A wear-resistant coating for a boiler membrane water wall tube and a method of making the same

Abstract

The application provides a wear-resistant coating of a boiler membrane water wall tube and a preparation method thereof, and relates to the field of additive manufacturing technology. The wear-resistant coating comprises a bottom layer and a surface layer, which are prepared on the surface of the water wall tube by laser cladding technology. The bottom layer is formed by a Ni-based powder and comprises the following components in percentage by weight: Ti 4wt%-7wt%, Cr 16wt%-22wt%, Mo 4.5wt%-7wt%, Co 1.5wt%-6wt%, Si 0.5wt%-1wt%, Mn 2wt%-4wt%, W 0.5wt%-2wt%, and the balance of Ni. The surface layer is formed by a metal ceramic composite powder, which comprises a ceramic phase powder and a binder phase powder. The application effectively alleviates the difference in thermophysical properties between the water wall tube and the ceramic phase by the gradient structure of the Ni-based bottom layer and the metal ceramic composite surface layer, and reduces defects such as pores and cracks in the coating from the root.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a wear-resistant coating for boiler membrane water-cooled wall tubes and its preparation method. Background Technology

[0002] The membrane water-cooled wall of an electric boiler, as the core heating surface, is a tube-panel structure welded from water-cooled wall tubes and flat steel. It not only performs heat transfer but is also a key component for improving boiler thermal efficiency. However, in actual operation, the wear problem of the tube wall in the transition area between the lower combustion zone and the water-cooled wall is particularly prominent. This is due to the high flow velocity and high material concentration along the wall, with high-speed particles (such as ash or fuel particles) continuously scouring and cutting the water-cooled wall, ultimately leading to tube wall thinning, wear, and frequent tube rupture accidents. This wear not only shortens the service life of the water-cooled wall tubes but may also trigger boiler shutdowns for maintenance, causing significant economic losses and safety risks. Therefore, the development of efficient wear-resistant protection technology is urgently needed.

[0003] To address water-cooled wall wear, traditional methods employ anti-wear beams, or a combination of thermal spraying and welding. While anti-wear beams are structurally simple, their protective range is limited and they can easily disrupt the flow field within the furnace. Thermal spraying, although capable of forming a coating, suffers from low bonding strength, easy peeling, and insufficient durability. Welding, on the other hand, has drawbacks such as low hardness, high dilution rate, and susceptibility to post-weld cracking, making it unsuitable for high-temperature, high-wear conditions. Although these technologies alleviate wear problems to some extent, their overall performance still falls short of the demands of harsh environments such as circulating fluidized bed boilers or waste incinerators, particularly in terms of coating failure and short protective lifespan, necessitating more advanced surface engineering solutions. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a wear-resistant coating for boiler membrane water-cooled wall tubes and a method for preparing the same, in order to solve at least one technical problem in the background art.

[0005] The first aspect of the present invention provides a wear-resistant coating for a boiler membrane water-cooled wall tube, the wear-resistant coating comprising a base layer and a top layer, which are sequentially prepared on the surface of the water-cooled wall tube by laser cladding technology; The bottom layer is formed by laser cladding of Ni-based powder, which comprises the following components by weight percentage: Ti 4wt%~7wt%, Cr 16wt%~22wt%, Mo 4.5wt%~7wt%, Co 1.5wt%~6wt%, Si 0.5wt%~1wt%, Mn 2wt%~4wt%, W 0.5wt%~2wt%, with the balance being Ni; The surface layer is formed by laser cladding of metal-ceramic composite powder, which includes ceramic phase powder and binder phase powder, wherein the mass fraction of ceramic phase powder is 75%~95% and the binder phase powder is Ni-based powder.

[0006] According to one aspect of the above technical solution, the thickness of the bottom layer is 400μm~600μm.

[0007] According to one aspect of the above technical solution, the thickness of the surface layer is 400μm~800μm.

[0008] According to one aspect of the above technical solution, the ceramic phase powder includes at least one of tungsten carbide, molybdenum carbide, titanium carbide, titanium nitride, titanium carbonitride, niobium carbide, silicon carbide, and titanium boride.

[0009] According to one aspect of the above technical solution, the surface layer has a (Cr,Ti,W)3C2 and (Ti,Cr,W)C dual-phase composite structure.

[0010] A second aspect of the present invention provides a method for preparing a wear-resistant coating for a boiler membrane water-cooled wall tube, the method comprising: Provide a boiler membrane water-cooled wall tube; The boiler membrane water-cooled wall tubes are covered with a Ni-based powder by laser cladding to form a bottom layer. The Ni-based powder comprises the following components by weight percentage: Ti 4wt%~7wt%, Cr 16wt%~22wt%, Mo 4.5wt%~7wt%, Co 1.5wt%~6wt%, Si 0.5wt%~1wt%, Mn 2wt%~4wt%, W 0.5wt%~2wt%, with the balance being Ni. A surface layer is formed on the bottom surface by laser cladding of metal-ceramic composite powder, wherein the metal-ceramic composite powder includes ceramic phase powder and binder phase powder, wherein the mass fraction of ceramic phase powder is 75%~95% and the binder phase powder is Ni-based powder.

[0011] Furthermore, the laser cladding step specifically includes: Argon is used as the protective gas, and the rated output power is 4kW~6kW. Laser cladding is performed using a fiber laser, with a spot diameter of 1mm~5mm, a powder feeding speed of 10g / min~30g / min, and an overlap rate of 20%~40%.

[0012] Furthermore, the mixing step of the Ni-based powder or the metal-ceramic composite powder specifically includes: Weigh the powdered raw materials of each component and dry them at 80℃~160℃ for 1h~2h; The powder raw materials of each component are mechanically mixed for 1 to 3 hours.

[0013] A third aspect of the present invention provides a boiler membrane water-cooled wall tube, wherein the surface of the boiler membrane water-cooled wall tube is provided with a wear-resistant coating as described above.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The bottom layer uses Ni-based powder, and the top layer uses metal-ceramic composite powder. The resulting double-layer gradient structure effectively bridges the thermophysical performance differences between the water-cooled wall tube and the ceramic phase, fundamentally alleviating defects such as pores and cracks that are prone to occur during coating preparation and service, and ensuring the structural integrity and service reliability of the coating.

[0015] 2. The Ni-based powder base layer possesses both good toughness and metallurgical compatibility, providing a stable adhesion foundation for the surface layer and enhancing overall corrosion resistance and high-temperature oxidation resistance. The high proportion of ceramic powder hard phase in the surface layer endows the coating with excellent wear resistance, effectively resisting the scouring and cutting of high-speed material particles in the furnace. Meanwhile, the Ni-based powder binder phase, consistent with the base layer, ensures the firm bonding of the hard phase, avoiding the problem of hard phase detachment during use, thus achieving a balance between wear resistance and toughness.

[0016] 3. Compared with traditional anti-wear beams, thermal spraying and welding technologies, this invention uses laser cladding process to prepare the coating, which has the characteristics of low dilution rate and high bonding strength, so that the coating and the substrate form a tight metallurgical bond, significantly improving the adhesion stability of the coating and extending the overall service life of the water-cooled wall tube. At the same time, the coating has strong adaptability and can be adapted to circulating fluidized bed boilers, waste incinerators and other scenarios, reducing downtime maintenance losses. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the wear-resistant coating of the boiler membrane water-cooled wall tube in this invention; In the figure: water-cooled wall tube 1, water-cooled wall tube substrate 10, heat-affected layer 11, bottom layer 2, top layer 3.

[0018] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0019] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] This invention provides a wear-resistant coating for boiler membrane water-cooled wall tubes, the wear-resistant coating comprising a base layer 2 and a top layer 3, which are sequentially prepared on the surface of the water-cooled wall tube 1 by laser cladding technology; The bottom layer 2 is formed by laser cladding of Ni-based powder, which comprises the following components by weight percentage: Ti 4wt%~7wt%, Cr 16wt%~22wt%, Mo 4.5wt%~7wt%, Co 1.5wt%~6wt%, Si 0.5wt%~1wt%, Mn 2wt%~4wt%, W 0.5wt%~2wt%, with the balance being Ni; The bottom layer 2 has a thickness of 400μm~600μm and is made of Ni-based powder. Its thermophysical properties (coefficient of thermal expansion and thermal conductivity) are between those of the water-cooled wall tube 1 (metal) and the top layer 3 (cermet powder). This can alleviate the thermal stress difference between the top layer 3 and the water-cooled wall tube 1, preventing cracks in the coating due to thermal stress concentration. Furthermore, the Ni-based powder has good metallurgical compatibility with the water-cooled wall tube 1, and can form a strong metallurgical bond with it during laser cladding, providing a stable adhesion base for the top layer 3.

[0022] Furthermore, Cr and Mo elements can improve the corrosion resistance and high-temperature oxidation resistance of the bottom layer 2, while Ti and W elements provide element reserves for the formation of a two-phase composite structure in the subsequent surface layer 3. Si and Mn, as deoxidizers, can reduce oxide inclusions during the cladding process.

[0023] Furthermore, the water-cooled wall tube 1 includes a water-cooled wall tube substrate 10 and a heat-affected layer 11. When the laser beam clads the powder to form the bottom layer 2, the generated high temperature is conducted to the water-cooled wall tube 1, causing the heat-affected layer 11 adjacent to the molten pool to be heated to a very high temperature (but below the melting point), and then rapidly cooled. This rapid heating and cooling process leads to a microstructural transformation of the heat-affected layer 11, forming a critical transition zone between the bottom layer 2 and the water-cooled wall tube substrate 10.

[0024] The surface layer 3 is formed by laser cladding of metal-ceramic composite powder, which includes ceramic phase powder and binder phase powder, wherein the mass fraction of ceramic phase powder is 75%~95% and the binder phase powder is Ni-based powder.

[0025] The thickness of the surface layer 3 is 400μm~800μm, and the ceramic phase powder includes at least one of tungsten carbide, molybdenum carbide, titanium carbide, titanium nitride, titanium carbonitride, niobium carbide, silicon carbide, and titanium boride. The ceramic phase powder has extremely high hardness and is the core source of the coating's wear resistance, effectively resisting the erosion and cutting of high-speed material particles. The binder phase powder possesses both toughness and adhesion, firmly encapsulating the ceramic phase powder particles to prevent them from falling off, while also mitigating the damage to the wear-resistant coating from impact loads and preventing brittle fracture of the wear-resistant coating.

[0026] Therefore, the high hardness of the ceramic phase powder and the high toughness and high corrosion resistance of the binder phase powder complement each other, enabling the wear-resistant coating to simultaneously meet the multiple requirements of wear resistance, crack resistance and corrosion resistance, and adapt to the complex working conditions of boilers.

[0027] It should be noted that the surface layer 3 forms a two-phase composite solid solution of (Cr,Ti,W)3C2 and (Ti,Cr,W)C through Ti, W, Cr, and C. This achieves atomic-level uniform dispersion of the inhibitor elements (Ti, W) and the hard phase matrix element (Cr), effectively controlling the dissolution and exudation process of the Cr3C2 hard phase in the binder phase of the Ni-based powder. This prevents Cr3C2 from growing into coarse rod-shaped grains (coarse grains easily lead to stress concentration and brittleness inside the coating), thereby achieving grain refinement and solid solution strengthening. The introduction of Ti and W simultaneously strengthens the binder phase of the Ni-based powder, improving the strength and hardness of the binder phase, promoting the sintering and densification of the coating, and reducing porosity. The Mo element can further refine the Cr3C2 hard phase grains. Through the synergistic effect of grain refinement and solid solution strengthening, the comprehensive mechanical properties (hardness, toughness, and wear resistance) of the cermet are significantly improved.

[0028] Accordingly, the method for preparing the wear-resistant coating of the boiler membrane water-cooled wall tube includes: steps S1 to S3. Step S1: Provide a boiler membrane water-cooled wall tube; Specifically, boiler membrane water-cooled wall tubes made of 20G material were selected; sandblasting was performed before cladding.

[0029] For example, select 80-120 mesh brown corundum as quartz sand, keep the distance between the sandblasting gun and the boiler membrane water-cooled wall tube at 10cm-20cm, and at 45°-60° to the boiler membrane water-cooled wall tube. Move the sandblasting gun at a uniform speed to cover all cladding areas and ensure that the surface roughness reaches Ra=25μm-50μm.

[0030] Step S2: A bottom layer is formed on the surface of the boiler membrane water-cooled wall tube by laser cladding of Ni-based powder. The Ni-based powder comprises the following components by weight percentage: Ti 4wt%~7wt%, Cr 16wt%~22wt%, Mo 4.5wt%~7wt%, Co 1.5wt%~6wt%, Si 0.5wt%~1wt%, Mn 2wt%~4wt%, W 0.5wt%~2wt%, with the balance being Ni. The mixing step of the Ni-based powder includes: Weigh the powder raw materials of each component and dry them at 80℃~160℃ for 1h~2h. Temperatures below 80℃ cannot completely remove the moisture adsorbed by the powder, while temperatures above 160℃ will cause some easily oxidized components to oxidize.

[0031] Use a mixer to mechanically mix the powder raw materials of each component for 1 to 3 hours at a speed of 5 to 15 revolutions per minute. Insufficient mixing time will result in uneven composition, while mixing for more than 3 hours will cause powder agglomeration.

[0032] Furthermore, the laser cladding step specifically includes: Argon is used as the protective gas, and the rated output power is 4kW~6kW. Laser cladding is performed using a fiber laser. Argon has stable chemical properties, which can prevent the powder from oxidizing with the molten pool and ensure smooth powder feeding. If the rated output power is too low, the powder cannot be completely melted, while if it is too high, the powder will be over-melted and the dilution rate will increase.

[0033] Furthermore, the spot diameter is 1mm~5mm. If the spot diameter is too small, it will easily lead to excessively high local temperature. If it is too large, the coating thickness will be uneven. The flow rate of the protective gas is 5L / min~15L / min, and the flow rate of the powder feeding gas is 10L / min~20L / min. The powder feeding speed is matched with the rated output power to ensure that the powder is completely melted and the coating thickness is uniform.

[0034] The overlap rate should be between 20% and 40%. Insufficient overlap rate will cause gaps between weld beads, while excessive overlap rate will cause local heat accumulation and coating cracking.

[0035] Step S3: A surface layer is formed on the bottom layer by laser cladding of metal-ceramic composite powder. The metal-ceramic composite powder includes ceramic phase powder and binder phase powder, wherein the mass fraction of ceramic phase powder is 75%~95% and the binder phase powder is Ni-based powder.

[0036] The mixing steps of the metal-ceramic composite powder and the mixing steps of the Ni-based powder in step S2 are identical except for the powder raw materials.

[0037] Furthermore, the laser cladding steps for the bottom layer are consistent with the laser cladding steps for the top layer in step S2, ensuring the metallurgical bonding between the bottom and top layers and avoiding poor interface bonding due to parameter differences.

[0038] In addition, the present invention also provides a boiler membrane water-cooled wall tube, wherein the surface of the boiler membrane water-cooled wall tube is provided with the wear-resistant coating of the above-mentioned boiler membrane water-cooled wall tube.

[0039] The present invention is further illustrated below with specific embodiments: Example 1 Embodiment 1 of the present invention provides a wear-resistant coating for a boiler membrane water-cooled wall tube. The wear-resistant coating includes a base layer and a top layer, which are sequentially prepared on the surface of the water-cooled wall tube by laser cladding technology. The bottom layer is formed by laser cladding of Ni-based powder, which comprises the following components by weight percentage: Ti 4wt%, Cr 16wt%, Mo 5.5wt%, Co 3.5wt%, Si 0.7wt%, Mn 3wt%, W 1.2wt%, with the balance being Ni; The thickness of the bottom layer is 500μm.

[0040] The surface layer is formed by laser cladding of metal-ceramic composite powder, which includes ceramic phase powder and Ni-based binder phase powder. The mass fraction of ceramic phase powder is 75%, and the binder phase powder is Ni-based powder.

[0041] The thickness of the surface layer is 600 μm, and the ceramic phase powder comprises 60 wt% chromium carbide and 40 wt% titanium carbide. The surface layer forms a two-phase composite solid solution with (Cr,Ti,W)3C2 and (Ti,Cr,W)C through Ti, W and Cr, C.

[0042] Accordingly, the method for preparing the wear-resistant coating of the boiler membrane water-cooled wall tube includes: steps S1 to S3. Step S1: Provide a boiler membrane water-cooled wall tube; Among them, boiler membrane water-cooled wall tubes made of 20G material were selected; sandblasting was carried out before cladding.

[0043] Step S2: A bottom layer is formed on the surface of the boiler membrane water-cooled wall tube by laser cladding of Ni-based powder. The Ni-based powder comprises the following components by weight percentage: Ti 4wt%, Cr 16wt%, Mo 5.5wt%, Co 3.5wt%, Si 0.7wt%, Mn 3wt%, W 1.2wt%, with the balance being Ni. The mixing step of the Ni-based powder includes: Weigh the powdered raw materials of each component and dry them at 120℃ for 1.5h; The powder raw materials of each component were mechanically mixed for 2 hours at a speed of 10 rpm.

[0044] Furthermore, the laser cladding step specifically includes: Argon is used as the protective gas, and the rated output power is 5kW. Laser cladding is performed using a fiber laser.

[0045] Furthermore, the spot diameter is 3mm, the powder feeding speed is 15g / min, the overlap rate is 35%, and the flow rate of the protective gas is 9L / min.

[0046] Step S3: A surface layer is formed on the bottom surface by laser cladding of metal-ceramic composite powder. The metal-ceramic composite powder includes ceramic phase powder and binder phase powder, wherein the mass fraction of ceramic phase powder is 75% and the binder phase powder is Ni-based powder.

[0047] The mixing steps of the metal-ceramic composite powder and the mixing steps of the Ni-based powder in step S2 are identical except for the powder raw materials.

[0048] Furthermore, the laser cladding steps for the bottom layer are consistent with the laser cladding steps for the top layer in step S2.

[0049] Example 2 The wear-resistant coating for a boiler membrane water-cooled wall tube provided in Embodiment 2 of the present invention differs from the wear-resistant coating for the boiler membrane water-cooled wall tube in Embodiment 1 in that: The Ni-based powder in the top layer comprises the following components by weight percentage: Ti 5.5wt%, Cr 19wt%, Mo 5.5wt%, Co 3.5wt%, Si 0.7wt%, Mn 3wt%, W 1.2wt%, with the balance being Ni. The proportion of Ni-based powder in the bottom layer remains unchanged. The mass fraction of the ceramic phase powder is 85%.

[0050] Example 3 The wear-resistant coating for a boiler membrane water-cooled wall tube provided in Embodiment 3 of the present invention differs from the wear-resistant coating for the boiler membrane water-cooled wall tube in Embodiment 1 in that: The Ni-based powder in the top layer comprises the following components by weight percentage: Ti 7wt%, Cr 22wt%, Mo 5.5wt%, Co 3.5wt%, Si 0.7wt%, Mn 3wt%, W 1.2wt%, with the balance being Ni. The proportion of Ni-based powder in the bottom layer remains unchanged. Please refer to Table 1, which shows the parameters corresponding to the above embodiments of the present invention. The hardness was tested using a micro Vickers hardness tester, and the high-temperature friction coefficient was determined using a high-temperature friction and wear testing machine.

[0051] Table 1

[0052] As shown in Table 1, the hardness and high-temperature friction coefficient of Example 2 both reached the optimal level.

[0053] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0054] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A wear-resistant coating for boiler membrane water-cooled wall tubes, characterized in that, The wear-resistant coating comprises a base layer and a top layer, which are sequentially prepared on the surface of the water-cooled wall tube using laser cladding technology. The bottom layer is formed by laser cladding of Ni-based powder with a mesh size of 140-320. The Ni-based powder comprises the following components by weight percentage: Ti 4wt%-7wt%, Cr 16wt%-22wt%, Mo 4.5wt%-7wt%, Co 1.5wt%-6wt%, Si 0.5wt%-1wt%, Mn 2wt%-4wt%, W 0.5wt%-2wt%, with the balance being Ni. The surface layer is formed by laser cladding of 140-320 mesh metal-ceramic composite powder. The metal-ceramic composite powder includes ceramic phase powder and binder phase powder, wherein the mass fraction of ceramic phase powder is 75%-95% and the binder phase powder is Ni-based powder.

2. The wear-resistant coating for boiler membrane water-cooled wall tubes according to claim 1, characterized in that, The thickness of the bottom layer is 400μm~600μm.

3. The wear-resistant coating for boiler membrane water-cooled wall tubes according to claim 1, characterized in that, The thickness of the surface layer is 400μm~800μm.

4. The wear-resistant coating for boiler membrane water-cooled wall tubes according to claim 1, characterized in that, The ceramic phase powder includes at least one of tungsten carbide, molybdenum carbide, titanium carbide, titanium nitride, titanium carbonitride, niobium carbide, silicon carbide, and titanium boride.

5. The wear-resistant coating for boiler membrane water-cooled wall tubes according to claim 4, characterized in that, The surface layer has a dual-phase composite structure of (Cr,Ti,W)3C2 and (Ti,Cr,W)C.

6. A method for preparing a wear-resistant coating for a boiler membrane water-cooled wall tube, characterized in that, The preparation method is used to prepare the wear-resistant coating of the boiler membrane water-cooled wall tube according to any one of claims 1 to 5, and the preparation method includes: Provide a boiler membrane water-cooled wall tube; The boiler membrane water-cooled wall tubes are covered with a Ni-based powder by laser cladding to form a bottom layer. The Ni-based powder comprises the following components by weight percentage: Ti 4wt%~7wt%, Cr 16wt%~22wt%, Mo 4.5wt%~7wt%, Co 1.5wt%~6wt%, Si 0.5wt%~1wt%, Mn 2wt%~4wt%, W 0.5wt%~2wt%, with the balance being Ni. A surface layer is formed on the bottom surface by laser cladding of metal-ceramic composite powder, wherein the metal-ceramic composite powder includes ceramic phase powder and binder phase powder, wherein the mass fraction of ceramic phase powder is 75%~95% and the binder phase powder is Ni-based powder.

7. The method for preparing the wear-resistant coating of the boiler membrane water-cooled wall tube according to claim 6, characterized in that, The laser cladding process specifically includes: Argon is used as the protective gas, and the rated output power is 4kW~6kW. Laser cladding is performed using a fiber laser, with a spot diameter of 1mm~5mm, a powder feeding speed of 10g / min~20g / min, and an overlap rate of 20%~40%.

8. The method for preparing the wear-resistant coating of the boiler membrane water-cooled wall tube according to claim 6, characterized in that, The mixing step of the Ni-based powder or the metal-ceramic composite powder specifically includes: Weigh the powdered raw materials of each component and dry them at 80℃~160℃ for 1h~2h; The powder raw materials of each component are mechanically mixed for 1 to 3 hours.

9. A boiler membrane water-cooled wall tube, characterized in that, The surface of the boiler membrane water-cooled wall tube is provided with a wear-resistant coating as described in any one of requirements 1 to 5.

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