WO2022052334A1

WO2022052334A1 - Room-temperature nitriding process based on thermal-mechanical effects of laser, and processing device

Info

Publication number: WO2022052334A1
Application number: PCT/CN2020/133238
Authority: WO
Inventors: 孟宪凯; 李礼; 汪卉; 周建忠; 鲁金忠; 黄舒
Original assignee: 江苏大学
Priority date: 2020-09-11
Filing date: 2020-12-02
Publication date: 2022-03-17
Also published as: GB202304209D0; GB2614984A; CN112226724A; CN112226724B; GB2614984B

Abstract

A room-temperature nitriding process based on thermal-mechanical effects of laser, and a processing device. The method comprises the following steps: at room temperature, a sealed box (9) where a workpiece to be nitrided is placed is filled with ammonia gas; a first laser beam and second laser beams having different energies are output by means of a diffractive beam splitter (2); several second laser beams are focused above the surface of the workpiece (14), and the ammonia gas is ionized by the thermal effect of laser to form free nitrogen atoms; several second laser beams are distributed around the first laser beam, the first laser beam irradiates the surface of the workpiece (14), plasma generated by laser carries the nitrogen atoms into the surface of the workpiece (14) along with dislocation motion induced by the mechanical effect. Using the thermal and mechanical effects of laser to perform surface strengthening treatment can obtain higher strength, hardness, and fatigue performance than a single strengthening treatment. In addition, room-temperature nitriding can improve the defect of coarse crystal grains caused by conventional high-temperature nitriding.

Description

A normal temperature nitriding process and processing device based on laser thermo-mechanical effect

technical field

The invention relates to the technical field of heat treatment or the technical field of surface nitriding, in particular to a normal temperature nitriding process and a processing device based on laser thermo-mechanical effect.

Background technique

Nitriding technology is generally a chemical heat treatment process in which nitrogen atoms are infiltrated into the surface of the workpiece at high temperatures. The traditional gas nitriding is to put the workpiece into a sealed container, pass the flowing ammonia gas and heat it. After a long time of heat preservation, the ammonia gas thermally decomposes to generate active nitrogen atoms, which are continuously adsorbed to the surface of the workpiece and diffuse into the surface of the workpiece. , thereby changing the chemical composition and structure of the surface layer, such as the Chinese invention patent with the application number 202010284906.6, but there are the following shortcomings: high temperature leads to deformation of parts, high tensile stress, and easy formation of high temperature cracks. The Chinese invention patent with the application number of 201710591680.2 discloses a method for preparing a TiN gradient coating with low laser power on the surface of a titanium alloy, using the all-solid-state laser thermal effect (heating, melting) to promote the self-diffusion of nitrogen atoms to realize the preparation of the TiN coating. However, there are the following shortcomings: 1. The thermal effect of the laser will still lead to deformation of the parts, the tensile stress is large, and it is easy to form high temperature cracks; 2. Relying on self-diffusion nitriding, the nitrogen content of the nitriding layer is low.

In order to improve the nitriding effect and increase the thickness of the nitriding layer, some pretreatment can achieve this purpose. The Chinese invention patents with application numbers 201810123908.X and 201210492108.8 respectively disclose a laser shock process for improving the efficiency of ion nitriding and a method for increasing infiltration by laser plasma shock wave in chemical heat treatment, both of which utilize the mechanical effect induced by the laser. Plastic deformation occurs on the surface of the material, forming high-density dislocations, grain refinement and even nanocrystals, which promote the diffusion of nitrogen atoms, but the above technologies or methods still require traditional high-temperature nitriding processes, and there are high-temperature deformation, tensile stress, high-temperature cracks, etc. defect. The Chinese invention patent application number 201811160014.4 discloses a laser high temperature shock-nitriding composite processing device and method. First, high-temperature gas nitriding is performed, and then high-temperature assisted laser shock strengthening is performed. The laser-induced force effect is mainly used to prepare dislocations, Dislocation entanglement and sub-grain boundaries achieve a certain infiltration effect. However, this method also has certain defects: first, the gas nitriding treatment time is long and the temperature is high, which will cause coarse grains and shallow compressive stress; at the same time, the dislocation slip process cannot be used for dynamic infiltration, and the effect of laser infiltration is reduced. The Chinese Patent Application No. 03141802.3 discloses a method for co-processing materials with microwave plasma and laser at room temperature, using microwave discharge to generate plasma, and then realizing ion penetration under the thermal effect of laser (heating, melting, solidification). However, there are the following technical deficiencies: 1. The processing technology is complicated by using two energy sources, microwave and laser; 2. Although ion penetration is achieved at room temperature, the laser thermal effect (heating, melting, solidification) will still cause cracks on the surface of the material , tensile stress and other defects.

The prior art Chinese invention patent application number 201110367288.2 discloses a method and device for continuous synthesis of carbon nanotubes by strong laser irradiation to prepare diamond thin films. The laser is reflected and split by a beam splitter to form two laser beams, one of which is The laser beam acts on the non-transparent carbon nanotube powder, which is bombarded into the surface of the substrate after gasification and explosion, and another laser beam is used to heat to form a high temperature micro-area, which promotes the entry of the carbon nanotube powder, and finally forms a diamond film. This patent has the following shortcomings: 1. The use of laser to induce gasification and explosion of non-transparent carbon nanotube powder, and then bombarding the carbon material into the surface of the substrate, cannot be applied to transparent gases/liquids such as ammonia and ammonia water, and is difficult to be used for nitriding treatment; 2. High-temperature micro-domains are formed on the surface of the material, and there are still defects such as high-temperature tensile stress and cracks; 3. Material penetration is achieved by bombardment force and diffusion, and the penetration effect is poor.

SUMMARY OF THE INVENTION

Aiming at the defects such as high temperature tensile stress and cracks existing in the prior art, the present invention provides a normal temperature nitriding process and processing device based on laser thermal-mechanical effect. It is adsorbed on the surface of the sample, and the moving dislocation/grain boundary is used as the nitriding channel, which can increase the thickness of the nitriding layer, and at the same time avoid the traditional high-temperature nitriding induced materials such as coarse grains, high-temperature tensile stress and cracks. A high density of dislocations occurs on the surface of the material, and nitrogen atoms penetrate into the material along the grain boundaries and dislocations, which helps to further improve the strength, hardness and fatigue properties of the nitrided layer.

The present invention achieves the above technical purpose through the following technical means.

A normal temperature nitriding process based on laser thermo-mechanical effect, comprising the following steps:

Under normal temperature, the airtight box where the workpiece to be nitrided is placed is filled with ammonia gas;

A first laser beam and a second laser beam with different energies are output through a diffractive beam splitter; several second laser beams are focused on the surface of the workpiece, and ammonia gas is ionized to form free nitrogen atoms by laser thermal effect; several of the second laser beams The beam is distributed around the first laser beam, and the first laser beam irradiates the surface of the workpiece, and the plasma generated by the laser carries nitrogen atoms and penetrates into the surface of the workpiece along the motion dislocation induced by the force effect.

Further, the energy of the first laser beam is smaller than the energy of the second laser beam.

Further, the ratio of the energy of the first laser beam to the energy of the second laser beam is 4:6.

Further, the focus of the first laser beam is located 3-10mm below the surface of the workpiece; the focus of the second laser beam is located 0.2-0.5mm above the surface of the workpiece.

Further, the focused spot diameter of the first laser beam is not less than 3 mm, and the focused spot diameter of the second laser beam is 0.2-0.8 mm.

A processing device for a normal temperature nitriding process based on laser thermo-mechanical effect, comprising a laser, a sealing box, a diffractive beam splitter and an ammonia gas device; a workpiece to be nitrided is placed in the sealing box, and the laser is used for Laser is emitted, and the diffractive beam splitter is used to split the laser emitted by the laser into a first laser beam and a second laser beam with different energies, and a plurality of the second laser beams are distributed around the first laser beam; The second laser beam is focused on the surface of the workpiece through the sealing box, and the first laser beam is focused on the surface of the workpiece through the sealing box; the sealing box is communicated with the ammonia gas device.

Further, it also includes a combined lens A, a combined lens B, a reflecting mirror and a focusing mirror; the first laser beam and the second laser beam enter the sealing box after passing through the combined lens A, the reflecting mirror and the combined lens B in sequence, and the combined lens A is used for collimating the first laser beam and the second laser beam, the combined lens B is used for deflecting the first laser beam and the second laser beam; a focusing mirror is installed in the sealing box to make the deflected laser beam The first laser beam and the second laser beam are focused on the workpiece to be nitrided.

The beneficial effects of the present invention are:

1. The normal temperature nitriding process based on the laser thermal-mechanical effect of the present invention, ionizes ammonia gas through the laser thermal effect, so that more nitrogen atoms are adsorbed on the surface of the sample, and the moving dislocation is used as the nitriding channel, which can The thickness of the nitriding layer is increased, and the defects of coarse grains of traditional high-temperature nitriding-induced materials are avoided at the same time; high-density dislocations are also induced on the surface of the material through the laser force effect, and the plasma generated by laser shock strengthening acts as a carrier, which can carry nitrogen atoms The dislocations moving along the grain boundaries penetrate into the material, which helps to further improve the strength, hardness and fatigue properties of the nitrided layer.

2. The normal temperature nitriding process based on the laser thermal-mechanical effect of the present invention uses the thermal-mechanical composite effect of the laser to carry out surface strengthening treatment, which can obtain higher strength, hardness and fatigue performance than single strengthening treatment.

3. In the normal temperature nitriding process based on the laser thermo-mechanical effect of the present invention, multiple laser beams act on the ammonia gas, and the transparent ammonia gas is ionized to form free nitrogen ions by using the higher laser energy at the focus. While the laser thermal effect induces the generation of nitrogen ions, the force effect of the laser is used to induce dislocation slip and grain boundary movement. Thick and uniform nitrided layer.

4. The normal temperature nitriding process based on the laser thermo-mechanical effect of the present invention forms defects such as subgrain boundaries and dislocations on the surface and high-amplitude residual compressive stress, which can promote the nitrogen atoms to move along the moving position. The dislocation diffuses into the matrix, which helps to further increase the thickness and nitrogen content of the nitrided layer.

5. The processing device of the normal temperature nitriding process based on the laser thermo-mechanical effect of the present invention reduces the clamping time of materials in the composite processing process, improves the work efficiency, and makes the operation more convenient. In addition, the device of the present invention performs nitriding at normal temperature, which greatly shortens the processing time compared with the need for high temperature treatment in the traditional nitriding process.

Description of drawings

FIG. 1 is a schematic diagram of the processing device of the normal temperature nitriding process based on the laser thermo-mechanical effect according to the present invention.

Figure 2 shows the surface microhardness of TC4 titanium alloy under different treatments

Figure 3 shows the cross-sectional structure of the matrix of TC4 titanium alloy

Figure 4 shows the cross-sectional structure of TC4 titanium alloy after traditional gas nitriding

Figure 5 shows the cross-sectional structure of TC4 titanium alloy after laser nitriding

In the picture:

1-laser; 2-diffractive beam splitter; 3-combination lens A; 4-pressure sensor; 5-inlet flow valve; 6-reflector; 7-combination lens B; 8-high temperature and high pressure quartz glass; 9-sealed box; 10-air outlet flow valve; 11-exhaust gas storage bottle; 12-first focusing mirror; 13-three-axis linkage table; 14-workpiece; 15-second focusing mirror; 16-ammonia cylinder; 17 - Computer.

detailed description

The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

As shown in FIG. 1, the processing device of the normal temperature nitriding process based on the laser thermo-mechanical effect according to the present invention includes a laser 1, a sealing box 9, a diffractive beam splitter 2, a combined lens A3, a combined lens B7, The reflecting mirror 6, the first focusing mirror 12, the second focusing mirror 15 and the ammonia gas cylinder 16; the workpiece 14 to be nitrided is placed in the sealing box 9, and the bottom of the workpiece 14 to be nitrided is provided with a three-axis linkage table 13 for The workpiece 14 to be nitrided moves three-dimensionally. A high temperature and high pressure quartz glass 8 is installed on the upper part of the sealing box 9 , and the laser is irradiated on the workpiece 14 through the high temperature and high pressure quartz glass 8 . An air inlet flow valve 5 is arranged between the ammonia gas cylinder 16 and the sealing box 9 , and an air outlet flow valve 10 is arranged between the waste gas storage bottle 11 and the sealing box 9 . When the ammonia gas is working, the air pressure is maintained at 150-300Pa. According to the feedback information of the pressure sensor 4, the computer 17 adjusts the flow valve in and out to realize the closed-loop control of the pressure in the sealed box.

The laser 1 is used for emitting laser light, and the laser 1 is a nanosecond pulse laser with a laser pulse width of 20-25ns. The diffractive beam splitter 2 is used to split the laser light emitted by the laser 1 into a first laser beam and a second laser beam with different energies, and a plurality of the second laser beams are distributed around the first laser beam; The second laser beam passes through the sealing box 9 and is focused on the surface of the workpiece, and the first laser beam passes through the sealing box 9 and focuses on the surface of the workpiece; the sealing box 9 is communicated with the ammonia gas device. The first laser beam and the second laser beam enter the sealing box 9 after passing through the combined lens A3, the reflector 6 and the combined lens B7 in turn. The combined lens A3 is used to collimate the first laser beam and the second laser beam, so The combined lens B7 is used to deflect the first laser beam and the second laser beam; the first focusing mirror 12 and the second focusing mirror 15 are installed in the sealed box 9, which are used to deflect the first laser beam and the second laser beam. Two laser beams are focused on the workpiece to be nitrided.

Example 1

The following will take Cr12MoV cold work die steel with a size of 30mm×30mm×5mm as an example, and use the normal temperature nitriding process based on the laser thermo-mechanical effect according to the present invention to carry out surface strengthening treatment. Specific steps are as follows:

The workpiece 14 to be nitrided is polished to a mirror surface with #400-#2000 SiC sandpaper, ultrasonically cleaned with absolute ethanol, and placed on the three-axis linkage worktable 13 .

Turn on the pressure sensor 4, and let in ammonia gas. According to the feedback information of the pressure sensor 4, the computer adjusts the flow valve in and out to realize the closed-loop control of the pressure in the sealing box, and control the pressure in the sealing box to be maintained at around 200Pa.

After the pressure in the sealed box is stable, set the parameters of laser 1 as pulse width 25ns and laser energy 30J.

The diffractive beam splitter 2 is turned on, the laser light emitted by the laser 1 is divided into a first laser beam and a second laser beam with different energies, and several second laser beams are focused on the surface of the workpiece 14 to be nitrided, and the ammonia gas is ionized by the laser thermal effect. Free nitrogen atoms are formed; a number of the second laser beams are distributed around the first laser beam, and the first laser beam irradiates the workpiece 14 to be nitrided, and the plasma generated by the laser carries nitrogen atoms and induces a force effect The moving dislocations penetrate into the workpiece surface; the energy of the first laser beam is 12J, and the energy of the second laser beam is 18J.

The spot diameter of each laser beam is adjusted by the focusing mirror. The corresponding spot size of the first laser beam is 3mm, the corresponding spot size of the second laser beam is 0.6mm, and the focal point of the second laser beam is 0.3mm high from the workpiece surface.

The three-axis table 13 moves according to a predetermined path until the end of the processing, and in this process, the spot overlap ratio of the laser beam corresponding to the force effect is guaranteed to be 50%.

After processing, the exhaust gas is collected in the sealed box, and the exhaust gas is collected in the exhaust gas storage bottle, and then the workpiece is unloaded.

Turn off the laser, diffractive beam splitter, pressure sensor.

The thickness of the nitrided layer of the processed Cr12MoV workpiece is expected to reach 60-70 μm, and the connection line between the nitrided layer and the substrate can be relatively flat.

Example 2

The following will take 38CrMoAl nitriding steel with a size of 20mm×20mm×5mm as an example, and use the normal temperature nitriding process based on the laser thermo-mechanical effect according to the present invention to carry out surface strengthening treatment. Specific steps are as follows:

Turn on the pressure sensor 4 and pass in ammonia gas. According to the feedback information of the pressure sensor 4, the computer adjusts the flow valve in and out to realize the closed-loop control of the pressure in the sealing box, and control the pressure in the sealing box to be maintained at around 240Pa.

After the pressure in the sealed box is stable, set the parameters of laser 1 as pulse width 20ns and laser energy 20J.

The diffractive beam splitter 2 is turned on, the laser light emitted by the laser 1 is divided into a first laser beam and a second laser beam with different energies, and several second laser beams are focused on the surface of the workpiece 14 to be nitrided, and the ammonia gas is ionized by the laser thermal effect. Free nitrogen atoms are formed; a number of the second laser beams are distributed around the first laser beam, and the first laser beam irradiates the workpiece 14 to be nitrided, and the plasma generated by the laser carries nitrogen atoms and induces a force effect The moving dislocations penetrate into the workpiece surface; the energy of the first laser beam is 8J, and the energy of the second laser beam is 12J.

The spot diameter of each laser beam is adjusted by a focusing mirror. The focus of the first laser beam is located 10mm below the workpiece surface, the corresponding spot size is 6mm, the corresponding spot size of the second laser beam is 0.8mm, and the focus of the second laser beam is far from the workpiece surface. Height 0.5mm.

Turn off the laser, diffractive beam splitter, pressure sensor.

The thickness of the nitrided layer of the processed 38CrMoAl workpiece is expected to reach 280-300 μm, and the connection line between the nitrided layer and the substrate can be relatively flat.

Example 3

Taking the TC4 aviation titanium alloy with the size of 20mm×20mm×2mm as an example, the surface strengthening treatment is carried out by using the normal temperature nitriding process based on the laser thermo-mechanical effect according to the present invention. Specific steps are as follows:

Turn on the pressure sensor 4 and pass in ammonia gas. According to the feedback information of the pressure sensor 4, the computer adjusts the flow valve in and out to realize the closed-loop control of the pressure in the sealing box, and control the pressure in the sealing box to be maintained at around 270Pa.

After the pressure in the sealed box is stable, set the parameters of laser 1 as pulse width 25ns and laser energy 40J.

The diffractive beam splitter 2 is turned on, the laser light emitted by the laser 1 is divided into a first laser beam and a second laser beam with different energies, and several second laser beams are focused on the surface of the workpiece 14 to be nitrided, and the ammonia gas is ionized by the laser thermal effect. Free nitrogen atoms are formed; a number of the second laser beams are distributed around the first laser beam, and the first laser beam irradiates the workpiece 14 to be nitrided, and the plasma generated by the laser carries nitrogen atoms and induces a force effect The moving dislocations penetrate into the workpiece surface; the energy of the first laser beam is 16J, and the energy of the second laser beam is 24J.

The spot diameter of each laser beam is adjusted by the focusing mirror. The focus of the first laser beam is located 6mm below the surface of the workpiece, the corresponding spot size is 4mm, the corresponding spot size of the second laser beam is 0.2mm, and the focus of the second laser beam is far from the workpiece. Surface height 0.2mm.

Turn off the laser, diffractive beam splitter, pressure sensor.

It can be seen from Figure 2 that the Vickers hardness of the TC4 workpiece after laser nitriding is 1306.5HV, which is 272.3% and 18.1% higher than that of the substrate and traditional gas nitriding, respectively.

It can be seen from Figure 3, Figure 4 and Figure 5 that the cross-sectional structure of the matrix of TC4 titanium alloy is mainly composed of α-Ti and β-Ti, and the thickness of the nitrided layer on the surface of the TC4 workpiece after laser nitriding can reach 26.3 μm, Compared with gas nitriding, it increased by 42.9%.

The embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or All modifications belong to the protection scope of the present invention.

Claims

A normal temperature state nitriding process based on laser thermo-mechanical effect, is characterized in that, comprises the following steps:

Under normal temperature, the airtight box where the workpiece to be nitrided is placed is filled with ammonia gas;

The diffractive beam splitter (2) outputs a first laser beam and a second laser beam with different energies; several second laser beams are focused on the surface of the workpiece, and the ammonia gas is ionized to form free nitrogen atoms through the laser thermal effect; The second laser beam is distributed around the first laser beam, and the first laser beam irradiates the workpiece surface, and the plasma generated by the laser carries nitrogen atoms and penetrates into the workpiece surface along the motion dislocation induced by the force effect.
The normal temperature nitriding process based on laser thermo-mechanical effect according to claim 1, wherein the energy of the first laser beam is smaller than the energy of the second laser beam.
The normal temperature nitriding process based on laser thermo-mechanical effect according to claim 1, wherein the ratio of the energy of the first laser beam to the energy of the second laser beam is 4:6.
The normal temperature nitriding process based on the laser thermo-mechanical effect according to claim 1, wherein the diameter of the focused spot of the first laser beam is not less than 3 mm, and the diameter of the focused spot of the second laser beam is not less than 3 mm. 0.2 to 0.8 mm.
The method for nitriding at room temperature based on laser thermo-mechanical effect according to claim 1, wherein the focal points of a plurality of the second laser beams are located 0.2-0.5 mm above the surface of the workpiece; the focal points of the first laser beams Located 3-10mm below the workpiece surface.
A processing device for a normal temperature nitriding process based on laser thermo-mechanical effect according to claim 1, characterized in that it comprises a laser (1), a sealing box (9), a diffractive beam splitter (2) and Ammonia device; a workpiece to be nitrided is placed in the sealing box (9), the laser (1) is used for emitting laser light, and the diffractive beam splitter (2) is used for dividing the laser light emitted by the laser (1) A first laser beam and a second laser beam with different energies are formed, and a plurality of the second laser beams are distributed around the first laser beam; a plurality of the second laser beams pass through the sealing box (9) and are focused on the surface of the workpiece , the first laser beam passes through the sealing box (9) and is focused on the surface of the workpiece; the sealing box (9) is communicated with the ammonia gas device.
The processing device of the normal temperature nitriding process based on the laser thermo-mechanical effect according to claim 1, characterized in that it further comprises a combined lens A (3), a combined lens B (7), a mirror (6) and a focusing lens mirrors (12, 15); the first laser beam and the second laser beam pass through the combined lens A (3), the reflecting mirror (6) and the combined lens B (7) in sequence and then enter the sealing box (9), and the combined The lens A (3) is used to collimate the first laser beam and the second laser beam, and the combined lens B (7) is used to deflect the first laser beam and the second laser beam; inside the sealed box (9) A focusing mirror (12, 15) is installed for focusing the deflected first laser beam and the second laser beam on the workpiece to be nitrided.