CN108274011A - A kind of preparation method with bimodal distribution metal powder suitable for 3D printing - Google Patents

Abstract

A kind of preparation method with bimodal distribution metal powder suitable for 3D printing belongs to metal powder material technical field.Metal powder of the average grain diameter in 0.5~1.5 μ m is used to prepare slurry for initial feed；Then agglomeration granulation is carried out to metal powder, the particle diameter distribution of micro-sized metal powder prepared by the rotating speed control by adjusting atomizing disk；Finally micro-sized metal powder after granulation is heat-treated, by degumming and densification consolidation, obtains the metal powder granulates with bimodal size distribution that sphericity, mobility and oxygen content meet 3D printing requirement.This method is compared with other existing associated metal powder preparation methods, it is strong to the controllability of the sphericity of metal powder granulates, particle diameter distribution and oxygen content, the metal powder being distributed with particular size can be prepared in same batch, and there is advantage simple for process, at low cost.

Description

A preparation method of metal powder with bimodal distribution suitable for 3D printing

technical field

The invention relates to a method for preparing spherical metal powder with bimodal particle size distribution, which is suitable for 3D printing to obtain high-density printed parts, and belongs to the technical field of metal powder materials.

Background technique

Based on the principle of layer-by-layer accumulation, 3D printing technology can replace the traditional manufacturing process and can produce three-dimensional workpieces with complex shapes with high efficiency and high precision. Therefore, it has received extensive attention and hot research in recent years. However, high-quality metal printing materials are the primary bottleneck restricting the application of 3D printing technology and obtaining high-performance metal printing parts. For metal powder materials for 3D printing, it is usually required that the particle size of the metal powder is small (<50 μm), uniform, high sphericity, high fluidity and low oxygen content. On this basis, high-performance metal printing components put forward higher requirements for powder materials, such as special particle size distribution metal powder with bimodal distribution. Because the powder with bimodal distribution can not only maintain high fluidity, but also realize the small-sized particles to fill the pores between the large-sized particles, thereby effectively increasing the powder packing density, so that the surface is smooth and the structure is dense without changing the printing process. high-performance prints. At present, a large number of researchers pay attention to metal powders with special particle size distribution, but the bimodal distribution powders used in the research reports are mixed with powder particles of two particle sizes. This method is likely to cause poor powder fluidity and uneven density of printed parts due to uneven mixing, and the introduction of metal elements contained in the balls and impurity elements such as oxygen and carbon due to long-term ball milling and mixing. The powder material obtained by the existing metal powder preparation technology usually has a single-peak particle size distribution, such as gas atomization method, plasma rotating electrode method, radio frequency plasma spheroidization method, etc. Moreover, the metal or alloy powder prepared by the gas atomization method and the plasma rotating electrode method has a low yield of particle size below 50 μm; the radio frequency plasma spheroidization method consumes a lot of energy and has high production costs. Therefore, there is an urgent need for a method for preparing metal powders for 3D printing with high purity, low cost, and special particle size distribution.

In view of the background of the above field, in order to solve the limitations of the prior art, the present invention provides a method for preparing spherical metal powder with high purity and bimodal special particle size distribution suitable for 3D printing.

Contents of the invention

The process flow and principle of the preparation method provided by the present invention are as follows: use metal powder with an average particle size in the range of 0.5-1.5 μm as the initial raw material to prepare slurry; Control the particle size distribution of the prepared micron-sized metal powder; finally, heat-treat the granulated micron-sized metal powder, through degumming and densification and consolidation, to obtain a bimodal sphericity, fluidity and oxygen content that meet the requirements of 3D printing Size distribution of metal powder particles. Compared with other existing related metal powder preparation methods, this method has strong controllability to the sphericity, particle size distribution and oxygen content of metal powder particles, and can prepare powder with special particle size distribution, and has the advantages of simple process, The advantage of low cost.

A method for preparing a metal spherical powder with a bimodal distribution suitable for 3D printing provided by the present invention is characterized in that it comprises the following steps:

(1) The initial metal powder is mixed with polyvinyl alcohol, polyethylene glycol and deionized water to prepare a slurry, and ball milled for 1 to 2 hours to obtain a stable slurry, wherein the initial metal powder is one of Fe, Co, Ni, W, etc., The average particle size is in the range of 0.5-1.5 μm, the mass of the initial metal powder is 50-78% of the total mass of the slurry, polyvinyl alcohol is 0.8-2% of the mass of the initial metal powder, and polyethylene glycol is the mass of the initial metal powder 1~2% of

(2) Perform centrifugal spray drying on the slurry prepared in step (1), and obtain spherical metal particles with a particle size below 50 μm and a bimodal distribution by adjusting the rotation speed of the atomizing disc, and adopt staged spray drying, the first stage 50% to 80% of the total volume of the slurry is atomized and dried, and the rotation speed of the atomization disc is 12000 to 13500rpm. The rotating speed of the disc is 16000～18000rpm;

(3) heat-treat the spherical particles obtained in step (2) using an argon-protected tube furnace, and use staged heat treatment for degumming and densification consolidation; the first stage of degumming uses 300 ° C for 120 minutes, and then uses the second stage and the third stage heat treatment to complete the densification and consolidation, the second stage heat treatment temperature is T _m /2+120℃～T _m /2+200℃, T _m is the melting point of the metal, the holding time is 5~10min, the third stage heat treatment directly From the second stage, the temperature is lowered to T _m /2℃～T _m /2+120℃, and then kept for 120～180min, and finally a micron-sized spherical metal powder with bimodal particle size distribution with high density and fluidity is obtained.

The second stage temperature of the above step (3) is different from the third stage temperature.

The technical characteristics and advantages of the inventive method mainly contain:

(1) Suspension solution slurry is prepared with pure metal powder as the initial material. The average particle size of the initial powder is in the range of 0.5-1.5 μm, which greatly reduces the cost compared with the process of using nano-powder for granulation;

(2) During the slurry preparation process, the proportion of polyvinyl alcohol, polyethylene glycol and deionized water is low and the proportion is determined by the initial powder particle size and the degree of agglomeration. If the average particle size is large, reduce the polyethylene The ratio of alcohol, polyethylene glycol and deionized water;

(3) The preparation of a stable and uniform slurry plays a vital role in the morphology and particle size distribution of the granulated powder. In the present invention, the ball milling process is adopted, and its effect is to avoid heavy large particle powder from sinking into the At the bottom of the slurry, the adsorption of organic binder and dispersant on the particle surface is unbalanced;

(4) During the centrifugal spray drying process, the control of the rotational speed of the atomizing disc determines whether to obtain a spherical powder with a bimodal particle size distribution that meets the requirements. For uniformly dispersed slurry, the feed rate is constant, the centrifugal force is approximately equal to the cohesive force between the slurry, and the radius of the atomized droplet has the following relationship with the rotation speed of the atomizing disc: r=3σ/(ρω ² R), where σ is the surface tension of the slurry, proportional to the viscosity of the slurry, ρ is the density of the slurry, ω is the rotational speed of the atomizing disc, R is the radius of the atomizing disc, r is the radius of the atomized droplet (approximately equal to the atomization Get the particle size of the powder particles). By adjusting various process parameters, metal powders for 3D printing with bimodal particle size distribution, high sphericity and high fluidity can be prepared;

(5) The heat treatment process after granulation is very important to finally ensure the quality of metal powder for 3D printing. In the present invention, the staged heat treatment method is adopted to complete the densification and consolidation. The function of the first stage heat treatment is to make the small particles inside the granulated powder particles melt at high temperature instantaneously to form solid phase bonding, and the granulated powder particles do not sinter as a whole; The heat treatment temperature of the second stage is lower than that of the first stage, and its function is to make the inside of the granulated powder particles achieve densification under the condition of low temperature and long-term heat preservation. This staged heat treatment method can effectively prevent the fine particles in the granulated powder from overheating and coarsening Particles are bonded to form satellite spheres or larger particles are not densely combined, thereby improving the quality of the powder;

(6) The method of the present invention achieves the preparation of metal powders with bimodal particle size distribution in the same batch with relatively simple process steps, and the sphericity and particle size distribution of the powder particles are highly controllable. Compared with the existing The preparation process of spherical metal powder has high production efficiency and significantly reduced cost.

Description of drawings

Fig. 1 is the micromorphological figure and the particle size distribution statistical diagram of the spherical metal powder with bimodal distribution prepared by the present invention; wherein, a and b are the micromorphological and particle diameter of the metallic cobalt powder in Example 1 respectively Distribution statistical diagram, c, d are the microscopic morphology and particle size distribution statistical diagram of metal nickel powder in embodiment 2 respectively, e, f are respectively the microscopic morphology and particle size distribution statistics of metallic tungsten powder in embodiment 3 picture.

The phase detection spectrum of the micron-scale spherical metal powder that Fig. 2 present invention prepares; Wherein a is the phase detection spectrum of cobalt powder in embodiment 1, b is the phase detection spectrum of nickel powder in embodiment 2, c is the implementation The phase detection spectrum of tungsten powder in example 3.

Table 1 Test results of sphericity, fluidity and density of metal cobalt, nickel and tungsten powder particles prepared in Example 1, Example 2 and Example 3 of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the examples, but the present invention is not limited to the following examples.

Example 1. The pure cobalt powder raw material with 50% slurry mass and an average particle diameter of 0.5 μm, polyvinyl alcohol with 2% cobalt powder mass, polyethylene glycol with 2% cobalt powder mass, and deionized water to prepare a suspension Slurry, ball milling for 1h to obtain a uniform and stable suspension slurry, use centrifugal atomization drying equipment to carry out agglomeration and granulation, 50% of the total volume of the slurry is granulated using an atomization disc speed of 12000rpm, and the remaining The 50% volume slurry is granulated with an atomization disc speed of 16000rpm to obtain spherical cobalt particles with a bimodal distribution; the granulated cobalt powder is heat-treated in an argon-protected tube furnace, and the heat treatment temperature of the first stage is 300°C, holding time 120min; the second stage heat treatment temperature is 940°C, holding time 5min, the third stage heat treatment temperature drops to 870°C, holding time 180min, to obtain 3D printing with bimodal particle size distribution and high fluidity Micron spherical cobalt powder is used. The microscopic morphology and particle size distribution statistics of the prepared cobalt powder are as shown in a and b in Fig. 1, and the phase detection spectrum is as a in Fig. 2. The measurement results of sphericity, bulk density and fluidity are shown in Table 1, see Table 2 for the density comparison between the printed parts prepared by this cobalt powder and the printed parts prepared by the monomodal particle size distribution powder.

Embodiment 2, the average particle diameter of 68% slurry quality is the pure nickel powder raw material of 1 μm and the polyvinyl alcohol of 1% nickel powder quality, the polyethylene glycol of 1.5% nickel powder quality and deionized water preparation suspension liquid material Slurry, ball milled for 1.5h to obtain a uniform and stable suspension slurry, granulate 65% of the total volume of the slurry using a 13,000rpm atomization disc rotation speed, and use a 17,000rpm atomization disc to granulate the remaining 35% of the volume of the slurry The disc rotates at a rotating speed for granulation to obtain spherical nickel particles with a bimodal distribution; the granulated nickel powder is heat treated in an argon-protected tube furnace. The first stage heat treatment temperature is 300°C, and the holding time is 120 minutes; the second stage The heat treatment temperature is 870°C, the holding time is 8 minutes, the heat treatment temperature in the third stage is lowered to 800°C, and the holding time is 150 minutes, and a micron-sized spherical nickel powder for 3D printing with bimodal particle size distribution and high fluidity is obtained. The microscopic morphology and particle size distribution statistics of the prepared nickel powder are as c and d in Fig. 1, the phase detection spectrum is as b in Fig. 2, and the measurement results of sphericity, bulk density and fluidity are shown in Table 1. See Table 2 for the density comparison between the printed parts prepared by this nickel powder and the printed parts prepared by the single peak particle size distribution powder.

Example 3. Prepare a suspension with 78% of the pure tungsten powder raw material with an average particle size of 1.5 μm, 0.9% of the tungsten powder’s polyvinyl alcohol, 1.2% of the tungsten powder’s polyethylene glycol, and deionized water Slurry, ball milled for 2 hours to obtain a uniform and stable suspension slurry, granulate 80% of the total volume of the slurry using a 13500rpm atomization disc rotation speed, and use 18000rpm atomization for the remaining 20% of the volume of the slurry The tungsten powder is granulated at a rotating speed of the disc to obtain spherical tungsten particles with a bimodal distribution; the tungsten powder after granulation is heat-treated in an argon-protected tube furnace. The heat treatment temperature is 1800°C, the holding time is 10 minutes, the heat treatment temperature in the third stage is lowered to 1700°C, and the holding time is 180 minutes, and the micron-sized spherical tungsten powder for 3D printing with both bimodal particle size distribution and high fluidity is obtained. The microscopic morphology and particle size distribution statistics of the prepared tungsten powder are shown in e and f in Figure 1, and the phase detection spectrum is shown in c in Figure 2. The measurement results of sphericity, bulk density and fluidity are shown in Table 1, see Table 2 for the density comparison between the printed parts prepared by using this tungsten powder and the printed parts prepared by the unimodal particle size distribution powder.

Table 1 The physical parameters of the metal powders prepared in Examples 1-3 of the present invention

Table 2 Density of bimodal particle size distribution metal powder prints and unimodal particle size distribution metal powder prints in Examples 1-3 of the present invention

Claims (2)

1. A method for preparing metal spherical powders with bimodal distribution suitable for 3D printing, characterized in that, comprising the following steps: (1) The primary metal powder is mixed with polyvinyl alcohol, polyethylene glycol and deionized water to prepare a slurry, and ball milled for 1-2 hours to obtain a stable slurry, wherein the average particle size of the primary metal powder is in the range of 0.5-1.5 μm, and The powder mass is 50-78% of the total mass of the slurry, polyvinyl alcohol is 0.8-2% of the initial metal powder mass, and polyethylene glycol is 1-2% of the initial metal powder mass; (2) Perform centrifugal spray drying on the slurry prepared in step (1), and obtain spherical metal particles with a particle size below 50 μm and a bimodal distribution by adjusting the rotation speed of the atomizing disc, and adopt staged spray drying, the first stage 50% to 80% of the total volume of the slurry is atomized and dried, and the rotation speed of the atomization disc is 12000 to 13500rpm. The rotating speed of the disc is 16000～18000rpm; (3) heat-treat the spherical particles obtained in step (2) using an argon-protected tube furnace, and use staged heat treatment for degumming and densification consolidation; the first stage of degumming uses 300 ° C for 120 minutes, and then uses the second stage and the third stage heat treatment to complete the densification and consolidation, the second stage heat treatment temperature is T _m /2+120℃～T _m /2+200℃, T _m is the melting point of the metal, the holding time is 5~10min, the third stage heat treatment directly From the second stage, the temperature is lowered to T _m /2℃～T _m /2+120℃, and then kept for 120～180min, and finally a micron-sized spherical metal powder with bimodal particle size distribution with high density and fluidity is obtained; The second stage temperature of the above step (3) is different from the third stage temperature. 2. A method for preparing a metal spherical powder with a bimodal distribution suitable for 3D printing according to claim 1, wherein the initial metal powder is one of Fe, Co, Ni, W.