Disclosure of Invention
The invention aims to provide a method for realizing ultrahigh strain rate plastic deformation strengthening in metal.
The specific scheme for realizing the aim of the invention is as follows:
a method for realizing ultrahigh strain rate plastic deformation strengthening in metal comprises the following steps:
step 1, processing a metal material into the shape of a sample with a required shape according to the density and the elastic modulus of the metal material, so that ultrasonic waves can generate resonance in a deformation area to form ultrahigh-frequency stress waves;
in step 1, the sample is a tensile sample with a middle part in a uniform cross section plate shape, and the sample is full of
The foot ultrasonic wave can generate resonance in a deformation area and needs the resonance length L3The following formula is satisfied:
using the vibration equation U (x) of the longitudinal direction of the sample as:
wherein:
sample resonant length L3Comprises the following steps:
the maximum stress amplitude of the plate-shaped sample is as follows:
the displacement stress coefficient is:
A0=μI
wherein L is1Is the half length of the plastic deformation zone of the specimen, L2The parallel distance of the arc transition ends is b1Thickness of the plastically deformed region of the specimen, b2The thickness of the connecting end; e is the modulus of elasticity; rho is density; the resonant frequency f of the ultra-high strain rate loading system is 20 kHz. C is the longitudinal wave velocity; w is the angular velocity; mu is a displacement amplification coefficient corresponding to the equipment, and the equipment mu used in the invention is 16; i is the current (which can be regulated) supplied by the device power supply; alpha is alpha1,β1And k is a physical derivation process quantity, which can be represented by a basic quantity.
Step 2: connecting the processed sample with an ultrasonic device, and selecting the ultrasonic power.
The step 2 specifically comprises the following steps: the peak value of the ultrasonic loading should be higher than the yield strength of the sample material
And step 3: one end of the sample is connected with the bottom end of the ultrasonic equipment amplifier through the internal thread, and the other end of the sample is free.
And 4, step 4: and starting ultrasonic resonance, transmitting the longitudinal wave of the mechanical vibration to the free end of the sample, reflecting the longitudinal wave, generating resonance between the frequency of the reflected wave and the frequency of the incident wave, forming a load of ultrahigh frequency stress along the axial direction of the sample, and forming plastic deformation on the sample.
And 4, circularly cooling the sample by adopting cooling liquid.
Under the action of ultrahigh frequency alternating load, the material has obvious internal friction heat generation, and the deformation tissue generated by plastic deformation caused by overhigh temperature is prevented from being subjected to recovery recrystallization.
Compared with the prior art, the invention has the following remarkable advantages:
(1) the extremely high frequency during resonance enables the single loading time to be extremely short, so that the strain rate of the metal is extremely high, and the strain rate of the metal subjected to plastic deformation by the method far exceeds that of the traditional cold deformation mode.
(2) The invention adopts a processing mode to change the shape of the metal very little, and can strengthen the metal material under the condition of basically not changing the shape, while the traditional deformation means has a larger change to the shape and the size of the sample.
(3) In the plastic deformation treatment process of the metal material, one end of the metal material is always exposed, so that the exposed end of the metal material can be soaked in liquid nitrogen for continuous deep cooling plastic deformation, which cannot be realized by the traditional plastic deformation mode.
(4) The method has the advantages of simple operation process, good controllability and high efficiency.
Detailed Description
The invention will be further explained with reference to the drawings and the embodiments
Example 1
Ultra-high rate plastic deformation processing of 316L stainless steel.
1. The 316L stainless steel was cut into test samples as shown in fig. 1, and the surface was polished smooth using sandpaper. Relevant parameters for a given 316L stainless steel sample: f 20kHz, E206 GPa, p 7.85g/cm3L1-25 mm, L2-20 mm, b 1-3 mm, b 2-12 mm according to the formula in step 1
Wherein:
sample resonant length L3Comprises the following steps:
the resonance length L3 is 8.78mm
2. Setting ultrasonic parameters, wherein the peak value of ultrasonic loading is higher than the yield strength of a sample material according to the setting standard of the parameters, the more the peak value is higher than the yield strength of an original material, the more the strengthening is generally obvious according to the step 2, the known yield strength of the adopted 316L stainless steel is about 300MPa, the load peak value is set to be 390MPa, and the loading current I is calculated through a formula according to the load peak value.
A0=μI(μ=16)
Calculated to obtain 2.5 ampere
3. The 316L stainless steel sample was plastically deformed at an ultra-high strain rate of 20 minutes, during which time water was continuously sprayed as a cooling liquid onto the surface so that the temperature did not rise excessively.
The characterization results of the deformed part of the treated 316L stainless steel sample are as follows:
in FIG. 4, the left graph is the metallographic graph of the 316L stainless steel original sample before treatment, and the right graph is the metallographic graph of the 316L stainless steel after plastic deformation at ultrahigh strain rate
As can be seen from the gold phase diagram, a large amount of deformed tissues appear in the 316L stainless steel treated by the invention, and obvious plastic deformation is seen.
b. Hardness test
The Vickers microhardness tester is used for testing the original 316L stainless steel material and the 316L stainless steel material treated by the invention, and the result shows that the Vickers hardness of the original sample is about 160Hv, and the Vickers hardness of the original sample reaches 220Hv after the original sample is plastically deformed at the ultrahigh strain rate. A significant hardness increase is shown.
Example 2
Ultra-high rate plastic deformation treatment of 5a02 aluminum alloy.
1. The 5a02 aluminum alloy was cut into test specimens as shown in fig. 1, and the surface was smoothed using sandpaper. Given the relevant parameters for the 5a02 aluminum alloy sample: f 20kHz, E71 GPa, p 2.7g/cm3,L1=24mm,L2=20mm,,b1=6mm,b2=14mm
According to the correlation formula in step 1
Wherein:
sample resonant length L3Comprises the following steps:
the resonance length L3 was calculated to be 10 mm.
2. Setting ultrasonic parameters, wherein the peak value of ultrasonic loading is higher than the yield strength of the sample material according to the setting standard of the parameters, the more the peak value is higher than the yield strength of the original material, the more the strengthening is generally more obvious according to the step 2, the yield strength of the adopted 5A02 aluminum alloy is known to be about 120MPa, and the peak value of the loading is set to be 200 MPa.
And calculating the loading current I according to the peak value of the load through a formula.
A0=μI(μ=16)
Calculated to obtain 1.8 ampere
3. The 5a02 aluminum alloy specimens were plastically deformed at an ultra-high strain rate for about 10 minutes without excessive temperature increase during the deformation by continuously spraying the surface with water as a coolant.
The deformation parts of the treated 5A02 aluminum alloy sample are characterized as follows:
in the attached figure 5, the left picture is a polarizing microscope metallographic picture of a 5A02 aluminum alloy original sample before treatment, and the right picture is a metallographic picture of a 5A02 aluminum alloy after plastic deformation at an ultrahigh strain rate
As can be seen from the gold phase diagram, a large amount of deformed structures appear in the 5A02 aluminum alloy treated by the method, the structures are obviously thinned, and the obvious plastic deformation is seen.
b. Hardness test
The Vickers microhardness tester is used for testing the original 5A02 aluminum alloy material and the 5A02 aluminum alloy material treated by the invention, and the result shows that the Vickers hardness of the original sample is about 60Hv, and the Vickers hardness of the original sample reaches 100Hv after the original sample is plastically deformed at an ultrahigh strain rate. A significant hardness increase is shown.
Example 3
Ultra-high speed plastic deformation treatment of red copper.
1. The red copper was cut into test samples as shown in fig. 1, and the surface was polished smooth using sandpaper.
Relevant parameters for a given red copper sample: f 20kHz, E108 GPa, p 8.9g/cm3,L1=16mm,L2=12mm,b1=3mm,b2=10mm。
According to the correlation formula in step 1
Wherein:
sample resonant length L3Comprises the following steps:
the resonance length is calculated, and L3 is 9.4mm
2. Setting ultrasonic parameters, wherein the peak value of ultrasonic loading is higher than the yield strength of the sample material according to the setting standard of the parameters, and according to the step 2, the more the peak value is higher than the yield strength of the original material, the more the strengthening is generally obvious, the yield strength of the adopted red copper is known to be about 120MPa, and the load peak value is set to be 300 MPa. And calculating the loading current I according to the peak value of the load through a formula.
A0=μI(μ=16)
Calculated to obtain 2.2A
3. The red copper sample was subjected to plastic deformation at an ultra-high strain rate for about 5 minutes, during which time water was continuously sprayed as a cooling liquid onto the surface thereof so that the temperature thereof was not excessively increased.
The characterization results of the deformed part of the treated red copper sample are as follows:
in the attached figure 6, the left picture is the gold phase picture of the polarizing microscope of the original red copper sample before treatment, and the right picture is the gold phase picture of the red copper after plastic deformation at ultrahigh strain rate
As can be seen from the gold phase diagram, a large amount of deformed tissues appear in the red copper treated by the method, the tissues are obviously thinned, and the obvious plastic deformation of the tissues is seen.
b. Hardness test
The vickers microhardness tester is used for testing the original red copper and the red copper treated by the method, and the result shows that the vickers hardness of the original sample is about 60Hv, and the vickers hardness of the original sample reaches 110Hv after the original sample is subjected to plastic deformation at an ultrahigh strain rate. A significant hardness increase is shown.
Example 4
And (3) carrying out ultrahigh-speed plastic deformation treatment on the copper-chromium pickaxe alloy.
1. Mixing copper and chromiumThe pick alloy was cut into test specimens as shown in fig. 1, and the surface was smoothed using sandpaper. Relevant parameters of a given copper-chromium pickaxe alloy sample are as follows: f 20kHz, E110 GPa, p 8.9g/cm3,L1=16mm,L2=12mm,b1=3mm,b2=11mm
According to the correlation formula in step 1
Wherein:
sample resonant length L3Comprises the following steps:
the resonance length L3 was calculated to be 8.7 mm.
2. Setting ultrasonic parameters, wherein the peak value of ultrasonic loading is higher than the yield strength of the sample material according to the setting standard of the parameters, and according to the step 2, the more the peak value is higher than the yield strength of the original material, the more the strengthening is generally obvious, the known copper-chromium pickaxe alloy has the yield strength of about 120MPa, and the peak value of the loading is set to 300 MPa.
And calculating the loading current I according to the peak value of the load through a formula.
A0=μI(μ=16)
Calculated to obtain 2.2A
3. The copper-chromium pickaxe alloy sample is subjected to plastic deformation with an ultrahigh strain rate of about 5 minutes, and water is continuously sprayed on the surface of the copper-chromium pickaxe alloy sample as a cooling liquid during the deformation so that the temperature of the copper-chromium pickaxe alloy sample is not excessively increased.
The characterization result of the deformation part of the processed copper-chromium pickaxe alloy sample is as follows:
FIG. 7 shows the left diagram of the gold phase of a polarizing microscope of an original sample of copper-chromium-zirconium alloy before treatment and the right diagram of the phase of copper-chromium-zirconium alloy after plastic deformation at an ultra-high strain rate
As can be seen from the gold phase diagram, a large amount of deformed tissues appear in the copper-chromium-zirconium alloy treated by the method, the tissues are obviously refined, and the obvious plastic deformation of the tissues is seen.
b. Hardness test
The original copper chromium zirconium alloy and the copper chromium zirconium alloy treated by the invention are tested by using a Vickers microhardness tester, and the result shows that the Vickers hardness of the original sample is about 90Hv, and the Vickers hardness of the original sample reaches 140Hv after the original sample is subjected to plastic deformation at an ultrahigh strain rate. A significant hardness increase is shown.
In the invention, the selection of resonance frequency is that the higher the resonance frequency is, the shorter the single loading time is, a formula d epsilon/dt is calculated according to the strain rate, wherein epsilon is strain, t is time, d epsilon can be obtained from an engineering stress-strain curve of a metal material needing to be strengthened, specifically, the strength point corresponding to the stress amplitude from an obvious yield point to resonance is actual strain, dt is related to the resonance frequency of a system, the loading time in one period is 1/f, and dt is the time t of the period where the plastic deformation actually occursσ-tMAXAs shown in FIG. 3, then Δ t is calculated to be 10 according to the resonant frequency of the apparatus 20000Hz-6Level, true and trueThe peak value of the stress reaches more than 1.3 times of the yield strength of the material, and the average strain rate can reach 103. The shorter the time the higher the strain rate when the strain is constant. Increasing the strain rate can be achieved by increasing the resonant frequency.
2: stress amplitude, the stress amplitude is given a relevant calculation formula in step 1, which is mainly determined by the loading current of the ultrasonic generator, and the required loading current can be obtained by calculating the required stress amplitude. The key to its selection is that the stress amplitude of the ultrasound in the resonance region must correspond to a load that far exceeds the yield strength of the sample.
The ultrasonic wave is a mechanical wave, a longitudinal wave of mechanical vibration is transmitted to the free end of the sample and then reflected, the frequency of the reflected wave is consistent with that of the incident wave, and two lines of interference waves generate resonance, so that a load of ultrahigh frequency stress is formed along the axial direction of the sample. One end of the sample is connected with the bottom end of the amplifier through an internal thread, and the other end is free (see figure 2 in detail). From the steps 1 and 2, the stress amplitude of the middle parallel section of the sample is the largest and is a plastic deformation area.