Surface modification method and application of intermetallic compound powder

Abstract

The invention provides a surface modification method of intermetallic compound powder. The surface modification method comprises the following steps: S1) pretreating the intermetallic compound powder; s2) performing high-frequency thermal plasma treatment on the intermetallic compound powder obtained in the step S1), and cooling; and S3) carrying out jet milling treatment on the intermetallic compound powder obtained in the step S2). The invention further provides application of the intermetallic compound powder subjected to surface modification in additive manufacturing. According to the surface modification method provided by the invention, micro powder of the powder is eliminated through high-frequency thermal plasma treatment, meanwhile, the sphericity degree of the powder is improved, high-speed collision and friction are generated among the powder and the surface roughness of the powder is increased by continuously combining jet milling treatment, so that the friction force of mutual contact among the powder is increased; and the powder blowing phenomenon in the electron beam selective melting forming process is inhibited, and the intermetallic compound powder which is difficult to melt and machine and suitable for the electron beam selective melting forming additive manufacturing technology is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a surface modification method and application of intermetallic compound powder. Background Art

[0002] Intermetallic compounds have a series of advantages such as high melting point, low density, high temperature resistance and corrosion resistance. They have important application value in many fields such as aerospace, automobile manufacturing, electronic equipment, energy conversion and catalytic chemistry. However, the intrinsic brittleness of intermetallic compounds makes their preparation and processing extremely difficult.

[0003] The electron beam selective melting process can achieve powder bed preheating, significantly reducing thermal stress during the forming process, and provides a feasible technical route for the near-net forming of low-plasticity, difficult-to-process intermetallic compound components. However, during the electron beam selective melting process, when the electron beam acts on the powder bed, the powder particles are negatively charged, causing Coulomb interactions, resulting in powder scattering and powder blowing. This phenomenon may cause problems such as electron gun discharge, beam instability, and uneven powder spreading, which in turn lead to process instability and even forced processing to stop. At the same time, if there is a thick oxide film on the surface of the powder particles, since the oxide film resistance is greater than the metal powder resistance, negative charges will accumulate in the powder bed during electron beam irradiation. If the Coulomb force exceeds the powder gravity, powder blowing will inevitably occur.

[0004] Therefore, reducing the Coulomb force between powder particles and increasing the friction between powders are effective ways to avoid powder blowing. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide a surface modification method for intermetallic compound powder. The method obtains spherical powder with a thin surface oxide layer, low oxide layer resistance and high surface roughness by surface modification of the intermetallic compound powder, thereby effectively suppressing the powder blowing phenomenon in electron beam selective melting.

[0006] In view of this, the present application provides a surface modification method for intermetallic compound powder, comprising the following steps:

[0007] S1) pretreating the intermetallic compound powder;

[0008] S2) subjecting the intermetallic compound powder obtained in step S1) to high-frequency thermal plasma treatment and cooling;

[0009] S3) jet milling the intermetallic compound powder obtained in step S2).

[0010] In some specific embodiments, the intermetallic compound powder includes Nb—Si intermetallic compound powder, TiAl intermetallic compound powder, NiTi intermetallic compound powder, or Ni 3 Al intermetallic compound powder.

[0011] In some specific embodiments, in step S1), the particle size distribution of the intermetallic compound powder is 50-150 μm.

[0012] In some specific embodiments, in step S1), the pretreatment is a drying treatment, and the drying treatment temperature is 50 to 200° C. and the time is 1 to 5 hours.

[0013] In some specific embodiments, in step S2), the gas for high-frequency thermal plasma treatment is a mixed gas of argon and hydrogen, and the flow rate of the mixed gas is 0.5 to 2 L / min; and / or, during the high-frequency thermal plasma treatment, the feed rate of the intermetallic compound powder is 5 to 20 g / min.

[0014] In some specific embodiments, in step S2), the cooling is performed by rapid cooling using cooling argon gas.

[0015] In some specific embodiments, in step S2), the flow rate of the cooling argon gas is 1 to 5 L / min.

[0016] In some specific embodiments, in step S3), the gas for the jet milling process is argon; and / or the gas pressure for the jet milling process is 1 to 5 bar; and / or the gas flow rate for the jet milling process is 10 to 20 m 3 / h.

[0017] In some specific embodiments, in step S3), the powder feed rate of the jet mill treatment is 1-5 kg / h, and the time is 1-10 min.

[0018] The present application also provides the use of intermetallic compound powder prepared by the surface modification method in additive manufacturing.

[0019] The present application provides a surface modification method for intermetallic compound powder, which first pre-treats the intermetallic compound powder to remove moisture or impurities on the surface, then subjects the intermetallic compound powder to high-frequency thermal plasma treatment to micro-melt the powder surface to remove the oxide film on the powder surface and improve the sphericity of the powder; rapid cooling after the high-frequency thermal plasma treatment allows the surface to quickly solidify to solidify the surface modification effect; then, the powder with high sphericity is subjected to air flow milling treatment to cause high-speed, high-frequency collision and friction between the powders, thereby increasing the surface roughness of the spherical powder, reducing the surface thickness, and converting the oxide film on the powder surface into a conductive deformation layer, thereby increasing the bonding strength of the surface-modified intermetallic compound powder in additive manufacturing, and ultimately effectively alleviating charge accumulation and avoiding powder blowing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a SEM photograph of the initial Nb-Si intermetallic compound powder in Example 1 of the present invention;

[0021] Figure 2 This is a SEM photograph of the Nb-Si intermetallic compound powder treated with high-frequency thermal plasma in Example 1 of the present invention;

[0022] Figure 3 This is a SEM photograph of the Nb-Si intermetallic compound powder treated by jet milling in Example 1 of the present invention;

[0023] Figure 4 This is a SEM photograph of the initial TiAl intermetallic compound powder in Example 2 of the present invention;

[0024] Figure 5 This is a SEM photograph of the TiAl intermetallic compound powder subjected to jet milling in Example 2 of the present invention. DETAILED DESCRIPTION

[0025] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0026] In view of the fact that the intermetallic compound powder used in additive manufacturing in the prior art reduces the Coulomb force between powder particles, increases the friction between powders, and ultimately avoids the problem of intermetallic compound powder blowing during additive manufacturing, the present application provides a surface modification method for intermetallic compound powder, which effectively increases the surface roughness of the powder by combining a high-frequency thermal plasma treatment and then an airflow milling treatment, thereby increasing the friction between the powders in contact with each other and suppressing the "powder blowing" phenomenon during the electron beam selective melting forming process; specifically, the high-frequency thermal plasma treatment is conducive to eliminating the micro-powder of the refractory and difficult-to-process intermetallic compound powder, improving the sphericity of the powder, and then combined with the subsequent airflow milling treatment, high-speed collisions and friction occur between the powders, causing tiny pits to form on the smooth surface treated with high-frequency thermal plasma, etc., increasing the surface roughness of the powder, thereby increasing the friction between the powders in contact. Specifically, the embodiment of the present invention discloses a surface modification method for intermetallic compound powder, comprising the following steps:

[0027] S1) pretreating the intermetallic compound powder;

[0028] S2) subjecting the intermetallic compound powder obtained in step S1) to high-frequency thermal plasma treatment and cooling;

[0029] S3) jet milling the intermetallic compound powder obtained in step S2).

[0030] The intermetallic compound powder described in the present application has intrinsic brittleness and is difficult to process. Powder scattering and powder blowing phenomena will occur during the electron beam selective melting forming process of additive manufacturing, thereby affecting the smooth progress of additive manufacturing. The present application effectively solves the above problems through the above-mentioned surface modification method. In the present application, the intermetallic compound powder includes Nb-Si intermetallic compound powder, TiAl intermetallic compound powder, NiTi intermetallic compound or Ni3Al intermetallic compound; the source of the above-mentioned intermetallic compound powder is not particularly limited in this application. The particle size distribution of the intermetallic compound powder is 50 to 150 μm, specifically, the particle size distribution of the intermetallic compound powder is 53 to 150 μm, more specifically, the particle size distribution of the intermetallic compound powder is 60 to 140 μm, more specifically, the particle size distribution of the intermetallic compound powder is 80 to 120 μm.

[0031] In the surface modification method of intermetallic compound powder, the present application first pre-treats the intermetallic compound powder. The pre-treatment is specifically a drying treatment. The drying treatment employs techniques well known to those skilled in the art and is not particularly limited in the present application. In a specific embodiment, the drying treatment is performed in an oven. Specifically, the drying treatment temperature is 50-200°C for 1-5 hours; more specifically, the drying treatment temperature is 80-140°C for 1-2 hours. The pre-treatment removes moisture or other impurities from the surface of the intermetallic compound powder.

[0032] The present application then subjects the pretreated intermetallic compound powder to a high-frequency thermal plasma treatment. The high-frequency thermal plasma treatment is a method of generating a high-temperature, highly active plasma by exciting a gas with a high-frequency electromagnetic field. In the present application, the high-temperature, highly active plasma generated by the high-frequency thermal plasma treatment modifies the surface of the intermetallic compound powder, causing micro-melting of the powder surface, removing the oxide film on the powder surface, and improving the sphericity of the powder. In the present application, the gas used for the high-frequency thermal plasma treatment is a mixture of argon and hydrogen, with a flow rate of 0.5 to 2 L / min. Specifically, the flow rate of the mixed gas is 0.8 to 1.8 L / min, and more specifically, the flow rate of the mixed gas is 1 to 1.5 L / min. For example, the flow rate of the mixed gas in the present application is 0.6 L / min, 0.7 L / min, 0.9 L / min, 1.1 L / min, 1.2 L / min, 1.3 L / min, 1.6 L / min, 1.7 L / min, and 1.9 L / min. During this process, the feed rate of the intermetallic compound powder is 5 to 20 g / min, specifically, the feed rate of the intermetallic compound powder is 8 to 18 g / min, more specifically, the feed rate of the intermetallic compound powder is 10 to 15 g / min; for example, the feed rate of the intermetallic compound powder described in the present application is 6 g / min, 7 g / min, 9 g / min, 11 g / min, 12 g / min, 13 g / min, 14 g / min, 16 g / min, 17 g / min, and 19 g / min.

[0033] After the high-frequency thermal plasma surface treatment, the resulting powder is rapidly cooled, causing the powder surface to solidify rapidly to stabilize the surface modification effect. Argon gas is used as the cooling gas, and the cooling gas flow rate is 1 to 5 L / min, specifically, 1 to 3 L / min, and more specifically, 1.5 to 2 L / min.

[0034] According to the present invention, the cooled intermetallic compound powder is then subjected to airflow milling. The airflow milling technology causes the powder after the high-frequency thermal plasma surface treatment to undergo high-speed collision and friction, thereby increasing the roughness of the powder surface. The airflow milling process uses argon as a powder carrier gas, and the gas pressure of the airflow milling process is 1 to 5 bar. Specifically, the gas pressure of the airflow milling process is 1 to 4 bar, and more specifically, the gas pressure of the airflow milling process is 2 to 3 bar. The gas flow rate of the airflow milling process is 10 to 20 m 3 / h, specifically, the gas flow rate of the jet mill is 12 to 18m 3 / h, more specifically, the gas flow rate of the jet mill is 15-17m 3 The powder feeding rate of the jet mill treatment is 1-5 kg / h, and the time is 1-10 min; specifically, the powder feeding rate of the jet mill treatment is 1.5-4 kg / h, and the time is 2-8 min; more specifically, the powder feeding rate of the jet mill treatment is 2-3.5 kg / h, and the time is 3-7 min.

[0035] The present application also provides the use of intermetallic compound powder prepared by the above surface modification method in additive manufacturing.

[0036] The intermetallic compound powder treated with the high-frequency thermal plasma and airflow milling mentioned above can be used in additive manufacturing to avoid powder scattering and powder blowing problems, thereby ensuring the smooth progress of additive manufacturing.

[0037] The present invention provides a surface modification method for intermetallic compound powder, which uses high-frequency thermal plasma surface treatment technology to weaken the oxide film on the powder surface under a reducing atmosphere, reduce the surface resistance of the powder, and enable the electrons accumulated on the powder when the electron beam bombards the powder to be quickly discharged, thereby reducing the powder blowing phenomenon caused by the charging effect of the powder; at the same time, the high-frequency thermal plasma surface treatment technology can also greatly improve the sphericity of the powder, increase the fluidity of the powder, and ensure the stability and consistency of the additive manufacturing powder laying process; on this basis, the powder is further treated by air flow milling, so that the powder collides and rubs during high-speed movement, on the one hand, increasing the roughness of the powder surface, increasing the friction between the powders in the powder bed, and reducing the occurrence of powder blowing; on the other hand, the mechanical deformation caused by the powder collision can also convert the oxide film on the powder surface into a conductive deformation layer, which will effectively alleviate the charge accumulation and avoid the powder blowing phenomenon.

[0038] Therefore, the present invention combines high-frequency thermal plasma treatment and air flow milling technology to modify the surface of intermetallic compound powder for additive manufacturing, obtaining spherical powder with a thin surface oxide layer, low oxide layer resistance and high surface roughness, providing a raw material optimization technology for suppressing the powder blowing phenomenon in electron beam selective melting.

[0039] In order to further understand the present invention, the surface modification method and application of the intermetallic compound powder provided by the present invention are described in detail below with reference to the examples. The protection scope of the present invention is not limited by the following examples.

[0040] Example 1

[0041] (1) Powder pretreatment: Nb-Si intermetallic compound powder with a particle size distribution in the range of 53 to 150 μm was used as raw material. The Nb-Si intermetallic compound powder was dried in an oven at a drying temperature of 80°C for 2 h.

[0042] (2) High-frequency thermal plasma surface treatment: The powder pretreated in step (1) is placed in a high-frequency thermal plasma treatment device for high-frequency thermal plasma treatment. The gas used for high-frequency thermal plasma treatment is a mixed gas of argon and hydrogen. The gas flow rate is 1 L / min, and the powder feed rate is 15 g / min.

[0043] (3) Powder Cooling and Collection The powder treated with high-frequency thermal plasma was rapidly cooled using argon as the cooling gas at a gas flow rate of 1.5 L / min. The rapid cooling allowed the surface to solidify rapidly to fix the surface modification effect.

[0044] (4) Airflow milling: The cooled powder is placed in an airflow mill for airflow milling. During the airflow milling process, argon is used as the carrier gas, the gas pressure is 2 bar, and the gas flow rate is 15m 3 / h, the powder feeding rate is 1.5kg / h, and the processing time is 2min. During this process, the powders collide and rub against each other at high speed, which increases the roughness of the powder surface.

[0045] (5) Powder collection.

[0046] Figure 1 is a SEM photograph of the initial Nb-Si intermetallic compound powder in this embodiment, Figure 2 is a SEM photograph of the Nb-Si intermetallic compound powder treated with high-frequency thermal plasma in this embodiment. Figure 3 is a SEM photograph of the Nb-Si intermetallic compound powder after the jet milling process in this embodiment; Figure 2 It can be seen that the sphericity of the Nb-Si intermetallic compound powder is improved after high-frequency thermal plasma treatment. Figure 3 It can be seen that the surface roughness of the Nb—Si intermetallic compound powder increases after the jet milling treatment.

[0047] Example 2

[0048] (1) Powder pretreatment: TiAl intermetallic compound powder with a particle size distribution in the range of 53 to 150 μm was used as raw material. The TiAl intermetallic compound powder was dried in an oven at a drying temperature of 80° C. for 2 h.

[0049] (2) High-frequency thermal plasma surface treatment: The powder pretreated in step (1) is placed in a high-frequency thermal plasma treatment device for high-frequency thermal plasma surface treatment. The gas used for high-frequency thermal plasma treatment is a mixed gas of argon and hydrogen, the gas flow rate is 2 L / min, and the powder feed rate is 8 g / min;

[0050] (3) Powder Cooling and Collection The powder treated with high-frequency thermal plasma was rapidly cooled using argon as the cooling gas at a gas flow rate of 1.5 L / min. The rapid cooling allowed the surface to solidify rapidly to fix the surface modification effect.

[0051] (4) Airflow milling: The cooled powder is placed in an airflow mill for airflow milling. During the airflow milling process, argon is used as the carrier gas, the gas pressure is 2 bar, and the gas flow rate is 15m 3 / h, the powder feeding rate is 1.5kg / h, and the processing time is 2min. The powders collide and rub against each other at high speed, which increases the roughness of the powder surface.

[0052] (5) Powder collection.

[0053] Figure 4 is the SEM photo of the initial TiAl intermetallic compound powder of this embodiment, Figure 5 : is a SEM photograph of the TiAl intermetallic compound powder after the air flow milling treatment in this embodiment; it can be seen from the figure that the surface roughness of the TiAl intermetallic compound powder is increased after the high-frequency thermal plasma treatment and air flow milling treatment.

[0054] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0055] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for surface modification of an intermetallic compound powder, comprising the following steps: S1) pretreating the intermetallic compound powder; S2) subjecting the intermetallic compound powder obtained in step S1) to high-frequency thermal plasma treatment and cooling; S3) jet milling the intermetallic compound powder obtained in step S2).

2. The surface modification method according to claim 1, characterized in that The intermetallic compound powder includes Nb-Si intermetallic compound powder, TiAl intermetallic compound powder, NiTi intermetallic compound powder or Ni3Al intermetallic compound powder.

3. The surface modification method according to claim 1, wherein In step S1), the particle size distribution of the intermetallic compound powder is 50 to 150 μm.

4. The surface modification method according to claim 1, wherein In step S1), the pretreatment is a drying treatment, and the drying treatment temperature is 50 to 200° C. and the time is 1 to 5 hours.

5. The surface modification method according to claim 1, wherein In step S2), the gas for high-frequency thermal plasma treatment is a mixed gas of argon and hydrogen, and the flow rate of the mixed gas is 0.5 to 2 L / min; and / or, during the high-frequency thermal plasma treatment, the feed rate of the intermetallic compound powder is 5 to 20 g / min.

6. The surface modification method according to claim 5, characterized in that In step S2), the cooling is performed by rapid cooling with cooling argon gas.

7. The surface modification method according to claim 6, characterized in that In step S2), the flow rate of the cooling argon gas is 1 to 5 L / min.

8. The surface modification method according to claim 1 or 6, characterized in that: In step S3), the gas for the jet milling process is argon; and / or the gas pressure for the jet milling process is 1 to 5 bar; and / or the gas flow rate for the jet milling process is 10 to 20 m 3 / h.

9. The surface modification method according to claim 8, characterized in that In step S3), the powder feeding rate of the jet mill treatment is 1 to 5 kg / h, and the time is 1 to 10 minutes.

10. Use of the intermetallic compound powder prepared by the surface modification method according to any one of claims 1 to 9 in additive manufacturing.

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