METHOD FOR PREPARING FERRITE/REDUCING METAL COMPOSITE PARTICLES AND METHOD FOR PREPARING HIGH TEMPERATURE RESISTANT STEALTH COATING BASED ON 3D LASER PRINTING

Abstract

The present invention relates to a method for preparing ferrite/reducing metal composite particles and a method for preparing a high temperature resistant stealth coating based on 3D laser printing, belonging to the technical field of preparation of absorbing coatings. The present invention aims to solve the problems that an existing high-temperature absorbing coating has insufficient coating/matrix bonding force, the microstructure of the coating is difficult to control, and electromagnetic properties cannot be ensured. In the present invention, nano ferrite powder and nano reducing metal powder are prepared into composite particles by a mixing granulation process. In a sealed preparation chamber of a 3D printing device, composite particles are subjected to laser-induced in-situ reaction on the surface of a substrate to prepare a high temperature resistant stealth coating. The present invention is applied to high temperature resistance and stealth of components and prevention and control of electromagnetic pollution.

Claims

1. A method for preparing ferrite/reducing metal composite particles, wherein the ferrite/reducing metal composite particles are prepared by a mixing granulation process, comprising: (a) uniformly mixing nano ferrite powder, nano reducing metal powder and an additive to obtain slurry; and (b) performing granulation by centrifugal spray drying, performing stage treatment after the granulation is completed, and selecting particles with a spherical shape and a size of 10-60 m to obtain ferrite/reducing metal composite particles; wherein the additive in step (a) is polyvinyl alcohol (PVA) or carboxymethyl cellulose (CMC).

2. The method for preparing ferrite/reducing metal composite particles according to claim 1, wherein in step (a), the ferrite particles are one of Fe.sub.3O.sub.4, BaFe.sub.12O.sub.19 and CoFe.sub.2O.sub.4; and the ferrite powder is spherical with a diameter of 50-500 nm.

3. The method for preparing ferrite/reducing metal composite particles according to claim 1, wherein the reducing metal particles in step (a) 4 are Al particles, Zn particles or Zr particles; and the reducing metal powder is spherical with a diameter of 50-500 nm.

4. The method for preparing ferrite/reducing metal composite particles according to claim 1, wherein in step (a), the weight ratio of the ferrite powder to the reducing metal powder is (1-5):1; and the usage of the additive is 0.1%-3% of the total weight of the ferrite powder and the reducing metal powder.

5. The method for preparing ferrite/reducing metal composite particles according to claim 1, wherein process parameters for the granulation in step (b) are an inlet temperature of a spray drying tower is 220-260 C., an outlet temperature of the spray drying tower is 100-120 C., and a rotating speed of an atomizing disc in the spray drying tower is 18000-30000 r/min.

6. A method for preparing a high temperature resistant stealth coating based on 3D laser printing, comprising: (a) sandblasting the surface of a substrate to remove oxide films and pollutants; (b) placing the substrate treated in step (a) on a worktable in a preparation chamber, and cleaning the preparation chamber with argon 3-5 times; loading ferrite/reducing metal composite particles prepared by the method of claim 1 into a powder feeder; and (c) after setting the process parameters, starting a program to perform 3D printing, wherein in the printing process, the powder feeder synchronously sends powder to a laser irradiation area to perform laser-induced reaction and preparation; after the 3D printing of the set area is finished, shutting down the laser and a powder feeding mechanism, and taking out the substrate after the substrate is cooled, to obtain the high temperature resistant stealth coating on the surface of the substrate.

7. A method for preparing a high temperature resistant stealth coating based on 3D laser printing, comprising: (a) sandblasting the surface of a substrate to remove oxide films and pollutants; (b) placing the substrate treated in step (a) on a worktable in a preparation chamber, and cleaning the preparation chamber with argon 3-5 times; loading ferrite/reducing metal composite particles prepared by the method of claim 2 into a powder feeder; and (c) after setting the process parameters, starting a program to perform 3D printing, wherein in the printing process, the powder feeder synchronously sends powder to a laser irradiation area to perform laser-induced reaction and preparation; after the 3D printing of the set area is finished, shutting down the laser and a powder feeding mechanism, and taking out the substrate after the substrate is cooled, to obtain the high temperature resistant stealth coating on the surface of the substrate.

8. A method for preparing a high temperature resistant stealth coating based on 3D laser printing, comprising: (a) sandblasting the surface of a substrate to remove oxide films and pollutants; (b) placing the substrate treated in step (a) on a worktable in a preparation chamber, and cleaning the preparation chamber with argon 3-5 times; loading ferrite/reducing metal composite particles prepared by the method of claim 3 into a powder feeder; and (c) after setting the process parameters, starting a program to perform 3D printing, wherein in the printing process, the powder feeder synchronously sends powder to a laser irradiation area to perform laser-induced reaction and preparation; after the 3D printing of the set area is finished, shutting down the laser and a powder feeding mechanism, and taking out the substrate after the substrate is cooled, to obtain the high temperature resistant stealth coating on the surface of the substrate.

9. A method for preparing a high temperature resistant stealth coating based on 3D laser printing, comprising: (a) sandblasting the surface of a substrate to remove oxide films and pollutants; (b) placing the substrate treated in step (a) on a worktable in a preparation chamber, and cleaning the preparation chamber with argon 3-5 times; loading ferrite/reducing metal composite particles prepared by the method of claim 4 into a powder feeder; and (c) after setting the process parameters, starting a program to perform 3D printing, wherein in the printing process, the powder feeder synchronously sends powder to a laser irradiation area to perform laser-induced reaction and preparation; after the 3D printing of the set area is finished, shutting down the laser and a powder feeding mechanism, and taking out the substrate after the substrate is cooled, to obtain the high temperature resistant stealth coating on the surface of the substrate.

10. A method for preparing a high temperature resistant stealth coating based on 3D laser printing, comprising: (a) sandblasting the surface of a substrate to remove oxide films and pollutants; (b) placing the substrate treated in step (a) on a worktable in a preparation chamber, and cleaning the preparation chamber with argon 3-5 times; loading ferrite/reducing metal composite particles prepared by the method of claim 5 into a powder feeder; and (c) after setting the process parameters, starting a program to perform 3D printing, wherein in the printing process, the powder feeder synchronously sends powder to a laser irradiation area to perform laser-induced reaction and preparation; after the 3D printing of the set area is finished, shutting down the laser and a powder feeding mechanism, and taking out the substrate after the substrate is cooled, to obtain the high temperature resistant stealth coating on the surface of the substrate.

11. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 6, wherein the material of the substrate in step (a) is a titanium alloy plate or a steel plate.

12. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 7, wherein the material of the substrate in step (a) is a titanium alloy plate or a steel plate.

13. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 8, wherein the material of the substrate in step (a) is a titanium alloy plate or a steel plate.

14. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 9, wherein the material of the substrate in step (a) is a titanium alloy plate or a steel plate.

15. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 10, wherein the material of the substrate in step (a) is a titanium alloy plate or a steel plate.

16. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 6, wherein the substrate in step (a) has a thickness of 4-10 mm.

17. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 7, wherein the substrate in step (a) has a thickness of 4-10 mm.

18. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 8, wherein the substrate in step (a) has a thickness of 4-10 mm.

19. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 6, wherein the 3D printing process parameters in step (c) are an optical fiber laser is adopted, the laser power is set to 400-1000 W, a laser spot diameter is 1-3 mm, an overlap rate of adjacent passes of printing is 20%-30%, a laser scanning speed is 600-1200 mm/min; a powder feeding amount is 1-5 rap/min, and a moving speed of the powder feeder is consistent with the scanning speed of the laser.

20. The method for preparing a high temperature resistant stealth coating based on 3D laser printing according to claim 6, wherein a thickness of the coating prepared by printing in each pass in the printing process in step (c) is 100-1200 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 shows the morphology (an SEM image) of Fe.sub.3O.sub.4/Al composite particles;

[0030] FIG. 2 shows the surface morphology of an Fe/Al.sub.2O.sub.3 laser-induced in-situ reaction coating;

[0031] FIG. 3 shows a phase composition and microstructure of an Fe/Al.sub.2O.sub.3 laser-induced in-situ reaction coating;

[0032] FIG. 4 shows the microstructure of an Fe/Al.sub.2O.sub.3 laser-induced in-situ reaction coating, where FIG. 4(a) shows a coating surface microstructure, and FIG. 4(b) shows a coating cross-section;

[0033] FIG. 5 shows electromagnetic wave absorption properties of an Fe/Al.sub.2O.sub.3 laser-induced in-situ reaction coating; and

[0034] FIG. 6 is a typical wave absorbing curve of reflection loss characteristics of a coating measured by a free space approach in Example 2.

DETAILED DESCRIPTION

[0035] Example 1: A method for preparing ferrite/reducing metal composite particles used in this example is implemented by a mixing granulation process. The method specifically includes the following steps:

[0036] Step 1: Uniformly mix spherical Fe.sub.3O.sub.4 particles with a diameter of 80 nm, spherical Al particles with a diameter of 50 nm and a PVA additive to obtain slurry, where the weight ratio of Fe.sub.3O.sub.4 to Al is 3.2:1 and a usage of the additive is 0.5% of the total weight of ferrite powder and reducing metal powder.

[0037] Step 2: Granulate the obtained slurry by centrifugal spray drying, where spray drying process parameters are as follows: an inlet temperature of a spray drying tower is 220 C., an outlet temperature of the spray drying tower is 100 C., and a rotating speed of an atomizing disc in the spray drying tower is 20000 r/min; after the granulation is completed, perform stage treatment, where the particles each have a spherical shape and an average size of 50 m, with the typical morphology of the particles shown in FIG. 1, thus obtaining Fe.sub.3O.sub.4/Al composite particles.

[0038] In this example, a method for preparing a high temperature resistant stealth coating based on 3D laser printing includes the following steps:

[0039] Step 1: Use a titanium alloy plate with a thickness of 5 mm as a substrate, and sandblast the surface of the substrate to remove oil stains and oxide films.

[0040] Step 2: Place the titanium alloy substrate into a preparation chamber, and repeatedly inflate and deflate the preparation chamber with argon to clean the preparation chamber 3 times; and load Fe.sub.3O.sub.4/Al composite particles prepared by the foregoing method into a powder feeder.

[0041] Step 3: After setting the process parameters, starting a program to perform 3D printing, where in the printing process, the powder feeder synchronously sends powder to a light beam irradiation position on the substrate to perform laser-induced reaction (that is, once the powder is sent to the surface of the substrate, the powder is ignited by laser to react, and reaction products are uniformly deposited on the surface of the substrate and rapidly perform metallurgical bonding); after the 3D printing of the set area is finished, shut down the laser and a powder feeding mechanism, and take out the substrate after the substrate is cooled, to obtain the high temperature resistant stealth coating on the surface of the substrate.

[0042] The 3D printing process parameters set in this example were as follows: an optical fiber laser was adopted, the laser power was set to 700 W, a laser spot diameter was 3 mm, an overlap rate of adjacent passes of printing was 30%, and a laser scanning speed was 600 mm/min; a powder feeding amount was 2 rap/min, and a moving speed of the powder feeder was consistent with the scanning speed of the laser; and the coating had a thickness of 700 m.

[0043] In this example, in-situ thermit reaction was performed under the induction by laser. When Fe.sub.3O.sub.4/Al composite particles were used in the laser-induced reaction process, refined thermite reaction sites in the particles enabled the generated Fe and Al.sub.2O.sub.3 to have fine micro-composite structures: fine Fe particles were uniformly dispersed in a matrix composed of Al.sub.2O.sub.3; and the coating obtained in this example had obvious electromagnetic absorption properties.

[0044] In this example, as soon as the laser was started in the coating preparation process, the composite powder at the irradiation position was ignited, accompanied by bright flame and smoke, indicating that the thermite reaction was very strong. According to a preset scanning path, the whole coating was finally formed by gradual scanning. The surface morphology of the coating formed by the reaction is shown in FIG. 2. The coating formed by each pass of scanning can be clearly distinguished from the figure. As can be seen from the figure, the coating prepared by this process had a complete structure and compact surface.

[0045] XRD analysis shows that the phase composition of the coating after reaction is Fe, Al.sub.2O.sub.3 and Fe.sub.3O.sub.4 that was not reacted completely, as shown in the left figure in FIG. 3.

[0046] The typical characteristics of the microstructure of the coating surface are shown in FIG. 4(a). It can be seen from the figure that Fe particles were uniformly dispersed on the Al.sub.2O.sub.3/Fe.sub.3O.sub.4 ceramic matrix; and there were a certain number of pores in the matrix. Statistics show that the Fe particles had a size of 5-80 m, and mostly had a size about 50 m. An SEM image of the cross-section of the coating is shown in FIG. 4(b). The observation shows that the coating was complete and compact and bonded well with the matrix, and the coating had a thickness of about 700 m.

[0047] The reflection loss characteristics of the coating were tested by using a 200 mm200 mm test plate and a free space approach. A typical reflection loss curve is shown in FIG. 5. As can be seen from the figure, the maximum absorption of the coating at 15.3 GHz was greater than 25 dB. The coating was subjected to a high-temperature test. The coating was placed in a 600 C. muffle furnace for treatment for 30 minutes, then taken out and directly put into cold water, so that the coating did not peel off and still maintained a compact and complete structure. Moreover, the weight of each sample hardly changed before and after high temperature treatment, as shown in Table 1, indicating that the coating had outstanding oxidation resistance.

TABLE-US-00001 TABLE 1 Weight changes of Fe/Al.sub.2O.sub.3 laser-induced in-situ reaction coatings before and after heat preservation at 600 C. for 30 min Weight (g) before Weight (g) after high temperature high temperature Weight Sample No. treatment treatment difference (g) 1 15.709 15.711 0.002 2 16.854 16.852 0.002 3 15.804 15.788 0.016 4 15.972 15.964 0.008 5 17.710 17.701 0.009

[0048] The core of this example is thermit reaction, and its specific reaction formula is:

Fe.sub.3O.sub.4 (powder)+Al (powder).fwdarw.Al.sub.2O.sub.3 (coating matrix)+Fe (wave absorbing particles)

[0049] Example 2: In this example, a method for preparing a high temperature resistant stealth coating based on 3D laser printing includes the following steps:

[0050] A method for preparing ferrite/reducing metal composite particles used in this example is implemented by a mixing granulation process. The method specifically includes the following steps:

[0051] Step 1: Uniformly mix spherical BaFe.sub.12O.sub.19 particles with a diameter of 100 nm, spherical Al particles with a diameter of 50 nm and an additive (CMC) to obtain slurry, where the weight ratio of the BaFe.sub.12O.sub.19 particles to the Al particles is 3.2:1, and a usage of the additive is 1% of the total weight of ferrite powder and reducing metal powder.

[0052] Step 2: Granulate the obtained slurry by centrifugal spray drying, where spray drying process parameters are as follows: an inlet temperature of a spray drying tower is 260 C., an outlet temperature of the spray drying tower is 120 C., and a rotating speed of an atomizing disc in the spray drying tower is 20000 r/min; after the granulation is completed, perform stage treatment to obtain spherical BaFe.sub.12O.sub.19/Al composite particles with an average size of 30 m.

[0053] In this example, a method for preparing a high temperature resistant stealth coating based on 3D laser printing includes the following steps:

[0054] Step 1: Use a steel plate with a thickness of 8 mm as a substrate, and sandblast the surface of the substrate to remove oil stains and oxide films.

[0055] Step 2: Place the substrate into a preparation chamber, and clean the preparation chamber 3 times; and load BaFe.sub.12O.sub.19/Al composite particles prepared by the foregoing method into a powder feeder.

[0056] Step 3: After setting the process parameters, starting a program to perform 3D printing, where in the printing process, the powder feeder synchronously sends powder to a light beam irradiation position on the substrate to perform laser-induced reaction (that is, once the powder is sent to the surface of the substrate, the powder is ignited by laser to react, and reaction products are uniformly deposited on the surface of the substrate and rapidly perform metallurgical bonding); after the 3D printing of the set area is finished, shut down the laser and a powder feeding mechanism, and take out the substrate after the substrate is cooled, to obtain the high temperature resistant stealth coating on the surface of the substrate.

[0057] The 3D printing process parameters in this example were as follows: an optical fiber laser was adopted, the laser power was set to 1000 W, a laser spot diameter was 2 mm, an overlap rate of adjacent passes of printing was 20%, and a laser scanning speed was 800 mm/min; a powder feeding amount was 4 rap/min, and a moving speed of the powder feeder was consistent with the scanning speed of the laser. The coating had a thickness of 700 m.

[0058] The core of this example is thermit reaction, and its specific reaction formula is:

BaFe.sub.12O.sub.19 (powder)+Al (powder).fwdarw.Al.sub.2O.sub.3(coating matrix)+Fe (wave absorbing particles)

[0059] The reflection loss characteristics of the coating were tested by using a free space approach. A typical wave absorbing curve is shown in FIG. 6. As can be seen from the figure, the absorption of the coating in the 11.8-17.6 GHz band was greater than 5 dB.