Large-density-difference ceramic particle reinforced medium-entropy alloy powder as well as preparation method and application thereof

Abstract

The invention discloses ceramic particle reinforced medium-entropy alloy powder with large density difference as well as a preparation method and application thereof. The composite powder consists of 3-5wt% of B4C powder and the balance of CoCrNi alloy powder. The average particle size of the B4C powder is less than 0.5 mu m, and the average particle size of the CoCrNi alloy powder is 80-150 mu m; b4C powder and CoCrNi alloy powder are mixed through an acoustic resonance mixing technology, and the surface of the CoCrNi alloy powder is coated with nanometer B4C powder. According to the method, the surface of CoCrNi alloy powder is evenly coated with small-particle-size B4C powder through the acoustic resonance mixing technology to prepare the CoCrNi-B4C composite powder, the optimal balance of strength and toughness is achieved, uniform powder feeding cladding is achieved, the surface of a to-be-cladded plate is cladded with the composite powder subsequently through rectangular light spot laser equipment, and therefore the composite powder is obtained. The large-area crack-free laser cladding high-hardness CoCrNi-B4C composite coating is obtained, the cladding efficiency is greatly improved, and the hardness of the coating exceeds 400 HV.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser cladding processing, in particular to a ceramic particle reinforced medium-entropy alloy powder with large density difference, a preparation method and application thereof. BACKGROUND

[0002] In recent years, multi-principal element alloys, especially medium-entropy alloys (MEAs), have become a research hotspot in the field of materials science due to their unique microstructure and excellent low-temperature mechanical properties. Among them, CoCrNi medium-entropy alloy has attracted much attention due to its excellent toughness, but its absolute strength and hardness are insufficient, which limits its application in the field of wear resistance. The introduction of high-hardness ceramic particles for reinforcement is an effective solution.

[0003] At present, a large number of studies have been devoted to the development of various ceramic particle reinforced metal matrix composites. For example, the patent with publication number CN116727686B discloses a method for laser additive manufacturing of CoCrNi medium-entropy alloy reinforced by TiC ceramic powder. It uses micron-sized TiC ceramic particles (10-60 μm), but the use of micron-sized TiC ceramic particles has the following technical limitations: it can cause poor interfacial bonding between the particles and the matrix; it has a large size difference with the matrix, which induces stress concentration and becomes a source of micro-crack initiation; at the same time, the large density difference between the ceramic particles and the metal powder leads to serious segregation and stratification during powder mixing, transportation and filling, making it impossible to obtain a uniform mixed precursor, which ultimately leads to material performance dispersion, anisotropy, and the formation of crack sources in the enrichment zone during laser cladding coating preparation, completely failing to achieve the design goal of uniform performance improvement of the composite material. The patent with publication number CN119710431A uses carbide and CoCrNi to prepare a carbide reinforced CoCrNi-based medium-entropy alloy by vacuum melting, but it requires multiple melting and large energy consumption.

[0004] Therefore, there is an urgent need in the art to develop a new powder processing and forming process that can fundamentally solve the problem of uneven powder mixing and sintered precursor stratification caused by density difference, thereby preparing a ceramic particle reinforced medium-entropy alloy powder with large density difference, uniform distribution of reinforcing phase, stable performance and excellent properties. SUMMARY

[0005] In order to solve the problems in the prior art, the application provides a ceramic particle reinforced medium-entropy alloy powder with large density difference and a preparation method and application thereof, wherein small-particle-size B4C powder is uniformly coated on the surface of CoCrNi alloy powder, the best balance between strength and toughness is achieved, and uniform powder feeding cladding is achieved, and then a rectangular spot laser equipment is used to cladding composite powder on the surface of a plate to be cladded, a large-area crack-free laser cladding high-hardness CoCrNi-B4C composite coating is obtained, the cladding efficiency is greatly improved, and the hardness of the coating is more than 400HV.

[0006] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme: In a first aspect of the application, a ceramic particle reinforced medium-entropy alloy powder with large density difference is provided, and the composite powder is composed of 3-5wt% of B4C powder and the balance of CoCrNi alloy powder. The CoCrNi alloy powder is a CoCrNi medium-entropy alloy gas atomized spherical powder, the purity of which is greater than 99.95%, and the particle size distribution thereof is controlled in an optimal range of 80-150μm, so as to ensure good powder flowability and cladding process stability. The purity of the B4C reinforcing phase ceramic powder is greater than 99.9%, and the average particle number diameter (D50) thereof is strictly less than 0.5μm. The addition amount of B4C is designed to be 3-5wt% (mass percentage), which is aimed at achieving the best balance between strength and toughness, and avoiding cracking or sharp decrease in toughness of the coating due to too much ceramic phase. The B4C powder and the CoCrNi alloy powder are mixed by using a sound resonance mixing technology, and the nano B4C powder is coated on the surface of the CoCrNi alloy powder.

[0007] In order to completely solve the problems of uneven mixing and segregation of metal and ceramic powder due to large density difference, the application creatively adopts an advanced sound resonance mixing technology. First, the accurately weighed CoCrNi alloy powder and B4C powder are jointly loaded into a stainless steel powder mixing tank which has been cleaned with ethanol and dried, and is sealed and vacuumized or filled with inert protective gas (argon) to prevent oxidation. Then, the powder mixing tank is fixed on the working platform of the sound resonance powder mixing equipment, the resonance acceleration is set to 60-80g (g is the acceleration of gravity), and the different density powder particles are mixed in a highly uniform state in macro and micro scales by using the high-strength and high-amplitude three-dimensional vibration energy field. The resonance mixing process lasts for 10-20min, which is long enough to achieve the coating of nano B4C powder on the surface of CoCrNi alloy powder after long-term optimization and verification.

[0008] Further, the particle size range of the composite powder is 100-150μm.

[0009] Specifically, after the mixing process of the composite powder is completed, in order to obtain a powder special for cladding with optimal flowability and uniformity, the mixed composite powder needs to be screened. A standard sample screen is used to vibrate and screen the powder through a 100-mesh screen (pore size about 150 mu m) and a 150-mesh screen (pore size about 100 mu m) in sequence. This step aims to screen out a small amount of fine agglomerates (B4C powder) that may be generated in the mixing process and a small number of large particles (CoCrNi-B4C composite powder with excessive coating) that exceed the upper limit, and finally collect the composite powder with a particle size distribution of 100-150 mu m as the raw material for laser cladding. This particle size range ensures that the composite powder has excellent powder flowability in the subsequent coaxial powder feeding process and can form good coupling with the laser spot.

[0010] Further, the content of oxygen element in the CoCrNi alloy powder is less than 140 ppm. A higher content of O element is easy to generate pores in the cladding layer.

[0011] It is worth noting that the B4C ceramic particle powder is easy to agglomerate, and after ultrasonic dispersion, statistical analysis is performed. The average particle size difference between the dispersed B4C ceramic particle powder and the CoCrNi powder should be greater than 100 times.

[0012] In a second aspect, the application provides a preparation method of the above-mentioned ceramic particle reinforced medium-entropy alloy powder with large density difference, comprising the following steps: S1, weighing the formula amount of B4C powder and CoCrNi alloy powder, and sealing the vacuum or inert protective gas in the mixed powder tank; S2, fixing the mixed powder tank on the working platform of the acoustic resonance powder mixing device, setting the resonance acceleration to 60-80g, and continuously mixing for 10-20min to coat the nano B4C powder on the surface of the CoCrNi alloy powder to obtain uniformly mixed composite powder; S3, performing particle size screening and grading on the composite powder, and collecting the composite powder with a particle size distribution of 100-150 mu m.

[0013] Further, in step S2, when the acoustic resonance powder mixing device is used, the outside of the stainless steel mixed powder tank should be cooled by water circulation to avoid the generation of excessive heat due to the friction between the powders in the tank.

[0014] It is worth noting that the acoustic resonance powder mixing device can generate an acceleration of 0-100g. If the acceleration is too low, the coating efficiency is low, and a higher resonance time is required. If the acceleration is too high, the shear force between the powders will cause the coated powder to fall off.

[0015] In a third aspect, the application provides a use of the ceramic particle reinforced medium-entropy alloy powder with large density difference, characterized in that a rectangular spot laser device is used to clad the composite powder on the surface of a plate to be cladded to prepare a CoCrNi-B4C composite coating.

[0016] Further, the composite powder injection focus and the laser spot focus are in the same focal plane, and the angle between the composite powder injection head and the surface of the plate to be cladded is 90 degrees.

[0017] Further, the laser power is 6000-8000 W, and too high laser power will increase the dilution rate of the base material; too low laser power will affect the cladding quality, and the powder is difficult to completely melt to form a coating. The laser cladding scanning speed is 4-6 mm / s, and the powder feeding rate is matched therewith, being 30-50 g / min.

[0018] The rectangular spot laser-coaxial powder feeding processing system is used to prepare the CoCrNi-B4C composite coating on the surface of the pretreated base material. The system accurately delivers the dried composite powder to the molten pool area through the coaxial powder feeder, and the powder feeding gas is high-purity argon. The laser beam is shaped into a rectangular spot with a size of 19 mm x 6.3 mm. Compared with the traditional circular spot, the energy distribution of the spot mode is more uniform, which can effectively reduce the convection in the molten pool, and is conducive to the stable distribution of the B4C particle powder and the reduction of composition segregation. In the process debugging, the light path and the powder feeding nozzle are accurately adjusted to ensure that the powder injection focus and the laser spot focus are in the same focal plane, and the optimal coupling of the powder flow and the laser energy is realized. By optimizing the core process parameters such as laser power, scanning speed, and powder feeding rate, a high-quality CoCrNi-based composite coating with low dilution rate, no cracks, few porosity defects, and uniform distribution of B4C reinforcing phase is finally prepared on the surface of the base material.

[0019] Further, the base material and the composite powder are pretreated before laser cladding processing: Before laser cladding, the powder and the surface of the base material must be strictly pretreated to ensure the quality of the coating. First, the screened CoCrNi-B4C composite powder is placed in a vacuum drying box, and is kept at a temperature of 120℃ for 2-3 h to completely remove the trace amount of water and crystal water that may be adsorbed on the surface of the powder, effectively preventing the porosity defects caused by water vapor evaporation during the cladding process. At the same time, the surface of the base material to be cladded (such as a 316 steel plate) is pretreated: the area to be cladded is polished using an angle grinder with a diamond grinding wheel to remove the oxide scale and rust; then the surface is polished step by step using sandpaper of different grits until the surface presents a metallic luster; finally, the surface of the pretreated base material is cleaned in an ultrasonic cleaning machine using anhydrous ethanol or acetone to completely remove oil stains and residual abrasive particles, and is dried with an electric hair dryer to obtain a clean and activated surface.

[0020] Compared with the prior art, the present application has the following beneficial effects: (1) In the present application, a layer of B4C nano powder is coated on CoCrNi by acoustic resonance mixing technology, which avoids the difficulty of ceramic particle reinforced phase entering the molten pool due to the density gap of the powder during laser cladding powder feeding, improves the reinforcing effect of B4C ceramic particles on the cladding layer, and realizes uniform powder feeding cladding.

[0021] (2) The particle size of the coated B4C powder is strictly controlled to be less than 0.5 μm, which ensures the coating effect of B4C nano powder on the surface of CoCrNi, and the addition amount of B4C is designed to be 3-5 wt% (mass percentage), which aims to achieve the best balance between strength and toughness, avoid the cracking or sharp decline in toughness of the coating due to excessive ceramic phase, and avoid low utilization rate of coating due to excessive addition amount of B4C powder, and insufficient performance of the cladding coating due to low addition amount of B4C powder.

[0022] (3) Compared with the traditional CoCrNi-based entropy alloy, the hardness performance of the CoCrNi-based entropy alloy is improved by introducing B4C ceramic particles, so that it has a certain degree of wear resistance, which widens the service range of the CoCrNi-based entropy alloy, and the subsequent use of rectangular light spot laser equipment to cladding composite powder on the surface of the to-be-cladded plate forms a large-area crack-free laser cladding high-hardness CoCrNi-B4C composite coating, and the hardness of the coating is more than 400 HV, and the use of rectangular wide light spot cladding greatly improves the cladding efficiency compared with the conventional original light spot. BRIEF DESCRIPTION OF DRAWINGS

[0023] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0024] Figure 1 It is the body microscope graph of CoCrNi entropy alloy powder in Example 1; Figure 2 It is the body microscope graph of B4C powder in Example 1; Figure 3 It is the body microscope graph of CoCrNi-B4C powder after the same frequency resonance mixing in Example 1; Figure 4 It is the body microscope graph of CoCrNi-B4C powder after screening in Example 1; Figure 5 It is the element scanning graph of CoCrNi entropy alloy cladding layer in Example 1; Figure 6 It is the element scanning graph of CoCrNi-B4C cladding layer formed on the surface of the plate in Example 1; Figure 7Elemental mapping of the CoCrNi-B4C cladding layer formed on the surface of the plate in Example 2; Figure 8 Elemental mapping of the CoCrNi-B4C cladding layer formed on the surface of the plate in Example 3; Figure 9 Hardness-depth curves of the cladding layer formed on the surface of the plate in each example. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0026] Example 1 (1) Powder component ratio: CoCrNi entropy alloy was weighed by an electronic balance, the purity of the powder was >99.95%, the O element content was 138 ppm, and the particle size was 80-150 μm; B4C ceramic particle powder was weighed according to the addition amount of 3wt%, the purity of the powder was >99.9%, and the average particle size was 0.229 μm.

[0027] (2) Preparation of CoCrNi-B4C composite powder: the weighed CoCrNi entropy alloy powder and B4C powder with a total mass of 100 g were loaded into a 50 mL volume stainless steel powder mixing tank, a cooling water circulation pipeline and a water cooler were installed on the periphery of the powder mixing tank, a sound resonance powder mixing device was selected to perform sound resonance powder mixing on the stainless steel powder mixing tank, the resonance parameters were set to an acceleration of 80 g, and the resonance time was set to 10 min.

[0028] (3) Screening of CoCrNi-B4C composite powder: the mixed powder was screened through 100 mesh and 150 mesh screens, and the composite powder with a particle size range of 100-150 μm was screened out for testing.

[0029] (4) Pretreatment before laser cladding coating: the screened CoCrNi-B4C composite powder was dried in a vacuum drying box, the holding temperature was 120°C, the holding time was 2 h, and the crystal water in the powder was removed; an angle grinder was used to polish and polish the surface of the 316 plate to be cladded, alcohol was used to clean the oil stains on the surface of the plate to be cladded, and an electric hair dryer was used to dry.

[0030] (5) Laser cladding CoCrNi-B4C composite coating: CoCrNi-B4C composite coating was prepared on the surface of the substrate by using the coaxial powder feeding method of the rectangular spot laser processing system. The angle between the cladding head and the substrate was 90°, the power of the laser was 6000 W, the laser cladding scanning speed was 4 mm / s, and the powder feeding rate was 30 g / min.

[0031] Figure 1 It is a stereomicroscope image of CoCrNi medium-entropy alloy powder used in this embodiment, which is in a dispersed state. Figure 2 It is a stereomicroscope image of B4C ceramic particle powder used in this embodiment, which is in an agglomerated state due to its small particle size and the influence of Van der Waals force.

[0032] Figure 3 It is a stereomicroscope image of CoCrNi-B4C powder after mixing by the same frequency resonance in step (2), and it can be seen that the particle size difference of the composite powder is large, and there are a large number of composite powders with too large or too small size.

[0033] Figure 4 It is a stereomicroscope image of CoCrNi-B4C powder after screening in step (3), and the particle size distribution is relatively uniform.

[0034] Figure 5 It is an element scanning image of the CoCrNi medium-entropy alloy cladding layer, Figure 6 It is an element scanning image of the CoCrNi-B4C cladding layer formed on the surface of the plate in this embodiment, and it can be seen that the addition of B4C causes the segregation of Cr element, and the carbon chromium compound precipitated between the crystals can effectively improve the hardness of the CoCrNi-B4C cladding layer.

[0035] The CoCrNi-B4C composite coating prepared in this embodiment has a thickness of 1.6 mm and a dilution rate of 10.2%. According to the microhardness test standard GB / T4340.1-2024, the hardness of the cladding layer can reach 448HV 0.2 , see Figure 9 It is a hardness curve of the cladding layer on the surface of the plate with depth.

[0036] Example 2 (1) Powder composition ratio: CoCrNi medium-entropy alloy was weighed by an electronic balance, the purity of the powder was >99.95%, the O element content was 130 ppm, and the particle size was 80-150 μm; B4C ceramic particle powder was weighed according to the addition amount of 5wt%, the purity of the powder was >99.9%, and the average particle size was 0.238 μm.

[0037] (2) Preparation of CoCrNi-B4C composite powder: CoCrNi entropy alloy powder and B4C powder with a total weight of 300 g were weighed and loaded into a 100 mL volume powder mixing tank. A cooling water circulation pipeline and a water cooler were installed on the periphery of the powder mixing tank. The stainless steel powder mixing tank was subjected to the same frequency resonance powder mixing by selecting a sound resonance powder mixing device through the water cooler. The resonance parameters were set to an acceleration of 60 g and a resonance time of 10 min.

[0038] (3) Screening of CoCrNi-B4C composite powder: The mixed powder was screened through 100 mesh and 150 mesh screens to screen out composite powder of 100-150 μm for testing.

[0039] (4) Pretreatment before laser cladding coating preparation: The screened CoCrNi-B4C composite powder was dried using a vacuum drying oven at a holding temperature of 120°C for 3 h to remove crystallization water in the powder. An angle grinder was used to polish and polish the surface of the 316 plate to be cladded. Alcohol was used to clean the oil stains on the surface of the plate to be cladded, and an electric hair dryer was used to dry it.

[0040] (5) Preparation of CoCrNi-B4C composite coating by laser cladding: A rectangular spot laser processing system was used to prepare a CoCrNi-B4C composite coating on the surface of the substrate by coaxial powder feeding. The included angle between the cladding head and the substrate was 90°. The power of the laser was 6000 W, the laser cladding scanning speed was 6 mm / s, and the powder feeding rate was 40 g / min.

[0041] Figure 7 The element scanning diagram of the CoCrNi-B4C cladding layer formed on the surface of the plate in this embodiment shows that with the increase of B4C powder, the carbon element concentration is correspondingly increased, which induces more chromium element to precipitate, and finally realizes the strengthening of the hardness of the cladding layer.

[0042] The CoCrNi-B4C composite coating prepared in this embodiment has a thickness of 1.8 mm and a dilution rate of 5.5%. According to the microhardness test standard GB / T4340.1-2024, the hardness of the cladding layer can reach 583HV 0.2 , see Figure 9 for the hardness-depth curve of the cladding layer on the surface of the plate.

[0043] Example 3 (1) Powder composition ratio: An electronic balance was used to weigh CoCrNi entropy alloy, the purity of which was >99.95%, and the O element content was 138 ppm, and the particle size was 80-150 μm. B4C ceramic particle powder was weighed according to the addition amount of 5wt%, the purity of which was >99.9%, and the average particle size was 0.229 μm.

[0044] (2) Preparation of CoCrNi-B4C composite powder: the weighed CoCrNi entropy alloy powder and B4C powder with a total mass of 200 g were loaded into a 75 mL volume stainless steel powder mixing tank, a cooling water circulation pipeline and a water cooler were installed on the periphery of the powder mixing tank, and the stainless steel powder mixing tank was subjected to the same frequency resonance powder mixing by selecting a sound resonance powder mixing device, the resonance parameters were set to an acceleration of 80 g and a resonance time of 15 min.

[0045] (3) Screening of CoCrNi-B4C composite powder: the mixed powder was screened through 100 mesh and 150 mesh screens, and the composite powder with a size of 100-150 μm was screened out for testing.

[0046] (4) Pretreatment before laser cladding coating preparation: the screened CoCrNi-B4C composite powder was dried in a vacuum drying oven, the holding temperature was 120°C, the holding time was 3 h, and the crystal water in the powder was removed; the surface of the 316 plate to be cladded was polished using an angle grinder, the surface oil stains of the plate to be cladded were cleaned using alcohol, and the plate was dried with a hair dryer.

[0047] (5) Preparation of CoCrNi-B4C composite coating by laser cladding: the CoCrNi-B4C composite coating was prepared on the substrate surface by using a rectangular spot laser processing system with coaxial powder feeding method, the cladding head and the substrate had an included angle of 90°, the laser power was 8000 W, the laser cladding scanning speed was 6 mm / s, and the powder feeding rate was 50 g / min.

[0048] Figure 8 The element scanning diagram of the CoCrNi-B4C cladding layer formed on the surface of the plate in this embodiment shows that the increase of laser power promotes the decomposition of B4C, and the increase of carbon content promotes the formation of chromium-containing precipitated phase, thereby significantly improving the macro hardness of the material.

[0049] The CoCrNi-B4C composite coating prepared in this embodiment has a thickness of 1.9 mm and a dilution rate of 8.4%, and according to the microhardness test standard GB / T4340.1-2024, the hardness of the cladding layer can reach 580 HV 0.2 , see Figure 9 for the hardness-depth curve of the cladding layer on the surface of the plate.

[0050] Example 4 (1) Powder composition ratio: an electronic balance was used to weigh CoCrNi entropy alloy, the purity of the powder was >99.95%, the O element content was 138 ppm, and the particle size was 80-150 μm; B4C ceramic particle powder was weighed according to the addition amount of 3wt%, the purity of the powder was >99.9%, and the average particle size was 0.46 μm.

[0051] (2) Preparation of CoCrNi-B4C composite powder: CoCrNi entropy alloy powder and B4C powder with a total weight of 100 g were weighed and loaded into a 50 mL volume powder mixing tank. A cooling water circulation pipeline and a water cooler were installed on the periphery of the powder mixing tank. The stainless steel powder mixing tank was mixed by sound resonance using a water cooler and a sound resonance mixing device. The resonance parameters were set to an acceleration of 80 g and a resonance time of 10 min.

[0052] (3) Screening of CoCrNi-B4C composite powder: The mixed powder was screened through 100 mesh and 150 mesh screens to obtain composite powder with a particle size of 100-150 μm for testing.

[0053] (4) Pretreatment before laser cladding coating preparation: The screened CoCrNi-B4C composite powder was dried in a vacuum drying oven at a holding temperature of 120°C for 2 h to remove the crystal water in the powder. The surface of the 316 plate to be cladded was polished using an angle grinder, cleaned with alcohol to remove oil stains, and dried with a hair dryer.

[0054] (5) Preparation of CoCrNi-B4C composite coating by laser cladding: A rectangular spot laser processing system was used to prepare a CoCrNi-B4C composite coating on the substrate surface by coaxial powder feeding. The angle between the cladding head and the substrate was 90°, the laser power was 6000 W, the laser cladding scanning speed was 4 mm / s, and the powder feeding rate was 30 g / min.

[0055] The CoCrNi-B4C composite coating prepared in this example had a thickness of 1.6 mm and a dilution rate of 10%. According to the microhardness test standard GB / T4340.1-2024, the hardness of the cladding layer was up to 427 HV. 0.2 , see Figure 9 for the hardness of the cladding layer on the surface of the plate as a function of depth.

[0056] Comparative Example 1 Comparative Example 1 is a comparative test example of Example 1, which uses B4C powder with an average particle size (D50) of 0.58 μm. The other implementation steps and specific parameters are the same as those of Example 1.

[0057] The CoCrNi-B4C composite powder prepared in the present comparative example is unqualified in quality. Specifically, the B4C powder has a large particle size and cannot be coated on the surface of CoCrNi. Only a part of small-particle-size B4C is successfully coated. The B4C powder and CoCrNi are obviously layered in a static state. The low-density B4C powder is always in the upper layer and cannot form a coated powder. After powder particle size screening, a large amount of agglomerated B4C powder cannot be screened out. During laser cladding, the low-density B4C powder is affected by powder feeding gas and surface air convection of the molten pool. Most of the powder is blown away and cannot uniformly enter the molten pool, so as to effectively improve the coating microstructure performance. The CoCrNi-B4C composite coating prepared in the present comparative example has a thickness of 1.2 mm and a dilution rate of 16.1%. According to the microhardness test standard GB / T4340.1-2024, the average hardness of the cladding layer is 348HV 0.2 .

[0058] Comparative Example 2 Comparative Example 2 is a comparative test example of Example 1, which uses B4C powder with an average particle size (D50) of 1 μm. The other implementation steps and specific parameters are the same as those of Example 1.

[0059] The CoCrNi-B4C composite powder prepared in the present comparative example is unqualified in quality. The B4C powder and CoCrNi are obviously layered in a static state. The low-density B4C powder is always in the upper layer and cannot form a coated powder. After powder particle size screening, a large amount of agglomerated B4C powder cannot be screened out. During laser cladding, the low-density B4C powder is affected by powder feeding gas and surface air convection of the molten pool. Most of the powder is blown away and cannot uniformly enter the molten pool, so as to effectively improve the coating microstructure performance. The CoCrNi-B4C composite coating prepared in the present comparative example has a thickness of 0.9 mm and a dilution rate of 21.2%. According to the microhardness test standard GB / T4340.1-2024, the average hardness of the cladding layer is 327HV 0.2 .

[0060] Comparative Example 3 Comparative Example 3 is a comparative test example of Example 1, which uses CoCrNi powder with a particle size of 50-100 μm. The other implementation steps and specific parameters are the same as those of Example 1.

[0061] CoCrNi and B4C powder particle size greater than 100 times can be coated, but the CoCrNi-B4C composite powder prepared in the present comparative example is unqualified in quality. Since the particle size of the CoCrNi powder is small, the surface coating thickness is limited, the utilization rate of the B4C powder is insufficient, and there is partial delamination between the B4C powder and the CoCrNi in the static state. Some of the successfully coated powders are in the lower layer, and most of the low-density B4C powders are always in the upper layer. After powder particle size screening, there are still a large number of agglomerated B4C powders that cannot be screened out. During laser cladding, the low-density B4C powders are affected by the powder feeding gas and the surface air convection of the molten pool, most of the powders are blown away, and cannot uniformly enter the molten pool, so the coating cannot be effectively prepared. The CoCrNi-B4C composite coating prepared in the present comparative example has a thickness of 1.1 mm and a dilution rate of 14.7%. According to the microhardness test standard GB / T4340.1-2024, the average hardness of the cladding layer is 420HV 0.2 .

[0062] Comparative Example 4 Comparative Example 4 is a comparative test example of Example 1, which adds 6wt% of B4C powder, and the other implementation steps and specific parameters are the same as those of Example 1.

[0063] The CoCrNi-B4C composite powder prepared in the present comparative example is screened out a large amount of B4C powder in the powder screening stage. The essence is that the B4C content is too high, and the excess B4C powder cannot be coated on the surface of the CoCrNi. After powder particle size screening, the screened B4C powder is mixed with part of the small particle size CoCrNi, affecting the density of the screened powder, which cannot be recycled, resulting in powder waste and low material utilization. The CoCrNi-B4C composite coating prepared in the present comparative example has a thickness of 1.7 mm and a dilution rate of 6.7%. According to the microhardness test standard GB / T4340.1-2024, the average hardness of the cladding layer is 603HV 0.2 , and at the same time, there are cracks on the macroscopic surface of the cladding layer. The increase of boron carbide content further improves the hardness, but the high hardness leads to cracking of the cladding layer.

[0064] Comparative Example 5 Comparative Example 5 is a comparative test example of Example 1, which adds 10wt% of B4C powder, and the other implementation steps and specific parameters are the same as those of Example 1.

[0065] The volume ratio of the CoCrNi-B4C composite powder prepared in the comparative example is about 3:1. Since B4C is easy to agglomerate into large particles, the excess B4C powder cannot be sieved out in the powder sieving stage. During laser cladding, the low-density B4C powder is affected by the powder feeding gas and the air thermal convection on the surface of the molten pool, most of the powder is blown away and cannot enter the molten pool. At the same time, the floating B4C powder shields the laser, affecting the laser irradiation, and the coating cannot be effectively prepared. At the same time, the prepared coating has macroscopic cracks.

[0066] Comparative Example 6 Comparative Example 6 is a comparative test example of Example 1, which adds 2wt% of B4C powder, and other implementation steps and specific parameters are the same as those of Example 1.

[0067] The coating prepared after laser cladding of the CoCrNi-B4C composite powder prepared in the comparative example has a thickness of 1.6mm, a dilution rate of 10.5%, and a hardness of 354HV according to the microhardness test standard GB / T4340.1-2024. 0.2 Compared with the CoCrNi cladding layer without adding B4C ceramic particles, the performance is improved to a certain extent, but it is insufficient to widen the service range of CoCrNi-based medium-entropy alloy.

[0068] Comparative Example 7 Comparative Example 7 is a comparative test example of Example 1, which adds 0.5wt% of B4C powder, and other implementation steps and specific parameters are the same as those of Example 1.

[0069] The coating prepared after laser cladding of the CoCrNi-B4C composite powder prepared in the comparative example has a thickness of 1.6mm, a dilution rate of 10.4%, and a hardness of 255HV according to the microhardness test standard GB / T4340.1-2024. 0.2 Compared with the CoCrNi cladding layer without adding B4C ceramic particles, the performance is improved to a certain extent, but it is insufficient to widen the service range of CoCrNi-based medium-entropy alloy.

[0070] Comparative Example 8 Comparative Example 8 is a comparative test example of Example 1, but the powder is not sieved strictly, and a large amount of small powder and large powder with particle sizes of 100-150μm are mixed in the powder.

[0071] The CoCrNi-B4C composite coating prepared in the example has a thickness of 1.6mm, a dilution rate of 9.4%, and a hardness of 442HV. 0.2 There are a large number of pores in the coating.

[0072] Comparative Example 9 Comparative Example 9 is a comparative example of Example 1, which uses a laser power of 5000W, cooperates with a laser scanning speed of 8mm / s, and other implementation steps and specific parameters are the same as those of Example 1.

[0073] The CoCrNi-B4C composite coating prepared in the example has a thickness of 0.8mm, a dilution rate of 4.4%, and a cladding layer hardness of 404HV 0.2 , there are pores in the coating, the un-melted powder is more than 50%, the powder utilization rate is low, and the cladding efficiency is not high.

[0074] Comparative Example 10 Comparative Example 10 is a comparative example of Example 1, which uses a laser power of 9000W, cooperates with a laser scanning speed of 3mm / s, and other implementation steps and specific parameters are the same as those of Example 1.

[0075] The CoCrNi-B4C composite coating prepared in the example has a thickness of 2.2mm, a dilution rate of 17.2%, and a cladding layer hardness of 482HV 0.2 , there are cracks on the surface of the cladding layer.

[0076] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A ceramic particle-reinforced medium-entropy alloy powder with a large density difference, characterized in that, The composite powder is composed of 3-5wt% B4C powder and the balance CoCrNi alloy powder; The average particle size of the B4C powder is less than 0.5μm, and the average particle size of the CoCrNi alloy powder is 80-150μm; The B4C powder and the CoCrNi alloy powder are mixed by using acoustic resonance mixing technology, and the nano B4C powder is coated on the surface of the CoCrNi alloy powder.

2. The ceramic particle-reinforced medium-entropy alloy powder of a large density difference according to claim 1, characterized in that, The particle size of the composite powder is 100-150μm.

3. The high-density-diffraction-contrast ceramic particle reinforced medium-entropy alloy powder of claim 1, wherein, When the B4C powder and the CoCrNi alloy powder are mixed by using acoustic resonance mixing technology, the resonance acceleration is 60-80g, and the resonance mixing process lasts for 10-20min.

4. The high-density-diffraction-contrast ceramic particle reinforced medium-entropy alloy powder of claim 1, wherein, The content of oxygen in the CoCrNi alloy powder is less than 140ppm.

5. A method of producing a ceramic particle-reinforced medium-entropy alloy powder having a large density difference according to any one of claims 1 to 4, characterized by, The method comprises the following steps: S1, weighing the formula amount of B4C powder and CoCrNi alloy powder, and loading them into a powder mixing tank together and sealing and vacuumizing or filling with inert protective gas; S2, fixing the powder mixing tank on the working platform of the acoustic resonance powder mixing equipment, setting the resonance acceleration to 60-80g, and making the resonance mixing process last for 10-20min, so that the nano B4C powder is coated on the surface of the CoCrNi alloy powder, and a uniformly mixed composite powder is obtained; S3, performing particle size screening and grading on the composite powder, and collecting the composite powder with a particle size distribution of 100-150μm.

6. The method of claim 5, wherein the ceramic particles are of a large density difference. In step S2, the outside of the powder mixing tank is circulated and cooled during the acoustic resonance mixing process.

7. Use of ceramic particles of large density difference reinforcing middle-entropy alloy powder according to any one of claims 1 to 4, characterized in that, A rectangular spot laser device is used to melt the composite powder on the surface of the plate to be cladded, and a CoCrNi-B4C composite coating is prepared.

8. Use of ceramic particles of large density difference reinforcing middle-entropy alloy powder according to claim 7, characterized in that, The composite powder injection focus and the laser spot focus are in the same focal plane, and the angle between the composite powder injection head and the surface of the plate to be cladded is 90 degrees.

9. Use of ceramic particles of large density difference reinforcing middle-entropy alloy powder according to claim 7, characterized in that, The laser power is 6000-8000W, the laser cladding scanning speed is 4-6mm / s, and the powder feeding rate is 30-50g / min.

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