Biomass boiler pipeline surface high-temperature corrosion resistant protective coating and preparation method
By preparing a NiCoFeCrSiAlW high-entropy alloy coating on the surface of biomass boiler pipes, the high-temperature corrosion problem of high-temperature heating surface pipes in biomass boilers was solved, achieving high-efficiency corrosion resistance and extended service life.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- MAANSHAN SPECIAL EQUIP SUPERVISION & INSPECTION CENT
- Filing Date
- 2026-04-09
- Publication Date
- 2026-06-09
AI Technical Summary
Existing biomass boilers' high-temperature heating surface pipes are susceptible to high-temperature molten salt corrosion in environments rich in alkali metals and chlorine, resulting in easy peeling of the coating, insufficient corrosion resistance, short service life, and unstable effectiveness of existing protection technologies when fuel quality fluctuates.
A NiCoFeCrSiAlW high-entropy alloy coating is formed on the surface of biomass boiler pipes using laser cladding technology. The coating material is designed in a specific ratio and is metallurgically bonded to the substrate. The high-entropy alloy utilizes the hysteresis diffusion effect and Si and Al elements to generate a protective film. The broadband laser cladding technology ensures the density and bonding strength of the coating.
It significantly improves the coating's resistance to high-temperature oxidation and molten salt corrosion, extends its service life, and makes the coating less prone to peeling off under high-temperature and severe thermal shock. It also has high bonding strength and adapts to fluctuations in fuel quality.
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Figure CN122169081A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of biomass energy utilization and surface engineering protection technology, and in particular to a high-temperature corrosion resistant protective coating for the surface of biomass boiler pipes and its preparation method. Background Technology
[0002] Biomass energy is a clean and renewable energy source, and its efficient development is of great significance for optimizing the energy structure and alleviating the shortage of fossil fuels. Biomass boilers are the core equipment for biomass energy utilization, and the high-temperature corrosion of the boiler's high-temperature heating surface pipes is a key factor leading to unplanned unit shutdowns and restricting the long-term safe and stable operation of the equipment. It can cause rapid thinning of the pipe walls, a significant reduction in service life, and even lead to pipe rupture accidents, resulting in serious economic losses and safety risks.
[0003] Biomass fuels contain far higher levels of alkali metals (potassium, sodium) and chlorine than traditional fossil fuels. During combustion, these components form low-melting-point eutectic molten salts on the surfaces of pipes such as water-cooled walls and superheaters. When the pipe wall temperature exceeds 500°C, the molten salts are in a molten state and react with the metal pipes at high temperatures, destroying the protective oxide film on the pipe surface. This is the root cause of pipe corrosion failure.
[0004] Existing mainstream protection technologies all have core defects that cannot be solved: First, combustion operation optimization and adjustment can only alleviate corrosion, but cannot inhibit the corrosion process from the root, and the protection effect is greatly affected by the fluctuation of fuel quality; Second, existing surface protection systems, high-temperature organic-inorganic composite coatings have problems such as low coating-substrate bonding strength and poor thermal shock resistance, thermal spray protective coatings have defects such as high porosity and easy peeling failure after long-term service, and traditional laser cladding nickel-based and cobalt-based alloy coatings have insufficient long-term service performance in the high-temperature and harsh environment of high alkali metals and high chloride ions, and the cost of precious metal raw materials is relatively high.
[0005] High-entropy alloys, with their simple solid solution structure formed by multi-principal element design and hysteresis diffusion effect, possess both excellent high-temperature mechanical properties and corrosion resistance, providing a new technical approach to solving the problem of high-temperature corrosion in biomass boiler pipelines. Summary of the Invention
[0006] To overcome the above deficiencies, this invention provides a high-temperature corrosion resistant protective coating for the surface of biomass boiler pipes and its preparation method, which solves the problems in the prior art where the protective coating of biomass boilers is prone to peeling, has insufficient corrosion resistance, and has a short service life due to high-temperature molten salt corrosion in harsh environments where alkali metals and chlorine elements are enriched.
[0007] To achieve the above objectives, the present invention employs the following technical solution: a high-temperature corrosion-resistant protective coating for the surface of biomass boiler pipes, wherein the coating is formed on the surface of the high-temperature biomass boiler pipe substrate using laser cladding technology.
[0008] The coating material is a NiCoFeCrSiAlW high-entropy alloy, and its chemical composition by atomic percentage is as follows: Ni: 10%~36%, Co: 10%~36%, Fe: 10%~36%, Cr: 10%~36%, Si: 2%~20%, Al: 6%~20%, W: 6%~20%; and the sum of the atomic percentages of each component is 100%.
[0009] Furthermore, the chemical composition of the NiCoFeCrSiAlW high-entropy alloy, by atomic percentage, is as follows: Ni: 16.0%, Co: 16.0%, Fe: 16.0%, Cr: 16.0%, Si: 4.0%, Al: 16.0%, W: 16.0%.
[0010] Furthermore, the chemical composition of the NiCoFeCrSiAlW high-entropy alloy, by atomic percentage, is as follows: Ni: 20.0%, Co: 15.0%, Fe: 15.0%, Cr: 20.0%, Si: 6.0%, Al: 12.0%, W: 12.0%.
[0011] Furthermore, the chemical composition of the NiCoFeCrSiAlW high-entropy alloy, by atomic percentage, is as follows: Ni: 14.0%, Co: 14.0%, Fe: 14.0%, Cr: 18.0%, Si: 5.0%, Al: 15.0%, W: 20.0%.
[0012] Furthermore, the coating is a BCC single-phase solid solution structure, and the coating is metallurgically bonded to the pipe substrate, with a coating thickness of 0.8–1.0 mm.
[0013] A method for preparing a high-temperature corrosion resistant protective coating for the surface of biomass boiler pipes includes the following steps:
[0014] Step S1: Preparation of composite powder raw materials
[0015] According to the designed atomic percentage, Ni, Co, Fe, and Cr metal powders were weighed as the first component, and Si, Al, and W metal powders were weighed as the second component. The first component metal powders were first mixed by mechanical stirring to obtain a primary mixed powder. Then, the second component metal powders were added to the primary mixed powder and mixed evenly by ball milling to obtain a secondary mixed powder. After drying the secondary mixed powder, high-entropy alloy powder for laser cladding was obtained.
[0016] Step S2: Pretreatment of pipe substrate
[0017] High-temperature pipes for biomass boilers are selected as the base material, and the surface of the base material is polished, degreased, and derusted.
[0018] Step S3: Laser cladding to prepare a protective coating
[0019] Broadband laser cladding technology is used to pre-place or simultaneously deliver the high-entropy alloy powder prepared in step S1 onto the surface of the substrate treated in step S2, and laser cladding is performed under inert gas protection to form a high-entropy alloy protective coating that is metallurgically bonded to the substrate.
[0020] Furthermore: in step S1, the particle size range of the first group of elemental metal powders is 250 mesh to 350 mesh, and the purity is not less than 99.7%; the particle size range of the second group of elemental metal powders is 320 mesh to 450 mesh, and the purity is not less than 99.9%.
[0021] Furthermore: the mechanical stirring time in step S1 shall not be less than 30 minutes; the ball mill mixing shall be carried out using a planetary ball mill, and the mixing time shall not be less than 60 minutes; the drying temperature of the secondary mixed powder shall be 80°C, and the drying time shall not be less than 120 minutes.
[0022] Furthermore: in step S2, the substrate is 20G alloy steel or 12Cr1MoVG alloy steel, the outer diameter of the pipe is 20.0 to 600.0 mm, and the wall thickness is 2.0 to 50.0 mm; after pretreatment, the surface roughness of the substrate reaches Ra5 to 10 μm.
[0023] Furthermore, the process parameters for laser cladding in step S3 are as follows: laser power 2.0–5.5 kW, laser scanning speed 1.5–6.0 mm / s, laser beam size 20 mm × 1.5 mm, overlap rate 25%–30%, protective gas is argon gas with a purity of 99.99% and a flow rate of 18–25 L / min, and powder feeding speed 12.0–60.0 g / min.
[0024] Compared with the prior art, the present invention has the following beneficial effects:
[0025] 1. This invention addresses the harsh operating environment of biomass boilers, characterized by high temperature, high alkali metal content, and high chlorine levels. It designs a NiCoFeCrSiAlW high-entropy alloy system, forming a dense and stable simple solid solution structure by precisely controlling the proportions of each main element. The addition of Si and Al elements allows them to react with oxygen at high temperatures to preferentially generate a continuous and dense SiO2 and Al2O3 protective film, significantly improving the coating's resistance to high-temperature oxidation and effectively inhibiting oxygen penetration.
[0026] 2. This invention utilizes the hysteresis diffusion effect of high-entropy alloys by adding Cr and W elements to the alloy. Cr itself has excellent resistance to molten salt and chloride ion corrosion. Cr and W, with their large atomic radii and low diffusion coefficients, can, on the one hand, maintain a dense composite oxide film (Cr2O3, Al2O3) to inhibit the penetration of alkali metal molten salts and chloride ions into the matrix; on the other hand, they can maintain the structural stability of the high-entropy alloy matrix and prevent coating performance degradation due to excessive element diffusion.
[0027] 3. This invention uses broadband laser cladding technology to prepare the coating. The coating material and the base metal are rapidly melted and solidified by a high-energy laser beam, forming a strong metallurgical interface with a bonding strength far exceeding that of physical bonding methods such as thermal spraying. At the same time, the laser cladding layer has a dense structure, avoiding defects such as pores and cracks. This makes the coating less prone to peeling off under the severe thermal shock generated by the frequent start-up and shutdown of biomass boilers, significantly improving the service reliability and service life of the coating. Attached Figure Description
[0028] Figure 1 The metallographic structure of the laser cladding layer in Example 1;
[0029] Figure 2 XRD phase analysis of the laser cladding layer in Example 1;
[0030] Figure 3 This is a comparison of the Vickers hardness of the laser cladding layer and the 12Cr1MoVg base material in Example 1.
[0031] Figure 4 This example compares the molten salt corrosion resistance of the laser cladding layer and the 12Cr1MoVg base material in Example 1.
[0032] Figure 5 This is a comparison of the oxidation resistance of the laser cladding layer and the 12Cr1MoVg base material in Example 1. Detailed Implementation
[0033] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0034] Example 1
[0035] Reference Figure 1-5 This embodiment provides a laser cladding high-entropy alloy coating for high-temperature pipes of biomass boilers and its preparation method, which obtains a protective coating with uniform structure and excellent performance through low laser heat input.
[0036] This embodiment employs a high-entropy alloy system with near-equiatomic ratios to fully utilize the high-entropy effect. The coating material is a NiCoFeCrSiAlW high-entropy alloy, with the following chemical composition by atomic percentage: Ni: 16.0%, Co: 16.0%, Fe: 16.0%, Cr: 16.0%, Si: 4.0%, Al: 16.0%, W: 16.0%. The close proportions of the main elements in this composition are conducive to the formation of a stable single solid solution structure.
[0037] Weigh the metal powders according to the above atomic percentages. The Ni, Co, Fe, and Cr metal powders have a particle size of 280 mesh and a purity of 99.8%; the Si, Al, and W metal powders have a particle size of 350 mesh and a purity of 99.9%. A two-step mixing method is used: first, the Ni, Co, Fe, and Cr powders are stirred and mixed in a mechanical mixer at a speed of 150 r / min for 30 min to obtain a primary mixed powder; then, the Si, Al, and W powders are added to the primary mixed powder and mixed in a planetary ball mill at a revolution speed of 100 r / min and a rotation speed of 300 r / min for 60 min to obtain a secondary mixed powder; the secondary mixed powder is dried in an 80℃ drying oven for 120 min for later use.
[0038] The substrate is a 12Cr1MoVG alloy steel pipe with an outer diameter of 60mm and a wall thickness of 5.0mm. The surface of the substrate to be clad is subjected to acetone degreasing, alcohol cleaning, and sandblasting roughening treatment in sequence to achieve a surface roughness of Ra5~10μm, and laser cladding is performed within 2 hours.
[0039] A broadband laser cladding device was used, with a laser beam size of 20mm × 1.5mm. In this embodiment, a low laser heat input was adopted. The process parameters were: laser power 2.50kW, laser scanning speed 5.0mm / s, overlap rate 25%, protective gas purity 99.99% argon, flow rate 20L / min, and powder feeding speed 15g / min.
[0040] The coating microstructure and properties were tested. The high-entropy alloy coating prepared in this embodiment had a thickness of approximately 0.8–1.0 mm, exhibiting good metallurgical bonding with the substrate. The bonding interface was free of defects such as cracks and pores. XRD phase analysis showed that the cladding layer had a BCC single-phase structure. The coating microhardness was 681.8 HV0.5. Static corrosion tests at 650℃ in a NaCl-KCl molten salt environment showed a corrosion rate of only 16.8 mg / cm². 2 Compared with the unprotected 12Cr1MoVG substrate, the corrosion weight loss is reduced by about 94%, showing excellent resistance to high-temperature molten salt corrosion. Oxidation tests in an air environment at 800℃ show that the oxidation rate of the coating is reduced by about 86% compared with the unprotected 12Cr1MoVG substrate, showing excellent resistance to high-temperature oxidation.
[0041] Example 2
[0042] To further improve the corrosion resistance of the coating in high-temperature and high-chlorine environments, this embodiment achieves this by optimizing the proportion of alloying elements.
[0043] The coating material in this embodiment is a NiCoFeCrSiAlW high-entropy alloy, whose chemical composition by atomic percentage is: Ni: 20.0%, Co: 15.0%, Fe: 15.0%, Cr: 20.0%, Si: 6.0%, Al: 12.0%, W: 12.0%.
[0044] Weigh the metal powders according to the above atomic percentages. The Ni, Co, Fe, and Cr metal powders have a particle size of 300 mesh and a purity of 99.8%; the Si, Al, and W metal powders have a particle size of 400 mesh and a purity of 99.9%. A two-step mixing method is used: First, the Ni, Co, Fe, and Cr powders are stirred and mixed in a mechanical mixer at 200 r / min for 30 min to obtain a primary mixed powder. Then, the Si, Al, and W powders are added to the primary mixed powder, and the mixture is mixed in a planetary ball mill at 180 r / min revolution and 400 r / min rotation for 60 min to obtain a secondary mixed powder. The secondary mixed powder is then dried in an 80℃ drying oven for 120 min for later use.
[0045] The substrate is a 20G alloy steel pipe with an outer diameter of 100mm and a wall thickness of 8.0mm. The surface of the substrate to be clad is subjected to acetone degreasing, alcohol cleaning, and sandblasting roughening treatment in sequence to achieve a surface roughness of Ra5~10μm.
[0046] The coating was prepared using a broadband laser cladding system with a laser beam size of 20mm × 1.5mm. This embodiment employed a moderate laser heat input, with the following process parameters: laser power 3.50kW, laser scanning speed 4.0mm / s, overlap rate 30%, protective gas purity 99.99% argon, flow rate 26L / min, and powder feeding speed 25g / min.
[0047] This embodiment increases the Cr and Si content in the composition design to enhance the coating's corrosion resistance in alkali metal molten salt environments while maintaining good solid solution structure stability.
[0048] Example 3
[0049] This embodiment achieves a thick, dense protective coating by adjusting the laser cladding process parameters, making it suitable for areas in high-temperature pipelines where wear and corrosion coupling is more intense.
[0050] The coating material in this embodiment is a NiCoFeCrSiAlW high-entropy alloy, whose chemical composition by atomic percentage is: Ni: 14.0%, Co: 14.0%, Fe: 14.0%, Cr: 18.0%, Si: 5.0%, Al: 15.0%, W: 20.0%.
[0051] Weigh the metal powders according to the above atomic percentages. The Ni, Co, Fe, and Cr metal powders have a particle size of 250 mesh and a purity of 99.7%; the Si, Al, and W metal powders have a particle size of 320 mesh and a purity of 99.9%. A two-step mixing method is used: First, the Ni, Co, Fe, and Cr powders are stirred and mixed in a mechanical mixer at 200 r / min for 40 min to obtain a primary mixed powder. Then, the Si, Al, and W powders are added to the primary mixed powder, and the mixture is mixed for 120 min using a planetary ball mill at 200 r / min revolution and 400 r / min rotation to obtain a secondary mixed powder. The secondary mixed powder is then dried in an 80℃ drying oven for 120 min for later use.
[0052] The substrate is a 12Cr1MoVG alloy steel pipe with an outer diameter of 150mm and a wall thickness of 12.0mm. The surface of the substrate to be clad is subjected to acetone degreasing, alcohol cleaning, and sandblasting roughening treatment in sequence to achieve a surface roughness of Ra5~10μm.
[0053] A composite coating was prepared using a broadband laser cladding system with a laser beam size of 20mm × 1.5mm. This embodiment employed a high laser heat input to obtain a thicker cladding layer. The process parameters were: laser power 5.0kW, laser scanning speed 4.5mm / s, overlap rate 25%, protective gas purity 99.99% argon, flow rate 28L / min, and powder feeding speed 45g / min.
[0054] In this embodiment, the content of W element is increased to utilize its high melting point and high-temperature creep resistance to enhance the structural stability and wear resistance of the coating under high-temperature conditions.
Claims
1. A high-temperature corrosion resistant protective coating for the surface of biomass boiler pipes, characterized in that, The coating is formed on the surface of the high-temperature pipe substrate of the biomass boiler using laser cladding technology. The coating material is a NiCoFeCrSiAlW high-entropy alloy, and its chemical composition by atomic percentage is as follows: Ni: 10%~36%, Co: 10%~36%, Fe: 10%~36%, Cr: 10%~36%, Si: 2%~20%, Al: 6%~20%, W: 6%~20%; and the sum of the atomic percentages of each component is 100%.
2. The high-temperature corrosion resistant protective coating for biomass boiler pipes according to claim 1, characterized in that, The chemical composition of the NiCoFeCrSiAlW high-entropy alloy, by atomic percentage, is as follows: Ni: 16.0%, Co: 16.0%, Fe: 16.0%, Cr: 16.0%, Si: 4.0%, Al: 16.0%, W: 16.0%.
3. The high-temperature corrosion resistant protective coating for biomass boiler pipes according to claim 1, characterized in that, The chemical composition of the NiCoFeCrSiAlW high-entropy alloy, by atomic percentage, is as follows: Ni: 20.0%, Co: 15.0%, Fe: 15.0%, Cr: 20.0%, Si: 6.0%, Al: 12.0%, W: 12.0%.
4. The high-temperature corrosion resistant protective coating for biomass boiler pipes according to claim 1, characterized in that, The chemical composition of the NiCoFeCrSiAlW high-entropy alloy, by atomic percentage, is as follows: Ni: 14.0%, Co: 14.0%, Fe: 14.0%, Cr: 18.0%, Si: 5.0%, Al: 15.0%, W: 20.0%.
5. A high-temperature corrosion resistant protective coating for the surface of biomass boiler pipes according to any one of claims 1-4, characterized in that, The coating has a BCC single-phase solid solution structure, and the coating is metallurgically bonded to the pipe substrate. The coating thickness is 0.8–1.0 mm.
6. A method for preparing a high-temperature corrosion-resistant protective coating for the surface of biomass boiler pipes, characterized in that, Includes the following steps: Step S1: Preparation of composite powder raw materials According to the designed atomic percentage, Ni, Co, Fe, and Cr metal powders were weighed as the first component, and Si, Al, and W metal powders were weighed as the second component. The first component metal powders were first mixed by mechanical stirring to obtain a primary mixed powder. Then, the second component metal powders were added to the primary mixed powder and mixed evenly by ball milling to obtain a secondary mixed powder. After drying the secondary mixed powder, high-entropy alloy powder for laser cladding was obtained. Step S2: Pretreatment of pipe substrate High-temperature pipes for biomass boilers are selected as the base material, and the surface of the base material is polished, degreased, and derusted. Step S3: Laser cladding to prepare a protective coating Broadband laser cladding technology is used to pre-place or synchronously transport the high-entropy alloy powder prepared in step S1 to the surface of the substrate after step S2 treatment, and laser cladding is performed under inert gas protection to form a high-entropy alloy protective coating that is metallurgically bonded to the substrate.
7. The method for preparing a high-temperature corrosion resistant protective coating on the surface of a biomass boiler pipe according to claim 6, characterized in that, In step S1, the particle size range of the first group of elemental metal powders is 250 mesh to 350 mesh, and the purity is not less than 99.7%; the particle size range of the second group of elemental metal powders is 320 mesh to 450 mesh, and the purity is not less than 99.9%.
8. The method for preparing a high-temperature corrosion resistant protective coating for the surface of a biomass boiler pipe according to claim 6, characterized in that, In step S1, the mechanical stirring time shall not be less than 30 minutes; the ball milling shall be carried out using a planetary ball mill, and the mixing time shall not be less than 60 minutes; the drying temperature of the secondary mixed powder shall be 80°C, and the drying time shall not be less than 120 minutes.
9. The method for preparing a high-temperature corrosion resistant protective coating on the surface of a biomass boiler pipe according to claim 6, characterized in that, In step S2, the substrate is 20G alloy steel or 12Cr1MoVG alloy steel, the outer diameter of the pipe is 20.0 to 600.0 mm, and the wall thickness is 2.0 to 50.0 mm; after pretreatment, the surface roughness of the substrate reaches Ra5 to 10 μm.
10. The method for preparing a high-temperature corrosion resistant protective coating on the surface of a biomass boiler pipe according to claim 6, characterized in that, The laser cladding process parameters in step S3 are as follows: laser power 2.0-5.5kW, laser scanning speed 1.5-6.0mm / s, laser beam size 20mm×1.5mm, overlap rate 25%-30%, protective gas is argon with a purity of 99.99% and a flow rate of 18-25L / min, and powder feeding speed 12.0-60.0g / min.