Preparation method of gradient porous alloy aerogel based on 3D printing

Abstract

The invention discloses a preparation method of gradient porous alloy aerogel based on 3D printing. The preparation method comprises the following steps that a, high-temperature alloy powder, nano aluminum-magnesium mixed powder and a pore forming agent are mixed, and composite powder is formed; b, constructing a three-dimensional model based on gradient porosity distribution, wherein the three-dimensional model is divided into a compact layer, a transition layer and a porous layer from outside to inside in the thickness direction; c, the selective laser melting (SLM) technology is adopted, the three-dimensional model is printed according to preset layering parameters, the laser power is reduced layer by layer from the outer layer to the inner layer, the scanning speed is increased layer by layer, and the sacrificial pore forming agent is decomposed to form multi-scale pores; and d, the pore-forming agent residues in the step c are removed through acid pickling, interface bonding is strengthened through vacuum annealing, and the alloy aerogel is obtained. According to the invention, gradient porous structure design, a composite alloy system, a dynamic pore-forming process and process parameter optimization are adopted.

Description

Technical Field

[0001] The present invention belongs to the technical field of new material preparation, and particularly relates to a preparation method of a gradient porous alloy aerogel based on 3D printing. Background Art

[0002] With the continuous development of equipment, the performance requirements for thermal protection systems are becoming increasingly stringent. Although traditional aerogels (such as silica and carbon-based aerogels) have ultra-low density and excellent heat insulation characteristics, their mechanical properties are poor and they cannot be used as load-bearing structures. In order to continuously improve the performance of equipment, lightweight, high-efficiency heat insulation, and fast deployment speed have become the main considerations. Therefore, the direction of integrated materials has become a research hotspot. However, there are still the following technical problems hindering the development of load-bearing and heat-protection integrated materials.

[0003] The existing preparation technologies have the following defects: 1. Although traditional aerogel materials (such as silica and carbon-based aerogels) have low thermal conductivity (<0.03 W / m·K), their mechanical properties are poor (compressive strength <0.1 MPa) and they cannot be used as load-bearing structural members.

[0004] 2. Although metal aerogels can improve strength by stacking nanoparticles, they are prone to brittle fracture at high porosity (>90%) and lack effective heat insulation design.

[0005] 3. Existing 3D-printed porous metal structures (such as lattice structures) improve strength by reducing porosity (<80%), but sacrifice lightweight and heat insulation performance. Summary of the Invention

[0006] Aiming at the above problems, the purpose of the present invention is to provide a preparation method of an alloy aerogel with lightweight, high load-bearing and heat insulation performance.

[0007] The present invention is realized through the following technical solutions: A preparation method of a gradient porous alloy aerogel based on 3D printing, comprising the following steps: Step a: Mix superalloy powder, nano aluminum-magnesium mixed powder and pore-forming agent to form composite powder; Step b: Construct a three-dimensional model based on the gradient porosity distribution, and the gradient porosity is divided into a dense layer, a transition layer and a porous layer from the outside to the inside along the thickness direction; Step c: Adopt selective laser melting (SLM) technology to print the three-dimensional model according to preset layer parameters, wherein the laser power decreases layer by layer from the dense layer on the outer layer to the porous layer on the inner layer of the three-dimensional model, and the scanning speed increases layer by layer, so as to decompose the sacrificial pore-forming agent to form multi-scale pores; Step d: Pickling is used to remove the residual pore-forming agent in step c, and vacuum annealing is carried out to strengthen the interfacial bonding, obtaining an alloy aerogel.

[0008] The porosity of the dense layer described in step a is (5 - 10%); the porosity of the transition layer is (10 - 70%); the porosity of the porous layer is (70 - 90%).

[0009] The pore-forming agent described in step c is calcium carbonate (CaCO3) with a particle size of 50 - 200 nm or polymethyl methacrylate (PMMA) microspheres with a particle size of 100 - 500 nm; the addition amount of the pore-forming agent is 5 - 15 wt%. The superalloy powder described in step a is Inconel 718 or Hastelloy X with a particle size of 15 - 45 μm; the particle size of the nano aluminum-magnesium mixed powder is 50 - 100 nm, and the addition amount is 3 - 8 wt%. The laser parameters in step c: the laser power of the dense layer is 150 - 200 W, the scanning speed is 600 - 800 mm / s, and the layer thickness is 20 - 30 μm; the laser power of the transition layer is 100 - 150 W, the scanning speed is 800 - 1000 mm / s, and the layer thickness is 30 - 40 μm; the laser power of the porous layer is 80 - 100 W, the scanning speed is 1000 - 1200 mm / s, and the layer thickness is 40 - 50 μm.

[0010] During the printing process of step c, the pore-forming agent decomposes under the action of laser to generate gas, forming an outer dense layer mainly composed of closed pores with a pore diameter of 50 - 100 nm; the inner porous layer is mainly composed of through holes with a pore diameter of 100 - 200 nm.

[0011] The vacuum annealing described in step d includes: the first stage: holding at 600 °C for 1 h to eliminate residual stress; the second stage: holding at 800 - 1000 °C for 2 h to promote the formation of Ni - Al intermetallic compounds.

[0012] The beneficial effects of the present invention: 1. Gradient porous structure design: The outer dense layer (porosity 5 - 10%) provides load-bearing capacity, while the inner porous layer (porosity 70 - 90%) realizes heat insulation, and the transition layer avoids stress concentration through a gradually changing porosity.

[0013] 2. Composite alloy system: A mixture of nickel-based superalloy (such as Inconel 718) and low-melting-point metals (aluminum, magnesium) powders is used to in-situ form intermetallic compounds (such as NiAl, Ni3Al) through 3D printing, improving the high-temperature strength.

[0014] 3. Dynamic pore - forming process: Introduce carbonates (such as CaCO3) as pore - forming plates during the SLM process. When laser scanning, CO2 gas is decomposed to form controllable pores. After - treatment removes residues through pickling to further optimize the pore structure, and combines with surface deposition of anti - radiation layers to further improve the heat - insulation performance.

[0015] 4. Process parameter optimization: Co - regulate the laser power (80 - 200W), scanning speed (600 - 1200mm / s), and layer thickness (20 - 50μm) to achieve the integrated forming of dense layers and porous layers. Brief Description of the Drawings

[0016] The present invention will be further described in detail below with reference to the accompanying drawings.

[0017] Figure 1 It is a schematic structural diagram of the present invention.

[0018] Figure 2 It is a process flow chart of the present invention.

[0019] As shown in the figure: 1 - porous layer; 2 - transition layer; 3 - dense layer. Specific Embodiments

[0020] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0021] It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in the art to understand and read, and are not used to limit the limited conditions under which the present invention can be implemented. Therefore, they do not have technical essence. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" cited in this specification are only for the convenience of narration and are not used to limit the scope under which the present invention can be implemented. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope within which the present invention can be implemented.

[0022] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "connected" and "connected to" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. It should be noted that the terms "include", "comprise" or any other variant are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. Example 1

[0023] Step a: Mix Inconel 718 powder with 5wt% nano-aluminum powder (particle size 50 - 100nm) and 5wt% - 15wt% CaCO3 pore-forming agent (particle size 100nm) by ball milling under argon protection.

[0024] Steps b and c: Equipment: SLM 280HL metal printer; Parameters: Dense layer (laser power 150W, scanning speed 800mm / s), transition layer (power 120W, speed 1000mm / s), porous layer (power 80W, speed 1200mm / s); layer thickness: 30μm, under argon protection.

[0025] Table 1 shows the relationship between SLM setting parameters and porosity:

[0026] Table 1 Step d: Pickle (5% HCl solution, 30min) to remove CaCO3 residue, and vacuum anneal (800°C / 2h, heating rate 10°C / min) to obtain the final material.

[0027] The material performance parameters obtained are as follows: For the dense layer, the density is 0.65 - 1.1 g / cm³, and the compressive strength is 70 - 98 MPa; the thermal conductivity of the porous layer is 0.08 - 0.22 W / (m·K), which is higher than that of traditional aerogel materials (<0.03 W / m·K), has a lower thermal conductivity, and has good heat insulation performance.

[0028] Table 2 shows the comparison of material properties obtained with different amounts of pore-forming agent added:

[0029] Table 2 From the above table, when 5 wt% of CaCO3 pore former is added in step a, the obtained density is 1.1 (g / cm³), the compressive strength is 98 (MPa), and the thermal conductivity is 0.22 (W / (m·K)). Although adding a small amount of pore former can make the overall strength higher, the heat insulation effect becomes worse. When 0 wt% of CaCO3 pore former is added, the obtained density is 0.8 (g / cm³), the compressive strength is 85 (MPa), and the thermal conductivity is 0.12 (W / (m·K)). The overall compressive strength is sufficient and it has good heat insulation properties. Example 2

[0030] 1. Material preparation: Mix Haynes 188 (particle size 20 - 50 μm) powder with 5 wt% nano-aluminum powder (particle size 50 - 100 nm), TiH2 nanoparticles (200 nm, 5 wt%) + PS nanospheres (300 nm, 8 wt%) by ball milling under argon protection.

[0031] 2. 3D printing: Equipment: SLM 280HL metal 3D printer; Parameters: Dense layer (laser power 180 W, scanning speed 600 mm / s), transition layer (power 120 W, speed 800 mm / s), porous layer (power 800, speed 1000 mm / s); Layer thickness: 40 μm.

[0032] 3. Post-treatment: Aluminizing treatment (950 °C / 3 h to form an Al2O3 antioxidant layer), vacuum annealing (800 °C / 2 h, heating rate 10 °C / min) to obtain the final material.

[0033] The obtained material property parameters are as follows: Porosity: 70%, Density: 1.3 g / cm³, Compressive strength 116 MPa (dense layer), Thermal conductivity: 0.2 W / (m·K) (porous layer) Comparative Example 1 (without gradient design) 1. Material preparation: Mix Inconel 718, powder with a particle size of 15 - 45 μm with 5 wt% nano-aluminum powder with a particle size of 50 - 100 nm and 15 wt% PMMA microspheres (particle size 5 - 10 μm) by ball milling under argon protection.

[0034] 2. 3D printing: Equipment: SLM 280HL metal 3D printer; Parameters: 120 W (constant), 1000 mm / s (constant), unidirectional scanning (no rotational layering); Thickness: 30 μm, under argon protection.

[0035] 3. Post-treatment: Pickling with 5% HCl to remove residues, no vacuum annealing (only stress relief), and obtain the final material.

[0036] The material performance parameters are as follows: Porosity: 70%, Density: 1.6 g / cm³, Compressive strength: 50 MPa, Thermal conductivity: 0.38 W / (m·K).

[0037] Table 3 shows the performance index comparison of Example 1, Example 2, and Comparative Example 1:

[0038] Table 3 It can be seen from Table 3 that Example 1 has the lowest thermal conductivity while meeting a relatively high compressive strength, with a relatively low density, and the pore distribution and pore size type are also relatively ideal, showing the best overall performance.

[0039] The protection scope of the present invention is not limited to the technical solutions disclosed in the specific embodiments. Any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A preparation method of a gradient porous alloy aerogel based on 3D printing, characterized in that It includes the following steps: Step a: Mix superalloy powder, nano aluminum-magnesium mixed powder and pore-forming agent to form composite powder; Step b: Construct a three-dimensional model based on the gradient porosity distribution. The three-dimensional model is divided into a dense layer (3), a transition layer (2) and a porous layer (1) from the outside to the inside along the thickness direction; Step c: Use selective laser melting (SLM) technology to print the three-dimensional model according to the preset layer-by-layer parameters. Among them, the laser power decreases layer by layer from the dense layer (3) on the outer layer of the three-dimensional model to the porous layer (1) on the inner layer, and the scanning speed increases layer by layer, and the sacrificial pore-forming agent is used to decompose to form multi-scale pores; Step d: Pickle to remove the residue of the pore-forming agent in step c, and perform vacuum annealing to strengthen the interface bonding to obtain an alloy aerogel.

2. The preparation method of a gradient porous alloy aerogel based on 3D printing according to claim 1, characterized in that: In step a, the porosity of the dense layer (3) is (5-10%); the porosity of the transition layer (2) is (10-70%); the porosity of the porous layer (1) is (70-90%).

3. The preparation method of a gradient porous alloy aerogel based on 3D printing according to claim 1, characterized in that: In step c, the pore-forming agent is calcium carbonate (CaCO3) with a particle size of 50-200 nm or polymethyl methacrylate (PMMA) microspheres with a particle size of 100-500 nm; the addition amount of the pore-forming agent is 5-15 wt%.

4. The preparation method of a gradient porous alloy aerogel based on 3D printing according to claim 1, wherein: In step a, the superalloy powder is Inconel 718 or Hastelloy X with a particle size of 15-45 μm; the particle size of the nano aluminum-magnesium mixed powder is 50-100 nm, and the addition amount is 3-8 wt%.

5. The preparation method of a gradient porous alloy aerogel based on 3D printing according to claim 1, characterized in that: The laser parameters in step c are as follows: for the dense layer (3), the laser power is 150-200 W, the scanning speed is 600-800 mm / s, and the layer thickness is 20-30 μm; for the transition layer (2), the laser power is 100-150 W, the scanning speed is 800-1000 mm / s, and the layer thickness is 30-40 μm; for the porous layer (1), the laser power is 80-100 W, the scanning speed is 1000-1200 mm / s, and the layer thickness is 40-50 μm.

6. The preparation method of a gradient porous alloy aerogel based on 3D printing according to claim 1, characterized in that: During the printing process of step c, the pore-forming agent decomposes under the action of laser to generate gas, forming a dense layer (3) on the outer layer mainly composed of closed pores with a pore diameter of 50-100 nm; the porous layer (1) on the inner layer is mainly composed of through pores with a pore diameter of 100-200 nm.

7. A preparation method of a gradient porous alloy aerogel based on 3D printing according to claim 1, characterized in that: The vacuum annealing in step d includes: the first stage: keep the temperature at 600 °C for 1 h to eliminate residual stress; the second stage: keep the temperature at 800-1000 °C for 2 h to promote the formation of Ni-Al intermetallic compounds.

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