Method for preparing multi-scale high porosity titanium foam

Abstract

The application discloses a kind of multi-scale high porosity foam titanium preparation methods, belong to porous metal material preparation technical field.The method is aimed at solving the problem of low porosity, single pore structure of foam titanium prepared by existing space-occupying body sintering method.The core is to use millimeter and micron two kinds of decomposable space-occupying body as composite pore former, including steps: first, titanium powder is mixed with micron space-occupying body powder;Then millimeter space-occupying body is treated with binder solution, so that its surface has stickiness;Then the mixed powder is adhered to the surface of millimeter space-occupying body to form a hybrid composite;Then the blank is obtained by cold isostatic pressing;Then millimeter and micron space-occupying bodies are removed by hydrolysis and pyrolysis process respectively;Finally, vacuum sintering is carried out.The application can prepare multi-scale pore structure foam titanium with millimeter large pores and micron small pores by constructing composite structure and step-by-step removal process, which has high porosity, uniform structure and excellent comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of porous metal material preparation technology, and more specifically, to a method for preparing multi-scale high-porosity foam titanium. Background Technology

[0002] Titanium foam is a material structure with a large number of pores inside, based on titanium alloy. It not only retains the properties of metallic titanium such as low density, high specific strength, good corrosion resistance and excellent biocompatibility, but also has the characteristics of porous materials such as light weight, energy absorption and vibration reduction. Therefore, it has received widespread attention from military fields such as aviation and aerospace, as well as civilian fields such as chemical, metallurgical, pharmaceutical and automobile manufacturing.

[0003] Based on the pore structure characteristics of titanium foam, titanium foam materials can be divided into closed-cell titanium foam and open-cell titanium foam. The placer sintering method is the main method for preparing closed-cell titanium foam. It uses titanium powder as raw material, adds a certain amount of placer, and sinterstens the titanium alloy into a porous material with a certain strength and porosity. The specific operation process is to mix the titanium powder and the placer evenly, then press it into shape. After molding, the blank is placed in an oven or vacuum resistance furnace for pretreatment to remove the placer, and finally sintering is performed.

[0004] At present, the preparation of closed-cell foam titanium is mainly based on the sintering method of the placer, but this method has the following shortcomings: (1) The porosity is low, not exceeding 80%. When the volume fraction of the placer is too large, the billet is prone to collapse during the pyrolysis removal of the placer; (2) The pore distribution is uneven, which leads to differences in performance. Summary of the Invention

[0005] (a) Technical problems to be solved The technical problem to be solved by the present invention is that existing foamed titanium has low porosity and uneven pore distribution.

[0006] (II) Technical Solution To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing multi-scale high-porosity titanium foam, comprising the following steps: S1. Titanium powder is mixed with micron-sized decomposable site-forming powder (such as polymethyl methacrylate powder) to obtain a mixed powder; this mixed powder will become the source of micron-sized pores in future materials and the basis for the formation of pore walls.

[0007] S2. Mix millimeter-sized decomposable spacers (such as urea or ammonium bicarbonate particles) with an aqueous binder solution to cover the surface of the millimeter-sized decomposable spacers with the aqueous binder solution, thereby obtaining a composite with an adhesive surface. S3. The mixed powder is mixed with the composite, and vibration is used to make the mixed powder adhere to the surface of the millimeter-sized decomposable spacer, forming a core-shell hybrid composite with millimeter-sized particles as the "core" and the mixed powder of titanium powder and micron-sized spacer as the "outer shell". This structure is a key precursor for forming future millimeter-sized macropores and micron-sized micropores on their walls.

[0008] S4. The hybrid composite is packed into a sleeve and subjected to cold isostatic pressing. The isotropic hydrostatic pressure makes the composite uniform and dense, and sufficient bonding strength is generated between the particles to obtain a foam titanium green blank with a regular shape and uniform structure.

[0009] S5. The foamed titanium blank is subjected to hydrolysis to remove the millimeter-scale decomposable occupiers and pyrolysis to remove the micrometer-scale decomposable occupiers. First, the millimeter-scale decomposable occupiers (such as urea or ammonium bicarbonate) are removed by hydrolysis (e.g., immersion in deionized water) to form a millimeter-scale macroscopic pore framework. Then, the micrometer-scale decomposable occupiers (such as polymethyl methacrylate) are removed by pyrolysis (heating in a vacuum or protective atmosphere), leaving micrometer-scale secondary pores in the remaining titanium powder skeleton (i.e., the future pore walls).

[0010] S6. The foamed titanium billet after removing the spacers is sintered at high temperature in a vacuum environment to obtain multi-scale high-porosity foamed titanium. During this process, the titanium powder particles form a strong metallurgical bond through atomic diffusion, resulting in a final multi-scale high-porosity foamed titanium product with sufficient strength.

[0011] Preferably, the micron-sized decomposable site-forming powder is polymethyl methacrylate (PMMA) powder. PMMA has a moderate pyrolysis temperature, and the decomposition products are gases, which are thoroughly removed without leaving any impurities.

[0012] Preferably, the volume ratio of the titanium powder to the polymethyl methacrylate powder is greater than or equal to 1:4, and the mixing time is 2-4 hours; the particle size of both the titanium powder and the polymethyl methacrylate powder is 200-400 mesh.

[0013] Preferably, the millimeter-sized decomposable site is at least one of urea and ammonium bicarbonate. These substances are readily soluble in water and can be completely removed through a simple hydrolysis process, and the decomposition products (such as ammonia and carbon dioxide) are easily discharged without contaminating the green body.

[0014] Preferably, the binder to water in the aqueous binder solution has a mass ratio of 1:20. This concentration provides suitable adhesion, ensuring that the mixed powder effectively adheres to the surface of millimeter-sized particles, while the binder itself can be completely removed during subsequent pyrolysis.

[0015] Preferably, the volume ratio of the mixed powder to the millimeter-sized spacers is 1:3. This optimized ratio ensures that the millimeter-sized pores form pore walls of moderate thickness rich in micrometer-sized spacers, thereby balancing the proportion of macroscopic and microscopic pores and the overall structural strength of the material.

[0016] Preferably, in step S4, the process parameters for the cold isostatic pressing treatment are: pressurizing to 150-200 MPa at a pressurization rate of 10-20 MPa / min, and holding the pressure for 5-10 minutes. Slow pressurization facilitates the expulsion of gas from the casing, avoiding defects; higher pressure and holding pressure ensure that the billet reaches sufficient density and strength, preventing structural collapse during subsequent processing.

[0017] Preferably, the hydrolysis treatment involves immersing the foamed titanium billet in deionized water for more than 24 hours. Sufficient immersion time ensures that the millimeter-sized spacers completely dissolve and diffuse out from the interior of the billet, forming clean, unobstructed millimeter-sized channels.

[0018] Preferably, the pyrolysis treatment is performed by holding the material at 400-500°C in a vacuum sintering furnace for 1-2 hours.

[0019] Preferably, the vacuum sintering includes the following steps: sintering in a vacuum environment by heating to 1100-1400℃ and holding at that temperature for 2-4 hours, followed by furnace cooling. This temperature range ensures complete decomposition and vaporization of PMMA, and since this temperature is lower than the significant sintering temperature of titanium, it avoids pore closure due to densification during sintering before the micron-level pores are formed.

[0020] (III) Beneficial Effects The above-described technical solution of the present invention has at least the following advantages: 1. By precisely controlling the types, sizes, and proportions of millimeter-scale and micrometer-scale occupiers, this invention enables the independent and controllable design of the size, morphology, distribution, and relative proportion of millimeter-scale macropores and micrometer-scale micropores in the final foamed titanium, achieving cross-scale integrated manufacturing from macroscopic support structures to microscopic functional surfaces.

[0021] 2. In the foamed titanium prepared by this invention, the micron-sized occupiers introduce a large number of secondary micropores into the titanium skeleton that constitutes the millimeter-sized pore walls. This results in the material having millimeter-sized macropores while having a total porosity (which can exceed 85%) and a specific surface area that are much higher than those of foamed titanium prepared by traditional single occupiers, greatly enhancing its heat insulation and other functional properties.

[0022] 3. This invention employs a process sequence of first compound pressing, followed by step-by-step removal. First, a high-strength green body is obtained through cold isostatic pressing, providing structural support for subsequent removal of spacers. Then, different spacers are removed through two distinct physicochemical processes: hydrolysis (liquid) and pyrolysis (gaseous). This avoids the problem of simultaneous decomposition of both spacers generating violent gases that could lead to cracking of the green body or collapse of the pore structure, effectively ensuring the integrity and independence of the multi-level pore structure.

[0023] 4. In the foamed titanium prepared by this invention, the millimeter-sized macropores provide the main mechanical support and material transport channels, while the micron-sized micropores not only significantly increase the specific surface area, but may also play a certain toughening role by refining the sintering neck and introducing more interfaces, so that the material can still have suitable mechanical properties while maintaining high porosity.

[0024] 5. The site-filling agents (urea, PMMA) used in the preparation method provided by this invention are all common, low-cost chemical raw materials. The overall process flow is highly compatible with existing powder metallurgy equipment, has no extremely harsh process conditions, and has the potential for large-scale production. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is one of the schematic diagrams of the structural morphology of multi-scale high-porosity titanium foam provided in the embodiments of the present invention.

[0027] Figure 2 This is the second schematic diagram of the structural morphology of multi-scale high-porosity titanium foam provided in the embodiments of the present invention. Detailed Implementation

[0028] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0029] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0030] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments: Example 1 Titanium powder and polymethyl methacrylate powder (PMMA powder) micron-sized decomposable spacers were loaded into a three-dimensional powder mixer for mixing. The volume ratio of titanium powder to polymethyl methacrylate powder (micron-sized decomposable spacers) was 1:4, and the mixing time was 2 hours to obtain mixed powder. The titanium powder and polymethyl methacrylate powder had similar particle sizes, with a particle size of 200 mesh. The urea spacer (millimeter-sized decomposable spacer) is thoroughly mixed with a certain amount of binder aqueous solution, so that the surface of the urea spacer is completely covered with the binder aqueous solution. The mass ratio of binder / aqueous solution is 1:20 to obtain the composite. The mixed powder and urea spacers covered with binder are placed in a container. The volume ratio of the mixed powder to the millimeter-sized decomposable spacers is 1:3. The container is vibrated. Due to the action of the binder, the mixed powder will be uniformly adhered to the surface of the urea spacers, thus preparing a hybrid composite. A cylindrical casing was prepared using polyurethane as the casing material. The hybrid composite was then placed inside the casing, compacted by vibration, and sealed with a soft plug. The package filled with the hybrid composite was placed into a cold isostatic press and pressurized to 150 MPa at a pressurization rate of 10 MPa / min. After holding the pressure for 10 min, the package was removed and opened to prepare the foamed titanium billet. The foamed titanium blank was immersed in deionized water to remove urea locants by hydrolysis for 48 hours, and then removed and dried. The foamed titanium billet is loaded into a vacuum sintering furnace and evacuated to a vacuum level of 2×10⁻⁶. -2 At Pa, the temperature is increased according to the set curve, and the temperature is increased to 400℃ at a heating rate of 5℃ / min. The temperature is held for 2 hours to remove the micron-sized decomposable occupants by pyrolysis. Then the temperature is increased to 1100℃ at a heating rate of 10℃ / min and held for 4 hours. When the furnace is cooled to room temperature, the vacuum system is turned off and the foamed titanium material is taken out.

[0032] Example 2 Titanium powder and polymethyl methacrylate powder (PMMA powder) micron-sized decomposable spacers were loaded into a three-dimensional powder mixer for mixing. The volume ratio of titanium powder to polymethyl methacrylate powder (micron-sized decomposable spacers) was 1:2, and the mixing time was 4 hours to obtain a mixed powder. The titanium powder and polymethyl methacrylate powder had similar particle sizes, with a particle size of 400 mesh. Ammonium bicarbonate site (millimeter-sized decomposable site) is thoroughly mixed with a certain amount of binder aqueous solution, so that the surface of the ammonium bicarbonate site is completely covered with the binder aqueous solution. The mass ratio of binder to aqueous solution is 1:20, and a composite is obtained. The mixed powder and the composite are loaded into a container with a volume ratio of 1:3 between the mixed powder and the millimeter-sized decomposable occupiers. The container is then vibrated, and due to the action of the binder, the mixed powder will adhere evenly to the surface of the ammonium bicarbonate occupiers to prepare the hybrid composite. A rectangular enclosure was prepared using polyurethane as the encapsulation material. The hybrid composite was then placed inside the enclosure, compacted by vibration, and sealed with a soft plug. The package filled with the hybrid composite was placed into a cold isostatic press and pressurized to 200 MPa at a pressurization rate of 20 MPa / min. After holding the pressure for 5 min, the package was removed and opened to prepare the foamed titanium billet. The foamed titanium blank was immersed in deionized water to remove the ammonium bicarbonate occupiers by hydrolysis for 60 hours, and then removed and dried. The foamed titanium billet is loaded into a vacuum sintering furnace and evacuated for 3×10 seconds. -2 At Pa, the temperature is increased according to the set curve, and the temperature is increased to 500℃ at a heating rate of 5℃ / min. The temperature is held for 1 hour to remove the micron-sized decomposable occupants by pyrolysis. Then the temperature is increased to 1400℃ at a heating rate of 10℃ / min and held for 2 hours. When the furnace is cooled to room temperature, the vacuum system is turned off and the foamed titanium material is taken out.

[0033] The structural morphology of the prepared foamed titanium material is as follows: Figure 1 and Figure 2 As shown, based on observation and testing: The product has a uniform gray-black color and retains the original shape of the blank.

[0034] Observation using scanning electron microscopy (SEM) revealed that the material exhibits a distinct dual-scale pore structure: millimeter-scale macropores (approximately 1-1.4 mm) are interconnected, forming the main framework; on the walls of these macropores, a large number of uniformly distributed and interconnected micrometer-scale micropores (approximately 10-50 μm) are clearly visible.

[0035] This structure combines the advantages of millimeter-scale channels facilitating mass transport with micrometer-scale pores providing a huge specific surface area.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing multi-scale high-porosity titanium foam, characterized in that, Includes the following steps: S1. Mix titanium powder with micron-sized decomposable spacer powder to obtain mixed powder; S2. Mix the millimeter-sized decomposable spacer with the adhesive aqueous solution to cover the surface of the millimeter-sized decomposable spacer with the adhesive aqueous solution to obtain a composite. S3. Mix the mixed powder with the composite, and use vibration to make the mixed powder adhere to the surface of the millimeter-scale decomposable occupier to form a hybrid composite. S4. The hybrid composite is packed into a sleeve and subjected to cold isostatic pressing to obtain a foamed titanium blank. S5. The foamed titanium blank is subjected to hydrolysis treatment to remove the millimeter-sized decomposable occupants, and to pyrolysis treatment to remove the micron-sized decomposable occupants. S6. The foamed titanium blank after removing the occupiers is sintered at high temperature in a vacuum environment to obtain multi-scale high-porosity foamed titanium.

2. The method for preparing multi-scale high-porosity titanium foam as described in claim 1, characterized in that, The micron-sized decomposable spacer powder is polymethyl methacrylate powder.

3. The method for preparing multi-scale high-porosity titanium foam as described in claim 2, characterized in that, The volume ratio of the titanium powder to the polymethyl methacrylate powder is greater than or equal to 1:4, and the mixing time is 2-4 hours; the particle size of both the titanium powder and the polymethyl methacrylate powder is 200 mesh to 400 mesh.

4. The method for preparing multi-scale high-porosity titanium foam as described in claim 1, characterized in that, The millimeter-scale decomposable occupier is at least one of urea and ammonium bicarbonate.

5. The method for preparing multi-scale high-porosity titanium foam as described in claim 1, characterized in that, In the adhesive aqueous solution, the mass ratio of adhesive to water is 1:

20.

6. The method for preparing multi-scale high-porosity titanium foam as described in claim 1, characterized in that, The volume ratio of the mixed powder to the millimeter-sized occupier is 1:

3.

7. The method for preparing multi-scale high-porosity titanium foam as described in claim 1, characterized in that, In step S4, the process parameters for the cold isostatic pressing treatment are: pressurize to 150-200MPa at a pressurization rate of 10-20MPa / min, and hold the pressure for 5-10 minutes.

8. The method for preparing multi-scale high-porosity titanium foam as described in claim 1, characterized in that, The hydrolysis process involves immersing the foamed titanium billet in deionized water for more than 24 hours.

9. The method for preparing multi-scale high-porosity titanium foam as described in claim 1, characterized in that, The pyrolysis treatment involves holding the material at 400-500°C for 1-2 hours in a vacuum sintering furnace.

10. The method for preparing multi-scale high-porosity titanium foam as described in claim 1, characterized in that, The vacuum sintering includes the following steps: sintering in a vacuum environment by heating to 1100-1400℃ and holding for 2-4 hours, and finally cooling with the furnace.

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