Metal powder freezing forming product and technology

Abstract

The invention discloses a metal powder freezing forming product and technology, and the technology comprises the following steps: S1, metal powder, a binder and water are mixed to form a uniform metal powder mixture; s2, a mold is pre-cooled to-10 DEG C to-20 DEG C, and then the metal powder mixture is injected into a mold cavity; s3, the mold injected with the liquid is put into a freezing box, a mixture of the mold and the metal powder is cooled to-45 DEG C to-55 DEG C in a gradient cooling mode, heat preservation and curing are conducted, and a completely-cured blank is separated from the mold; s4, separating the completely cured blank from the mold, and putting the blank into a vacuum freeze-drying machine for vacuum freeze-drying to remove moisture; and S5, sintering the green body under the protection of inert gas to obtain a finished product. Traditional high-pressure / binder shaping is replaced with low-temperature freezing curing, high-precision, low-pollution and rapid forming of the metal powder blank with the complex shape is achieved, the mold cost is reduced, and the production period is shortened.

Description

Technical Field

[0001] This invention relates to the field of metal powder forming technology, specifically to a metal powder cryogenic forming product and process. Background Technology

[0002] Currently, the mainstream powder metal forming processes are "compression molding" and "injection molding". Compression molding applies high pressure (usually 10-80 MPa) to metal powder through a rigid mold, causing the particles to undergo plastic deformation and cold welding to shape the blank, forming a blank with a density of 80-95% of the theoretical density. Compression molding has poor adaptability to complex shaped components, and is prone to problems such as incomplete filling of edges and corners and uneven density. In addition, the mold cost is high, and the economics of small-batch production are low.

[0003] Metal injection molding (MIM) is a novel advanced manufacturing process that combines powder metallurgy and injection molding technologies. It involves mixing metal powder with a binder to form a feedstock, which is then injected into a mold using an injection molding machine. After debinding and sintering, high-precision, high-performance metal parts are obtained. Metal powder (typically 5-30 μm in particle size) is mixed with an organic binder to form a flowable feedstock, which is then injected into a precision mold under high temperature (approximately 150-200°C) and high pressure using an injection molding machine. The resulting green blank contains a large amount of binder and needs to be removed through debinding to form a brown blank. The brown blank is then heated at high temperature and in a protective atmosphere (such as nitrogen, argon, or hydrogen) or in a vacuum environment to metallurgically bond the metal particles, achieving a final density of 95-99% of the theoretical density. The sintered product has high density, mechanical properties close to forged materials, high dimensional accuracy, and excellent surface finish. However, injection molding requires a large amount of organic binder, and the subsequent degreasing process (such as thermal degreasing, solvent degreasing, catalytic degreasing) takes a long time (usually 24-72 hours) and is prone to cracking and deformation of the preform. At the same time, the large-scale use of organic binder will cause environmental pollution.

[0004] Neither of the two metal powder forming processes mentioned above can meet the comprehensive requirements of "complex shape preparation", "high precision", "low pollution" and "low cost", and cannot meet the requirements of the fields of handicrafts and luxury goods for the preparation of micro-complex three-dimensional powder metal components. Summary of the Invention

[0005] To address the shortcomings of existing metal powder molding processes, such as poor adaptability to complex shapes, significant binder pollution, and time-consuming debinding, this invention provides a metal powder cryogenic molding product and process. It replaces traditional high-pressure / binder shaping with low-temperature cryogenic curing, achieving high-precision, low-pollution, and rapid molding of complex-shaped metal powder blanks, thereby reducing mold costs and production cycles.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a metal powder cryogenic forming process, comprising the following steps: S1. Preparation of metal powder mixture: Mix metal powder, binder and water, and disperse by ultrasonic vibration (power 300-500W, time 10-20min) to ensure that the powder does not agglomerate, and the binder fully coats the micron-sized metal powder to form a uniform metal powder mixture with a viscosity of 1500-7500m.Pa.s. The mass ratio of metal powder, binder, and water is (9–15):(0.8–1.2):(0.06–0.08). S2. Mold pre-cooling and liquid injection: The customized mold (made of silicone, with a cavity corresponding to the shape of the target component, which is conducive to demolding of complex shapes) is pre-cooled to -10 to -20°C. Then, the metal powder mixture is injected into the mold cavity at a uniform speed. A vibration platform (including but not limited to ultrasound, with an injection speed of 5 to 10 mL / min) is required to avoid the generation of air bubbles. Pre-cooling to -10 to -20°C in this step can form a micro-freezing layer on the mold surface, which helps the metal powder mixture to quickly and initially set after injection and prevents flow deformation; low-speed injection (5 to 10 mL / min) can reduce bubble formation and avoid defects in the blank. S3, Gradient freeze curing: The mold after liquid injection is placed in a freezer and the mold and metal powder mixture are cooled to -45 to -55°C using a gradient cooling method. The mixture is then kept at this temperature for curing. The completely cured preform is then separated from the mold. In this step, the water in the metal powder mixture is freeze-dried under freezing conditions to facilitate demolding. S4. Vacuum freeze drying: The fully solidified preform is separated from the mold and placed in a vacuum freeze dryer to remove moisture. Under vacuum and low temperature conditions, the ice in the preform directly sublimates into water vapor, bypassing the liquid stage, avoiding preform shrinkage or structural collapse caused by surface tension, resulting in higher product dimensional accuracy. S5. Sintering densification treatment: The dried green body is placed in a sintering furnace and sintered under inert gas protection to obtain the finished product; under inert atmosphere protection, the green body is slowly heated to below the metal melting point for solid sintering, and the metal particles form neck connections through diffusion, ultimately achieving densification. In addition, the binder in the green body can be removed during the sintering process.

[0007] Furthermore, the types of adhesives include, but are not limited to: cellulose and its derivatives, xanthan gum, carrageenan, agar, gum arabic, starch and its derivatives, guar gum, gelatin, gellan gum, carbomer, acrylate / C10-30 alkyl acrylate crosspolymers, sodium polyacrylate, sodium polyacrylate grafted starch, strychnine gum, polyvinylpyrrolidone, pectin, ammonium acryloyl dimethyl taurate / VP copolymer, sodium acryloyl dimethyl taurate / VP copolymer, polyacrylate crosspolymer-6, polyacrylate crosspolymer-11, acrylate / vinyl isodecanoate crosspolymer, ammonium acryloyl dimethyl taurate / behenol polyether-25 methacrylate crosspolymer, polyacrylate-1 crosspolymer, or mixtures of any combination thereof.

[0008] Preferably, in step S1, the adhesive is a mixture of disodium EDTA, thixotropic adhesive, and octyl glycol, with a ratio of 0.05:6:1.

[0009] The above-mentioned adhesive is a water-based adhesive, which is environmentally friendly and pollution-free.

[0010] This process, by selecting a specific water-based adhesive system, replaces the traditional "hot pressing + organic degreasing" with "freezing setting + vacuum desolventizing", thus fundamentally solving the three major technical problems of pollution, shrinkage, and long cycle time.

[0011] Specifically, water acts as a solvent and temporary binder, serving as the mobile phase of the metal powder mixture and the former of the ice crystal skeleton. During the gradient freeze-curing stage, it freezes into ice, forming a solid skeleton that fixes the metal powder particles and other binder components within it.

[0012] As a thickener and structural enhancer, gelling glue can form a three-dimensional network structure after dissolving in water, which greatly increases the viscosity of the metal powder mixture, prevents powder sedimentation, and provides additional mechanical strength during freezing and drying, supporting the green body structure and preventing collapse.

[0013] Octyl glycol helps reduce the surface tension of mixtures, improves the uniformity of powder dispersion, and has a low freezing point. In formulations, it forms a eutectic mixture with water, improving freezing properties, lowering the overall freezing temperature, making the freezing process more controllable, and preventing ice crystals from growing too quickly.

[0014] Disodium EDTA is primarily used as a dispersant. Its molecules can adsorb onto the surface of metal powder particles, preventing particle agglomeration through electrostatic repulsion (electric double layer effect), thus making the suspension more stable and uniform. During freezing, as water freezes into ice, disodium EDTA precipitates in crystal form, distributing between the ice crystals and powder particles, ensuring uniform dispersion.

[0015] During the vacuum freeze-drying stage, the solvent (water) and volatile components (octyl glycol) are mainly removed. The gelling agent and disodium EDTA remain in solid form in the green body after freeze-drying, forming part of the porous framework. This step achieves "solvent removal" rather than the "degreasing" of traditional MIM, thus resulting in no shrinkage, no pollution, and high efficiency. The sintering stage thoroughly removes polymers and salts (gelling agent, disodium EDTA) and densifies the metal particles.

[0016] Further, in step S3, the gradient cooling process is as follows: first, the temperature is lowered from the current pre-cooling temperature of the mold to -35℃ to -40℃ at a rate of 4 to 5℃ / min and held for 60 to 120 minutes. The rapid cooling causes the moisture and binder in the metal powder mixture to gradually freeze along the cavity wall towards the center, fixing the position of the metal powder. Then, the temperature is lowered to -45℃ to -55℃ at a rate of 1 to 2℃ / min and held for 90 to 180 minutes. The temperature is slowly lowered to an even lower temperature to ensure that the interior of the blank is completely solidified, avoiding stress concentration and cracks caused by rapid freezing.

[0017] In this step, a gradient cooling strategy is adopted. First, the temperature is rapidly reduced to gradually freeze the moisture from the outside in, fixing the position of the powder. Then, the temperature is slowly reduced to an even lower temperature to ensure that the internal moisture is completely solidified, avoiding stress concentration and cracks caused by rapid freezing. This avoids cracking and deformation of the billet, ensuring the structural integrity and dimensional accuracy of the billet, and is suitable for forming high-precision, complex-shaped components.

[0018] This invention achieves precise control over the freezing process of metal powder suspensions by designing specific gradient cooling curves. In the first stage, a high cooling rate and temperature gradient induce ice crystals to grow directionally from the cavity wall towards the center, thereby uniformly and densely fixing and enriching the metal powder particles within the ice crystal network. This ensures the uniformity of the green body composition and the perfect reproduction of complex shapes; even minute edges are fully filled, something difficult to achieve in compression molding. In the second stage, a lower cooling rate and deep cryogenic insulation achieve uniform shrinkage of the green body and full release of internal stress, ensuring complete solidification of the water-based binder system and forming a robust overall framework. This completely avoids cracking and deformation of the green body, laying the foundation for subsequent freeze-drying and high-precision sintering.

[0019] Furthermore, in step S4, the parameters for vacuum freeze drying are: vacuum degree ≤10Pa, temperature -20℃~-55℃, and drying time 8-24h.

[0020] This step uses vacuum freeze drying (8-12 hours) to replace the lengthy (24-72 hours) and defect-prone hot degreasing or solvent degreasing steps, greatly shortening the production cycle. Moreover, because ice sublimation has no liquid phase surface tension, the green body does not shrink, deform, or crack during the drying process, maintaining extremely high dimensional accuracy and shape integrity, resulting in high-quality green bodies.

[0021] Furthermore, in step S5, during the sintering process, the temperature is increased to 85-95% of the melting point of the metal powder at a rate of 2-3℃ / min, held for 2-4 hours, and then cooled to room temperature in the furnace. Furthermore, in step S1, the particle size of the metal powder is 0.5–60 μm, the purpose of which is to achieve densification through sintering.

[0022] Furthermore, the metal powder includes stainless steel powder, alloy powder, or copper-based powder.

[0023] Specifically, the materials of the metal powder include stainless steel (316L; 304; 17-4; 430; 440C; 303), titanium alloy (Ti6Al4V), aluminum alloy (AlSi10Mg), nickel-based alloy (GH4099), tungsten alloy (W95Fe3Ni2), tungsten copper alloy (W85Cu10Ni5), copper-based alloy, molybdenum-based alloy, and high-entropy alloy.

[0024] The present invention also provides a metal powder cryogenic product, which is prepared by the above-mentioned metal powder cryogenic process. The qualified rate of complex shaped components (such as components with micropores and thin walls) is increased to more than 98%. Vacuum freeze drying has no blank shrinkage and the finished product dimensional accuracy is controlled within ±0.1mm. After sintering, the relative density of the product is ≥95%, and the mechanical properties (such as hardness and tensile strength) are comparable to those of the molded product.

[0025] The present invention also provides an application of the above-mentioned cryogenically molded metal powder product, wherein the cryogenically molded metal powder product is used in handicrafts (artistic ornaments). Compared with the prior art, the present invention has the following beneficial effects: (1) This process does not require high pressure molds and organic binders. The forming qualification rate of complex shaped components (such as components with micropores and thin walls) is increased to more than 98%. Vacuum freeze drying has no blank shrinkage. The finished product size accuracy is controlled within ±0.1mm. The relative density after sintering is ≥95%. The mechanical properties (such as hardness and tensile strength) are comparable to those of molded products. (2) The mold does not need to withstand high pressure, reducing manufacturing costs by 40-60%, and is more adaptable to small-batch production; no organic binder is used and no degreasing step is required, shortening the production cycle by 50%, and there are no pollutant emissions, which meets the requirements of green manufacturing. Attached Figure Description

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] Figure 1 This is a process flow diagram of the preparation of complex stainless steel powder frozen molding in Example 1; Figure 2 This is a photograph of the copper-based metal product after freezing and demolding in Example 4. Figure 3 This is a photograph of the sintered copper-based metal product from Example 4. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 The preparation process of complex stainless steel powder cryogenic molding is as follows: Figure 1 As shown, the specific steps are as follows: S1. Preparation of metal powder mixture: First, the binder (EDTA disodium, thiocyanate, and octyl glycol in a mass ratio of 0.05:6:1) and water are mixed, and then added to 316L stainless steel powder (particle size 1-50μm, purity 99.9%). The 316L stainless steel powder, binder, and water are mixed in a mass ratio of 14:1:0.07 and dispersed by ultrasonic vibration (400W power, 15min) to ensure that the powder does not agglomerate and that the binder fully coats the micron-sized metal powder to form a uniform metal powder mixture.

[0030] S2. Mold precooling and filling: The mold cavity for the craft has a module of 1 and an irregular and complex three-dimensional structure. The mold material is silicone. It is pre-cooled to -15℃. The metal powder mixture in step S1 is injected into the mold cavity at a uniform speed of 8mL / min to avoid generating air bubbles.

[0031] S3, Gradient freeze-curing: After the liquid is injected, the mold is placed in a freezing box. The freezing box first lowers the temperature of the mold from the current temperature to -40℃ at a rate of 5℃ / min and holds it for 90 minutes. Then it lowers the temperature to -55℃ at a rate of 2℃ / min and holds it for 120 minutes. The green body is completely solidified. The completely solidified green body is then separated from the mold.

[0032] S4. Freeze-drying and sintering: The parameters for the vacuum freeze dryer are: vacuum degree 5Pa, temperature -55℃, drying time 10h; The dried preform is placed in a sintering furnace, and argon and nitrogen are introduced into the furnace. The temperature is increased to 1360℃ at 2.5℃ / min and held for 3 hours. The preform is then cooled to room temperature in the furnace to obtain the finished product.

[0033] S5. Finished Product Performance Testing: The dimensional error of the frozen stainless steel powder artifacts obtained after testing is ≤0.05mm, and the relative density is 96.2%, with an actual measured density of 7.8g / cm³. 3 The testing standard is based on Archimedes' principle. The Vickers hardness is HV160, and the testing standard is GB / T 4340.1-2024 "Metallic materials - Vickers hardness test - Part 1: Test method". The tensile strength is 480 MPa, and the testing standard is GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1: Test method at room temperature".

[0034] Example 2 The preparation process of complex crafts made by cryogenic molding of titanium alloy powder is as follows: S1. Preparation of metal powder mixture: First, the binder (EDTA disodium, gelling agent, water, and octyl glycol in a mass ratio of 0.05:6:1) and water are mixed, and then added to titanium alloy powder (model CT4, particle size 0.5-60μm, purity 99.9%). The titanium alloy powder, binder, and water are mixed in a mass ratio of (9:0.8:0.06) and dispersed by ultrasonic vibration (power 500W, time 15min) to ensure that the powder does not agglomerate and that the binder fully coats the micron-sized metal powder to form a uniform metal powder mixture.

[0035] S2. Mold precooling and filling: The mold cavity for the craft has a module of 1 and an irregular and complex three-dimensional structure. The mold material is silicone. It is pre-cooled to -10℃. The metal powder mixture in step S1 is injected into the mold cavity at a uniform speed of 5mL / min to avoid generating air bubbles.

[0036] S3, Gradient freeze-curing: After the liquid is injected, the mold is placed in a freezing box. The freezing box first lowers the temperature of the mold from the current temperature to -35℃ at a rate of 4℃ / min and holds it for 120 minutes, then lowers it to -45℃ at a rate of 1℃ / min and holds it for 180 minutes. The green body is completely solidified. The completely solidified green body is then separated from the mold.

[0037] S4. Freeze-drying and sintering: The parameters for the vacuum freeze dryer are: vacuum degree 8Pa, temperature -55℃, and drying time 8h; The dried preform is placed in a sintering furnace, and argon and nitrogen are introduced into the furnace. The temperature is increased to 840°C at 2°C / min, held for 3 hours, and then cooled to room temperature in the furnace to obtain the finished product.

[0038] S5. Finished Product Performance Testing: The dimensional error of the frozen-formed titanium alloy powder artifacts obtained was tested to be 0.05-0.1 mm, with a relative density of 97.6% and a density of 4.28 g / cm³. 3 It has a Vickers hardness of HV290 and a tensile strength of 760 MPa.

[0039] Example 3 The preparation process of complex crafts made by cryogenic molding of aluminum alloy powder is as follows: S1. Preparation of metal powder mixture: First, the binder (EDTA disodium, thiocyanate, and octyl glycol in a mass ratio of 0.05:6:1) and water are mixed, and then added to aluminum alloy powder (grade 6160, particle size 1.5-60μm, purity 99.9%). The aluminum alloy powder, binder, and water are mixed in a mass ratio of 15:1.2:0.08 and dispersed by ultrasonic vibration (power 500W, time 15min) to ensure that the powder does not agglomerate and that the binder fully coats the micron-sized metal powder to form a uniform metal powder mixture.

[0040] S2. Mold precooling and filling: The mold cavity of the craft product has a module of 1 and an irregular and complex three-dimensional structure. The mold material is silicone. It is pre-cooled to -20℃. The metal powder mixture in step S1 is injected into the mold cavity at a uniform speed of 8mL / min to avoid generating air bubbles.

[0041] S3, Gradient freeze-curing: After the liquid is injected, the mold is placed in a freezing box. The freezing box is first lowered to -40℃ at 5℃ / min and kept at that temperature for 60min; then it is lowered to -50℃ at 2℃ / min and kept at that temperature for 90min. The green body is completely solidified. The completely solidified green body is then separated from the mold.

[0042] S4. Freeze-drying and sintering: The parameters for the vacuum freeze dryer are: vacuum degree 6Pa, temperature -55℃, and drying time 12h. The dried preform is placed in a sintering furnace, and argon and nitrogen are introduced into the furnace. The temperature is increased to 570°C at 2°C / min, held for 3 hours, and then cooled to room temperature in the furnace to obtain the finished product.

[0043] S5. Finished Product Performance Testing: The dimensional error of the cryogenically formed aluminum alloy powder artifacts was tested to be 0.05-0.1 mm, the relative density was 95.8%, and the measured density was 2.68 g / cm³. 3 The sintered Brinell hardness is HB47 and the tensile strength is 118 MPa.

[0044] Example 4 The specific steps of the preparation process of complex artifacts made by cryogenic molding of copper-based metal powder are as follows: S1. Preparation of metal powder mixture: First, the binder (EDTA disodium, thiocyanate, and octyl glycol in a mass ratio of 0.05:6:1) and water are mixed, and then added to copper-based metal powder (grade T2, particle size D10 / 3.9um, D50 / 11.6um, D90 / 25.7um, purity 99.9%). The copper-based metal powder, binder, and water are mixed in a mass ratio of 14:1:0.07 and dispersed by ultrasonic vibration (400W power, 15min) to ensure that the powder does not agglomerate and that the binder fully coats the micron-sized metal powder to form a uniform metal powder mixture.

[0045] S2. Mold precooling and filling: The mold cavity for the craft has a module of 1 and an irregular and complex three-dimensional structure. The mold material is silicone. It is pre-cooled to -15℃. The metal powder mixture in step S1 is injected into the mold cavity at a uniform speed of 8mL / min to avoid generating air bubbles.

[0046] S3, Gradient freeze-curing: After liquid injection, the mold is placed in a freezing oven. The freezing oven first lowers the temperature from the mold's current temperature to -40°C at a rate of 5°C / min and holds for 90 minutes, then lowers the temperature to -55°C at a rate of 2°C / min and holds for 120 minutes until the green body is completely solidified. The completely solidified green body is then separated from the mold. The actual copper-based metal product after freezing and demolding is shown below. Figure 2 As shown.

[0047] S4. Freeze-drying and sintering: The parameters for the vacuum freeze dryer are: vacuum degree 5Pa, temperature -55℃, drying time 10h; The dried blank was placed in a sintering furnace, which was then purged with argon and nitrogen gas. The temperature was increased to 1360℃ at a rate of 2.5℃ / min and held for 3 hours. The blank was then cooled to room temperature in the furnace to obtain the finished product. The physical examples of the sintered copper-based metal products are shown below. Figure 3 As shown.

[0048] S5. Finished Product Performance Testing: The dimensional error of the frozen-molded copper-based metal powder artifacts was tested to be 0.1 mm, and the relative density was 95%, with an actual measured density of 8.45 g / cm³.3 It has a Vickers hardness of HV82 and a tensile strength of 260 MPa.

[0049] Comparative Example 1 Comparative Example 1 is a comparative test example of Example 1: The difference between the two is that in step S3 of Comparative Example 1, a direct cooling method is used for freeze-curing, specifically: After the liquid is injected, the mold is placed in a freezing box. The freezing box directly cools the mold from its current temperature to -55℃ at a rate of 5℃ / min and holds the temperature for 120 minutes until the preform is completely solidified. The completely solidified preform is then separated from the mold.

[0050] The dimensional error of the stainless steel powder cryogenically molded artifacts prepared in Comparative Example 1 was ≤0.1mm, and the relative density was 90%, with a measured density of 7.11g / cm³. 3 It has a Vickers hardness of HV120 and a tensile strength of 410 MPa.

[0051] Comparative Example 2 Comparative Example 2 is a comparative test case of Example 1: The difference between the two is that in step S3 of Comparative Example 2, a direct cooling method is used for freeze-curing, specifically: After the liquid is injected, the mold is placed in a freezing box. The freezing box directly cools the mold from its current temperature to -55℃ at a rate of 2℃ / min and holds the temperature for 120 minutes until the preform is completely solidified. The completely solidified preform is then separated from the mold.

[0052] The stainless steel powder cryogenically molded artifacts prepared in Comparative Example 2 had a dimensional error ≤0.08mm and a relative density of 93%, with a measured density of 7.34g / cm³. 3 It has a Vickers hardness of HV135 and a tensile strength of 425 MPa.

[0053] Comparative Example 3 Comparative Example 3 is a comparative test case of Example 1: The difference between the two is that in Comparative Example 3, the mold was not pre-cooled, and the metal powder mixture was directly injected into the mold cavity at room temperature.

[0054] The dimensional error of the stainless steel powder cryogenically molded handicrafts prepared in Comparative Example 3 was ≤0.1mm, and the relative density was 93%, with a measured density of 7.29 g / cm³. 3 It has a Vickers hardness of HV129 and a tensile strength of 418 MPa.

[0055] Comparative Example 4 Comparative Example 4 is a comparative test example of Example 2: The difference between the two is that the mass ratio of titanium alloy powder, binder and water in Comparative Example 4 is (9:0.6:0.06).

[0056] The titanium alloy powder cryogenically molded product obtained in Comparative Example 4 has a dimensional error ≤0.15mm and a relative density of 88%, with a density of 3.87g / cm³. 3 It has a Vickers hardness of HV245 and a tensile strength of 650 MPa.

[0057] Crystallization occurred on the surface of the titanium alloy powder cryogenic molding product.

[0058] Comparative Example 5 Comparative Example 5 is a comparative test case of Example 3: The difference between the two is that the mass ratio of titanium alloy powder, binder and water in Comparative Example 5 is (9:1.4:0.06).

[0059] The titanium alloy powder cryogenically molded product obtained in Comparative Example 5 has a dimensional error ≤0.1mm and a relative density of 93%, with a density of 4.09g / cm³. 3 It has a Vickers hardness of HV270 and a tensile strength of 680 MPa.

[0060] No cracks or other defects were found on the surface of the aluminum alloy powder cryogenic molding product.

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A metal powder freeze forming process characterized by, The method comprises the following steps: S1, metal powder mixture preparation: mixing metal powder, binder and water to form a uniform metal powder mixture, wherein the mass ratio of metal powder, binder and water is (9-15):(0.8-1.2):(0.06-0.08); S2, mold pre-cooling liquid injection: pre-cooling the mold to -10 to -20℃, and then injecting the metal powder mixture into the mold cavity; S3, gradient freezing solidification: placing the injected mold into a freezing box, cooling the mold and the metal powder mixture to -45 to -55℃ by gradient cooling, and isolating the completely solidified embryo from the mold; S4, vacuum freeze-drying: separating the completely solidified embryo from the mold, and placing the embryo into a vacuum freeze-drying machine for vacuum freeze-drying to remove water; S5, sintering densification treatment: placing the dried embryo into a sintering furnace for sintering treatment under inert gas protection to obtain a finished product.

2. The metal powder freeze forming process of claim 1, wherein, In step S1, the binder is a mixture of disodium EDTA, cold adhesive and octanol.

3. The metal powder freeze forming process of claim 1, wherein, In step S3, the gradient cooling process is: first, reducing the mold temperature to -35 to -40℃ at a rate of 4-5℃ / min and keeping for 60-120min, and then reducing the temperature to -45 to -55℃ at a rate of 1-2℃ / min and keeping for 90-180min.

4. The metal powder freeze forming process of claim 1, wherein, In step S4, the parameters of vacuum freeze-drying are: vacuum degree ≤10Pa, temperature -20 to -55℃, and drying time 8-12h.

5. The metal powder freeze forming process of claim 1, wherein, In step S5, during the sintering treatment, the temperature is increased to 85-95% of the melting point of the metal powder at a rate of 2-3℃ / min, and kept for 2-4h, and then the furnace is cooled to room temperature.

6. The metal powder freeze forming process of claim 1, wherein, In step S1, the particle size of the metal powder is 0.5-60μm.

7. The metal powder freeze forming process of claim 6, wherein, The metal powder comprises stainless steel powder, alloy powder or copper-based powder.

8. A metal powder freeze formed product characterized by, The metal powder freeze-forming product is prepared by the metal powder freeze-forming process according to any one of claims 1-7.

9. Use of a metal powder freeze formed product according to claim 8, characterized in that, The metal powder freeze-forming product is used for handicrafts.

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