Background
Neodymium iron boron (NdFeB) as a third-generation rare earth permanent magnet material has excellent magnetic performance and high cost performance, currently, the China NdFeB industry accounts for nearly 80% of the global market share, and is the industrial center of the global sintered NdFeB magnet. Because of the characteristics of high efficiency, energy conservation, light weight, small volume, good control and speed regulation performance and the like, the neodymium-iron-boron magnet is widely applied to the sunward industry such as wind power generation, new energy automobiles, energy-saving household appliances and the like. However, the poor corrosion resistance of ndfeb magnets has severely hindered their large-scale application in industrial fields. Therefore, the improvement of the corrosion resistance of the neodymium iron boron magnetic material has important significance and value for the application and development of the neodymium iron boron magnetic material.
At present, the technology for improving the surface corrosion resistance of the neodymium iron boron magnet mainly comprises two main types: firstly, a proper amount of alloy elements such as Dy, Co and the like are added into the neodymium iron boron magnet, and although the chemical activity of the Nd-rich phase can be reduced and the electrochemical potential of the Nd-rich phase is close to that of the main phase, the aim of reducing the electrochemical corrosion speed is achieved, the magnetic performance of the magnet is also reduced, and the improvement on the corrosion resistance is limited. And secondly, preparing a coating with corrosion resistance on the surface of the neodymium iron boron magnet. The technology does not affect the magnetic performance of the magnet when improving the corrosion resistance of the surface of the neodymium iron boron magnet, so the method is a common means for improving the corrosion resistance of the surface of the neodymium iron boron magnet at present.
The main methods for realizing the preparation of the coating at present are as follows: electroplating, electroless plating, physical vapor deposition, and the like. The electroplating and chemical plating film becomes the current domestic mainstream industrial-scale neodymium iron boron magnet surface protection treatment method due to the higher process maturity and lower cost, but the technology has certain defects. First, both electroplating and electroless plating solutions can cause environmental pollution. Secondly, because the structure of the neodymium iron boron magnet is loose and porous, plating solution of electroplating and chemical plating may remain inside the neodymium iron boron magnet and be gradually released during the use process to damage the coating on the surface. As a physical vapor deposition technology with low cost, no waste, green and no pollution, the magnetron sputtering technology is widely applied to the improvement of the surface performance of various substrates. Compared with the traditional method, the magnetron sputtering technology has the unique advantages that: firstly, no pollutant is generated in the preparation process, and the method is a green and environment-friendly surface modification technology; secondly, the surface of the deposited coating is smooth and compact, and thirdly, the deposition rate of the coating is fast and can be controlled accurately; fourthly, the coating and the substrate have stronger bonding strength.
However, in the conventional magnetron sputtering technique, the ionization rate of sputtering atoms of the target is low, so that the plasma reaching the vicinity of the substrate has low energy, thereby reducing the mobility of the plasma on the surface of the substrate. Therefore, the coating prepared by magnetron sputtering often grows in a columnar crystal structure, and the grain boundary trend is vertical to the surface, so that the coating becomes a rapid channel of corrosive liquid and the failure of the protective performance of the coating is accelerated.
Disclosure of Invention
Therefore, the embodiment of the invention provides a composite modification method for surface protection of a neodymium iron boron magnet, which combines a conventional magnetron sputtering coating technology, high-power pulse magnetron sputtering and a composite surface modification method for plasma immersion ion implantation and deposition, and solves the problem that the conventional magnetron sputtering coating technology is insufficient in improvement of the surface corrosion resistance of the neodymium iron boron magnet.
In order to achieve the above object, an embodiment of the present invention provides the following: a composite modification method for surface protection of a neodymium iron boron magnet comprises the following steps:
step 100, cleaning pretreatment, namely cleaning the surface of the neodymium iron boron magnet, and drying the neodymium iron boron magnet;
200, performing surface glow cleaning, namely placing the neodymium iron boron magnet in a vapor deposition vacuum chamber, and adding negative bias to the surface of the neodymium iron boron magnet for ion etching;
300, modifying the surface of the neodymium iron boron magnet, namely providing negative bias for the Al target by utilizing a high-power pulse magnetron sputtering power supply, simultaneously providing negative high voltage for the neodymium iron boron magnet by an external power supply, matching pulse waveforms of the high-power pulse magnetron sputtering power supply and the neodymium iron boron magnet, realizing effective control on plasma energy, and modifying the surface of the neodymium iron boron magnet;
and 400, coating and depositing, namely providing negative bias for the Al target by using a unipolar pulse magnetron sputtering power supply, and simultaneously providing negative bias for the neodymium iron boron magnet by using an external power supply to realize surface coating of the neodymium iron boron magnet.
500, increasing the thickness of the deposited film, and repeating the step 300 and the step 400 until the surface of the neodymium iron boron magnet substrate obtains a composite modified coating with the required thickness;
and 600, finishing the coating of the neodymium iron boron magnet, releasing the residual gas in the vacuum chamber, and taking out the neodymium iron boron magnet.
As a preferable scheme of the present invention, in the step 200, the specific steps of performing glow cleaning on the surface of the neodymium iron boron magnet are as follows:
step 201, neodymium is addedThe ferroboron magnet is arranged on a neodymium iron boron magnet frame in the vacuum chamber, and air is pumped away by a mechanical pump and a molecular pump, so that the cavity of the vacuum chamber reaches a high vacuum level, and the vacuum degree is less than or equal to 10~3Pa;
Step 202, introducing inert gas into the vacuum chamber by using a mass flow device, and controlling the air pressure of the vacuum chamber to be 1.5 Pa;
step 203, providing a negative pulse power supply for the workpiece holder, and setting a preset voltage value and a preset duty ratio of the power supply;
and 204, continuously providing a pulse power supply for 10-30 min to finish the ion etching on the surface of the neodymium iron boron magnet.
In a preferred embodiment of the present invention, in step 203, the voltage value of the negative pulse power supply is 500V to 1000V, and the duty ratio is 50% to 90%.
As a preferable scheme of the present invention, in step 300, the surface modification of the ndfeb magnet specifically includes:
step 301, after ion cleaning, inert gas is introduced through gas flow control adjustment, so that the air pressure of a vacuum chamber is kept at 0.3 Pa-1 Pa;
step 302, adjusting the position of a neodymium iron boron magnet workpiece rack, and enabling the iron boron magnet workpiece rack to be opposite to an Al target;
303, providing a high-power pulse magnetron sputtering power supply for the Al target to apply negative bias;
step 304, providing negative bias voltage for the Al target, simultaneously providing negative high voltage for the workpiece holder through an external power supply, and matching pulse waveforms of the two, thereby realizing effective control on plasma energy;
and 305, keeping the surface modification time of the magnet to be 10-20 min.
As a preferable scheme of the invention, the voltage value of the high-power pulse magnetron sputtering power supply is 600V-800V, the pulse width is 50 mus-200 mus, and the frequency is 50 Hz-300 Hz.
As a preferred scheme of the invention, the negative high-voltage value provided for the workpiece holder is 10kV to 50kV, the pulse width is 50 mus to 200 mus, and the frequency is 50Hz to 300 Hz.
As a preferable scheme of the present invention, in the step 400, the coating deposition specifically includes:
step 401, keeping the position of a workpiece frame unchanged, introducing inert gas through a gas flow controller, and adjusting the gas pressure of a vacuum chamber to 0.3-1 Pa;
step 402, providing negative bias voltage for the Al target by a unipolar pulse magnetron sputtering power supply according to a preset current value and a preset duty ratio;
step 403, while providing a negative bias to the Al target, the external power supply provides a negative bias to the workpiece holder according to the set voltage value and duty ratio;
and step 404, keeping the working time of depositing the Al film on the surface of the workpiece within 30-60 min.
As a preferable scheme of the invention, the current value of the unipolar pulse magnetron sputtering power supply is 2A-5A, and the duty ratio is 50% -90%;
as a preferred scheme of the invention, the voltage value of negative high voltage is 50V-150V, and the duty ratio is 50% -90%.
As a preferable embodiment of the present invention, the number of times of repeating the modification and the plating deposition in step 500 is 5 to 10.
The embodiment of the invention has the following advantages:
(1) the invention comprises three technologies of conventional magnetron sputtering, high-power pulse magnetron sputtering and plasma immersion ion implantation deposition. Wherein the conventional magnetron sputtering technology is used for ensuring the overall deposition rate of the coating; the high-power pulse magnetron sputtering technology is used for generating high-density Al plasma and loading pulse high voltage on a substrate to realize the plasma immersion ion injection deposition process of Al ions.
(2) The plasma immersion ion injection deposition technology is adopted before the film deposition, so that a mixed interface can be formed between the substrate and the coating, and the binding force is improved; in the subsequent alternate deposition process, the atomic arrangement of the surface of the Al film can be broken by high-energy ions in the plasma immersion ion injection deposition technology, a nanocrystalline or amorphous layer is formed, and the columnar crystal structure of the Al film is broken.
(3) The combination of the high-power pulse magnetron sputtering technology and the plasma immersion ion implantation deposition technology ensures the binding force and the compactness of the coating. In addition, different technologies are alternately deposited to form a multi-layer coating structure, so that the defects of the coating are reduced, the grain boundary penetrating through the coating is blocked, and the corrosion resistance of the Ru iron boron (NdFeB) magnet is obviously improved.
Detailed Description
The present invention is described in terms of particular embodiments, other advantages and features of the invention will become apparent to those skilled in the art from the following disclosure, and it is to be understood that the described embodiments are merely exemplary of the invention and that it is not intended to limit the invention to the particular embodiments disclosed. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
As shown in fig. 1, the invention provides a composite modification method for surface protection of a neodymium iron boron magnet, and the method comprises three technologies of conventional magnetron sputtering, high-power pulse magnetron sputtering and plasma immersion ion implantation deposition. Wherein the conventional magnetron sputtering technology is used for ensuring the overall deposition rate of the coating; the high-power pulse magnetron sputtering technology is used for generating high-density Al plasma and loading pulse high voltage on a substrate to realize the plasma immersion ion injection deposition process of Al ions.
The method comprises the following steps:
step 100, cleaning pretreatment, cleaning the surface of the neodymium iron boron magnet, and drying the neodymium iron boron magnet.
The pretreatment comprises surface oxidation layer treatment, oil removal treatment, rust removal treatment and dirt treatment of the magnet, mechanical polishing treatment is firstly carried out on the neodymium iron boron magnet, then the neodymium iron boron magnet is sequentially placed in acetone and alcohol for ultrasonic cleaning, mechanical residues and rust on the surface are cleaned, and then the surface of the magnet is dried by an air pump.
200, performing surface glow cleaning, namely placing the neodymium iron boron magnet in a vapor deposition vacuum chamber, and adding negative bias to the surface of the neodymium iron boron magnet for ion etching.
The specific steps of performing glow cleaning on the surface of the neodymium iron boron magnet are as follows:
step 201, placing the neodymium iron boron magnet on a neodymium iron boron magnet frame in a vacuum chamber, and pumping away air by using a mechanical pump and a molecular pump to enable the cavity of the vacuum chamber to reach a high vacuum level, wherein the vacuum degree is less than or equal to 10~3Pa;
Step 202, introducing inert gas into the vacuum chamber by using a mass flow device, and controlling the air pressure of the vacuum chamber to be 1.5 Pa;
step 203, providing a negative pulse power supply for the workpiece frame, and setting a preset voltage value and a preset duty ratio of the power supply, wherein the voltage value of the pulse power supply is 500V-1000V, and the duty ratio is 50% -90%;
and 204, continuously providing a pulse power supply for 10-30 min to finish the ion etching on the surface of the neodymium iron boron magnet.
Ion etching is the most common form of dry etching, and is based on the principle that a gas exposed to an electron region forms a plasma, thereby generating ionized gas and a gas composed of released energetic electrons, thereby forming plasma or ions, and atoms of the ionized gas, when accelerated by an electric field, release enough force to tightly adhere to a material or etch a surface with surface expulsion force.
And 300, modifying the surface of the neodymium iron boron magnet, namely providing negative bias for the Al (aluminum) target by utilizing a high-power pulse magnetron sputtering power supply, and simultaneously providing negative high voltage for the neodymium iron boron magnet by an external power supply to modify the surface of the neodymium iron boron magnet.
The surface modification method of the neodymium iron boron magnet comprises the following specific steps:
step 301, after the ion cleaning, controlling the flow of the introduced inert gas through a gas flow meter, so that the pressure of the vacuum chamber is kept at 0.3 Pa-1 Pa, wherein the inert gas used in the embodiment is argon;
step 302, adjusting the position of a workpiece frame, and enabling the workpiece frame to face an Al target;
303, providing a high-power pulse magnetron sputtering power supply for the Al target to apply negative bias, and ensuring that the voltage value of the high-power pulse power supply is 600V-800V, the pulse width is 50 mus-200 mus and the frequency is 50 Hz-300 Hz;
step 304, providing negative bias voltage for the Al target material, simultaneously providing negative high voltage for the workpiece holder through an external power supply, wherein the negative high voltage value is 10kV to 50kV, the pulse width is 50 mus to 200 mus, the frequency is 50Hz to 300Hz,
and 305, keeping the surface modification time of the magnet to be 10-20 min.
In the embodiment, a high-power pulse magnetron sputtering power supply provides negative bias for an Al target to generate high-density Al plasma, the density of the plasma is improved by utilizing higher pulse peak power and lower pulse duty ratio, and meanwhile, negative high voltage is provided for a workpiece frame by an external power supply and pulse waveforms of the workpiece frame and the workpiece frame are matched to complete Al plasma immersion of a workpiece, so that ion implantation deposition is realized.
And 400, coating and depositing, namely providing negative bias for the Al target by using a unipolar pulse magnetron sputtering power supply, and providing negative bias for the neodymium iron boron magnet by using an external power supply to realize surface coating modification of the neodymium iron boron magnet.
The specific steps of the coating deposition are as follows:
step 401, keeping the position of a workpiece frame unchanged, introducing inert gas through a gas flow controller, and adjusting the gas pressure of a vacuum chamber to 0.3-1 Pa;
step 402, providing negative bias voltage for the Al target by the unipolar pulse magnetron sputtering power supply according to a preset current value and a preset duty ratio, wherein the current value of the unipolar pulse magnetron sputtering power supply is 2A-5A, and the duty ratio is 50% -90%;
step 403, while providing negative bias voltage for the Al target, an external power supply provides negative bias voltage for the workpiece holder according to a set voltage value and a duty ratio, wherein the current value of the unipolar pulse magnetron sputtering power supply is 2-5A, and the duty ratio is 50-90%;
and step 404, keeping the working time of depositing the Al film on the surface of the workpiece within 30-60 min.
Step 300 is specifically plasma pre-implantation, wherein the implantation target in the plasma immersion ion implantation deposition is a magnet, and the purpose is to improve the binding force between the film and the substrate, so that high-energy Al ions can enter the surface layer of the neodymium iron boron magnet, and an Al film is formed on the surface layer of the neodymium iron boron magnet, thereby improving the affinity of the substrate for the coating and improving the binding strength between the coating and the substrate.
The step 400 is specifically the alternate deposition of the film, in the process of alternately depositing the film, the high-energy Al ions can bombard the columnar crystal grains of the magnetron sputtering Al film, so that the lattice of the columnar crystal grains of the magnetron sputtering Al film is broken, recrystallization occurs at the bombardment temperature, the crystal grains are refined, a nanocrystalline or amorphous layer is formed, and the phenomenon that the nanocrystalline or amorphous layer penetrates through gaps among columnar crystal structures of the magnetron sputtering Al film and blocks a corrosion channel is effectively inhibited. Therefore, the method can obviously improve the density of the coating and the bonding strength of the film substrate, and improve the corrosion resistance of the surface of the neodymium iron boron magnet.
In conclusion, the combination of the high-power pulse magnetron sputtering technology and the plasma immersion ion implantation deposition technology provides compactness guarantee for the binding force between the magnet and the film coating. In addition, different technologies are alternately deposited to form a multi-layer coating structure, so that the defects of the coating are reduced, the grain boundary penetrating through the coating is blocked, and the corrosion resistance of the Ru iron boron (NdFeB) magnet is obviously improved.
And 500, increasing the thickness of the deposited film, and repeating the step 300 and the step 400 for 5-10 times until the surface of the neodymium iron boron magnet substrate obtains a composite modified coating with the required thickness.
And 600, finishing the vegetation of the neodymium iron boron magnet coating, releasing the residual gas in the vacuum chamber, and taking out the neodymium iron boron magnet.
Example 2
The invention is further described in detail in the following with reference to the accompanying drawings and practical examples. Taking an example of depositing an Al coating on the surface of a neodymium iron boron magnet, selecting a neodymium iron boron magnet with the size of 25mm × 12mm, and specifically comprising the following steps:
the method comprises the following steps: pre-treating a neodymium iron boron magnet coating: and (3) carrying out mechanical polishing treatment on the neodymium iron boron magnet, sequentially placing the neodymium iron boron magnet in acetone and alcohol for ultrasonic cleaning, and then drying the surface of the magnet by using an air pump.
Step two: and placing the neodymium iron boron magnet on a workpiece frame in a vacuum chamber, and vacuumizing by using a mechanical pump and a molecular pump to ensure that the cavity reaches a high vacuum level and the vacuum degree is less than or equal to 10-3 Pa.
Step three: argon gas introduced into the vacuum chamber is controlled by a mass flow device, and the gas in the vacuum chamber is 1.5 Pa.
Step four: the method comprises the steps of providing negative pulse voltage for a workpiece frame through an external power supply, setting a preset voltage value and a preset duty ratio, wherein the voltage value is 900V, the duty ratio is 90%, the treatment time is 20min, and cleaning the surface of the neodymium iron boron magnet is completed.
Step five: keeping the workpiece to face the Al target, and introducing argon through gas flow control adjustment to ensure that the air pressure of the vacuum chamber is 0.5 Pa. Providing negative bias voltage for the Al target through a high-power pulse magnetron sputtering power supply (high-power pulse magnetron sputtering technology), setting a preset voltage value, a preset pulse width and a preset frequency, wherein the voltage value is 750V, the pulse width is 100 mus, the frequency is 100Hz, simultaneously, providing negative high voltage for the workpiece frame through an external power supply, setting a preset voltage value and a preset duty ratio, the voltage value is 12kV, the pulse width is 100 mus, the frequency is 100Hz, and then starting a modification process of the surface of the neodymium iron boron magnet, and the processing time is 10 min.
Step six: keeping the workpiece to face the Al target, and introducing argon through gas flow control adjustment to ensure that the air pressure of the vacuum chamber is 0.5 Pa. And (2) providing negative bias voltage for the Al target material through unipolar pulse magnetron sputtering, setting a preset current value, a preset duty ratio and a preset frequency, wherein the current value is 5A, the duty ratio is 90%, and the preset frequency is 40kHz, meanwhile, providing negative bias voltage for the workpiece holder through an external power supply, setting a preset voltage value, a preset duty ratio and a preset frequency, the preset voltage value is 75V, the preset duty ratio is 90%, and the preset frequency is 40kHz, and then beginning to deposit an Al coating on the surface of the neodymium iron boron magnet, wherein the treatment time is 30 min.
Step seven: repeating the fifth step and the sixth step in the process for 5 times to obtain the composite modified coating positioned on the surface of the workpiece substrate.
Step eight: and (5) exhausting the vacuum chamber, taking out the pattern and finishing the preparation of the coating on the surface of the workpiece.
The prepared neodymium iron boron magnet is subjected to a neutral salt spray test, and the fact that the neodymium iron boron magnet prepared by the composite surface modification method can resist the neutral salt spray test for 200 hours is found, and the neodymium iron boron magnet prepared by conventional magnetron sputtering can resist the neutral salt spray test for 100 hours under the same condition is found, so that the corrosion resistance of the neodymium iron boron magnet is remarkably improved by the composite surface modification technology of the magnetron sputtering technology and the plasma immersion ion implantation and deposition (plasma immersion ion implantation deposition) technology.
Although the invention has been described in detail above with reference to a general description and specific examples, it will be apparent to one skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.