CN106893855A - A kind of turbo blade dominates the two-sided asynchronous excitation impact reinforcing method in side - Google Patents

Abstract

The invention relates to a double-sided asynchronous laser shock strengthening method for the leading edge of a turbine blade. Two laser beams with the same wavelength, pulse width, spot diameter, and pulse energy are used to asynchronously perform double-sided laser shock strengthening on the leading edge of the turbine blade, that is, one laser beam is used to carry out laser shock strengthening along the front of the leading edge of the blade, and the delay is delayed for a period of time. At the same position, another laser beam with the same parameters is used for laser shock strengthening on the back. The starting point and impact path of laser shock strengthening on the front and back of the leading edge of the blade are the same; The time required for the shock wave to propagate to the back of the blade and the front laser beam first, according to this double-sided asynchronous shock method, the laser shock strengthening is continuously performed on the blade until the impact area of the front and back of the leading edge of the blade is completed.

Description

A double-sided asynchronous laser shock strengthening method for the dominant edge of a turbine blade

technical field

The invention relates to the field of laser processing, in particular to a designed asynchronous double-sided laser shock strengthening method to achieve a better strengthening effect on the dominant edge of a turbine blade.

technical background

Laser shock peening/processing (LSP) is a new type of surface strengthening technology, which has the characteristics of "three highs and one fast": high energy (tens of J), high pressure (GPa-TPa), high strain rate (10 ⁷ S ^-1 ) and ultrafast (ns). Its main action process is that the high-energy, ultra-fast laser passes through the transparent confinement layer and irradiates the surface of the metal material with the absorbing layer. The absorbing layer absorbs the laser energy and quickly forms explosive gasification and evaporation, generating high-temperature and high-pressure plasma, plasma The laser energy is absorbed to form a shock wave that expands outward. Due to the constraint of the outer layer, the high-pressure shock wave propagates into the material, and the force effect of the shock wave is used to plastically deform the surface layer of the material, which changes the microstructure of the surface material. At the same time, it introduces Residual compressive stress can improve the strength, hardness, wear resistance and stress corrosion resistance of materials, especially effectively improve the fatigue fracture resistance of materials and increase the fatigue life of materials.

When laser shock strengthening is performed on the leading edge of a turbine blade, since the leading edge of the blade is thin, when the laser energy is large, the induced shock wave pressure is too large to easily cause macroscopic deformation of the leading edge of the blade, resulting in damage to the blade. When the laser energy is small, the induced If the generated shock wave pressure is too small, a stable and maximum plastic deformation cannot be formed inside the blade, and the strengthening effect is not good. Therefore, how to generate the maximum plastic deformation inside the blade and obtain the best strengthening effect without causing damage to the blade due to macroscopic deformation has become an urgent problem to be solved.

Contents of the invention

In view of the above problems, the present invention proposes a double-sided asynchronous laser shock strengthening method for the leading edge of a turbine blade. Two laser beams with the same wavelength, pulse width, spot diameter, and pulse energy are used to asynchronously perform double-sided laser shock strengthening on the leading edge of the turbine blade, that is, one laser beam is used to carry out laser shock strengthening along the front of the leading edge of the blade, and the delay is delayed for a period of time. At the same position, another laser beam with the same parameters is used for laser shock strengthening on the back. The starting point and impact path of laser shock strengthening on the front and back of the leading edge of the blade are the same; The time required for the shock wave to propagate to the back of the blade and the front laser beam first, according to this double-sided asynchronous shock method, the laser shock strengthening is continuously carried out on the blade until the impact area of the front and back of the leading edge of the blade is completed. Studies have shown that when the peak pressure P satisfies 2V _HEL <P<2.5V _HEL , the maximum plastic deformation can be obtained inside the target. In the present invention, the front laser beam of the leading edge of the blade is mainly used to produce plastic deformation, and the delayed back laser beam is mainly used to offset the shock wave pressure that produces macroscopic deformation, thereby obtaining the largest plastic deformation. If it is too large, it will cause macroscopic deformation of the leading edge of the blade.

The specific implementation steps are as follows:

(1) According to the material and thickness of the turbine blade, determine the delay time _t of double- _{sided asynchronous} laser shock strengthening on the leading edge. Calculated, where L is the thickness of the blade, _C0 is the wave velocity of the stress wave, E is the elastic modulus, υ is Poisson's ratio, ρ is the material density, and the delay time of the double-sided asynchronous laser shock strengthening of the dominant edge of the turbine blade t is taken as 0<t<t ₀ , so that the shock wave induced by the laser on the front and back is within the blade from the front of the blade meet at the point, the yield strength of the blade material under the dynamic load is For permanent plastic deformation to occur, the peak pressure generated by laser shock strengthening must be greater than the Hugoniot elastic limit (HEL) V _HEL of the material, and V _HEL satisfies the formula: In the formula, υ is Poisson's ratio.

(2) Use a laser beam to perform laser shock strengthening on the front of the leading edge of the turbine blade. The laser shock strengthening processing parameters are: laser pulse energy 1-50J, laser pulse width 10-40ns, repetition frequency 0.5-10Hz; spot diameter D ＝1-6mm, the peak pressure of laser shock strengthening is determined by Draw, wherein, α is the distribution coefficient of internal energy, is taken as 0.1, and I ₀ is the laser power density, E is the laser energy (J), d is the spot diameter (cm), τ is the laser pulse width (ns), Z is the reduced acoustic impedance, Z _target is the acoustic impedance of the target, and Z _overlay is the acoustic impedance of the constrained layer, satisfying The laser light intensity obeys the Gaussian distribution, and the space-time distribution of the pressure pulse is expressed by the following quasi-Gaussian formula: P(x,y,t)=Pexp[-(x ² +y ² )/2R ² ], where x, y is the surface coordinate, and R is the radius of the spot; studies have shown that when the peak pressure P satisfies 2V _HEL <P<2.5V _HEL , the workpiece can obtain the maximum plastic deformation. In order to obtain a better laser shock strengthening effect, the shock wave peak pressure should meet 2V _HEL <P<2.5V _HEL , and the pressure value P(R)>V _HEL at the edge of the spot, so that the blade can obtain the maximum plastic deformation, and the transverse and longitudinal overlap rate of laser shock strengthening is 50%.

(3) Timing starts after the starting point of laser shock strengthening on the front of the leading edge of the blade is impacted. After a delay of t seconds, the second laser beam begins to perform laser shock strengthening on the same position on the back of the leading edge of the blade; laser shock strengthening on the front and back of the leading edge of the blade The parameters of the laser beam used are the same, the starting point and impact path of laser shock strengthening on the front and back of the leading edge of the blade are the same, and the transverse and longitudinal overlap rates are both 50%.

(4) According to this double-sided asynchronous impact method, laser shock strengthening is continuously performed on the leading edge of the blade until the impact area of the front and back of the leading edge of the blade is impacted, and the entire laser shock strengthening process ends.

Description of drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings that are used in the examples or the description of the prior art.

Figure 1 is a schematic diagram of double-sided asynchronous laser shock peening on the leading edge of a turbine blade.

Figure 2 is a plane view of an aircraft turbine blade.

Fig. 3 is a schematic diagram of the waveform of the double-sided asynchronous laser shock strengthening of the dominant edge of the turbine blade (in the figure, the laser beam 2 is emitted with a delay of t seconds after the laser beam 1 is emitted, and the shock wave induced by the laser beam 1 first propagates inside the dominant edge of the blade, and then interacts with the laser beam The shock wave induced by beam 2 is within the leading edge of the blade from the front of the blade where L is the thickness of the blade, C ₀ is the wave velocity of the stress wave, and shock waves in opposite directions cancel each other out).

Table 1 shows the comparison of material residual stress under different experimental parameters

The meanings of the symbols in the figure are as follows:

Figure 1: 1. Laser beam; 2. Water spray system; 3. Second laser beam; 4. Blade.

Figure 2: 4A, the front of the blade; 4B, the back of the blade.

Figure 3: 1. Laser beam; 3. Second laser beam; 4. Blade; 5. Absorbing layer; 6. Constraining layer; 7. Plasma shock wave.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings, but the present invention should not be limited to the embodiments.

The double-sided asynchronous double-sided laser shock strengthening method of the turbine blade used in this embodiment is shown in Figure 1, and the sample material is TC4.

A double-sided asynchronous laser shock strengthening method for a dominant edge of a turbine blade, the specific steps of which are:

(1) Select TC4 as the example sample, the blade thickness is 1mm, the elastic modulus of TC4 is 110GPa, Poisson's ratio is 0.34, and the density is 4.5g cm ^-3 , by the formula Calculated, C ₀ =6132m/s, substituting into the formula t ₀ =L/C ₀ , get t ₀ =16ns, where L is the thickness of the blade, C ₀ is the wave velocity of the stress wave, E is the modulus of elasticity, υ is Poisson's ratio, ρ is the material density, taking the delay time t=8ns, then the shock wave induced by the laser on the front and back will meet at the inside of the blade at a distance of 3L/4 from the front of the blade, TC4 Poisson's ratio is υ=0.34, and the dynamic yield strength is 1.43GPa, get the Hugoniot elastic limit of TC4:

(2) Use laser beam 1 to carry out laser shock strengthening on the front of the leading edge of the turbine blade. The laser shock strengthening processing parameters are: laser pulse energy is 7J, laser pulse width is 10ns, repetition frequency is 1Hz; spot diameter d=3mm; laser shock The enhanced peak power is given by:

in, Substitute, E=10J, d=3mm, τ=10ns, α is 0.1, Z _water ＝1.14×10 ⁶ g·cm ^-2 ·s ^-1 , Z _target ＝2.75×10 ⁶ g·cm ^-2 ·s ^{- 1} , the value of P is 7.02GPa, which satisfies 5.9GPa=2V _HEL <P<2.5V _HEL ＝7.375GPa.

The shock wave pressure at the edge of the spot P=7.02×exp(-R ² /2R ² )=4.26GPa>2.95GPa=V _HEL , which satisfies the condition, and the transverse and longitudinal overlap rate of laser shock strengthening is 50%.

(3) Timing starts after the starting point of laser shock strengthening on the front of the leading edge of the blade is impacted. After a delay of 10 ns, the second laser beam 3 begins to perform laser shock strengthening on the same position on the back of the leading edge of the blade; laser shock strengthening on the front and back of the leading edge of the blade The parameters of the laser beam used (such as wavelength, pulse width, spot diameter, laser energy, etc.) are the same, the starting point and impact path of laser shock strengthening on the front and back of the leading edge of the blade are the same, and the transverse and longitudinal overlap rates are both 50%.

(4) According to this double-sided asynchronous impact method, laser shock strengthening is continuously performed on the leading edge of the blade until the impact area of the front and back of the leading edge of the blade is impacted, and the entire laser shock strengthening process ends.

Table 1 shows the comparison of residual stress under different experimental parameters, which are divided into single-sided laser shock strengthening, double-sided synchronous laser shock strengthening and double-sided asynchronous laser shock strengthening designed by this method. The parameters used for the three kinds of laser shock strengthening are: laser The pulse energy is 7J, the laser pulse width is 10ns, and the repetition frequency is 1Hz; the spot diameter is d=3mm; the delay time of double-sided asynchronous laser shock peening is 8ns, and the residual stress test is carried out after laser shock peening. Each sample is tested for 5 The residual stress at each point is respectively the residual stress value at the surface, L/4, L/2, 3L/4, and L from the surface.

From the comparison of residual stress in Table 1, it can be seen that when single-sided laser shock peening, the surface is residual compressive stress, and the value of residual compressive stress gradually decreases with the increase of the depth from the surface; when double-sided laser shock peening, The residual compressive stress at the surface and depth L is the largest, the stresses at L/4 and 3L/4 are roughly the same, and both are smaller than the residual compressive stress at the surface, and the residual tensile stress appears at L/2, that is, when the shock wave meets Residual tensile stress appears at the position; when double-sided asynchronous laser shock peening, there is the largest residual compressive stress at the surface and depth L, and the depths L/4, L/2, and 3L/4 all show residual compressive stress; compared with Single-sided laser shock peening, this method produces larger residual compressive stress at the surface and depth L, compared with double-sided synchronous laser shock peening, this method has no residual tensile stress in the area where the shock waves meet, therefore, it can be It can be seen that this method can produce a better residual compressive stress field, and the residual compressive stress has a direct relationship with the improvement of blade fatigue life, so the blade treated by this method can obtain better fatigue life.

Table 1

state surface L/4 L/2 3L/4 L single impact -703MPa -501MPa -201MPa -90MPa 12MPa Simultaneous impact on both sides -712MPa -493MPa 73MPa -482MPa -707MPa Double-sided asynchronous impact -709MPa -512MPa -287MPa -334MPa -720MPa

Claims (7)

1. A turbine blade leading edge double-sided asynchronous laser shock peening method is characterized in that: two laser beams with the same wavelength, pulse width, spot diameter and pulse energy are adopted to asynchronously carry out double-sided laser shock strengthening on the main guide edge of the turbine blade, namely one laser beam is used for carrying out laser shock strengthening along the front side of the main guide edge of the blade, another laser beam with the same parameters is adopted to carry out laser shock strengthening on the back side at the same position after a period of time t is delayed, and the starting point and the shock path of the laser shock strengthening on the front side and the back side of the main guide edge of the blade are the same; and for the time difference between the front laser beam and the back laser beam at the same position of the main guide edge, which is smaller than the time required by the front shock wave to propagate to the back of the blade, and the front laser beam is first, continuously carrying out laser shock strengthening on the blade according to the double-sided asynchronous shock method until the shock of all shock areas of the front and the back of the main guide edge of the blade is finished.

2. The turbine blade leading edge double-sided asynchronous laser shock peening method as recited in claim 1, comprising the steps of:

(1) determining the delay time t of the double-sided asynchronous laser shock peening of the main leading edge of the turbine blade according to the material and the thickness of the turbine blade;

(2) carrying out laser shock strengthening on the front surface of the main guide edge of the turbine blade by using laser beams;

(3) starting timing after the starting point of the front laser shock peening of the main leading edge of the blade is impacted, and delaying for t seconds, and then starting laser shock peening on the same position of the back of the main leading edge of the blade by a second laser beam;

(4) and continuously carrying out laser shock strengthening on the main guide edge of the blade according to the double-sided asynchronous shock method until all shock areas on the front surface and the back surface of the main guide edge of the blade are shocked, and finishing the whole laser shock strengthening process.

3. The turbine blade leading edge double-sided asynchronous laser shock peening method as recited in claim 2, wherein: in the step (1), the delay time t of the double-sided asynchronous laser shock peening of the main guide edge of the turbine blade is 0<t<t₀So that the shock waves induced by the laser on the front and back surfaces are spaced from the front surface of the blade inside the bladeWhere L is the blade thickness, C₀Is the wave velocity of the stress wave; t is t₀The time for a stress wave generated in the material to propagate to the bottom of the material, t₀＝L/C₀，Wherein E is the elastic modulus, upsilon is the Poisson ratio, and rho is the density of the turbine blade material.

4. The turbine blade leading edge double-sided asynchronous laser shock peening method as recited in claim 2, wherein: in the step (2), the laser shock peening parameters are as follows: laser energy is 1-50J, laser pulse width is 10-40ns, and repetition frequency is 0.5-10 Hz; the diameter D of the light spot is 1-6 mm; the laser shock peening peak pressure P satisfies 2V_HEL<P<2.5V_HELDuring the process, the workpiece can obtain maximum plastic deformation, and the peak pressure of the shock wave can meet 2V for obtaining better laser shock strengthening effect_HEL<P<2.5V_HELAnd the pressure value P (R) of the light spot edge>V_HELSo as to obtain maximum plastic deformation of the blade; v_HELIs the Hugoniot Elastic Limit (HEL), V, of the blade material_HELSatisfies the formula:wherein upsilon is Poisson's ratio;is the yield strength of the blade material under dynamic loading.

5. The turbine blade leading edge double-sided asynchronous laser shock peening method of claim 4, wherein: the peak pressure of laser shock peening is obtained by

$P\left(GPa\right)=0.01\sqrt{\frac{\mathrm{\&alpha;}}{2\mathrm{\&alpha;}+3}}\sqrt{Z(g/{\mathrm{cm}}^2{s}^{-1})}\sqrt{I_0(GW/{\mathrm{cm}}^2)}$

Wherein α is distribution coefficient of internal energy, and is 0.1, I₀In order to be the power density of the laser,e is laser energy (J), d is spot diameter (cm), τ is laser pulse width (ns), Z is reduced acoustic impedance, and Z is reduced acoustic impedance_targetIs the acoustic impedance of the target material, Z_overlayTo constrain the acoustic impedance of the layer

6. The turbine blade leading edge double-sided asynchronous laser shock peening method as recited in claim 1 or 2, wherein: the laser intensity follows Gaussian distribution, and the space-time distribution condition of the pressure pulse is represented by the following quasi-Gaussian formula: p (x, y, t) ═ Pexp [ - (x)²+y²)/2R²]In the formula, x and y are surface coordinates, and R is a spot radius.

7. The turbine blade leading edge double-sided asynchronous laser shock peening method as recited in claim 1 or 2, wherein: the transverse and longitudinal lap joint rates of laser shock strengthening of the front surface and the back surface of the main guide edge of the blade are both 50%.