Method for strengthening nanocrystalline material through laser shock

Abstract

The invention discloses a method for strengthening a nanocrystalline material through laser shock, belongs to the field of metal material laser shock processing, and aims at solving the problem that the application field of an existing nanocrystalline material is limited due to the fact that the mechanical property of the existing nanocrystalline material is poor. Laser pulses penetrate through the restraint layer transparent material to directly reach the ablation layer, the ablation layer instantaneously absorbs high-energy-density pulse lasers and instantaneously vaporizes and ionizes the high-energy-density pulse lasers to form high-energy shock waves, the peak pressure of the shock waves is instantaneously increased under the limitation of the restraint layer and can reach the GPa level, a large number of defects are introduced into the nanocrystalline foil, and therefore the high-energy-density nanocrystalline foil is obtained. Therefore, the nanocrystalline material is strengthened. The method is mainly used for surface strengthening of nanocrystalline materials.

Description

Technical Field

[0001] The present invention belongs to the field of laser shock processing of metal materials, and particularly relates to a method for laser shock strengthening of nanocrystalline materials. Background Art

[0002] Metal materials play an extremely important role in modern national defense and military industries, and are widely used in fields such as aerospace, nuclear industry, precision instrument equipment, and power equipment, constituting the technical pillars of various high-tech applications. Metal materials have excellent strength, high temperature resistance, and good chemical stability, and can operate safely and stably in various extreme environments, ensuring the long-term durability of equipment. With the rapid progress of technology and the continuous improvement of industrial demands, the performance requirements for metal materials are also getting higher and higher, and their performance directly affects the rapid development of various fields.

[0003] The grain size of metal nanocrystalline materials is at the nanometer level (less than 100 nm), and the number of grain boundaries is extremely large. Compared with coarse-grained materials, they have higher strength, hardness, and more excellent wear resistance and corrosion resistance, and show increasingly important application values in modern science and technology and industries. They have been applied in many key fields such as electronic devices, energy, medical treatment, aerospace, and automotive industries, and are of great significance for improving the modern level, promoting industrial upgrading, and promoting sustainable development. However, the existing metal nanocrystalline materials are still relatively weak in mechanical properties, which also limits their application fields. Therefore, in order to enable nanocrystalline materials to have greater development prospects in various fields, a method for laser shock strengthening of nanocrystalline materials is developed. Summary of the Invention

[0004] The present invention aims to solve the problem that the existing nanocrystalline materials have relatively weak mechanical properties themselves, which limits their application fields, and further provides a method for laser shock strengthening of nanocrystalline materials;

[0005] A method for laser shock strengthening of nanocrystalline materials, which is realized through the following steps:

[0006] Step 1: Preparation of nanocrystalline foil: The whole nanocrystalline material is cut by mechanical processing to obtain the shape of the nanocrystalline material to be strengthened as required, and the cut nanocrystalline material foil is ground and surface-treated to obtain the nanocrystalline foil to be shocked;

[0007] Step 2: Selection of the laser shock confinement layer, laser shock ablation layer, and laser shock backplane used in the laser shock strengthening process; The laser shock confinement layer is selected from solid materials with high light transmittance or flexible liquids with high light transmittance, the laser shock ablation layer is selected from materials with excellent light absorption and low melting point, and the laser shock backplane is selected from materials with high strength and hardness and strong anti-shock ability;

[0008] Step 3: Stack the laser shock constraint layer, the laser shock ablation layer, the nanocrystalline material layer to be shocked, and the laser shock backplate from top to bottom in sequence to form a body to be shocked, and ensure perfect fitting between adjacent two layers in the body to be shocked;

[0009] Step 4: Install the high-energy laser emitter on a high-precision three-dimensional moving platform. The high-energy pulsed laser is instantaneously excited by a constant pulse from the high-energy pulsed laser, and under the drive of the high-precision three-dimensional moving platform, it impacts the body to be shocked according to a predetermined shock path, so as to shock and strengthen the nanocrystalline foil in the body to be shocked to obtain a strengthened nanocrystalline foil;

[0010] Step 5: After the shock is completed, remove the ablation layer from the surface of the nanocrystalline foil to obtain a strengthened nanocrystalline foil, and perform ultrasonic cleaning, so as to obtain a clean and high-strength nanocrystalline material;

[0011] Furthermore, the machining method in the step 1 is wire cutting, laser cutting or blanking, etc.;

[0012] Furthermore, the surface treatment in the step 1 mainly includes ultrasonic cleaning in alcohol, acetone, acid solution or alkali solution to ensure complete removal of impurity particles and oil stains on the surface of the nanocrystalline material. The nanocrystalline material to be shocked after cleaning is rinsed with a large amount of clear water, and finally dried with a hair dryer to obtain a nanocrystalline material layer to be shocked for standby. The thickness of the nanocrystalline material layer to be shocked is between 100 nm and 100 μm, and the ultrasonic cleaning time is 10 - 30 min;

[0013] Furthermore, the laser shock constraint layer in the step 2 is a solid material constraint layer with high light transmittance. The thickness of the laser shock constraint layer is 100 μm - 10 mm, specifically K9 glass or PMMA resin;

[0014] Furthermore, the laser shock constraint layer in the step 2 is a flexible liquid constraint layer with high light transmittance. The thickness of the laser shock constraint layer is 100 μm - 10 mm, specifically a water layer or an oil layer;

[0015] Furthermore, the thickness of the laser shock ablation layer in the step 2 is 10 nm - 1 mm, specifically black paint, black tape or aluminum foil;

[0016] Furthermore, the thickness of the laser shock backplate in the step 2 is 1 mm - 50 mm, specifically die steel, hard alloy steel or K9 glass plate;

[0017] Furthermore, the planar size of the laser shock backplate in the step 2 is larger than the planar size of the nanocrystalline material to be shocked;

[0018] Further, in the step 4, the output parameters of the high-energy pulsed laser are as follows: the wavelength is 1064 nm, the laser energy is 0.5 - 10 J, the pulse duration is 1 - 40 ns, the spot diameter is 0.5 - 10 mm, and the output laser density is 10 6 ~10 9 W / cm 2 ;

[0019] Further, in the step 5, the strengthened nanocrystalline foil is cleaned with an organic solvent in an ultrasonic environment, and the treatment time is 10 - 30 min.

[0020] The beneficial effects of the present application compared with the prior art:

[0021] A method for laser shock strengthening of nanocrystalline materials provided by the present application has the advantage of innovatively using laser shock to strengthen nanocrystalline foils. Currently, existing laser shock technologies mainly focus on coarse-grained materials (grain size in the μm level), mainly achieving work hardening of materials by the tangling of dislocations within grains to generate features such as dislocation cells and dislocation walls. However, the laser shock technology in this patent mainly focuses on generating an ordered 9R phase structure ( Figure 2 ) within grains. It is initially discovered that laser shock will generate the 9R phase within nanocrystalline grains. As a more stable structure compared to dislocation tangling, dislocation walls, stacking faults, and twins, the 9R phase can more effectively hinder dislocation movement, enabling dislocations to accumulate within nanocrystalline grains where they could not accumulate before, thereby obtaining higher material strength under the same grain size. In addition, fewer dislocations interacting with grain boundaries will reduce the occurrence of phenomena such as dislocation-induced grain boundary sliding, grain rotation, and grain boundary migration, and reduce grain growth caused by dislocations under quasi-static and high-speed impact conditions, thereby effectively suppressing the reduction of strength from the aspect of grain size. Moreover, while suppressing grain growth, larger grains within the material will break under the powerful energy generated by the laser, which is conducive to suppressing grain growth. The strengthening effect of the 9R phase and the suppression of grain growth can effectively improve the strength of nanocrystalline materials. It should be emphasized here that under general conditions (quasi-static or high strain rate), a powerful force will cause obvious growth of nanocrystalline grains, and the ultra-high strain rate generated by laser shock enables the material to effectively overcome this point. In addition, laser shock belongs to flexible forming, with simple equipment and process, and the impact strengthening area and related paths can be designed according to requirements. At the same time, it can close macroscopic defects such as holes in nanocrystalline materials, enhancing the wear resistance, corrosion resistance, and fatigue resistance of the materials. Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the laser shock strengthening process in the present application;

[0023] Figure 2The crystal phase structure diagram of the 9R phase formed inside the nanocrystalline foil material after being subjected to laser shock in this application:

[0024] Figure 3 The strength improvement curve graph of the nanocrystalline foil material in this application after laser shock;

[0025] In the figure, 1 is a high-energy laser emitter, 2 is a laser shock confinement layer, 3 is a laser shock ablation layer, 4 is the nanocrystalline foil material to be shocked, and 5 is a laser shock back plate. Detailed implementation manners

[0026] Detailed implementation manner 1: In combination with Figure 1 To illustrate this implementation manner, a method for laser shock strengthening of nanocrystalline materials is provided in this implementation manner, and the method is achieved through the following steps:

[0027] Step 1: Preparation of the nanocrystalline foil material: The whole nanocrystalline material is cut by mechanical processing to obtain the shape of the nanocrystalline material to be strengthened as required, and the cut nanocrystalline material is ground and surface-treated to obtain the nanocrystalline foil material 4 to be shocked;

[0028] Step 2: Selection of the laser shock confinement layer 2, laser shock ablation layer 4, and laser shock back plate 5 used in the laser shock strengthening process; The laser shock confinement layer 2 is selected from solid materials with high light transmittance or flexible liquids with high light transmittance, the laser shock ablation layer 3 is selected from materials with excellent light absorption and low melting point, and the laser shock back plate 5 is selected from materials with high strength and hardness and strong impact resistance;

[0029] Step 3: Stack the laser shock confinement layer 2, laser shock ablation layer 3, the nanocrystalline material layer 4 to be shocked, and the laser shock back plate 5 from top to bottom in sequence to form a body to be shocked, and ensure perfect fitting between adjacent layers in the body to be shocked;

[0030] Step 4: Install the high-energy laser emitter 1 on a high-precision three-dimensional moving platform. The high-energy pulsed laser is instantaneously excited by the high-energy pulsed laser at a constant pulse, and drives the high-precision three-dimensional moving platform to shock the body to be shocked along a predetermined shock path, so as to shock and strengthen the nanocrystalline foil material 4 in the body to be shocked to obtain a strengthened nanocrystalline foil material;

[0031] Step 5: After the shock is completed, remove the ablation layer from the surface of the nanocrystalline foil material to obtain a strengthened nanocrystalline foil material, and perform ultrasonic cleaning to obtain a clean and high-strength nanocrystalline material.

[0032] A method for laser shock strengthening nanocrystalline materials provided by this embodiment has a working principle that a high-energy laser pulse is generated by a laser emitter 1. The laser pulse passes through the constraint layer of transparent material and directly reaches the ablation layer. The ablation layer instantaneously absorbs the pulsed laser with high energy density and instantaneously vaporizes and ionizes to form a high-energy shock wave. Under the restriction of the constraint layer, the peak pressure of the shock wave instantaneously increases, reaching the GPa level, introducing a large number of defects inside the nanocrystalline foil material, thereby realizing the strengthening of the nanocrystalline material.

[0033] Specific Embodiment 2: In combination with Figure 1 Describe this embodiment. The difference between this embodiment and Specific Embodiment 1 is that the mechanical processing method in Step 1 is wire cutting, laser cutting, blanking, etc. Other compositions and connection methods are the same as those in Specific Embodiment 1.

[0034] In this embodiment, considering that the surface flatness of the nanocrystalline material cut by mechanical processing is uneven, directly using it in the laser shock strengthening process will affect the final strengthening effect of the nanocrystalline material. Therefore, it is necessary to mechanically grind the surface of the cut nanocrystalline material with different types of sandpaper. The nanocrystalline material to be shocked after grinding has a high flatness and can avoid the generation of obvious warping.

[0035] Specific Embodiment 3: In combination with Figure 1 Describe this embodiment. The difference between this embodiment and Specific Embodiment 2 is that the surface treatment in Step 1 mainly includes ultrasonic cleaning in alcohol, acetone, acid solution or alkali solution to ensure that impurities and oil on the surface of the nanocrystalline material are fully removed. The nanocrystalline material to be shocked after cleaning is rinsed with a large amount of clean water, and finally dried with a hair dryer to obtain a nanocrystalline material layer to be shocked for standby. The thickness of the nanocrystalline material layer to be shocked is between 100 nm and 100 μm, and the ultrasonic cleaning time is 10 - 30 min. Other compositions and connection methods are the same as those in Specific Embodiment 2.

[0036] Specific Embodiment 4: In combination with Figure 1 Describe this embodiment. The difference between this embodiment and Specific Embodiment 3 is that the laser shock constraint layer 2 in Step 2 is a solid material constraint layer with high light transmittance. The thickness of the laser shock constraint layer 2 is 100 μm - 10 mm, specifically K9 glass or PMMA resin. Other compositions and connection methods are the same as those in Specific Embodiment 3.

[0037] Specific Embodiment 5: In combination with Figure 1To describe this embodiment, the difference between this embodiment and the fourth specific embodiment is that in step 2, the laser shock confinement layer 2 is a flexible liquid confinement layer with high light transmittance. The thickness of the laser shock confinement layer 2 is 100 μm - 10 mm, specifically a water layer or an oil layer. Other components and connection methods are the same as those in the fourth specific embodiment.

[0038] Combined with the fourth to fifth specific embodiments, the solid material confinement layer has high strength and hardness, which can greatly increase the pressure brought by the shock wave. The flexible liquid confinement layer has extremely high flexibility. While increasing the pressure brought by the shock wave, it can timely replenish the confinement layer and effectively conduct continuous shocks. The specific type selection of the laser shock confinement layer 2 is made by the staff themselves. The thickness of the laser shock confinement layer 2 is between 100 μm - 10 mm, which can effectively limit the shock wave and increase the shock wave pressure.

[0039] Specific embodiment six: Combined with Figure 1 To describe this embodiment, the difference between this embodiment and the fifth specific embodiment is that in step 2, the thickness of the laser shock ablation layer 3 is 10 nm - 1 mm, specifically black paint, black tape or aluminum foil. Other components and connection methods are the same as those in the fifth specific embodiment.

[0040] In this embodiment, the main function of the laser shock ablation layer 3 is to absorb high-energy laser, thus instantaneously explode to generate plasma and generate the impact force required in the forming process. It mainly includes materials with strong light absorption and low melting points such as black paint, black tape, and aluminum foil. During the forming process, it must be tightly combined with the confinement layer and the nanocrystalline foil material. In addition, its thickness needs to be selected according to its material properties and impact energy. Usually, the thickness is generally between 10 nm - 1 mm, and it is necessary to ensure that all impact positions are covered.

[0041] Specific embodiment seven: Combined with Figure 1 To describe this embodiment, the difference between this embodiment and the sixth specific embodiment is that in step 2, the thickness of the laser shock back plate 5 is 1 mm - 50 mm, specifically die steel, hard alloy steel or K9 glass plate. Other components and connection methods are the same as those in the sixth specific embodiment.

[0042] In this embodiment, the laser shock back plate 5 is required to have high strength and hardness and strong impact resistance. It can effectively prevent the plastic flow of the nanocrystalline material along the laser shock propagation direction, provide a strong impact force, and at the same time, it is required to have high flatness to ensure the stability of the nanocrystalline material layer 4 to be shocked during strengthening.

[0043] Specific embodiment eight: Combined with Figure 1Description of this embodiment: The difference between this embodiment and the seventh specific embodiment is that the planar size of the laser shock backplane in step 2 is larger than the planar size of the nanocrystalline material layer to be shocked. Other components and connection methods are the same as those in the seventh specific embodiment.

[0044] Specific embodiment nine: Figure 1 Description of this embodiment: The difference between this embodiment and the eighth specific embodiment is that the output parameters of the high-energy pulsed laser in step 4 are a wavelength of 1064 nm, a laser energy of 0.5 - 10 J, a pulse duration of 1 - 40 ns, a spot diameter of 0.5 - 10 mm, and the output laser density is 10 6 ~10 9 W / cm 2 . Other components and connection methods are the same as those in the eighth specific embodiment.

[0045] Step 4 in this embodiment is the core step. Applying high-energy laser on the surface of the object to be shocked, a super-high-speed and ultra-high-intensity shock wave is generated by the explosion to strengthen the nanocrystalline foil. It can overcome the phenomenon of grain growth caused by quasi-static or high-speed shock, and inhibit the reduction of the strength of the nanocrystalline material. At the same time, a large number of defects will be generated inside the nanocrystalline grains, thus playing a strengthening role and realizing the strengthening of the nanocrystalline material. In addition, under the action of a strong impact force, the corrosion resistance, wear resistance and fatigue resistance of the nanocrystalline material will be correspondingly improved, and at the same time, the nanocrystalline material will be made more dense.

[0046] Specific embodiment ten: Figure 1 Description of this embodiment: The difference between this embodiment and the ninth specific embodiment is that in step 5, the strengthened nanocrystalline foil is cleaned using an organic solvent in an ultrasonic environment, and the treatment time is 10 - 30 min. Other components and connection methods are the same as those in the eighth specific embodiment.

[0047] In this embodiment, ultrasonic cleaning of the strengthened nanocrystalline foil is beneficial to removing impurities on the surface of the strengthened nanocrystalline foil and ensuring the cleanliness of the strengthened nanocrystalline foil.

[0048] The present invention has been disclosed above with preferred embodiments. However, it is not intended to limit the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, can make some modifications or equivalents by using the disclosed structure and technical content as equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention. Specific examples:

[0050] Taking the strengthening process of laser shock strengthening of nanocrystalline nickel-cobalt foil as an example;

[0051] Step 1: Use blanking to process the nanocrystalline material foil to be shocked on the whole piece of nanocrystalline nickel-cobalt foil according to a predetermined shape, and carefully grind the blanked nanocrystalline material foil to be shocked with 2000# and 3000# sandpapers to ensure that the nanocrystalline material foil to be shocked has a high flatness. Then put it into an acetone solution and ultrasonically clean it for 20 minutes to ensure that surface oil stains and impurities are completely removed, which is convenient for the attachment of the ablation layer. Then rinse it with a large amount of clean water and dry it with a hair dryer to ensure that the final thickness of the nanocrystalline material foil to be shocked is 33 μm;

[0052] Step 2: Select aluminum foil as the laser shock ablation layer. The thickness of the aluminum foil is 120 μm. The aluminum foil has the characteristics of good light absorption and low melting point, and can efficiently generate shock pressure. At the same time, it can block the transfer of heat and ensure the stability of the nanocrystalline material. Select a water layer with high light transmittance as the laser shock confinement layer, and its thickness is 1 mm. The water layer has good light transmittance and can be replenished in time during the laser shock process to better achieve the confinement of the impact force; Select hard alloy steel as the back plate, and keep the surface of the back plate flat. At the same time, it is required that there are no any impurity particles on the surface, which will affect the effect of laser shock, so as to better provide a strong supporting force during the laser shock process and realize the strengthening of the nanocrystalline foil;

[0053] Step 3: Stack the water layer with high light transmittance, aluminum foil, polished and cleaned nanocrystalline nickel-cobalt foil and hard alloy steel plate from top to bottom in sequence to form an object to be shocked, and ensure perfect fitting and close attachment between adjacent layers;

[0054] Step 4: Use a high-energy pulsed laser and a three-dimensional high-precision moving platform in combination, and shock the object to be shocked according to a predetermined shock path. The parameters of the pulsed laser are wavelength of 1064 nm, laser energy of 10 J, pulse width of 15 ns, spot diameter of 2 mm, and the output laser density is 10 7 W / cm 2 , the high-energy laser passes through the water layer and irradiates on the aluminum foil. The aluminum foil is quickly vaporized and ionized into plasma, generating a strong shock wave that is transmitted to the nanocrystalline nickel-cobalt foil to complete the strengthening of the nanocrystalline material;

[0055] Step 5: Put the strengthened nanocrystalline material into an acetone solution and clean it for 10 minutes, then rinse it with a large amount of clean water and dry it to obtain a clean and high-strength nanocrystalline material.

[0056] After testing, the strength of the nanocrystalline nickel-cobalt foil prepared by this application can be increased by 10% - 20%. At the same time, the wear resistance, corrosion resistance and fatigue resistance of the nanocrystalline nickel-cobalt foil can all be improved.

Claims

1. A method for laser shock strengthening nanocrystalline materials, characterized in that: The method is achieved by the following steps: Step 1: Preparation of nanocrystalline foil: Use mechanical processing to cut the entire nanocrystalline material to obtain the shape of the predetermined nanocrystalline material to be strengthened, grind and surface treat the cut nanocrystalline material foil to obtain the nanocrystalline foil to be impacted; Step 2: Select the laser shock confinement layer, laser shock ablation layer and laser shock back plate used in the laser shock strengthening process; the laser shock confinement layer is made of a solid material with high light transmittance or a flexible liquid with high light transmittance, the laser shock ablation layer is made of a material with excellent light absorption and low melting point, and the laser shock back plate is made of a material with high hardness and strong impact resistance; Step 3: stacking the laser shock confinement layer, the laser shock ablation layer, the nanocrystalline material layer to be impacted, and the laser shock back plate from top to bottom in sequence to form an impacted body, and ensuring that two adjacent layers in the impacted body are perfectly fitted; Step 4: Install a high-energy laser transmitter on a high-precision three-dimensional mobile platform, and the high-energy pulse laser instantaneously excites the high-energy pulse laser with a constant pulse, and drives the high-precision three-dimensional mobile platform to impact the impacted body according to a predetermined impact path, so as to achieve impact strengthening of the nanocrystalline foil to be impacted in the impacted body to obtain a strengthened nanocrystalline foil; Step 5: After the impact is completed, the ablation layer is removed from the surface of the nanocrystalline foil to obtain a strengthened nanocrystalline foil, and ultrasonic cleaning is performed to obtain a clean and high-strength nanocrystalline material.

2. The method for laser shock strengthening nanocrystalline materials according to claim 1, characterized in that: The mechanical processing method in step 1 is wire cutting, laser cutting or punching.

3. The method for laser shock strengthening nanocrystalline materials according to claim 2, characterized in that: The surface treatment in step 1 mainly includes ultrasonic cleaning in alcohol, acetone, acid solution or alkaline solution to ensure that the impurity particles and oil stains on the surface of the nanocrystalline material are fully removed. The nanocrystalline material to be impacted after cleaning is rinsed with a large amount of clean water, and finally blown dry with a hair dryer to obtain a nanocrystalline material layer to be impacted for standby use. The thickness of the nanocrystalline material layer to be impacted is between 100nm-100μm, and the ultrasonic cleaning time is 10-30min.

4. The method for laser shock strengthening nanocrystalline materials according to claim 3, characterized in that: In the step 2, the laser shock confinement layer is a highly light-transmitting solid material confinement layer, and the thickness of the laser shock confinement layer is 100 μm-10 mm, specifically K9 glass or PMMA resin.

5. The method for laser shock strengthening nanocrystalline materials according to claim 3, characterized in that: In the step 2, the laser shock confinement layer is a flexible liquid confinement layer with high light transmittance, and the thickness of the laser shock confinement layer is 100 μm-10 mm, specifically a water layer or an oil layer.

6. The method for laser shock strengthening nanocrystalline materials according to claim 1, characterized in that: The thickness of the laser shock ablation layer in step 2 is 10 nm-1 mm, specifically black paint, black tape or aluminum foil.

7. The method for laser shock strengthening nanocrystalline materials according to claim 6, characterized in that: The depth of the laser impact back plate in step 2 is 1mm-50mm, specifically mold steel, carbide steel or K9 glass plate.

8. The method for laser shock strengthening nanocrystalline materials according to claim 7, characterized in that: In step 2, the planar size of the laser impacting the back plate is larger than the planar size of the nanocrystalline material layer to be impacted.

9. The method for laser shock strengthening nanocrystalline materials according to claim 1, characterized in that: The output parameters of the high-energy pulse laser in step 4 are: wavelength of 1064nm, laser energy of 0.5-10J, pulse duration of 1-40ns, spot diameter of 0.5-10mm, output laser density of 10 6 ~10 9 W / cm 2 .

10. The method for laser shock strengthening nanocrystalline materials according to claim 1, characterized in that: In step 5, the strengthened nanocrystalline foil is cleaned with an organic solvent in an ultrasonic environment, and the treatment time is 10-30 minutes.

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