Composite coating for improving corrosion resistance of neodymium iron boron and preparation method thereof

Abstract

The invention relates to the field of corrosion protection of neodymium iron boron magnetic materials, and discloses a composite coating for improving corrosion resistance of neodymium iron boron and a preparation method of the composite coating. The method comprises the following steps: manually grinding and mechanically polishing a neodymium-iron-boron magnetic material, and then carrying out ultrasonic cleaning, drying, preheating and Cr ion bombardment cleaning to obtain a pretreated neodymium-iron-boron matrix; preparing a CrN transition layer on the surface of the pretreated neodymium-iron-boron substrate by adopting a chromium target in a nitrogen atmosphere through arc ion plating; and a CrAlN layer is prepared on the surface of the CrN transition layer through arc ion plating by adopting a chromium-aluminum target in a nitrogen atmosphere, and the corrosion-resistant composite coating is obtained. According to the method, CrN and CrAlN are subjected to arc ion plating on the surface of the neodymium-iron-boron magnetic material, the internal stress of a coating layer is reduced after CrN plating, then the CrAlN plating layer is plated, the film-substrate binding force is enhanced, the corrosion resistance of the neodymium-iron-boron magnetic material is remarkably improved, meanwhile, the magnetic performance is not affected, and the service life of the material is prolonged.

Description

Technical Field

[0001] The invention relates to the field of corrosion protection of NdFeB magnetic materials, and in particular to a preparation method of a composite coating obtained by vacuum plating. Background Art

[0002] NdFeB permanent magnet materials have the advantages of excellent magnetic properties, low raw material cost, simple preparation process, etc., and are widely used in fields such as computer hard disk technology, electric vehicles, consumer electronics technology, etc. However, NdFeB has a multi-phase structure with a large potential difference between each phase, which makes it prone to high-temperature oxidation corrosion, wet heat hydrogen absorption corrosion and electrochemical corrosion during use.

[0003] So far, the surface protection of NdFeB has made some progress. The methods to improve the corrosion resistance of NdFeB can be divided into two main categories, one is the alloying method and the other is the surface coating method. Improving the corrosion resistance of magnets by alloy doping often faces defects such as high cost and degradation of magnetic properties. The chemical conversion film, electroplating and chemical plating methods commonly used in surface coating methods all have their own shortcomings. Passivation and phosphating treatment in chemical conversion film can no longer meet market demand. They are often used as pre-treatment or post-treatment processes to provide an effective adhesion surface or increase the density of the existing film layer. Although the electroplating process has strong market adaptability and is widely used, the bonding strength between the electroplated layer and NdFeB is poor, and it can cause serious pollution and cause great harm to the environment. As a supplement to the electroplating process, chemical plating can prepare a film layer on complex parts with excellent bonding strength and hardness. However, the plating solution will corrode and destroy the substrate, resulting in a loss of magnetic properties.

[0004] However, as the application scope of NdFeB expands, the existing protection process still cannot fully meet the actual needs. Therefore, an environmentally friendly technology is needed to improve the corrosion resistance of the magnet while maintaining the original excellent magnetic properties of the magnet. Arc ion plating technology, as a dry film forming technology, largely avoids damage to the substrate and is easy to prepare high-quality film layers. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a method for preparing a composite coating that improves the corrosion resistance of NdFeB. The composite coating prepared by the present invention has high bonding strength and excellent corrosion resistance, and will not affect the magnetic properties of the magnet itself.

[0006] The technical solution adopted by the present invention is:

[0007] A NdFeB protective coating with a composite structure comprises a CrN transition layer and a CrAlN protective layer which are sequentially arranged on the surface of a NdFeB substrate.

[0008] Further preferably, the thickness of the CrN transition layer is 0.4-1.1 μm.

[0009] Further preferably, the thickness of the CrAlN protective layer is 2.5-3.5 μm.

[0010] Further preferably, the atomic ratio of Cr to Al in the CrAlN layer is 7:3.

[0011] A method for preparing the composite coating for improving the corrosion resistance of NdFeB as described above comprises the following steps:

[0012] 1) manually grinding and mechanically polishing the NdFeB magnetic material, and then ultrasonically cleaning, drying, preheating and Cr ion bombardment cleaning to obtain a pretreated NdFeB matrix;

[0013] 2) using a chromium target to prepare a CrN transition layer on the surface of a pretreated NdFeB substrate by arc ion plating in a nitrogen atmosphere;

[0014] 3) A CrAlN layer is prepared on the surface of the CrN transition layer by arc ion plating using a chromium-aluminum target in a nitrogen atmosphere to obtain a corrosion-resistant composite coating.

[0015] Further preferably, in step 1), manual grinding is to grind the surface of the NdFeB magnetic material in order from coarse to fine using sandpaper of 180 mesh, 400 mesh, 800 mesh and 1200 mesh.

[0016] Further preferably, the mechanical polishing in step 1) refers to subjecting the ground material to a mirror finish using a diamond abrasive paste on a rotating polishing disc covered with flannel.

[0017] Further preferably, the solvent used in the ultrasonic cleaning in step 1) is alcohol, and the cleaning time is 5 min to 15 min.

[0018] Further preferably, the drying in step 1) is carried out at 100° C. to 200° C., and the drying time is 10 min to 20 min.

[0019] Further preferably, the preheating temperature in step 1) is 100° C. to 300° C., and the preheating time is 50 min to 70 min.

[0020] Further preferably, the Cr ion bombardment cleaning in step 1) is carried out under the conditions of an argon pressure of 0.4Pa to 1.0Pa, a target current of 60A to 90A, and a bias voltage of 400V to 600V, and the arc ion plating time is 5min to 10min.

[0021] Further preferably, the purity of the chromium target in step 2) is greater than 99.95%.

[0022] Further preferably, the arc ion plating in step 2) is carried out under the conditions of a nitrogen pressure of 0.8Pa to 1.5Pa, a target current of 60A to 90A, and a bias voltage of 100V to 200V, and the arc ion plating time is 5min to 25min.

[0023] Further preferably, the purity of the chromium-aluminum target in step 3) is greater than 99.95%.

[0024] Further preferably, in step 3), the arc ion plating is carried out under the conditions of a nitrogen pressure of 0.8 Pa to 1.5 Pa, a target current of 90 A to 100 A, and a bias voltage of 100 V to 200 V, and the arc ion plating time is 50 min to 70 min.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention performs arc ion plating of CrN and CrAlN on the surface of NdFeB magnetic material. After CrN plating, the internal stress of the coating layer is reduced. After the CrAlN coating layer is plated, the film-base bonding force is enhanced. The present invention significantly improves the corrosion resistance of NdFeB magnetic material without affecting the magnetic properties, prolongs the service life of the material, and meets the current market requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a cross-sectional SEM morphology image of the NdFeB magnetic material of the present invention.

[0028] Figure 2 The figure shows the dynamic polarization curves of NdFeB magnetic materials without coating and with CrN / CrAlN composite coating in 3.5% NaCl solution.

[0029] Figure 3 These are the demagnetization curves of NdFeB magnetic materials without coating and with CrN / CrAlN composite coating.

[0030] Figure 4 This is a scratch image of NdFeB magnetic material coated with CrN / CrAlN composite coating. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.

[0032] Example 1

[0033] Preparation of CrN / CrAlN composite coating on the surface of NdFeB magnetic material:

[0034] (1) The material of the substrate is NdFeB magnetic material, and the surface of the NdFeB magnetic material is ground from coarse to fine with sandpaper of 180 mesh, 400 mesh, 800 mesh, and 1200 mesh respectively; then mechanical polishing is performed, and mechanical polishing refers to the polishing of the ground material with diamond grinding paste on a rotating polishing disk with flannel cloth; the polishing process first uses W5 diamond polishing paste and then uses W2.5 diamond polishing paste, and the ultrasonic cleaning process uses alcohol cleaning for 10-15 minutes, and the temperature during drying is 100° C., and the drying time is 15-20 minutes;

[0035] (2) The diffusion pump is preheated to 150°C for 1 hour;

[0036] (3) After the roughing valve is opened, the rough vacuum is about 90Pa. The Roots pump is turned on to roughly vacuum the pump to below 3Pa. The fine pumping valve and the main valve are opened to vacuum the pump to 7×10 -3 Pa below, reaching the background vacuum;

[0037] (4) Argon gas was introduced to a pressure of 0.5-0.6 Pa, the pulse negative bias voltage was 500 V, the duty cycle was 60%, and the substrate was bombarded with Cr ions for 5 minutes;

[0038] (5) Adjust the nitrogen flow rate to make the vacuum degree reach 0.5-0.6 Pa, turn on the chromium target, the arc current of the chromium target is 75A, the negative bias voltage is 100V, and the deposition time of the CrN transition layer is 10 minutes;

[0039] (6) After closing the chromium target, evacuate to local vacuum, slowly introduce nitrogen until the nitrogen pressure is about 1.0 Pa, turn on the chromium aluminum target, the target current is 100 A, the negative bias voltage is 150 V, and the deposition time is 60 minutes;

[0040] (7) Turn off the chromium-aluminum target, turn off the nitrogen, turn off the bias power supply, turn off the diffusion pump, Roots pump, and mechanical pump, and take out the sample after the vacuum chamber is cooled by circulating cooling water and the temperature in the chamber reaches below 80°C.

[0041] Figure 1 This is a cross-sectional SEM image of a NdFeB magnetic material coated with a CrN / CrAlN composite coating. Figure 1 From bottom to top, they are NdFeB magnetic material substrate, CrN film, and CrAlN film. The thickness of the CrN film on the surface of the NdFeB magnetic material prepared in this embodiment is 0.6 microns, and the thickness of the CrAlN film is 3.2 microns.

[0042] Example 2

[0043] (1) The material of the substrate is NdFeB magnetic material, and the surface of the NdFeB magnetic material is ground from coarse to fine with sandpaper of 180 mesh, 400 mesh, 800 mesh, and 1200 mesh respectively; then mechanical polishing is performed, and mechanical polishing refers to the polishing of the ground material with diamond grinding paste on a rotating polishing disk with flannel cloth; the polishing process first uses W5 diamond polishing paste and then uses W2.5 diamond polishing paste, and the ultrasonic cleaning process uses alcohol cleaning for 10-15 minutes, and the temperature during drying is 100° C., and the drying time is 15-20 minutes;

[0044] (2) The diffusion pump is preheated to 150°C for 1 hour;

[0045] (3) After the roughing valve is opened, the rough vacuum is about 90Pa. The Roots pump is turned on to roughly vacuum the pump to below 3Pa. The fine pumping valve and the main valve are opened to vacuum the pump to 7×10 -3 Pa below, reaching the background vacuum;

[0046] (4) Argon gas was introduced to a pressure of 0.5-0.6 Pa, the pulse negative bias voltage was 500 V, the duty cycle was 60%, and the substrate was bombarded with Cr ions for 5 minutes;

[0047] (5) adjusting the nitrogen flow rate to make the vacuum degree reach 0.5-0.6 Pa, turning on the chromium target, the arc current of the chromium target is 75 A, the negative bias voltage is 100 V, and the deposition time of the CrN transition layer is 20 minutes;

[0048] (6) After closing the chromium target, evacuate to local vacuum, slowly introduce nitrogen until the nitrogen pressure is about 1.0 Pa, turn on the chromium aluminum target, the target current is 100 A, the negative bias voltage is 150 V, and the deposition time is 50 minutes;

[0049] (7) Turn off the chromium-aluminum target, turn off the nitrogen, turn off the bias power supply, turn off the diffusion pump, Roots pump, and mechanical pump, and take out the sample after the vacuum chamber is cooled by circulating cooling water and the temperature in the chamber reaches below 80°C.

[0050] The thickness of the CrN film on the surface of the NdFeB magnetic material prepared in this embodiment is 1.0 micrometer, and the thickness of the CrAlN film is 2.8 micrometer.

[0051] Example 3

[0052] (1) The material of the substrate is NdFeB magnetic material, and the surface of the NdFeB magnetic material is ground from coarse to fine with sandpaper of 180 mesh, 400 mesh, 800 mesh, and 1200 mesh respectively; then mechanical polishing is performed, and mechanical polishing refers to the polishing of the ground material with diamond grinding paste on a rotating polishing disk with flannel cloth; the polishing process first uses W5 diamond polishing paste and then uses W2.5 diamond polishing paste, and the ultrasonic cleaning process uses alcohol cleaning for 10-15 minutes, and the temperature during drying is 100° C., and the drying time is 15-20 minutes;

[0053] (2) The diffusion pump is preheated to 150°C for 1 hour;

[0054] (3) After the roughing valve is opened, the rough vacuum is about 90Pa. The Roots pump is turned on to roughly vacuum the pump to below 3Pa. The fine pumping valve and the main valve are opened to vacuum the pump to 7×10 -3 Pa below, reaching the background vacuum;

[0055] (4) Argon gas was introduced to a pressure of 0.5-0.6 Pa, the pulse negative bias voltage was 500 V, the duty cycle was 60%, and the substrate was bombarded with Cr ions for 5 minutes;

[0056] (5) Adjust the nitrogen flow rate to make the vacuum degree reach 0.5-0.6 Pa, turn on the chromium target, the arc current of the chromium target is 75 A, the negative bias voltage is 150 V, and the deposition time of the CrN transition layer is 10 minutes;

[0057] (6) After closing the chromium target, evacuate to local vacuum, slowly introduce nitrogen until the nitrogen pressure is about 1.0 Pa, turn on the chromium aluminum target, the target current is 100 A, the negative bias voltage is 150 V, and the deposition time is 60 minutes;

[0058] (7) Turn off the chromium-aluminum target, turn off the nitrogen, turn off the bias power supply, turn off the diffusion pump, Roots pump, and mechanical pump, and take out the sample after the vacuum chamber is cooled by circulating cooling water and the temperature in the chamber reaches below 80°C.

[0059] The thickness of the CrN film on the surface of the NdFeB magnetic material prepared in this embodiment is 0.5 microns, and the thickness of the CrAlN film is 3.2 microns.

[0060] Test example

[0061] Performance test of NdFeB magnetic material coated with CrN / CrAlN composite coating;

[0062] The corrosion resistance of NdFeB magnetic materials coated with CrN / CrAlN composite coating was tested by electrochemical workstation; the magnetic properties of NdFeB magnetic materials coated with CrN / CrAlN composite coating were tested by permanent magnet measuring instrument; the binding force of NdFeB magnetic materials coated with CrN / CrAlN composite coating was tested by scratch tester.

[0063] Figure 2 The figure shows the dynamic polarization curves of NdFeB magnetic materials without coating and with CrN / CrAlN composite coating in 3.5% NaCl solution.

[0064] Figure 3 These are the demagnetization curves of NdFeB magnetic materials without coating and with CrN / CrAlN composite coating.

[0065] Figure 4 This is a scratch image of NdFeB magnetic material coated with CrN / CrAlN composite coating.

[0066] Table 1 shows the self-corrosion potential and self-corrosion current density of NdFeB magnetic materials coated with CrN / CrAlN composite coating and uncoated NdFeB magnetic materials.

[0067] Table 2 shows the magnetic properties of NdFeB magnetic materials coated with CrN / CrAlN composite coating and uncoated NdFeB magnetic materials.

[0068] Table 1

[0069] Sample <![CDATA[Corrosion potential E corr (V)]]> <![CDATA[Corrosion current density I corr (A / cm 2 )]]> bare NdFeB -0.94 <![CDATA[7.06×10 -5 ]]> CrN / CrAlN layers -0.90 <![CDATA[8.62×10 -6 ]]>

[0070] Depend on Figure 2 It can be seen from Table 1 that the present invention reduces the self-corrosion current density of NdFeB magnetic materials by about one to two orders of magnitude, indicating that the corrosion resistance of NdFeB magnetic materials is significantly improved.

[0071] Table 2

[0072]

[0073] Depend on Figure 3 It can be concluded from Table 2 that, compared with the magnetic properties of the uncoated NdFeB magnetic material, the magnetic parameters of the NdFeB magnetic material coated with CrN / CrAlN composite coating provided by the present invention, the residual magnetic induction intensity value, coercive force and maximum magnetic energy product do not change, indicating that the composite coating does not affect the magnetic properties of the magnet itself.

[0074] Depend on Figure 4 It can be obtained that the upper critical load L of the coating under the scratch of the diamond indenter with a loading force ranging from 0 to 100N C2 It is 43.5N (>30N), indicating that the composite coating has good bonding strength.

[0075] It should be understood that the above detailed description of the technical solution of the present invention with the help of optimized embodiments is illustrative rather than restrictive, and it cannot be determined that the specific implementation methods of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, modifications to the technical solutions recorded in the embodiments, or equivalent replacement of some of the technical features therein, should be deemed to fall within the scope of patent protection determined by the claims submitted for the present invention.

[0076] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a composite coating for improving the corrosion resistance of NdFeB, characterized in that: The steps include: 1) manually grinding and mechanically polishing the NdFeB magnetic material, and then ultrasonically cleaning, drying, preheating and Cr ion bombardment cleaning to obtain a pretreated NdFeB matrix; 2) using a chromium target to prepare a CrN transition layer on the surface of a pretreated NdFeB substrate by arc ion plating in a nitrogen atmosphere; 3) A CrAlN layer is prepared on the surface of the CrN transition layer by arc ion plating using a chromium-aluminum target in a nitrogen atmosphere to obtain a corrosion-resistant composite coating.

2. A method for preparing a composite coating for improving the corrosion resistance of NdFeB as claimed in claim 1, characterized in that: In step 1), the manual grinding is to grind the surface of the NdFeB magnetic material with sandpaper of 180 mesh, 400 mesh, 800 mesh and 1200 mesh in sequence from coarse to fine.

3. A method for preparing a composite coating for improving the corrosion resistance of NdFeB as claimed in claim 1, characterized in that: In step 1), the mechanical polishing refers to treating the ground material with a diamond paste on a rotating polishing disc with a flannel cloth to perform mirror polishing; the ultrasonic cleaning adopts alcohol as the solvent, and the cleaning time is 5 min to 15 min; the drying is carried out at 100° C. to 200° C., and the drying time is 10 min to 20 min.

4. A method for preparing a composite coating for improving the corrosion resistance of NdFeB as claimed in claim 1, characterized in that: In step 1), the preheating temperature is 100° C. to 300° C., and the preheating time is 50 min to 70 min.

5. The method for preparing a composite coating for improving the corrosion resistance of NdFeB as claimed in claim 1, characterized in that: In step 1), the Cr ion bombardment cleaning is carried out under the conditions of an argon pressure of 0.4Pa to 1.0Pa, a target current of 60A to 90A, and a bias voltage of 400V to 600V, and the arc ion plating time is 5min to 10min.

6. A method for preparing a composite coating for improving the corrosion resistance of NdFeB as claimed in claim 1, characterized in that: The purity of the chromium target in step 2) is greater than 99.95%; the arc ion plating is carried out under the conditions of a nitrogen pressure of 0.8Pa to 1.5Pa, a target current of 60A to 90A, and a bias voltage of 100V to 200V, and the arc ion plating time is 5min to 25min.

7. A method for preparing a composite coating for improving the corrosion resistance of NdFeB as claimed in claim 1, characterized in that: In step 3), the purity of the chromium-aluminum target is greater than 99.95%; the arc ion plating is carried out under the conditions of a nitrogen pressure of 0.8Pa to 1.5Pa, a target current of 90A to 100A, and a bias voltage of 100V to 200V, and the arc ion plating time is 50min to 70min.

8. A composite coating for improving the corrosion resistance of NdFeB prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The invention comprises a CrN transition layer and a CrAlN protective layer which are sequentially arranged on the surface of a NdFeB substrate.

9. The composite coating for improving the corrosion resistance of NdFeB according to claim 8, characterized in that: The thickness of the CrN transition layer is 0.4-1.1 μm.

10. The composite coating for improving the corrosion resistance of NdFeB according to claim 8, characterized in that: The thickness of the CrAlN protective layer is 2.5-3.5 μm.

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