A method for preparing low expansion alloy powder for 3D printing

Abstract

The present invention relates to a method for preparing low expansion alloy powder for 3D printing, which belongs to the technical field of metal material processing, and solves the problems that the powder preparation technology in the prior art is not suitable for low expansion alloys, the obtained powder has low sphericity, poor rolling performance, high oxygen content, low powder yield, and the uniformity and density of subsequent printed products still need to be improved. The present invention provides a method for preparing low expansion alloy powder for 3D printing, S1: preparing electrode rods for processing; S2: using a process of pre-starting + three-stage step-by-step increase in motor speed to process the electrode rods to obtain a coarse alloy powder product; S3: screening the coarse powder product. The sphericity of the powder for 3D printing prepared by the method is 99%, the hollow powder rate is less than 0.4%, the oxygen content is less than 60ppm, the powder yield of 15-53μm after screening can reach 50%, and the normal distribution kurtosis coefficient is not greater than 3, which greatly improves the rolling performance of the powder and helps to improve the uniformity and density of downstream printed products.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material processing, and in particular to a method for preparing low expansion alloy powder for 3D printing. Background Art

[0002] Low expansion alloys are materials with unique physical properties that exhibit abnormal negative thermal expansion behavior when the temperature changes. Specifically, within a specific temperature range, the thermal expansion coefficient is significantly reduced to almost zero. Such alloys have attracted much attention due to their potential applications in high-end fields such as aerospace remote sensors, precision laser technology, and optical measurement systems. Additive manufacturing (3D printing) technology places high demands on powder materials, including good fluidity, high sphericity, and low oxygen content.

[0003] Due to the characteristics of low expansion alloys, the existing powder preparation technology and related empirical formulas are not suitable for the preparation of low expansion alloys. There are also problems such as unreasonable powder particle size distribution, poor fluidity, and low sphericity, which will also have an adverse effect on the quality of subsequent 3D printed products. Summary of the invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide a method for preparing low expansion alloy powder for 3D printing, so as to solve at least one of the problems that the existing powder preparation technology is not suitable for low expansion alloys, the sphericity of the prepared powder is low, the rolling property is poor, the oxygen content is high, the powder yield is low, and the uniformity and density of subsequent printed products still need to be improved.

[0005] The present invention provides a method for preparing low expansion alloy powder for 3D printing, which specifically comprises the following steps:

[0006] S1: Prepare low expansion alloy rods according to preset formula and through "melting + machining" process to obtain electrode rods for processing;

[0007] S2: Load the electrode rod into the plasma rotating electrode atomizing powder making equipment, fill it with inert gas, and process the electrode rod using the process of pre-starting + three-stage step-by-step increase of the motor speed. After the processing is completed, the coarse alloy powder product is collected;

[0008] S3: Screening the coarse powder product, screening out alloy powder with a particle size of 15 μm to 53 μm and performing quality inspection on the alloy powder.

[0009] Specifically, the electrode rod has a length of 100 to 250 mm, a diameter of 28 to 32 mm, and a surface roughness of less than 3 μm.

[0010] Specifically, the inert gas in step S2 is argon gas, and the gas pressure is 0.08-0.12 MPa.

[0011] Specifically, in the pre-starting step described in step S2, the motor speed is gradually increased from 0 r / min to 12000 r / min, and after stable operation for not less than 30 seconds, the speed is increased to 28000 r / min and maintained stable operation for not less than 2 minutes.

[0012] Furthermore, the motor speed corresponding to the three-stage process of gradually increasing the motor speed is: the first stage: 28000-30000r / min, the second stage: 30001r / min-34000r / min, and the third stage 34001r / min-36000r / min.

[0013] Specifically, the supporting process parameters for the first stage of processing are: motor speed 28000~30000r / min, distance between plasma gun and end of electrode rod 20~30mm, working current 400~550A, feed speed 0.5mm / s~0.8mm / s, and the median diameter of the powder obtained in this stage is about 52μm.

[0014] Specifically, the supporting process parameters for the second stage of processing are: motor speed 30001r / min~34000r / min, distance between plasma gun and end of electrode rod 15~25mm, working current 500~600A, feed speed 0.7mm / s~1.0mm / s, and the median diameter of the powder obtained in this stage is about 45μm.

[0015] Specifically, the supporting process parameters of the third stage processing are: motor speed 34001r / min~36000r / min, distance between plasma gun and end of electrode rod 10~20mm, working current 650~800A, feed speed 0.9mm / s~1.2mm / s, and the median diameter of the powder obtained in this stage is about 35μm.

[0016] Specifically, the length of the electrode rod processed in the first stage is L1, the length of the electrode rod processed in the second stage is L2, and the length of the electrode rod processed in the third stage is L3, L1: L2: L3 = 2.8~3.5: 2.5~3.2: 0.8~1.2.

[0017] Specifically, the length of the electrode rod processed in the first stage is t1, the length of the electrode rod processed in the second stage is t2, and the length of the electrode rod processed in the third stage is t3, t1: t2: t3 = 4.7~5.8: 3.1~4: 0.8~1.2.

[0018] Specifically, the composition of the low expansion alloy is calculated by mass percentage as follows: C: 0-0.05%, Mn: 0.2-0.6%, Si: 0-0.2%, P: 0-0.02%, S: 0-0.002%, Cu: 0.4-0.8%, Co: 3.2-4.2%, Ni: 31.5-33%, and the rest is Fe and unavoidable impurities.

[0019] The present invention also provides a low expansion alloy powder for 3D printing, the alloy powder is prepared by the preparation method; the alloy powder has a particle size range of 15 μm to 53 μm, a normal distribution kurtosis coefficient ≤3, a sphericity rate ≥99%, a powder hollow rate ≤0.4%, an oxygen content ≤60 ppm, and a Hall flow rate ≥16S·(50g) -1 .

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. The present invention significantly improves the powder yield by adopting the process of "pre-starting + three-stage step-by-step increase of motor speed", the yield of 15-53μm powder is ≥45%, and the highest can reach 50%, and a normal distribution particle size with a kurtosis coefficient of ≤3 is obtained, thereby significantly improving the fluidity of the powder, and the Hall flow rate is ≥16S·(50g) -1 .

[0022] The present invention performs heat engine by pre-starting, which reduces damage to equipment on the one hand and reduces ineffective loss of electrode rods on the other hand, that is, basically qualified alloy powder can be produced as soon as entering the first stage, and the yield of 15-53μm powder is significantly improved.

[0023] The process of gradually increasing the motor speed in three stages is coordinated with the process parameters of the corresponding stages to prepare coarse powder, medium powder and fine powder respectively. Compared with the sharp single-peak distribution or discrete double-peak distribution of powder particle size in traditional technologies, the present invention provides a new preparation idea, which allows three similar particle size peaks to be superimposed to obtain a relatively flat particle size distribution. It has been found through tests and experiments that this particle size distribution, on the one hand, helps to improve powder fluidity, and on the other hand, significantly improves the density and uniformity of subsequent prints, and greatly reduces the occurrence of structural defects of prints compared to existing powders.

[0024] 2. The present invention uses a step-by-step accelerated process design to greatly avoid mutual interference between powders of different particle sizes during the preparation process. As is well known, a major problem in the preparation of metal powders is that fine powders are difficult to settle and are easily attached to the surface of powders with larger particle sizes, which leads to a decrease in powder quality. The present invention uses a step-by-step accelerated process design to first prepare powders with larger particle sizes. Powders with large particle sizes settle quickly, and when preparing powders with small particle sizes, powders with large particle sizes have already completed settling, greatly reducing the problems of fine powder adhesion and low yield.

[0025] 3. Since the performance of low expansion alloys during heating and melting is very different from that of conventional alloys, and the change law of surface tension after the molten alloy liquid is formed is not easy to measure, conventional parameters and empirical formulas are not applicable to the preparation of low expansion alloy powders; the use of empirical formulas and parameters for the preparation of low expansion alloy powders will lead to defects such as poor sphericity and uncontrollable particle size distribution. These defects are related to the breakage of the low expansion alloy liquid film and the cooling process of the droplets, but this process is difficult to predict, and even if it can be measured, it will consume a huge amount of manpower and material resources.

[0026] The present invention targets a low expansion alloy with a composition of C: 0-0.05%, Mn: 0.2-0.6%, Si: 0-0.2%, P: 0-0.02%, S: 0-0.002%, Cu: 0.4-0.8%, Co: 3.2-4.2%, Ni: 31.5-33%, and the remainder being Fe and inevitable impurities. After theoretical design and a large number of experimental adjustments and optimizations, the optimal process matching parameters are obtained, thereby greatly improving the comprehensive performance of the powder.

[0027] 4. The present invention also takes into account the distribution law of particle size at different stages, designs a combination of process parameters at different stages for the target particle size range, and obtains a more ideal yield. For example, the target yield range of the present invention is 15-53 μm, and the median particle size of the first stage is 52 μm, which is close to the boundary value. This is because large-particle powders are prone to form spikes, and the powder particle size will be concentrated near the median. In addition, large-particle particles can play the role of the main frame in the subsequent printing process. Therefore, under the premise of meeting the use requirements, it should be ensured that the powder close to the upper limit of the particle size is not too little, which is conducive to the printing and preparation of subsequent products; and for the third stage, the particle size distribution of fine powders is often more divergent, and a very flat particle size distribution peak will be formed. Therefore, the particle size is set to 35 μm, which is far enough away from the lower limit of the particle size, thereby improving the yield.

[0028] 5. Since different types of equipment have different degrees of difficulty in controlling the processing length and processing time, the present invention, on the premise of giving the specific process parameters of each stage, further provides the control parameters of the processing time and processing length, which reduces the difficulty of operation and is more conducive to the promotion and reproduction of the technology.

[0029] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0031] Figure 1 is a microscopic photograph of the low expansion alloy powder in Example 1;

[0032] Figure 2 is a particle size distribution diagram of the low expansion alloy powder in Example 1;

[0033] Figure 3 This is a surface photo of the low expansion alloy powder 3D printed component in Example 1;

[0034] Figure 4 This is a microscopic photograph of the low expansion alloy powder in Comparative Example 3. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0036] Since the performance of low expansion alloys during heating and melting is very different from that of conventional alloys, and the change pattern of surface tension after the molten alloy liquid is formed is not easy to measure, conventional parameters and empirical formulas are not applicable to the preparation of low expansion alloy powders; the use of empirical formulas and parameters for the preparation of low expansion alloy powders will lead to defects such as poor sphericity and uncontrollable particle size distribution. These defects are related to the breakage of the low expansion alloy liquid film and the cooling process of the droplets, but this process is difficult to predict, and even if it can be measured, it will consume a huge amount of manpower and material resources.

[0037] Based on the above technical problems, the present invention proposes a method for preparing powder for 3D printing of low expansion alloys after a lot of theoretical analysis and experimental optimization.

[0038] The present invention provides a method for preparing low expansion alloy powder for 3D printing, which specifically comprises the following steps:

[0039] S1: Prepare low expansion alloy rods according to preset formula and through "melting + machining" process to obtain electrode rods for processing;

[0040] S2: Load the electrode rod into the plasma rotating electrode atomizing powder making equipment, fill it with inert gas, and process the electrode rod using the process of pre-starting + three-stage step-by-step increase of the motor speed. After the processing is completed, the coarse alloy powder product is collected;

[0041] S3: Screening the coarse powder product, screening out alloy powder with a particle size of 15 μm to 53 μm and performing quality inspection on the alloy powder.

[0042] The present invention performs a heat engine by pre-starting, which reduces damage to the equipment on the one hand, and reduces the ineffective loss of the electrode rod on the other hand, that is, basically qualified alloy powder can be produced as soon as the first stage is entered, and the yield of 15-53μm powder is significantly improved. The three-stage process of gradually increasing the motor speed is matched with the process parameters of the corresponding stages to prepare coarse powder, medium powder and fine powder respectively. Compared with the sharp single-peak distribution or discrete double-peak distribution of powder particle size in traditional technology, the present invention provides a new preparation idea, which makes three similar particle size peaks superimposed to obtain a relatively flat particle size distribution. It is found through testing and experiments that this kind of particle size distribution helps to improve the fluidity of the powder on the one hand, and significantly improves the density and uniformity of subsequent prints on the other hand, and greatly reduces the generation of structural defects of prints compared with the pre-existing powder.

[0043] Specifically, the electrode rod has a length of 100 to 250 mm, a diameter of 28 to 32 mm, and a surface roughness of less than 3 μm. The electrode rod should not be too long, otherwise it may cause the motor to rotate eccentrically or damage the equipment; the cross-sectional area of ​​the electrode rod is related to the heating power and the melting form of the alloy, and the above diameter range has been verified to be more appropriate by experiments; the surface roughness of the electrode rod will affect the powder uniformity and process stability. In theory, the lower the surface roughness, the better. Considering the cost factor, the surface roughness can be less than 3 μm.

[0044] Specifically, the screening described in step S3 adopts vibration screening, the screening mesh size is 200-800 mesh, and the screening time is 10-30 minutes.

[0045] Specifically, the inert gas in step S2 is argon gas, and the gas pressure is 0.08-0.12 MPa. The inert gas pressure is related to the powder particle size. Generally speaking, the higher the pressure, the larger the powder particle size. Since the powder particle size distribution involved in the present invention is not very wide, the above gas pressure can meet the needs. On the other hand, it is not advisable to repeatedly adjust the gas pressure during the processing, because the gas pressure adjustment has a lag, and it will cause the gas atmosphere in the equipment to be disturbed, thereby affecting the powder quality.

[0046] Specifically, in the pre-starting step described in step S2, the motor speed is gradually increased from 0 r / min to 12000 r / min, and after stable operation for not less than 30 seconds, the speed is increased to 28000 r / min and maintained stable operation for not less than 2 minutes. The present invention performs a heat engine through pre-starting, which reduces damage to the equipment on the one hand, and reduces the ineffective loss of the electrode rod on the other hand, that is, basically qualified alloy powder can be produced as soon as the first stage is entered, and the yield of 15-53 μm powder is significantly improved.

[0047] Furthermore, the motor speed corresponding to the three-stage process of gradually increasing the motor speed is: the first stage: 28000-30000r / min, the second stage: 30001r / min-34000r / min, and the third stage 34001r / min-36000r / min.

[0048] The present invention uses a step-by-step accelerated process design to greatly avoid mutual interference between powders of different particle sizes during the preparation process. As is well known, a major problem in the preparation of metal powders is that fine powders are difficult to settle and are easily attached to the surface of powders with larger particle sizes, which leads to a decrease in powder quality. The present invention uses a step-by-step accelerated process design to first prepare powders with larger particle sizes. Powders with large particle sizes settle quickly, and when preparing powders with small particle sizes, powders with large particle sizes have already completed settling, greatly reducing the problems of fine powder adhesion and low yield.

[0049] Specifically, the supporting process parameters for the first stage of processing are: motor speed 28000~30000r / min, distance between plasma gun and end of electrode rod 20~30mm, working current 400~550A, feed speed 0.5mm / s~0.8mm / s, and the median diameter of the powder obtained in this stage is about 52μm.

[0050] Specifically, the supporting process parameters for the second stage of processing are: motor speed 30001r / min~34000r / min, distance between plasma gun and end of electrode rod 15~25mm, working current 500~600A, feed speed 0.7mm / s~1.0mm / s, and the median diameter of the powder obtained in this stage is about 45μm.

[0051] Specifically, the supporting process parameters of the third stage processing are: motor speed 34001r / min~36000r / min, distance between plasma gun and end of electrode rod 10~20mm, working current 650~800A, feed speed 0.9mm / s~1.2mm / s, and the median diameter of the powder obtained in this stage is about 35μm.

[0052] Specifically, the faster the electrode speed, the smaller the powder particle size; but it needs to match the heating power (related to distance and current), that is, the alloy melting rate at the end must match, and at the same time, the appropriate feed speed must be matched to maintain the stability of the process so as not to affect the powder uniformity.

[0053] The present invention also takes into account the distribution law of particle size at different stages, designs a combination of process parameters at different stages for the target particle size range, and then obtains a more ideal yield. For example, the target yield range of the present invention is 15-53 μm, and the median particle size of the first stage is 52 μm, which is close to the boundary value. This is because large-particle powders are prone to form spikes, and the powder particle size will be concentrated near the median. In addition, large-particle particles can play the role of the main frame in the subsequent printing process. Therefore, under the premise of meeting the use requirements, it should be ensured that the powder close to the upper limit of the particle size is not too little, which is conducive to the printing and preparation of subsequent products; and for the third stage, the particle size distribution of fine powders is often more divergent, and a very flat particle size distribution peak will be formed, so the particle size is set to 35 μm, which is far enough away from the lower limit of the particle size, thereby improving the yield.

[0054] Specifically, the length of the electrode rod processed in the first stage is L1, the length of the electrode rod processed in the second stage is L2, and the length of the electrode rod processed in the third stage is L3, L1: L2: L3 = 2.8~3.5: 2.5~3.2: 0.8~1.2.

[0055] It is worth noting that the particle size distribution of powder for 3D printing is generally based on the counting distribution. Considering that the volume of nearly spherical powder is proportional to the cube of the diameter, the present invention first preliminarily calculates the processing length required for each section in combination with the estimated ideal normal distribution curve. Then, combined with specific experimental results and taking into account that the yield of fine powder is lower than that of coarse powder in actual implementation, the above-mentioned optimized processing length result is obtained.

[0056] Specifically, the length of the electrode rod processed in the first stage is t1, the length of the electrode rod processed in the second stage is t2, and the length of the electrode rod processed in the third stage is t3, t1: t2: t3 = 4.7-5.8: 3.1-4: 0.8-1.2. Since the difficulty of controlling the processing length and processing time of different types of equipment is different, the present invention further provides the processing time control parameters (calculated by the processing length and feed speed) on the premise of providing the specific process parameters of each stage, which reduces the difficulty of operation and is more conducive to the promotion and reproduction of technology.

[0057] Specifically, the composition of the low expansion alloy is calculated by mass percentage as follows: C: 0-0.05%, Mn: 0.2-0.6%, Si: 0-0.2%, P: 0-0.02%, S: 0-0.002%, Cu: 0.4-0.8%, Co: 3.2-4.2%, Ni: 31.5-33%, and the rest is Fe and inevitable impurities. The present invention obtains the best process matching parameters for the low expansion alloy of this composition through theoretical design and a large number of experimental adjustments and optimizations, which greatly improves the comprehensive performance of the powder.

[0058] The present invention also provides a low expansion alloy powder for 3D printing, the alloy powder is prepared by the preparation method; the alloy powder has a particle size range of 15 μm to 53 μm, a normal distribution kurtosis coefficient ≤3, a sphericity rate ≥99%, a powder hollow rate ≤0.4%, an oxygen content ≤60 ppm, and a Hall flow rate ≥16S·(50g) -1 .

[0059] Specifically, the alloy powder provided by the present invention can be used for 3D printing to prepare related products. For example, a possible 3D printing process is as follows:

[0060] Import the 3D design of the part into the SLM printing equipment, put the low expansion alloy powder into the selective laser melting device, set the process parameters, and then print.

[0061] Specifically, the printing parameters of the low expansion alloy powder are scanning speed of 800-1000 mm / s, line spacing of 0.12-0.25 mm, layer thickness of 20-30 μm, output power of 200-240 W, and low expansion alloy components are prepared according to the three-dimensional design drawing.

[0062] Specifically, the linear expansion coefficient of the low expansion alloy component prepared by laser additive manufacturing (i.e., 3D printing) in the horizontal and vertical directions at -60 to 100°C is ≤0.8×10 -6 / ℃.

[0063] Examples and Comparative Examples

[0064] The present invention adopts the following mass compositions: C: 0.015%, Mn: 0.36%, Si: 0.12%, P: 0.005%, S: 0.001%, Cu: 0.6%, Co: 3.6%, Ni: 32.5%, and the rest is Fe and inevitable impurities for powder preparation and subsequent performance testing.

[0065] The electrode rod is 200 mm long, 30 mm in diameter, and has a surface roughness of less than 3 μm (about 2.8 μm). To avoid differences in powder quality due to different electrode rod materials, all embodiments and comparative examples are processed using the same electrode rod, and the single consumption length does not exceed 10 mm.

[0066] Pre-starting step: fill with argon protective gas, the pressure is 0.10MPa. The motor speed is gradually increased from 0r / min to 12000r / min, and it runs stably for 30s. The speed is increased to 28000r / min and keeps running stably for 2min. The subsequent specific preparation process and parameters are shown in Table 1:

[0067] Table 1 Summary of process parameters of various embodiments and comparative examples

[0068]

[0069]

[0070] The alloy powder was collected and vibrated and sieved, the mesh size of the sieve was 200-800 mesh, and the sieving time was 20 min. The performance parameters of the powders of each embodiment and comparative example are shown in Table 2:

[0071] Table 2 Performance parameters of powders in various embodiments and comparative examples

[0072] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 15~53μm yield, % 48.7 50.1 47.6 46.3 33.4 43.2 Sphericity, % ＞99 ＞99 ＞99 ＞99 97 94 Hollow rate, % 0.31 0.38 0.27 0.41 0.37 0.6 Oxygen content, ppm 55 57 59 65 61 63 Kurtosis 2.7 2.4 2.5 9 2.6 — <![CDATA[Hall flow rate, S·(50 g) -1 > 16.31 16.42 16.59 7.82 13.42 14.56

[0073] The powder yield of each embodiment is ≥45%, and can reach up to 50%, the sphericity rate is greater than 99%, the hollow rate is ≤0.4%, the oxygen content is ≤80ppm, the kurtosis coefficient is <3, and the Hall flow rate is >16S·50g -1 .

[0074] Among them, since Comparative Example 1 does not adopt the three-stage electrode speed acceleration process, although the indicators such as sphericity and hollowness are similar to those of the embodiment, the kurtosis coefficient is significantly enlarged, resulting in a significant decrease in powder fluidity, which is not conducive to subsequent 3D printing;

[0075] In Comparative Example 2, since the electrode rotation speed exceeded the limit range, the particle size of some powders exceeded the limit range of 15 to 53 μm, especially the coarse powder exceeded the upper limit of the particle size range, resulting in a significant decrease in yield, and the sphericity rate was affected due to the poor matching of the rotation speed and other parameters;

[0076] In Comparative Example 3, due to poor coordination of parameters in each step, the sphericity of the powder decreased, and because the processing time was not operated according to the recommended practice, a normally distributed particle size distribution could not be formed, especially there was less powder close to the upper limit of the particle size, and the final distribution was similar to a bimodal powder distribution. The powder fluidity was reduced compared to that of the embodiment, and would have an adverse effect on the subsequent 3D printing effect.

[0077] The low expansion alloy powders of each embodiment and comparative example were placed in a selective laser melting device, and the process parameters were set to a scanning speed of 900 mm / s, a line spacing of 0.12 mm, a layer thickness of 20 μm, and an output power of 200 W to prepare low expansion alloy components according to the three-dimensional design drawing.

[0078] During the printing process of Examples 1 to 3, the metal powder is sprayed evenly, the flow dispersion is good, and the obtained component surface is fine and has no structural defects; the metal powder flow of the component corresponding to Comparative Example 1 is poor, the forming speed is slow, and the component has a certain degree of distortion and twisting; the component quality of Comparative Example 2 is close to that of the embodiment, but due to the slightly lower sphericity and fluidity, the surface quality of the component is slightly rough; the component of Comparative Example 3 has less large-particle powder, the component forming effect is affected, there are tiny structural defects (fine cracks), and the component quality is worse than Comparative Example 1 but not as good as Comparative Example 2.

[0079] In summary, the preparation method of low expansion alloy powder for 3D printing provided by the present invention is suitable for the manufacture of low expansion alloy powder, the alloy powder yield with a particle size range of 15 μm to 53 μm is ≥45%, the normal distribution kurtosis coefficient of the powder particle size is ≤3, the sphericity rate is ≥99%, the powder hollow rate is ≤0.4%, the oxygen content is ≤60ppm, and the Hall flow rate is ≥16S·(50g) -1 , with excellent comprehensive performance.

[0080] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing low expansion alloy powder for 3D printing, characterized in that: The specific steps include: S1: Prepare low expansion alloy rods according to preset formula and through "melting + machining" process to obtain electrode rods for processing; S2: Load the electrode rod into the plasma rotating electrode atomizing powder making equipment, fill it with inert gas, and process the electrode rod using the process of pre-starting + three-stage step-by-step increase of the motor speed. After the processing is completed, the coarse alloy powder product is collected; S3: Screening the coarse powder product to select alloy powder with a particle size of 15 μm to 53 μm and conducting quality inspection on the alloy powder.

2. The preparation method according to claim 1, characterized in that: In the pre-starting step described in step S2, the motor speed is gradually increased from 0 r / min to 12000 r / min. After stable operation for not less than 30 seconds, the speed is increased to 28000 r / min and maintained stable operation for not less than 2 minutes.

3. The preparation method according to claim 1, characterized in that: The motor speed corresponding to the three-stage process of gradually increasing the motor speed is: the first stage: 28000-30000r / min, the second stage: 30001r / min-34000r / min, and the third stage 34001r / min-36000r / min.

4. The preparation method according to claim 3, characterized in that: The supporting process parameters for the first stage of processing are: motor speed 28000-30000r / min, distance between plasma gun and end of electrode rod 20-30mm, working current 400-550A, feed speed 0.5mm / s-0.8mm / s.

5. The preparation method according to claim 3, characterized in that: The supporting process parameters for the second stage processing are: motor speed 30001r / min~34000r / min, distance between plasma gun and end of electrode rod 15~25mm, working current 500~600A, feed speed 0.7mm / s~1.0mm / s.

6. The preparation method according to claim 3, characterized in that: The supporting process parameters of the third stage processing are: motor speed 34001r / min~36000r / min, distance between plasma gun and end of electrode rod 10~20mm, working current 650~800A, feed speed 0.9mm / s~1.2mm / s.

7. The preparation method according to claim 3, characterized in that: The length of the electrode rod processed in the first stage is L1, the length of the electrode rod processed in the second stage is L2, and the length of the electrode rod processed in the third stage is L3, L1: L2: L3 = 2.8-3.5: 2.5-3.2: 0.8-1.

2.

8. The preparation method according to claim 3, characterized in that: The length of the electrode rod processed in the first stage is t1, the length of the electrode rod processed in the second stage is t2, and the length of the electrode rod processed in the third stage is t3, t1: t2: t3 = 4.7-5.8: 3.1-4: 0.8-1.

2.

9. The preparation method according to claim 1, characterized in that: The composition of the low expansion alloy is calculated by mass percentage: C: 0-0.05%, Mn: 0.2-0.6%, Si: 0-0.2%, P: 0-0.02%, S: 0-0.002%, Cu: 0.4-0.8%, Co: 3.2-4.2%, Ni: 31.5-33%, and the rest is Fe and inevitable impurities.

10. A low expansion alloy powder for 3D printing, characterized in that: The alloy powder is prepared by the preparation method according to any one of claims 1 to 9; the alloy powder has a particle size range of 15 μm to 53 μm, a normal distribution kurtosis coefficient ≤ 3, a sphericity rate ≥ 99%, a powder hollow rate ≤ 0.4%, an oxygen content ≤ 60 ppm, and a Hall flow rate ≥ 16S·(50g) -1 .

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