A method for improving the fatigue properties of a coating alloy

Abstract

This invention discloses a method for improving the fatigue performance of coated alloys. The method includes the following steps: S1, pretreatment: cleaning the surface of the alloy with a thin coating; S2, cooling treatment: cooling the cleaned alloy using a cooling source, which includes at least one of a gas phase, a solid phase, and a liquid phase; during treatment, the gas phase and liquid phase act on the outer surface of the alloy, while the solid phase is placed inside the alloy or acts on the inner sidewall of the alloy; S3, impact-type ultrasonic shot peening treatment: subjecting the cooled alloy to multiple impact-type ultrasonic shot peening treatments. This invention uses a cooling-impact-type ultrasonic shot peening process to strengthen the alloy surface coating, eliminating microscopic defects such as surface grooves and microcracks present during the coating preparation process, reducing the surface roughness of the coating, changing its grain boundary morphology, increasing the residual pressure of the coating, and effectively improving the fatigue life of the alloy substrate.

Description

Technical Field

[0001] This invention relates to the field of alloy surface treatment technology, and in particular to a method for improving the fatigue performance of coated alloys. Background Technology

[0002] Existing research has found that coatings are not conducive to the fatigue performance of alloy substrates. This is mainly because some coatings have lower plasticity than the alloy itself, and the coating preparation process inevitably introduces defects such as microcracks and grooves, which can lead to a deterioration in the fatigue performance of the substrate. Furthermore, the surface integrity of the coating (residual stress, roughness, crystal morphology, etc.) has a significant impact on fatigue performance. Therefore, coating quality is particularly important for the fatigue resistance of alloy substrates.

[0003] After strengthening alloy coatings using traditional metal surface strengthening techniques—shot peening—the surface roughness of the coating increases. Under external loads, this rough surface accelerates crack nucleation, thus reducing the fatigue life of the alloy. Therefore, improving coating surface roughness and grain morphology, increasing residual stress, and eliminating microscopic defects such as grooves and cracks introduced during existing coating preparation processes are urgent problems to be solved. Simultaneously, secondary defects such as pipe wall deformation, coating cracking, and peeling that occur during the surface strengthening process of thin-walled alloy pipes also present technical challenges that need to be overcome. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the fatigue performance of coated alloys.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for improving the fatigue performance of coated alloys, comprising the following steps:

[0006] S1. Pretreatment: Cleaning the surface of the alloy with a thin coating;

[0007] S2. Cooling treatment: The cleaned alloy is cooled using a cooling source, which includes at least one of gas phase, solid phase and liquid phase; during the treatment, the gas phase and liquid phase act on the outer surface of the alloy, while the solid phase is placed inside the alloy or acts on the inner wall of the alloy.

[0008] S3, Impact-type ultrasonic shot peening: The cooled alloy is subjected to multiple impact-type ultrasonic shot peening treatments.

[0009] Preferably, in step S1, the thin coating is made of metallic Cr, FeCrAl alloy, NbMoTaW high-entropy alloy, or AlCrMoNbZr high-entropy alloy.

[0010] Preferably, in step S1, the thickness of the thin coating is 0.01 to 3 mm.

[0011] Preferably, in step S2, the gas phase is nitrogen, argon, or helium, the solid phase is ice, and the liquid phase is water.

[0012] Preferably, in step S2, the temperature of the cooled alloy is -20 to 40°C.

[0013] Preferably, the alloy is a thin-walled tube with a wall thickness of 0.3 to 0.7 mm, and the cooling source is a solid phase, a gas phase, or a liquid phase, with the solid phase placed inside the cavity of the thin-walled tube.

[0014] Alternatively, the alloy can be in the form of bars or plates, with the cooling source being either gas or liquid.

[0015] Preferably, in step S3, during the impactor-type ultrasonic shot peening, the impactor is made of Q345 steel, ZG30 cast steel, No. 45 steel, diamond, or zirconium oxide.

[0016] Preferably, in step S3, during the impactor-type ultrasonic shot peening, the diameter of the working head of the impactor is 0.2–5 mm, and the vibration frequency is 20–50 kHz.

[0017] Preferably, in step S3, the process parameters for the impact-type ultrasonic shot peening are as follows: shot peening power of 10-250W, spindle speed of 10-200R / min, amplitude of 1-10μm, feed speed of 0.01-50mm / min, impact speed of the impact pin of 1-10m / s, shot peening coverage of 100-150%, and pre-pressure of 1-20N; and 1-10 impact-type ultrasonic shot peening treatments are performed.

[0018] Preferably, in step S3, the thickness of the thin coating treated by the impactor ultrasonic shot peening is reduced by less than 0.2% of the total thickness.

[0019] The beneficial effects of this invention are as follows: This invention uses a cooling-impact ultrasonic shot peening process to strengthen the coating on the alloy surface, eliminating microscopic defects such as surface grooves and microcracks that may exist in the coating during the preparation process, reducing the surface roughness of the coating, changing its grain boundary morphology, increasing the residual pressure of the coating, thereby improving the coating's ability to resist crack initiation and propagation, effectively improving the fatigue life of the alloy substrate, and solving the problem of the decline in the fatigue performance of the alloy substrate due to coating quality. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0021] Figures 1-2 These are EBSD images of the alloy coating before and after processing in Embodiment 1 of the present invention;

[0022] Figures 3-4 These are SEM images of the alloy coatings before and after processing in Embodiment 1 of the present invention;

[0023] Figures 5-6 These are residual stress diagrams of the coating before and after alloy processing in Embodiment 1 of the present invention;

[0024] Figure 7 This is a comparison of the low-cycle fatigue performance at 350℃ before and after alloy processing in Example 1 of the present invention. Detailed Implementation

[0025] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the invention and do not constitute a limitation on the scope of protection of this invention.

[0026] This invention proposes a method for improving the fatigue performance of coated alloys, comprising the following steps:

[0027] S1. Pretreatment: The alloy with the thin coating is surface cleaned. Specifically, the alloy is cleaned with water to prevent surface contamination and ensure processing quality. The thin coating is made of metallic Cr, FeCrAl alloy, NbMoTaW high-entropy alloy, or AlCrMoNbZr high-entropy alloy. Other metallic materials can also be used, and the composition can be selected based on the alloy substrate. The thickness of the thin coating is 0.01–3 mm, i.e., it can be 0.01 mm, 0.05 mm, 0.1 mm, 0.5 mm, 1 mm, 2 mm, or 3 mm. Existing technologies can be used to prepare the thin coating, such as magnetron sputtering, cold spraying, and arc ion plating, which will not be elaborated here. The alloy can be zirconium alloy, magnesium alloy, aluminum alloy, or copper alloy, etc., which are suitable for preparing a thin surface coating.

[0028] S2. Cooling Treatment: The cleaned alloy is cooled using a cooling source. The temperature of the cooled alloy is between -20°C and 40°C, i.e., the alloy temperature can be -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, or 40°C. The purpose of cooling is to prevent the coating surface temperature from becoming too high during the treatment process, which would lead to oxidation and affect the coating performance. The cooling source includes at least one of a gas phase, a solid phase, and a liquid phase. During treatment, the gas phase and liquid phase act on the outer surface of the alloy, carrying away the surface heat through high-speed airflow or liquid flow; the solid phase is placed inside the alloy or acts on the inner sidewall of the alloy, which can simultaneously achieve the functions of cooling the alloy and supporting the alloy to prevent deformation. The gas phase is nitrogen, argon, or helium, or other inert gases can also be used. Based on production cost considerations, nitrogen is preferred as the gas phase; the solid phase is ice, and the liquid phase is water. Neither of these will chemically react with the alloy coating or cause contamination to the alloy coating.

[0029] In some embodiments, the alloy is a thin-walled tube with a wall thickness of 0.3–0.7 mm, i.e., the wall thickness can be 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, or 0.7 mm. The cooling source is preferably a solid phase, or one of a gaseous phase and a liquid phase. The solid phase is placed inside the cavity of the thin-walled tube, while the gaseous or liquid phase is sprayed onto the outer surface of the thin-walled tube. In other embodiments, the alloy is a rod or plate, and the cooling source is preferably a gaseous or liquid phase, which is sprayed onto the outer surface of the rod or plate.

[0030] S3. Impact-type ultrasonic shot peening: The cooled alloy undergoes multiple impact-type ultrasonic shot peening treatments. The impact pin is made of Q345 steel, ZG30 cast steel, 45# steel, diamond, or zirconium oxide. The working head (spherical) of the impact pin has a diameter of 0.2–5 mm (0.2 mm, 0.8 mm, 1 mm, 3 mm, 5 mm) and a vibration frequency of 20–50 kHz (20 kHz, 25 kHz, 30 kHz, 35 kHz, 40 kHz, 45 kHz, 50 kHz). This allows the working head to achieve a large impact acceleration and generate significant kinetic energy through high-frequency ultrasonic vibration. This energy, acting on the alloy surface coating, increases the residual stress of the coating, improves fatigue life, and optimizes the columnar grain boundary orientation, thus achieving an optimized surface morphology.

[0031] The process parameters for impact-type ultrasonic shot peening are as follows: shot peening power is 10–250W, for example, 10W, 50W, 100W, 150W, 200W, 250W; spindle speed is 10–200 R / min, for example, 10R / min, 50R / min, 100R / min, 150R / min, 200R / min; amplitude is 1–10μm, for example, 1μm, 3μm, 5μm, 8μm, 10μm; feed rate is 0.01–50mm / min, for example, 0.01mm / min, 0.1mm / min. The speeds are: in, 1mm / min, 10mm / min, 30mm / min, 50mm / min; the impact velocity of the impact pin is 1-10m / s, for example, 1m / s, 3m / s, 5m / s, 8m / s, 10m / s; the shot peening coverage is 100-150%, for example, 100%, 110%, 120%, 130%, 140%, 150%; the pre-pressure is 1-20N, for example, 1N, 5N, 10N, 15N, 20N; and 1-10 cycles of impact-type ultrasonic shot peening are performed, for example, 1 time, 3 times, 5 times, 8 times, 10 times.

[0032] The number of ultrasonic shot peening treatments using the impactor should be selected based on the optimization effect on the grain size. This optimization effect is influenced by the combined effects of the process parameters of the impactor ultrasonic shot peening treatment. However, excessive impactor ultrasonic shot peening treatments may affect the crystal structure of the alloy and alter stress. Therefore, the number of ultrasonic shot peening treatments in this invention is selected as 1 to 10 times. The thickness reduction of the alloy thin coating after impactor ultrasonic shot peening is less than 0.2% of the total thickness, without affecting the coating's beneficial effects on the alloy substrate, such as corrosion resistance and high-temperature oxidation resistance. Understandably, a reduction in the thickness of the alloy thin coating of less than 0.2% of the total thickness is sufficient; this invention does not impose a specific limitation.

[0033] As a traditional machining technique for strengthening metal surfaces, shot peening involves propelling a high-speed stream of shot onto the metal surface, causing plastic deformation and forming a reinforced layer of a certain thickness. However, shot peening increases the surface roughness of the metal. Under external loads, this rough surface accelerates crack nucleation, reducing the metal's fatigue life. Other surface treatment technologies include laser impact peening, deep rolling, ultrasonic shot peening, and ultrasonic rolling.

[0034] The effects of different surface treatment technologies, including shot peening, laser shock peening, deep rolling, ultrasonic shot peening, and ultrasonic rolling, on the mechanical properties of materials were compared. The results are shown in Table 1. Lower values ​​indicate a more unfavorable impact on material properties, while higher values ​​indicate a more favorable impact. Specifically, a value of 1 represents the worst impact, and a value of 5 represents the best impact. Table 1 shows that ultrasonic shot peening, deep rolling, and ultrasonic rolling all have a beneficial effect on the surface roughness of the material, significantly reducing it. Shot peening and laser shock peening even increase surface roughness. Laser shock peening, deep rolling, ultrasonic shot peening, and ultrasonic rolling have the best overall effect on residual stress, hardness, and depth, while shot peening has the worst effect on residual stress, hardness, and depth. Laser shock peening, ultrasonic shot peening, and ultrasonic rolling have a beneficial effect on microstructure, while shot peening and deep rolling are detrimental to microstructure. While ultrasonic rolling can effectively address issues such as grain refinement, surface roughness, and residual stress, it still presents technical challenges for thin-walled pipes. Excessive rolling depth can lead to surface coating cracking or even pipe wall deformation. Therefore, ultrasonic shot peening offers certain advantages in metal surface strengthening treatments.

[0035] Table 1. Effects of different surface treatment technologies on substrate materials

[0036] Processing technology Shot peening Laser shock Deep rolling Ultrasonic shot peening Ultrasonic rolling Energy source Particle jet Laser thermal static load Ultrasonic dynamic load Static load + dynamic load Surface roughness 2 1 4 4 5 Residual stress 1 5 4 4 4 Hardness and depth 1 4 3 3 5 microstructure 2 5 1 4 4

[0037] The impactor-type ultrasonic shot peening technology of this invention combines ultrasonic vibration with traditional shot peening techniques. It can process alloy materials with high hardness and strength, refine the grain size of the alloy surface coating, eliminate textures generated by surface processing, and maintain the morphology and properties of the alloy matrix, thereby improving fatigue life. Furthermore, ultrasonic shot peening induces drastic deformation on the alloy material surface through mechanical processing to achieve surface strengthening modification. Its principle is simple, cost-effective, and easy to implement. Compared to surface coating and chemical heat treatment, it has advantages such as not introducing impurities during the deformation process and forming a fine-grained structure layer that is less prone to peeling. It can be applied in many fields such as aerospace, construction, and machinery manufacturing.

[0038] The following is an illustration through specific examples:

[0039] Example 1

[0040] Zirconium alloys are widely used as cladding materials for Accident Tolerant Fuels (ATF). Applying a Cr coating to the surface of zirconium alloys can effectively improve their corrosion resistance, high-temperature oxidation resistance, and wear resistance. However, when coated zirconium alloys are subjected to cumulative alternating loads during operation, the Cr coating on the alloy surface may degrade the service life of zirconium alloy components, potentially leading to major safety accidents. Therefore, the quality of the Cr coating is particularly important for the fatigue performance of zirconium alloy cladding, and improving the fatigue performance of Cr-coated zirconium alloys has become one of the important technical issues in nuclear safety protection.

[0041] This invention proposes a method for improving the fatigue performance of coated alloys, which can perform surface strengthening treatment on zirconium alloy chromium coatings. The method includes the following steps:

[0042] S1. Pretreatment: The alloy with a thin coating is cleaned with water. The thin coating is made of metallic Cr and has a thickness of 0.015 mm. The Cr coating is prepared on the surface of the zirconium alloy using magnetron sputtering technology.

[0043] S2. Cooling Treatment: The cleaned alloy is cooled using a cooling source to a temperature of 30°C. The alloy is a thin-walled tube (e.g., a zirconium alloy clad tube) with a wall thickness of 0.5 mm. The cooling source consists of a gaseous phase (nitrogen) and a solid phase (ice). During the cooling treatment, ice is placed inside the thin-walled tube while nitrogen is sprayed onto its outer surface.

[0044] S3. Impact-type ultrasonic shot peening: The cooled alloy undergoes five impact-type ultrasonic shot peening treatments. The impact pin is made of diamond, with a working head diameter of 1 mm and a vibration frequency of 35 kHz. The process parameters for impact-type ultrasonic shot peening are: shot peening power of 26 W, spindle speed of 100 RPM, amplitude of 10 μm, feed rate of 0.02 mm / min, impact velocity of the impact pin of 5 m / s, shot peening coverage of 100%, and preload of 10 N. The thickness reduction of the thin coating after impact-type ultrasonic shot peening is less than 0.2% of the total thickness.

[0045] Example 2

[0046] A method for improving the fatigue properties of coated alloys includes the following steps:

[0047] S1. Pretreatment: The alloy with a thin coating is cleaned with water. The thin coating is made of FeCrAl alloy with a thickness of 0.01 mm, and is prepared on the magnesium alloy surface using cold spraying technology.

[0048] S2. Cooling Treatment: The cleaned alloy is cooled using a cooling source to a temperature of -20℃. The alloy is in the form of a rod, and the cooling source is gaseous argon. During the cooling treatment, argon gas is sprayed onto the outer surface of the rod.

[0049] S3. Impact-type ultrasonic shot peening: The cooled alloy undergoes two impact-type ultrasonic shot peening treatments. The impact pin is made of Q345 steel, with a working head diameter of 0.2 mm and a vibration frequency of 50 kHz. The process parameters for impact-type ultrasonic shot peening are: shot peening power 250 W, spindle speed 200 RPM / min, amplitude 1 μm, feed speed 50 mm / min, impact pin impact velocity 1 m / s, shot peening coverage 150%, and preload 1 N. The thickness reduction of the thin coating after impact-type ultrasonic shot peening is less than 0.2% of the total thickness.

[0050] Example 3

[0051] A method for improving the fatigue properties of coated alloys includes the following steps:

[0052] S1. Pretreatment: The alloy with a thin coating is cleaned with water. The thin coating is made of NbMoTaW high-entropy alloy with a thickness of 3 mm, and is prepared on the aluminum alloy surface using arc ion plating technology.

[0053] S2. Cooling Treatment: The cleaned alloy is cooled using a cooling source to a temperature of 40°C. The alloy is a sheet metal, and the cooling source is liquid water. During the cooling treatment, water is sprayed onto the outer surface of the sheet metal.

[0054] S3. Impact-type ultrasonic shot peening: The cooled alloy undergoes 10 cycles of impact-type ultrasonic shot peening. The impact pin is made of ZG30 cast steel, with a working head diameter of 5mm and a vibration frequency of 20kHz. The process parameters for impact-type ultrasonic shot peening are: shot peening power 10W, spindle speed 10R / min, amplitude 5μm, feed speed 25mm / min, impact pin impact velocity 10m / s, shot peening coverage 120%, and preload 20N. The thickness reduction of the thin coating after impact-type ultrasonic shot peening is less than 0.2% of the total thickness.

[0055] Performance testing:

[0056] The coated alloy of Example 1 was subjected to EBSD (electron backscatter diffraction) microstructure observation, SEM (scanning electron microscopy) micromorphology observation, residual stress measurement, and a 350℃ low-cycle fatigue test. The changes in the coated alloy before and after surface strengthening treatment were compared. The test results are as follows: Figures 1 to 7 As shown.

[0057] Depend on Figures 1-2 It is evident that after surface coating strengthening treatment, the columnar grain boundaries of the coating undergo a transformation, shifting by approximately 10° from the vertical direction, which is prone to fatigue failure. Furthermore, the grains are slightly refined, increasing the crack initiation and propagation threshold and improving the fatigue life of the alloy matrix. Figures 3-4 As can be seen, after surface coating strengthening treatment, the surface roughness of the coating decreased from 0.3 μm to 0.1 μm. Figures 5-6 As can be seen, after surface coating strengthening treatment, the residual stress of the coating increased from 201 MPa to 299 MPa. Figure 7 It can be seen that after surface coating strengthening treatment, the number of cycles corresponding to the same strain amplitude of the coating increases by 1 to 2 times, which improves the fatigue performance of the coated alloy at 350℃ by 1 to 2 times and significantly improves the fatigue life.

[0058] This invention employs a cooling-impact ultrasonic shot peening process to strengthen the coating on the alloy surface, eliminating microscopic defects such as surface grooves and microcracks that may exist during the coating preparation process. This reduces the surface roughness of the coating, alters its grain boundary morphology, and increases the residual pressure of the coating, thereby improving the coating's resistance to crack initiation and propagation, effectively increasing the fatigue life of the alloy substrate, and solving the problem of decreased fatigue performance of the alloy substrate due to coating quality.

[0059] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method of improving the fatigue properties of a coating alloy, characterized by, Includes the following steps: S1. Pretreatment: Cleaning the surface of the alloy with a thin coating; S2. Cooling treatment: The cleaned alloy is cooled using a cooling source, which includes at least one of a gas phase, a solid phase, and a liquid phase; during the treatment, the gas phase and the liquid phase act on the outer surface of the alloy, while the solid phase is placed inside the alloy. S3, Impact-type ultrasonic shot peening: The cooled alloy is subjected to multiple impact-type ultrasonic shot peening treatments. In step S1, the thickness of the thin coating is 0.01~0.015mm; The alloy is used for thin-walled tubing, and the wall thickness of the thin-walled tubing is 0.3~0.7mm; In step S2, the temperature of the alloy after cooling is -20~40℃; In step S3, the thickness of the thin coating treated with impact-type ultrasonic shot peening is reduced by less than 0.2% of the total thickness.

2. The method of improving the fatigue performance of a coated alloy of claim 1 wherein, In step S1, the thin coating is made of metallic Cr, FeCrAl alloy, NbMoTaW high-entropy alloy, or AlCrMoNbZr high-entropy alloy.

3. The method of improving the fatigue performance of a coated alloy of claim 1 wherein, In step S2, the gas phase is nitrogen, argon, or helium, the solid phase is ice, and the liquid phase is water.

4. The method of improving the fatigue performance of a coated alloy of claim 1 wherein, The cooling source is one of solid phase, gas phase and liquid phase, and the solid phase is placed in the inner cavity of the thin-walled tube.

5. The method of improving the fatigue performance of a coated alloy of claim 1 wherein, In step S3, the impactor-type ultrasonic shot peening process uses an impactor made of Q345 steel, ZG30 cast steel, 45 steel, diamond, or zirconium oxide.

6. The method of improving the fatigue performance of a coated alloy of claim 1 wherein, In step S3, the diameter of the working head of the impactor in the ultrasonic shot peening process is 0.2~5 mm, and the vibration frequency is 20~50KHz.

7. The method of improving the fatigue performance of a coated alloy of claim 1 wherein, In step S3, the process parameters for the impact-type ultrasonic shot peening treatment are as follows: shot peening power of 10~250W, spindle speed of 10~200R / min, amplitude of 1~10μm, feed speed of 0.01~50mm / min, impact speed of the impact pin of 1~10m / s, shot peening coverage of 100~150%, and pre-pressure of 1~20N; and 1~10 impact-type ultrasonic shot peening treatments are performed.

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