A method for preparing hollow metal spheres

Abstract

The present invention discloses a method for preparing a hollow metal sphere, the method comprising: first, using non-spherical metal powders of two different powder particle sizes as raw materials, mixing and then pressing to obtain a cubic or cylindrical green body; second, using non-spherical metal powders of finer powder particle size to prepare a powder slurry, spraying it on the surface of the cubic or cylindrical green body to obtain a sprayed green body; third, sintering the sprayed green body at high temperature to obtain a sintered green body; fourth, placing the sintered green body in an electrostatic suspension device for high-temperature melting and heat preservation, and rapidly cooling to obtain a hollow metal sphere. The present invention achieves control of the porosity of the hollow metal sphere by selecting non-spherical metal powders of two different particle sizes as raw materials, and achieves near-net-shape forming without a container or crucible by using an electrostatic suspension method, thereby obtaining a hollow metal sphere with a solid outer wall and a dense shell. This fills the size gap of the hollow metal sphere from micro-nanoscale to several millimeters, and is suitable for energy absorption, damping and vibration reduction, explosion-proof flame retardancy, heat insulation and other fields.

Description

Technical Field

[0001] The invention belongs to the technical field of porous metal materials, and particularly relates to a method for preparing hollow metal spheres. Background Art

[0002] After using metal hollow spheres as units to prepare structural materials, they can be used in the fields of sound insulation, heat insulation, energy absorption, explosion protection, etc. At present, the metal hollow spheres that can be directly purchased on the market are mostly large in size (≥3mm), and the materials are relatively limited. The hollow spheres produced are mostly two hemispheres spliced ​​together and welded into a whole sphere; the metal hollow spheres prepared by other methods, such as the template method, have porous walls and low sphere strength; the hollow spheres prepared by the additive manufacturing method have a powder outlet hole on the surface of the wall, which needs to be sealed through a process before use; the hollow spheres produced by the atomization method and the replacement reaction sintering method are mostly micron- or nano-sized hollow spheres with small sizes. The post-processing process has a certain impact on the performance of the metal hollow spheres, and if the wall is porous, it is not easy to use in the fields of energy absorption and vibration and explosion protection.

[0003] Based on the shortcomings of the above methods, it is necessary to provide a method for preparing hollow metal spheres. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned prior art and provide a method for preparing hollow metal spheres. This method utilizes non-spherical metal powders with two levels of particle size as raw materials to control the porosity of the hollow metal spheres. By employing an electrostatic suspension method to achieve near-net-shape forming without a container or crucible, the resulting hollow metal spheres are hollow inside and solid outside, with a dense shell. This improves their strength and addresses the problems of conventional hollow metal spheres, which suffer from low strength due to porous walls and limited size, which affect their performance.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a hollow metal sphere, characterized in that the method comprises the following steps:

[0006] Step 1: Using two levels of non-spherical metal powders with different powder particle sizes as raw materials, mixing them evenly and then pressing them with a mold to obtain a cubic or cylindrical green body with a porous structure;

[0007] Step 2: Using the non-spherical metal powder with a finer powder particle size in the raw materials described in step 1, uniformly mixing it with the low-concentration slurry to obtain a powder slurry, and then uniformly spraying the powder slurry on the surface of the cubic or cylindrical green body obtained in step 1 to obtain a sprayed green body;

[0008] Step 3: placing the sprayed green body obtained in step 2 in a high temperature furnace for high temperature sintering to obtain a sintered green body;

[0009] Step 4: Place the sintered green body obtained in step 3 in an electrostatic suspension device for high-temperature melting and heat preservation, and obtain a metal hollow sphere after rapid cooling.

[0010] The above-mentioned method for preparing hollow metal spheres is characterized in that the two levels of non-spherical metal powders with different powder particle sizes in step 1 are non-spherical metal powders with powder particle sizes of 25μm to 44μm and 75μm to 125μm, or non-spherical metal powders with powder particle sizes of 44μm to 90μm and 106μm to 180μm.

[0011] The above-mentioned method for preparing hollow metal spheres is characterized in that the non-spherical metal powder in step 1 is stainless steel powder, titanium alloy powder or tungsten alloy powder.

[0012] The above-mentioned method for preparing hollow metal spheres is characterized in that the porosity of the cubic or cylindrical green body in step 1 is 10% to 50%.

[0013] The above-mentioned method for preparing a metal hollow sphere is characterized in that the temperature of the high-temperature sintering in step 3 is 0.95T m , T m The melting point of the raw metal powder used in the preparation of the spray green body is controlled. By controlling the high-temperature sintering temperature of the spray green body, the spray green body can achieve metallurgical bonding. The overlapping points of the raw material powders of different powder particle sizes in the spray green body form a certain strength, thereby forming a channel for the powder melt to bridge each other in the subsequent electrostatic suspension melting process in advance, which is beneficial to the formation of a dense spherical shell of the metal hollow sphere prepared later.

[0014] The above-mentioned method for preparing a hollow metal sphere is characterized in that the temperature of the high-temperature melting in step 4 is 1.1T m ~1.3T m , T m The melting point of the raw metal powder used to prepare the spray green body is determined by using a higher temperature than the melting point of the raw metal powder to ensure that both non-spherical metal powders of different powder sizes reach a molten state. This allows the large-particle powder to have a uniform microstructure after low superheating during the electrostatic suspension melting process, resulting in a metal hollow sphere with better performance.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. The present invention mixes and presses non-spherical metal powders of two levels of particle size into a green body with pores, sprays non-metallic powder on the surface for high-temperature sintering, and then adopts an electrostatic suspension method to melt and cool to prepare a metal hollow sphere. By selecting non-spherical metal powders of two levels of particle size, the porosity of the metal hollow sphere can be regulated. By adopting the electrostatic suspension method to achieve near-net forming without a container or a crucible, a metal hollow sphere with a hollow interior and a solid exterior and a dense shell as the sphere wall is obtained. The metal hollow sphere has high strength and the sphere wall does not have a porous structure. It is suitable for energy absorption, damping and vibration reduction, explosion-proof flame retardancy, heat insulation and other fields.

[0017] 2. The present invention selects two-level particle size non-spherical metal powder as raw material, which not only realizes the controllability of porosity, but also facilitates mold forming through particle size grading. At the same time, in the subsequent high-temperature sintering molding process, the finer particle size non-spherical metal powder plays the role of a low-temperature metallurgical bonding aid, promotes the sintering connection of the metal powder, and improves the integrity of the dense shell on the surface of the metal hollow sphere.

[0018] 3. The two-grade non-spherical metal powder raw material used in the present invention is relatively common and easy to purchase, and the inner cavity of the mold involved in the pressing molding is cylindrical or cubic, which is easy to implement, and the process is mature and the molding rate is high.

[0019] 4. The present invention adopts an electrostatic suspension method to prepare the hollow metal spheres, which not only achieves no crucible pollution, but also has no pollution to the microstructure and macrostructure of the hollow metal spheres, as well as the equipment and the use environment, and is green and environmentally friendly.

[0020] 5. The method of the present invention can realize the preparation of small-sized dense-walled metal hollow spheres, filling the size gap of metal hollow spheres from micro-nanoscale to several millimeters.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a physical picture of the sintered green body prepared in Example 1 of the present invention.

[0023] Figure 2 This is a physical picture of the metal hollow sphere prepared in Example 1 of the present invention.

[0024] Figure 3 This is a photo of the metal hollow sphere prepared in Example 1 of the present invention after being cut in half.

[0025] Figure 4 This is a photo of a metallographic sample made by inlaying the metal hollow spheres prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] Example 1

[0027] This embodiment includes the following steps:

[0028] Step 1: Using non-spherical stainless steel powders with a particle size of 44 μm and 180 μm as raw materials, mixing them in equal mass proportions and then pressing them using a mold to obtain a cubic green body with a porosity of 30%;

[0029] Step 2: Using non-spherical stainless steel powder with a powder particle size of 44 μm, and mixing it with polyvinyl alcohol slurry with a mass concentration of 3% in a mass ratio of 1:4 to obtain a powder slurry, and then using a spray gun to evenly spray the powder slurry on the surface of the cubic green body obtained in step 1 to obtain a sprayed green body;

[0030] Step 3: Place the sprayed green body obtained in step 2 in a vacuum sintering furnace for high temperature sintering. The high temperature sintering temperature is 1200℃ and the holding time is 1h to obtain a sintered green body. Figure 1 As shown;

[0031] Step 4: Place the sintered green body obtained in step 3 in an electrostatic suspension device, adjust the laser temperature to 1500℃ for high temperature melting and keep it warm for 30s, and then quickly cool it to obtain a stainless steel hollow ball with a porosity of 10%. Figure 2 shown.

[0032] Figure 3 This is a photo of the metal hollow sphere prepared in this example after being cut in half. Figure 4 This is a metallographic sample of a hollow metal ball prepared in this embodiment. Figure 3 and Figure 4 It can be seen that the metal hollow sphere has a hollow inner and solid outer structure, and the sphere wall is a dense shell without a porous structure.

[0033] The non-spherical stainless steel powder in step 1 and step 2 of this embodiment can also be replaced by tungsten alloy powder.

[0034] Example 2

[0035] This embodiment includes the following steps:

[0036] Step 1: Using non-spherical TC4 titanium alloy powders with a powder size of 30 μm and 150 μm as raw materials, mixing them in equal mass proportions and then pressing them using a mold to obtain a cylindrical green body with a porosity of 50%;

[0037] Step 2: Using non-spherical TC4 titanium alloy powder with a powder particle size of 30 μm, and mixing it with a polyvinyl alcohol slurry with a mass concentration of 3% in a mass ratio of 1:3 to obtain a powder slurry, and then using a spray gun to evenly spray the powder slurry on the surface of the cylinder obtained in step 1 to obtain a sprayed green body;

[0038] Step 3: Place the sprayed green body obtained in step 2 in a vacuum sintering furnace for high-temperature sintering at a temperature of 1600° C. and a holding time of 2 h to obtain a sintered green body;

[0039] Step 4: Place the sintered green body obtained in step 3 in an electrostatic suspension device, adjust the laser temperature to 1800° C. for high-temperature melting and keep the temperature for 1 minute, and obtain TC4 titanium alloy hollow spheres with a porosity of 25% after rapid cooling.

[0040] Example 3

[0041] This embodiment includes the following steps:

[0042] Step 1: Using non-spherical tungsten alloy powders of 25 μm and 125 μm as raw materials, mixing them in equal mass proportions and then pressing them using a mold to obtain a cylindrical green body with a porosity of 10%;

[0043] Step 2: Using non-spherical tungsten alloy powder with a powder particle size of 25 μm, mix it with polyvinyl alcohol slurry with a mass concentration of 3% in a mass ratio of 1:3 to obtain a powder slurry, and then use a spray gun to evenly spray the powder slurry on the surface of the cylinder obtained in step 1 to obtain a sprayed green body;

[0044] Step 3: Place the sprayed green body obtained in step 2 in a vacuum sintering furnace for high-temperature sintering at a temperature of 1900° C. and a holding time of 2 h to obtain a sintered green body;

[0045] Step 4: Place the sintered green body obtained in step 3 in an electrostatic suspension device, adjust the laser temperature to 2200° C. for high-temperature melting and keep the temperature for 1 minute, and obtain a tungsten alloy hollow sphere with a porosity of 8% after rapid cooling.

[0046] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a hollow metal sphere, characterized in that: The method comprises the following steps: Step 1: Using two levels of non-spherical metal powders with different powder particle sizes as raw materials, mixing them evenly and then pressing them using a mold to obtain a cubic or cylindrical green body with a porous structure; the two levels of non-spherical metal powders with different powder particle sizes are non-spherical metal powders with powder particle sizes of 25 μm to 44 μm and 75 μm to 125 μm, or non-spherical metal powders with powder particle sizes of 44 μm to 90 μm and 106 μm to 180 μm; Step 2: Using the non-spherical metal powder with a finer powder particle size in the raw materials described in step 1, uniformly mixing it with a polyvinyl alcohol slurry with a mass concentration of 3% to obtain a powder slurry, and then evenly spraying the powder slurry on the surface of the cubic or cylindrical green body obtained in step 1 to obtain a sprayed green body; Step 3: Place the sprayed green body obtained in step 2 in a high temperature furnace for high temperature sintering to obtain a sintered green body; the high temperature sintering temperature is 0.95T m , T m The melting point of the non-spherical metal powder used as the raw material for preparing the spray green body; Step 4: Place the sintered green body obtained in step 3 in an electrostatic suspension device for high-temperature melting and heat preservation, and obtain a metal hollow sphere after rapid cooling; the high-temperature melting temperature is 1.1T m ~1.3T m , T m The melting point of the non-spherical metal powder used as the raw material for preparing the spray green body.

2. The method for preparing a hollow metal sphere according to claim 1, wherein: The non-spherical metal powder in step 1 is stainless steel powder, titanium alloy powder or tungsten alloy powder.

3. The method for preparing a hollow metal sphere according to claim 1, wherein: The porosity of the cubic or cylindrical green body in step 1 is 10% to 50%.

Images