A method for preparing a binderless WC-VC cemented carbide high-pressure nozzle

Abstract

This invention relates to the field of cemented carbide material preparation technology, and discloses a method for preparing a binderless WC-VC cemented carbide high-pressure nozzle. The method includes WC-VC composite powder preparation, segmented temperature-controlled discharge plasma sintering, precision machining, and nano-Al2O3 coating preparation steps. A uniform composite powder is obtained by wet ball milling high-purity WC and VC grain inhibitors. A three-stage rapid sintering process is used to achieve high density and fine grain strengthening of the matrix. Precision machining ensures dimensional accuracy, and a low-porosity, high-bonding-strength nano-wear-resistant coating is prepared by spray granulation and high-speed flame spraying. This invention solves the problems of coarse grains, uneven performance, easy coating peeling, poor consistency, and long preparation cycle in traditional nozzles. The resulting nozzle has high density, excellent hardness and toughness matching, and significantly improved service life. The process is highly efficient and energy-saving, suitable for industrial mass production of high-pressure water jet applications in marine rust removal robots.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide material preparation technology, specifically to a method for preparing a binderless WC-VC cemented carbide high-pressure nozzle. Background Technology

[0002] Ship rust removal robots utilize high-pressure water jets for rust removal, placing stringent requirements on the wear resistance, impact resistance, dimensional accuracy, and service life of the accompanying high-pressure nozzles. Currently, the mainstream manufacturing processes for high-pressure nozzles in this scenario can be categorized into four types based on the substrate material: copper alloy or stainless steel nozzles are made from bar stock, machined by CNC machining, and then simply polished to obtain the finished product; ceramic nozzles are made from alumina and zirconia ceramic powders, sequentially through molding, atmospheric pressure high-temperature sintering, and precision grinding; traditional WC-Co hard alloy nozzles are made by mixing tungsten carbide powder with cobalt binder, followed by molding, conventional hot pressing sintering, and machining, with some products additionally coated with a micron-level wear-resistant coating; composite nozzles are made by preparing a wear-resistant coating on the metal substrate surface using conventional impregnation or ordinary flame spraying, followed by simple post-treatment to obtain the finished product. All of the above manufacturing processes are centered on the selection of the substrate material, primarily relying on conventional machining, atmospheric pressure sintering, or hot pressing sintering to complete the molding process, and then combining this with a simple coating treatment process to produce the high-pressure nozzle.

[0003] Existing high-pressure nozzle manufacturing technologies have significant drawbacks, making it difficult to meet the requirements of long-term stable operation and industrial-scale mass production for marine rust removal robots. Traditional hot-pressing sintering involves slow heating rates and long high-temperature holding times, which easily leads to abnormal coarsening of WC grains, low matrix density, and significant performance gradients in the axial and radial directions of large-sized blanks. This results in large differences in wear resistance and impact resistance at different locations of the nozzle, making it prone to localized erosion failure during use.

[0004] Conventional coating preparation processes are poorly compatible with nano-alumina powder, failing to address the issues of poor flowability and easy agglomeration of nano-powder. The resulting coatings have high porosity and low bonding strength with the substrate. Under the continuous scouring action of high-pressure water jets and abrasives, the coatings are prone to cracking and peeling, making it difficult to provide durable and effective protection for the nozzle substrate.

[0005] The existing manufacturing process lacks precise control over the parameters of the entire process, including powder mixing, sintering, precision machining, and coating preparation. This results in significant fluctuations in the dimensional accuracy, mechanical properties, and service life of different batches of nozzles, making it impossible to achieve standardized and large-scale production of rust removal robot nozzles.

[0006] In addition, traditional hot pressing sintering has a single batch cycle of several hours, resulting in low production efficiency and high energy consumption; the multi-step open processing process is prone to introducing impurities such as ferromagnetism, which affects the safety of nozzle use. At the same time, the raw material utilization rate is not high, the overall preparation cost is relatively high, and the adaptability to industrial mass production is weak. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a binderless WC-VC hard alloy high-pressure nozzle. By using a segmented temperature-controlled discharge plasma sintering and nano-Al2O3 coating composite process, a high-density, high-hardness, high-toughness, and long-life high-pressure nozzle is prepared.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a binderless WC-VC cemented carbide high-pressure nozzle includes the following steps: 1) Preparation of WC-VC composite powder: Using WC powder as the matrix and VC powder as the grain inhibitor, wet ball milling was carried out in a planetary ball mill under the protection of high-purity argon gas and anhydrous ethanol as the ball milling medium to avoid oxidation and agglomeration of the powder during the preparation process, thus providing a high-quality raw material basis for subsequent ball milling processes. After vacuum drying, WC-VC composite powder was obtained by sieving. 2) Segmented temperature-controlled discharge plasma sintering: WC-VC composite powder is loaded into a graphite mold. Graphite carbon paper is laid between the powder and the graphite mold, pressure head, and electrodes to prevent the powder from sticking to the mold and to ensure uniform current conduction, ensuring uniform heating of the entire blank. This lays a good foundation for subsequent vacuum sintering. After evacuating the sintering chamber, three-stage heating and sintering are performed. After pressure holding and cooling, the nozzle blank is obtained. Heating is stopped during the cooling stage, and the pressure is maintained until the blank cools naturally to room temperature to avoid the formation of pores and micro-particles during the cooling process. Cracks are prevented to ensure the quality of the green body forming. After sintering and cooling, the nozzle green body is removed from the graphite mold, and the graphite carbon paper and impurities attached to the surface are removed. The green body surface is checked to ensure that there are no cracks or deformations, and that all basic forming indicators meet the process requirements of subsequent precision machining. SPS (spark plasma sintering) technology has a faster heating (>100℃ / min) and cooling rate, and requires a shorter sintering time. Sintering can be completed in as little as ten minutes, avoiding the sintered body from staying in the high temperature zone for a long time, which can effectively inhibit grain growth.

[0009] 3) Precision machining: The nozzle blank is rough turned, fine ground and polished to obtain the nozzle semi-finished product; the SPS sintered nozzle blank that has passed the initial inspection is used as the processing base material, and the sintered nozzle blank is processed into a nozzle semi-finished product that meets the installation and use requirements of the rust removal robot. The core is to achieve high-precision machining of the nozzle shape, internal flow channel and nozzle orifice to ensure the spraying efficiency and use effect of high pressure water jet; 4) Preparation of Nano-Al2O3 Coating: Nano-α-Al2O3 powder is spray-granulated and cold isostatically pressed into spherical agglomerates for feeding. These agglomerates are then sprayed onto the surface of the nozzle semi-finished product using a high-speed HVOF flame to form a coating. The finished nozzle is obtained after low-temperature hot pressing and remelting. Using the dimensionally accurate nozzle semi-finished product as the substrate, a uniform and robust nano-Al2O3 wear-resistant and corrosion-resistant coating is prepared on its surface. This further enhances the nozzle's erosion and corrosion resistance, extends its service life, and achieves uniform coating deposition and high bonding strength control.

[0010] This invention employs a complete process encompassing composite powder refinement, segmented temperature-controlled discharge plasma sintering, precision machining, and nano-Al2O3 coating preparation. Segmented temperature-controlled discharge plasma sintering replaces traditional hot-pressing sintering, combined with spray granulation and cold isostatic pressing composite granulation, and high-speed flame spraying coating preparation. Precise control of all process parameters fundamentally prevents WC grain coarsening at high temperatures, achieving a highly dense and homogeneous nozzle substrate. The sintering cycle for a single batch is reduced to within 30 minutes, significantly reducing energy consumption and improving production efficiency. Simultaneously, it solves the problems of poor flowability and easy agglomeration of nano-Al2O3 powder during spraying, ensuring uniform and firm deposition of the nano-coating in key areas of the nozzle, preventing coating peeling and failure under high-pressure erosion, and guaranteeing dimensional accuracy and batch consistency of the finished product. The resulting high-pressure nozzle substrate exhibits a density ≥99.5%, hardness ≥2000 HV, and fracture toughness ≥8.0 MPa·m. 1 / 2 The nano-Al2O3 coating has a porosity of ≤0.8% and a bonding strength of ≥45MPa. Its overall service life is more than 30% longer than that of traditional products. The preparation process is green and environmentally friendly with high raw material utilization. It can meet the standardization and mass production requirements of high-pressure water jet nozzles for rust removal robots and has excellent industrial promotion value.

[0011] The preparation of WC-VC composite powder lays the foundation for the subsequent sintering preparation of high-performance nozzle substrates. The core of this method is to achieve precise control of the raw material ratio and uniform dispersion of the powder. Segmented temperature controlled discharge plasma sintering, or SPS sintering, is the core process for preparing nozzle blanks with high density, uniform structure, and no performance gradient through segmented temperature controlled SPS sintering. The key is to achieve precise temperature control and densification control during the sintering process.

[0012] Preferably, in step 1), the purity of WC powder is ≥99.9% and the average particle size is 0.3μm; the purity of VC powder is ≥99.5% and the average particle size is 0.1μm; the amount of VC powder added is 0.1%~1.0% of the mass of WC powder, preferably 0.5%.

[0013] Preferably, in step 1), the ball-to-material mass ratio of wet ball milling is (8:1) to (10:1), preferably 9:1; the ball milling speed is 300 to 600 r / min, preferably 450 r / min; the ball milling time is 20 to 40 h, preferably 30 h; during the ball milling process, the temperature rise of the mill cylinder is controlled to not exceed 50°C to avoid the volatilization of anhydrous ethanol and oxidation of the powder; vacuum drying is carried out in a vacuum drying oven at a temperature of 50 to 80°C to completely remove the anhydrous ethanol medium; the dried powder is sieved through a mesh of 100 to 200 mesh to remove a small amount of agglomerated particles, and finally a uniformly dispersed, non-agglomerated, and narrowly particle size distribution WC-VC composite powder is obtained, which meets the raw material requirements for subsequent SPS sintering. When the VC addition is 0.5 wt.%, a high-performance ultra-hard WC cemented carbide material can be obtained, with the smallest grain size (0.22 μm), the highest Vickers hardness (2655 HV30), and good fracture toughness (8.11 MPa·m). 1 / 2 ).

[0014] Preferably, in step 2), the filling density of the WC-VC composite powder in the graphite mold is 1.8~2.2 g / cm³. 3 The vacuum degree of the sintering chamber after evacuation is ≤10Pa, preferably 0.05~5Pa. The vacuum environment can prevent the powder from oxidizing during high-temperature sintering, while ensuring the normal generation of discharge plasma, fully activating the surface of powder particles, and reducing the densification energy barrier.

[0015] Preferably, in step 2), the three-stage heating sintering is as follows: the first stage involves heating at 100~150℃ / min to 400~450℃ and holding for 10~30s to remove residual trace moisture and gas from the powder, thus preventing porosity from forming during subsequent sintering; the second stage involves heating at 150~200℃ / min to 1450~1550℃ and holding for 2~5min to achieve initial densification of the powder, inhibit abnormal grain growth, and ensure the uniformity of the matrix structure; the third stage involves holding at 1500~1550℃ and 30~50MPa pressure for 4~10min to achieve complete densification of the powder, forming a uniformly structured nozzle blank; the temperature fluctuation throughout the process is controlled within ±5℃.

[0016] Preferably, in step 3), the rough machining allowance is 0.1~0.3mm, the surface roughness Ra≤0.8μm, and the dimensional tolerance is ≤±0.01mm. A CNC lathe is used to rough machine the nozzle blank to remove excess material and machine the basic shape of the nozzle. The rough machining allowance is controlled to be uniformly maintained at 0.1~0.3mm to avoid uneven allowance and dimensional deviations in subsequent finishing. Based on the rough machining, a precision grinding machine is used to finish the inner flow channel and nozzle orifice of the nozzle, ensuring smooth inner walls of the flow channel and accurate nozzle orifice dimensions. The surface roughness Ra is controlled to ≤0.8μm, preferably Ra=0.5~0.6μm, and the dimensional tolerance is controlled within ±0.01mm. The outer surface of the nozzle is polished to improve surface smoothness and prevent erosion caused by water-borne impurities. The semi-finished nozzles after finishing are subjected to full-size, high-precision inspection. High-precision measuring instruments are used to perform full-size inspection of the semi-finished nozzles after finishing to ensure that the nozzle shape, nozzle diameter, and flow channel size all meet the requirements of the design drawings. This ensures that the semi-finished nozzles are accurately matched with the rust removal robot and provides a qualified substrate for subsequent coating preparation.

[0017] Preferably, in step 4), the particle size of the nano-α-Al2O3 powder is 50 nm; the particle size of the spherical agglomerate feed is 15~45 μm, and the Hall flow rate is ≤25 s / 50 g. To meet the requirements of subsequent spraying processes, 50 nm high-purity α-Al2O3 nanopowder is used as raw material, and PVA is used as binder. Through slurry mixing, spray granulation, cold isostatic pressing densification, crushing and sieving, a spherical agglomerate feed of 15~45 μm is prepared, with a feed Hall flow rate ≤25 s / 50 g. This solves the problem of poor flowability and easy agglomeration of pure nano-Al2O3 powder during spraying, and meets the requirements of HVOF (high-speed flame spraying coating) preparation process.

[0018] Preferably, in step 4), the parameters for HVOF high-speed flame spraying are: spraying distance 100~150mm, oxygen flow rate 800~1200L / min, kerosene flow rate 20~25L / h, and powder feed rate 20~30g / min. Al2O3 spherical agglomerates are uniformly sprayed onto the nozzle surface, focusing on covering the nozzle orifice and inner flow channel area, forming a 50~100μm thick nano-Al2O3 coating. The coating forms a strong metallurgical bond with the substrate. The sprayed nozzle undergoes low-temperature hot-pressing remelting to effectively eliminate residual porosity within the coating and further improve coating density. The nozzle orifice is finely ground to ensure dimensional accuracy and surface roughness, ultimately yielding the high-pressure nozzle product. The finished product undergoes comprehensive testing for coating bonding strength, porosity, dimensional accuracy, and appearance quality. Products that pass the tests are uniformly stored, completing the entire nozzle manufacturing process.

[0019] Preferably, the prepared nozzle is a binderless WC-VC cemented carbide, with a nano-Al2O3 wear-resistant and corrosion-resistant coating laminated on the nozzle orifice and inner flow channel surfaces. The water jet high-pressure nozzle, prepared through a closed-loop control system, is made of a binderless WC-VC cemented carbide matrix composited with a nano-Al2O3 wear-resistant and corrosion-resistant coating. This composite structure combines a dense WC-VC cemented carbide matrix with a nano-Al2O3 functional coating. Using WC-VC cemented carbide as the nozzle body substrate, a 50-100 μm thick nano-Al2O3 coating is deposited on critical erosion-prone areas such as the nozzle orifice and inner flow channel, forming a synergistic structure of substrate load-bearing and coating protection. Compared to traditional copper alloy, stainless steel, WC-Co cemented carbide, and alumina ceramic nozzles, this nozzle has a substrate density ≥99.5%, a hardness ≥2000 HV, and a fracture toughness ≥8.0 MPa·m. 1 / 2 The nano-Al2O3 coating has a porosity of ≤0.8% and a bonding strength of ≥45MPa. It achieves an efficient balance between compressive strength, wear and erosion resistance and impact toughness, solving the problems of low hardness, easy wear and deformation, or high brittleness and easy breakage of traditional nozzles. It improves the corrosion protection performance of the nozzle, reduces the overall wear rate by more than 40% compared with traditional WC-Co nozzles, and increases the service life by more than 30%, making it better suited for the harsh working conditions of high-pressure water jet rust removal. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all 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.

[0021] Example 1 is the optimal example. 1) Preparation of WC-VC composite powder: WC powder with a purity of 99.9% and an average particle size of 0.3μm and VC powder with a purity of 99.5% and an average particle size of 0.1μm were selected, and the amount of VC added was 0.5% of the mass of WC powder. The two powders were vacuum dried at 100℃ for 3h, mixed according to the ratio, and placed in a planetary ball mill. Wet ball milling was carried out under the protection of high-purity argon gas and anhydrous ethanol as the medium. The ball-to-powder mass ratio was 9:1, the liquid-to-solid volume ratio was 1.8:1, the ball milling speed was 450r / min, and the ball milling time was 30h. The slurry after ball milling was vacuum dried at 60℃ and sieved through a 150-mesh sieve to obtain uniformly dispersed WC-VC composite powder. 2) Segmented temperature-controlled discharge plasma sintering (SPS) molding: Composite powder is loaded into a graphite mold with a powder filling density of 2.0 g / cm³. 3Graphite carbon paper is laid between the powder and the mold for isolation; the mold is placed in an SPS device and evacuated to 5 Pa; a three-stage heating and sintering process is adopted: the first stage heats up to 420℃ at 120℃ / min and holds for 20s; the second stage heats up to 1500℃ at 180℃ / min and holds for 3min; the third stage holds at 1500℃ and 30MPa pressure for 4min; then it is naturally cooled to room temperature and demolded to obtain the nozzle blank; 3) Precision machining: The nozzle blank is subjected to rough turning, fine grinding and polishing in sequence to make the surface roughness of the nozzle orifice Ra=0.6μm and the dimensional tolerance ±0.01mm, so as to obtain the nozzle semi-finished product; 4) Preparation of nano-Al2O3 coating: Using 50nm high-purity α-Al2O3 nanopowder as raw material, 20~40μm spherical agglomerates were prepared by spray granulation and cold isostatic pressing; HVOF high-speed flame spraying was used with a spraying distance of 120mm, oxygen flow rate of 1000L / min, kerosene flow rate of 22L / h, and powder feed rate of 25g / min to deposit a nano-Al2O3 coating with a thickness of 80μm on the nozzle surface; the coating porosity was eliminated by low-temperature hot pressing and remelting treatment to obtain the finished nozzle.

[0022] Performance results: The nozzle matrix has a density of 99.7%, a hardness of 2150 HV, and a fracture toughness of 8.5 MPa·m. 1 / 2 Wear rate 7.2×10 -7 mm 3 / (N·m); The nano-Al2O3 coating has a porosity of 0.6%, a bonding strength of 48MPa, and a microhardness of 1250HV. 0.1 Under high-pressure water jet rust removal conditions on ships, its service life is increased by 35% compared to traditional WC-Co nozzles, with no coating peeling and no obvious wear at the nozzle orifice.

[0023] Example 2 The only difference from Example 1 is that the segmented temperature-controlled SPS sintering parameters are different; the first stage is to heat up to 400℃ at 100℃ / min and hold for 30s; the second stage is to heat up to 1450℃ at 150℃ / min and hold for 5min; the third stage is to hold for 10min at 1450℃ and 40MPa pressure; the remaining steps are the same as in Example 1.

[0024] Performance results: The nozzle matrix has a density of 99.5%, a hardness of 2080 HV, and a fracture toughness of 8.2 MPa·m. 1 / 2 Wear rate 7.5×10 -7 mm 3 / (N·m); The coating performance is basically the same as that of Example 1; The service life under ship rust removal conditions is 30% longer than that of traditional WC-Co nozzles, and it is suitable for medium and low pressure rust removal operations.

[0025] Example 3 The only difference from Example 1 is that the segmented temperature-controlled SPS sintering parameters are different; the first stage is to heat up to 450°C at 150°C / min and hold for 10 seconds; the second stage is to heat up to 1550°C at 200°C / min and hold for 2 minutes; the third stage is to hold for 4 minutes at 1550°C and 50MPa pressure; the remaining steps are the same as in Example 1.

[0026] Performance results: The nozzle matrix has a density of 99.8%, a hardness of 2200 HV, and a fracture toughness of 8.3 MPa·m. 1 / 2 Wear rate 7.0×10 -7 mm 3 / (N·m); The coating performance is basically the same as in Example 1; The service life under ship rust removal conditions is 38% higher than that of traditional WC-Co nozzles, with outstanding wear resistance, and it is suitable for high abrasive and high-intensity rust removal operations.

[0027] Example 4 The only difference from Example 1 is that a large-size graphite mold of φ50mm×200mm is used for molding, and the temperature fluctuation during the sintering process is controlled within ±5℃; the remaining steps are the same as in Example 1.

[0028] Performance results: The axial density of the large-sized billet is 99.7%, the radial density is 99.6%, the overall hardness is 2140 HV, and the fracture toughness is 8.4 MPa·m. 1 / 2 Wear rate 7.3×10 -7 mm 3 / (N·m), axial / radial performance difference ≤0.1%; good coating uniformity, no local thick / thin areas, meeting the needs of industrial mass production and large-size customization.

[0029] Comparative Example 1 (Traditional hot-pressed sintered WC-Co nozzle) Compared with Example 1, WC-Co composite powder (Co mass fraction 10%) was used as raw material, and the matrix was prepared by conventional hot pressing sintering: the temperature was raised to 1500℃ at 10℃ / min and held at 30MPa pressure for 60min; no nano Al2O3 coating was prepared; the remaining machining steps were the same.

[0030] Performance results: matrix density 98.5%, hardness 1500 HV, fracture toughness 7.0 MPa·m 1 / 2 Wear rate 12.0×10 -7 mm 3 / (N·m); Co phase wear and shedding and nozzle orifice expansion and deformation occurred during use, and the service life was only 60% of that in Example 1.

[0031] Comparative Example 2 (Ambient Pressure Sintered Ceramic Nozzle) Alumina ceramic powder is used as raw material. The same size nozzle is made by molding, sintering at 1650℃ and normal pressure for 2 hours, and precision grinding. No coating treatment is required.

[0032] Performance results: Hardness 1900 HV, fracture toughness 3.5 MPa·m 1 / 2 Wear rate 10.0×10 -7 mm 3 / (N·m); High-pressure water jet impact for 0.5h resulted in nozzle orifice cracking failure.

[0033] Comparative Example 3 (No added VC, pure WC matrix) The only difference from Example 1 is that only WC powder is used as the raw material, and no VC grain inhibitor is added; the remaining sintering, processing, and coating steps are the same.

[0034] Performance results: matrix density 97.8%, hardness 1860 HV, fracture toughness 6.8 MPa·m 1 / 2 Wear rate 13.6×10 -7 mm 3 / (N·m), WC grains coarsened to 2.1μm; coating bonding strength decreased to 30MPa, easy to peel off, and service life was only 50% of that of Example 1.

[0035] Comparative Example 4 (Single-stage heating SPS sintering) The only difference from Example 1 is that the SPS sintering adopts a single-stage heating method, directly heating to 1500°C at 50°C / min and holding for 10min; the other steps are the same.

[0036] Performance results: matrix density 98.1%, hardness 1790 HV, fracture toughness 6.5 MPa·m 1 / 2 Wear rate 14.3×10 -7 mm 3 / (N·m), WC grains coarsen to 3.0μm; the matrix is ​​prone to erosion pits, and its service life is significantly shortened.

[0037] Comparative Example 5 (without nano Al2O3 coating) The only difference from Example 1 is that no nano-Al2O3 coating is prepared after finishing; the other steps are the same.

[0038] Performance results: The mechanical properties of the matrix are consistent with those of Example 1, but under the combined conditions of corrosion and erosion, erosion pits are easily formed on the surface, the nozzle orifice wear is accelerated, and the service life is reduced by 25% compared with Example 1.

[0039] Comparative Example 6 (Ordinary flame spraying of micron-sized Al2O3 coating) The only difference from Example 1 is that the micron-sized Al2O3 coating is prepared using a conventional flame spraying process, without spray granulation and cold isostatic pressing; the other steps are the same.

[0040] Performance results: Coating porosity 2.0%, bond strength 32 MPa, microhardness 850 H 0.1 Microcracks and peeling are easily generated during use, and the service life is reduced by 30% compared with Example 1.

[0041] Comparing Example 1 with Comparative Examples 1-3, it can be seen that the present invention adopts a preparation process of segmented temperature-controlled discharge plasma sintering combined with high-speed flame spraying of nano-coatings. Compared with existing preparation methods such as traditional hot pressing sintering, conventional machining, and atmospheric pressure sintering, the nozzles produced have significant advantages in terms of substrate density, hardness, wear rate, dimensional accuracy, and actual service life. It solves the core problems of uneven substrate performance, easy failure, and short service life caused by traditional nozzle preparation methods from the root of the process.

[0042] The comparison between Example 1 and Comparative Examples 1 and 4 shows that the segmented heating and precise temperature control of the discharge plasma sintering process is the key to achieving high densification and fine grain strengthening of the nozzle substrate. Single-stage heating and slow heating sintering methods will cause significant coarsening of tungsten carbide grains, thereby greatly reducing the mechanical properties and actual service life of the nozzle substrate.

[0043] Comparing Example 1 with Comparative Examples 5 and 6, it can be found that the nano-alumina coating prepared by the present invention using composite granulation combined with high-speed flame spraying can effectively improve the erosion and corrosion resistance of the nozzle. The coating has the characteristics of high bonding strength and low porosity, and its protective effect is significantly better than that of uncoated structures and coatings prepared by conventional spraying processes. It can prevent the nozzle from undergoing surface failure under combined corrosion and erosion conditions.

[0044] The comparison results between Comparative Example 3 and Examples 1, 2, and 3 demonstrate that precise control of raw material ratio and refined management of powder preparation process are important foundations for ensuring subsequent sintering effect. The results of Example 4 show that the preparation process adopted in this invention can stably prepare large-size nozzle blanks with uniform axial and radial properties and no obvious performance gradient, effectively solving the problem of uneven microstructure of large-size blanks in traditional preparation processes, and meeting the actual needs of industrial mass production.

[0045] A comprehensive comparison of Examples 1-4 with all comparative examples shows that the performance advantages of the high-pressure nozzle prepared by the present invention do not stem from the improvement of a single process, but are the result of the synergistic effect of four core processes: composite powder preparation, segmented temperature-controlled discharge plasma sintering, precision machining, and nano-coating preparation. Only by systematically optimizing the entire process can the nozzle achieve high performance and long service life under the combined working conditions of ship rust removal, and better adapt to the operational requirements of rust removal robots.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a binderless WC-VC hard alloy high-pressure nozzle, characterized in that, Includes the following steps: 1) Preparation of WC-VC composite powder: Using WC powder as the matrix and VC powder as the grain inhibitor, wet ball milling was carried out under the protection of high-purity argon gas and anhydrous ethanol as the ball milling medium. After vacuum drying, WC-VC composite powder was obtained by sieving. 2) Segmented temperature-controlled discharge plasma sintering: WC-VC composite powder is loaded into a graphite mold, the sintering cavity is evacuated and then subjected to three-stage heating and sintering, and the nozzle blank is obtained after pressure holding and cooling. 3) Precision machining: The nozzle blank is rough turned, fine ground and polished to obtain a semi-finished nozzle; 4) Preparation of nano-Al2O3 coating: Nano-α-Al2O3 powder is spray granulated and cold isostatically pressed into spherical agglomerates for feeding. The agglomerates are then sprayed onto the surface of the nozzle semi-finished product using HVOF high-speed flame to form a coating. The finished nozzle is obtained after low-temperature hot pressing and remelting.

2. The method for preparing the binderless WC-VC hard alloy high-pressure nozzle according to claim 1, characterized in that, In step 1), the purity of WC powder is ≥99.9% and the average particle size is 0.3μm; the purity of VC powder is ≥99.5% and the average particle size is 0.1μm. The amount of VC powder added is 0.1% to 1.0% of the mass of WC powder.

3. The method for preparing a binderless WC-VC hard alloy high-pressure nozzle according to claim 1 or 2, characterized in that, In step 1), the ball-to-material mass ratio of wet ball milling is (8:1) to (10:1), the ball milling speed is 300 to 600 r / min, the ball milling time is 20 to 40 h, the vacuum drying temperature is 50 to 80 ℃, and the sieve mesh is 100 to 200 mesh.

4. The method for preparing a binderless WC-VC hard alloy high-pressure nozzle according to claim 1 or 2, characterized in that, In step 2), the filling density of the WC-VC composite powder in the graphite mold is 1.8~2.2 g / cm³. 3 The vacuum level of the sintering cavity after evacuation is ≤10Pa.

5. The method for preparing a binderless WC-VC hard alloy high-pressure nozzle according to claim 1 or 2, characterized in that, In step 2), the three-stage heating sintering is as follows: the first stage is to heat up to 400-450℃ at 100-150℃ / min and hold for 10-30s; the second stage is to heat up to 1450-1550℃ at 150-200℃ / min and hold for 2-5min; the third stage is to hold at 1500-1550℃ and 30-50MPa pressure for 4-10min; the temperature fluctuation throughout the process is controlled within ±5℃.

6. The method for preparing a binderless WC-VC hard alloy high-pressure nozzle according to claim 1 or 2, characterized in that, In step 3), the roughing allowance is 0.1~0.3mm, the surface roughness Ra≤0.8μm, and the dimensional tolerance is ≤±0.01mm.

7. The method for preparing a binderless WC-VC hard alloy high-pressure nozzle according to claim 1 or 2, characterized in that, In step 4), the particle size of the nano α-Al2O3 powder is 50 nm; the particle size of the spherical agglomerate feed is 15~45 μm, and the Hall flow rate is ≤25 s / 50 g.

8. The method for preparing a binderless WC-VC hard alloy high-pressure nozzle according to claim 1 or 2, characterized in that, In step 4), the parameters for HVOF high-speed flame spraying are: spraying distance 100~150mm, oxygen flow rate 800~1200L / min, kerosene flow rate 20~25L / h, powder feed rate 20~30g / min; coating thickness 50~100μm.

9. The method for preparing a binderless WC-VC hard alloy high-pressure nozzle according to claim 1 or 2, characterized in that, The prepared nozzle is a binderless WC-VC hard alloy, and the nozzle orifice and inner flow channel surface are coated with a nano-Al2O3 wear-resistant and corrosion-resistant coating.

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