A method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment

Abstract

A method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment relates to a method for preparing a modified coating for the metal surface of chemical equipment. The composite coating uses 316L stainless steel as the substrate and is prepared by mixing Ni45 nickel-based self-fluxing alloy powder and SiC ceramic powder in a specific ratio, followed by a coaxial powder feeding laser cladding process. The Ni45 powder has a mass fraction of 60–90 wt.%, and the SiC powder has a mass fraction of 10–40 wt.%. This invention utilizes the partial decomposition or dissolution of SiC in the laser molten pool to provide Si and C sources for the Ni45 cladding layer, promoting the synergistic effect of solid solution strengthening, in-situ reaction strengthening, and grain refinement. This significantly improves the hardness, load-bearing capacity, and dry sliding wear resistance of the 316L stainless steel surface, and can be used for surface strengthening and repair of wear-resistant parts such as pumps, valves, bushings, sealing surfaces, and chemical equipment.

Description

Technical Field

[0001] This invention relates to a method for preparing a corrosion-resistant coating for chemical equipment, and more particularly to a method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment. Background Technology

[0002] In chemical equipment and load-bearing components, 316L stainless steel is widely used in pumps, valves, bushings, and sealing surfaces due to its excellent corrosion resistance, ductility, toughness, and formability. However, under service conditions such as high-load dry sliding, particle erosion, abrasive wear, or alternating loads, 316L stainless steel has low surface hardness and insufficient resistance to plastic deformation, making it prone to ploughing, adhesion transfer, fatigue spalling, and localized wear failure, which limits its long-term service reliability in harsh friction environments.

[0003] Laser cladding technology, characterized by high energy density, controllable heat input, low dilution rate, and strong metallurgical bonding, can form a dense, wear-resistant cladding layer on the surface of a metal substrate, making it an important method for improving the surface hardness and wear resistance of 316L stainless steel. Ni45 nickel-based self-fluxing alloys possess good wettability, formability, and wear resistance, making them suitable for preparing nickel-based wear-resistant coatings. However, the number of reinforcing phases in a single Ni45 cladding layer is limited, and under high-load dry sliding conditions, deep furrowing, adhesive wear, and spalling may still occur, making it difficult to meet the requirements for higher load-bearing capacity and low wear.

[0004] To further improve the hardness and abrasive resistance of nickel-based cladding layers, existing technologies typically incorporate ceramic reinforcing phases such as SiC, WC, and TiC into nickel-based alloy powders. SiC, in particular, possesses high hardness, good thermal stability, and strong wear-resistant strengthening capabilities. It not only serves as a hard reinforcing particle but also undergoes partial decomposition or dissolution in the high-temperature environment of the laser cladding pool, providing a source of Si and C elements for the cladding layer and promoting the formation of in-situ reinforcing phases such as silicides and carbides. However, improper control of the SiC addition amount, powder mixing method, and laser cladding parameters can easily lead to reinforcing phase agglomeration, insufficient interfacial bonding, microstructure coarsening, or localized embrittlement, thereby affecting the overall performance of the coating.

[0005] Therefore, it is necessary to control the SiC content, powder mixing state, and laser cladding process to enable the SiC-induced solid solution strengthening, in-situ reaction strengthening, and grain refinement effects to work synergistically. This will ensure that the 316L stainless steel in chemical equipment has enhanced surface hardness, strong resistance to plastic deformation, and is free from plowing, adhesion transfer, fatigue spalling, and severe local wear, which limits its long-term service reliability in harsh friction environments. It will also improve the coating hardness, load-bearing capacity, and dry sliding wear resistance under corrosion-resistant conditions. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a composite coating for surface reinforcement of corrosion-resistant components of chemical equipment. This method addresses the problems of low surface hardness of 316L stainless steel in chemical equipment, insufficient wear resistance and reinforcement of a single Ni45 cladding layer, and uneven distribution of reinforcing phase and insufficient interface stability in traditional ceramic reinforced coatings. The method involves combining Ni45 nickel-based alloy powder with SiC ceramic powder and using a coaxial powder feeding laser cladding process. This causes SiC to partially decompose or dissolve during the cladding process, further inducing the formation of Ni-Si silicides and Cr-rich carbides, thereby obtaining a composite cladding layer with γ-Ni as the matrix and a dispersed or networked distribution of hard reinforcing phases.

[0007] The objective of this invention is achieved through the following technical solution: A method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment, the method comprising the following preparation steps: S1, Substrate pretreatment; Substrate pretreatment includes: sanding the surface of the 316L stainless steel substrate with sandpaper to remove the oxide film and surface impurities, followed by ultrasonic cleaning with anhydrous ethanol and drying; S2, Ni45 powder and SiC powder are composite mixed; Ni45 powder composite mixing: average particle size is about 45 μm, SiC powder purity is not less than 99.9%, and particle size range is 45-100 μm; Ni45 powder and SiC powder are mixed in a planetary ball mill at a speed of 200 r / min for 2 h, with a pause and reverse rotation for 5 min every 30 min, and vacuum drying is performed after mixing; S3. Coaxial powder-feeding laser cladding is performed on the pretreated 316L stainless steel substrate under argon protection. The coaxial powder-feeding laser cladding uses a fiber laser with a wavelength of 1064 nm, a laser power of 1200–1600 W, a scanning speed of 4–8 mm / s, a powder feeding rate of 10–18 g / min, a spot diameter of 2.5–3.5 mm, and an overlap rate of 40%–60%. Preferably, the laser power is 1400 W, the scanning speed is 6 mm / s, the powder feeding rate is 15 g / min, the spot diameter is 3 mm, the overlap spacing is 1.5 mm, and the overlap rate is 50%. The coating is a SiC-reinforced Ni45 nickel-based laser cladding composite coating, prepared on the surface of the 316L stainless steel substrate. It is prepared by laser cladding of a mixture of Ni45 nickel-based self-fluxing alloy powder and SiC ceramic powder. The mass fraction of Ni45 powder is 60–90 wt.%, and the mass fraction of SiC powder is 10–40 wt.%. S4, after cooling, a Ni45-SiC nickel-based laser cladding composite coating is obtained; the composite coating uses γ-Ni solid solution as a continuous matrix and contains Ni-Si silicide and Cr-rich carbide reinforcing phases, and forms a metallurgical bonding interface with the 316L stainless steel matrix.

[0008] The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment, wherein the mass fraction of the SiC ceramic powder is preferably 30-40 wt.%, when the mass fraction of SiC is 40 wt.%, the composite coating has high hardness and low dry sliding wear rate; when the mass fraction of SiC is 30 wt.%, the composite coating has both high hardness, low wear rate and good frictional stability.

[0009] The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment, wherein the Ni-Si silicide includes at least one of Ni2Si and Ni3Si, and the Cr-rich carbide includes Cr3C2, Cr7C3, and (Cr,Fe). 23 At least one of C6.

[0010] The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment, wherein the strengthening phase in the composite coating is distributed in the intercellular region of cellular crystals, columnar cellular crystals or dendrites, and forms a granular, semi-continuous network or continuous network structure, wherein solid solution strengthening, second phase strengthening and grain refinement strengthening are all synergistic effects.

[0011] The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment, wherein the average thickness of the composite coating is 0.7 to 1.2 mm, the dilution rate is 10% to 15%, and the composite coating exhibits a gradient hardness distribution from the surface to the substrate, consisting of a high-hardness cladding layer, a fusion zone, a heat-affected zone, and the substrate.

[0012] The method for preparing a composite coating to strengthen the surface of corrosion-resistant components of chemical equipment involves a laser cladding process using a bidirectional S-shaped multi-channel scanning strategy, with adjacent cladding channels scanning in opposite directions. Both the protective gas and the powder feeding carrier gas are high-purity argon to reduce oxidation and ensure powder feeding stability.

[0013] The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment, wherein the SiC mass fraction is 30-40 wt.%, the average microhardness of the composite coating is not less than 850 HV. 0.2 When the SiC mass fraction is 40 wt.%, the wear rate of the composite coating under the conditions of 10 N load, 1 Hz reciprocating frequency, and 30 min dry sliding wear is no higher than 2.0 × 10⁻⁶. -5 mm 3 N -1 ·m -1 .

[0014] The significant features and positive effects of this invention are: 1. This invention introduces SiC ceramic powder into Ni45 nickel-based cladding powder, causing SiC to partially decompose or dissolve in the high-temperature environment of the laser molten pool, providing a source of Si and C elements, and promoting the in-situ formation of Ni-Si silicides and Cr-rich carbides, thus avoiding the problem of insufficient interfacial bonding caused by simply adding hard particles.

[0015] 2. The composite coating obtained by the present invention uses γ-Ni solid solution as a continuous matrix, and the reinforcing phase is distributed in the interdendritic, intercellular or grain boundary regions, which can form a granular, semi-continuous network or continuous network reinforcing structure, thereby achieving the synergistic effect of solid solution strengthening, second phase strengthening, dispersion strengthening and grain refinement strengthening.

[0016] 3. As the SiC content increases, the coating structure gradually changes from coarse dendrites to refined cellular and columnar cellular crystals. The reinforcing phase changes from discrete particles to semi-continuous or continuous networks, which can improve the coating's resistance to indentation deformation, load-bearing capacity, and resistance to abrasive cutting.

[0017] 4. Compared with the Ni45 cladding layer without SiC, the composite coating of this invention significantly improves the microhardness and wear resistance; preferably under 40 wt.% SiC conditions, the average microhardness can reach 897.18 HV. 0.2 The wear rate can be reduced to 1.98×10. -5 mm 3 ·N -1 ·m -1 It reduces by approximately 78.8% compared to the version without the SiC coating.

[0018] 5. This invention employs a coaxial powder feeding laser cladding and a bidirectional S-shaped multi-channel scanning strategy, combined with a 50% overlap rate, to obtain a composite coating with stable thickness, low dilution rate, and good metallurgical bonding with the 316L stainless steel substrate, which is suitable for surface strengthening and repair of engineering parts. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the hardness test of the laser cladding composite coating of the present invention; Figure 2 These are microstructure images of composite coatings with different SiC contents according to the present invention; Figure 3 These are wear morphology diagrams of composite coatings with different SiC contents according to the present invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings.

[0021] The composite coating of this invention is prepared on the surface of a 316L stainless steel substrate and is obtained by mixing Ni45 nickel-based self-fluxing alloy powder and SiC ceramic powder, coaxial powder feeding, and laser cladding. The Ni45 powder has a mass fraction of 60–90 wt.%, and the SiC powder has a mass fraction of 10–40 wt.%. The composite coating uses γ-Ni solid solution as a continuous matrix and contains Ni-Si silicides such as Ni2Si and Ni3Si, as well as Cr3C2, Cr7C3, and (Cr,Fe). 2 3 At least one of Cr-rich carbides such as C6. The preferred mass fraction of SiC in the composite coating is 30–40 wt.%. When the mass fraction of SiC is 30 wt.%, the coating can achieve a good balance of hardness, frictional stability, and wear resistance; when the mass fraction of SiC is 40 wt.%, the coating can achieve higher average microhardness and lower wear rate, which is suitable for working conditions where wear resistance enhancement is the main objective.

[0022] The preparation method of this invention includes substrate pretreatment, composite powder preparation, and laser cladding forming. Substrate pretreatment is used to remove oxide film and contaminants from the surface of 316L stainless steel, and improve the powder adhesion and cladding interface bonding quality; composite powder preparation is used to achieve uniform mixing of Ni45 powder and SiC powder; laser cladding forming is used to form a metallurgically bonded Ni45-SiC composite coating on the substrate surface.

[0023] The composite coating of this invention is suitable for strengthening or repairing the surface of wear-resistant parts or worn-out components on chemical equipment, such as 316L stainless steel pumps, valves, bushings, and sealing surfaces.

[0024] The specific implementation method is described below: Example 1

[0025] This embodiment provides a high wear-resistant SiC-reinforced Ni45 nickel-based laser cladding composite coating. The substrate material is 316L stainless steel, and the substrate dimensions are 40 mm × 30 mm × 10 mm. The substrate surface is polished with 500-grit SiC sandpaper to remove the surface oxide film and impurities, followed by ultrasonic cleaning with anhydrous ethanol and drying.

[0026] The cladding powder consists of Ni45 powder and SiC powder, with Ni45 powder comprising 60 wt.% and SiC powder comprising 40 wt.%. The average particle size of the Ni45 powder is approximately 45 μm; the purity of the SiC powder is 99.9%, and the particle size ranges from 45 to 100 μm. The Ni45 powder and SiC powder are mixed in a planetary ball mill at a speed of 200 r / min for 2 h, with a pause every 30 min and a 5 min counter-clockwise rotation. After mixing, the composite powder is vacuum dried.

[0027] Laser cladding employs a coaxial powder feeding method, with a laser wavelength of 1064 nm. The laser power is 1400 W, the scanning speed is 6 mm / s, the powder feeding rate is 15 g / min, the spot diameter is 3 mm, the spacing between adjacent cladding channels is 1.5 mm, and the overlap rate is 50%. Both the protective gas and the powder carrier gas are high-purity argon. The scanning method is a bidirectional S-shaped scan, meaning adjacent cladding channels use opposite scanning directions.

[0028] After preparation, the average coating thickness is approximately 0.9 mm, with a dilution rate of approximately 10%–15%, forming a continuous metallurgical interface with the 316L stainless steel substrate. XRD and SEM / EDS results indicate that the coating mainly consists of γ-Ni solid solution, Ni-Si silicide, and Cr-rich carbides, with the reinforcing phase exhibiting a relatively continuous distribution in the columnar cellular and interdendritic regions.

[0029] Performance test results show that the average microhardness of the coating obtained in this embodiment is 897.18 HV. 0.2 Under dry sliding wear conditions at room temperature, using 5 mm GCr15 steel balls as the friction pair, a load of 10 N, a reciprocating frequency of 1 Hz, a wear time of 30 min, and a stroke of 5 mm, the measured wear rate was 1.98 × 10⁻⁶. -5 mm 3 ·N -1 ·m -1 The results demonstrate that the coating obtained in this embodiment has strong resistance to indentation deformation and material removal. Example 2

[0030] This embodiment provides a friction-stabilized SiC-reinforced Ni45 nickel-based laser cladding composite coating. Except for the different composite powder ratio, the substrate pretreatment, powder mixing method, and laser cladding parameters are the same as in Example 1.

[0031] In this embodiment, the Ni45 powder has a mass fraction of 70 wt.% and the SiC powder has a mass fraction of 30 wt.%. The prepared coating uses γ-Ni solid solution as the matrix and forms refined cellular crystals and continuous or semi-continuous interdendritic reinforcing phase networks.

[0032] Performance test results show that the average microhardness of the coating obtained in this embodiment is 856.87 HV. 0.2 The wear rate is 3.73 × 10⁻⁶. -5 mm 3 ·N -1 ·m -1 Compared to Example 1, the wear rate of this example is slightly higher, but its friction coefficient is relatively more stable, and the risk of spalling caused by local hard phase enrichment is lower. It is suitable for surface strengthening scenarios that balance wear resistance and friction stability.

[0033] Comparative Example 1 This comparative example provides a Ni45 laser cladding coating without added SiC. The substrate material, substrate pretreatment, laser cladding equipment, and process parameters are the same as in Example 1, except that the cladding powder is only Ni45 powder, without the addition of SiC powder.

[0034] The coating after preparation mainly consists of γ-Ni solid solution and a small amount of interdendritic precipitates. The microstructure is dominated by coarse dendrites with strong directionality, and the number of reinforcing phases is small and their distribution is discontinuous.

[0035] Performance test results show that the average microhardness of the coating obtained in this comparative example is 450.43 HV. 0.2 The wear rate was 9.36 × 10⁻⁶. -5 mm 3 ·N -1 ·m -1 The worn surface showed deep furrows, adhesive tears, and localized spalling, indicating that the single Ni45 coating was insufficient in its resistance to abrasive cutting and plastic deformation under high-load dry sliding conditions.

[0036] Performance comparison between the examples and the comparative examples Table 1 lists the powder ratios and main performance results of Ni45-SiC composite coatings with different SiC contents. As can be seen from Table 1, the addition of SiC can significantly improve the microhardness of the Ni45 cladding layer and reduce the wear rate; the wear resistance improvement is most obvious under the condition of 40 wt.% SiC, while the condition of 30 wt.% SiC shows a better overall balance.

[0037] Comparative Example 1 100 0 450.43 <![CDATA[9.36×10 -5 ]]> Example 1 60 40 897.18 <![CDATA[1.98×10 -5 <!-- 4 -->]]> Example 2 70 30 856.87 <![CDATA[3.73×10 -5 ]]> Example 3 80 20 665.05 <![CDATA[4.51×10 -5 ]]> Example 4 90 10 574.42 <![CDATA[4.07×10 -5 ]]> Note: The preparation steps of Examples 3 and 4 are the same as those of Example 1, the only difference being the different mass ratio of Ni45 to SiC powder.

[0038] Mechanism of action explanation During laser cladding, Ni45 powder and the surface layer of the 316L stainless steel substrate rapidly melt under the action of a high-energy laser beam to form a transient molten pool. After SiC particles enter the molten pool, some can be retained as hard reinforcing particles, while others decompose or dissolve in the high-temperature environment, releasing Si and C elements. Si elements can enter the γ-Ni matrix to form a substitutional solid solution, while C elements can enter interstitial sites or react with elements such as Cr, thereby causing lattice distortion and increasing the resistance to dislocation movement in the matrix.

[0039] Meanwhile, the diffusion and redistribution of Si and C elements in the molten pool promotes the formation of Ni-Si silicides such as Ni2Si and Ni3Si, as well as Cr3C2, Cr7C3, and (Cr,Fe). 2 3C6 and other Cr-rich carbides are formed. These hard phases are distributed in the interdendritic or grain boundary regions, which can bear the external load, hinder dislocation movement and pin grain boundary migration, so that the coating structure is refined from coarse dendrites to cellular or columnar cellular crystals.

[0040] During the wear process, the Ni45 coating without SiC has low hardness, making it easy for friction pairs and wear debris to be pressed into the surface and form deep furrows. The wear mechanism is mainly abrasive wear and adhesive wear. After adding SiC, the coating hardness and load-bearing capacity are improved, the abrasive cutting depth is reduced, and wear debris and oxidation products are gradually compacted at the friction interface to form a third body layer or oxide film. This changes the wear mechanism to a combination of slight abrasive wear, oxidative wear, and third body layer protection.

[0041] When the SiC content is further increased to 30–40 wt.%, the continuous or semi-continuous hard phase network can significantly improve the coating's resistance to material removal. However, excessively high SiC content may also lead to localized enrichment of the hard phase and stress concentration. Therefore, in specific engineering applications, the choice between 30 wt.% and 40 wt.% SiC solutions can be made according to service requirements: the former is suitable for a balanced overall performance, while the latter is suitable for operating conditions where low wear rate is the primary objective.

Claims

1. A method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment, characterized in that, The method includes the following preparation process: S1, matrix pretreatment; The substrate pretreatment includes: sanding the surface of the 316L stainless steel substrate with sandpaper to remove the oxide film and surface impurities, followed by ultrasonic cleaning with anhydrous ethanol and drying; S2, Ni45 powder and SiC powder are composite mixed; Ni45 powder composite mixing: average particle size is about 45 μm, SiC powder purity is not less than 99.9%, and particle size range is 45-100 μm; Ni45 powder and SiC powder are mixed in a planetary ball mill at a speed of 200 r / min for 2 h, with a pause and reverse rotation for 5 min every 30 min, and vacuum drying is performed after mixing; S3. Coaxial powder-feeding laser cladding is performed on the pretreated 316L stainless steel substrate under argon protection. The coaxial powder-feeding laser cladding uses a fiber laser with a wavelength of 1064 nm, a laser power of 1200–1600 W, a scanning speed of 4–8 mm / s, a powder feeding rate of 10–18 g / min, a spot diameter of 2.5–3.5 mm, and an overlap rate of 40%–60%. Preferably, the laser power is 1400 W, the scanning speed is 6 mm / s, the powder feeding rate is 15 g / min, the spot diameter is 3 mm, the overlap spacing is 1.5 mm, and the overlap rate is 50%. The coating is a SiC-reinforced Ni45 nickel-based laser cladding composite coating, prepared on the surface of the 316L stainless steel substrate. It is prepared by laser cladding of a mixture of Ni45 nickel-based self-fluxing alloy powder and SiC ceramic powder. The mass fraction of Ni45 powder is 60–90 wt.%, and the mass fraction of SiC powder is 10–40 wt.%. S4, after cooling, a Ni45-SiC nickel-based laser cladding composite coating is obtained; the composite coating uses γ-Ni solid solution as a continuous matrix and contains Ni-Si silicide and Cr-rich carbide reinforcing phases, and forms a metallurgical bonding interface with the 316L stainless steel matrix.

2. The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment according to claim 1, characterized in that, The preferred mass fraction of the SiC ceramic powder is 30–40 wt.%. When the mass fraction of SiC is 40 wt.%, the composite coating has high hardness and low dry sliding wear rate. When the mass fraction of SiC is 30 wt.%, the composite coating has both high hardness, low wear rate and good frictional stability.

3. The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment according to claim 1, characterized in that, The Ni-Si silicide includes at least one of Ni2Si and Ni3Si, and the Cr-rich carbide includes Cr3C2, Cr7C3, and (Cr,Fe). 2 3 At least one of C6.

4. The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment according to claim 1, characterized in that, The reinforcing phase in the composite coating is distributed in the cellular, columnar cellular, or dendritic regions, forming granular, semi-continuous, or continuous network structures. Solid solution reinforcement, second-phase reinforcement, and grain refinement reinforcement all have synergistic effects.

5. The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment according to claim 1, characterized in that, The average thickness of the composite coating is 0.7 to 1.2 mm, the dilution rate is 10% to 15%, and the composite coating exhibits a gradient hardness distribution from the surface to the substrate, consisting of a high-hardness cladding layer, a fusion zone, a heat-affected zone, and the substrate.

6. The method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment according to claim 1, characterized in that, The laser cladding employs a bidirectional S-shaped multi-channel scanning strategy, with adjacent cladding channels scanning in opposite directions. Both the protective gas and the powder carrier gas are high-purity argon to reduce oxidation and ensure powder feeding stability.

7. A method for preparing a surface-strengthening composite coating for corrosion-resistant components of chemical equipment according to claim 1, characterized in that, When the SiC mass fraction is 30–40 wt.%, the average microhardness of the composite coating is not less than 850 HV. 0.2 When the SiC mass fraction is 40 wt.%, the wear rate of the composite coating under the conditions of 10 N load, 1 Hz reciprocating frequency, and 30 min dry sliding wear is no higher than 2.0 × 10⁻⁶. -5 mm 3 ·N -1 ·m -1 .

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