Rigidity-adjustable memory alloy copper-based grinding wheel and preparation method

Abstract

The invention relates to a rigidity-adjustable memory alloy copper-based grinding wheel and a preparation method. A rigidity-adjustable memory alloy copper-based grinding wheel comprises a wheel body, the wheel body comprises an inner layer and an outer layer, and a conductive layer is arranged on the axial end face of the wheel body. The outer layer is formed by mixing copper powder, Ni-Ti memory alloy powder and nano-diamond particles and then performing powder metallurgy, pressing and sintering; and the inner layer is formed by mixing copper powder and stainless steel powder and then pressing and sintering the mixture through powder metallurgy, or the inner layer is formed by compounding a copper layer and a stainless steel layer. The rigidity change of the wheel body of the copper-based grinding wheel can be realized by controlling the on-off of current, and collaborative optimization of high grinding efficiency and low surface roughness can be realized without replacing the grinding wheel. The device has the advantages that the rigidity is adjustable, the grinding efficiency can be improved, and it can be guaranteed that the groove profile roughness of the roll collar is small.

Description

Technical Field

[0001] This invention relates to a shape memory alloy copper-based grinding wheel with adjustable stiffness and its preparation method. Background Technology

[0002] In existing technologies, the groove shape of the carbide roller ring is usually machined first using a copper-based grinding wheel, and then the groove shape is trimmed using a grinding machine.

[0003] In conventional techniques, a copper-based grinding wheel with a fixed stiffness is used to grind the groove. However, through comparison, it has been found that the higher the stiffness of the copper-based grinding wheel's material composition, the higher the grinding efficiency; the lower the stiffness of the copper-based grinding wheel's material composition, the smaller the surface roughness of the roller ring groove. Therefore, in order to achieve the best results, a high-stiffness copper-based grinding wheel is used for processing first, and when the processing is about to be completed, a low-stiffness copper-based grinding wheel is selected to improve the surface quality of the groove and reduce the roughness.

[0004] However, when replacing copper-based grinding wheels, multiple adjustments are required to ensure that the replaced copper-based grinding wheel fits the previously machined groove shape. Moreover, each type of roller ring groove requires copper-based grinding wheels of different thicknesses and shapes for machining. Therefore, each groove shape needs to be equipped with a high-rigidity copper-based grinding wheel and a low-rigidity copper-based grinding wheel. Furthermore, copper-based grinding wheels are consumables, which makes the handling and maintenance of materials quite troublesome. Summary of the Invention

[0005] The purpose of this invention is to provide a stiffness-adjustable shape memory alloy copper-based grinding wheel that can improve grinding efficiency while ensuring low roughness of the roller ring groove.

[0006] To achieve the above objectives, the present invention employs a stiffness-adjustable shape memory alloy copper-based grinding wheel, comprising a wheel body, the wheel body comprising an inner layer and an outer layer, and a conductive layer provided at the axial end face of the wheel body; the outer layer is formed by powder metallurgy pressing and sintering of a mixture of copper powder, Ni-Ti shape memory alloy powder and nano-diamond particles; the inner layer is formed by powder metallurgy pressing and sintering of a mixture of copper powder and stainless steel powder, or the inner layer is a composite of a copper layer and a stainless steel layer.

[0007] The stiffness variation of the copper-based grinding wheel of this invention can be achieved by controlling the on / off state of the current, thus realizing the synergistic optimization of high grinding efficiency and low surface roughness without replacing the grinding wheel. In the initial stage of grinding, direct current is applied through the conductive layer, and Joule heating raises the outer layer to the austenitic phase, increasing the elastic modulus and thus increasing the stiffness of the outer layer. In the final stage of grinding, the current is cut off, and the outer layer cools to the martensitic phase, decreasing the elastic modulus and reducing the stiffness, thereby improving the surface quality of the roller ring groove and reducing roughness.

[0008] The outer layer also contains copper, which ensures the porosity, hardness, and machinability of the wheel body.

[0009] The coefficient of thermal expansion of Ni-Ti shape memory alloys differs significantly from that of steel, making them prone to stress during temperature changes and affecting connection strength. In contrast, the coefficients of thermal expansion of copper and stainless steel are closer to those of grinding machine spindle materials (usually steel), reducing stress and deformation caused by temperature changes and improving connection reliability.

[0010] Meanwhile, copper has a much higher thermal conductivity than Ni-Ti shape memory alloys. During grinding, the grinding wheel generates a significant amount of heat, and materials with high thermal conductivity can dissipate this heat more quickly, preventing heat buildup, reducing the temperature of the grinding wheel and workpiece, improving grinding efficiency and surface quality, and extending the grinding wheel's lifespan. Copper's high thermal conductivity also helps with rapid heat dissipation, protecting the grinding machine spindle.

[0011] Stainless steel possesses high strength and rigidity, providing excellent structural support to ensure the grinding wheel maintains its shape and is not easily deformed during high-speed rotation and under stress. The inner layer of the grinding wheel needs sufficient strength to resist various stresses during grinding and to securely connect the wheel to the grinding machine spindle. A combination of pure copper and stainless steel can provide a balanced structure, offering both good thermal conductivity and sufficient strength and rigidity.

[0012] Preferably, the wheel body comprises an inner layer, a middle layer and an outer layer from the inner side to the outer side of the circumference, wherein the middle layer is formed by powder metallurgy pressing and sintering of a mixture of copper powder and Ni-Ti shape memory alloy powder.

[0013] By incorporating a shape memory alloy into the intermediate layer, the grinding wheel can participate in the temperature phase transition of the shape memory alloy, thereby preventing the grooved arc surface of the grinding wheel body from cracking after multiple heating and cooling cycles, thus extending the service life of the grinding wheel of the present invention.

[0014] Preferably, the outer layer has a phase transition temperature of 50°C to 80°C.

[0015] Designed with a phase transformation temperature of 50-80℃, the material is typically in the martensitic phase (low-temperature phase) at room temperature (approximately 25℃), but transforms into the austenitic phase (high-temperature phase) when heated above the phase transformation temperature. This characteristic makes the material easy to process and shape at room temperature, and facilitates processing, transportation, and storage at room temperature without requiring special temperature control equipment.

[0016] Preferably, the conductive layer is a copper film attached to the end face of the wheel body, with a thickness of 70 to 150 micrometers.

[0017] Copper film can reduce resistance and improve conductivity. A thicker copper film can improve the adhesion to the grinding wheel substrate and prevent it from falling off during use. Although a thicker copper film can improve performance, the cost will also increase accordingly, by a factor of several. This invention achieves a balance between performance and cost.

[0018] Preferably, the Ni-Ti shape memory alloy powder in the outer layer has a particle size of 10-30 μm, and the nanodiamond particles have a particle size of 5-10 nm, accounting for 11-13 wt%.

[0019] By controlling the particle size of Ni-Ti shape memory alloy powder within the range of 10-30 μm, relatively uniform dispersion can be achieved. This dispersion helps to form a composite matrix with moderate stiffness and elasticity. Too small a particle size may lead to agglomeration and difficulty in dispersion, while too large a particle size may cause localized stress concentration, reducing the overall performance of the material.

[0020] Nanodiamond particles have extremely high hardness and strength. By controlling their particle size within the range of 5-10 nm, they can be highly dispersed in the grinding wheel matrix. This dispersion enables nanodiamond particles to effectively perform cutting and grinding, thereby significantly improving the hardness and grinding performance of the grinding wheel.

[0021] The proportion of nanodiamond particles directly affects the overall performance of the grinding wheel. Within the range of 11-13 wt% (11% to 13% of the total mass), nanodiamond particles can provide sufficient hardness and wear resistance, helping to improve the wear resistance of the grinding wheel. Too high a proportion may cause the grinding wheel to be too brittle and prone to breakage during use; while too low a proportion may not be able to fully exert the reinforcing effect of nanodiamond particles.

[0022] Preferably, the copper powder is electrolytic copper powder with a particle size of 50~100μm and a purity of ≥99.9%, and the outer layer and the middle layer are produced with polyurethane composite additives with a purity of ≥99.9% and composite rare earth additives accounting for 2~3wt%.

[0023] High-purity copper powder ensures the electrical and thermal conductivity of the grinding wheel. In the outer layer, controlling the particle size range affects the porosity, hardness, and cutting performance of the grinding wheel; coarser particle size generally means greater porosity, which helps with heat dissipation and chip removal, while finer particle size can provide a smoother surface finish. A particle size range of 50-100μm provides sufficient mechanical strength while maintaining a certain level of porosity, making it suitable for grinding various materials.

[0024] By adding polyurethane composite additives, the contact area between rare earth elements and copper-based shape memory alloys can be significantly increased, promoting their blending and thus improving the shape recovery rate and reducing grain size of the copper-based shape memory alloys. With a purity ≥99.9% and extremely low impurities, the material's uniformity and stability are ensured, thereby guaranteeing the phase transition temperature and performance of the shape memory alloy. The polyurethane composite additives, through the synergistic effect of their internal components, have multiple positive impacts on the performance of copper-based shape memory alloy grinding wheels; the silane coupling agent in the additives has one end that can form a strong chemical bond with inorganic substances (such as rare earth elements in copper-based alloys), while the other end can react with organic polyurethane resins. This significantly improves the shape recovery rate of copper-based shape memory alloys; the active components in the additives also play a role in inhibiting grain growth during alloy solidification.

[0025] Rare earth elements can improve the properties of alloys, such as increasing strength, toughness, corrosion resistance and high temperature resistance. The addition range of 2-3 wt% is an optimized result that can significantly improve performance without causing excessive cost or increased material brittleness due to too much rare earth.

[0026] The present invention also provides a method for preparing the above-mentioned stiffness-adjustable shape memory alloy copper-based grinding wheel, comprising the following steps: S1. The powders for the inner, middle, and outer layers are mixed separately; S2. The blanks for the inner, middle, and outer layers are all formed using a cold isostatic pressing process; S3. The billets for the inner, middle, and outer layers are all sintered in a vacuum sintering furnace in sections; S4. The sintered inner layer blank, middle layer blank and outer layer blank are joined together by brazing process to form a wheel body; S5. Perform surface finishing on the wheel body and fine-tune the wheel's arc. S6. Form a conductive layer on the end face of the wheel body.

[0027] Cold isostatic pressing, a forming process that applies uniform pressure in all directions at low temperatures, can effectively compress powder or loose materials, improve their density and uniformity, and reduce defects. It can significantly increase the density of grinding wheels, reduce porosity, and make the material structure more uniform, which helps to improve the hardness, strength, and wear resistance of the grinding wheel body. It can also reduce defects such as cracks and pores in the grinding wheel body, thereby improving its service life and safety.

[0028] Segmented sintering allows for precise control of temperature and time during the sintering process, thereby removing volatile substances, reducing porosity, and increasing density. The thermal stress during sintering helps reduce closed porosity. It can also suppress accelerated grain growth in the later stages of sintering, resulting in finer grains and thus improving the strength and toughness of the wheel body.

[0029] Preferably, in step S1, the powder used in the intermediate layer and the powder used in the outer layer are mixed in a ball mill for 4-4.5 hours under argon protection, with a ball-to-powder ratio of 4.5: to 5:1 and a ball mill drum speed of 230±5 rpm; the powder used in the inner layer is mixed in a ball mill for 2-2.5 hours under argon protection, with a ball-to-powder ratio of 4.5: to 5:1 and a ball mill drum speed of 230±5 rpm.

[0030] Using argon gas for protection can isolate reactions, block the risks of nitriding and hydrogenation, protect the stability of alloy composition, avoid impurity contamination, prevent particle agglomeration, control particle size distribution, maintain powder flowability, and reduce the formation of volatile substances. If the ball milling mixing time is too short, the mixing will be insufficient and the components will not be evenly distributed. This may lead to local component segregation and affect the overall performance of the material. If the ball milling mixing time is too long, the surface area of ​​the material will be too large, the activity will be enhanced, and even oxidation or other adverse reactions may be triggered.

[0031] A larger ball-to-powder ratio increases the probability of ball collisions, resulting in more mechanical energy absorbed by the powder per unit time and volume. Consequently, the ball milling time required to achieve the same milling effect is shorter. However, this leads to increased wear on the grinding media and the inner wall of the ball mill, shortening the equipment's lifespan. Furthermore, during the milling process, alloy ball metal components are incorporated into the slurry; a larger ball-to-powder ratio increases the proportion of alloy balls entering the slurry. Conversely, a smaller ball-to-powder ratio typically leads to reduced grinding efficiency, requiring longer grinding times to achieve the desired particle size, making it difficult to obtain very fine product particles. This invention, employing this specific milling time and ratio, extends the ball mill's lifespan, avoids the incorporation of alloy ball metal components, ensures milling efficiency, and achieves the desired material properties.

[0032] Preferably, in step S2, the molding process involves holding the pressure at 300 MPa for 20 minutes.

[0033] Preferably, in step S3, the blanks of the outer and middle layers are first heated to 600°C to 630°C and sintered for 2 to 2.1 hours to remove the binder inside the pressed blank; then the temperature is raised to 900°C to 910°C and sintered for 4 to 4.1 hours to densify the copper matrix; finally, the temperature is raised to 1050°C to 1060°C and sintered for 50 to 60 minutes to activate the diffusion bonding between the shape memory alloy and the copper matrix interface.

[0034] Preferably, in step S6, a conductive layer is deposited on the end face of the wheel body using a magnetron sputtering process.

[0035] Magnetron sputtering uses high-energy particles to bombard a target, causing target atoms to deposit onto a substrate to form a thin film. This method can produce very uniform, dense films with strong adhesion; for wheel end faces, high-quality copper films can provide better surface finish and longer service life. Magnetron sputtering is typically performed at room temperature or lower temperatures, ensuring that the substrate material (shape memory alloy) is not damaged by high temperatures during the copper film deposition process, thus preserving the properties of the shape memory alloy.

[0036] Preferably, the magnetron sputtering process includes the following steps: A1. Clean the surface of the grinding wheel to remove oil and dirt; A2. Fix the grinding wheel in the sputtering chamber and adjust the distance between it and the copper target to 10~15cm; A3. Evacuate to a background vacuum level of 10. -3 ~10 -4 Pa; A4. Fill with argon gas and adjust the working pressure to 0.1~1.0 Pa; A5. Set the sputtering power density to 2~10 W / cm³ 2 Perform pre-sputtering for 5-10 minutes; A6. Formal sputtering, controlling the deposition rate to approximately 0.1~1 nm / s, until the copper film thickness reaches the set thickness.

[0037] One method is to use a mixture of isoacetone and potassium hydroxide for cleaning, which is more effective than ultrasonic cleaning or plasma cleaning. The mixture combines the organic solvent properties of isoacetone with the strong alkalinity of potassium hydroxide, effectively removing oil, grease, and other organic contaminants from the surface of the grinding wheel. Isoacetone can dissolve many organic substances, while potassium hydroxide can decompose fats through saponification, resulting in a lower cost.

[0038] The present invention has the advantages of adjustable stiffness, which can improve grinding efficiency and ensure that the roughness of the roller ring groove is small. Attached Figure Description

[0039] Figure 1 This is a cross-sectional view of the wheel body of the present invention.

[0040] Figure 2 This is a metallographic image of the outer layer of the copper-based grinding wheel of Embodiment 1 of the present invention at 25 degrees Celsius.

[0041] Figure 3 This is a metallographic image of the outer layer of the copper-based grinding wheel of Embodiment 1 of the present invention at 65 degrees Celsius.

[0042] Figure 4 This is a metallographic image of the outer layer of the copper-based grinding wheel of Comparative Example 1 of the present invention at 25 degrees Celsius.

[0043] Figure 5 This is a metallographic image of the outer layer of the copper-based grinding wheel of Comparative Example 1 of the present invention at 65 degrees Celsius. Detailed Implementation

[0044] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0045] Example 1 Depend on Figure 1 As shown, this embodiment discloses a shape memory alloy copper-based grinding wheel with adjustable stiffness, including a wheel body 100. The wheel body 100 includes an inner layer 1, a middle layer 2, and an outer layer 3 sequentially from the inner circumferential side to the outer circumferential side. Conductive layers 4 are provided at both axial end faces of the wheel body 100, and the conductive layers are connected to DC wires (not shown in the figure). In this embodiment, the contact surface between the inner layer 1 and the middle layer 2 is an arc surface, and the inner layer 1, the middle layer 2, and the outer layer 3 are brazed together.

[0046] The outer layer 3 is formed by powder metallurgy pressing and sintering a mixture of copper powder, Ni-Ti shape memory alloy powder and nano diamond particles; the middle layer 2 is formed by powder metallurgy pressing and sintering a mixture of copper powder and Ni-Ti shape memory alloy powder; and the inner layer 1 is formed by powder metallurgy pressing and sintering a mixture of copper powder and stainless steel powder.

[0047] The outer layer 3 has a phase transition temperature of 50°C to 80°C, and the conductive layer 4 is a copper film attached to the end face of the wheel body 100 with a thickness of 100 micrometers.

[0048] The Ni-Ti shape memory alloy powder in outer layer 3 and middle layer 2 has a particle size of 10-30 μm, and the nanodiamond particles have a particle size of 5-10 nm, accounting for 11-13 wt%. The copper powder is electrolytic copper powder with a particle size of 50~100μm and a purity of ≥99.9%. The outer and middle layers are produced with polyurethane composite additives with a purity of ≥99.9% and composite rare earth additives with a proportion of 2~3wt%.

[0049] This embodiment also discloses a method for preparing the above-mentioned shape memory alloy copper-based grinding wheel, comprising the following steps: S1. The powders for the inner, middle, and outer layers are mixed separately; S2. The inner, middle, and outer layers are all formed using a cold isostatic pressing process; S3. Segmented sintering in a vacuum sintering furnace; S4. The sintered inner, middle and outer layers are joined together by brazing to form the wheel body; S5. Perform surface machining on the wheel body and finish the arc of the grinding wheel; among which, use a time-space grinding machine to finish the arc of the outer layer of the wheel body with an accuracy of ±0.015mm; S6. A copper-film-like conductive layer is deposited on the end face of the wheel body using a magnetron sputtering process.

[0050] In step S1, the powder used in the middle layer and the powder used in the outer layer are mixed in a ball mill for 4-4.1 hours under argon protection, with a ball-to-powder ratio of 5:1 and a ball mill drum speed of 230±5 rpm; the powder used in the inner layer is mixed in a ball mill for 2 hours under argon protection, with a ball-to-powder ratio of 5:1 and a ball mill drum speed of 230±2 rpm.

[0051] In step S2, the molding process is carried out under a pressure of 300 MPa for 20 minutes.

[0052] In step S3, the blanks for the outer and middle layers are first heated to 600°C and sintered for 2 hours to remove the binder inside the pressed blank; then heated to 900°C and sintered for 4 hours to densify the copper matrix; finally heated to 1050°C and sintered for 50 minutes to activate the diffusion bonding between the shape memory alloy and the copper matrix. The inner layer uses a conventional segmented sintering method.

[0053] In step S6, the magnetron sputtering process includes the following steps: A1. Clean the wheel surface to remove oil stains; soak the wheel in a mixture of isoacetone and potassium hydroxide to remove oil stains, then rinse and dry repeatedly with distilled water. If necessary, the surface can be further purified by ultrasound to ensure no residual contaminants remain. A2. Fix the wheel in the sputtering chamber and adjust its position to target the copper target. The sputtering distance between the wheel and the target should be uniform, generally controlled at 10~15cm. Install the high-purity copper target and check that there is no oxide layer or contamination on the target surface. If necessary, remove the surface oxides by pre-sputtering (air sputtering). A3. Start the mechanical pump to evacuate to a low vacuum below 5 Pa, then turn on the molecular pump to evacuate to a high vacuum (evacuate to a background vacuum of 10 Pa). -3 ~10 -4 (Pa); After the vacuum level reaches the standard, the high vacuum measuring gauge tube is shut off to protect the ionization gauge filament; A4. Fill with argon gas and adjust the working pressure to 0.1~1.0 Pa; A5. Set the sputtering power density to 2~10 W / cm³ 2 Perform pre-sputtering for 5-10 minutes; A6. Formal sputtering, controlling the deposition rate to approximately 0.1~1 nm / s, until the copper film thickness reaches the set thickness.

[0054] When the aforementioned shape memory alloy copper-based grinding wheel is used for roller ring groove machining, in the initial stage of grinding, a DC current of 15 to 20A is applied through the conductive layer. Joule heating causes the outer layer to heat up to the austenitic phase, increasing the elastic modulus by 50% to 80%, thereby increasing the stiffness of the outer layer. At the end of the grinding process, the current is cut off, the outer layer cools to the martensitic phase, the elastic modulus decreases, and the stiffness decreases, thereby improving the surface quality of the roller ring groove and reducing the roughness.

[0055] Comparative Example 1 The inner, middle and outer layers of the copper-based grinding wheel of Comparative Example 1 and Example 1 are made of the same materials. The only differences in production process and method are as follows: (1) When mixing materials, the ball milling time of the middle and outer layers is 3 hours; (2) When sintering in sections, the blanks of the outer and middle layers are first heated to 500°C and sintered for 3 hours to remove the binder in the pressed blank; then the temperature is raised to 950°C and sintered for 4 hours to achieve densification of the copper matrix; finally, the temperature is raised to 110°C and sintered for 50 minutes.

[0056] See Figure 4 and Figure 5 The metallographic structure of the copper-based grinding wheel in Comparative Example 1 showed coarse inclusions, indicating that the ball milling and sintering processes needed to be adjusted. The ball milling process tested failed to uniformly mill the raw material particles, and grain agglomeration and growth occurred during the sintering process.

[0057] See Figure 2 and Figure 3 Compared with Comparative Example 1, the metallographic results of Example 1 are more uniform.

[0058] After physical performance testing, at 25°C, the elastic modulus of the existing copper-based grinding wheel was 98 GPa, the elastic modulus of Example 1 was 94 GPa, and the elastic modulus of Comparative Example 1 was 87 GPa; at 65°C, the elastic modulus of the existing copper-based grinding wheel was 98 GPa (unchanged), the elastic modulus of Example 1 was 108 GPa, and the elastic modulus of Comparative Example 1 was 105 GPa.

[0059] Under electrically heated conditions, the elastic modulus of the outer layer of the copper-based grinding wheels in Example 1 and Comparative Example 1 is higher than that of conventional copper-based grinding wheels. The outer layer of the grinding wheels in Example 1 and Comparative Example 1 has higher stiffness, resulting in better grinding performance and improved grinding efficiency. Under power-off conditions, the elastic modulus of the outer layer of the copper-based grinding wheels in Example 1 and Comparative Example 1 is lower than that of conventional copper-based grinding wheels. The outer layer of the copper-based grinding wheels in Example 1 and Comparative Example 1 is softer, resulting in higher surface quality of the grooved surfaces. Although the elastic modulus of the outer layer of the grinding wheel in Comparative Example 1 is smaller than that in Example 1 under power-off conditions, [the following is unclear and likely incomplete]. Figure 4 and Figure 5The metallographic results of Comparative Example 1 show obvious coarse inclusions, and the probability of fracture around the coarse grains during use is higher, resulting in a significantly shorter service life compared to Example 1.

Claims

1. A shape memory alloy copper-based grinding wheel with adjustable stiffness, comprising a wheel body, characterized in that: The wheel body includes an inner layer and an outer layer, and a conductive layer is provided at the axial end face of the wheel body; the outer layer is formed by powder metallurgy pressing and sintering after mixing copper powder, Ni-Ti shape memory alloy powder and nano diamond particles; the inner layer is formed by powder metallurgy pressing and sintering after mixing copper powder and stainless steel powder, or the inner layer is a composite of copper layer and stainless steel layer.

2. The shape memory alloy copper-based grinding wheel with adjustable stiffness according to claim 1, characterized in that: The wheel body comprises an inner layer, a middle layer, and an outer layer from the inner circumferential side to the outer circumferential side. The middle layer is formed by powder metallurgy pressing and sintering of a mixture of copper powder and Ni-Ti shape memory alloy powder.

3. The shape memory alloy copper-based grinding wheel with adjustable stiffness according to claim 1 or 2, characterized in that: The outer layer has a phase transition temperature of 50°C to 80°C.

4. The shape memory alloy copper-based grinding wheel with adjustable stiffness according to claim 1 or 2, characterized in that: The conductive layer is a copper film attached to the end face of the wheel body, with a thickness of 70 to 150 micrometers.

5. The shape memory alloy copper-based grinding wheel with adjustable stiffness according to claim 1, characterized in that: The outer layer contains Ni-Ti shape memory alloy powder with a particle size of 10-30 μm and nanodiamond particles with a particle size of 5-10 nm, accounting for 11-13 wt%. The copper powder is electrolytic copper powder with a particle size of 50~100μm and a purity of ≥99.9%. The outer layer and the middle layer are produced with polyurethane composite additives with a purity of ≥99.9% and composite rare earth additives with a proportion of 2~3wt%.

6. A method for preparing a shape memory alloy copper-based grinding wheel according to any one of claims 2-5, characterized in that... Includes the following steps: S1. The powders for the inner, middle, and outer layers are mixed separately; S2. The blanks for the inner, middle, and outer layers are all formed using a cold isostatic pressing process; S3. The billets for the inner, middle, and outer layers are all sintered in a vacuum sintering furnace in sections; S4. The sintered inner layer blank, middle layer blank and outer layer blank are joined together by brazing process to form a wheel body; S5. Perform surface finishing on the wheel body and fine-tune the wheel's arc. S6. Form a conductive layer on the end face of the wheel body.

7. The preparation method according to claim 6, characterized in that: In step S1, the powder used in the intermediate layer and the powder used in the outer layer are mixed in a ball mill for 4-4.5 hours under argon protection, with a ball-to-powder ratio of 4.5: to 5:1 and a ball mill drum speed of 230±5 rpm; the powder used in the inner layer is mixed in a ball mill for 2-2.5 hours under argon protection, with a ball-to-powder ratio of 4.5: to 5:1 and a ball mill drum speed of 230±5 rpm.

8. The preparation method according to claim 6, characterized in that: In step S2, the blank is formed by holding the pressure at 300MPa for 20 minutes.

9. The preparation method according to claim 6, characterized in that: In step S3, the blanks of the outer and middle layers are first heated to 600°C to 630°C and sintered for 2 to 2.1 hours to remove the binder inside the pressed blank; then the temperature is raised to 900°C to 910°C and sintered for 4 to 4.1 hours to achieve densification of the copper matrix; finally, the temperature is raised to 1050°C to 1060°C and sintered for 50 to 60 minutes to activate the diffusion bonding between the shape memory alloy and the copper matrix interface.

10. The preparation method according to claim 6, characterized in that... In step S6, a conductive layer is deposited on the end face of the wheel body using a magnetron sputtering process; The magnetron sputtering process includes the following steps: A1. Clean the surface of the grinding wheel to remove oil and dirt; A2. Fix the grinding wheel in the sputtering chamber and adjust the distance between it and the copper target to 10~15cm; A3. Evacuate to a background vacuum level of 10. -3 ~10 -4 Pa; A4. Fill with argon gas and adjust the working pressure to 0.1~1.0 Pa; A5. Set the sputtering power density to 2~10W / cm² and perform pre-sputtering for 5~10 minutes; A6. Formal sputtering, controlling the deposition rate to approximately 0.1~1 nm / s, until the copper film thickness reaches the set thickness.

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