Amorphous alloy powder precision forming method based on multi-stage pressure gradient regulation and control

Abstract

The invention discloses an amorphous alloy powder precision forming method based on multistage pressure gradient regulation and control. The amorphous alloy powder precision forming method comprises the following steps that firstly, amorphous alloy powder to be pressed is placed in a mold cavity; step 2, applying a first-stage pressure P1 to the amorphous powder in the mold cavity, and maintaining the pressure for a first preset time t1 under the first-stage pressure P1; 3, after the first preset time t1, the applied pressure is adjusted to be second-stage pressure P2, and the pressure is kept for second preset time t2 under the second-stage pressure P2; through the implementation of the method, immediate crushing of particles and generation of microcracks caused by too fast concentration of stress in the initial pressurization stage are avoided, generation and expansion of the cracks are effectively inhibited, the cracking tendency of a pressed blank is greatly reduced, the integrity of a molded product is improved, and the method has certain use value and popularization value.

Description

Technical Field

[0001] The present invention relates to the technical field of powder metallurgy, and in particular to a method for precision forming of amorphous alloy powder based on multi-stage pressure gradient regulation. Background Art

[0002] Amorphous materials, due to their unique atomically disordered structure, typically exhibit excellent physical and chemical properties, such as high strength, high hardness, good wear resistance, and corrosion resistance. These unique properties give them broad application prospects in aerospace, electronics, precision molds, and other fields.

[0003] However, these properties, particularly high hardness and brittleness, also pose significant challenges to the compaction of amorphous powders. During the compaction process, amorphous powder particles are resistant to plastic deformation, and contact between particles is primarily point contact, making it difficult to form a dense compact and resulting in low green strength. This point contact state is due to the inability of particles to increase contact area through plastic flow, resulting in high stress concentration.

[0004] When traditional single-shot rapid press forming methods are applied to such hard and brittle amorphous powders, stress tends to concentrate on a few contact points between particles due to the powder's poor deformability. When local stress exceeds the material's fracture strength, microcracks form within the compact. These microcracks easily expand during increased or unloaded pressure, as well as during subsequent demolding and handling, ultimately developing into macroscopic cracks. Furthermore, the powder's inherent physical properties (such as poor particle size distribution, irregular shape, and rough surface) can make effective filling and densification difficult, making molding more difficult and exacerbating cracking. These issues severely restrict the application of amorphous powders in components requiring precision molding and structural integrity.

[0005] Currently, advanced technologies such as isostatic pressing, hot pressing, and spark plasma sintering (SPS) have been used to press some powder materials. However, technologies such as hot pressing and SPS usually require more complex forming conditions and involve high-temperature environments, which may cause the amorphous material to crystallize, thereby losing its valuable amorphous properties and related excellent performance. Although cold isostatic pressing can be carried out in stages at room temperature, avoiding the risk of crystallization and providing a more uniform pressure distribution, its effect on solving the cracking problem caused by local stress concentration and uncoordinated deformation of hard and brittle amorphous powders in conventional uniaxial pressing molds is still limited. In addition, the equipment is complex, and the equipment investment cost is 3-5 times higher than that of conventional pressing equipment; the production efficiency is low, and the single molding cycle is extended by more than 40%; continuous production is difficult, and the batch production capacity is low. The production cost is high and it is not suitable for all occasions.

[0006] Therefore, there is an urgent need to develop a simple, effective and low-cost amorphous powder pressing method to overcome the shortcomings of the above-mentioned existing technologies, especially under conventional uniaxial pressing conditions, to effectively prevent the cracking of the pressed green body and improve the molding quality. Summary of the Invention

[0007] In response to the shortcomings of the existing technology, the present invention provides a precision forming method for amorphous alloy powder based on multi-level pressure gradient regulation, aiming to solve the problems in the existing technology of poor forming effect and easy cracking of the pressed green body due to the high hardness, high brittleness and difficulty in deformation of amorphous powder during pressing.

[0008] To achieve the above object, the present invention provides a method for densification and pressing of an amorphous soft magnetic composite magnetic powder core, comprising the following steps:

[0009] Step 1: Place the amorphous alloy powder to be pressed into the mold cavity;

[0010] Step 2: applying a first stage pressure P1 to the amorphous powder in the mold cavity, and maintaining the pressure at the first stage pressure P1 for a first preset time t1;

[0011] Step 3: After the first preset time t1, the applied pressure is adjusted to a second stage pressure P2, and the pressure is maintained at the second stage pressure P2 for a second preset time t2;

[0012] Step 4: After the second preset time t2, the applied pressure is adjusted to the final target pressure P f , at the final target pressure P f The pressing is completed to obtain a pressed body.

[0013] Preferably, in step 2, the first stage pressure P1 is the final target pressure P f The first preset ratio satisfies the following relationship: 5% ≤ first stage pressure P1 / final target pressure P f ≤30%.

[0014] Preferably, in step 2, the first preset time t1 is 0.5 seconds to 10 seconds.

[0015] Preferably, in step 3, the second stage pressure P2 is higher than the first stage pressure P1.

[0016] Preferably, the second stage pressure P2 is the final target pressure P f The second preset ratio satisfies the following relationship: 30%<second stage pressure P2 / final target pressure P f ≤70%.

[0017] Preferably, in step 3, the second preset time t2 is 0.5 seconds to 10 seconds.

[0018] Preferably, the second stage pressure P2 and the final target pressure P f There is also at least one segmented pressurization and pressure holding step, and the pressure of each subsequent step is higher than the previous step and lower than the final target pressure P f .

[0019] Preferably, the final target pressure P f The range is 600MPa to 2500MPa.

[0020] Substantial effects of the present invention:

[0021] 1. In the present invention, by applying pressure in stages and coordinating the holding time in the middle, the response characteristics of the material at different pressure stages are utilized. In the initial low pressure stage, the hard and brittle amorphous powder particles are able to undergo preliminary stacking adjustment and a small amount of elastic deformation. The key is that the holding time in this stage allows the particles to perform necessary sliding and rotation to seek a more stable stacking position and release the local high stress caused by the initial uneven filling, thereby avoiding the immediate breakage of particles and the initiation of microcracks due to the rapid concentration of stress in the initial pressurization stage; the subsequent intermediate pressure stage and its holding time, after the initial stability Further pressure is applied to the particle system to promote a tighter packing of particles, which may be accompanied by some minor plastic deformation or controlled micro-crushing to fill the pores. The pressure holding at this stage is also important, as it allows the internal stress generated under higher pressure to be relaxed and redistributed to a certain extent. Since the stress peak is effectively weakened, the generation and expansion of cracks are effectively suppressed. When the full pressure is finally applied, the powder is already in a relatively uniform and pre-compacted state, which can better withstand the final high-pressure impact, thereby greatly reducing the cracking tendency of the green compact and improving the integrity of the molded product.

[0022] 2. In the present invention, the gradual pressurization process, especially the combination of the holding time, is conducive to the discharge of gas between powder particles and the reduction of the formation of closed pores. At the same time, the particles have more time to rearrange, gradually transitioning from the initial unstable point contact to the more stable limited surface contact, thereby increasing the effective bonding area between the particles. This not only achieves a higher and more uniform compact density, but also correspondingly improves the green strength of the compact, laying a good foundation for subsequent possible sintering or other processing steps. The higher green strength also means that the compact is less likely to be damaged during demolding, transportation and subsequent processing.

[0023] 3. In the present invention, the control of the pressurization program can be achieved on a conventional hydraulic press or mechanical press by modifying the control system or operating procedures, without the need to purchase complex and expensive special equipment. Therefore, the method has low equipment modification cost, simple operation, and easy industrial production. It has good economy and broad application prospects, and is particularly suitable for occasions that are cost-sensitive or have high output requirements. It has certain use value and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a pressure-time diagram of the amorphous powder segmented pressurization molding method of Example 1. DETAILED DESCRIPTION

[0025] In order to facilitate understanding of the present invention, the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments.

[0026] Unless otherwise defined, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification are intended solely to describe specific embodiments and are not intended to limit the invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the related listed items.

[0027] Example 1:

[0028] This embodiment is basically the same as embodiment 1, except that this embodiment provides a method for pressing and molding iron-based amorphous powder. The Fe-Si-B-Cr amorphous powder used is prepared by water atomization method, and the average particle size D of the iron-based amorphous powder is 1.37mm. 50 The particle size is 15 μm, with high hardness and obvious brittleness.

[0029] The pressing steps are as follows:

[0030] Step 1: Powder preparation and mold loading: 2 grams of amorphous powder granulation powder is evenly loaded into a carbide steel mold cavity with an inner diameter of 12 mm in the middle mold and an outer diameter of 7 mm in the lower punch. The loading amount is determined based on the target green sheet thickness (e.g., 4.7 mm) and the desired density.

[0031] Step 2: Pressurize and maintain pressure in stages (refer to Figure 1 , showing the process of pressure being applied in stages over time, including the initial pressure stage, the intermediate pressure stage, and the final pressure stage, as well as the holding time of each stage, intuitively reflecting the core technical features of the present invention):

[0032] Step 2.1: Initial pressurization and holding pressure: Use a servo press to apply pressure to the carbide steel mold cavity until the powder is subjected to a pressure of 90 MPa, which is 5% of the final target pressure (set to 1800 MPa). Hold the pressure at 90 MPa for 10 seconds.

[0033] Step 2.2: Intermediate pressurization and pressure holding: Subsequently, the pressure is steadily increased from 90 MPa to 40% of the final target pressure, that is, 720 MPa, and the pressure is held at this 720 MPa for 5 seconds.

[0034] Step 2.3: Final pressurization: Finally, the pressure was steadily increased from 720 MPa to the final target pressure of 1800 MPa. After reaching 1800 MPa, the pressure was maintained for 2 seconds to ensure uniform pressure transmission, and then the pressure was released.

[0035] Step 3: Demolding and inspection: After unloading the pressure, eject the pressed green sheet from the mold, observe the green sheet's macroscopic integrity, check for defects such as cracks and missing corners, and measure the density and hardness of the green sheet.

[0036] Using the method of this embodiment, the surface of the obtained amorphous iron-based powder compact is smooth, without obvious cracks, complete in shape, and the density can reach 82% of the theoretical density, indicating that the molding effect is good. In this embodiment, the initial 5% pressure and 10 seconds of holding pressure mainly play the role of overcoming the initial friction resistance between the powder particles and promoting their initial sliding and a small amount of rearrangement. The pressure at this stage is relatively low, but it is sufficient to form a relatively stable initial skeleton of the particle system. The holding time gives the particles sufficient time to complete this adjustment, avoiding immediate brittle fracture of the particles due to excessive initial impact. The key to this stage is to establish initial soft contact between particles, lay the foundation for the subsequent densification process, and reduce the stress concentration source in the subsequent high-pressure stage.

[0037] The subsequent 40% pressure (720 MPa) and 5-second hold further compress the powder based on the already initially stabilized particle skeleton, forcing the particles to pack more tightly and increasing the contact area and coordination number between particles. Because the particles have already undergone preliminary rearrangement, the stress distribution caused by the increased pressure at this stage is more uniform. The hold helps redistribute and relax stress between particles, reducing new crack sources caused by localized excessive stress or closing existing micropores.

[0038] The final pressurization, reaching 1800 MPa, completes the primary densification process. Thanks to the effective pretreatment in the first two stages, the powder now possesses a strong pressure-bearing capacity and a relatively uniform internal structure, enabling it to withstand the final high pressure without catastrophic cracking. This process achieves the desired molding effect by precisely controlling the pressurization path to guide material behavior.

[0039] Example 2:

[0040] This embodiment is basically the same as embodiment 1, except that this embodiment provides a method for pressing and molding an iron-based amorphous powder. The Fe-Si-B-Nb-Cr amorphous powder used is prepared by water atomization method, and the average particle size D 50 The particle size is 12.8 μm, with high hardness and obvious brittleness.

[0041] The pressing steps are as follows:

[0042] Step 1: Powder preparation and mold loading: 2 grams of the above-mentioned amorphous powder granulation powder is evenly loaded into a carbide steel mold cavity with an inner diameter of 12 mm in the middle mold and an outer diameter of 7 mm in the lower punch.

[0043] Step 2: Segmented pressurization and pressure maintenance:

[0044] Step 2.1: Initial pressurization and holding pressure: Apply pressure to the mold through the press until the pressure on the powder reaches 20% of the final target pressure (set to 2500 MPa), that is, 500 MPa. Hold the pressure at 500 MPa for 3 seconds.

[0045] Step 2.2: Intermediate pressurization and pressure holding: Subsequently, the pressure is steadily increased from 500 MPa to 60% of the final target pressure, that is, 1500 MPa. The pressure is held at this 1500 MPa for 3 seconds.

[0046] Step 2.3: Final pressurization: Finally, steadily increase the pressure from 1500 MPa to the final target pressure of 2500 MPa. After reaching 2500 MPa, hold the pressure for 1 second and then release the pressure.

[0047] Step 3: Demolding and Inspection: After pressure is released, the compact is ejected from the mold. Observe the macroscopic integrity of the compact and check for defects such as cracks and chipping. The density and hardness of the compact can also be measured.

[0048] The method of this example yields amorphous iron-based powder compacts with smooth surfaces, no visible cracks, and a well-defined shape. The density reaches 85% of the theoretical density, achieving excellent molding results. In this example, the three stages of compaction function in the same manner as in Example 1. Precise control of the pressurization path guides material behavior, achieving the desired molding effect.

[0049] Example 3:

[0050] This embodiment is basically the same as embodiment 1, except that this embodiment provides a method for pressing and molding iron-based amorphous powder. The Fe-Si-B-Nb-Cr amorphous powder used is prepared by water atomization method, and the average particle size D50 The particle size is 11.6 μm, with high hardness and obvious brittleness.

[0051] The pressing steps are as follows:

[0052] Step 1. Powder preparation and mold filling: 2 grams of the above-mentioned amorphous powder granulation powder is evenly loaded into a carbide steel mold cavity with an inner diameter of 12 mm in the middle mold and an outer diameter of 7 mm in the lower punch.

[0053] Step 2. Pressurize and maintain pressure in stages:

[0054] Step 2.1: Initial pressurization and holding pressure: Apply pressure to the mold through the press until the pressure on the powder reaches 30% of the final target pressure (set to 600 MPa), that is, 180 MPa. Hold the pressure at this 180 MPa for 5 seconds.

[0055] Step 2.2: Intermediate pressurization and pressure holding: Subsequently, the pressure is steadily increased from 180 MPa to 70% of the final target pressure, that is, 420 MPa, and the pressure is held at this 420 MPa for 10 seconds.

[0056] Step 2.3: Final pressurization: Finally, the pressure was steadily increased from 420 MPa to the final target pressure of 600 MPa. After reaching 600 MPa, the pressure was maintained for 5 seconds to ensure uniform pressure transmission, and then the pressure was released.

[0057] Step 3. Demolding and Inspection: After pressure is released, the compact is ejected from the mold. Observe the macroscopic integrity of the compact, checking for defects such as cracks and chipping. The density and hardness of the compact can also be measured.

[0058] By using the method of this embodiment, the Fe-Si-B-Nb-Cr powder compact obtained has a smooth surface, no obvious cracks, a complete shape, and a density of about 78% of the theoretical density, with a good molding effect.

[0059] Example 4:

[0060] The amorphous alloy powder precision forming method of this embodiment is not limited to two intermediate pressurization and holding stages. As needed, more (e.g., three or four total) staged pressurization and holding steps can be implemented, with each subsequent step applying a higher pressure than the previous one. This allows for a smoother and more refined final densification process, which is particularly beneficial for particularly sensitive or brittle amorphous powder systems.

[0061] This embodiment uses the following four-stage pressing sequence to press the Fe-Si-B-Cr amorphous powder:

[0062] Stage 1: Apply 20% of the final target pressure and hold the pressure for 2 seconds;

[0063] The second stage: increase the pressure to 40% of the final target pressure and maintain the pressure for 2 seconds;

[0064] Stage 3: Increase the pressure to 75% of the final target pressure and maintain the pressure for 2 seconds;

[0065] Stage 4: Increase the pressure to the final target pressure (2000 MPa) and maintain the pressure for 2 seconds.

[0066] This more refined pressure gradient can further reduce the pressure increment ratio at each step, thereby more effectively controlling stress accumulation and release, and minimizing cracking. Using the method of this embodiment, the amorphous Fe-Si-B-Cr powder compact obtained has a smooth surface, no obvious cracks, a complete shape, and a density of 84.5% of the theoretical density, achieving excellent forming results.

[0067] The method of the present invention is applicable to various types of amorphous powders, including but not limited to iron-based amorphous powders, cobalt-based amorphous powders, nickel-based amorphous powders, zirconium-based amorphous alloy powders, and other metal or alloy-based amorphous powders. In addition, the method may also be applicable to certain ceramic powders with similar high hardness and high brittleness characteristics, as long as they face similar cracking problems caused by high hardness and brittleness during cold pressing.

[0068] Comparative Example 1:

[0069] The same iron-based amorphous Fe-Si-B-Cr powder and mold were used as in Example 1. The difference was that a traditional single pressurization method was used: the pressure was directly and quickly applied from 0 to the final target pressure of 1800 MPa, and the pressure was maintained at 1800 MPa for 3 seconds.

[0070] Comparative Example 2:

[0071] The same iron-based amorphous Fe-Si-B-Nb-Cr powder and mold were used as in Example 3. The difference was that a traditional single pressurization method was adopted: the pressure was directly and quickly applied from 0 to the final target pressure of 600 MPa, and the pressure was maintained at 600 MPa for 3 seconds.

[0072] Ten green compact samples were prepared for each of Examples 1-4 and Comparative Examples 1-2, and the results are recorded in Table 1 below.

[0073] Table 1: Comparison of amorphous powder pressing effects of the method of the present invention and the traditional method.

[0074]

[0075] From the comparison results in Table 1, it can be seen that by adopting the segmented pressure molding method of the present invention, the cracking problem of the amorphous powder compact has been significantly improved, the molding success rate has been greatly improved, and a compact with better appearance quality and higher density has been obtained. This fully demonstrates the effectiveness and superiority of the technical solution of the present invention. These specific parameters and comparative data are provided to meet the requirements of the patent law for the sufficiency of invention disclosure, so that those skilled in the art can understand and reproduce the present invention, and also clearly demonstrate the significant progress of the present invention over the prior art. The parameters such as the final pressure, powder type and particle size are selected to construct a scene that is actually operable and can highlight the effect of the invention.

[0076] Through the above technical solution, the present invention cleverly utilizes the principle of exchanging time for space, that is, by maintaining pressure at a specific pressure stage, the hard and brittle amorphous powder particles are given enough time to adjust their own position and disperse stress, thereby avoiding the destructive consequences brought about by traditional rapid one-time pressurization, and realizing effective and high-quality molding of amorphous powder.

[0077] Those skilled in the art will understand that the present invention is not limited to the specific embodiments described above, and that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention. For example, the pressure value and holding time at each stage can be optimized and adjusted based on the specific amorphous powder type, particle size, mold design, and performance requirements of the final product. The rates of pressurization and depressurization can also be controlled as process parameters.

[0078] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0079] The above are only preferred embodiments of the present invention and do not limit the present invention in any way. Any simple modifications, changes and equivalent transformations made to the above embodiments based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for precision forming of amorphous alloy powder based on multi-stage pressure gradient control, characterized in that: The following steps are involved: Step 1: Place the amorphous alloy powder to be pressed into the mold cavity; Step 2: applying a first stage pressure P1 to the amorphous powder in the mold cavity, and maintaining the pressure at the first stage pressure P1 for a first preset time t1; Step 3: After the first preset time t1, the applied pressure is adjusted to a second stage pressure P2, and the pressure is maintained at the second stage pressure P2 for a second preset time t2; Step 4: After the second preset time t2, the applied pressure is adjusted to the final target pressure P f , at the final target pressure P f The pressing is completed to obtain a pressed body.

2. The method for precision forming of amorphous alloy powder based on multi-stage pressure gradient control according to claim 1, characterized in that: In step 2, the first stage pressure P1 is the final target pressure P f The first preset ratio satisfies the following relationship: 5% ≤ first stage pressure P1 / final target pressure P f ≤30%.

3. The method for precision forming of amorphous alloy powder based on multi-stage pressure gradient control according to claim 2, characterized in that: In step 2, the first preset time t1 is 0.5 seconds to 10 seconds.

4. The method for precision forming of amorphous alloy powder based on multi-stage pressure gradient control according to claim 3, characterized in that: In step 3, the second stage pressure P2 is higher than the first stage pressure P1.

5. The method for precision forming of amorphous alloy powder based on multi-stage pressure gradient control according to claim 4, characterized in that: The second stage pressure P2 is the final target pressure P f The second preset ratio satisfies the following relationship: 30%<second stage pressure P2 / final target pressure P f ≤70%.

6. The method for precision forming of amorphous alloy powder based on multi-stage pressure gradient control according to claim 5, characterized in that: In step 3, the second preset time t2 is 0.5 seconds to 10 seconds.

7. The method for precision forming of amorphous alloy powder based on multi-stage pressure gradient control according to claim 6, characterized in that: When applying the second stage pressure P2 and the final target pressure P f There is also at least one segmented pressurization and pressure holding step, and the pressure of each subsequent step is higher than the previous step and lower than the final target pressure P f .

8. The method for precision forming of amorphous alloy powder based on multi-stage pressure gradient control according to claim 7, characterized in that: The final target pressure P f The range is 600MPa to 2500MPa.

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