Diamond-iron-based magnetic composite abrasive and preparation method thereof

Abstract

The invention discloses a diamond-iron-based magnetic composite abrasive and a preparation method thereof, and relates to the technical field of powder metallurgy. According to the diamond-iron-based magnetic composite abrasive material, gas atomization iron powder with the large particle size, iron oxide powder with the small particle size, soft magnetic metal powder and diamond powder serve as raw materials, a low-temperature pre-reduction and high-temperature reduction sintering process is adopted, a Fe-Ni-diamond coating layer is formed on the surface of the gas atomization iron powder, and finally the diamond-iron-based magnetic composite abrasive material is obtained. By utilizing the characteristics of low cost, high sintering activity and the like of the iron oxide / nickel oxide powder, the problem that the diamond powder is easy to graphitize under aerobic and high-temperature conditions is solved through a multi-step reduction sintering process, and effective solidification of the diamond on an iron matrix is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, in particular to a diamond-iron-based magnetic composite abrasive and a preparation method thereof. Background Art

[0002] Magnetorheological finishing (MRF) technology was first proposed by Kordonski in the 1990s. Unlike traditional surface finishing methods, MRF uses an external magnetic field to control the rheological behavior of a magnetic polishing fluid, forming a flexible "small grinding head" with viscoelastic behavior. This drives non-magnetic abrasive particles to shear against the workpiece surface, thereby polishing the workpiece surface material. This characteristic enables MRF to achieve high material removal rates and excellent surface quality.

[0003] As a smart fluid, magnetorheological fluid (MRF) exhibits low viscosity and high fluidity, similar to a Newtonian fluid, in the absence of an external magnetic field. However, it exhibits high viscosity and low fluidity, similar to a Bingham fluid, in the presence of an applied magnetic field. Currently, MRF primarily consists of a mixture of three components: a base fluid (including water, organic solvents, mineral oil, and stabilizers), magnetic particles (such as carbonyl iron powder (CIPs) and Fe₃O₄), and abrasive particles (such as diamond powder, SiO₂, CeO₂, Al₂O₃, and ZrO₂). During the MR polishing process, the magnetic particles align along the magnetic field, forming strong magnetic chains. The abrasive is clamped in the gaps between these chains. The magnetic field indirectly controls the abrasive particles through the magnetic particles, resulting in limitations in both control force and precision. Furthermore, the relatively weak grip of the magnetic chains on the abrasive makes it easy for the abrasive to slip through the chains and escape from the polishing area during MR polishing, ultimately reducing polishing efficiency and effectiveness. In short, in existing magnetorheological fluid systems, the magnetic particles and non-magnetic abrasives fail to form a cohesive whole, making it difficult to effectively control the force, trajectory, and distribution uniformity of the non-magnetic abrasive particles through the magnetic field. This is a common pain point in magnetorheological polishing.

[0004] In response to the above problems, an obvious solution is to combine magnetic particles and abrasive particles to form a composite abrasive. Common methods include chemical method, spray granulation method, gas atomization method, or high-temperature sintering method. Among them, the chemical method has many restrictions on the abrasive system. Usually, it can only coat the surface of the magnetic particles with oxide abrasives such as SiO2, TiO2, Al2O3 that can be hydrolyzed or precipitated. The coating layer has low strength, thin thickness, and high cost, making it difficult to obtain practical application. For example, Zhai et al. (Synthesis and characterization of nanocomposite Fe3O4 / SiO2 core-shell abrasives for high-efficiency ultrasound-assisted magneto-rheological polishing of sapphire[J].CERAMICS INTERNATIONAL, 2021, 47(22):31681-31690.) used a chemical synthesis method to coat the surface of Fe3O4 magnetic particles with a layer of SiO2 about 20nm thick. Our team (A multi-micro-edged diamond-iron-based spherical composite magnetic abrasive, its preparation method, and application, Chinese invention patent, application number: 202410800284.6) prepared a diamond-iron-based spherical composite magnetic abrasive using iron-based magnetic powder and 1.0-1.5μm diamond abrasive particles as raw materials, using a spray granulation method and reduction sintering. However, in the composite abrasive obtained by this method, most of the hard phase abrasive particles are distributed within the iron matrix, which not only reduces the magnetic saturation strength of the composite abrasive, but also, due to the weak grinding characteristics of magnetorheological flow, the internal hard abrasive particles cannot be exposed during the magnetorheological process, making it difficult to perform the grinding effect.

[0005] Gas atomization and high-temperature sintering methods usually require high temperatures. For example, Zhang et al. (Preparation of white alumina spherical composite magnetic abrasive by gas atomization and rapid solidification [J]. SCRIPTA MATERIALIA, 2011, 65(5): 416-419.) prepared spherical composite abrasives using 7μm white corundum as abrasive particles and a Fe-Si-Al-Ni soft magnetic alloy as a matrix by gas atomization at an atomization temperature of 1580°C. A.Anupam (Synthesis and Characterization of Sintered MagneticAbrasive Particles having Alumina and Carbonyl Iron Powder[C].IOP CONFERENCESERIES:MATERIALS SCIENCE&ENGINEERING,2020,804(1):012002) cold-pressed alumina abrasives and hydroxy iron powder after high-energy ball milling, and sintered and crushed the pressed green sheet at a high temperature of 1000-1545°C to obtain a magnetic composite abrasive of hydroxy iron powder-alumina. Zhang Xinjian et al. (CN119709125A) mixed iron powder, nano-iron powder with abrasives such as corundum or silicon carbide, and then sintered and crushed them at 800-1200°C to obtain a magnetic abrasive with a core-shell structure. All three methods require high-temperature processes, which can easily cause diamond to react with the iron matrix or graphitize. Therefore, the hardest material diamond is rarely used as abrasive, and most hard ceramic abrasives such as alumina or silicon carbide are used. This results in a relatively short service life and efficiency of the composite abrasive. Furthermore, to improve the bonding strength between the metal matrix and the hard abrasive grains, the above method has to use expensive nano-scale metal powders as raw materials, which significantly increases the production cost of the composite abrasive.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide a diamond-iron based magnetic composite abrasive and a preparation method thereof, aiming to improve the hardness and service life of the abrasive grains in the composite abrasive.

[0008] The present invention is achieved in that:

[0009] In a first aspect, the present invention provides a method for preparing a diamond-iron-based magnetic composite abrasive, comprising:

[0010] The soft magnetic metal powder, iron oxide powder, metal oxide powder containing a solid solution element, and diamond abrasive grains are uniformly mixed to obtain a mixed powder; wherein the particle sizes of the iron oxide powder, the metal oxide powder containing a solid solution element, and the diamond abrasive grains are all smaller than the particle size of the soft magnetic metal powder; the solid solution element contained in the metal oxide powder containing a solid solution element is selected from at least one of nickel, cobalt, and tin; and the mass ratio of the total amount of the iron oxide powder and the metal oxide powder containing a solid solution element to the diamond abrasive grains is (5-10):1;

[0011] The mixed powder is cold pressed to obtain a block-shaped green body;

[0012] The block green body is subjected to high-temperature reduction to obtain a reduced body; the high-temperature reduction process includes: keeping warm in a hydrogen atmosphere at 400°C-450°C for 0.2h-1.0h, then keeping warm in a hydrogen atmosphere at 450°C-550°C for 0.2h-1.0h, and then keeping warm in a hydrogen atmosphere at 750°C-800°C for 0.5h-1.5h.

[0013] In an optional embodiment, the metal oxide powder containing solid-solution elements is nickel oxide powder, and the mass ratio of iron element to nickel element in the iron oxide powder and the metal oxide powder containing solid-solution elements is (2.3-9.0):1.

[0014] In an optional embodiment, the mass ratio of the total amount of the iron oxide powder and the metal oxide powder containing solid-solution elements to the soft magnetic metal powder is (1.00-2.33):1.

[0015] In an optional embodiment, the soft magnetic metal powder is aerosolized iron powder with a particle size of 38 μm-150 μm.

[0016] In an optional embodiment, the iron oxide powder and the nickel oxide powder are iron oxide powder and nickel oxide powder with a particle size of ≤1 μm;

[0017] And / or, the particle size of the diamond abrasive grains is 1 μm-10 μm.

[0018] In a second aspect, the present invention further provides a diamond-iron-based magnetic composite abrasive prepared by the preparation method in any of the above embodiments.

[0019] In an optional embodiment, it includes a magnetic metal core and a magnetic metal-abrasive composite shell layer coated on the surface of the magnetic metal core;

[0020] The magnetic metal-abrasive composite shell contains soft magnetic metal and diamond abrasive particles. The soft magnetic metal is an iron-nickel alloy. The thickness of the magnetic metal-abrasive composite shell is 1-20 μm, and the mass fraction of iron is 50%-90%, the mass fraction of nickel is 1%-30%, and the mass fraction of diamond is 1%-40%.

[0021] In an optional embodiment, commercial ferric oxide and nickel oxide powders are used as raw materials, which are not only cheap and easy to obtain, but also have a fine powder particle size (≤1μm, usually 300-500nm). This powder can be quickly reduced at low temperatures (400-550°C) to a reduction degree of more than 90%, thereby reducing the damage caused to the diamond abrasive by the oxygen element while maintaining high sintering activity. In addition, the elemental nickel generated by the nickel oxide powder can not only be further alloyed with iron to increase the strength and hardness of the shell and its bonding force with the diamond abrasive, but also nickel can further inhibit the promotion of high-temperature graphitization of diamond by iron and improve the corrosion resistance of the shell. In order to improve the efficiency of magnetorheological polishing, corrosive solvents such as hydrogen peroxide, acid, and alkali are usually added to the magnetorheological fluid. Improving the corrosion resistance of the shell by nickel can further improve the service life of the composite abrasive.

[0022] It should be noted that diamond is extremely prone to graphitization in the presence of oxygen, high temperature, and iron-based catalysts, losing its hard abrasive function. Therefore, when preparing magnetic composite abrasives using high-temperature sintering methods, iron and nickel oxides are basically not used as shell consolidation raw materials. Instead, elemental iron powder or its alloy powder is used. This results in excessively high consolidation temperatures. In order to reduce the consolidation temperature, some studies have had to use expensive nano-iron powder as raw materials. Even so, in order to achieve effective consolidation of the shell metal to the hard abrasive, the final sintering temperature is usually above 1000°C. Because diamond will undergo significant graphitization above 900°C, there are few reports on diamond-iron-based composite abrasives. However, as the hardest substance in nature, diamond has significant performance advantages in terms of service life compared to other abrasives (such as ceramic abrasives such as corundum and silicon carbide).

[0023] The present invention has the following beneficial effects: It uses inexpensive and readily available iron oxide powder, nickel oxide powder, and diamond abrasive grains as shell raw materials. It employs a low-temperature pre-reduction followed by a high-temperature reduction sintering process. First, more than 90% of the iron oxide powder and metal oxide powder containing dissolved elements (such as nickel oxide) are reduced at a low temperature, reducing oxygen damage to diamond under high-temperature conditions while maintaining the powder's sintering activity. The iron and nickel are then alloyed and densified by sintering at a maximum temperature of 800°C, improving the shell's strength, hardness, and corrosion resistance, as well as its effective bonding with the diamond abrasive grains, while preventing significant graphitization or thermal damage to the diamond. The present invention can significantly improve the polishing efficiency and service life of magnetic composite abrasives. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is an SEM image of the magnetic composite abrasive with a core-shell structure prepared in Example 1;

[0026] Figure 2 Schematic diagram of the structure of the magnetic composite abrasive with a core-shell structure prepared in Example 1;

[0027] Figure 3 This is the element surface distribution diagram of the magnetic composite abrasive with a core-shell structure. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0029] Existing core-shell magnetic abrasives generally cannot use diamond as the hard phase, and can only use hard phases with shorter hardness and service life, such as silicon carbide, which greatly affects product performance. The embodiments of the present invention creatively utilize iron oxide and nickel oxide, which are not generally used in the field, as the solid phase raw materials of the shell layer. They have higher sintering activity and can be consolidated below 800°C. Through an optimized high-temperature reduction process, a high-strength, high-hardness, and highly corrosion-resistant Fe-Ni matrix can be formed, while preventing graphitization of the diamond in the shell layer.

[0030] An embodiment of the present invention provides a method for preparing a diamond-iron-based magnetic composite abrasive, comprising:

[0031] S1. Preparation of mixed powder

[0032] Soft magnetic metal powder, iron oxide powder, metal oxide powder containing a solid solution element, and diamond are uniformly mixed to prepare a mixed powder. The particle sizes of the iron oxide powder, the metal oxide powder containing a solid solution element, and the diamond are all smaller than those of the soft magnetic metal powder to ensure that the larger iron powder particles are fully coated as possible during the subsequent pressing process. The metal oxide powder containing a solid solution element contains at least one of nickel, cobalt, and tin, and the solid solution element contained can be any one or more of these.

[0033] Specifically, the solid solution elements in the embodiments of the present invention refer to elements that form a solid solution with the main element (iron). Nickel, cobalt, and tin can all form solid solutions. In addition to increasing strength and hardness, nickel can also improve corrosion resistance, which is beneficial to improving product performance compared to other solid solution elements.

[0034] In some embodiments, the mixed powder preparation process includes mixing soft magnetic metal powder, iron oxide powder, metal oxide powder containing a solid solution element, diamond, a solvent, and a binder, followed by drying to remove the solvent. The addition of the solvent allows the binder to be evenly dispersed and the raw materials to be mixed uniformly. The binder strengthens the bonding between the particles during the cold pressing process and is subsequently decomposed and removed during the high-temperature reduction process.

[0035] In order to better form the coating, form a core-shell structure with better morphology and structure, and obtain a composite powder of the expected particle size, the particle size of each raw material is regulated: the soft magnetic metal powder can be aerosolized iron powder or hydroxy iron powder, such as aerosolized iron powder with a particle size of 38μm-150μm; the iron oxide powder is ferric oxide powder with a particle size of ≤1μm; the metal oxide powder containing solid solution elements is nickel oxide powder with a particle size of ≤1μm; the particle size of the diamond abrasive is 1μm-10μm. Specifically, the above-mentioned aerosolized iron powder is a commercially available raw material, which is a fine iron-based powder prepared by gas atomization technology (Gas Atomization), which is widely used in powder metallurgy, 3D printing, magnetic materials, welding materials and other fields. The particle size of the composite abrasive is mainly related to the particle size of the raw material (aerosolized iron powder), the cold pressing process, the heat treatment temperature, and the degree of crushing. This composite abrasive can be heat-treated later to not only increase the bonding strength of the powder but also strengthen the matrix's grip on the diamond abrasive grains. Therefore, magnetorheological fluids made with composite abrasives have advantages such as excellent magnetorheological effects, high grinding and polishing efficiency, short response time, high grinding and polishing precision, and long service life.

[0036] To produce a nearly spherical particle product, the inventors optimized the dosage of the main raw materials: the mass ratio of iron to nickel in the iron oxide powder and the metal oxide powder containing solid solution elements is (2.3-9.0):1, such as 2.3:1, 3.0:1, 4.0:1, 5.0:1, 6.0:1, 7.0:1, 8.0:1, 9.0:1, etc. Preferably, the metal oxide powder containing solid solution elements is nickel oxide powder, and the mass ratio of iron to nickel in the iron oxide powder and nickel oxide powder is 4:1. The mass ratio of the total amount of the iron oxide powder and the metal oxide powder containing solid solution elements to the soft magnetic metal powder is (1.00-2.33):1, preferably 7:3. The mass ratio of the total amount of the iron oxide powder and the metal oxide powder containing solid solution elements to the diamond is (5-10):1, such as 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc., preferably 10:1. It is advisable to control the amount of each raw material within the above range, which is beneficial to maintaining the magnetic saturation strength of the magnetic metal shell while improving its own hardness, corrosion resistance and holding power for diamond abrasive particles.

[0037] In some embodiments, the binder may be a polyvinyl alcohol solution, but is not limited thereto. The solvent may be water, ethanol, acetone, etc. The amounts of the binder and solvent are not limited and can be used in a wide range of combinations.

[0038] In some embodiments, drying after mixing can be carried out by oven drying, and the drying temperature is controlled to be 50°C-80°C, such as 50°C, 60°C, 70°C, 80°C, etc.; the drying time is 10h-15h, such as 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0039] S2, cold pressing

[0040] The mixed powder is cold pressed to obtain a block-shaped green body.

[0041] In some embodiments, the dried mixed powder of S1 is placed in a mold and cold pressed at a pressure of 10 MPa to 40 MPa. The specific pressure can be 10 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, or 40 MPa. To achieve a uniform pressing effect, the holding time is 1 to 3 minutes, such as 1 minute, 2 minutes, or 3 minutes.

[0042] It should be noted that during the cold pressing process, a suitable mold is required to achieve a better density after powder mixing. To avoid the impact of the external environment and impurities on the mixed powder, such as impurities in the mold, cold pressing should be carried out in a clean mold at room temperature and pressure.

[0043] S3, high temperature reduction

[0044] The block green body prepared by S2 is subjected to high-temperature reduction to reduce the oxides to form an iron-iron alloy-diamond reduced body.

[0045] In some embodiments, in order to allow the reduction to proceed fully, the high-temperature reduction process can be divided into three stages: reacting at 400°C-450°C for 0.2h-1.0h, then reacting at 450°C-550°C for 0.2h-1.0h, and then reacting at 750°C-800°C for 0.5h-1.5h. The total reaction time can be controlled to be 1h-3h. The embodiment of the present invention adopts a low-temperature pre-reduction + high-temperature reduction sintering process, so that iron oxide and nickel oxide can be used as shell raw materials. The maximum sintering temperature is 800°C, which can form a high-strength, high-hardness, and high-corrosion-resistant Fe-Ni matrix, while avoiding graphitization of the diamond in the shell.

[0046] Specifically, the temperature of the first stage high-temperature reduction can be 400°C, 430°C, 450°C, etc., and the reaction time can be 0.2h, 0.5h, 0.8h, 1.0h, etc.; the temperature of the second stage high-temperature reduction can be 450°C, 480°C, 500°C, 530°C, 550°C, etc., and the reaction time can be 0.2h, 0.5h, 0.8h, 1.0h, etc.; the temperature of the first stage high-temperature reduction can be 750°C, 780°C, 800°C, etc., and the reaction time can be 0.5h, 1.0h, 1.5h, etc.

[0047] In some embodiments, the reduction atmosphere may be, but is not limited to, a hydrogen atmosphere. To avoid the influence of the external environment on the reduction process, such as oxygen in the air, the high-temperature reduction may be performed in 99.99% pure hydrogen at a gas flow rate of 2 L / min.

[0048] Taking nickel as an example of the doping element to illustrate the reaction principle, during the high-temperature reduction process, Ni2O3 is reduced to Ni, Fe2O3 is first reduced to Fe3O4 and then to FeO, and finally to Fe. At the same time, at a high temperature of 800°C, Ni and Fe will diffuse to form Fe-Ni alloy.

[0049] S4, crushing and screening

[0050] The magnetic composite abrasive with a core-shell structure is obtained by crushing and screening the reduced blank.

[0051] Specifically, the block green body is first placed in a crusher to be crushed into powder, and then passed through a 200-300 mesh sieve to finally obtain a magnetic composite abrasive with a core-shell structure.

[0052] It should be noted that the preparation of a composite abrasive with a spherical structure by mixing, stirring, drying, cold pressing, high-temperature reduction and crushing and screening is not only simple in process and low in cost, but also can better control its particle size (for example, equal to 75-105 μm), so that the magnetorheological fluid prepared from the composite powder has better magnetic response while also having better magnetorheological effect and grinding and polishing performance.

[0053] An embodiment of the present invention further provides a diamond-iron-based magnetic composite abrasive, which is prepared by the preparation method in any of the above embodiments. The prepared diamond-iron-based magnetic composite abrasive has the advantages of high strength and hardness, corrosion resistance, and long service life.

[0054] In some embodiments, it includes a magnetic metal core and a magnetic metal-diamond abrasive composite shell layer coated on the surface of the magnetic metal core; wherein the magnetic metal-diamond abrasive composite shell layer contains soft magnetic metal and diamond abrasive particles, and the soft magnetic metal is an iron-nickel alloy.

[0055] Furthermore, the thickness of the magnetic metal-diamond abrasive composite shell is 1-20 μm (e.g., 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, etc.), wherein the mass fraction of the iron element is 50%-90% (e.g., 50%, 60%, 70%, 80%, 90%, etc.), the mass fraction of the nickel element is 1%-30% (e.g., 1%, 5%, 10%, 15%, 20%, 25%, 30%, etc.), and the mass fraction of the diamond abrasive is 1%-40% (e.g., 1%, 5%, 10%, 20%, 30%, 40%, etc.). If the nickel content is too low, the shell's holding force on the diamond abrasive or its corrosion and wear resistance will decrease. If the iron content is too low, the magnetic properties of the core-shell structure magnetic abrasive will be reduced. If the reduction temperature is too low, the Fe-Ni alloy layer will not form on the surface, resulting in a lower bonding strength between the shell and the abrasive.

[0056] In a preferred embodiment, the magnetic metal-diamond abrasive composite shell is composed of an iron-nickel alloy and diamond abrasive grains, wherein the mass fraction of iron is 80%, the mass fraction of nickel is 20%, and the mass fraction of diamond abrasive grains is 10%. The mass fractions of iron, alloying elements, and diamond abrasive grains are preferably within the above-mentioned ranges. Within this range, the iron content and diamond abrasive grain content can be adjusted as needed to meet different process requirements.

[0057] It should be noted that properly controlling the proportion of diamond abrasive grains can effectively improve grinding and polishing efficiency. However, an excessively high proportion of diamond abrasive grains will reduce the volume fraction of the metal matrix, thereby reducing the specific saturation magnetic strength of the composite abrasive, prolonging the composite abrasive's response time, and weakening the grinding force. At the same time, an excessive amount of diamond abrasive grains will result in insufficient grip of the matrix on the diamonds, which can easily cause diamond grains to fall off. Diamond abrasive grain size affects both grinding and polishing efficiency. Increasing diamond abrasive grain size, while improving grinding and polishing efficiency, will also reduce grinding and polishing quality.

[0058] Embodiments of the present invention further provide a magnetic composite abrasive, including the diamond-iron-based magnetic composite abrasive of any of the aforementioned embodiments. Specifically, because the diamond-iron-based magnetic composite abrasive provided in embodiments of the present invention is a solid powder with high bonding strength, controllable particle size, and high particle size concentration, it can impart good magnetorheological properties to magnetorheological fluids and can be used for magnetorheological polishing.

[0059] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0060] Example 1

[0061] This embodiment provides a method for preparing a diamond-iron-based magnetic composite abrasive, and the steps are as follows:

[0062] (1) Preparation of mixed powder

[0063] Mixing: 30g of atomized iron powder, 56.18g of Fe2O3 powder, 13.82g of Ni2O3 powder, and 7g of diamond (Dia) powder were mixed in a mixer (under normal temperature and pressure) for 2 hours. The mixture contained 64.76wt% Fe and 9.16wt% Ni. The atomized iron powder had a particle size of 50-75μm, the Fe2O3 powder had a particle size of <1μm, the Ni2O3 powder had a particle size of 10μm, and the Dia had a particle size of 7μm.

[0064] Stirring: Add 35 g of anhydrous ethanol and 5 g of PVA solution (30% polyvinyl alcohol, 70% deionized water) to the mixed powder and stir in an air atmosphere for half an hour.

[0065] Drying: Place the stirred powder in a drying oven and dry it at 80°C for 12 hours to obtain a mixed powder, which is then vacuum-packed.

[0066] Among the raw materials used in this embodiment, the mass ratio of iron to nickel in the total amount of iron oxide and nickel oxide is 4:1; the mass ratio of the total amount of iron oxide and nickel oxide to iron powder is 2.33:1; and the mass ratio of the total amount of iron oxide and nickel oxide to diamond abrasive is 10:1.

[0067] (2) Cold pressing

[0068] Prepare the mold: Place the obtained mixed powder into a clean mold (the mold is circular, with a radius and height of 7.5 cm and 10 cm respectively) and spread and compact it.

[0069] Cold pressing: Place the mold filled with the mixed powder into the center of the hydraulic press platform, set the pressure parameters, and press to form. Control the operating pressure to 20MPa and the pressing time to 2 minutes.

[0070] (3) High temperature reduction

[0071] The green block was placed in a vacuum furnace and vacuumed to 1×10 -1 Pa, then introduce hydrogen (99.99% purity) at a flow rate of 2 L / min. Maintain at 400°C for 0.5 h, 500°C for 0.5 h, and 800°C for 1 h, for a total holding time of 2 h.

[0072] (4) Crushing and screening

[0073] The reduced green body is placed in a crusher and fully crushed. The crushed powder is passed through a 100-200 mesh sieve to obtain a diamond-iron-based magnetic composite abrasive.

[0074] Example 2

[0075] The only difference from Example 1 is that the amounts of raw materials used in step (1) are different. The specific raw materials are as follows:

[0076] Mixing: Mix 40g of atomized iron powder, 48.1g of Fe2O3 powder, 11.9g of Ni2O3 powder, and 6g of diamond (Dia) powder in a mixer for 2 hours. The atomized iron powder has a particle size of 50-75μm, the Fe2O3 powder has a particle size of <1μm, the Ni2O3 powder has a particle size of 10μm, and the Dia powder has a particle size of 7μm.

[0077] In this embodiment, the mass ratio of iron to nickel in the total amount of iron oxide and nickel oxide is 4:1; the mass ratio of the total amount of iron oxide and nickel oxide to iron powder is 1.5:1; and the mass ratio of the total amount of iron oxide and nickel oxide to diamond abrasive grains is 10:1. The mixed raw material has an Fe content of 69.4 wt% and a Ni content of 7.92 wt%.

[0078] Example 3

[0079] The only difference from Example 1 is that the amounts of raw materials used in step (1) are different. The specific raw materials are as follows:

[0080] Mixing: Mix 50g of atomized iron powder, 40.1g of Fe2O3 powder, 9.9g of Ni2O3 powder, and 5g of diamond (Dia) powder in a mixer for 2 hours. The atomized iron powder has a particle size of 50-75μm, the Fe2O3 powder has a particle size of <1μm, the Ni2O3 powder has a particle size of 10μm, and the Dia powder has a particle size of 7μm.

[0081] In this embodiment, the mass ratio of iron to nickel in the total amount of iron oxide and nickel oxide is 4:1; the mass ratio of the total amount of iron oxide and nickel oxide to iron powder is 1:1; and the mass ratio of the total amount of iron oxide and nickel oxide to diamond abrasive grains is 10:1. The mixed raw material has an Fe content of 74.33 wt% and a Ni content of 6.67 wt%.

[0082] Example 4

[0083] The only difference from Example 1 is that the amount of raw materials used in step (1) is different, the mass of diamond (Dia) powder is 14g, and the amounts of other raw materials are the same as in Example 1.

[0084] In this embodiment, the mass ratio of iron to nickel in the total amount of iron oxide and nickel oxide is 4:1 (the same as in Example 1); the mass ratio of the total amount of iron oxide and nickel oxide to iron powder is 2.33:1 (the same as in Example 1); and the mass ratio of the total amount of iron oxide and nickel oxide to diamond abrasive grains is 5:1. The mixed raw material has an Fe content of 60.78 wt% and a Ni content of 8.60 wt%.

[0085] Example 5

[0086] The only difference from Example 1 is that the amounts of raw materials used in step (1) are different, the mass of iron oxide powder is 63.05 g, the mass of nickel oxide is 6.95 g, and the amounts of other raw materials are the same as in Example 1.

[0087] In this embodiment, the mass ratio of iron to nickel in the total amount of iron oxide and nickel oxide is 9:1; the mass ratio of the total amount of iron oxide and nickel oxide to iron powder is 2.33:1; and the mass ratio of the total amount of iron oxide and nickel oxide to diamond abrasive grains is 10:1. The mixed raw material has an Fe content of 69.25 wt% and a Ni content of 4.61 wt%.

[0088] Example 6

[0089] The only difference from Example 1 is that the amounts of raw materials used in step (1) are different, the mass of iron oxide powder is 52.68 g, the mass of nickel oxide is 17.32 g, and the amounts of other raw materials are the same as in Example 1.

[0090] In this embodiment, the mass ratio of iron to nickel in the total amount of iron oxide and nickel oxide is 3:1; the mass ratio of the total amount of iron oxide and nickel oxide to iron powder is 2.33:1; and the mass ratio of the total amount of iron oxide and nickel oxide to diamond abrasive grains is 10:1. The mixed raw material has an Fe content of 62.47 wt% and a Ni content of 11.49 wt%.

[0091] Comparative Example 1

[0092] The only difference from Example 1 is that nickel oxide is not added and is replaced by an equal amount of iron oxide.

[0093] Comparative Example 2

[0094] The powders in Example 1 of this comparative example were simply mechanically mixed and then used for magnetorheological polishing.

[0095] Comparative Example 3

[0096] The only difference from Example 1 is that the diamond abrasive grains in step (1) are replaced with aluminum oxide abrasive grains of the same particle size.

[0097] Comparative Example 4

[0098] The only difference from Example 1 is that the operating temperature during the high-temperature reduction process was controlled at 850° C. and the total holding time was 2 h. Raman spectroscopy showed that the diamond graphitization rate exceeded 7%, and no subsequent polishing test was performed.

[0099] Comparative Example 5

[0100] The only difference from Example 1 is that the amount of raw materials used in step (1) is different, the mass of diamond (Dia) powder is 21g, and the amounts of other raw materials are the same as in Example 1.

[0101] In this comparative example, the mass ratio of iron to nickel in the total amount of iron oxide and nickel oxide was 4:1 (the same as in Example 1); the mass ratio of the total amount of iron oxide and nickel oxide to iron powder was 2.33:1 (the same as in Example 1); and the mass ratio of the total amount of iron oxide and nickel oxide to diamond abrasive grains was 3.33:1. The mixed raw material had an Fe content of 57.27 wt %, and a Ni content of 8.11 wt %.

[0102] Test Example 1 The composite powder prepared in Example 1 was observed by scanning electron microscopy. Figure 1 As shown, the scanning electron microscope image shows that multiple tiny diamond abrasive particles are embedded in the surface of the iron-based particles.

[0103] like Figure 2 , which is a cross-sectional view of the composite powder prepared in Example 1, has core-shell structure characteristics.

[0104] The composition of the obtained core-shell structured iron-based diamond composite abrasive was analyzed by EDS. Figure 3 As shown in the figure, it verifies that the diamond particles are embedded in the surface of the spherical particles, and the Fe and Ni elements are evenly distributed in the composite abrasive.

[0105] The magnetic properties of the core-shell iron-based diamond composite abrasive were characterized multiple times by a vibrating sample magnetometer. The magnetic strength of the samples ranged from 140.8 to 176.1 emu / g, but was always maintained above 140 emu / g.

[0106] Test Example 2

[0107] The test examples and comparative examples provide composite abrasives for magnetorheological polishing of single crystal silicon wafers. The polishing results are shown in Table 1.

[0108] Test method: Use Japan Mitutoyo SJ-210 handheld roughness tester to measure the roughness of single crystal silicon workpiece before and after polishing.

[0109] Table 1 provides a comparison of the magnetorheological processing effects of composite abrasives in the examples and comparative examples.

[0110]

[0111]

[0112] As can be seen from Table 1, the polishing effect of Example 1 is the best. Comparative Example 3 shows that when aluminum oxide is used as the hard abrasive, the polishing efficiency is low and the composite abrasive easily loses its polishing ability.

[0113] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a diamond-iron-based magnetic composite abrasive, characterized in that: include: Soft magnetic metal powder, iron oxide powder, metal oxide powder containing solid solution elements, and diamond abrasive grains are uniformly mixed to obtain a mixed powder; wherein the particle sizes of the iron oxide powder, the metal oxide powder containing solid solution elements, and the diamond abrasive grains are all smaller than the particle size of the soft magnetic metal powder; the solid solution element contained in the metal oxide powder containing solid solution elements is selected from at least one of nickel, cobalt, and tin; and the mass ratio of the total amount of the iron oxide powder and the metal oxide powder containing solid solution elements to the diamond abrasive grains is (5-10):1; cold-pressing the mixed powder to obtain a block-shaped green body; The block green body is subjected to high-temperature reduction to obtain a reduced body; the high-temperature reduction process comprises: keeping warm in a hydrogen atmosphere at 400°C-450°C for 0.2h-1.0h, then keeping warm in a hydrogen atmosphere at 450°C-550°C for 0.2h-1.0h, and then keeping warm in a hydrogen atmosphere at 750°C-800°C for 0.5h-1.5h.

2. The preparation method according to claim 1, characterized in that The metal oxide powder containing solid-solution elements is nickel oxide powder, and the mass ratio of iron element to nickel element in the iron oxide powder and the metal oxide powder containing solid-solution elements is (2.3-9.0):

1.

3. The preparation method according to claim 1, characterized in that The mass ratio of the total amount of the iron oxide powder and the metal oxide powder containing solid solution elements to the soft magnetic metal powder is (1.00-2.33):

1.

4. The preparation method according to claim 1, characterized in that The soft magnetic metal powder is aerosolized iron powder with a particle size of 38 μm-150 μm.

5. The preparation method according to claim 1, characterized in that The iron oxide powder and nickel oxide powder are iron oxide powder and nickel oxide powder with a particle size of ≤1 μm; And / or, the diamond abrasive particles have a particle size of 1 μm-10 μm.

6. The preparation method according to claim 1, characterized in that Also includes: The reduced blanks are crushed, screened, and vacuum-packed.

7. A diamond-iron based magnetic composite abrasive, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 6.

8. The diamond-iron based magnetic composite abrasive according to claim 7, characterized in that: It comprises a magnetic metal core and a magnetic metal-abrasive composite shell layer coated on the surface of the magnetic metal core; The magnetic metal-abrasive composite shell layer contains soft magnetic metal and diamond abrasive grains, and the soft magnetic metal is an iron-nickel alloy.

9. The diamond-iron based magnetic composite abrasive according to claim 8, characterized in that: The thickness of the magnetic metal-abrasive composite shell is 1-20 μm, wherein the mass fraction of iron element is 50%-90%, the mass fraction of nickel element is 1%-30%, and the mass fraction of diamond is 1%-40%.

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