A powder metallurgy sintering forming method of gradient porous material

Abstract

The application relates to a powder metallurgy sintering forming preparation method of a gradient porous material, and specifically comprises the following steps: proportionally ball-milling aluminum powder, foaming agent powder and tackifier powder to obtain aluminum powder mixture, respectively performing cold pressing and hot pressing on the mixed powder to obtain a foamed aluminum preform; adding anhydrous ethanol to mixed powder of proportionally mixed hollow microbeads and aluminum powder, uniformly stirring, drying and cold pressing to form a microbead reinforced aluminum-based porous material preform; arranging the foamed aluminum preform and the microbead reinforced aluminum-based porous material preform in a graphite mold in a certain direction, and then placing the mold into a sintering furnace to sinter and form the gradient porous material. In the sintering process, the foamed aluminum expands and is metallurgically combined with the microbead reinforced aluminum-based porous material at the contact surface. The gradient porous material is prepared through one-step sintering forming, and the gradient porous material with a complex shape can be produced, and the production efficiency is high.

Description

Technical Field

[0001] This invention relates to the preparation of porous materials, specifically a powder metallurgy sintering method for preparing gradient porous materials. Background Technology

[0002] Porous materials, possessing both structural and functional properties, have found increasingly widespread applications in aerospace, transportation, military, and construction industries. Currently, emerging gradient porous materials arrange porous materials with different characteristics (such as porous material type, pore size, and porosity) along a specific spatial arrangement, causing their properties to exhibit gradient changes, thereby achieving the desired effect. Traditional closed-cell aluminum foam is lightweight but has low strength, while microsphere-reinforced aluminum-based porous materials have higher strength but increased density. Therefore, combining these two porous materials to prepare gradient porous materials can fully leverage their respective advantages.

[0003] Traditional methods for preparing closed-cell metal foam generally include melt foaming, gas injection foaming, and powder metallurgy. Commonly used methods for preparing microsphere-reinforced metal-based porous materials include flow casting, powder metallurgy, and stirred casting. In powder metallurgy, closed-cell metal foam is prepared by pressing metal powder and a foaming agent into shape. During sintering, the foaming agent decomposes to generate gas, thus forming pores. In contrast, the powder metallurgy method for preparing microsphere-reinforced metal-based porous materials involves cold pressing metal powder and hollow microspheres, followed by sintering.

[0004] Traditional methods for preparing gradient porous materials involve a two-step process: first, a single porous material is prepared, and then the entire gradient porous material is formed. Gradient porous materials prepared using this method generally suffer from insufficient internal interfacial bonding strength and limited impact on mechanical properties and deformation failure behavior. Summary of the Invention

[0005] The purpose of this invention is to provide a powder metallurgy sintering method for preparing gradient porous materials, in order to solve the problems of insufficient internal interfacial bonding strength and limited impact on mechanical properties and deformation failure behavior of gradient porous materials prepared by existing methods.

[0006] The objective of this invention is achieved as follows:

[0007] A method for preparing gradient porous materials by powder metallurgy sintering includes the following steps:

[0008] S1. Add aluminum powder, foaming agent powder and thickener powder into a ball mill according to the proportion, and ball mill at 200 rpm to 400 rpm for 40 min to 100 min to form a mixed powder.

[0009] S2. The mixed powder is placed in a cold press mold for cold pressing. The cold pressing pressure is 300MPa to 500MPa, and the pressure is held for 3min to 10min to form powder blocks.

[0010] S3. Place the powder block in a hot press furnace, preheat it at a temperature of 150℃~300℃ for 5min~10min, and then hot press it at a pressure of 100MPa~150MPa to obtain the aluminum foam preform.

[0011] S4. Mix hollow microspheres and aluminum powder by volume ratio, add solvent accounting for 50% to 200% of the total volume of the mixture to make the hollow microspheres and aluminum powder into a paste, so that the two can be better and more evenly mixed. Stir in a mixer for 0.5h to 2h, and then dry in a dryer at 50℃ to 90℃ for 2h to 3h.

[0012] S5. Add 1% to 5% of solvent by volume to the dried mixed powder to dilute the powder, which is beneficial for cold pressing. After stirring evenly, put it into the mold for cold pressing. The cold pressing pressure is 200MPa to 400MPa, and the pressure is held for 5 min to 10 min to form a microsphere-reinforced aluminum-based porous material preform.

[0013] S6. Place the foamed aluminum preform prepared in step S3 and the microbead-reinforced aluminum-based porous material preform prepared in step S5 into a graphite mold, and pre-lay graphite paper in the graphite mold for easy demolding.

[0014] S7. Place the graphite mold containing the two preforms in a tube furnace for sintering. Inert gas is introduced as a protective gas. First, the temperature is raised to 200℃~300℃ at a heating rate of 2℃ / min and held for 1h~2h. Then, the temperature is raised to 550℃~700℃ at a heating rate of 10℃ / min and sintered for 0.5h~2h. After sintering, the material is naturally cooled to room temperature under an inert atmosphere to obtain a gradient porous material.

[0015] Further, the foaming agent in step S1 is titanium hydride particles, accounting for 1% to 8% of the total mass of the mixed powder; the thickener is silicon carbide particles, accounting for 5% to 15% of the total mass of the mixed powder.

[0016] Furthermore, the hollow microspheres in step S4 are ceramic microspheres, and their volume ratio with aluminum powder is 3:7 to 6:4.

[0017] Furthermore, the inert gas introduced in step S7 is argon or helium, and the inert gas flow rate is 200 ml / min to 300 ml / min. The purpose of introducing the inert gas is to expel oxygen from the tube furnace and prevent aluminum from oxidizing at high temperatures.

[0018] Further, the solvent is at least one selected from anhydrous ethanol, isopropanol, acetone, methyl ketone, and ethyl acetate. These solvents are characterized by good solubility and dispersibility, and are also highly volatile. The addition of the solvent in step S4 makes the mixed powder form a paste, which facilitates thorough mixing and effectively prevents clumping and oxidation. Because these solvents themselves have good solubility and dispersibility, and are highly volatile, they can be easily separated while ensuring uniform mixing of the powder. The addition of the solvent in step S5 facilitates cold pressing. This type of solvent can wet the mixed powder, causing it to aggregate into a cohesive whole, thus preventing difficulties in agglomeration and pressing during cold pressing.

[0019] The preparation method of this invention involves first mixing powdered materials, then pressing them to obtain a foamed aluminum preform and a microsphere-reinforced aluminum-based porous material preform. Subsequently, the two preforms are placed in a mold and sintered to form a gradient porous material. During sintering, the foaming agent decomposes and releases gas, expanding to form foamed aluminum. During this expansion, chemical reactions or elemental diffusion occur between the foamed aluminum and the microsphere-reinforced aluminum-based porous material at the contact surface of the aluminum matrix, thereby forming a metallurgical bond at the interface.

[0020] This invention employs a one-step sintering process to prepare gradient porous materials, avoiding the problems of insufficient interfacial bonding strength and limited impact on mechanical properties and deformation failure behavior inherent in existing two-step molding methods. The powder metallurgy method used in this invention has a wide applicability to matrix materials, allowing adjustment of the porosity of closed-cell aluminum foam based on the foaming agent content, and control over the amount of hollow microspheres added. Furthermore, by designing the shape of the preform, the powder metallurgy method employed in this invention can prepare gradient porous materials with complex shapes and gradients that can vary in any direction. The preparation method of this invention is simple to operate and enables one-step sintering of gradient porous materials. Attached Figure Description

[0021] Figure 1 This is a flowchart of the preparation method of the present invention.

[0022] Figure 2 This is a schematic diagram of a gradient porous material arranged along the height direction.

[0023] Figure 3 This is a schematic diagram of a gradient porous material arranged along its length and width.

[0024] In the figure: 1. Graphite mold, 2. Aluminum foam preform, 3. Metallurgical interface, 4. Microsphere-reinforced aluminum-based porous material preform. Detailed Implementation

[0025] Example 1

[0026] like Figure 1 , Figure 2 As shown, the powder metallurgy sintering method for preparing gradient porous materials of the present invention includes the following steps:

[0027] S1. Place 1% by mass of titanium hydride powder, 7% by mass of silicon carbide particles and aluminum powder into a ball mill, and ball mill at 320 rpm for 40 minutes to mix them evenly.

[0028] S2. Place the mixed powder into a steel cold press mold for cold pressing. The cold pressing pressure is 500MPa and the holding time is 8min to reduce the oxidation of the powder during hot pressing.

[0029] S3. Place the cold-pressed powder block in a hot press furnace, preheat it at 200℃ for 5 minutes, and then hot press it at 120MPa to obtain the square aluminum foam preform 2.

[0030] S4. Mix alumina ceramic microspheres and aluminum powder at a volume ratio of 4:6. To promote uniform mixing of microspheres and aluminum powder, add anhydrous ethanol accounting for 200% of the total volume of the mixed powder and stir in a mixer for 0.5 hours. Then place it in a dryer and dry at 60°C for 2.2 hours.

[0031] S5. Add 1% anhydrous ethanol to the mixture of hollow microspheres and aluminum powder. Adding anhydrous ethanol can dilute the powder, which is beneficial for cold pressing. After stirring evenly, put it into a cold pressing mold for cold pressing to obtain square microsphere reinforced aluminum-based porous material preform 4. The cold pressing pressure is selected as 340MPa and the holding time is 7min.

[0032] S6. Place the foamed aluminum preform 2 and the microsphere-reinforced aluminum-based porous material preform 4 into the graphite mold 1 along the height direction. Graphite paper is laid around the graphite mold 1 in advance to facilitate subsequent demolding.

[0033] S7. The graphite mold 1 containing the square aluminum foam preform 2 and the square microsphere reinforced aluminum-based porous material preform 4 is placed in a tube furnace for sintering. In order to remove oxygen from the tube furnace and prevent aluminum from oxidizing at high temperature, argon gas is introduced into the tube furnace as a protective gas. The argon gas flow rate is 230 ml / min. First, the temperature is raised to 280℃ at 2℃ / min and held for 1.3h to evaporate the excess anhydrous ethanol in the microsphere reinforced aluminum-based porous material preform. Then, the temperature is raised to 550℃ at 10℃ / min and sintered for 0.9h. After sintering, it is naturally cooled to room temperature under an inert atmosphere to obtain a gradient porous material with a gradient arranged along the height direction. A metallurgical interface 3 is formed at the contact surface of the aluminum foam and the microsphere reinforced aluminum-based porous material.

[0034] Example 2

[0035] like Figure 1 , Figure 3 As shown, the powder metallurgy sintering method for preparing gradient porous materials of the present invention includes the following steps:

[0036] S1. Place 3% by mass of titanium hydride powder, 10% by mass of silicon carbide particles and aluminum powder into a ball mill, and ball mill at 400 rpm for 55 minutes to mix them evenly.

[0037] S2. Place the mixed powder into a steel cold press mold and cold press it into a hollow square block. The cold pressing pressure is 300MPa and the holding time is 10min to reduce the oxidation of the powder during hot pressing.

[0038] S3. Place the cold-pressed powder block in a hot press furnace, preheat it at 150°C for 8 minutes, and then hot press it at 150MPa to obtain a hollow square aluminum foam preform 2.

[0039] S4. Mix fly ash microspheres and aluminum powder at a volume ratio of 5:5. To promote uniform mixing of microspheres and aluminum powder, add isopropanol accounting for 100% of the total volume of the mixed powder and stir in a mixer for 0.8 hours. Then place it in a dryer and dry at 75°C for 2 hours.

[0040] S5. Add 5% acetone to the mixture of hollow microspheres and aluminum powder. Adding acetone can dilute the powder and facilitate cold pressing. After stirring evenly, put it into a cold pressing mold for cold pressing to obtain square microsphere reinforced aluminum-based porous material preform 4. The cold pressing pressure is selected as 250MPa and the holding time is 8min.

[0041] S6. Place the square microbead reinforced aluminum-based porous material preform 4 into the hollow part of the foamed aluminum preform 2, and then place both into the graphite mold 1. Graphite paper is laid around the graphite mold 1 in advance to facilitate subsequent demolding.

[0042] S7. The graphite mold 1 containing two preforms is placed in a tube furnace for sintering. In order to remove oxygen from the tube furnace and prevent aluminum from oxidizing at high temperature, helium is introduced into the tube furnace as a protective gas at a flow rate of 260 ml / min. The temperature is first raised to 300℃ at 2℃ / min and held for 1 hour to evaporate excess anhydrous ethanol in the microsphere-reinforced aluminum-based porous material preform. Then, the temperature is raised to 700℃ at 10℃ / min and sintered for 0.5 hours. After sintering, the material is naturally cooled to room temperature under an inert atmosphere to obtain a gradient porous material with a gradient arranged along the length and width directions. A metallurgical interface 3 is formed at the contact surface between the foamed aluminum and the microsphere-reinforced aluminum-based porous material.

[0043] Example 3

[0044] The powder metallurgical sintering method for preparing gradient porous materials of the present invention includes the following steps:

[0045] S1. Place 5% by mass of titanium hydride powder, 15% by mass of silicon carbide particles and aluminum powder into a ball mill, and ball mill at 250 rpm for 85 minutes to mix them evenly.

[0046] S2. Place the mixed powder into a steel cold press mold for cold pressing. The cold pressing pressure is 380MPa and the holding time is 5min to reduce the oxidation of the powder during hot pressing.

[0047] S3. Place the cold-pressed powder block in a hot press furnace, preheat it at 250°C for 10 minutes, and then hot press it at 100MPa to obtain a square aluminum foam preform.

[0048] S4. Mix silicon carbide ceramic microspheres and aluminum powder at a volume ratio of 3:7. To promote uniform mixing of microspheres and aluminum powder, add 50% of the total volume of methyl ketone to the mixed powder and stir in a mixer for 2 hours. Then place it in a dryer and dry at 90°C for 2.6 hours.

[0049] S5. Add ethyl acetate, accounting for 3% of the total volume of the mixed powder, to the mixture of hollow microspheres and aluminum powder. Adding ethyl acetate can dilute the powder, which is beneficial for cold pressing. After stirring evenly, put it into a cold pressing mold for cold pressing to obtain a square microsphere-reinforced aluminum-based porous material preform. The cold pressing pressure is selected as 200 MPa, and the holding time is 10 min.

[0050] S6. Place the foamed aluminum preform and the microsphere-reinforced aluminum-based porous material preform into a graphite mold. Beforehand, lay graphite paper around the graphite mold to facilitate subsequent demolding.

[0051] S7. Place the graphite mold containing the two preforms in a tube furnace for sintering. In order to remove oxygen from the tube furnace and prevent aluminum from oxidizing at high temperature, argon gas is introduced into the tube furnace as a protective gas at a flow rate of 200 ml / min. First, the temperature is raised to 240℃ at 2℃ / min and held for 1.7h to evaporate the excess anhydrous ethanol in the microsphere-reinforced aluminum-based porous material preform. Then, the temperature is raised to 670℃ at 10℃ / min and sintered for 2h. After sintering, the material is naturally cooled to room temperature under an inert atmosphere to obtain a gradient porous material.

[0052] Example 4

[0053] The powder metallurgical sintering method for preparing gradient porous materials of the present invention includes the following steps:

[0054] S1. Place 8% by mass of titanium hydride powder, 5% by mass of silicon carbide particles and aluminum powder into a ball mill, and ball mill at 200 rpm for 100 min to mix them evenly.

[0055] S2. Place the mixed powder into a cold pressing mold for cold pressing. The cold pressing pressure is 420MPa and the holding time is 3min to reduce the oxidation of the powder during hot pressing.

[0056] S3. Place the cold-pressed powder block in a hot press furnace, preheat it at 300℃ for 7 minutes, and then hot press it at 135MPa to obtain a square aluminum foam preform.

[0057] S4. Mix fly ash microspheres and aluminum powder at a volume ratio of 6:4. To promote uniform mixing of microspheres and aluminum powder, add acetone accounting for 160% of the total volume of the mixed powder and stir in a mixer for 1.3 hours. Then place it in a dryer and dry at 50°C for 3 hours.

[0058] S5. Add 1.5% anhydrous ethanol to the mixture of hollow microspheres and aluminum powder. Adding anhydrous ethanol can dilute the powder, which is beneficial for cold pressing. After stirring evenly, put it into a cold pressing mold for cold pressing to obtain a square microsphere-reinforced aluminum-based porous material preform. The cold pressing pressure is 400MPa and the holding time is 5min.

[0059] S6. Place the foamed aluminum preform and the microsphere-reinforced aluminum-based porous material preform into a graphite mold. Beforehand, lay graphite paper around the graphite mold to facilitate subsequent demolding.

[0060] S7. Place the graphite mold containing the two preforms in a tube furnace for sintering. In order to remove oxygen from the tube furnace and prevent aluminum from oxidizing at high temperature, helium is introduced into the tube furnace as a protective gas at a flow rate of 300 ml / min. First, heat the furnace to 200℃ at a rate of 2℃ / min and hold for 2 hours to evaporate excess anhydrous ethanol from the microsphere-reinforced aluminum-based porous material preform. Then, heat the furnace to 620℃ at a rate of 10℃ / min and sinter for 1.5 hours. After sintering, allow the furnace to cool naturally to room temperature under an inert atmosphere to obtain a gradient porous material.

Claims

1. A method for preparing gradient porous materials by powder metallurgy sintering, characterized in that, Includes the following steps: S1. Add aluminum powder, foaming agent powder and thickener powder into a ball mill according to the proportion, and ball mill at 200 rpm to 400 rpm for 40 min to 100 min to form a mixed powder. S2. The mixed powder is placed in a cold press mold for cold pressing. The cold pressing pressure is 300MPa to 500MPa, and the pressure is held for 3min to 10min to form powder blocks. S3. Place the powder block in a hot press furnace, preheat it at a temperature of 150℃~300℃ for 5min~10min, and then hot press it at a pressure of 100MPa~150MPa to obtain the aluminum foam preform. S4. Mix hollow microspheres and aluminum powder by volume ratio, then add solvent accounting for 50% to 200% of the total volume of the mixture, stir in a mixer for 0.5 to 2 hours, and then put it in a dryer to dry at 50°C to 90°C for 2 to 3 hours. S5. Add 1% to 5% of the solvent by the total volume of the dried mixed powder, stir evenly, and then put it into a cold press mold for cold pressing. The cold pressing pressure is 200MPa to 400MPa, and the pressure is held for 5min to 10min to form a microsphere-reinforced aluminum-based porous material preform. S6. Place the foamed aluminum preform prepared in step S3 and the microbead-reinforced aluminum-based porous material preform prepared in step S5 into a graphite mold, and pre-lay graphite paper in the graphite mold for easy demolding. S7. Place the graphite mold containing the two preforms in a tube furnace for sintering. Inert gas is introduced as a protective gas. First, the temperature is raised to 200℃~300℃ at a heating rate of 2℃ / min and held for 1h~2h. Then, the temperature is raised to 550℃~700℃ at a heating rate of 10℃ / min and sintered for 0.5h~2h. After sintering, the material is naturally cooled to room temperature under an inert atmosphere to obtain a gradient porous material.

2. The powder metallurgy sintering preparation method according to claim 1, characterized in that, The foaming agent in step S1 is titanium hydride particles, accounting for 1% to 8% of the total mass of the mixed powder; the thickener is silicon carbide particles, accounting for 5% to 15% of the total mass of the mixed powder.

3. The powder metallurgy sintering preparation method according to claim 1, characterized in that, The hollow microspheres in step S4 are ceramic microspheres, and their volume ratio with aluminum powder is 3:7 to 6:

4.

4. The powder metallurgy sintering and forming preparation method according to claim 1, characterized in that, The inert gas introduced in step S7 is argon or helium, and the inert gas flow rate is 200 ml / min to 300 ml / min.

5. The powder metallurgy sintering preparation method according to claim 1, characterized in that, The solvent is at least one of anhydrous ethanol, isopropanol, acetone, methyl ketone, and ethyl acetate.

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