses in industrial production due to valve sealing surface failure. Nano-titanium oxide (TiO2) possesses high strength, a high melting point, and good thermal expansion matching, making it an excellent choice for a reinforcing phase. The addition of rare earth oxide CeO2 refines the grain size while also ensuring a uniform distribution of the hard phase, improving the density and crack propagation resistance of the weld layer. Therefore, this invention, by employing a Fe55 composite powder system synergistically reinforced with cerium oxide (CeO2) and nano-titanium oxide (TiO2), rather than the traditional single ceramic particle reinforcement method, solves the problems of reduced weld layer toughness, easy microcrack formation, and reduced bonding strength that are easily caused by traditional ceramic reinforcing phases. Combined with optimized plasma spraying technology, this significantly improves the overall performance of the spray-welded layer. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost and stable plasma spraying method for preparing a highly wear-resistant, highly dense, and strongly bonded sprayed layer by optimizing the composition of composite powder and process parameters, for use in the repair and surface strengthening of industrial valve sealing surfaces.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2 includes the following steps:

[0008] S1. Mixed Powder: Weigh the corresponding weights of Fe55 iron-based alloy powder, CeO2 powder and nano TiO2 powder, mix them evenly in proportion and dry them to obtain composite powder;

[0009] S2. Valve sealing surface pretreatment: Clean the valve sealing surface, preheat it and remove the surface oxide layer;

[0010] S3. Using a plasma transfer arc welding machine, the composite powder obtained in step S1 is sprayed onto the preheated valve sealing surface in step S2 to form a CeO2-TiO2 / Fe55 iron-based sprayed layer.

[0011] S4. Slow cooling: Place the spray-welded workpiece in insulation material or move it into an insulation furnace for slow cooling.

[0012] S5. Post-processing: After cooling, the workpiece is machined to remove the surface oxide layer and uneven parts, so that it achieves the required geometric accuracy and surface finish.

[0013] Preferably, in step S1, the composite powder composition by mass percentage is: 0.5-1.2% nano-TiO2; 0.3-1.0% CeO2; with the balance being Fe55.

[0014] Preferably, in step S1, the Fe55 iron-based alloy powder has a particle size of 150-300 mesh, and its chemical composition by mass percentage is: C: 0.7-1.0%; Si: 3.0-4.0%; B: 3.5-4.0%; Cr: 16-18%; Ni: 10-13%; with the balance being Fe; the CeO2 powder has an average particle size of 100 nm, and the nano-TiO2 powder has an average particle size of 5 nm.

[0015] Preferably, in step S1, a protective atmosphere ball milling method is used. CeO2 powder, nano-TiO2 powder, and Fe55 iron-based alloy powder are placed in a ball mill, a small amount of ethanol is added to assist dispersion, and the mixture is intermittently ball-milled for 4-10 hours. The ball-to-material ratio is 3:1, the rotation speed is 150 rpm, and the argon gas flow rate is 2-5 L / m³. 3 ·min.

[0016] Preferably, in step S2, the pretreatment process is as follows: cleaning the surface with organic solvents such as acetone to remove oil stains, and removing the surface oxide layer by mechanical polishing to avoid introducing impurities; the preheating temperature is 300-400℃, and the preheating method is natural gas flame heating, oxyacetylene flame heating, electromagnetic induction heating, or heating in a heating furnace.

[0017] Preferably, in step S3, the parameters during the spray welding process are set as follows: transfer arc voltage 30-50V; transfer arc current 120-140A; powder feed rate 20g / min; scanning speed 25mm / min; plasma arc length 20mm; plasma gas flow rate 3.5-5.5L / min; shielding gas flow rate 10-15L / min; welding torch vertical swing amplitude 30mm; spray distance 12mm; coating thickness 2-4mm.

[0018] Preferably, in step S4, the insulation material is insulation cotton, asbestos ash, or fiberglass felt, etc.

[0019] Preferably, in step S5, the machining process includes: turning to remove excess weld layer, precision grinding to ensure the flatness and concentricity of the workpiece, and finally polishing to mirror level, i.e. Ra≤0.1μm, to reduce sealing friction resistance.

[0020] This invention also discloses the application of the Fe-based plasma sprayed layer, which is synergistically reinforced by nano-TiO2 and CeO2 prepared by the above method, in the repair and surface strengthening of industrial valve sealing surfaces. The application is characterized by forming the Fe-based plasma sprayed layer on the surface of the failed industrial valve sealing surface to improve the microhardness, impact toughness and bonding strength of the industrial valve sealing surface, reduce its friction and wear rate and corrosion rate, and extend the service life of the industrial valve sealing surface under high wear conditions.

[0021] The design mechanism of this invention is as follows:

[0022] In this invention, TiO2 primarily promotes the formation of equiaxed grains and increases the number of grain boundaries by providing more nucleation sites and grain boundary pinning, thereby refining the grains and improving the weld strength. However, nano-TiO2, due to its low density, may float or agglomerate in molten steel. The addition of CeO2 not only refines the grains but, more importantly, effectively prevents the agglomeration of nano-TiO2 particles, allowing them to be uniformly dispersed in the Fe55 matrix at the nanoscale. CeO2 adheres to the surface of some titanium oxide particles. The high chemical reactivity of Ce prompts the titanium oxide particles encapsulated in CeO2 to attract solute atoms (such as C, Cr, and Si) from the molten steel, forming new intermetallic compounds. This increases the viscosity of the molten steel, reduces the fluidity of the molten pool, and inhibits the agglomeration of TiO2, thereby forming more nucleation sites and promoting the formation of equiaxed crystals and grain refinement. On the other hand, it reduces the diffusion coefficient of Cr and C elements, resulting in a reduction in the size of the eutectic structure. At the same time, it prevents columnar crystals from forming enough Cr and C atoms to form grain boundaries during growth, which also promotes the formation of equiaxed crystals and grain refinement. Therefore, the addition of CeO2 not only refines the grains but also ensures a uniform distribution of the hard phase, making the microstructure of the weld layer more uniform. In summary, in this invention, TiO2 provides strong dispersion strengthening and abrasive wear resistance, while CeO2 counteracts the brittleness tendency brought by TiO2 by optimizing the microstructure and releasing stress. Under the synergistic effect of the two, the toughness and hardness of the weld layer are simultaneously and significantly improved. Furthermore, when the addition of titanium oxide and cerium oxide is too low, neither can achieve a significant grain refinement effect. When the addition is too high, nano-titanium oxide particles will agglomerate, and Ce will segregate to form a brittle phase, which will lead to a decrease in the impact toughness of the weld layer and an increase in porosity. Therefore, based on experimental analysis, the addition of CeO2 and TiO2 in this invention is designed to be 0.3-1.0% and 0.5-1.2%, respectively.

[0023] The present invention has the following beneficial effects:

[0024] By employing the above technical solution, the present invention provides a Fe-based spray-welded layer with a dense and crack-free microstructure, synergistically reinforced by nano-TiO2 and CeO2. The average microhardness of the weld layer reaches 815 HV0.3, which is approximately 40% higher than the 585 HV0.3 of the traditional Fe55 weld layer, and the impact toughness reaches 18.5 J / cm. 2The bonding strength is no less than 440 MPa. In friction and wear tests, the weight loss of the weld layer of this invention is 0.25 mg / min, a 40-60% reduction in wear rate compared to traditional Fe55 weld layers. The worn surface is smooth, exhibiting only slight ploughing without severe brittle spalling. Its hardness and wear resistance far exceed traditional iron-based materials, even surpassing the more expensive nickel-based alloy Ni60. After 500 hours of neutral salt spray testing, the corrosion rate is only 0.08 mm / y, demonstrating excellent wear and corrosion resistance. This can extend the service life of valve sealing surfaces by 2-3 times, increasing the maintenance cycle from 6-12 months to 18-24 months, significantly reducing losses and maintenance costs caused by valve sealing surface failure in industrial production. Furthermore, compared to nickel-based alloy coatings, this invention uses an iron-based system, significantly reducing costs while maintaining performance, resulting in better economic benefits and promising industrial application prospects. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the process of repairing the valve sealing surface according to the present invention.

[0026] Figure 2 Photo of repairing slurry valve

[0027] Figure 3 Microstructure of traditional Fe55 spray-welded layer

[0028] Figure 4 This is a microstructure diagram of the CeO2-TiO2 / Fe55 iron-based spray-welded layer of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0030] This invention provides a Fe-based plasma spray coating synergistically reinforced with nano-TiO2 and CeO2 for repairing the sealing surface of industrial valves. It is prepared by using Fe55 alloy powder as the main powder, and adding CeO2 powder and nano-TiO2 powder, with the mass percentages of the two being 0.3-1.0% and 0.5-1.2%, respectively.

[0031] Specifically, this method describes the preparation of a Fe-based plasma spray coating layer synergistically reinforced by nano-TiO2 and CeO2, including the following steps:

[0032] S1. Mixed Powder: Weigh the corresponding weights of Fe55 iron-based alloy powder, CeO2 powder, and nano TiO2 powder, mix them evenly in proportion, and dry them to obtain composite powder; the composition of the composite powder by mass percentage is: 0.5-1.2% nano TiO2; 0.3-1.0% CeO2; balance Fe55; the particle size of the Fe55 iron-based alloy powder is 150-300 mesh, and its chemical composition by mass percentage is: C: 0.7-1.0%; Si: 3.0-4.0%; B: 3.5-4.0%; Cr: 16-18%; Ni: 10-13%; balance Fe; the average particle size of the CeO2 powder is 100 nm, and the average particle size of the nano TiO2 powder is 5 nm.

[0033] S2. Valve sealing surface pretreatment: The valve sealing surface is cleaned, preheated and the surface oxide layer is removed; the pretreatment process is as follows: the surface is cleaned with organic solvents such as acetone to remove oil stains, and the surface oxide layer is removed by mechanical grinding to avoid introducing impurities; the preheating temperature is 300-400℃, and the preheating method is natural gas flame heating, oxyacetylene flame heating, electromagnetic induction heating or heating in a heating furnace.

[0034] S3. Using a plasma transfer arc welding machine, the composite powder obtained in step S1 is sprayed onto the preheated valve sealing surface in step S2 to form a CeO2-TiO2 / Fe55 iron-based sprayed layer. The parameters during the spraying process are set as follows: transfer arc voltage 30-50V; transfer arc current 120-140A; powder feed rate 20g / min; scanning speed 25mm / min; plasma arc length 20mm; plasma gas flow rate 3.5-5.5L / min; shielding gas flow rate 10-15L / min; welding torch vertical swing amplitude 30mm; spray distance 12mm; coating thickness 2-4mm.

[0035] S4. Slow cooling: Place the spray-welded workpiece in insulation material or move it into an insulation furnace for slow cooling; the insulation material is insulation cotton, asbestos ash, or glass fiber felt, etc.

[0036] S5. Subsequent processing: After cooling, the workpiece is machined to remove the surface oxide layer and uneven parts, so that it achieves the required geometric accuracy and surface finish. The machining process includes: turning to remove excess weld layer, precision grinding to ensure the flatness and concentricity of the workpiece, and finally polishing to mirror level, i.e. Ra≤0.1μm, to reduce sealing friction resistance.

[0037] I. Example 1

[0038] A Fe-based plasma spraying layer synergistically reinforced by nano-TiO2 and CeO2 and its method for repairing valve sealing surfaces are disclosed. The spraying powder is 100% Fe55 alloy powder, and its chemical composition is as follows: C: 0.7-1.0%; Si: 3.0-4.0%; B: 3.5-4.0%; Cr: 16-18%; Ni: 10-13%; balance Fe.

[0039] In this embodiment, the above-mentioned sprayed layer is prepared by plasma spraying, and the following steps are performed:

[0040] (1) Preparation of welding powder: Weigh 500g of Fe55 iron-based alloy powder and put it into a high-energy ball mill with a small amount of alcohol. Mill for 6 hours with a ball-to-powder ratio of 3:1, a rotation speed of 150rpm, and an argon gas flow rate of 5L / m. 3 After 1 minute, the mixed powder is taken out and placed in a vacuum drying oven at 120°C for 2 hours to remove moisture and obtain the desired mixed powder.

[0041] (2) Surface pretreatment of valve sealing surface: Clean the valve sealing surface to be sprayed with acetone to remove surface oil stains; then polish with sandpaper to remove the surface oxide layer until the metal luster is exposed; preheat by induction heating, use ceramic clamps to fix the valve, keep the distance between the valve sealing surface and the sensor at 5mm, use a contoured copper tube coil, and use a 30kHz intermediate frequency power supply to heat the valve sealing surface to 300℃ and keep it at that temperature for 5min.

[0042] (3) Prepare a sprayed layer on the valve sealing surface: After preheating, place the valve in the spraying station, keep the valve sealing surface horizontal, and spray the mixed powder onto the valve sealing surface using a plasma spraying machine. The parameters during the spraying process are set as follows: transfer arc voltage 30V; transfer arc current 120A; powder feed rate 20g / min; scanning speed 25mm / min; plasma arc length 20mm; plasma gas flow rate 4.5L / min; shielding gas flow rate 10L / min; welding torch up and down swing amplitude: 30mm; spray distance: 12mm.

[0043] (4) Place the spray-welded valve core and valve seat into an insulated bucket wrapped with insulation cotton for slow cooling.

[0044] Testing revealed that the average microhardness of the Fe55 alloy weld layer without any added powder was 585HV0.3, the weight loss in the friction and wear test was 0.45 mg / min, and the impact toughness was 12 J / cm. 2 The porosity is 3.0%, the bonding strength is 320 MPa, and the corrosion rate after 500 hours of neutral salt spray testing is 0.18 mm / y. In this embodiment, the sprayed welding powder does not contain cerium oxide or titanium oxide, and is an iron-based sprayed welding layer of 100% Fe55 alloy powder, which has low hardness and poor wear resistance.

[0045] II. Example 2

[0046] A Fe-based plasma spray coating synergistically reinforced with nano-TiO2 and CeO2 and its method for repairing valve sealing surfaces, wherein the coating composition is 99.5% Fe55 alloy powder with 0.5% nano-TiO2 added.

[0047] In this embodiment, the above-mentioned sprayed layer is prepared by plasma spraying, and the following steps are performed:

[0048] Preparation of welding powder: Weigh 497.5g of Fe55 iron-based alloy powder and 2.5g of nano TiO2 powder into a high-energy ball mill and add a small amount of alcohol. Ball mill for 6 hours with a ball-to-material ratio of 3:1, a rotation speed of 150 rpm, and an argon gas flow rate of 5 L / m³. 3 After 1 minute, the mixed powder is taken out and placed in a vacuum drying oven at 120°C for 2 hours to remove moisture and obtain the desired mixed powder.

[0049] The subsequent steps are the same as in Example 1.

[0050] Testing revealed that the Fe55 alloy weld layer containing 0.5% nano-TiO2 had an average microhardness of 720 HV0.3, a weight loss of 0.33 mg / min in the friction and wear test, and an impact toughness of 10.5 J / cm². 2 It has a porosity of 4.5%, a bonding strength of 300 MPa, and a corrosion rate of 0.14 mm / y after 500 hours of neutral salt spray testing.

[0051] In Example 2, nano-TiO2 was added to the spray welding powder but CeO2 was not added. Although the hardness of the weld layer increased significantly, the uneven distribution of the hard phase led to a decrease in the toughness of the weld layer, an increase in porosity, a decrease in bonding strength, poor impact resistance, and a tendency to generate microcracks. The wear and corrosion resistance were also insufficient.

[0052] III. Example 3

[0053] A Fe-based plasma spray coating synergistically reinforced with nano-TiO2 and CeO2 and its method for repairing valve sealing surfaces, wherein the coating composition is 99.2% Fe55 alloy powder, with the addition of 0.5% nano-TiO2 and 0.3% CeO2.

[0054] In this embodiment, the above-mentioned sprayed layer is prepared by plasma spraying, and the following steps are performed:

[0055] Prepare the welding powder: Weigh 496g of Fe55 iron-based alloy powder, 2.5g of nano TiO2 powder, and 1.5g of CeO2 powder and place them in a high-energy ball mill. Add a small amount of alcohol and ball mill for 6 hours. The ball-to-material ratio is 3:1, the rotation speed is 150 rpm, and the argon gas flow rate is 5 L / m³. 3 After 1 minute, the mixed powder is taken out and placed in a vacuum drying oven at 120°C for 2 hours to remove moisture and obtain the desired mixed powder.

[0056] The subsequent steps are the same as in Example 1.

[0057] Testing revealed that the Fe55 alloy weld layer containing 0.5% nano-TiO2 and 0.3% CeO2 had an average microhardness of 785HV0.3, a weight loss of 0.29 mg / min in the friction and wear test, and an impact toughness of 16.0 J / cm². 2 It has a porosity of 1.8%, a bonding strength of 480 MPa, and a corrosion rate of 0.10 mm / y after 500 hours of neutral salt spray testing.

[0058] Compared to Example 2, Example 3 added CeO2 to the same amount of TiO2, which refined the grains and made the distribution of the hard phase more uniform. The uniformity of the microstructure of the weld layer was improved, and the uniform microstructure can effectively prevent valve sealing surface failure and extend its service life.

[0059] IV. Example 4

[0060] A Fe-based plasma spray coating synergistically reinforced with nano-TiO2 and CeO2 and its method for repairing valve sealing surfaces, wherein the coating composition is 98.6% Fe55 alloy powder, with the addition of 0.8% nano-TiO2 and 0.6% CeO2.

[0061] In this embodiment, the above-mentioned sprayed layer is prepared by plasma spraying, and the following steps are performed:

[0062] To prepare the welding powder, weigh 493g of Fe55 iron-based alloy powder, 4.0g of nano TiO2 powder, and 3.0g of CeO2 powder and place them in a high-energy ball mill. Add a small amount of alcohol and ball mill for 6 hours. The ball-to-material ratio is 3:1, the rotation speed is 150 rpm, and the argon gas flow rate is 5 L / m³. 3 After 1 minute, the mixed powder is taken out and placed in a vacuum drying oven at 120°C for 2 hours to remove moisture and obtain the desired mixed powder.

[0063] The subsequent steps are the same as in Example 1.

[0064] Testing revealed that the Fe55 alloy weld layer containing 0.8% nano-TiO2 and 0.6% CeO2 had an average microhardness of 815HV0.3, a weight loss of 0.25 mg / min in friction and wear tests, and an impact toughness of 18.5 J / cm². 2 It has a porosity of 1.5%, a bonding strength of 460 MPa, and a corrosion rate of only 0.08 mm / y after 500 hours of neutral salt spray testing.

[0065] Example 4 increased the amount of nano-TiO2 and CeO2 added compared to Example 3, further refining the grain size of the weld layer and making the hard phase distribution more uniform. In this example, the average microhardness of the weld layer can reach 815HV0.3, which is about 40% higher than the 585HV0.3 of the traditional Fe55 weld layer. At the same time, the weld layer has good toughness and hardness matching, and can maintain a low surface roughness during erosion and wear. It has excellent wear and corrosion resistance, which can extend the service life of the slurry valve sealing surface from the original 6-12 months to 18-24 months. This significantly reduces the losses and maintenance costs caused by valve sealing surface failure in industrial production, and has good economic benefits and industrial application prospects.

[0066] V. Example 5

[0067] A Fe-based plasma spray-welded layer synergistically reinforced with nano-TiO2 and CeO2, and a method for repairing valve sealing surfaces thereof, wherein the weld layer composition is 98.5% Fe55 alloy powder, with the addition of 1.2% nano-TiO2 and 0.3% CeO2. The above-mentioned spray-welded layer is prepared by plasma spraying according to the following steps:

[0068] Prepare the welding powder: Weigh 492.5g of Fe55 iron-based alloy powder, 6.0g of nano TiO2 powder, and 1.5g of CeO2 powder and place them in a high-energy ball mill. Add a small amount of alcohol and ball mill for 6 hours. The ball-to-powder ratio is 3:1, the rotation speed is 150 rpm, and the argon gas flow rate is 5 L / m³. 3 After 1 minute, the mixed powder is taken out and placed in a vacuum drying oven at 120°C for 2 hours to remove moisture and obtain the desired mixed powder.

[0069] The subsequent steps are the same as in Example 1.

[0070] Testing revealed that the Fe55 alloy weld layer containing 1.2% nano-TiO2 and 0.3% CeO2 had an average microhardness of 780 HV0.3, a weight loss of 0.26 mg / min in the friction and wear test, and an impact toughness of 12.5 J / cm². 2The porosity was 2.5%, the bonding strength was 440 MPa, and the corrosion rate after 500 hours of neutral salt spray testing was 0.12 mm / y. In this embodiment, the amount of nano-TiO2 added was close to the upper limit. A small amount of titanium oxide agglomerates could be observed in the weld layer, the toughness of the weld layer decreased, the surface porosity increased, the bonding strength decreased, and the crack sensitivity increased.

[0071] VI. Example 6

[0072] A Fe-based plasma spray-welded layer synergistically reinforced by nano-TiO2 and CeO2, and a method for repairing valve sealing surfaces thereof, wherein the weld layer composition is 98.5% Fe55 alloy powder, with the addition of 0.5% nano-TiO2 and 1.0% CeO2. The above-mentioned spray-welded layer is prepared by plasma spraying according to the following steps:

[0073] To prepare the welding powder, weigh 492.5g of Fe55 iron-based alloy powder, 2.5g of nano TiO2 powder, and 5.0g of CeO2 powder and place them in a high-energy ball mill with a small amount of alcohol. Mill for 6 hours with a ball-to-material ratio of 3:1, a rotation speed of 150 rpm, and an argon gas flow rate of 2-5 L / m3·min. Then, take out the mixed powder and place it in a vacuum drying oven at a temperature of 120℃ for 2 hours to remove moisture completely and obtain the desired mixed powder.

[0074] The subsequent steps are the same as in Example 1.

[0075] Testing revealed that the Fe55 alloy weld layer containing 0.5% nano-TiO2 and 1.0% CeO2 had an average microhardness of 765 HV0.3, a weight loss of 0.28 mg / min in the friction and wear test, and an impact toughness of 14.0 / cm. 2 The porosity is 1.8%, the bonding strength is 460 MPa, and the corrosion rate after 500 hours of neutral salt spray testing is 0.12 mm / y. In this embodiment, the amount of CeO2 added is close to the upper limit. A small amount of cerium-rich oxide accumulates at the grain boundaries in the weld layer, leading to a tendency for reduced grain boundary strength and increased stress concentration, thus increasing the risk of microcracks.

[0076] VII. Experimental Verification

[0077] To verify the actual effect of the present invention, the valve disc repaired by the method of the present invention and the valve disc of the same model repaired by two commonly used processes, namely Fe55 powder and Ni60 powder spraying with oxy-acetylene flame, were installed together on the same red mud slurry valve of an alumina plant for field operation test. The medium was red mud slurry, the temperature was 85°C, and the solid content was about 30%. After a maintenance cycle (12 months), disassembly and inspection revealed that: valve sealing surfaces repaired with traditional Fe55 spray welding layers showed obvious erosion grooves and localized peeling, with leakage approaching the allowable limit, requiring immediate replacement; valve sealing surfaces repaired with Ni60 spray welding layers showed uniform wear overall, but the wear was significant, and the surface smoothness decreased, suggesting that repair would also be needed after another 2-3 months of operation; while the sealing surfaces repaired with the Fe-based spray welding layer synergistically strengthened by nano-TiO2 and CeO2 provided by this invention showed only slight wear marks, with a smooth surface, no erosion pits or cracks, and an expected service life of over 24 months, more than twice that of traditional Fe55 spray welding layers, and approximately 50%-80% longer than oxy-acetylene spray welding Ni60 layers.

[0078] The table below clearly shows the performance comparison between the present invention and the prior art, demonstrating its significant advantages.

[0079]

[0080]

[0081] Experimental results show that the Fe-based spray-welded layer, which is synergistically reinforced by nano-TiO2 and CeO2 provided by this invention, has a hardness and wear resistance far exceeding that of traditional iron-based materials, and even surpasses that of the expensive nickel-based alloy Ni60. The service life of the valve sealing surface repaired by this layer is 2.66 times that of the traditional Fe55 spray-welded layer and 1.6 times that of the oxy-acetylene flame Ni60 spray-welded layer. This not only greatly extends the valve's operating cycle and reduces the economic losses caused by unplanned downtime, but also significantly reduces maintenance costs and the labor intensity of workers.

[0082] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2, characterized in that, Includes the following steps: S1. Mixed Powder: Weigh the corresponding weights of Fe55 iron-based alloy powder, CeO2 powder and nano TiO2 powder, mix them evenly in proportion and dry them to obtain composite powder; S2. Valve sealing surface pretreatment: Clean the valve sealing surface, preheat it and remove the surface oxide layer; S3. Using a plasma transfer arc welding machine, the composite powder obtained in step S1 is sprayed onto the preheated valve sealing surface in step S2 to form a CeO2-TiO2 / Fe55 iron-based sprayed layer. S4. Slow cooling: Place the spray-welded workpiece in insulation material or move it into an insulation furnace for slow cooling. S5. Post-processing: After cooling, the workpiece is machined to remove the surface oxide layer and uneven parts, so that it achieves the required geometric accuracy and surface finish.

2. The method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2 according to claim 1, characterized in that, In step S1, the composite powder composition by mass percentage is: 0.5-1.2% nano-TiO2; 0.3–1.0% CeO2; balance Fe55.

3. The method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2 according to claim 2, characterized in that, In step S1, the Fe55 iron-based alloy powder has a particle size of 150-300 mesh, and its chemical composition by mass percentage is: C: 0.7-1.0%; Si: 3.0-4.0%. B: 3.5-4.0%; Cr: 16-18%; Ni: 10-13%; balance Fe; the average particle size of the CeO2 powder is 100 nm, and the average particle size of the nano TiO2 powder is 5 nm.

4. The method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2 according to claim 1, characterized in that, In step S1, a protective atmosphere ball milling method is used. CeO2 powder, nano-TiO2 powder, and Fe55 iron-based alloy powder are placed in a ball mill, and a small amount of ethanol is added to assist dispersion. The ball milling is carried out intermittently for 4-10 hours, with a ball-to-material ratio of 3:1, a rotation speed of 150 rpm, and an argon gas flow rate of 2-5 L / m³. 3 ·min.

5. The method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2 according to claim 1, characterized in that, In step S2, the pretreatment process is as follows: the surface is cleaned with organic solvents such as acetone to remove oil stains, and the surface oxide layer is removed by mechanical polishing to avoid introducing impurities; the preheating temperature is 300-400℃.

6. The method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2 according to claim 1, characterized in that, In step S2, the preheating method is natural gas flame heating, oxyacetylene flame heating, electromagnetic induction heating, or heating in a heating furnace.

7. The method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2 according to claim 1, characterized in that, In step S3, the parameters for the spray welding process are set as follows: transfer arc voltage 30-50V; transfer arc current 120-140A; powder feed rate 20g / min; scanning speed 25mm / min; plasma arc length 20mm; plasma gas flow rate 3.5-5.5L / min; shielding gas flow rate 10-15L / min; welding torch vertical swing amplitude 30mm; spray distance 12mm; coating thickness 2-4mm.

8. The method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2 according to claim 1, characterized in that, In step S4, the insulation material is insulation cotton, asbestos ash, or fiberglass felt, etc.

9. The method for preparing a Fe-based plasma spray coating synergistically reinforced by nano-TiO2 and CeO2 according to claim 1, characterized in that, In step S5, the machining process includes: turning to remove excess weld layer, precision grinding to ensure the flatness and concentricity of the workpiece, and finally polishing to mirror level, i.e. Ra≤0.1μm, to reduce sealing friction resistance.

10. The application of the Fe-based plasma sprayed layer with synergistic reinforcement of nano-TiO2 and CeO2 prepared by the method of any one of claims 1-9 in the repair and surface strengthening of industrial valve sealing surfaces, characterized in that, The application improves the microhardness, impact toughness, and bonding strength of the industrial valve sealing surface by forming the Fe-based plasma spray layer on the surface of the failed industrial valve sealing surface, thereby reducing its friction and wear rate and corrosion rate, and extending the service life of the industrial valve sealing surface under high wear conditions.

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