Laser cladding material for cavitation erosion resistance and its application in surface repair of hydraulic power station flow parts

Abstract

This invention provides a cavitation-resistant laser cladding material and its application in the surface repair of flow-through components in hydropower stations. The material contains the following components by weight percentage: cobalt 55%~70%; chromium: 15%~32%; tungsten: 1%~5%; metal nano-oxides: 10%~20%; carbon powder: 1%~10%, with the remainder being manganese and / or molybdenum. Due to the addition of ceramic particles, which are fused with the metal-based powder, the resulting coating after laser cladding possesses both the high chemical stability, high hardness, and wear resistance of ceramics, and the toughness of metals, thus achieving better resistance to cavitation and erosion.

Description

Technical Field

[0001] This invention belongs to the field of alloy coating technology, specifically relating to a laser cladding material resistant to cavitation and its application in the surface repair of flow-through components in hydropower stations. Background Technology

[0002] The turbine runner blade substrate is made of martensitic stainless steel, a commonly used substrate material for hydropower station blades. While it possesses good overall mechanical properties, its resistance to cavitation erosion is insufficient for long-term stable operation in complex fluid environments. During high-speed operation, it is susceptible to cavitation corrosion from water, and long-term service can lead to fish-scale-shaped fatigue damage on the blade substrate surface. Without intervention, this damage can even develop into microcrack propagation, posing a significant risk. Since damage first appears on the blade substrate surface, preparing a composite layer to enhance cavitation erosion resistance on the turbine blade substrate surface can improve its cavitation erosion resistance, thereby increasing service life and saving maintenance costs.

[0003] Currently, the main methods for coating protection of turbine blades in traditional hydropower plant engine units are welding and spraying. Welding is the most widely used method, achieving a strong metallurgical bond between the weld layer and the blade substrate. However, an excessively large heat-affected zone can damage or even deform the turbine blade substrate. To protect the turbine body while also resisting cavitation, another common method is spraying. However, its drawback is the relatively weak adhesion between the coating and the substrate. During turbine operation, the complex and harsh fluid erosion and cavitation environment can easily cause the coating to peel off, significantly reducing cavitation resistance and consequently affecting operating efficiency.

[0004] Existing domestic anti-cavitation coatings are generally classified into metallic coatings and non-metallic coatings based on their materials. Metallic coatings have the advantage of similar crystal structures to the substrate, consistent physicochemical properties, and high hardness, providing good resistance to high-speed fluids. However, a disadvantage is that metallic coatings are prone to accumulating significant internal stress, leading to microcracks and diminishing their anti-cavitation effect. Non-metallic coatings, such as ceramic materials, offer good chemical corrosion resistance, but their structure differs significantly from the blade substrate, resulting in insufficient adhesion. Summary of the Invention

[0005] This invention provides a laser cladding material for resisting cavitation erosion and its application in the surface repair of flow-through components in hydropower stations. It significantly improves the resistance to cavitation erosion and can achieve good metallurgical bonding with the substrate to be repaired.

[0006] The technical solution of the present invention is a laser cladding material resistant to cavitation erosion, containing the following components by weight percentage: cobalt 55%~70%; chromium: 15%~32%; tungsten: 1%~5%; metal nano-oxide: 10%~20%; carbon powder: 1%~10%, with the remainder being manganese and / or molybdenum.

[0007] Furthermore, the metal nano-oxide is nano-titanium dioxide and / or nano-zirconium dioxide.

[0008] Furthermore, the particle size of the metal nano-oxide is 30~55nm; the powder particle size of other metal components is 20~100μm.

[0009] Furthermore, the particle size of the toner is less than 200 μm.

[0010] Furthermore, the toner is replaced with graphene with a particle size ≤35μm.

[0011] The present invention also relates to the application of the material in laser cladding repair of the surface of flow-through components in hydropower stations.

[0012] This invention also relates to a method for laser cladding repair of the aforementioned material on the surface of flow-through components in a hydropower station, characterized by comprising the following steps:

[0013] S1. Draw the laser cladding area on the substrate to be repaired, inspect and detect defects, repair uneven defect areas by welding, grind smooth, and finally clean with anhydrous ethanol to complete the pretreatment; weigh the cladding material according to the ratio, mix well and dry for later use.

[0014] S2. For the selected laser cladding area, plan the cladding path and process parameters, ensuring that the coaxial powder feeder is perpendicular to the cladding surface and that the cladding process is complete before proceeding with the laser cladding operation. During the operation, the fiber laser power is 800~2000W, the powder feed rate is 20~50g / min, and the overlap rate is 25~50%.

[0015] S3. After the on-site operation is completed, perform grinding and polishing to ensure that the cladding layer thickness is greater than 0.6mm and the surface roughness is less than Ra0.6. Then, perform flaw detection and hardness testing. ， Complete the cladding process.

[0016] Furthermore, the cladding material is mixed in a mixer, rotating forward for 2 minutes and then reversed for 2 minutes, with a total mixing time of 120 minutes. After completion, it is taken out and dried at 60°C for 120 minutes for later use.

[0017] Furthermore, when preparing coatings using laser cladding, the scanning speed is 10~30mm / s, the protective gas is 5~10g / min, and the spot diameter is 2~4mm.

[0018] Furthermore, during flaw detection, it is ensured that the cladding coating is free of obvious cracks, defects, and porosity, and that the deformation of the substrate after cladding is less than 0.3 mm; during hardness testing, the surface Vickers hardness is greater than 550 Hv. 0.3 .

[0019] The present invention has the following beneficial effects:

[0020] 1. The laser cladding material of this invention incorporates metal nano-oxides and carbon powder. In the laser cladding process, the aforementioned mixed additive phases melt under high-energy-density laser beam irradiation to form a molten pool. Nanoparticles TiO2 and / or nano-ceramic phase ZrO2 in the alloy melt react with graphene to generate TiC and / or ZrC. As the molten pool temperature increases, the reaction proceeds spontaneously. Both TiC and ZrC have face-centered cubic structures with similar lattice constants, exhibiting good thermodynamic and chemical compatibility. Fine TiC and ZrC particles initially precipitate as particles, forming the particle-reinforcing phase of the cladding layer. As the molten pool temperature further decreases, TiC and ZrC readily combine and precipitate as strip-shaped reinforcing phases. Therefore, when a large number of TiC and ZrC particles are formed and precipitated, not only will particle strengthening occur, but also fine grain strengthening will occur. As a result, the cladding coating has high hardness. Furthermore, due to the excellent wear resistance of the generated ZrC particles themselves, the wear resistance of the composite coating is greatly enhanced, and the cavitation erosion resistance of the coating is improved. Moreover, the cladding coating has high compatibility with the substrate and strong bonding force. The laser cladding ceramic particle reinforced metal matrix composite coating has excellent process performance and has great potential for application in the maintenance and strengthening of turbine blades and runner chambers in hydropower stations.

[0021] 2. A ceramic particle-reinforced metal powder is clad onto the turbine blade substrate of the turbine runner using a laser cladding process. The substrate is martensitic stainless steel. The laser-clad ceramic particle-reinforced metal substrate anti-cavitation coating has a good metallurgical bond with the martensitic stainless steel substrate. At the same time, the addition of ceramic particle-reinforced anti-cavitation coating results in a more uniform distribution on the substrate, a finer grain structure, and higher hardness, wear resistance, anti-cavitation performance, and erosion resistance. This also helps to improve the service life of the turbine runner blade steel plate and increase indirect economic benefits.

[0022] 3. This process utilizes a high-power fiber laser, ensuring high laser purity and efficiency. The laser is mounted on a programmable robotic arm, and the laser head can be adjusted to address various parts of complex flow-through workpieces. Combined with a coaxial powder feeding device, the cladding material can be directly and evenly distributed to the marked laser cladding area. The cladding powder is uniform and stable, and the high purity and power of the laser fiber contribute to the continuous formation of a high-completeness cladding coating. This process features easily movable machinery, simple operation, and a high degree of mechanization. It can perform on-site cladding on large flow-through components and complex, variable workpiece surfaces, forming a cladding coating with uniform thickness and structure, free from obvious cracks and porosity defects. The cladding quality is stable, and the cladding efficiency is high, improving economic benefits and facilitating widespread application.

[0023] 4. This invention utilizes the in-situ reaction of metal oxides and carbon powder under the action of a high-energy laser beam to generate a multiphase composite ceramic particle-reinforced metal matrix coating. The laser beam provides energy to promote the spontaneous reaction, resulting in higher energy utilization efficiency. Simultaneously, during the laser cladding process, the mixed powder melts under the high-energy-density laser beam to form an alloy molten pool, ensuring uniform mixing of the cladding coating components and a more complete reaction. Due to the high melting point of the ceramic phase, when the molten pool cools, the carbide ceramic phase forms a miscible body, with small particles precipitating first. The higher temperature at the top of the molten pool further facilitates the precipitation of carbide particles. Therefore, the cladding layer generates the most carbide particles in situ at the top, decreasing progressively in the middle and bottom, resulting in a natural transition in hardness throughout the cladding layer. This reduces coating peeling caused by significant differences in physical properties between the coating and the substrate. The cladding coating and the substrate themselves have higher process compatibility and lower cost, making it suitable for large-scale applications. Attached Figure Description

[0024] Figure 1 These are low-magnification micrographs of the cladding coating surface obtained using the material from Example 2.

[0025] Figure 2 These are high-magnification micrographs of the cladding coating surface obtained using the material from Example 2.

[0026] Figure 3 Hardness distribution curves of coatings along the depth direction under different ceramic phase contents. Detailed Implementation

[0027] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0028] The metal elements used in the following examples are all spherical powders with a particle size of 20~100μm; the nano metal oxides have a particle size of 30~55nm; the graphene has a particle size of less than 35μm; and the carbon powder has a particle size of less than 200μm.

[0029] Example 1:

[0030] A laser cladding material resistant to cavitation erosion contains the following components by weight: cobalt: 58%; chromium: 18.5%; tungsten: 4%; nano-TiO2: 5%; nano-ZrO2: 5%; graphene: 8%; molybdenum: 0.5% and manganese: 1%.

[0031] Example 2:

[0032] A laser cladding material resistant to cavitation erosion contains the following components by weight: cobalt: 62%; chromium: 15.6%; tungsten: 4.2%; nano-TiO2: 6%; nano-ZrO2: 6%; graphene: 6%; molybdenum: 0.2%.

[0033] Example 3:

[0034] A laser cladding material resistant to cavitation erosion contains the following components by weight: cobalt: 65%; chromium: 15%; tungsten: 2%; nano-TiO2: 7%; nano-ZrO2: 7%; graphene: 2%; molybdenum: 1% and manganese: 1%.

[0035] Example 4:

[0036] A laser cladding material resistant to cavitation erosion contains the following components by weight: cobalt: 62%; chromium: 15.6%; tungsten: 4.2%; nano-TiO2: 12%; graphene: 6%; molybdenum: 0.2%.

[0037] Example 5:

[0038] A laser cladding material resistant to cavitation erosion contains the following components by weight: cobalt: 62%; chromium: 15.6%; tungsten: 4.2%; nano-ZrO2: 12%; graphene: 6%; molybdenum: 0.2%.

[0039] Example 6:

[0040] A laser cladding material resistant to cavitation erosion contains the following components by weight: cobalt: 62%; chromium: 15.6%; tungsten: 4.2%; nano-TiO2: 6%; nano-ZrO2: 6%; carbon powder: 6%; molybdenum: 0.2%.

[0041] Example 7:

[0042] A laser cladding material resistant to cavitation erosion contains the following components by weight: cobalt: 55%; chromium: 31%; tungsten: 1.2%; nano-TiO2: 6%; nano-ZrO2: 5%; graphene: 1%; molybdenum: 0.3% and manganese: 5%.

[0043] Example 8:

[0044] A laser cladding material resistant to cavitation erosion contains the following components by weight: cobalt: 55%; chromium: 18%; tungsten: 2%; nano-TiO2: 10%; nano-ZrO2: 9.6%; graphene: 4.5%; molybdenum: 0.5% and manganese: 0.4%.

[0045] Example 9:

[0046] 9-1: A laser cladding material resistant to cavitation erosion, comprising the following components by weight: cobalt: 61.5%; chromium: 30%; tungsten: 4.5%; carbon powder: 2%; molybdenum: 1% and manganese: 1%.

[0047] 9-2: A laser cladding material resistant to cavitation erosion, comprising the following components by weight: cobalt: 56.5%; chromium: 25%; nano-TiO2: 5%; nano-ZrO2: 5%; tungsten: 4.5%; carbon powder: 2%; molybdenum: 1% and manganese: 1%.

[0048] 9-3: A laser cladding material resistant to cavitation erosion, comprising the following components by weight: cobalt: 55.5%; chromium: 24.5%; nano-TiO2: 6%; nano-ZrO2: 6%; tungsten: 4.5%; carbon powder: 2%; molybdenum: 1% and manganese: 1%.

[0049] 9-4: A laser cladding material resistant to cavitation erosion, comprising the following components by weight: cobalt: 54.5%; chromium: 23.5%; nano-TiO2: 7%; nano-ZrO2: 7%; tungsten: 4.5%; carbon powder: 2%; molybdenum: 1% and manganese: 1%.

[0050] 9-5: A laser cladding material resistant to cavitation erosion, comprising the following components by weight: cobalt: 53.5%; chromium: 22.5%; nano-TiO2: 8%; nano-ZrO2: 8%; tungsten: 4.5%; carbon powder: 2%; molybdenum: 1% and manganese: 1%.

[0051] The laser cladding process, which uses the materials from Examples 2 and 9 respectively, is performed on-site in the rotary chamber and includes the following steps:

[0052] (1) Pretreatment: draw the laser cladding area on the turbine blade substrate of the turbine runner, observe the flatness of the substrate surface, and check for obvious cracks and pores. Repair the uneven defect area by welding and grind it flat. Clean it with anhydrous ethanol. Finally, the marked area of ​​the blade substrate meets the requirements of laser cladding.

[0053] (2) Debug the laser cladding system, examine the marked and selected laser cladding area, and plan the cladding path and process parameters. For the blade surface, ensure that the coaxial powder feeder is perpendicular to the cladding surface and does not accumulate, thus ensuring the integrity of the cladding process. The fiber laser has a laser power of 1800W, a powder feed rate of 20g / min, an overlap rate of 50%, a scanning speed of 20mm / s, a protective gas (argon) of 10g / min, and a spot diameter of 3mm.

[0054] (3) Mix the cladding material in a mixer according to the weight ratio. Set the mixer to rotate forward for 2 minutes and then reverse for 2 minutes. The total mixing time is 120 minutes. After completion, take it out and dry it at 60°C for 120 minutes for later use.

[0055] (4) After the laser cladding process is completed, the oxide scale is removed by grinding and polishing to observe the integrity and flatness of the cladding coating. The anti-cavitation coating is consistent with the designed cladding path and the marked cladding area. After polishing, it has a metallic luster and the surface roughness is less than Ra0.6.

[0056] (5) The anti-cavitation coating of the cladding is inspected. The flaw detection ensures that the anti-cavitation coating of the cladding has no obvious cracks or pores. The deformation of the blade substrate after cladding is less than 0.3 mm. The surface Vickers hardness is greater than 550 Hv0.3 in the hardness test. The thickness of the cladding layer after grinding needs to be greater than 0.6 mm. If the above standards are met, it basically means that the anti-cavitation coating of the hydropower station's turbine room is successfully prepared by laser cladding.

[0057] The coatings prepared by laser cladding were then polished and evaluated by characterization, metallographic analysis, cavitation erosion resistance test, and erosion resistance test.

[0058] Microstructure analysis

[0059] The microstructure of the cladding coating was observed and analyzed using a scanning electron microscope, revealing the presence of a matrix, a heat-affected zone, and a transition zone. The microstructure under low magnification is shown in the image. Figure 1 As shown in the figure (the coating after laser cladding of the material in Example 2), there are no obvious gaps between the substrate and the cladding coating, indicating that the laser cladding coating has high quality. It also demonstrates that the coating with added TiO2 nanoparticles and ZrO2 nano-ceramic phase still exhibits high compatibility with the steel substrate and strong coating inclusion. Under high magnification... Figure 2 As shown, the cladding layer has a fine and dense structure, with precipitated spherical particles, which are added ceramic particles to enhance the resistance to cavitation erosion. These particles have a grain-refining and particle-strengthening effect on the entire cladding coating, indicating that the cladding ceramic particles enhance the cavitation erosion resistance coating with high adhesion, metallurgical bonding with the substrate, and no obvious defects, cracks, or pores, making it worthy of process promotion.

[0060] Cavitation resistance

[0061] The cavitation erosion resistance of the cladding coating was evaluated using an ultrasonic cavitation erosion testing machine designed according to national standards. Comparative analysis showed that the cladding coating with added TiO2 nanoparticles and ZrO2 nano-ceramic phase (Example 2) exhibited only 38% of the cavitation corrosion mass loss of the coating without ceramic particle reinforcement (Example 9-1). This indicates that the cavitation erosion resistance of the cladding coating with added ceramic particles is more than double that of the unreinforced cladding coating, thus extending the service life of the turbine blades.

[0062] Erosion performance testing

[0063] Using an erosion corrosion tester, the erosion solution was prepared with diamond abrasive (<100 mesh) flakes at a concentration of 18 g / L. Comparative experiments showed that the erosion resistance weight loss of the cladding coating with nanoparticle TiO2 and nano-ceramic phase ZrO2 (Example 2) was only 50% of that of the cladding coating without nanoparticle TiO2 and nano-ceramic phase ZrO2 (Example 9-1). After adding nanoparticle TiO2 and nano-ceramic phase ZrO2, the erosion resistance of the cladding layer was significantly improved through ceramic particle reinforcement and dispersion strengthening.

[0064] Hardness testing

[0065] The microhardness of the coatings (Examples 9-1 to 9-4) was tested using a Vickers hardness tester. The experimental load was 0.98 N, and the treatment time was 15 s. The ceramic particle-reinforced anti-cavitation cladding coatings containing TiO2 nanoparticles and ZrO2 nano-ceramic phases hardened rapidly upon cooling after laser irradiation, with the hardness gradually increasing. Figure 3 The figures show the hardness distribution curves along the depth direction of the coatings after adding 0%, 10%, 12%, 14%, and 16% ceramic phase, respectively. As the ceramic particle content increases, the coating hardness gradually increases, and the hardness of the coatings after adding the ceramic phase is greater than 550 HV. 0.3 It meets the hardness requirements of the steel plate in the rotating chamber.

[0066] Abrasion resistance test

[0067] The high-speed, high-temperature friction and wear tester was used for testing. The experimental results show that the friction coefficient of the coating treated with the material in Example 2 is stable above 0.35. The ceramic particle-reinforced anti-cavitation cladding coating with added nanoparticles TiO2 and nano-ceramic phase ZrO2 has the smallest mass loss, which is only one-quarter of that without the addition, and has a significant friction reduction effect.

Claims

1. An application of nano-titanium dioxide and / or nano-zirconia with graphene in laser cladding repair of the surface of flow-through components in hydropower stations to improve cavitation resistance, characterized in that, The cladding material contains the following components by weight percentage: cobalt 55%~70%; chromium: 15%~32%; tungsten: 1%~5%; titanium dioxide and / or zirconium dioxide: 10%~20%; graphene: 1%~10%; the balance being molybdenum and / or manganese; wherein the particle size of nano-titanium dioxide and / or nano-zirconia is 30~55nm, the powder particle size of other metal components is 20~100μm, and the particle size of graphene is ≤35μm; The specific repair steps are as follows: S1. Draw the laser cladding area on the substrate to be repaired, inspect and detect defects, repair uneven defect areas by welding, grind smooth, and finally clean with anhydrous ethanol to complete the pretreatment; weigh the cladding material according to the ratio, mix well and dry for later use. S2. For the selected laser cladding area, plan the cladding path and process parameters, ensuring that the coaxial powder feeder is perpendicular to the cladding surface and that the cladding process is complete before proceeding with the laser cladding operation. During the operation, the fiber laser power is 800~2000W, the powder feed rate is 20~50g / min, and the overlap rate is 25~50%. S3. After the on-site operation is completed, grind and polish to ensure that the cladding layer thickness is greater than 0.6mm and the surface roughness is less than Ra0.

6. Perform flaw detection and hardness testing to complete the cladding process.

2. The application according to claim 1, characterized in that, The cladding material is mixed in a mixer, rotating clockwise for 2 minutes and then counterclockwise for 2 minutes, for a total mixing time of 120 minutes. After completion, it is taken out and dried at 60°C for 120 minutes for later use.

3. The application according to claim 1, characterized in that: When preparing coatings by laser cladding, the scanning speed is 10~30mm / s, the protective gas is 5~10g / min, and the spot diameter is 2~4mm.

4. The application according to claim 1, characterized in that: During flaw detection, ensure that the cladding coating is free of obvious cracks, defects, and porosity, and that the deformation of the substrate after cladding is less than 0.3 mm; during hardness testing, ensure that the surface Vickers hardness is greater than 550 Hv. 0.3 .

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