CN110629012A - A method for ultrahigh strain rate plastic deformation strengthening in metals - Google Patents

Abstract

The invention is a method for realizing superhigh strain rate plastic deformation strengthening in metal, and realizes superhigh strain rate plastic deformation through ultrasonic resonance. Ultrasonic waves are locally resonated to obtain extremely high and fast stress waves, resulting in plastic deformation with ultra-high strain rates. According to the plastic deformation theory of metal materials, it can achieve changes in the internal microstructure of metal materials, and finally achieve material strengthening. . This method passes high-energy ultrasonic waves through the interior of the metal material and makes it resonate locally in the metal material, thereby generating an ultra-high-frequency stress sine wave. Because the stress peak value is much higher than the yield strength of the material, the material undergoes an ultra-high strain rate. plastic deformation.

Description

A method for ultrahigh strain rate plastic deformation strengthening in metals

technical field

The invention relates to a method for realizing ultra-high strain rate plastic deformation strengthening in metals, and relates to the field of metal strengthening.

Background technique

Plastic deformation will lead to changes in the internal microstructure of metal materials, dislocation proliferation, movement, rearrangement and annihilation, etc. Severe plastic deformation can refine the grains of metal materials to submicron or even nanometer level, and can effectively prepare bulk ultrafine-grained materials with excellent mechanical properties, high density, and pollution-free. Common severe plastic deformation methods include high-pressure torsion, rotary forging, equal channel extrusion (ECAP), etc. Traditional plastic deformation methods such as forging, rolling or extrusion, etc., can also perform large plastic deformation on metal materials and make them Significant changes occurred in the microstructure. Metals treated with severe plastic deformation have high strength, high hardness and good friction properties, and become one of the very important strengthening methods for metals and metal matrix composites.

Wu et al published a paper entitled "Heterogeneous lamella structure units ultrafine-grain strength with coarse-grain ductility", which discloses a pure titanium with a heterogeneous layered structure with high strength and high plasticity. This structure introduces a rich microstructure through large plastic deformation. Soft recrystallized composition of isomerically pure titanium. The novel titanium metal rod prepared by the method can achieve both the high strength of the ultrafine grain and the high toughness of the coarse grain to a certain extent through the deformation coordination effect of the heterogeneous structure, and improve the comprehensive performance of the titanium metal.

Chinese invention patent application number: 99122670.4 discloses a method of impacting the surface of metal materials with rigid shot steel balls, causing severe plastic deformation on the surface of the substrate, with a high strain rate during deformation, so as to realize the refinement of the surface structure to nanometer size. Its limitation is that it can only plastically deform the surface of the metal material without changing the overall structure of the material.

A Chinese invention patent for an equal-channel extrusion device application number: 200710030188.4 discloses a method for preparing ultra-fine-grained materials by overall severe plastic deformation. Through the action of extrusion force, pure shear plastic deformation of metal materials occurs, thereby introducing rich Microstructure, refine the grain. Its limitations are: the overall appearance of the processed material is deformed, and its strain rate is not high during the plastic deformation process.

Contents of the invention

The purpose of the present invention is to provide a method for realizing ultra-high strain rate plastic deformation strengthening in metals.

Realize the specific scheme of the object of the present invention as follows:

A method of achieving ultrahigh strain rate plastic deformation strengthening in metals by:

Step 1. Process the metal material into the shape of the desired shape sample according to its density and elastic modulus, so that the ultrasonic wave can resonate in the deformation area to form an ultra-high frequency stress wave;

In step 1, the sample is a tensile sample with a central equal-section plate, and the sample is full of

Foot ultrasound can generate resonance in the deformed region, and its resonance length L3 needs to satisfy the following _formula :

The longitudinal vibration equation U(x) of the sample is:

in:

The resonant length L3 _of the sample is:

The maximum stress amplitude of the plate sample is:

The displacement stress coefficient is:

A ₀ =μI

Where L ₁ is the half length of the plastic deformation zone of the sample, L ₂ is the parallel distance of the arc transition end, b ₁ is the thickness of the plastic deformation zone of the sample, b ₂ is the thickness of the connecting end, E is the modulus of elasticity; ρ is Density; the resonant frequency f=20kHz of the ultra-high strain rate loading system. C is the longitudinal wave velocity; w is the angular velocity; μ is the displacement amplification factor corresponding to the equipment, and the equipment used in the present invention μ=16; I is the current provided by the equipment power supply (can be adjusted); α ₁ , β ₁ , k are physical derivation processes Quantities, which can be represented by base quantities.

Step 2: Connect the processed sample to the ultrasonic equipment and select the ultrasonic power.

Step 2 is specifically: the peak value of ultrasonic loading should be higher than the yield strength of the sample material

Step 3: Make sure that one end of the sample is connected to the bottom of the ultrasound equipment amplifier through the internal thread, and the other end is free.

Step 4: Start ultrasonic resonance, the longitudinal wave of mechanical vibration is transmitted to the free end of the sample and then reflected, the frequency of the reflected wave resonates with the incident wave, forming a load of ultra-high frequency stress along the axial direction of the sample, and forming plastic deformation on the sample.

In step 4, the sample is cooled by circulating cooling liquid.

Under the action of ultra-high frequency alternating load, the internal friction heat generation of the material is more obvious, so as to prevent the recovery and recrystallization of the deformed structure caused by plastic deformation caused by excessive temperature.

Compared with the prior art, the present invention has significant advantages as follows:

(1) The extremely high frequency during resonance makes the single loading time very short, so that the strain rate is very high, so the strain rate achieved by the present invention when plastically deforming metal far exceeds the traditional cold deformation method.

(2) The present invention adopts the processing method to change the shape of the metal very little, and can strengthen the metal material without changing the shape basically, while the traditional deformation means has a large change to the shape of the sample.

(3) During the plastic deformation treatment process of the metal material, one end of the metal material is always exposed, so the exposed end can be soaked in liquid nitrogen for continuous cryogenic plastic deformation, which cannot be achieved by traditional plastic deformation methods of.

(4) The present invention has simple operation process, good controllability and high efficiency.

Description of drawings

Fig. 1 is a schematic diagram of a deformed design sample of the present invention.

Figure 2 is a schematic diagram of the ultra-high strain rate loading device.

Figure 3 is a graph showing the relationship between stress and time at any point in the resonance part.

Fig. 4 is a metallographic diagram of 316L stainless steel after plastic deformation strengthening of the present invention.

Fig. 5 is a metallographic diagram of the aluminum alloy after plastic deformation strengthening according to the present invention.

Fig. 6 is a metallographic diagram of red copper after plastic deformation strengthening in the present invention.

Fig. 7 is a phase diagram of the copper-chromium-zirconium alloy after plastic deformation strengthening of the present invention.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the present invention will be further described

Example 1

Ultra-high rate plastic deformation treatment of 316L stainless steel.

1. Cut 316L stainless steel into a test sample as shown in Figure 1, and use sandpaper to smooth the surface. Given the relevant parameters of the 316L stainless steel sample: f=20kHz, E=206GPa, ρ=7.85g/cm ³ , L1=25mm, L2=20mm, b1=3mm, b2=12mm According to the relevant formula in step 1

in:

The resonant length L3 _of the sample is:

After calculation, the resonance length L3 = 8.78mm

2. Set the ultrasonic parameters. According to the parameter setting standard, the peak value of ultrasonic loading should be higher than the yield strength of the sample material. According to step 2, the more the peak value is higher than the yield strength of the original material, the more obvious the strengthening is generally. It is known that the yield strength of the 316L stainless steel used is about 300MPa, the peak value of the load is set to 390MPa, and the loading current I is calculated by the formula according to the peak value of the load.

A ₀ =μI(μ=16)

Calculated I = 2.5 ampere

3. The 316L stainless steel sample was plastically deformed at an ultra-high strain rate for 20 minutes. During the deformation, water was used as a cooling liquid to continuously spray its surface so that the temperature would not rise excessively.

The characterization results of the deformed part of the treated 316L stainless steel sample are as follows:

In accompanying drawing 4, the left picture is the metallographic diagram of the original 316L stainless steel sample before treatment, and the right picture is the metallographic picture of the 316L stainless steel after plastic deformation at an ultra-high strain rate

It can be seen from the metallographic diagram that a large number of deformed structures appear inside the 316L stainless steel treated by the present invention, which shows that it has undergone obvious plastic deformation.

b. Hardness test

Use the Vickers microhardness tester to test the original 316L stainless steel material and the 316L stainless steel material processed by the present invention, the results show that the Vickers hardness of the original sample is about 160Hv, and its Vickers hardness after plastic deformation at an ultra-high strain rate Reached 220Hv. A significant increase in hardness is shown.

Example 2

Ultra-high rate plastic deformation treatment of 5A02 aluminum alloy.

1. Cut the 5A02 aluminum alloy into a test sample as shown in Figure 1, and use sandpaper to smooth the surface. Given the relevant parameters of the 5A02 aluminum alloy sample: f=20kHz, E=71GPa, ρ=2.7g/cm ³ , L1=24mm, L2=20mm, b1=6mm, b2=14mm

According to the relevant formula in step 1

in:

The resonant length L3 _of the sample is:

The resonant length L3=10mm is obtained through calculation.

2. Set the ultrasonic parameters. According to the parameter setting standard, the peak value of ultrasonic loading should be higher than the yield strength of the sample material. According to step 2, the more the peak value is higher than the yield strength of the original material, the more obvious the strengthening is generally. It is known that the yield strength of the 5A02 aluminum alloy used is about 120MPa, and the peak load is set to 200MPa.

According to the peak value of the load, the loading current I is calculated by the formula.

A ₀ =μI(μ=16)

Calculated I = 1.8 ampere

3. The 5A02 aluminum alloy sample was plastically deformed at an ultra-high strain rate for about 10 minutes. During the deformation, water was used as a cooling liquid to continuously spray its surface so that the temperature would not rise excessively.

The characterization results of the deformed parts of the treated 5A02 aluminum alloy sample are as follows:

In attached drawing 5, the left picture is the metallographic picture of the original sample of 5A02 aluminum alloy before treatment, and the right picture is the metallographic picture of the 5A02 aluminum alloy after plastic deformation at an ultra-high strain rate

It can be seen from the metallographic diagram that a large number of deformed structures appear inside the 5A02 aluminum alloy treated by the present invention, and the structure is obviously refined, which shows that it has undergone obvious plastic deformation.

b. Hardness test

Vickers microhardness tester is used to test the original 5A02 aluminum alloy material and the 5A02 aluminum alloy material processed by the present invention, and the results show that the Vickers hardness of the original sample is about 60Hv, and it is maintained after plastic deformation at an ultra-high strain rate. Its hardness has reached 100Hv. A significant increase in hardness is shown.

Example 3

Ultra-high rate plastic deformation treatment of copper.

1. Cut the red copper into test samples as shown in Figure 1, and use sandpaper to smooth the surface.

Given the relevant parameters of the red copper sample: f=20kHz, E=108GPa, ρ=8.9g/cm ³ , L1=16mm, L2=12mm, b1=3mm, b2=10mm.

According to the relevant formula in step 1

in:

The resonant length L3 _of the sample is:

After calculation, the resonance length is obtained, L3=9.4mm

2. Set the ultrasonic parameters. According to the parameter setting standard, the peak value of ultrasonic loading should be higher than the yield strength of the sample material. According to step 2, the more the peak value is higher than the yield strength of the original material, the more obvious the strengthening is generally. It is known that the yield strength of the copper used is about 120MPa, and the peak load is set to 300MPa. According to the peak value of the load, the loading current I is calculated by the formula.

A ₀ =μI(μ=16)

Calculated I = 2.2 ampere

3. The copper sample was plastically deformed at an ultra-high strain rate for about 5 minutes. During the deformation, water was used as a cooling liquid to continuously spray its surface so that the temperature would not rise excessively.

The results of characterization of the deformed part of the treated red copper sample are as follows:

In accompanying drawing 6, the left picture is the metallographic image of the original copper sample before treatment under the polarizing microscope, and the right picture is the metallographic picture of the copper after plastic deformation at an ultra-high strain rate

It can be seen from the metallographic diagram that a large amount of deformed structures appear inside the red copper treated by the present invention, and the structures are obviously refined, which shows that it has undergone obvious plastic deformation.

b. Hardness test

The Vickers microhardness tester was used to test the original red copper and the red copper treated by the present invention, and the results showed that the Vickers hardness of the original sample was about 60Hv, and the Vickers hardness of the original sample reached 110Hv after plastic deformation at an ultra-high strain rate. A significant increase in hardness is shown.

Example 4

Ultrahigh-rate plastic deformation processing of copper-chromium pick alloys.

1. Cut the copper-chromium pick alloy into test samples as shown in Figure 1, and use sandpaper to polish the surface smoothly. Relevant parameters of a given copper-chromium pickaxe alloy sample: f=20kHz, E=110GPa, ρ=8.9g/cm ³ , L1=16mm, L2=12mm, b1=3mm, b2=11mm

According to the relevant formula in step 1

in:

The resonant length L3 _of the sample is:

The resonant length L3=8.7mm is obtained through calculation.

2. Set the ultrasonic parameters. According to the parameter setting standard, the peak value of ultrasonic loading should be higher than the yield strength of the sample material. According to step 2, the more the peak value is higher than the yield strength of the original material, the more obvious the strengthening is generally. It is known that the yield strength of the copper-chromium alloy used is about 120MPa, and the peak load is set at 300MPa.

According to the peak value of the load, the loading current I is calculated by the formula.

A ₀ =μI(μ=16)

Calculated I = 2.2 ampere

3. The copper-chromium pickaxe alloy sample was plastically deformed at an ultra-high strain rate for about 5 minutes. During the deformation, water was used as a cooling liquid to continuously spray its surface so that the temperature would not rise excessively.

The results of characterizing the deformed part of the treated copper-chromium pickaxe alloy sample are as follows:

In accompanying drawing 7, the left picture is the polarizing microscope metallographic picture of the original copper-chromium-zirconium alloy sample before treatment, and the right picture is the phase picture of the copper-chromium-zirconium alloy after plastic deformation at an ultra-high strain rate

It can be seen from the metallographic diagram that a large number of deformed structures appear inside the copper-chromium-zirconium alloy treated by the present invention, and the structure is obviously refined, which shows that it has undergone obvious plastic deformation.

b. Hardness test

Use the Vickers microhardness tester to test the original copper-chromium-zirconium alloy and the copper-chromium-zirconium alloy processed by the present invention. The results show that the Vickers hardness of the original sample is about 90Hv. Its hardness has reached 140Hv. A significant increase in hardness is shown.

In the present invention, the selection of the resonant frequency, the higher the resonant frequency, the shorter the single loading time, according to the strain rate calculation formula dε/dt, wherein ε is the strain, t is the time, and dε can be obtained from the metal material to be strengthened Obtained from the engineering stress-strain curve, specifically, the strength point corresponding to the stress amplitude from the apparent yield point to resonance is the actual strain, dt is related to the resonance frequency of the system, and its loading time in one cycle is 1/f, and dt is is the time t _σ ^-t _MAX during which plastic deformation actually occurs. More than 1.3 times of that, the average strain rate can reach 10 ³ . When the strain remains constant, the shorter the time, the higher the strain rate. To increase the strain rate can be obtained by continuously increasing the resonance frequency.

2: Stress amplitude, the relevant calculation formula of the stress amplitude has been given 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 load corresponding to the stress amplitude of the ultrasonic wave in the resonance region must far exceed the yield strength of the sample.

Ultrasound is a kind of mechanical wave. The 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 the frequency of the incident wave. The two columns of interference waves resonate, so the UHF stress is formed along the axial direction of the sample. load. One end of the sample is connected to the bottom of the amplifier through an internal thread, and the other end is free (see Figure 2 for details). From steps 1 and 2, it can be seen that the stress amplitude of the parallel section in the middle of the sample is the largest, which is the plastic deformation zone.

Claims (5)

1. A method for achieving ultra-high strain rate plastic deformation strengthening in metal, characterized by:

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;

and 2, connecting the processed sample with ultrasonic equipment, and selecting ultrasonic power.

And 3, ensuring that one end of the sample is connected with the bottom end of the ultrasonic equipment amplifier through the internal thread and the other end is free.

And 4, starting ultrasonic resonance, reflecting longitudinal waves of mechanical vibration after the longitudinal waves are transmitted to the free end of the sample, generating resonance between the frequency of the reflected waves and the frequency of the incident waves, forming a load of ultrahigh frequency stress along the axial direction of the sample, and forming plastic deformation on the sample.

2. The method of achieving ultra-high strain rate plastic deformation strengthening in metals of claim 1, wherein in step 1, the sample is a tensile specimen with a middle uniform-section plate shape.

3. The method of claim 1 or 2, wherein the sample has a resonant length L required for the ultrasonic wave to resonate in the deformation region₃The following formula is satisfied:

using the vibration equation U (x) of the longitudinal direction of the sample as: 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 b is₁、b₂、L₁、L₂For given design parameters, L₁Is 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, b₂Is the thickness of the connecting end; e is the modulus of elasticity; rho is density; the resonant frequency f of the ultrahigh 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 provided by the equipment power supply; alpha is alpha₁，β₁And k is a physical derivation process quantity, which can be represented by a basic quantity.

4. The method for achieving ultra-high strain rate plastic deformation strengthening in metals according to claim 1, wherein step 2 specifically comprises: the peak of the ultrasonic loading should be above the yield strength of the sample material.

5. The method of achieving ultra-high strain rate plastic deformation strengthening in metals of claim 1, wherein in step 4, the sample is cooled by circulating a cooling fluid.