Method for improving oxidation resistance of nickel-based superalloy

Abstract

The invention discloses a method for improving the oxidation resistance of nickel-based superalloy, and belongs to the technical field of metal material surface modification. Based on the high-energy transient effect of laser shock waves, the method mainly comprises the key steps of alloy surface pretreatment, laser shock peening process implementation, post-treatment and the like. Specifically, firstly, the surface of the nickel-based single crystal alloy is subjected to pretreatment such as polishing and cleaning, surface defects and pollutants are removed, and the treatment quality is guaranteed; then, according to the material characteristics and performance requirements of the nickel-based single crystal alloy, laser parameters such as laser energy, pulse width and light spot diameter are accurately set, and proper restraint layer and absorption layer materials are selected; then, high-energy pulse laser is utilized to irradiate the absorption layer, high-temperature and high-pressure plasma is induced to be generated, the plasma expands and explodes to generate strong shock waves, the shock waves act on the alloy surface, the surface material is subjected to severe plastic deformation, a residual compressive stress layer with the depth capable of reaching hundreds of micrometers is formed, meanwhile, surface grains are refined, and the microstructure is optimized; and after the strengthening treatment is completed, simple cleaning and performance detection post-treatment are carried out. Through laser shock strengthening, a special organization structure with high density and low defect density is formed on the surface of the nickel-based single crystal alloy, diffusion and invasion of oxygen atoms are effectively hindered, and the oxidation resistance of the alloy is remarkably improved. According to the method, the controllability of technological parameters is high, the strengthening effect can be accurately regulated and controlled, the treatment process is free of pollution and high in efficiency, the obtained strengthened nickel-based single crystal alloy can be widely applied to the fields such as aerospace engine hot end parts and nuclear energy equipment which have strict requirements for high-temperature oxidation resistance, the reliability of related parts is greatly improved, and the service life of the related parts is greatly prolonged.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically a method for improving the oxidation resistance of nickel-based superalloys. Background Technology

[0002] In the field of high-end equipment manufacturing such as aerospace and energy power, nickel-based single crystal alloys are widely used in hot-end components such as turbine blades due to their excellent high-temperature strength and creep resistance. However, their high-temperature oxidation resistance is still limited by problems such as insufficient bonding strength between the oxide film and the substrate and easy peeling of the oxide film at high temperatures. Traditional surface coating technology has defects such as complex processes and mismatch with the thermal expansion coefficient of the substrate. Existing laser processing technology focuses on improving the mechanical properties of alloys, and the research on the mechanism of improving their oxidation resistance is still insufficient. Therefore, it is urgent to develop a new laser strengthening method that can both enhance the density of the oxide film and improve its bonding strength with the substrate. Summary of the Invention

[0003] The purpose of this invention is to provide a method for improving the oxidation resistance of nickel-based superalloys. By precisely controlling the laser shock peening process parameters, a special microstructure and residual stress field are formed on the surface of the nickel-based single crystal alloy, which effectively inhibits the diffusion of oxygen and the growth of the oxide layer during high-temperature oxidation, thereby improving the oxidation resistance of the alloy and extending its service life.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for improving the oxidation resistance of nickel-based single-crystal alloys by laser shock peening is characterized by comprising the following steps: Sample preparation: Select a suitable nickel-based single-crystal alloy sample and perform surface pretreatment to remove oil, oxide layer, and impurities, ensuring a smooth and clean surface. Pretreatment methods can combine mechanical grinding and chemical cleaning. For example, first use sandpaper to gradually grind the sample surface to a certain roughness, then use organic solvents such as acetone and alcohol for ultrasonic cleaning, and finally rinse thoroughly with deionized water and dry.

[0005] Laser shock peening treatment: Laser parameter settings: A high-energy pulsed laser was selected, and the laser parameters were set according to the characteristics of the nickel-based single-crystal alloy and the desired strengthening effect. The laser wavelength range was 500-1100nm, the pulse width was 10-30ns, and the laser energy density was 5-20J / cm². 2 The diameter of the light spot is 1-5mm.

[0006] Selection of confinement and absorption layers: An absorption layer and a confinement layer are applied to the sample surface. The absorption layer can be made of materials such as black paint or aluminum foil, and its function is to absorb laser energy and rapidly vaporize and ionize it to form plasma. The confinement layer can be made of materials such as deionized water or K9 glass, which is used to confine the expansion of the plasma and increase the pressure and duration of the shock wave.

[0007] Impact path planning: Based on the sample size and shape, plan the laser impact path to ensure that the entire surface to be strengthened receives uniform impact treatment. Single-point impact, array impact, or scanning impact can be used.

[0008] Laser shock peening: The surface of the nickel-based single-crystal alloy sample is subjected to laser shock peening treatment according to the set laser parameters and shock path. During the treatment, the laser-induced plasma shock wave acts on the sample surface, causing plastic deformation of the surface material, forming a residual compressive stress layer, and refining the surface grains.

[0009] Post-processing: After laser shock peening, the sample undergoes simple cleaning to remove residual absorption layer and other impurities from the surface. Methods such as alcohol wiping or ultrasonic cleaning can be used.

[0010] Compared with the prior art, the beneficial effects of the present invention by adopting the above technical solution are as follows: 1. Significantly Improved Oxidation Resistance: The residual compressive stress introduced by laser shock peening on the surface of nickel-based single-crystal alloys effectively inhibits the initiation and propagation of cracks during oxidation. Simultaneously, the refined grain structure reduces the number of grain boundaries, lowering the oxygen diffusion rate along these boundaries, thereby significantly suppressing oxide layer growth and improving the alloy's oxidation resistance. Experimental results show that, under the same high-temperature oxidation conditions, the oxidation weight gain of laser-shock-peening-treated nickel-based single-crystal alloys is significantly lower than that of untreated samples, with an oxide layer thickness reduction of 30%–50%.

[0011] 2. No change to matrix composition: This method strengthens the alloy surface only through the physical effect generated by laser shock, without introducing other elements, and does not change the matrix composition and microstructure of the nickel-based single crystal alloy, thus ensuring that the original excellent high-temperature mechanical properties of the alloy are not affected.

[0012] 3. Simple and flexible process: Laser shock peening process parameters are easy to control precisely. Laser parameters and shock paths can be flexibly adjusted according to different nickel-based single-crystal alloy materials and application requirements, achieving precise control of alloy surface properties. Moreover, this process is relatively simple to operate, has a fast processing speed, and is suitable for large-scale industrial production.

[0013] 4. Enhanced surface integrity: Laser shock peening can improve the surface roughness of nickel-based single crystal alloys, reduce surface defects, improve surface quality, and further enhance the alloy's oxidation resistance and fatigue resistance. Attached Figure Description Figure 1 is a schematic diagram of the steps of a method for improving the oxidation resistance of nickel-based superalloys in an embodiment of the present invention. Detailed Implementation

[0014] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0015] This invention provides a method for improving the oxidation resistance of nickel-based superalloys, comprising the following steps: Step 1: Sample Preparation A nickel-based single-crystal alloy sample of a certain type, measuring 20mm × 20mm × 5mm, was selected. First, the sample surface was progressively polished using 240#, 400#, 600#, 800#, and 1000# sandpaper to remove obvious scratches and oxide layers, achieving a surface roughness Ra of approximately 1.6μm. Then, the sample was immersed in acetone solution and ultrasonically cleaned at 40kHz for 15 minutes to remove surface oil and impurities. Next, it was ultrasonically cleaned again with alcohol for 10 minutes. Finally, it was rinsed thoroughly with deionized water and dried in an oven at 60℃ for 30 minutes.

[0016] Step 2: Laser Shock Enhancement Treatment Laser parameter settings: A high-energy pulsed Nd:YAG laser with a wavelength of 1064 nm was selected, the pulse width was set to 20 ns, and the laser energy density was set to 12 J / cm². 2 The diameter of the light spot is 3mm.

[0017] Selection of constraint layer and absorption layer: After drying, a layer of black paint with a thickness of about 0.1 mm is uniformly sprayed on the sample surface as an absorption layer. Then, the sample is placed in a container filled with deionized water, so that the deionized water completely covers the sample surface as a constraint layer. The thickness of the deionized water layer is about 2 mm.

[0018] Impact path planning: An array impact method is adopted with an impact point spacing of 1.5mm to ensure that the entire 20mm×20mm surface can be uniformly impacted.

[0019] Laser shock peening: Following the planned impact path, the laser is activated to perform laser shock peening treatment on the sample surface. The duration of each impact point is 20 ns, and the impact is repeated twice to enhance the strengthening effect.

[0020] Step 3: Post-processing After laser shock osmosis (LSO) treatment, the sample was removed from deionized water, and the surface was gently wiped with an alcohol swab to remove any residue of the black paint absorption layer. The sample was then placed in an oven and dried at 50°C for 10 minutes to obtain a nickel-based single-crystal alloy sample that has undergone LOSO treatment.

[0021] Example 1 DD91 nickel-based single-crystal alloy samples were selected. First, the sample surface was progressively polished using 240#, 400#, 600#, 800#, and 1000# sandpaper to remove obvious scratches and oxide layers, achieving a surface roughness Ra of approximately 1.6 μm. Then, the sample was placed in an acetone solution and ultrasonically cleaned at 40 kHz for 15 minutes to remove surface oil and impurities. Next, it was ultrasonically cleaned again with alcohol for 10 minutes, and finally rinsed thoroughly with deionized water and dried in an oven at 60℃ for 30 minutes. During laser shock peening, the laser energy density was set to 8 J / cm². 2 The light spot diameter was 2 mm, and a single-point impact method was used with an impact point spacing of 1 mm. The impact was repeated once. The post-processing method was the same. The treated and untreated samples were simultaneously placed in a high-temperature oxidation furnace and subjected to isothermal oxidation at 900℃ for 100 h. Experimental results showed that the untreated sample gained 12.5 mg / cm³ of weight during oxidation. 2 The average thickness of the oxide layer was 45 μm; while the weight gain of the sample after laser shock peening treatment (parameters of this embodiment) was 8.2 mg / cm³. 2 The average thickness of the oxide layer is 28 μm, which significantly improves the antioxidant capacity.

[0022] Example 2 DD91 nickel-based single-crystal alloy samples were selected. First, the sample surface was progressively polished using 240#, 400#, 600#, 800#, and 1000# sandpaper to remove obvious scratches and oxide layers, achieving a surface roughness Ra of approximately 1.6 μm. Then, the sample was placed in acetone solution and ultrasonically cleaned at 40 kHz for 15 minutes to remove surface oil and impurities. Next, it was ultrasonically cleaned again with alcohol for 10 minutes, and finally rinsed thoroughly with deionized water and dried in an oven at 60℃ for 30 minutes. During laser shock peening, the laser energy density was set to 15 J / cm². 2The spot diameter was 4 mm, and a scanning impact mode was used with a scanning speed of 5 mm / s, repeated twice. The post-processing method remained unchanged. The treated and untreated samples were subjected to isothermal oxidation experiments at 1000℃ for 80 h. The results showed that the untreated sample gained 18.3 mg / cm³ of weight during oxidation. 2 The average thickness of the oxide layer is 60 μm; the oxidation weight gain of the sample treated with laser shock in this embodiment is 10.5 mg / cm³. 2 The average thickness of the oxide layer was 35 μm, and its antioxidant effect was significantly better than that of the untreated sample.

[0023] Example 3 A DD5 nickel-based single-crystal alloy sample with dimensions of 30mm × 30mm × 5mm was selected. First, the sample surface was progressively polished using 240#, 400#, 600#, 800#, and 1000# sandpaper to remove obvious scratches and oxide layers, achieving a surface roughness Ra of approximately 1.6μm. Then, the sample was placed in an acetone solution and ultrasonically cleaned at a frequency of 40kHz for 15 minutes to remove surface oil and impurities. Next, it was ultrasonically cleaned again with alcohol for 10 minutes, and finally rinsed thoroughly with deionized water and dried in an oven at 60℃ for 30 minutes. The laser shock peening parameters were set as follows: laser wavelength 532nm, pulse width 15ns, and laser energy density 10J / cm². 2 The laser spot diameter was 2.5 mm, and array impact was used with an impact point spacing of 1.2 mm, repeated 3 times. After post-treatment, the sample and the untreated sample were subjected to a cyclic oxidation experiment at 950℃ for 50 cycles, each oxidation lasting 2 hours. The experiment showed that the oxide layer of the untreated sample exhibited significant peeling, with the peeled area accounting for approximately 30% of the surface area, and the oxidation weight gain was 15.6 mg / cm³. 2 The sample treated with laser shock peening had an intact oxide layer with no obvious peeling, and the oxidation weight gain was only 9.8 mg / cm³. 2 This fully demonstrates the effectiveness of the method of the present invention in improving the oxidation resistance of nickel-based single crystal alloys.

Claims

1. A method of improving the oxidation resistance of a nickel-based superalloy, characterized by: The method comprises alloy surface pretreatment, laser shock peening treatment, post-treatment and performance detection.

2. The method of claim 1, wherein, The nickel-based single crystal alloy is selected from at least one of common nickel-based single crystal alloys in the field of aerospace engine hot end components and gas turbine blades, and has an initial surface roughness Ra value of 0.8-3.2 μm.

3. The method of claim 1, wherein, The alloy surface pretreatment comprises at least two of mechanical polishing, chemical cleaning and sand blasting treatment; the mechanical polishing adopts sandpaper with different grits for polishing in sequence, the chemical cleaning selects a specific cleaning agent capable of removing oil stains and oxides, and the sand blasting treatment selects sand particles with a particle size of 20-100 mesh and a sand blasting pressure of 0.2-0.8 MPa to remove alloy surface defects, contaminants and increase surface roughness, thereby improving laser shock absorption effect.

4. The method of claim 1, wherein, In the laser shock peening process, the laser parameters are set as follows: laser wavelength of 500-1100 nm, pulse width of 10-30 ns, and laser energy density of 5-20 GW / cm². 2 The spot diameter is 1-5mm, and the pulse repetition frequency is 1-10Hz. Meanwhile, transparent glass is used as the constraint layer with a thickness of 1-3mm, and aluminum foil or black coating is used as the absorption layer with a thickness of 0.05-0.2mm. The intensity and action range of the laser shock wave are controlled by precisely regulating laser parameters, constraint layer parameters and absorption layer parameters.

5. The method of claim 1, wherein, In the laser shock peening treatment process, the laser shock times are 1-10, and the shock path adopts at least one of crossing, parallel or spiral, so as to form a residual compressive stress layer with uniform distribution and a depth of 0.1-1 mm on the surface of the nickel-based single crystal alloy, refine surface grains to a size of 0.5-5 μm, optimize microstructure and hinder oxygen atom diffusion.

6. The method of claim 1, wherein, The post-treatment comprises cleaning treatment on the surface of the nickel-based single crystal alloy after laser shock peening to remove absorption layer residues and impurities, and the cleaning method selects at least one of ultrasonic cleaning and alcohol wiping; after cleaning, surface protection treatment is performed, and the surface protection treatment adopts at least one of coating an oxidation-resistant coating or performing surface infiltration layer treatment, the oxidation-resistant coating is selected from at least one of an aluminide coating and an MCrAlY coating (M is Ni, Co or the like), and the coating thickness is 10-50 μm; the surface infiltration layer treatment selects at least one of aluminizing and chromizing, and the infiltration layer depth is 10-30 μm.

7. The method of claim 1, wherein, The performance detection comprises oxidation resistance performance detection and mechanical property detection; the oxidation resistance performance detection adopts high-temperature oxidation experiment, the experimental temperature is 800-1200℃, the experimental time is 10-100 h, the oxidation resistance ability is evaluated by measuring oxidation weight gain and observing oxidation film morphology and structure; the mechanical property detection comprises hardness detection, residual stress detection and fatigue performance detection, the hardness detection adopts a Vickers hardness tester, the residual stress detection adopts an X-ray diffraction method, and the fatigue performance detection adopts a rotary bending fatigue test or a tensile-tensile fatigue test, so as to comprehensively evaluate the performance improvement effect of laser shock peening on the nickel-based single crystal alloy.

8. The nickel-base single-crystal alloy material prepared according to the method of any one of claims 1-7, characterized in that, The material surface residual compressive stress value is greater than or equal to 300 MPa, the surface oxidation film and substrate bonding strength is greater than or equal to 80 MPa, the oxidation weight gain after oxidation at 1000℃ for 50 h is reduced by 30%-60% compared with that of the un-strengthened alloy, the tensile strength is greater than or equal to 1000 MPa, the fatigue life is increased by 20%-50% compared with that of the un-strengthened alloy, the material relative density is greater than or equal to 99%, and the oxygen content is less than or equal to 0.05 wt%.

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