Ultrafine grain thermal spray powder and method of making same

Abstract

The application belongs to the technical field of nano metal ceramic composite powder preparation, and particularly relates to a superfine particle size thermal spraying powder and a preparation method thereof, wherein the preparation method of the superfine particle size thermal spraying powder comprises the following steps: S1, obtaining first carbonizing material and second carbonizing material, the first carbonizing material comprising dichromic anhydride and carbon black, and the second carbonizing material comprising nano tungsten powder and carbon black; S2, mixing the first carbonizing material and the second carbonizing material, and then performing high-temperature carbonization to obtain tungsten-chromium composite powder; S3, mixing the tungsten-chromium composite powder, cobalt powder, deionized water and a forming agent, and then performing ball milling, spray drying granulation, sintering and crushing to obtain superfine nano-crystal thermal spraying powder; in the process of preparing the tungsten-chromium composite powder, the addition of chromium can effectively inhibit the growth of tungsten carbide in the carbonization process of the nano tungsten powder, and the tungsten carbide can also inhibit the growth of chromium / carbonized chromium, and they inhibit each other, so that the preparation of the superfine particle size powder is realized.

Description

Technical Field

[0001] This invention belongs to the field of nano-metal-ceramic composite powder preparation technology, specifically an ultrafine-grained thermal spraying powder and its preparation method. Background Technology

[0002] In industries such as machinery manufacturing, petrochemicals, aerospace, and steel metallurgy, there are many critical and important internally bored components, such as engine cylinder blocks, gas turbine housings, hydraulic cylinders, and various pumping pipelines. These components often operate under harsh conditions including extreme temperatures, corrosive media, and high specific loads, making them prone to severe wear and corrosion failure. Internal bore thermal spraying technology is an important method for preparing coatings on the inner walls of parts, enabling the strengthening and modification of internally bored components or the remanufacturing of scrapped parts. Internal bore spraying powder differs significantly from conventional supersonic thermal spraying powder, requiring shorter spraying distances and smaller spaces, necessitating ultrafine-grained spraying powder as the processing raw material. However, ultrafine-grained spraying powder requires addressing the following technical challenges: Since the production of ultrafine agglomerated particles is necessary, the tungsten carbide used as the raw material must consist of some or all of tungsten carbide particles with a particle size below 200 nm to form powder particles with fine particle size distribution, small grain size, and good surface sphericity. Existing chromium powder and chromium carbide have coarse particle sizes, making them unsuitable for ultrafine powder agglomeration and granulation. This results in the inability of the prepared thermal spray powder to achieve the required particle size distribution within the ranges of 2~10μm, 2~15μm, 2~20μm, 5~15μm, and 5~20μm, or the corresponding particle size proportions are extremely low, leading to low yield and high cost. Furthermore, there are issues with uneven chromium distribution and poor powder morphology. This uneven distribution in the coating also results in poor corrosion resistance. Because the slurry mixture has a certain viscosity, it needs to be atomized, dispersed, dried, and shrunk into spherical shapes in a very short time to achieve the required particle size distribution range for the product. Therefore, there are also issues related to controlling the degree of sintering alloying, the growth of ultrafine powder grain size, and the agglomeration and adhesion between particles after sintering. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for preparing ultrafine-grained thermal spray powder, comprising the following steps:

[0004] S1. Obtain a first carbon material and a second carbon material, wherein the first carbon material includes nano-tungsten powder and carbon black, and the second carbon material includes chromium trioxide and carbon black;

[0005] S2. The first carbon material and the second carbon material are mixed and then subjected to high-temperature carbonization to obtain tungsten-chromium composite powder, wherein the tungsten-chromium composite powder includes tungsten carbide, chromium carbide and chromium.

[0006] S3. The tungsten-chromium composite powder, cobalt powder, deionized water and molding agent are mixed and then ball-milled, spray-dried and granulated, sintered and crushed to obtain ultrafine thermal spray powder.

[0007] In step S1, the mass ratio of nano-tungsten powder to carbon black in the first carbon feedstock is (15.1~15.5):1, the mass ratio of chromium trioxide to carbon black in the second carbon feedstock is (2.85~3.1):1, and the specific surface area of ​​the nano-tungsten powder in the first carbon feedstock is 4~8 m². 2 / g, the chromium trioxide in the second carbon feedstock has a Fisher particle size of 0.5~1.5μm.

[0008] In step S2, the mixing process specifically involves adding the first carbon material and the second carbon material to a mixer, wherein the mass ratio of the first carbon material to the second carbon material is (9.6~12.4):1, mixing in a protective gas atmosphere for 70~110 minutes, and discharging after cooling to room temperature to obtain a carbon mixture.

[0009] In step S2, the high-temperature carbonization specifically involves: loading the carbon mixture into a double-layer graphite boat, then placing it in a carbon tube furnace, and continuously carbonizing it at high temperature in a protective gas atmosphere to obtain the tungsten-chromium composite powder.

[0010] In step S2, the high-temperature carbonization time is 200-280 minutes, the high-temperature carbonization temperature is 1150-1250°C, and the specific surface area of ​​the tungsten-chromium composite powder is 4-5.5 m². 2 / g.

[0011] In step S3, the molding agent is polyethylene glycol, and the ball milling specifically involves adding 89.0wt%~91.0wt% of the tungsten-chromium composite powder, 9.0wt%~11.0wt% of cobalt powder, and 45wt%~50wt% of deionized water and 0.8wt%~1.5wt% of polyethylene glycol, equivalent to the sum of the masses of the tungsten-chromium composite powder and the cobalt powder, to a ball milling device, and then ball milling for 30~40 hours to obtain a ball milling slurry.

[0012] In step S3, the spray drying granulation specifically involves using a centrifugal spray drying device to dry and granulate the ball mill slurry to obtain a spherical mixture. The compressed gas pressure of the centrifugal spray drying device is 1~1.5MPa, and the feed rate is 3.0~4.5kg / min.

[0013] In step S3, the sintering specifically involves: loading the spherical mixture into a multi-layer graphite boat, and then placing it in a molybdenum wire furnace. The molybdenum wire furnace is continuously equipped with three heating zones of equal length along its length. Continuous sintering is carried out in a protective gas atmosphere to obtain the sintered product. The sintering time for each heating zone is 53-67 minutes, the sintering temperature of the first heating zone is 1050-1100℃, and the sintering temperatures of the second and third heating zones are 1100-1180℃.

[0014] In step S3, the crushing specifically involves: mechanically crushing the sintered product, and then using ultrasonic sieving and airflow classification to obtain the ultrafine-grained thermal spray powder; wherein the particle size distribution of the ultrafine-grained thermal spray powder includes a first size and a second size, the first size being 2~10μm, accounting for 28wt%~37wt%, and having a loose packing density of 4.0~4.5g / cm³. 3 The second specification has a particle size of 5~20μm, a content of 52wt%~60wt%, and a loose packing density of 4.8~5.5g / cm³. 3 ;

[0015] Furthermore, various particle size combinations can be prepared through airflow classification: for example, 2~10μm, 2~15μm, 2~20μm, 5~15μm, 5~20μm, etc., and can be classified and batch-processed according to different particle sizes as needed.

[0016] The present invention also provides an ultrafine-grained thermal spraying powder, which is prepared by the above-described method for preparing ultrafine-grained thermal spraying powder, and the ultrafine-grained thermal spraying powder is an ultrafine nanocrystalline WC86-Co10Cr4 thermal spraying powder.

[0017] In the tungsten-chromium composite powder prepared by this invention, the tungsten carbide, chromium carbide, and chromium have small particle sizes and uniform particle size distribution, which is beneficial to the uniform distribution of chromium, surface smoothness, sphericity, uniformity, and other comprehensive properties of the subsequent sprayed powder products. In the process of preparing the tungsten-chromium composite powder by this invention, the addition of chromium can effectively inhibit the growth of tungsten carbide during the carbonization of nano-tungsten powder. At the same time, tungsten carbide can also inhibit the growth of chromium / chromium carbide. They inhibit each other, thereby realizing the preparation of ultrafine particle powder and greatly improving the process stability. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a SEM image of the tungsten-chromium composite powder prepared in Example 1 of the present invention;

[0020] Figure 2 This is a SEM image of the ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder prepared in Example 1 of this invention;

[0021] Figure 3 This is a SEM image of the tungsten-chromium composite powder prepared in Example 2 of the present invention;

[0022] Figure 4 This is a SEM image of the ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder prepared in Example 2 of the present invention;

[0023] Figure 5 This is a SEM image of the tungsten carbide powder prepared in Comparative Example 1 of the present invention;

[0024] Figure 6 This is a SEM image of the thermal spray powder prepared in Comparative Example 1 of the present invention.

[0025] Figure 7 This is a SEM image of the thermal spray powder prepared in Comparative Example 2 of the present invention;

[0026] Figure 8 This is a SEM image of the thermal spray powder prepared in Comparative Example 3 of the present invention.

[0027] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0028] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention provides a method for preparing ultrafine-grained thermal spray powder, comprising the following steps:

[0030] S1. Obtain a first carbon material and a second carbon material, wherein the first carbon material includes nano-tungsten powder and carbon black, and the second carbon material includes chromium trioxide and carbon black.

[0031] The specific surface area of ​​the nano-tungsten powder used in this invention is 4~8m². 2 / g, if the specific surface area of ​​the nano-tungsten powder is too large, it is prone to spontaneous combustion; if the specific surface area of ​​the nano-tungsten powder is too small, it is impossible to prepare thermal spray powder that meets the requirements of this invention.

[0032] S2. The first carbon material and the second carbon material are mixed and then subjected to high-temperature carbonization to obtain tungsten-chromium composite powder, wherein the tungsten-chromium composite powder includes tungsten carbide, chromium carbide and chromium.

[0033] This invention utilizes nano-tungsten powder and chromium trioxide to form carbon, allowing the nano-tungsten powder and chromium trioxide to be simultaneously reduced and carbonized under high-temperature conditions. Due to the difference in their crystal structures, they can mutually inhibit grain growth. Specifically, the three raw materials—nano-tungsten powder, chromium trioxide, and carbon black—are first mixed in a carbon mixing device, and then carbonized at high temperature in a protective atmosphere to obtain tungsten-chromium composite powder (a composite powder composed of tungsten carbide, chromium carbide, and chromium). This invention fully utilizes the mutual inhibition effect between tungsten carbide and chromium, ensuring uniform particle size distribution of the raw materials and complete reaction of the tungsten powder. It achieves low-cost, industrially scalable preparation of nano-tungsten carbide, chromium carbide, and chromium composite powder (tungsten-chromium composite powder), providing raw materials for the preparation of WC86-Co10Cr4 thermal spray powder for ultra-fine internal pore spraying.

[0034] The equations for the multiple reactions that occur during high-temperature carbonization are as follows:

[0035] W+C→WC

[0036] 3Cr2O3 + 13C → 2Cr3C2 + 9CO

[0037] 5Cr2O3 + 27Cr3C2 → 13Cr7C3 + 15CO

[0038] Cr₂O₃ + 3C → 2Cr + 3CO

[0039] S3. The tungsten-chromium composite powder, cobalt powder, deionized water and polyethylene glycol are mixed, ball-milled, spray-dried and granulated, sintered and crushed to obtain ultrafine thermal spray powder.

[0040] In the spray drying granulation process of this invention, a centrifugal spray drying device is used for two-fluid or three-fluid atomization. High-pressure, high-speed compressed air is used to atomize the droplets of the slurry to obtain a spherical mixture (an agglomerated mixture with ultrafine particle size distribution). This mixture is then placed in a graphite boat and sintered in a molybdenum wire furnace under controlled temperature and time in a protective atmosphere to obtain a sintered product. After crushing, an ultrafine particle size thermal spray powder (ultrafine particle size distribution nanocrystalline WC86-Co10Cr4 thermal spray powder) is obtained.

[0041] Furthermore, after crushing, various particle size combinations can be prepared through airflow classification: for example, 2~10μm, 2~15μm, 2~20μm, 5~15μm, 5~20 micrometers, etc., which can be graded and batch-processed according to different particle sizes as needed.

[0042] Furthermore, the ultrafine thermal spray powder has two particle sizes: a first size and a second size. The first size has a particle size of 2~10μm, accounting for 28wt%~37wt%, and a bulk density of 4.0~4.5g / cm³. 3 The second specification has a particle size of 5~20μm, a proportion of 52wt%~60wt%, and a loose packing density of 4.8~5.5g / cm³. 3 The remainder consists of coarser particles that cannot be broken down and dispersed.

[0043] Example 1

[0044] The first carbon feedstock was prepared by mixing 807.3 kg of nano-tungsten powder and 53.3 kg of carbon black. The specific surface area of ​​the nano-tungsten powder was 4.2 m². 2 / g, to obtain 58.5kg of chromium trioxide and 19.0kg of carbon black, and mix them to obtain the second carbon feedstock. The chromium trioxide has a Fisher particle size of 1.2μm.

[0045] The first and second carbon feedstocks were added to the plow mixer for carbon mixing. Under nitrogen protection, the mixture was mixed for 90 minutes, cooled to room temperature, and then discharged to obtain a carbon mixture. This mixture was then placed in a double-layer graphite boat and placed in a carbon tube furnace. The furnace was heated for 240 minutes at 1200℃ under a nitrogen atmosphere for continuous high-temperature carbonization to obtain tungsten-chromium composite powder. The specific surface area of ​​the tungsten-chromium composite powder was determined to be 5.0 m². 2 / g; see also Figure 1 , Figure 1 The image shows a SEM image of the tungsten-chromium composite powder prepared in Example 1, where the fine particles are nano-tungsten carbide powder.

[0046] 900.0 kg of tungsten-chromium composite powder, 100 kg of cobalt powder, 500 kg of deionized water, and 15.0 kg of polyethylene glycol were added to a ball mill and mixed. The mixture was then ball-milled for 30 hours to obtain a ball mill slurry. The slurry was then atomized using an open centrifugal spray drying tower with a compressed gas pressure of 1.0 MPa and a slurry feed rate of 4.0 kg / min. After drying, a spherical mixture was obtained.

[0047] The spherical mixture was loaded into a multi-layer graphite boat and then placed in a molybdenum wire furnace. The sintering time for each heating zone was 60 min. The sintering temperature of the first heating zone was 1100℃, and the sintering temperature of the second and third heating zones was 1150℃. Continuous sintering was carried out in a hydrogen protective atmosphere to obtain the sintered product.

[0048] The sintered product was mechanically crushed, and the ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder was obtained by ultrasonic sieving and air classification. The ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder includes a first specification and a second specification. The first specification has a particle size of 2~10μm, weighs 343kg, accounts for 34.3wt%, and has a loose bulk density of 4.1g / cm³. 3 The second specification is 5~20μm, weighs 576kg, accounts for 57.6wt%, and has a loose packing density of 4.8g / cm³. 3 The remaining part mainly consists of coarse, agglomerated material on the screen and losses from grading;

[0049] Please see Figure 2 , Figure 2 This is a SEM image of the ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder prepared in Example 1 of this invention. Figure 2 Specifically, this is a SEM image of WC86-Co10Cr4 thermal spray powder with ultrafine nanocrystalline particles of 2~10μm.

[0050] Example 2

[0051] The first carbon feedstock was prepared by mixing 807.3 kg of nano-tungsten powder and 52.1 kg of carbon black. The specific surface area of ​​the nano-tungsten powder was 4.5 m². 2 / g, to obtain 58.5kg of chromium trioxide and 19.0kg of carbon black, mix to obtain the second carbon feedstock, the chromium trioxide has a Fisher particle size of 0.6μm;

[0052] The first and second carbon feedstocks were added to the plow mixer for carbon mixing. Under nitrogen protection, the mixture was mixed for 110 minutes, cooled to room temperature, and then discharged to obtain a carbon mixture. The carbon mixture was then placed in a double-layer graphite boat and placed in a carbon tube furnace. The furnace was heated for 280 minutes at 1250°C under a nitrogen atmosphere for continuous high-temperature carbonization to obtain tungsten-chromium composite powder. The specific surface area of ​​the tungsten-chromium composite powder was determined to be 5.1 m². 2 / g; see also Figure 3 , Figure 3 This is a SEM image of the tungsten-chromium composite powder prepared in Example 2, where the fine particles are nano-tungsten carbide powder;

[0053] 895.0 kg of tungsten-chromium composite powder, 105.0 kg of cobalt powder, 500 kg of deionized water, and 15.0 kg of polyethylene glycol were added to a ball mill and mixed. The mixture was then ball-milled for 30 hours to obtain a ball mill slurry. The slurry was then atomized using an open centrifugal spray drying tower with a compressed gas pressure of 1.5 MPa and a slurry feed rate of 4.5 kg / min. After drying, a spherical mixture was obtained.

[0054] The spherical mixture was loaded into a multi-layer graphite boat and then placed in a molybdenum wire furnace. The sintering time for each heating zone was 67 min. The sintering temperature of the first heating zone was 1100℃, and the sintering temperature of the second and third heating zones was 1180℃. Continuous sintering was carried out in a hydrogen protective atmosphere to obtain the sintered product.

[0055] The sintered product was mechanically crushed, and the ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder was obtained by ultrasonic sieving and air classification. The ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder includes two particle size specifications: a first specification and a second specification. The first specification has a particle size of 2~10μm, weighs 319kg, accounts for 31.9wt%, and has a loose bulk density of 4.3g / cm³. 3 The second specification has a particle size of 5~20μm, weighs 571kg, accounts for 57.1wt%, and has a loose packing density of 5.2g / cm³. 3 The remaining portion mainly consists of coarse, agglomerated material oversizes and losses from grading; please refer to [link / reference]. Figure 4 , Figure 4 This is a SEM image of the ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder prepared in Example 2 of this invention. Figure 4 Specifically, this is a SEM image of WC86-Co10Cr4 thermal spray powder with ultrafine nanocrystalline particles of 2~10μm.

[0056] Example 3

[0057] Unlike Example 1, the first and second carbon feedstocks were added to the plow mixer for carbon mixing. Under nitrogen protection, the mixture was mixed for 70 minutes, cooled to room temperature, and then discharged to obtain a carbon mixture. This mixture was then placed in a double-layered graphite boat and placed in a carbon tube furnace. Heating was carried out at 1150°C for 200 minutes under a nitrogen atmosphere to obtain tungsten-chromium composite powder. The specific surface area of ​​the tungsten-chromium composite powder was measured to be 5.3 m². 2 / g;

[0058] The ball mill slurry was atomized using a two-fluid system with a compressed gas pressure of 1.3 MPa and a slurry feed rate of 3.0 kg / min. After drying, a spherical mixture was obtained.

[0059] The spherical mixture was loaded into a multi-layer graphite boat and then placed in a molybdenum wire furnace. The sintering time for each heating zone was 53 min. The sintering temperature of the first heating zone was 1050℃, and the sintering temperature of the second and third heating zones was 1100℃. Continuous sintering was carried out in a hydrogen protective atmosphere to obtain the sintered product.

[0060] The sintered product was mechanically crushed, and the ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder was obtained by ultrasonic sieving and air classification. The ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder comprises two particle size specifications: a first specification and a second specification. The first specification has a particle size of 2~10μm, weighs 362kg, accounts for 36.2wt%, and has a loose bulk density of 4.05g / cm³. 3 The second specification has a particle size of 5~20μm, weighs 589kg, accounts for 58.9wt%, and has a loose packing density of 4.89g / cm³. 3 The remaining portion mainly consists of coarse, agglomerated material on the screen and losses from grading.

[0061] Comparative Example 1

[0062] Unlike Example 1, 938.0 kg of nano-tungsten powder and 62.0 kg of carbon black were mixed to obtain a carbon feedstock, and the specific surface area of ​​the nano-tungsten powder was 4.1 m². 2 / g; Tungsten carbide powder was obtained by continuous high-temperature carbonization in a nitrogen atmosphere, and the specific surface area of ​​the tungsten carbide powder was measured to be 2.1m². 2 / g;

[0063] Add 860.0 kg of tungsten carbide powder, 100 kg of cobalt powder, 40 kg of chromium powder (Fairwood particle size of 4 μm), 500 kg of deionized water, and 15.0 kg of polyethylene glycol to the ball mill and mix them.

[0064] Please see Figure 5 , Figure 5The image shows a SEM image of the tungsten carbide powder prepared in Comparative Example 1 of this invention. No chromium was added, and the tungsten carbide crystals showed significant growth and larger particle size.

[0065] The thermal spray powder includes two particle size specifications: a first specification and a second specification. The first specification has a particle size of 2~10μm, weighs 205kg, accounts for 20.5wt%, and has a loose bulk density of 4.2g / cm³. 3 The second specification is 5~20μm, 510kg, accounting for 51.0wt%, with a loose packing density of 4.4g / cm³. 3 The remaining part mainly consists of coarse, agglomerated material on the screen and losses from grading;

[0066] Please see Figure 6 , Figure 6 The image shows a SEM image of the thermal spray powder prepared in Comparative Example 1 of this invention. The powder exhibits uneven particle size and component segregation.

[0067] Comparative Example 2

[0068] Unlike Example 1, there was no carbon preparation process. Instead, 860.0 kg of tungsten carbide powder (Fishley particle size of 2.0 μm), 100 kg of cobalt powder, 40 kg of chromium powder (Fishley particle size of 4 μm), 500 kg of deionized water, and 15.0 kg of polyethylene glycol were directly added to the ball mill for mixing.

[0069] The thermal spray powder includes two particle size specifications: a first specification and a second specification. The first specification has a particle size of 2~10μm, weighs 150kg, accounts for 15wt%, and has a loose bulk density of 3.9g / cm³. 3 The second specification is 5~20μm, 450kg, accounting for 45wt%, with a loose packing density of 4.3g / cm³. 3 The remaining part mainly consists of coarse, agglomerated material on the screen and losses from grading;

[0070] Please see Figure 7 , Figure 7 The image shows an SEM image of the thermal spray powder prepared in Comparative Example 2 of this invention, which has uneven particle size and poor sphericity.

[0071] Comparative Example 3

[0072] Unlike Example 1, there was no carbon preparation process. Instead, 860.0 kg of tungsten carbide powder (Fishler particle size of 3 μm), 100 kg of cobalt powder, 40 kg of chromium powder (Fishler particle size of 4 μm), 500 kg of deionized water, and 15.0 kg of polyethylene glycol were directly added to the ball mill for mixing.

[0073] The thermal spray powder includes two particle size specifications: a first specification and a second specification. The first specification has a particle size of 2~10μm, a weight of 100kg, a proportion of 10wt%, and a bulk density of 3.7g / cm³. 3 The second specification is 5~20μm, 300kg, accounting for 30wt%, with a loose packing density of 4.15g / cm³. 3 The remaining part mainly consists of coarse, agglomerated material on the screen and losses from grading;

[0074] Please see Figure 8 , Figure 8 The image shows a SEM image of the thermal spray powder prepared in Comparative Example 3 of this invention. The powder exhibits uneven particle size, poor sphericity, and a large number of irregularly shaped particles.

[0075] Comparative Example 4

[0076] Unlike Example 1, a centrifugal spray drying device was used to centrifuge the ball mill slurry at a speed of 20,000 rpm and a feed rate of 3.0 kg / min. After drying, a spherical mixture was obtained.

[0077] The ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder includes two particle size specifications: a first specification and a second specification. The first specification has a particle size of 2~10μm, weighs 262kg, accounts for 26.2wt%, and has a loose packing density of 4.0g / cm³. 3 The second specification is 5~20μm, weighs 596kg, accounts for 59.6wt%, and has a loose packing density of 4.7g / cm³. 3 The remaining portion mainly consists of coarse, agglomerated material on the screen and losses from grading.

[0078] Comparative Example 5

[0079] Unlike Example 1, a second carbon feedstock was prepared by mixing 40 kg of chromium powder and 0.2 kg of carbon black, with the chromium powder having a Fisher particle size of 3 μm.

[0080] The ultrafine nanocrystalline WC86-Co10Cr4 thermal spray powder includes two particle size specifications: specification 1 and specification 2. Specification 1 has a particle size of 2~10μm, weighs 185kg, accounts for 18.5wt%, and has a bulk density of 3.9g / cm³. 3 The second specification is 5~20μm, 610kg, accounting for 61wt%, with a loose packing density of 4.6g / cm³. 3 The remaining portion mainly consists of coarse, agglomerated material on the screen and losses from grading.

[0081] The thermal spray powders prepared in some of the embodiments and comparative examples were used to prepare coatings on 45# carbon steel substrates by laser cladding. The coating deposition rate was calculated and the hardness, porosity, wear resistance and corrosion resistance were tested. The results are shown in Table 1.

[0082] Table 1

[0083]

[0084] The standards used in each test are as follows:

[0085] Spray deposition rate: GB / T 31564-2015 "Determination of thermal spray deposition efficiency";

[0086] Vickers hardness of coating: HB 5486-1991 "Test Method for Hardness of Thermal Spray Coatings";

[0087] Coating porosity: GB / Z 45463-2025 "Determination of porosity of thermal spray coatings";

[0088] Wear loss weight: ASTM G105-20 "Standard Test Method for Wear Test of Wet Sand / Rubber Wheel".

[0089] In the tungsten-chromium composite powder prepared by this invention, the tungsten carbide, chromium carbide, and chromium have small particle sizes and uniform particle size distribution, which is beneficial to the uniform distribution of chromium, surface smoothness, sphericity, uniformity, and other comprehensive properties of the subsequent sprayed powder products. In the process of preparing the tungsten-chromium composite powder by this invention, the addition of chromium can effectively inhibit the growth of tungsten carbide during the carbonization of nano-tungsten powder. At the same time, tungsten carbide can also inhibit the growth of chromium / chromium carbide. They inhibit each other, thereby realizing the preparation of ultrafine particle powder and greatly improving the process stability.

[0090] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for producing an ultrafine-grained thermal spray powder, characterized by, The method comprises the following steps: S1, obtaining first carbon material and second carbon material, the first carbon material comprising nano-tungsten powder and carbon black, and the second carbon material comprising chromium trioxide and carbon black; S2, mixing the first carbon material and the second carbon material, and then performing high-temperature carbonization to obtain tungsten-chromium composite powder, the tungsten-chromium composite powder comprising tungsten carbide, chromium carbide and chromium; S3, mixing the tungsten-chromium composite powder, cobalt powder, deionized water and a forming agent, and then performing ball milling, spray drying granulation, sintering and crushing to obtain ultra-fine particle thermal spraying powder; In the step S1, the mass ratio of the nano-tungsten powder and the carbon black in the first carbon material is (15.1-15.5):1, and the mass ratio of the chromium trioxide and the carbon black in the second carbon material is (2.85-3.1):1; In the step S2, the mass ratio of the first carbon material and the second carbon material is (9.6-12.4):

1.

2. A method of producing an ultrafine-grained thermal spray powder according to claim 1, characterized in that, The specific surface area of the nano-tungsten powder in the first carbon material is 4-8 m 2 / g, and the Fisher particle size of the chromium sesquioxide in the second carbon material is 0.5-1.5 μm.

3. A method of producing an ultrafine-grained thermal spray powder according to claim 1, characterized in that, In the step S2, the mixing specifically comprises: adding the first carbon material and the second carbon material into a mixer, mixing for 70-110 min in a protective gas atmosphere, and then discharging after cooling to room temperature to obtain a carbonized mixture.

4. A method of producing an ultrafine-grained thermal spray powder according to claim 3, characterized in that, In the step S2, the high-temperature carbonization specifically comprises: loading the carbonized mixture into a double-layer graphite boat, and then placing the double-layer graphite boat into a carbon tube furnace to perform continuous high-temperature carbonization in a protective gas atmosphere to obtain the tungsten-chromium composite powder.

5. A method of producing an ultrafine-grained thermal spray powder according to claim 4, characterized in that, The time of the high-temperature carbonization in the step S2 is 200-280 min, the temperature of the high-temperature carbonization is 1150-1250 ℃, and the specific surface area of the tungsten-chromium composite powder is 4-5.5 m 2 / g.

6. The method of claim 1, wherein the ultrafine grain thermally sprayed powder is prepared by the steps of: In the step S3, the forming agent is polyethylene glycol, and the ball milling specifically comprises: adding 89.0wt%-91.0wt% of the tungsten-chromium composite powder, 9.0wt%-11.0wt% of cobalt powder, and deionized water and polyethylene glycol corresponding to 45wt%-50wt% of the sum of the mass of the tungsten-chromium composite powder and the cobalt powder and 0.8wt%-1.5wt% of polyethylene glycol into a ball milling device, and performing ball milling for 30-40 h to obtain a ball milling slurry.

7. A method of producing an ultrafine-grained thermal spray powder according to claim 6, characterized in that, In the step S3, the spray drying granulation specifically comprises: drying and granulating the ball milling slurry by using a centrifugal spray drying device to obtain a spherical mixture, wherein the pressure of compressed gas of the centrifugal spray drying device is 1-1.5 MPa, and the feeding amount is 3.0-4.5 kg / min.

8. A method of producing an ultrafine-grained thermal spray powder according to claim 7, characterized in that, In the step S3, the sintering specifically comprises: loading the spherical mixture into a multi-layer graphite boat, and then placing the multi-layer graphite boat into a molybdenum wire furnace, the molybdenum wire furnace being provided with a first heating zone, a second heating zone and a third heating zone with equal lengths along the length direction, and performing continuous sintering in a protective gas atmosphere to obtain a sintered product; wherein the sintering time of each heating zone is 53-67 min, the sintering temperature of the first heating zone is 1050-1100℃, and the sintering temperature of the second heating zone and the third heating zone is 1100-1180℃.

9. A method of producing an ultrafine-grained thermal spray powder according to claim 8, characterized in that, The crushing in the step S3 is specifically: crushing the sintered product by a mechanical method, and obtaining the ultra-fine particle size thermal spraying powder by ultrasonic screening and airflow classification; wherein, the particle size specification of the ultra-fine particle size thermal spraying powder includes a first specification and a second specification, the first specification is 2-10 microns, the proportion is 28wt%-37wt%, the loose bulk density is 4.0-4.5 g / cm 3 , and the second specification is 5-20 microns, the proportion is 52wt%-60wt%, the loose bulk density is 4.8-5.5 g / cm 3 .

10. An ultrafine grain thermally sprayed powder, characterized in that, The ultra-fine particle thermal spraying powder is prepared by the preparation method of the ultra-fine particle thermal spraying powder according to any one of claims 1-9, and the ultra-fine particle thermal spraying powder is an ultra-fine nanocrystalline WC86-Co10Cr4 thermal spraying powder.

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