A core-shell structured magnetic abrasive and its preparation method

Abstract

This invention provides a core-shell structured magnetic abrasive and its preparation method, belonging to the field of magnetic abrasive technology. The invention involves mixing single-crystal silicon particles, magnetic iron-based powder, and yttrium oxide, followed by ball milling. Ball milling induces mechanical alloying between the magnetic iron-based powder and the single-crystal silicon, while simultaneously ensuring uniform distribution of the single-crystal silicon on the surface of the magnetic iron-based powder, forming a precursor. The resulting precursor is then subjected to nitriding heat treatment, forming a silicon nitride hard phase in situ on the surface of the single-crystal silicon. Simultaneously, under high-temperature conditions, the single-crystal silicon embeds into the surface of the magnetic iron-based powder, further transforming the mechanical alloying between the magnetic iron-based powder and the single-crystal silicon into a silicon-iron intermetallic compound, further strengthening the interfacial bonding between the two, thereby obtaining a core-shell structured magnetic abrasive. Furthermore, the core-shell structured magnetic abrasive prepared by this invention can achieve a roughness as low as 0.090±0.01μm when used to grind zirconium alloy tube walls.

Description

Technical Field

[0001] This invention relates to the field of magnetic abrasive technology, and in particular to a core-shell structured magnetic abrasive and its preparation method. Background Technology

[0002] Magnetic grinding is a surface treatment method that uses a magnetic field to act on magnetic abrasives, causing abrasive impacts between the abrasive particles and the workpiece. It is suitable for processing and treating the surfaces of various materials such as metals, ceramics, and plastics, and is widely used in manufacturing industries such as machinery, molds, automobiles, bearings, semiconductors, and aerospace.

[0003] Magnetic abrasives are crucial in magnetic grinding processes. Current research on magnetic abrasives mainly focuses on issues such as their short lifespan, poor cutting ability against metals, and low bonding strength between the ferromagnetic phase and the abrasive grains. For example, patent CN105665725A discloses a method for preparing free-fall dual-nozzle mixed powder gas atomization water-cooled rapid solidification metal-based CBN magnetic abrasives, which solves the problems of poor cutting ability against metals and low bonding strength between the ferromagnetic phase and the abrasive grains.

[0004] In reality, when a workpiece is exposed to air for a long time, a hard oxide film will form on its surface. Compared to the hardness of this oxide film, the internal metal matrix of the workpiece is relatively soft. Therefore, when using magnetic abrasives for magnetic grinding, once the oxide film is removed, the hardness of the magnetic abrasive and the workpiece surface becomes mismatched. This results in the surface roughness of the workpiece reaching a certain level and then being unable to be further reduced, leading to poor grinding results. Summary of the Invention

[0005] The purpose of this invention is to provide a core-shell structured magnetic abrasive and its preparation method. The core-shell structured magnetic abrasive provided by this invention can make the workpiece have a lower surface roughness when used for grinding.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a core-shell structured magnetic abrasive, comprising the following steps:

[0008] (1) The precursor was obtained by ball milling a mixture of single-crystal silicon particles, magnetic iron-based powder and yttrium oxide.

[0009] (2) The precursor obtained in step (1) is subjected to nitriding heat treatment to obtain a core-shell structured magnetic abrasive.

[0010] Preferably, in step (1), the mass ratio of single-crystal silicon particles to magnetic iron-based powder is 1:(4-6).

[0011] Preferably, the magnetic iron-based powder in step (1) includes one of iron powder, carbonyl iron powder, iron-silicon alloy powder, iron-aluminum alloy powder, and iron-nickel alloy powder.

[0012] Preferably, the particle size ratio of the magnetic iron-based powder to the single-crystal silicon particles in the precursor of step (1) is (20-50):1.

[0013] Preferably, in step (1), the ball milling speed is 150-300 rpm and the ball milling time is 8-10 h.

[0014] Preferably, the nitriding heat treatment temperature in step (2) is 1000-1300℃, and the nitriding heat treatment time is 2-4h.

[0015] The present invention also provides a core-shell structured magnetic abrasive prepared by the above preparation method, comprising a ferromagnetic matrix and an iron-silicon intermetallic compound and a silicon nitride hard phase sequentially coated on the surface of the ferromagnetic matrix from the inside out.

[0016] This invention provides a method for preparing a core-shell structured magnetic abrasive, comprising the following steps: (1) mixing single-crystal silicon particles, magnetic iron-based powder, and yttrium oxide and then ball-milling to obtain a precursor; (2) subjecting the precursor obtained in step (1) to nitriding heat treatment to obtain a core-shell structured magnetic abrasive. This invention involves mixing single-crystal silicon particles, magnetic iron-based powder, and yttrium oxide and then ball-milling them. Ball milling causes mechanical alloying between the magnetic iron-based powder and single-crystal silicon, strengthening the interfacial bond between them. Simultaneously, it also ensures that the single-crystal silicon is uniformly distributed on the surface of the magnetic iron-based powder, forming a precursor. Then, the obtained precursor is subjected to nitriding heat treatment, forming a silicon nitride hard phase in situ on the surface of the single-crystal silicon. Simultaneously, under high-temperature conditions, the single-crystal silicon embeds into the surface of the magnetic iron-based powder, further transforming the mechanical alloying between the magnetic iron-based powder and single-crystal silicon into an intermetallic compound of silicon and iron, further strengthening the interfacial bond between them, thereby obtaining a core-shell structured magnetic abrasive. The results of the examples show that the core-shell structured magnetic abrasive prepared by the present invention can grind the zirconium alloy tube wall to a roughness as low as 0.090±0.01μm. Attached Figure Description

[0017] Figure 1 The images show the XRD patterns of the core-shell magnetic abrasives obtained in Examples 1-4.

[0018] Figure 2 Here is a SEM image of the core-shell magnetic abrasive obtained in Example 1;

[0019] Figure 3 Here is a SEM image of the core-shell magnetic abrasive obtained in Example 2;

[0020] Figure 4Here is a SEM image of the core-shell magnetic abrasive obtained in Example 3;

[0021] Figure 5 Here is a SEM image of the core-shell magnetic abrasive obtained in Example 4;

[0022] Figure 6 The images show the cross-sectional SEM and EDS images of the core-shell magnetic abrasive obtained in Example 1.

[0023] Figure 7 The image shows the SEM image of the magnetic abrasive obtained in Comparative Example 1.

[0024] Figure 8 This is a test image of the surface roughness of an unprocessed zirconium tube;

[0025] Figure 9 The image shows the surface roughness test results of the zirconium alloy tube wall after being ground with magnetic abrasive with a core-shell structure, as obtained in Example 1.

[0026] Figure 10 This is a test image of the surface roughness of a zirconium tube after processing with traditional sintered magnetic abrasive. Detailed Implementation

[0027] This invention provides a method for preparing a core-shell structured magnetic abrasive, comprising the following steps:

[0028] (1) The precursor was obtained by ball milling a mixture of single-crystal silicon particles, magnetic iron-based powder and yttrium oxide.

[0029] (2) The precursor obtained in step (1) is subjected to nitriding heat treatment to obtain a core-shell structured magnetic abrasive.

[0030] This invention involves mixing single-crystal silicon particles, magnetic iron-based powder, and yttrium oxide, followed by ball milling to obtain a precursor.

[0031] In this invention, the particle size of the single-crystal silicon particles is preferably 1–5 μm, more preferably 2–3 μm. By limiting the particle size of the single-crystal silicon particles, this invention enables a more uniform distribution of the single-crystal silicon particles on the surface of the magnetic iron-based powder in the prepared precursor, thereby improving the processing effect of the magnetic abrasive on the workpiece.

[0032] In this invention, when the particle size of the monocrystalline silicon particles is not within the above-mentioned range, it is preferable to sieve the monocrystalline silicon particles. This invention does not impose any particular limitation on the sieving method; any sieving method well-known in the art can be used.

[0033] In this invention, the magnetic iron-based powder preferably includes one of iron powder, carbonyl iron powder, iron-silicon alloy, iron-aluminum alloy, and iron-nickel alloy. This invention limits the type of magnetic iron-based powder to ensure better magnetic properties of the resulting magnetic abrasive, thereby improving the machining effect of the magnetic abrasive on the workpiece.

[0034] In this invention, the particle size of the magnetic iron-based powder is preferably 80–200 μm, more preferably 120 μm. By limiting the particle size of the magnetic iron-based powder, this invention enables a more uniform distribution of single-crystal silicon particles on its surface, thereby improving the processing effect of the magnetic abrasive on the workpiece.

[0035] In this invention, the particle size ratio of the magnetic iron-based powder to the single-crystal silicon particles in the precursor is (20-50):1, more preferably (30-40):1. By limiting the particle size ratio of the magnetic iron-based powder to the single-crystal silicon particles in the precursor, this invention ensures that the single-crystal silicon particles completely coat the surface of the ferromagnetic matrix, thereby increasing the relative permeability of the resulting magnetic abrasive. This results in a relatively consistent cutting depth during processing, improving the processing efficiency of the magnetic abrasive.

[0036] In this invention, the preferred mass ratio of the monocrystalline silicon particles to the magnetic iron-based powder is 1:(4-6), more preferably 1:5. By limiting the mass ratio of monocrystalline silicon particles to magnetic iron-based powder, this invention ensures a more uniform distribution of the monocrystalline silicon particles on the surface of the magnetic iron-based powder, thereby improving the processing effect of the magnetic abrasive on the workpiece.

[0037] In this invention, the particle size of yttrium oxide is preferably 1–5 μm, more preferably 2–4 μm. By limiting the particle size of yttrium oxide, this invention ensures more thorough mixing with single-crystal silicon particles, thereby improving the catalytic effect on the in-situ formation of silicon nitride on the surface of single-crystal silicon during subsequent nitriding heat treatment.

[0038] In this invention, the mass of yttrium oxide is preferably 6-12% of the total mass of the single-crystal silicon particles, magnetic iron-based powder, and yttrium oxide, more preferably 8-10%. This invention, by limiting the mass of yttrium oxide, sufficiently reduces the temperature of the subsequent nitriding heat treatment, preventing the ferromagnetic matrix from completely melting, thereby maintaining its original morphology and ensuring a more complete catalytic effect on the in-situ formation of silicon nitride on the surface of the single-crystal silicon during the subsequent nitriding heat treatment.

[0039] In this invention, the mixing of the monocrystalline silicon particles, magnetic iron-based powder, and yttrium oxide is preferably carried out under stirring. The stirring rate is preferably 120–150 r / min; the stirring time is preferably 20–60 min, more preferably 30–50 min. This invention ensures a more thorough mixing of the monocrystalline silicon particles, magnetic iron-based powder, and yttrium oxide by limiting the stirring rate and time.

[0040] In this invention, the ball milling speed is preferably 150–300 rpm, more preferably 200–250 rpm. The ball milling time is preferably 8–10 hours, more preferably 9 hours. The grinding balls used in this invention are preferably steel balls. The ball-to-material ratio in this invention is preferably (8–12):1, more preferably 10:1. The filler coefficient during ball milling is preferably 0.4–0.6, more preferably 0.5. The ball milling is preferably performed under vacuum conditions. This invention, by limiting the ball milling parameters, ensures sufficient mechanical alloying between the ferromagnetic matrix and single-crystal silicon, thereby strengthening the interfacial bonding between them.

[0041] After obtaining the precursor, the precursor obtained in this invention is subjected to nitriding heat treatment to obtain a core-shell structured magnetic abrasive.

[0042] In this invention, during the nitriding heat treatment, the mechanized alloy between the ferromagnetic matrix and the single-crystal silicon is transformed into a Fe3Si iron-silicon intermetallic compound at the nitriding heat temperature. Simultaneously, under yttrium trioxide catalysis, a silicon nitride hard phase is generated in situ on the single-crystal silicon surface. In this invention, the nitriding heat treatment temperature is preferably 1000–1300°C, more preferably 1200°C. In this invention, the heating rate of the nitriding heat treatment is preferably 5–8 / min when the temperature is below 800°C, and preferably 3–5 / min when the temperature is above 800°C. In this invention, the nitriding heat treatment time is preferably 2–4 h, more preferably 3 h. In this invention, the nitriding heat treatment is preferably carried out under nitrogen atmosphere. This invention, by limiting the parameters of the nitriding heat treatment, ensures a more complete transformation of the mechanized alloy between the ferromagnetic matrix and the single-crystal silicon into a Fe3Si iron-silicon intermetallic compound, further improving the bonding between the ferromagnetic matrix and the hard phase; and ensuring a more complete reaction for the in-situ generation of the silicon nitride hard phase on the single-crystal silicon surface.

[0043] This invention involves mixing monocrystalline silicon particles, magnetic iron-based powder, and yttrium oxide, followed by ball milling. Ball milling causes mechanical alloying between the magnetic iron-based powder and the monocrystalline silicon, strengthening the interfacial bond between them. It also ensures that the monocrystalline silicon is uniformly distributed on the surface of the magnetic iron-based powder, forming a precursor. The resulting precursor is then subjected to nitriding heat treatment, forming a silicon nitride hard phase in situ on the surface of the monocrystalline silicon. Simultaneously, under high temperature conditions, the monocrystalline silicon embeds into the surface of the magnetic iron-based powder, further transforming the mechanical alloying between the magnetic iron-based powder and the monocrystalline silicon into an intermetallic compound of silicon and iron, further strengthening the interfacial bond between them, thereby obtaining a core-shell structured magnetic abrasive.

[0044] The present invention also provides a core-shell structured magnetic abrasive prepared by the above preparation method, comprising a ferromagnetic matrix and an iron-silicon intermetallic compound and a silicon nitride hard phase sequentially coated on the surface of the ferromagnetic matrix from the inside out.

[0045] In the core-shell structure magnetic abrasive provided by this invention, after the outermost silicon nitride hard phase of the core-shell structure magnetic abrasive is ground off the outermost oxide layer of the workpiece, the relatively low-hardness silicon-iron intermetallic compound continues to grind the softer metal surface below the oxide layer of the workpiece, thereby giving the workpiece a lower surface roughness; and the silicon-iron intermetallic compound in the core-shell structure magnetic abrasive can improve the bonding degree between the ferromagnetic matrix and the hard phase.

[0046] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0047] Example 1

[0048] A method for preparing a core-shell structured magnetic abrasive comprises the following steps:

[0049] (1) Single-crystal silicon particles with a particle size of 4 μm, spherical iron powder with a particle size of 120 μm, and yttrium oxide with a particle size of 1 μm are placed in a mixer and mixed at 100 rpm for 30 min, followed by ball milling to obtain a precursor; the mass ratio of the single-crystal silicon particles to the spherical iron powder is 1:4; the mass of the yttrium oxide is 8% of the total mass of the single-crystal silicon particles, spherical iron powder, and yttrium oxide; the ball milling speed is 150 rpm; the ball milling time is 8 h; the grinding balls are steel balls; the ball-to-material ratio is 1:10; the filler coefficient is 0.4; the particle size ratio of the spherical iron powder to the single-crystal silicon particles in the precursor is 30:1;

[0050] (2) The precursor obtained in step (1) is placed in a vacuum tube furnace and subjected to nitriding heat treatment at 1100°C for 8 hours under nitrogen conditions to obtain a core-shell structure magnetic abrasive; the heating rate of the nitriding heat treatment is 5 / min when the temperature is less than 800°C and 3 / min when the temperature is greater than 800°C.

[0051] Example 2

[0052] A method for preparing a core-shell structured magnetic abrasive comprises the following steps:

[0053] (1) Single-crystal silicon particles with a particle size of 5 μm, spherical iron powder with a particle size of 150 μm, and yttrium oxide with a particle size of 1.2 μm were placed in a mixer and mixed at 100 rpm for 30 min, followed by ball milling to obtain a precursor; the mass ratio of the single-crystal silicon particles to the spherical iron powder was 1:6; the mass of the yttrium oxide was 8% of the total mass of the single-crystal silicon particles, spherical iron powder, and yttrium oxide; the ball milling speed was 250 rpm; the ball milling time was 10 h; the grinding balls were steel balls; the ball-to-material ratio was 1:10; the filler coefficient was 0.4; the particle size ratio of the spherical iron powder to the single-crystal silicon particles in the precursor was 30:1;

[0054] (2) The precursor obtained in step (1) is placed in a vacuum tube furnace and subjected to nitriding heat treatment at 1100°C for 5 hours under nitrogen conditions to obtain a core-shell structure magnetic abrasive; the heating rate of the nitriding heat treatment is 5 / min when the temperature is less than 800°C and 3 / min when the temperature is greater than 800°C.

[0055] Example 3

[0056] A method for preparing a core-shell structured magnetic abrasive comprises the following steps:

[0057] (1) Single-crystal silicon particles with a particle size of 5.7 μm, spherical iron powder with a particle size of 170 μm, and yttrium oxide with a particle size of 1.3 μm were placed in a mixer and mixed at 100 rpm for 30 min, followed by ball milling to obtain a precursor; the mass ratio of the single-crystal silicon particles to the spherical iron powder was 1:6; the mass of the yttrium oxide was 8% of the total mass of the single-crystal silicon particles, spherical iron powder, and yttrium oxide; the ball milling speed was 250 rpm; the ball milling time was 10 h; the grinding balls were steel balls; the ball-to-material ratio was 1:10; the filler coefficient was 0.4; the particle size ratio of the spherical iron powder to the single-crystal silicon particles in the precursor was 30:1;

[0058] (2) The precursor obtained in step (1) is placed in a vacuum tube furnace and subjected to nitriding heat treatment at 1100°C for 5 hours under nitrogen conditions to obtain a core-shell structure magnetic abrasive; the heating rate of the nitriding heat treatment is 5 / min when the temperature is less than 800°C and 3 / min when the temperature is greater than 800°C.

[0059] Example 4

[0060] A method for preparing a core-shell structured magnetic abrasive comprises the following steps:

[0061] (1) Monocrystalline silicon particles with a particle size of 3.0 μm, spherical iron powder with a particle size of 90 μm, and yttrium oxide with a particle size of 1.0 μm were placed in a mixer and mixed at 100 rpm for 30 min, followed by ball milling to obtain a precursor; the mass ratio of monocrystalline silicon particles to spherical iron powder was 1:6; the mass of yttrium oxide was 8% of the total mass of monocrystalline silicon particles, spherical iron powder, and yttrium oxide; the ball milling speed was 250 rpm; the ball milling time was 10 h; the grinding balls were steel balls; the ball-to-material ratio was 1:10; the filler coefficient was 0.4; the particle size ratio of spherical iron powder to monocrystalline silicon particles in the precursor was 30:1;

[0062] (2) The precursor obtained in step (1) is placed in a vacuum tube furnace and subjected to nitriding heat treatment at 1100°C for 5 hours under nitrogen conditions to obtain a core-shell structure magnetic abrasive; the heating rate of the nitriding heat treatment is 5 / min when the temperature is less than 800°C and 3 / min when the temperature is greater than 800°C.

[0063] Comparative Example 1

[0064] A method for preparing a magnetic abrasive comprises the following steps:

[0065] (1) Iron powder with a particle size of 150 μm and silicon carbide with a particle size of 38 μm were placed in a mixer and stirred at 100 rpm for 30 min, and then ball-milled to obtain a precursor; the mass ratio of silicon carbide to iron powder was 1:4; the ball milling speed was 250 rpm; the ball milling time was 8 h; the grinding balls were steel balls; the ball-to-material ratio was 1:10; the filler coefficient was 0.4; the particle size ratio of iron powder to silicon carbide in the precursor was ~4:1;

[0066] (2) The precursor obtained in step (1) is mixed with the binder at 120 rpm for 30 min, pressed into blocks, dried in a vacuum drying oven at 100°C for 10 h, placed in a vacuum tube furnace, sintered at 1200°C for 2-3 h, cooled in the furnace and then mechanically crushed to obtain magnetic abrasive.

[0067] The structures of the core-shell magnetic abrasives prepared in Examples 1-4 were characterized using X-ray diffraction (XRD, PAN Analytical X'Pert PRO), and the results are as follows: Figure 1 As shown in the figure, diffraction peaks corresponding to the Fe3Si and Si3N4 phases appeared in the XRD pattern of the magnetic abrasive. The morphology of the core-shell structured magnetic abrasives prepared in Examples 1-4 was characterized using SEM electron microscopy, and the results are as follows. Figures 2-5 As shown in the figure, the silicon nitride hard phase of the core-shell structure magnetic abrasives prepared in Examples 1 to 4 is well and uniformly distributed on the surface of the spherical iron powder.

[0068] The cross-sectional morphology of the core-shell magnetic abrasive prepared in Example 1 was characterized by scanning electron microscopy (SEM) images and EDS spectral analysis. The results are as follows: Figure 6 As shown in the figure, the core-shell structured magnetic abrasive prepared by this method exhibits a good core-shell structure distribution. The outer layer is mainly composed of the hard phase Si3N4, while the interface with the spherical iron powder is an intermetallic compound of Fe3Si.

[0069] The morphology of the magnetic abrasive prepared in Comparative Example 1 was characterized using SEM electron microscopy, and the results are as follows: Figure 7 As shown in the figure, it can be seen that the hard phase of the magnetic abrasive prepared in Comparative Example 1 is not evenly distributed on the surface of the spherical iron powder.

[0070] The core-shell magnetic abrasive prepared in Example 1 and the magnetic abrasive prepared in Comparative Example 1 were used to grind the zirconium alloy tube wall. The surface roughness of the original zirconium alloy tube wall, the zirconium alloy tube wall after grinding with the core-shell magnetic abrasive prepared in Example 1, and the zirconium alloy tube wall after grinding with the magnetic abrasive prepared in Comparative Example 1 were tested using a TR200 roughness measuring instrument. The results are shown below. Figures 8-10 As shown in the figure, the surface roughness Ra of the original zirconium alloy tube wall is 0.508 ± 0.01 μm; the surface roughness Ra of the zirconium alloy tube wall after grinding with the magnetic abrasive prepared in Example 1 is 0.090 ± 0.01 μm; and the surface roughness Ra of the zirconium alloy tube wall after grinding with the magnetic abrasive prepared in Comparative Example 1 is 0.236 ± 0.01 μm.

[0071] In summary, the core-shell structured magnetic abrasive provided by this invention can achieve a lower surface roughness in workpieces during grinding processes.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell structured magnetic abrasive, comprising the following steps: (1) The precursor was obtained by ball milling a mixture of single-crystal silicon particles, magnetic iron-based powder and yttrium oxide; (2) The precursor obtained in step (1) is subjected to nitriding heat treatment to obtain a core-shell structured magnetic abrasive; In step (1), the mass ratio of single-crystal silicon particles to magnetic iron-based powder is 1:(4~6). The magnetic iron-based powder in step (1) includes one of iron powder, carbonyl iron powder, iron-silicon alloy powder, iron-aluminum alloy powder and iron-nickel alloy powder; In step (1), the particle size ratio of magnetic iron-based powder to single-crystal silicon particles in the precursor is (20~50):1; In step (1), the ball milling speed is 150~300 rpm and the ball milling time is 8~10 h; The nitriding heat treatment temperature in step (2) is 1000~1300℃, and the nitriding heat treatment time is 2~4h; The magnetic iron-based powder has a particle size of 80~200μm; The nitriding heat treatment is carried out under nitrogen atmosphere.

2. The core-shell magnetic abrasive prepared by the method of claim 1 comprises a ferromagnetic matrix and an iron-silicon intermetallic compound and a silicon nitride hard phase sequentially coated on the surface of the ferromagnetic matrix from the inside out.

Images