Laser cladding materials, products and methods with nanoparticle addition to enhance cavitation resistance

Abstract

The present invention provides a laser cladding material, product, and method for enhancing cavitation resistance with the addition of nanoparticles. These materials belong to the field of laser cladding repair. The powdered material comprises the following components, as determined by mass: 55% to 75% cobalt, 15% to 32% chromium, 1% to 10% tungsten, 1% to 10% nano-modified particles, and the remainder being molybdenum and manganese. The nano-modified particles are a mixture of carbon nanotubes and nano-Ti3AlC2, a mixture of nano-graphene and nano-Ti3AlC2, or a mixture of nano-titanium carbide and nano-Ti3AlC2. The present invention also provides the product and preparation method. The present invention addresses existing issues associated with the use of overlay welding or spray coating techniques for repairing flow-through components in liquid working environments, including large deformation due to overlay welding over large areas, the generation of difficult-to-detect cracks, poor cavitation and wear resistance, weak adhesion between the spray coating and the substrate, and thin thickness.

Description

Technical Field

[0001] The present invention belongs to the field of laser cladding repair, and more specifically, relates to a laser cladding material, product and method with nanoparticles added to enhance cavitation resistance. Background Art

[0002] At present, most of my country's hydropower stations are distributed in the southwest region. The water flow is fast, the flow rate is large, and the cavitation corrosion problem on the surface of flow-passing components such as propellers, turbine blades, pumps, valves, and pipes is particularly serious. Among them, more than 40% of turbine blades suffer from cavitation corrosion. The corrosion is more serious at the water outlet edge of the turbine blades, with many deep corrosion pits appearing in a fish-scale shape, which seriously damages the structure of the blades and seriously restricts the power generation efficiency of the generator set. At the same time, the vibration generated by the unit also threatens the safe operation of the unit.

[0003] At the same time, the steel plates inside the rotating chamber are made of martensitic stainless steel. When localized corrosion or damage occurs, they are often repaired by surfacing with martensitic stainless steel raw material welding rods. This repair process is prone to difficult-to-detect weld cracks and defects. At the same time, the local temperature is too high, and the material is extremely easy to deform. The repaired part has a short lifespan and requires repeated repairs, causing damage to the larger area. All these factors make the welding repair process unusable indefinitely. However, the method of replacing the entire material is long-term and labor-intensive, making it unsuitable for hydropower stations with short maintenance periods. Therefore, the development of a new material and process for repairing rotating chamber components is urgent.

[0004] Currently, China is trying to solve this problem by using the laser cladding process in surface strengthening technology. Specifically, cemented carbide is clad on turbine blades to improve the surface's cavitation resistance. However, the compatibility between metal coatings and substrates is generally not high, the coatings are thin, and the service life is short. Therefore, on turbine blades that have not yet experienced large-scale corrosion and crack defects, the on-site repair process of laser cladding is used in advance. New laser cladding repair materials with cavitation resistance are clad on them to improve the cavitation, erosion, and wear resistance of the wheel chamber steel plates, thereby extending the service life of the wheel chamber steel plates. This is a problem that hydropower companies at home and abroad need to solve.

[0005] Currently, cavitation-resistant coatings can be categorized as metallic or organic based on their materials. Metallic coatings primarily include nickel-titanium alloys, nickel-aluminum bronze, and high-entropy alloys. In practical applications, they enhance the hardness of the substrate to protect against cavitation. However, due to the complex service conditions of turbines and the high energy of cavitation corrosion, a simple "hard-for-hard" approach can easily lead to significant internal stress accumulation in the cladding layer, resulting in microcracks and subsequent detachment. This rapidly degrades cavitation resistance and can even accelerate corrosion of turbine blades. Organic coatings, typically including epoxy resins and polyurethanes, possess highly elastic properties. These coatings have long chemical molecular chains and are chemically stable, offering excellent anti-corrosion, anti-fouling, and anti-adhesion properties. However, due to their significant compositional disparity with the substrate, the substrate-coating bond is weak. Furthermore, the bombardment of cavitation energy generates a temperature rise, accelerating the aging of the polymer coating. This "soft-for-hard" approach is easily damaged or destroyed in practical applications, resulting in a short-lived and inefficient protection.

[0006] Research has found that increasing the hardness of the coating can effectively improve erosion resistance. However, the coating must maintain both strength and sufficient toughness to absorb the energy of cavitation impacts. High hardness with low toughness is insufficient. Furthermore, the cladding material must exhibit good compatibility and wettability with the substrate, meaning good processability. Currently, no material meets these requirements.

[0007] Therefore, it is necessary to develop a new material and process that can simultaneously possess the principles of strength, toughness and processability. Summary of the Invention

[0008] In response to the defects of the prior art, the purpose of the present invention is to provide a laser cladding material, product and method with added nanoparticles to enhance cavitation resistance. By adding nanoparticles for enhancing cavitation resistance to cobalt-based alloys, a new type of cavitation resistance material and process for laser cladding repair can be formed, which can solve the problems existing in the repair of flow-through components in existing liquid working environments using surfacing or spraying technology, including large deformation due to large-area surfacing, the generation of difficult-to-find crack defects, poor cavitation resistance and wear resistance, weak bonding between the spray coating and the substrate, and thin thickness.

[0009] To achieve the above object, the present invention provides a laser cladding material with enhanced cavitation resistance by adding nanoparticles, which is in powder form and includes the following components and the mass percentages of each component:

[0010] Cobalt: 55% to 75%, chromium: 15% to 32%, tungsten: 1% to 10%, nano-modified particles: 1% to 10%, and the balance is molybdenum and manganese. The nano-modified particles are a mixture of carbon nanotubes and nano-Ti3AlC2, a mixture of nano-graphene and nano-Ti3AlC2, or a mixture of nano-titanium carbide and nano-Ti3AlC2.

[0011] Furthermore, the components and the mass percentages of the components are as follows: cobalt: 60% to 65%, chromium: 20% to 25%, tungsten: 5% to 9%, the sum of the weight of graphene and nanoparticles Ti3AlC2: 4% to 10%, and the balance is molybdenum and manganese.

[0012] The particle size of nano-Ti3AlC2 ranges from 20nm to 50nm, the weight ratio of graphene to nano-particle Ti3AlC2 is 1:10 to 1:1, and each component is a spherical powder with a particle size of 50μm to 100μm.

[0013] The particle sizes of the carbon nanotubes, nanographene and nanotitanium carbide range from 10 nm to 100 nm.

[0014] According to the second aspect of the present invention, there is also provided an application of a laser cladding material with added nanoparticles to enhance cavitation resistance as described above, which is used for laser cladding forming on the surface of the flow-through components of the rotating chamber of a hydropower station, so as to cover the working surface of the flow-through components of the rotating chamber of the hydropower station with an anti-cavitation layer having a harderness higher than that of the substrate, wherein the substrate refers to the main body of the flow-through components of the rotating chamber of the hydropower station.

[0015] According to the third aspect of the present invention, there is also provided a flow-through component of a hydropower station turbine chamber made of the laser cladding material with nanoparticle-enhanced cavitation resistance as described above, a laser cladding layer is generated on the working surface of the component, and the thickness of the laser cladding layer is 0.8mm to 8mm.

[0016] Furthermore, its surface hardness is greater than Vickers hardness 450Hv, its roughness is less than Ra0.5, and the height difference between the highest point and the lowest point of each overlap point in the cladding layer does not exceed 0.2mm.

[0017] Furthermore, in the field of view magnified 1000 times by a scanning electron microscope, the substrate and the cladding layer are tightly fitted without cracks, and the tissue skeleton of the cladding layer is discontinuous and fragmented, with spherical precipitated particles.

[0018] According to a fourth aspect of the present invention, there is also provided a method for preparing the above-mentioned flow-through component of the hydropower station rotary chamber, which comprises the following steps:

[0019] S1: Perform flaw detection on the base area of ​​the flow-through components of the hydropower station's rotating chamber that requires laser cladding. Perform repair welding based on the flaw detection results, then polish and remove the surface oxide layer. Finally, clean the surface to ensure that the surface quality meets the cladding requirements.

[0020] S2: The laser cladding materials are mixed according to the set composition in weight percentage, then ball milled, vacuum dried, and finally preheated in an oven for subsequent use.

[0021] S3: Plan the cladding path and select the process parameters for the cladding area of ​​the flow-through components of the hydropower station's rotating chamber. Then, perform synchronous powder feeding laser cladding on the repaired area of ​​the flow-through components of the rotating chamber at the hydropower station site.

[0022] S4: After the cladding layer and substrate cool to room temperature, the surface of the cladding layer is polished and ground.

[0023] S5: The repaired flow-through components of the hydropower station's rotating chamber are subjected to cladding layer flaw detection, cladding layer thickness detection, cladding layer hardness test and deformation detection in sequence.

[0024] Furthermore, step S1 specifically includes: performing PT inspection on the base area of ​​the flow-through component of the hydropower station's rotating chamber to be laser clad, and performing repair welding on the cavitation area to ensure that there are no defects visible to the naked eye on the base material of the area to be clad, polishing the entire surface area of ​​the area to be clad to remove the surface oxide layer, and finally using anhydrous ethanol and acetone for cleaning to remove surface oil stains to ensure that the surface quality meets the cladding requirements.

[0025] Furthermore, step S2 is specifically as follows: the laser cladding powder is mixed and placed in a ball mill, the rotation speed is set to 130 rpm to 180 rpm, the ball milling time is 40 min to 80 min, and after the ball milling is completed, it is placed in a vacuum drying oven for 3 h to 5 h, and preheated in an oven at 55 ° C to 65 ° C for 50 min to 70 min before use to ensure that the moisture in the powder is removed, the powder fluidity is improved, and moisture is prevented from entering the cladding layer and clogging the powder outlet.

[0026] The cladding path planning and process parameters of step S3 are as follows: the laser power of the fiber laser is 1000W~9000W, the scanning speed is 10mm / s~50mm / s, the powder feeding amount is 5g / min~200g / min, the overlap rate is 25%~75%, the shielding gas flow rate is 5g / min~20g / min, the defocus amount is 5mm~100mm, and the symmetrical cladding is adopted in different areas, and the area size is (400mm~600mm)×(400mm~600mm).

[0027] Furthermore, the thickness of the cladding layer is greater than 0.8 mm, the surface roughness of the cladding layer after polishing is less than Ra0.5, and the effective thickness of the cladding layer after polishing is greater than 0.5 mm.

[0028] The height difference between the highest and lowest points of each overlap point does not exceed 0.2mm. The surface of the cladding layer is polished and ground before being inspected. PT inspection shows no obvious pores or cracks. The deformation of the test steel plate surface is less than 0.2mm, and the surface hardness is greater than Vickers hardness 450Hv.

[0029] In general, the above technical solutions conceived by the present invention have the following advantages compared with the prior art:

[0030] Beneficial effects:

[0031] The laser cladding material with nanoparticles added to enhance cavitation resistance of the present invention particularly introduces nano-modified particles, such as nano-graphene and nano-particle Ti3AlC2 as the added second phase, and graphene, carbon nanotubes and nano-titanium carbide introduce carbon elements, wherein the carbon atoms are sp 2 The nano-modified particles, due to their high specific surface area, form hybrid orbital bonding, increasing the contact area between the cladding layer and the substrate material, thereby improving bonding strength. Furthermore, nanoparticle Ti3AlC2 is a MAX phase metal-ceramic nanomaterial. Due to the multi-level synergistic strengthening mechanism of nanoparticles, the added Ti3AlC2 nanoparticles strengthen the material through various mechanisms, including fine grain strengthening, dispersion strengthening, the Kelly-Nicholson mechanism, and nano-transfer film, all of which work synergistically. The cobalt-based metal material used for laser cladding repair of hydropower station turbine chambers, after adding nanoparticle graphene and Ti3AlC2, significantly improves its cavitation resistance compared to unadded repair materials. The repaired cladding layer exhibits a finer structure and increased hardness. Furthermore, the bonding strength between the cladding layer and the substrate is enhanced by the increased contact area between the substrate and the cladding layer due to the addition of nanoparticles, which helps to extend the life of the turbine blade steel plates and increase indirect economic benefits.

[0032] In actual engineering practice, by adjusting and matching the mass percentage, particle size and range of the materials, the effect of adding nano-modified particles can be maximized, so that the anti-cavitation layer obtained by laser cladding is firmly bonded to the substrate, the anti-cavitation layer has a fine structure, excellent hardness, and good actual use effect.

[0033] In actual engineering, on-site repair can be carried out by using a high-power fiber laser and a laser cladding process with coaxial powder feeding technology, replacing the currently commonly used welding and spraying processes, to obtain a cladding layer with better cavitation resistance. The cladding layer has a fine and dense structure without obvious crack defects. The coating repaired on-site by laser cladding has stronger bonding strength than the coating repaired by the welding process, and the repair area is controllable, just like patching. It can be flexibly "patched" where repair is needed. The process is more flexible and free, and compared with the spraying process, it takes less time, can improve work efficiency, and extend the service life of the turbine rotor chamber.

[0034] In actual engineering, the rotary chamber steel plates are made of cast low-carbon martensitic stainless steel, with common grades being ZG0Cr13Ni4Mo and ZG0Cr13Ni5Mo (an ultra-low-carbon martensitic stainless steel with the following chemical composition: C ≤ 0.05, Si ≤ 0.60, Mn 0.50-1.00, P ≤ 0.030, S ≤ 0.030, Cr 11.50-14.00, Ni 3.50-5.50, Mo 0.50-1.00). Laser repair of steel plates not only considers the excellent cavitation resistance of the repair material itself, but also the compatibility between the repair powder material and the steel plate itself as the base material, including properties such as elemental compatibility, thermal expansion coefficient, and melting point. The novel cobalt-based alloy repair material proposed by the method of the present invention can simultaneously meet the above two requirements, because the cobalt-based alloy has excellent resistance to friction, cavitation, mortar abrasion and thermal wear, and has excellent corrosion resistance. In addition, it still has quite good hardness, strength and wear resistance at a red-hot temperature of 480°C, making it an extremely excellent high-temperature wear-resistant material, room-temperature wear-resistant material, and cavitation-resistant material. At the same time, the cobalt-based alloy in the present invention is relatively matched with the substrate in terms of melting point, thermal expansion coefficient, and dilution rate. After laser cladding, the material deformation is small, the bonding strength between the cladding layer and the substrate is high, and there are no obvious pores or cracks. It is very suitable for repairing the flow components of the rotating chamber of a hydropower station. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the mechanism of the nano-modified particle reinforced and toughened cladding layer provided by an embodiment of the present invention;

[0036] Figure 2 This is a microstructure picture of the repaired flow-through component under low magnification (80×) in an embodiment of the present invention;

[0037] Figure 3 The microstructure pictures of the repaired flow-through component in the embodiment of the present invention at high and low magnifications (1000×) are shown;

[0038] Figure 4This is the XRD spectrum of the alloy cladding layer in the flow-through component after repair in an embodiment of the present invention;

[0039] Figure 5 3 is a hardness distribution curve of the coating along the depth direction of the flow-through component after repair in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] The present invention provides a laser cladding material with nanoparticles added to enhance cavitation resistance. The material is in powder form and comprises the following components, as well as the mass percentages of the components: cobalt: 55% to 75%, chromium: 15% to 32%, tungsten: 1% to 10%, nano-modified particles: 1% to 10%, and the remainder being molybdenum and manganese. The nano-modified particles are a mixture of carbon nanotubes and nano-Ti3AlC2, a mixture of nano-graphene and nano-Ti3AlC2, or a mixture of nano-titanium carbide and nano-Ti3AlC2. In engineering practice, it is preferred that the components and the mass percentages of the components are as follows: cobalt: 60% to 65%, chromium: 20% to 25%, tungsten: 5% to 9%, the sum of the weight of graphene and nanoparticle Ti3AlC2: 4% to 10%, and the balance is molybdenum and manganese. The particle size of nano-Ti3AlC2 ranges from 20nm to 50nm, the weight ratio of graphene to nanoparticle Ti3AlC2 is 1:10 to 1:1, and each component is a spherical powder with a particle size of 50μm to 100μm. The particle size of carbon nanotubes, nanographene, and nano-titanium carbide ranges from 10nm to 100nm. In a more preferred embodiment, the mass percentage of molybdenum is less than 1.5%, and the mass percentage of manganese is less than 2%.

[0042] The new material for laser cladding repair in the present invention application adds new nanoparticles, which can break the original network structure, refine the grains of the cladding layer, improve the bonding between the substrate and the cladding layer, and improve the strength and toughness combination, and have better cavitation resistance and erosion resistance.

[0043] The present invention also provides an application of the laser cladding material with added nanoparticles to enhance cavitation resistance as described above, which is used for laser cladding forming on the surface of the flow-through components of the hydropower station's rotary chamber, so as to cover the working surface of the flow-through components of the hydropower station's rotary chamber with an anti-cavitation layer having a harderness higher than that of the substrate, wherein the substrate refers to the main body of the flow-through components of the hydropower station's rotary chamber.

[0044] The present invention also provides a hydropower station turbine chamber flow component fabricated using the aforementioned laser cladding material with nanoparticle-added cavitation resistance. A laser cladding layer is formed on the working surface of the component, with a thickness of 0.8 mm to 8 mm. The surface hardness is greater than 450 Hv Vickers hardness, the roughness is less than Ra 0.5, and the height difference between the highest and lowest points of each overlap in the cladding layer does not exceed 0.2 mm. Under a scanning electron microscope at 1000x magnification, the substrate and cladding layer are tightly bonded and crack-free. The cladding layer has a discontinuous, fragmented structure with spherical precipitated particles.

[0045] The present invention also provides a method for preparing the above-mentioned flow-through component of the hydropower station rotary chamber, which comprises the following steps:

[0046] S1: Perform flaw detection on the substrate area of ​​the flow-through component of the hydropower station's rotary chamber that needs to be laser clad, perform repair welding based on the flaw detection results, then polish and remove the surface oxide layer, and finally clean it to ensure that the surface quality meets the cladding requirements. Step S1 specifically includes: performing PT flaw detection on the substrate area of ​​the flow-through component of the hydropower station's rotary chamber that will be laser clad, and repair welding on the cavitation area to ensure that there are no visible defects in the substrate of the area to be clad, polishing the entire surface area of ​​the area to be clad to remove the surface oxide layer, and finally cleaning with anhydrous ethanol and acetone to remove surface oil and ensure that the surface quality meets the cladding requirements.

[0047] S2: The laser cladding materials are mixed according to the set composition in weight percentage, then mixed and ball-milled, vacuum-dried, and finally preheated in an oven for subsequent use. Step S2 specifically involves mixing the laser cladding powder and placing it in a ball mill jar, setting the speed to 130rpm~180rpm, and the ball milling time to 40min~80min. After the ball milling is completed, it is placed in a vacuum drying oven to dry for 3h~5h. Before the laser cladding process, it is preheated in an oven at 55℃~65℃ for 50min~70min before use to ensure that the moisture in the powder is removed, improve the powder fluidity, and prevent moisture from entering the cladding layer and clogging the powder outlet.

[0048] S3: Plan the cladding path and select the process parameters for the cladding area of ​​the flow passage components of the hydropower station's rotary chamber. Then, perform synchronous powder feeding laser cladding on the repaired area of ​​the flow passage components of the rotary chamber at the hydropower station site. The cladding path planning and process parameters for step S3 are as follows: the laser power of the fiber laser is 1000W to 9000W, the scanning speed is 10mm / s to 50mm / s, the powder feeding amount is 5g / min to 200g / min, the overlap rate is 25% to 75%, the shielding gas flow rate is 5g / min to 20g / min, the defocus distance is 5mm to 100mm, and symmetrical cladding is adopted in different areas, with the area size being (400mm to 600mm) × (400mm to 600mm).

[0049] S4: After the cladding layer and the substrate are cooled to room temperature, the surface of the cladding layer is polished and ground.

[0050] S5: The repaired hydropower station's rotating chamber flow passage components are sequentially subjected to cladding layer flaw detection, cladding layer thickness testing, cladding layer hardness testing, and deformation testing. The cladding layer thickness is required to be greater than 0.8mm, the surface roughness of the cladding layer after polishing is less than Ra0.5, the effective thickness of the cladding layer after polishing is required to be greater than 0.5mm, and the height difference between the highest and lowest points of each overlap is less than 0.2mm. The cladding layer surface is polished and then flaw detected. PT flaw detection shows no obvious pores or cracks, the deformation of the test steel plate is less than 0.2mm, and the surface hardness is greater than 450Hv Vickers hardness.

[0051] In order to illustrate the product and method of the present invention in more detail, the following is a further detailed description with reference to specific embodiments.

[0052] Example 1

[0053] A material with nanoparticles added to enhance cavitation resistance for laser cladding repair of hydropower station turbine chambers. The material comprises the following components, with their respective mass percentages: cobalt: 60%, chromium: 22.8%, tungsten: 6.4%. The modified nanoparticles are graphene and Ti3AlC2 nanoparticles, with a combined mass of 9.8%, molybdenum: 0.9%, and manganese: 1.3%. The weight ratio of graphene to Ti3AlC2 nanoparticles is 0.2. All components are spherical powders with a particle size of 50 to 100 μm. The nanographene particle size ranges from 10 to 40 nm. The nano-Ti3AlC2 particle size ranges from 40 to 50 nm.

[0054] Example 2

[0055] A material with nanoparticles added to enhance cavitation resistance for laser cladding repair of hydropower station turbine chambers contains the following components, with their respective mass percentages being: cobalt: 65%, chromium: 20%, tungsten: 9%, nano-modified particles comprising carbon nanotubes and Ti3AlC2 nanoparticles, with a combined mass of 4%, molybdenum: 1%, and manganese: 1.5%. The weight ratio of graphene to Ti3AlC2 nanoparticles is 0.1. All components are spherical powders with a particle size of 50 to 100 μm. The carbon nanotubes have a particle size range of 30 to 50 nm, and the nano-Ti3AlC2 has a particle size range of 20 to 40 nm.

[0056] Example 3

[0057] A material with nanoparticles added to enhance cavitation resistance for use in laser cladding repair of hydropower station turbine chambers. The material comprises the following components, with their respective mass percentages: 62% cobalt, 25% chromium, and 5% tungsten. The modified nanoparticles are a mixture of nano-titanium carbide and nano-Ti3AlC2, with the mass percentages being 6.7%, 0.8% molybdenum, and 0.5% manganese. The weight ratio of graphene to nano-Ti3AlC2 is 1. All components are spherical powders with a particle size of 50 to 100 μm. The nano-titanium carbide has a particle size range of 50 to 80 nm. The nano-Ti3AlC2 has a particle size range of 30 to 40 nm.

[0058] Example 4

[0059] A material with nanoparticles added to enhance cavitation resistance for use in laser cladding repair of hydropower station turbine chambers. The material comprises the following components, with their respective mass percentages: 55% cobalt, 32% chromium, and 10% tungsten. The modified nanoparticles are a mixture of nano-titanium carbide and nano-Ti3AlC2, with the mass percentages being 1%, 0.01% molybdenum, and 2% manganese. The weight ratio of graphene to nano-Ti3AlC2 is 0.5. All components are spherical powders with a particle size of 80 to 100 μm. The nano-titanium carbide has a particle size range of 70 to 100 nm, and the nano-Ti3AlC2 has a particle size range of 30 to 50 nm.

[0060] Example 5

[0061] A material with nanoparticles added to enhance cavitation resistance for use in laser cladding repair of hydropower station turbine chambers. The material comprises the following components, with their respective mass percentages: cobalt: 75%, chromium: 15%, tungsten: 1%. The modified nanoparticles are a mixture of nano-titanium carbide and nano-Ti3AlC2, with the mass percentages being 10%, molybdenum: 1.5%, and manganese: 0.01%. The weight ratio of graphene to nano-Ti3AlC2 is 1:1. All components are spherical powders with a particle size of 50 to 100 μm. The particle sizes of the carbon nanotubes, nano-graphene, and nano-titanium carbide range from 60 to 100 nm.

[0062] Figure 1This is a schematic diagram of the mechanism of the nano-modified particle reinforced and toughened cladding layer provided by an embodiment of the present invention. As can be seen from the figure, with the increase of the content of nano-modified particles, the nanoparticles are evenly dispersed in the γ-Co matrix, which has a dispersion strengthening effect. At the same time, since the nanoparticles provide more nucleation sites, micron-sized particles are precipitated in the γ-Co matrix, which can prevent grain growth and have a fine grain strengthening effect. The synergistic strengthening effect of this multi-level micro-nano structure enables the cladding layer to achieve enhanced toughness and improves the cavitation resistance of the cladding layer.

[0063] This invention involves modifying and optimizing the material used for laser cladding repair of hydropower station rotary chambers by adding two nanoparticles to conventional cobalt-based metal repair materials, resulting in a repair material with enhanced cavitation resistance. The laser cladding process for on-site repairs also involves parameters such as scanning speed, overlap ratio, shielding gas flow rate, and defocus. Specific parameters include: scanning speed of 10 mm / s to 50 mm / s, overlap ratio of 25% to 75%, shielding gas flow of 5 g / min to 20 g / min, and defocus of 5 mm to 100 mm.

[0064] Example 6

[0065] The process of laser cladding repair of the rotating chamber of a hydropower station using one of the above materials includes the following steps:

[0066] 1) Flaw detection: PT flaw detection is performed on the base area of ​​the turbine blade in the turbine chamber to be laser clad. The surface area to be repaired is polished to remove the surface oxide layer, and anhydrous ethanol and acetone are used to clean and remove surface oil stains.

[0067] 2) Prepare the required proportions of the cladding repair materials and mix them evenly by ball milling at 150 rpm for 60 minutes. Dry the mixture in a vacuum drying oven for 4 hours. Finally, preheat the mixture in an oven at 59°C for 65 minutes before use.

[0068] 3) On-site laser cladding repair: Cladding path planning and process parameter selection are performed for the cladding area. Laser cladding equipment is then used to perform on-site, synchronous powder feeding laser cladding repairs on the repaired area. Laser power is 1000W to 3500W, powder feed rate is 5g / min to 20g / min, overlap rate is 25%, and symmetrical cladding is performed in zones sized 400mm x 500mm. The laser cladding layer thickness is 0.8mm to 1mm, and the defocus is 40mm to 50mm.

[0069] 4) The surface of the cladding layer is polished and ground, and the surface presents a good metallic luster and meets the standard smoothness. The surface roughness of the cladding layer after multi-point measurement is less than Ra0.5.

[0070] 5) Perform flaw detection, deformation detection, hardness detection and thickness detection on the surface of the cladding layer to ensure that there are no pores or cracks. The deformation test shows that the warping deformation of the steel plate is less than 0.2mm. The surface Vickers hardness in the hardness test is greater than 450Hv. The thickness of the cladding layer after repair and polishing in the thickness test is greater than 0.5mm. The height difference between the highest point and the lowest point of each overlap point does not exceed 0.2mm. Meeting the above standards indicates that the laser cladding on-site repair of the hydropower station's rotating room is completed.

[0071] Example 7

[0072] The process of laser cladding repair of the rotating chamber of a hydropower station using the above materials includes the following steps:

[0073] 1) Flaw detection: PT flaw detection is performed on the base area of ​​the turbine blade in the turbine chamber to be laser clad. The surface area to be repaired is polished to remove the surface oxide layer, and anhydrous ethanol and acetone are used to clean and remove surface oil stains.

[0074] 2) Prepare the required proportions of the cladding repair materials and mix thoroughly by ball milling at 160 rpm for 70 minutes. Dry the mixture in a vacuum drying oven for 5 hours. Finally, preheat the mixture in an oven at 60°C for 60 minutes before use.

[0075] 3) On-site laser cladding repair: Cladding path planning and process parameter selection are performed for the cladding area. Laser cladding equipment is then used to perform on-site, synchronous powder feeding laser cladding repairs on the repaired area. Laser power is 3500-6000W, powder feed rate is 10g / min-15g / min, overlap rate is 50%, and symmetrical cladding is performed in zones sized 400mm x 600mm. The laser cladding layer thickness is 1mm-1.5mm. Defocus is 90mm-100mm.

[0076] 4) The surface of the cladding layer is polished and ground, and the surface presents a good metallic luster and meets the standard smoothness. The surface roughness of the cladding layer after multi-point measurement is less than Ra0.5.

[0077] 5) Perform flaw detection, deformation detection, hardness detection and thickness detection on the surface of the cladding layer to ensure that there are no pores or cracks. The deformation test shows that the warping deformation of the steel plate is less than 0.2mm. The surface Vickers hardness in the hardness test is greater than 450Hv. The thickness of the cladding layer after repair and polishing in the thickness test is greater than 0.9mm. The height difference between the highest point and the lowest point of each overlap point does not exceed 0.2mm. Meeting the above standards indicates that the laser cladding on-site repair of the hydropower station's rotating room is completed.

[0078] Example 8

[0079] The process of laser cladding repair of the rotating chamber of a hydropower station using the above materials includes the following steps:

[0080] 1) Flaw detection: perform PT flaw detection on the base area of ​​the turbine blade in the turbine chamber to be laser clad, polish the surface area to be repaired to remove the surface oxide layer, and use anhydrous ethanol and acetone to clean and remove surface oil stains.

[0081] 2) Prepare the required proportions of the cladding repair materials and mix thoroughly by ball milling at 130 rpm for 80 minutes. Dry the mixture in a vacuum drying oven for 4 hours. Finally, preheat the mixture in an oven at 55°C for 70 minutes before use.

[0082] 3) On-site laser cladding repair: Cladding path planning and process parameter selection are performed for the cladding area. Laser cladding equipment is then used to perform on-site, simultaneous powder feeding laser cladding repairs on the repaired area. Laser power is 5000-8000W, powder feed rate is 5-10g / min, overlap ratio is 75%, and symmetrical cladding is performed in zones sized 600mm x 600mm. The laser cladding layer thickness is 7mm-8mm, and the defocus is 50mm-70mm.

[0083] 4) The surface of the cladding layer is polished and ground, and the surface presents a good metallic luster and meets the standard finish. The surface roughness of the cladding layer after multi-point measurement is less than Ra0.5.

[0084] 5) Perform flaw detection, deformation detection, hardness detection and thickness detection on the surface of the cladding layer to ensure that there are no pores or cracks. The deformation test shows that the warping deformation of the steel plate is less than 0.2mm. The surface Vickers hardness in the hardness test is greater than 450Hv. The thickness of the cladding layer after repair and polishing in the thickness test is greater than 6mm. The height difference between the highest point and the lowest point of each overlap point does not exceed 0.2mm. Meeting the above standards indicates that the laser cladding on-site repair of the hydropower station's rotating room is completed.

[0085] Example 9

[0086] The process of laser cladding repair of the rotating chamber of a hydropower station using the above materials includes the following steps:

[0087] 1) Flaw detection: perform PT flaw detection on the base area of ​​the turbine blade in the turbine chamber to be laser clad, polish the surface area to be repaired to remove the surface oxide layer, and use anhydrous ethanol and acetone to clean and remove surface oil stains.

[0088] 2) Prepare the required proportions of the cladding repair materials and mix thoroughly by ball milling at 180 rpm for 40 minutes. Dry the mixture in a vacuum drying oven for 3 hours. Preheat the mixture in an oven at 65°C for 50 minutes before laser cladding.

[0089] 3) On-site laser cladding repair: Cladding path planning and process parameter selection are performed for the cladding area. Laser cladding equipment is then used to perform on-site, simultaneous powder feeding laser cladding repairs on the repaired area. Laser power is 6000-9000W, powder feed rate is 15-20g / min, overlap rate is 75%, and symmetrical cladding is performed in zones sized 500mm x 500mm. The laser cladding layer thickness is 5mm-6mm, and the defocus is 5mm-10mm.

[0090] 4) The surface of the cladding layer is polished and ground, and the surface presents a good metallic luster and meets the standard finish. The surface roughness of the cladding layer after multi-point measurement is less than Ra0.5.

[0091] 5) Perform flaw detection, deformation detection, hardness detection and thickness detection on the surface of the cladding layer to ensure that there are no pores or cracks. The deformation test shows that the warping deformation of the steel plate is less than 0.2mm. The surface Vickers hardness in the hardness test is greater than 450Hv. The thickness of the cladding layer after repair and polishing in the thickness test is greater than 4.5mm. The height difference between the highest point and the lowest point of each overlap point does not exceed 0.2mm. Meeting the above standards indicates that the laser cladding on-site repair of the hydropower station's rotating room is completed.

[0092] In this invention, the laser cladding repair materials with enhanced cavitation resistance, including nanoparticle graphene, carbon nanotubes, nano-titanium carbide, and Ti3AlC2, were tested for their performance through process performance evaluation, strengthening phase characterization, microstructure and phase analysis, mechanical property testing and analysis, and cavitation and erosion resistance testing and analysis. The equipment and methods used in each test are as follows:

[0093] (1) Microstructure analysis

[0094] Microstructure analysis was performed using an FEI-Quanta200 environmental scanning electron microscope (ESM), manufactured by FEI (The Netherlands). Sample composition was analyzed using EDS. The substrate, heat-affected zone, transition zone, and cladding layer structures were analyzed separately.

[0095] (2) X-ray diffraction analysis

[0096] The X-ray diffractometer used was an XRD-7000 diffractometer produced by Shimadzu Corporation of Japan. It used a copper target with a wavelength of 0.154056 nm, a scanning range of 20°-90°, a scanning speed of 10° / min, a power of 2.2 kW, a tube voltage of 40 kV, and a current of 60 mA. The repair material with added nanoparticles was tested to obtain a diffraction pattern.

[0097] (3) Microhardness test

[0098] The microhardness of the coating was tested using a Wilson 430VD Vickers hardness tester with a load of 0.98 N and an application time of 15 seconds. Starting from the cladding surface, each 70 μm interval was defined as a depth plane. On each depth plane, five points spaced 200 μm apart were recorded and their hardness values ​​were measured. The average of these five values ​​was used as the hardness at that depth.

[0099] (4) Friction and wear test

[0100] The tests were conducted using a UMT-Tribolab high-speed, high-temperature friction and wear tester manufactured by Bruker Corporation in the United States. The abrasive material was a 5mm diameter silicon nitride ball. The test load was 100N, the friction speed was 10mm / s, the test time was 40 minutes, and the travel was 10mm. The friction coefficient and mass loss were recorded.

[0101] (5) Cavitation corrosion test

[0102] The coating's cavitation resistance was evaluated using an XOQS-2500 ultrasonic cavitation tester manufactured by Nanjing Xianou Instrument Manufacturing Co. A 3.5% sodium chloride solution was used as the corrosive medium, with an ultrasonic power of 1.25 kW, an amplitude of 90 microns at the horn tip, and a test duration of 20 hours. The cavitation erosion resistance of the samples was characterized by mass loss. Comparison confirmed that the cladding layer with the addition of nano-modified particles exhibited significantly better cavitation erosion resistance than the cladding layer without the addition of nano-modified particles.

[0103] (6) Erosion test

[0104] An erosion corrosion tester was used, with an erosion solution prepared with diamond abrasive (<100 mesh) sheets at a concentration of 18 g / L. The erosion angle was 30 degrees, the nozzle diameter was 4 mm, the erosion flow rate was 18 L / min, the erosion distance was 15 cm, and the test time was 5 hours.

[0105] To demonstrate the effectiveness of the present invention, the process described in this embodiment was used to perform on-site laser cladding repairs on the rotating chamber of a hydropower station. The repair material composition described in the embodiment of the present invention was then used. After the repair was completed, the chamber was polished and subjected to process performance evaluation, as well as strengthening phase characterization, microstructure and phase analysis, mechanical property testing, and cavitation and erosion resistance testing. The specific methods and results of each analysis are as follows:

[0106] (1) Microstructure analysis

[0107] The substrate, heat-affected zone, transition zone, and cladding layer structures were analyzed using a scanning electron microscope. The microstructures of the components of Example 1 under the process of Example 7 at low magnification (80×) were as follows: Figure 2 As shown, Figure 2 This is a microstructure picture of the flow-through component after repair in the embodiment of the present invention at low magnification (80×). It can be seen that a good metallurgical bond is formed between the substrate and the cladding layer, indicating that the repair material with added nanoparticles of graphene and Ti3AlC2 has a high degree of matching with the cladding properties of the substrate, has no defects such as cracks and pores, and has good processability. Figure 3 Observe that Figure 3 Figure 3 is a microscopic image of the flow-through component after repair in an embodiment of the present invention at high and low magnifications (1000×). It can be seen from the figure that the skeleton of the cladding layer is discontinuous and fragmented, the structure is refined and dense, and spherical particles are precipitated, indicating that the added nanoparticles graphene and Ti3AlC2 have the effect of refining the grains of the cladding layer. That is, the degree of matching between this repair material and the laser cladding process is high, the cladding layer and the base material are highly compatible, the bonding force is strong, and it has strong process practical value.

[0108] (2) X-ray diffraction analysis

[0109] The repair material with added nanoparticles was tested and the diffraction pattern was obtained, see Figure 4 As shown, Figure 4 This is the XRD spectrum of the alloy cladding layer in the flow-through component after repair in one embodiment of the present invention. Among them, 0% indicates that the alloy cladding layer does not contain nano-modified particles, 2.0% indicates that the alloy cladding layer contains 2.0% nanoparticles, 4.0% indicates that the alloy cladding layer contains 4.0% nanoparticles, 6.0% indicates that the alloy cladding layer contains 6.0% nanoparticles, and 8.0% indicates that the alloy cladding layer contains 8.0% nanoparticles. Through PDF card analysis, it can be obtained that the phase composition of the cladding layer is mainly γ-Co matrix (Co, Fe, Cr, etc.), (Fe, W) 23 The cladding layer is composed of five phases: C6, Cr7C3 and TiC. The added nanoparticles are evenly dispersed in the cladding layer, which aggravates the lattice distortion and hardens the cladding layer.

[0110] (3) Cavitation resistance

[0111] The cavitation corrosion resistance of the samples was characterized by the mass loss of the samples. The comparison confirmed that the cavitation corrosion mass loss of the cladding layer with added nanoparticles graphene and Ti3AlC2 was reduced by more than half compared with the cladding layer without additions, indicating that the cavitation corrosion resistance of the cladding layer with added nanoparticles was more than doubled compared with the cladding layer without additions, which is of great significance to the improvement of the service life of the impeller steel plate of the rotor chamber.

[0112] (4) Erosion performance test

[0113] The results show that the erosion resistance weight loss of the cladding layer with added nanoparticle graphene and Ti3AlC2 is only less than 50% of the cladding layer without added nanoparticles. After adding nanoparticle graphene and Ti3AlC2, the erosion resistance of the cladding layer is more than doubled.

[0114] (5) Hardness test

[0115] The results show that the substrate is hardened by the laser heat, with an average hardness of 350Hv. The cladding layer with nanoparticle graphene and Ti3AlC2 hardens rapidly. Figure 5 As shown, Figure 5 This is a hardness distribution curve along the depth direction of the coating in the repaired flow-through component of the embodiment of the present invention. 0% indicates that the average surface hardness of the coating on the component without nano-modified particles is 450 Hv; 2.0% indicates that the average surface hardness of the coating on the component after adding 2.0% nano-particle graphene and Ti3AlC2 to the cladding layer is 500 Hv; 4.0% indicates that the average surface hardness of the coating on the component after adding 4.0% nano-particle graphene and Ti3AlC2 to the cladding layer is 550 Hv; 6.0% indicates that the average surface hardness of the coating on the component after adding 6.0% nano-particle graphene and Ti3AlC2 to the cladding layer is 580 Hv; and 8.0% indicates that the average surface hardness of the coating on the component after adding 8.0% nano-particle graphene and Ti3AlC2 to the cladding layer is 650 Hv. It can be seen that as the nanoparticle content increases to a certain extent, the hardness gradually increases, and all are greater than 450 Hv, meeting the hardness requirements of the rotary chamber steel plate.

[0116] (6) Wear resistance test

[0117] The experimental results show that the friction coefficient of the cladding layer is stable at 0.3, and the mass loss of the cladding layer after adding nanoparticle graphene and Ti3AlC2 is only 43.6% of that without addition, which has a wear-reducing effect.

[0118] (7) Bonding strength test

[0119] Tensile strength tests were conducted on tensile specimens of the cladding coating, coated substrate, and substrate. The tensile strength of the substrate specimens was 950 MPa, with a yield strength of 790 MPa; the tensile strength of the coating and substrate specimens was 1120 MPa, with a yield strength of 920 MPa; the tensile strength of the cobalt-based coating without nanoparticles was 1400 MPa, with a yield strength of 990 MPa; and the tensile strength of the cobalt-based coating reinforced with nanoparticles was 1450 MPa, with a yield strength of 1050 MPa. The results show that the bonding strength between the coating and the substrate is higher than the substrate strength, and the bulk strength of the coating is higher than the bonding strength between the coating and the substrate. The addition of nanoparticles further enhances the strength of the cobalt-based coating.

[0120] In the present invention, a new laser cladding repair material with nanoparticles added to enhance cavitation resistance is clad on the wheel chamber steel plate, which can indeed improve the cavitation resistance, erosion resistance, and wear resistance of the wheel chamber steel plate and increase the service life of the wheel chamber steel plate. It is very promising to become a solution to the current flow component problems of domestic and foreign hydropower companies.

[0121] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A laser cladding material with nanoparticles added to enhance cavitation resistance, characterized in that: It is used for laser cladding forming on the surface of the flow-through components of the rotating chamber of a hydropower station. It is in powder form and includes the following components and the mass percentages of each component: Cobalt: 55%~75%, chromium: 15%~32%, tungsten: 1%~10%, nano-modified particles: 1%~10%, the balance is molybdenum and manganese, the nano-modified particles are a mixture of carbon nanotubes and nano-Ti3AlC2, a mixture of nano-graphene and nano-Ti3AlC2, or a mixture of nano-titanium carbide and nano-Ti3AlC2, The particle size of nano-Ti3AlC2 ranges from 20nm to 50nm, the particle size of carbon nanotubes, nano-graphene and nano-titanium carbide ranges from 10nm to 100nm, and the weight ratio of graphene to nano-particle Ti3AlC2 is 1:10 to 1:

1. Each component is a spherical powder with a particle size of 50μm ~ 100μm.

2. The laser cladding material with nanoparticles added to enhance cavitation resistance according to claim 1, characterized in that: The components and the mass percentages of the components are as follows: Cobalt: 60%~65%, chromium: 20%~25%, tungsten: 5%~9%, the sum of the weight of graphene and nanoparticles Ti3AlC2: 4%~10%, and the remainder is molybdenum and manganese.

3. The use of a laser cladding material with nanoparticles added to enhance cavitation resistance according to any one of claims 1-2, characterized in that: It is used for laser cladding forming on the surface of the flow-through components of the hydropower station's rotating chamber, so as to cover the working surface of the flow-through components of the hydropower station's rotating chamber with an anti-cavitation layer with a harderness higher than that of the substrate. The substrate refers to the body of the flow-through components of the hydropower station's rotating chamber.

4. A hydropower station turbine chamber flow component manufactured using the laser cladding material with nanoparticles added to enhance cavitation resistance as described in any one of claims 1-2, characterized in that: A laser cladding layer is generated on the working surface, and the thickness of the laser cladding layer is 0.8mm ~ 8mm.

5. The flow-through component of the hydropower station rotor chamber according to claim 4, characterized in that: Its surface hardness is greater than Vickers hardness 450Hv, roughness is less than Ra0.5, and the height difference between the highest point and the lowest point of each overlap point in the cladding layer does not exceed 0.2mm.

6. The flow-through component of the hydropower station rotor chamber according to claim 5, characterized in that: In the field of view magnified 1000 times by a scanning electron microscope, the substrate and the cladding layer fit tightly together without cracks, and the tissue skeleton of the cladding layer is discontinuous and fragmented, with spherical precipitated particles.

7. A method for preparing a flow-through component of a hydropower station rotary chamber according to any one of claims 4 to 6, characterized in that: It includes the following steps: S1: Perform flaw detection on the base area of ​​the flow-through components of the hydropower station's rotating chamber that requires laser cladding. Perform repair welding based on the flaw detection results, then polish and remove the surface oxide layer. Finally, clean the surface to ensure that the surface quality meets the cladding requirements. S2: The laser cladding materials are mixed according to the set composition in weight percentage, then ball milled, vacuum dried, and finally preheated in an oven for subsequent use. S3: Plan the cladding path and select the process parameters for the cladding area of ​​the flow-through components of the hydropower station's rotating chamber. Then, perform synchronous powder feeding laser cladding on the repaired area of ​​the flow-through components of the rotating chamber at the hydropower station site. S4: After the cladding layer and substrate cool to room temperature, the surface of the cladding layer is polished and ground. S5: The repaired flow-through components of the hydropower station's rotating chamber are subjected to cladding layer flaw detection, cladding layer thickness detection, cladding layer hardness test and deformation detection in sequence.

8. The method for preparing the flow-through component of the hydropower station rotary chamber according to claim 7, characterized in that: Step S1 specifically includes: performing PT inspection on the base area of ​​the flow-through component of the hydropower station's rotating chamber to be laser clad, and performing repair welding on the cavitation area to ensure that there are no visible defects on the base material in the cladding area, polishing the entire surface area of ​​the cladding area to remove the surface oxide layer, and finally using anhydrous ethanol and acetone to clean the surface to remove surface oil stains to ensure that the surface quality meets the cladding requirements.

9. The method for preparing the flow-through component of the hydropower station rotary chamber according to claim 8, characterized in that: Step S2 specifically includes mixing the laser cladding powder and placing it in a ball mill, setting the rotation speed to 130 rpm to 180 rpm, and the ball milling time to 40 min to 80 min. After the ball milling is completed, it is placed in a vacuum drying oven for drying for 3 h to 5 h, and preheated in an oven at 55 ° C to 65 ° C for 50 min to 70 min before use to ensure that the moisture in the powder is removed, improve the powder fluidity, and prevent moisture from entering the cladding layer and clogging the powder outlet. The cladding path planning and process parameters of step S3 are as follows: the laser power of the fiber laser is 1000W~9000W, the scanning speed is 10mm / s~50mm / s, the powder feeding rate is 5g / min~200g / min, the overlap rate is 25%~75%, the shielding gas flow rate is 5g / min~20g / min, the defocus distance is 5mm~100mm, and the symmetrical cladding is adopted in different areas, with the area size being (400mm~600mm)×(400mm~600mm).

10. The method for preparing the flow-through component of the hydropower station rotary chamber according to claim 9, characterized in that: The thickness of the cladding layer is greater than 0.8mm, the surface roughness of the cladding layer after polishing is less than Ra0.5, and the effective thickness of the cladding layer after polishing is greater than 0.5mm. The height difference between the highest and lowest points of each overlap point does not exceed 0.2mm. The surface of the cladding layer is polished and ground before being inspected. PT inspection shows no obvious pores or cracks. The deformation of the test steel plate surface is less than 0.2mm, and the surface hardness is greater than Vickers hardness 450Hv.

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