Pulse current global auxiliary laser shock peening method

Abstract

The invention discloses a pulse current global auxiliary laser shock peening method which comprises the following steps: applying low-frequency high-energy pulse current before laser shock peening is started, so that the pulse current uniformly acts on the depth direction of a whole component, releasing internal residual stress of the component, and homogenizing the structure of a to-be-processed area in the depth direction; in the laser shock peening action process, intermediate-frequency intermediate-energy pulse current is applied, so that a pulse current action area is concentrated in the whole depth range of an area to be peened, and the influence depth of laser shock peening is improved by utilizing the skin effect of the intermediate-frequency pulse current; after laser shock peening of all the areas is completed, pulse current only acts on the surface layer and the near surface layer of the to-be-treated component through the high-frequency pulse current skin effect, dislocation and other substructures formed on the surface layer and the near surface layer through laser shock peening are restored, the completion of the near surface layer grain refining process is promoted, and the stability of surface layer nanocrystals is improved; and finally, the pulse current global auxiliary laser shock peening process is completed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material surface strengthening treatment, and particularly relates to a method for pulse current global auxiliary laser shock peening. BACKGROUND

[0002] With the development of modern industry, the performance requirements for aviation components are becoming more and more stringent. The design and material selection of components need to meet high strength, lightweight, high temperature resistance, wear resistance, corrosion resistance and the like. Laser shock peening (LSP) as an advanced surface severe plastic deformation technology, has unique advantages in improving the strength and corrosion resistance of components.

[0003] Laser shock peening technology has developed since the 1960s, and the basic process has been developed and perfected. A residual compressive stress layer of about 1mm can be induced on the material surface, and a nano gradient structure can be formed to simultaneously improve the strength and toughness of the material. However, the LSP process with a single laser beam still faces many challenges. Due to the inherent properties of the material of the aviation component, when LSP is loaded, excessive laser energy can easily cause layer cracking on the material surface, causing the material to fail prematurely. Moreover, the surface residual stress layer has a threshold value and cannot be further deepened. The nano gradient structure layer induced on the surface layer of the material has too many unstable substructures, poor thermal stability, and is not conducive to the application of the aviation component at high temperatures. The prior art discloses a laser warm shot peening surface strengthening method and device with controllable heat affected zone. The device uses a high-frequency alternating current power supply to control the surface temperature of the material, thereby greatly improving the mechanical properties of the surface of the workpiece without affecting the properties of the core material of the metal workpiece. However, during the treatment process, the high temperature can easily cause the release of residual stress on the surface layer, and the grains grow. Moreover, the increase in temperature leads to an increase in the number of substructures on the surface layer, increasing the risk of reducing the stability of the gradient structure. Another technology discloses a method for real-time coupling strengthening of electric pulse and laser shock wave. The method uses electric pulse and laser shock wave coupling to simultaneously improve the strength and toughness. However, the substructures generated after the impact are not processed, and a stable nano gradient structure cannot be obtained. SUMMARY

[0004] To solve the above technical problems, the present application provides a method for pulse current global auxiliary laser shock peening, which specifically comprises:

[0005] Before starting the first stage of laser shock peening, start the electric pulse generating device, adjust the pulse current waveform and pulse width τ1, and the pulse current frequency and pulse current peak value are f1 and J m1, that is, a low-frequency high-energy pulse current is applied to the component to be processed, the pulse current uniformly acts on the depth direction of the whole component to be processed, the material temperature is stabilized near the temperature T1, after a t1' time period, the residual stress inside the component to be processed is released, and a component to be strengthened with uniform distribution of structures along the depth direction is obtained;

[0006] At the t1 moment, during the second stage of the laser shock strengthening process, the pulse current pulse width and frequency are exchanged as τ2 and the medium frequency f2, and the pulse current peak value J is adjusted m2 , that is, a medium-frequency medium-energy pulse current is applied to the component to be processed with uniform distribution of structures along the depth direction, the component surface temperature is stabilized near T2; after the temperature is stabilized at T2, the laser generating device, the constraint layer and the workpiece cooperative working machine are started to work, and the laser shock processing technology is started to be executed, the skin effect of the medium-frequency pulse current is used to make the medium-frequency medium-energy pulse current concentrate on the whole depth range of the region to be processed, and a component with super-large strengthening depth is obtained, the electric pulse is stabilized at the temperature T2, and the stabilization time is t2';

[0007] At the t2 moment, after the laser shock of all regions in the third stage is completed, that is, after a t2 time period, the laser shock strengthening equipment is turned off; the pulse current pulse width and frequency are exchanged as τ3 and the high frequency f3, and the pulse current peak value J is adjusted m3 , that is, a high-frequency low-energy pulse current is applied to the component with super-large strengthening depth, the skin effect of the high-frequency low-energy pulse current is used to make the pulse current only act on the surface layer and the near-surface layer of the component with super-large strengthening depth, and the component surface temperature is stabilized near T3, the nanocrystal temperature stability and structure stability of the surface layer and the near-surface layer are improved;

[0008] After the temperature T3 is stabilized for a t3' time period, the pulse current generating device is turned off, and the pulse current whole-domain auxiliary laser shock strengthening processing process is completed.

[0009] Optionally, the pulse width τ is selected according to the material, and the pulse widths of the three stages satisfy τ1≥τ3≥τ2≥100 μs.

[0010] Optionally, the electric pulse is direct current, and the waveform can be adjusted to be a rectangular wave, a half-sine wave or a triangular wave.

[0011] Optionally, the low-frequency high-energy pulse current frequency f1 satisfies f1≤100 Hz.

[0012] The temperature T1 is set according to the material of the component to be processed, and is a value of 20-50 ℃ lower than the temperature of the recrystallization annealing of the material of the component to be processed; t1' is selected according to the component to be processed, and is 100 s≤t1'≤500 s.

[0013] Optionally, f2 is determined based on the thickness d1 of the component to be strengthened and the material properties of the component:

[0014]

[0015] wherein ρ e is the resistivity of the material and μ is the permeability of the material.

[0016] Optionally, T2 is determined based on the material properties of the component to be strengthened:

[0017] u max / kln(c0 / c S )-m≤T2≤-Q m / kln(a 2 / 12D0)-m

[0018] wherein Q m is the activation energy, a is the lattice constant, k is the Boltzmann constant, D0 is the diffusion coefficient, u max is the maximum interaction energy between the dissolved atoms and dislocations, c0 is the average concentration of the solute element, c s is the maximum concentration of the solute atoms in the alloy, and m is the temperature drop value caused by the non-thermal effect of the pulse current.

[0019] Optionally, t2' is the same as the laser shock processing time.

[0020] Optionally, the constraint layer for laser shock peening is water, and the other parameters are selected according to the material.

[0021] Optionally, f3 is determined based on the thickness d1 of the component to be processed, the thickness d2 of the plastic deformation layer, and the material properties of the component to be processed:

[0022]

[0023] wherein ρ e is the resistivity of the material and μ is the permeability of the material.

[0024] Optionally, the temperature T3 is the low-temperature tempering temperature of the material of the component to be processed; t3' is selected according to the component, and t3' is 10

[0025] s≤t3’≤50s.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] The method of the application can improve the elongation and toughness of the material through the electric pulse treatment in the early stage, so as to prepare for the breakthrough of the energy and the hardening layer threshold in the second stage of laser shock.

[0028] The method of the application can improve the elongation and toughness of the material through the electric pulse treatment in the early stage, so as to prepare for the breakthrough of the energy and the hardening layer threshold in the second stage of laser shock.

[0029] The method of the application can improve the elongation and toughness of the material through the electric pulse treatment in the early stage, so as to prepare for the breakthrough of the energy and the hardening layer threshold in the second stage of laser shock.

[0030] The method of the application can improve the elongation and toughness of the material through the electric pulse treatment in the early stage, so as to prepare for the breakthrough of the energy and the hardening layer threshold in the second stage of laser shock.

[0031] The method of the application can improve the elongation and toughness of the material through the electric pulse treatment in the early stage, so as to prepare for the breakthrough of the energy and the hardening layer threshold in the second stage of laser shock. BRIEF DESCRIPTION OF DRAWINGS

[0032] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a flowchart illustrating the steps of a pulsed current-assisted global laser shock enhancement method provided in an embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of the sample size and impact zone. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Example 1

[0037] A method for pulsed current-assisted global laser shock enhancement, such as Figure 1 As shown, the method includes:

[0038] Before laser shock activating, a low-frequency, high-energy pulsed current is applied to homogenize the depth direction of the area to be processed. Secondly, during laser shock, a high-frequency, medium-energy pulsed current is applied, concentrating the pulsed current's effect on the surface and subsurface layers of the area to be processed. Finally, after laser shock is completed, an ultra-high-frequency, low-energy pulsed current is applied to induce dynamic recovery of the surface grains in the processed area. This ultimately completes the pulsed current-assisted full-domain laser shock activating process. Specifically:

[0039] Before the first stage of laser shock enhancement is initiated, the electrical pulse generator is activated, and the pulse current waveform and pulse width τ1 are adjusted. The pulse current frequency and pulse current peak value are f1 and J, respectively. m1 This process involves applying a low-frequency, high-energy pulsed current to the component to be treated, ensuring the pulsed current acts uniformly along the entire depth direction of the component. This stabilizes the material temperature around temperature T1. After a stabilization period of t1', the residual stress inside the component is released, resulting in a component with a uniformly distributed microstructure along the depth direction. This stage of treatment improves the component's ductility and toughness, releases internal residual stress, and homogenizes the microstructure along the depth direction of the processed area.

[0040] In this embodiment, the pulse current is adjusted to direct current, and the waveform can be adjusted to a rectangular wave, a half-sine wave, or a triangular wave, etc. The pulse current frequency is f1, and the peak value J of the pulse current is adjusted. m1 This stabilizes the material temperature around T1, where f1 ≤ 100 Hz.

[0041] The pulse width is selected according to the material, τ≥100 μs, and the pulse widths of the three stages can be the same or different, τ2≤τ3≤τ1.

[0042] Wherein T1 is set according to the base material of the key component, and is a value 20-50 ℃ lower than the recrystallization annealing temperature of the base material; t1' is selected according to the component, and is 100 s≤t1'≤500 s.

[0043] At time t1, the pulse current width and frequency are changed to τ2 and f2 respectively, and the pulse current peak value J is adjusted m2 , i.e. the medium-frequency medium-energy pulse current is applied to the component with uniform distribution of the structure along the depth direction, so that the component surface temperature is stabilized at T2; after the temperature is stabilized at T2, the laser generating device, the constraint layer and the workpiece are started to work cooperatively, and the laser impact machining process is started to be executed, the skin effect of the medium-frequency pulse current is used to make the medium-frequency medium-energy pulse current concentrate on the entire depth range of the machining area, so that the component with super-large strengthening depth is obtained, and the electric pulse is stabilized at T2, and the stabilization time is t2'.

[0044] At time t1, the pulse current frequency is changed to f2, and the pulse current peak value J is adjusted m2 , so that the component surface temperature is stabilized at T2; after the temperature is stabilized at T2, the laser generating device, the constraint layer and the workpiece are started to work cooperatively, and the laser impact machining process is started to be executed, and the electric pulse is stabilized at T2, and the stabilization time is t2'.

[0045] In the embodiment, the constraint layer of the laser impact strengthening is water, and the remaining parameters are selected according to the material.

[0046] f2 is determined according to the component thickness d1 and the material characteristics: Wherein ρ e is the resistivity of the material, μ is the magnetic permeability of the material, and d1 is the component thickness.

[0047] T2 is determined according to the material characteristics:

[0048] u max / kln(c0 / cS )-m ≤ T2 ≤ -Q m / kln(a 2 / 12D0)-m, where Q m is the activation energy, a is the lattice constant, k is the Boltzmann constant, D0 is the diffusion coefficient, u max is the maximum interaction energy between the dissolved atoms and dislocations, c0 is the average concentration of the solute element, c s is the maximum concentration of solute atoms in the alloy, which is related to temperature; m is the temperature drop value caused by the non-thermal effect of the pulse current.

[0049] t2' and the laser shock processing time are the same

[0050] At the moment t2, after the laser shock of all regions in the third stage is completed, i.e. after the time period t2' is elapsed, the laser shock strengthening equipment is turned off; the pulse current pulse width and frequency are exchanged to τ3 and high frequency f3 respectively, and the pulse current peak value is adjusted to low energy J m3 , i.e. the high-frequency low-energy pulse current is applied to the component with super-large strengthening depth, the skin effect of the high-frequency low-energy pulse current is used to make the pulse current only act on the surface layer and near-surface layer of the component with super-large strengthening depth, and the surface temperature of the component is stabilized near T3, so as to improve the temperature stability and structure stability of the surface layer and near-surface layer of the component.

[0051] At the moment t2, the laser shock processing of all regions of the key component is completed, and the laser shock strengthening equipment is turned off; the pulse current frequency is exchanged to f3, and the pulse current peak value is adjusted to J m3 , so that the surface temperature of the component is stabilized near T3, and after the time period t3' is stabilized, the pulse current generating device is turned off, and the complete pulse current global auxiliary laser shock strengthening processing process is completed.

[0052] f3 is determined according to the component thickness d1, the plastic deformation layer thickness d2 and the material characteristics:

[0053] Where d2 is the plastic deformation layer thickness.

[0054] The temperature T3 is the low-temperature tempering temperature of the material of the component to be processed.

[0055] t3' is selected according to the component, and 10s ≤ t3' ≤ 50s.

[0056] Example Two

[0057] In this embodiment, a 60x10x4mm 3 sample is used as the component to be processed, such as Figure 2The material is TC4 titanium alloy. According to the required state of the component in different positions in different stages of the laser shock peening process, the global customized pulse current is applied in stages, and the specific steps are as follows:

[0058] (1) adjust the pulse current waveform to a rectangular wave, and adjust the pulse width τ1=100 μs;

[0059] (2) adjust the pulse current frequency to f1=100 Hz, adjust the pulse current peak value J m1 =100 A / mm 2 , start the power supply, and make the material temperature stable at about T1=920 ℃;

[0060] (3) after 250 s, adjust the pulse current frequency to f2=1000 Hz, and adjust the pulse current peak value J m2 =25 A / mm 2 , so that the component surface temperature is stable at about T2=400 ℃; after the temperature is stable, the laser shock parameters are set as follows: the frequency is 1 Hz, the 3 mm circular spot, the overlap rate is 50%, the energy is 5 GW / cm 2 , the constraint layer is 2 mm water, the absorption layer is aluminum foil without glue, the shock area is as Figure 2 , start the laser generating device and the constraint layer and the workpiece cooperative working machine, and start the laser shock processing technology;

[0061] (4) after 200 s, the laser shock processing of all areas of the key component is completed, and the laser shock peening equipment is turned off; simultaneously, the pulse current frequency is adjusted to f3=4000 Hz, and the pulse current peak value J m3 =5 A / mm 2 , so that the component surface temperature is stable at about T3=350 ℃;

[0062] (5) after 100 s, the pulse current generating device is turned off, and the complete pulse current global auxiliary laser shock peening processing process is completed.

[0063] TC4 titanium alloy samples with the size of 60×10×4 mm 3 without any treatment and treated by the same laser shock peening parameters as the present application are respectively recorded as S0 and S1; the sample treated by the method of the present application is recorded as S2.

[0064] Table 1 is the surface hardness value of S0, S1, S2 samples. As shown in Table 1, the surface hardness of S0 is 340HV, the surface hardness of S1 is 382HV, and the surface hardness of S2 is 456HV. Compared with S1, the surface hardness of S2 is improved by 74HV, about 19.4%, and compared with S0, it is about 34.1%, so it can be seen that the surface hardness of the sample treated by E P-LSP is more obviously improved than that of the sample treated by LSP, and E P-LSP can better improve the surface hardness of the material. The tensile strength and elongation of S2 are 1100MPa and 21% respectively, and compared with S1, they are improved by 19.4% and 50% respectively. The elongation of S1 has decreased.

[0065] Table 1

[0066] Specimen Hardness / HV Tensile strength / MPa Elongation S0 (original) 340 921 14％ S1 (LSP) 382 1020 12％ S2 (EP-LSP) 456 1100 21％

[0067] Therefore, the method of pulse current full domain auxiliary laser shock peening can obviously improve the elongation of the material, and better improve the hardness mechanical properties and fatigue resistance of the material.

[0068] The above-described embodiments are only descriptions of the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for pulsed current-assisted global laser shock enhancement, characterized in that, The method includes: Before the first stage of laser shock enhancement is initiated, the electrical pulse generator is activated, and the pulse current waveform and pulse width τ1 are adjusted. The pulse current frequency and pulse current peak value are f1 and J, respectively. m1 That is, a low-frequency high-energy pulsed current is applied to the component to be treated, so that the pulsed current is uniformly applied to the entire depth direction of the component to be treated, so that the material temperature is stabilized at around temperature T1. After stabilizing for a time period of t1', the residual stress inside the component to be treated is released, and a component to be strengthened with uniformly distributed structure along the depth direction is obtained. At time t1, during the second stage of laser shock enhancement, the pulse current pulse width and frequency are swapped to τ2 and the intermediate frequency f2, respectively, and the peak value J of the pulse current is adjusted. m2 The process involves applying a medium-frequency, medium-energy pulsed current to the component to be strengthened, which has a uniformly distributed structure along the depth direction, to stabilize the surface temperature of the component at around T2. After the temperature stabilizes at T2, the laser generator, the constraint layer, and the workpiece working robot are activated to begin the laser shock processing. Utilizing the skin effect of the medium-frequency pulsed current, the medium-frequency, medium-energy pulsed current is concentrated on the entire depth range of the area to be processed, resulting in a component with an ultra-large strengthening depth. The electrical pulse is stabilized at the T2 temperature for a duration of t2'. At time t2, after the laser shock in all areas of the third stage has been completed (i.e., after time period t2), the laser shock enhancement equipment is shut down; simultaneously, the pulse current pulse width and frequency are changed to τ3 and high frequency f3, respectively, and the peak value of the pulse current J is adjusted. m3 That is, a high-frequency low-energy pulsed current is applied to the component with ultra-large reinforcement depth. By utilizing the skin effect of the high-frequency low-energy pulsed current, the pulsed current is applied only to the surface and near-surface of the component with ultra-large reinforcement depth, and the surface temperature of the component is stabilized at around T3, thereby improving the temperature stability and structural stability of the nanocrystals in the surface and near-surface layers. After the temperature T3 stabilizes for a time period of t3', the pulse current generator is turned off, completing the pulse current-assisted laser shock strengthening process.

2. The method for pulsed current-assisted global laser shock enhancement according to claim 1, characterized in that, The pulse width τ is selected according to the material, and the pulse width of the three stages satisfies τ1≥τ3≥τ2≥100μs.

3. The method for pulsed current-assisted global laser shock enhancement according to claim 1, characterized in that, The electrical pulse is direct current, and the waveform can be adjusted to a rectangular wave, a half-sine wave, or a triangular wave, etc.

4. The method for pulsed current-assisted global laser shock enhancement according to claim 1, characterized in that, The frequency f1 of the low-frequency high-energy pulse current satisfies f1≤100Hz; the temperature T1 is set according to the material of the component to be treated, and is taken as a value 20~50℃ lower than the recrystallization annealing temperature of the component to be treated; t1' is selected according to the component to be treated, and is taken as 100s≤t1'≤500s.

5. The method for pulsed current-assisted global laser shock enhancement according to claim 1, characterized in that, f2 is determined based on the thickness d1 of the component to be strengthened and the material properties of the component: Where, ρ e denoted as resistivity and μ as magnetic permeability.

6. The method for pulsed current-assisted global laser shock enhancement according to claim 1, characterized in that, T2 is determined based on the material properties of the component to be strengthened. at max / kln(c0 / c S )-m≤T2≤-Q m / kln(a 2 / 12D0)-m Among them, Q m The activation energy is given by α, the lattice constant is given by α, the Boltzmann constant is given by β, D0 is the diffusion coefficient is given by umax, the maximum energy of the interaction between dissolved atoms and dislocations is given by umax, and c0 is the average concentration of the solute element is given by c. s It represents the maximum concentration of solute atoms in the alloy; m is the temperature drop caused by the non-thermal effect of the pulse current.

7. The method for pulsed current-assisted global laser shock enhancement according to claim 1, characterized in that, t2' is the same as the laser shock treatment time.

8. The method for pulsed current-assisted global laser shock enhancement according to claim 1, characterized in that, The constraint layer for laser shock strengthening is a flowing water layer, and the remaining parameters are selected based on the material.

9. The method for pulsed current-assisted global laser shock enhancement according to claim 1, characterized in that, f3 is determined based on the thickness d1 of the component in the area to be treated, the thickness d2 of the plastic deformation layer, and the material properties of the component to be treated. Where, ρ e denoted as resistivity and μ as magnetic permeability.

10. The method for pulsed current-assisted global laser shock enhancement according to claim 1, characterized in that, Temperature T3 is the low-temperature tempering temperature of the material to be treated; t3' is selected according to the component, and is taken as 10s≤t3'≤50s.

Images