A method for preparing WC-Co hard alloy based on electron beam selective melting

Abstract

This invention provides a method for preparing WC-Co cemented carbide based on electron beam selective melting, belonging to the field of cemented carbide additive manufacturing technology. The method includes: 1) mixing tungsten carbide powder and cobalt powder; 2) modeling the component to be printed; 3) setting substrate preheating parameters; 4) setting contour scanning parameters; 5) setting part scanning parameters; 6) setting the part scanning strategy; 7) loading the mixed powder into the hopper of an electron beam selective melting device, leveling the substrate, and evacuating the vacuum; 8) cyclically stacking the powder according to steps 2) to 6) to obtain the WC-Co cemented carbide. The microstructure of this cemented carbide shows that the average size of the WC grains is 50-60 μm, and the Co phase is uniformly distributed between the WC hard phases. Room temperature tribological tests show that the cemented carbide has a friction coefficient of 0.55–0.65 at room temperature, exhibiting excellent room temperature wear resistance, making it suitable for cutting tools, molds, mechanical parts, etc., where room temperature tribological performance is required.

Description

Technical Field

[0001] This invention belongs to the field of cemented carbide additive manufacturing technology, and particularly relates to a method for preparing WC-Co cemented carbide based on electron beam selective melting. Background Technology

[0002] WC-Co cemented carbide is a composite material composed of a hard phase (WC) and a binder phase (Co). Due to its extremely high hardness, excellent wear resistance, and good toughness, it has irreplaceable application value in various industrial fields such as tool manufacturing, mold processing, and wear-resistant parts production. Currently, the traditional manufacturing process of WC-Co cemented carbide mainly relies on powder metallurgy sintering. This process requires multiple steps, including powder mixing, pressing, and high-temperature sintering. Not only is the process cumbersome and the production cycle long, but it also makes it difficult to achieve near-net-shape forming of complex structural parts. For WC-Co cemented carbide parts with complex structures such as irregular shapes, thin walls, and internal hollows, traditional processes often suffer from high forming difficulty, low dimensional accuracy, and large amounts of subsequent machining, severely limiting its application expansion in the high-end equipment field.

[0003] Electron beam melting (EBM) technology, as one of the core technologies in additive manufacturing, has become the preferred technology for near-net-shape forming of complex structural metal materials due to its advantages such as high energy density, high forming efficiency, and clean vacuum forming environment. It can precisely and rapidly fabricate complex structural parts through layer-by-layer powder laying and electron beam scanning melting, effectively overcoming the limitations of traditional processes. In recent years, some research has attempted to apply EBM technology to the preparation of WC-8Co cemented carbide; however, for the specific composition system of WC-8Co (Co content of 8%), existing technologies still face many technical bottlenecks that urgently need to be addressed.

[0004] Specifically, existing WC-8Co cemented carbide EBM preparation technology has the following shortcomings: First, the matching between preheating temperature and electron beam energy density is poor. Insufficient preheating can easily lead to excessive temperature gradients during molding, generating thermal stress, which in turn causes defects such as cracks, warping, and deformation in the molded parts. On the other hand, excessive preheating can lead to premature powder sintering and difficulty in powder spreading, affecting the molding quality. Second, the optimization of electron beam scanning methods and process parameters is insufficient. Existing scanning methods and parameter settings cannot balance molding efficiency and molding quality, and are prone to problems such as uneven melt pool, excessive porosity, and excessive surface roughness. Third, there is a lack of a stable molding process window for the WC-8Co system. The molding effect varies greatly under different combinations of process parameters, the process stability is poor, and it is difficult to achieve large-scale and engineering production, which seriously limits the promotion and application of WC-8Co cemented carbide in the field of complex structural parts.

[0005] Based on the shortcomings of the existing technologies, there is an urgent need to develop an electron beam melting preparation method that is stable, produces excellent molding quality, and is compatible with the WC-8Co system. This method would solve the problems of numerous molding defects, unstable processes, and difficulty in engineering applications in the existing technologies, and promote the efficient preparation and industrial application of complex WC-8Co cemented carbide components. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for preparing WC-Co cemented carbide based on electron beam selective melting (EBM) and its applications. This invention solves the problems of poor forming, coarse grains, and insufficient room temperature wear resistance in 3D-printed WC-Co cemented carbide by optimizing the EBM process parameters. The process is highly controllable and facilitates industrial production.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing WC-Co cemented carbide based on electron beam selective melting, comprising the following steps: 1) Tungsten carbide powder and cobalt powder are mixed to obtain a mixed powder; 2) Model the components to be printed, slice them using slicing software, and import the sliced ​​files into the electron beam selective melting equipment; 3) Set the substrate preheating parameters: preheating temperature 950~1050℃, scanning current 38~42mA, scanning rate 18~22m / s, focusing current 48~52mA; 4) Set the contour scanning parameters: scanning current 15~20mA, scanning rate 1.5~2.5m / s, focusing current -7mA~7mA, melt pool spacing 0.1~0.3mm; 5) Set the part scanning parameters: scanning current 10~12mA, scanning rate 1.1~1.3m / s, scanning interval 0.09~0.11mm, focusing current -7mA~7mA; 6) Set the scanning strategy for the parts; 7) Load the mixed powder described in step 1) into the hopper of the electron beam selective melting equipment, level the substrate, and evacuate the vacuum. 8) Stack the materials in a cyclic manner according to steps 2) to 6) to obtain WC-Co cemented carbide.

[0008] Preferably, the mass percentage of tungsten carbide powder to cobalt powder is (90-94):(6-10).

[0009] Preferably, the mass percentage of tungsten carbide powder to cobalt powder is 92:8.

[0010] Preferably, the particle size of the tungsten carbide powder is 10-100 μm.

[0011] Preferably, the cobalt powder has a particle size of 50–150 μm.

[0012] Preferably, the substrate preheating parameters are: preheating temperature 1000℃, scanning current 40mA, scanning rate 20m / s, and focusing current 50mA.

[0013] Preferably, the scanning parameters for the part are: scanning current 11mA, scanning rate 1.2m / s, scanning spacing 0.1mm, and focusing current 5mA.

[0014] Preferably, the scanning strategy for the part is a starting angle of 45°, a rotation angle of 90°, and a rotation layer of 1.

[0015] The present invention also provides a WC-Co cemented carbide prepared by the above preparation method based on electron beam selective melting.

[0016] This invention also provides the application of the above-mentioned electron beam selective melting of WC-Co cemented carbide in the fabrication of complex structural parts in the fields of aerospace, mineral exploration, and precision cutting tools.

[0017] The beneficial effects of this invention are: 1. This invention constructs a stable forming process window adapted to the specific composition system of WC-8Co by precisely optimizing the preheating temperature, electron beam process parameters, and scanning method, thereby achieving efficient and stable near-net-shape forming of WC-8Co cemented carbide. It ensures that the resulting formed parts have a complete shape, no macroscopic cracks, no obvious warping deformation, and uniform microstructure, meeting the requirements for use in cutting tools, molds, wear-resistant parts, and other fields. At the same time, it simplifies the process flow and improves process stability, providing technical support for the large-scale and engineering production of complex WC-8Co cemented carbide parts.

[0018] 2. The electron beam selective melting process of this invention can successfully manufacture 3D printed components with specific shapes. By adjusting different process parameters, the printed components have basically complete shapes, clear outlines, uniform microstructures, and phase compositions similar to WC. The results are basically the same for 8Co cemented carbide.

[0019] 3. The WC-8Co component printed by electron beam selective melting process in this invention has a friction coefficient of 0.55–0.65 at room temperature, exhibiting excellent room temperature wear resistance, and is suitable for cutting tools, molds, mechanical parts and other fields that require room temperature friction and wear performance. Attached Figure Description

[0020] Figure 1 For 3D printing WC-8Co metal powder; Figure 2This refers to the electron beam selective melting 3D printing process. Figure 3 Samples for electron beam selective melting 3D printing; Figure 4 The room temperature tribological wear curves for WC-8Co are shown. Figure 5 XRD pattern and tissue morphology of WC-8Co. Detailed Implementation

[0021] This invention provides a method for preparing WC-Co cemented carbide based on electron beam selective melting, comprising the following steps: 1) Tungsten carbide powder and cobalt powder are mixed to obtain a mixed powder; 2) Model the components to be printed, slice them using slicing software, and import the sliced ​​files into the electron beam selective melting equipment; 3) Set the substrate preheating parameters: preheating temperature 950~1050℃, scanning current 38~42mA, scanning rate 18~22m / s, focusing current 48~52mA; 4) Set the contour scanning parameters: scanning current 15~20mA, scanning rate 1.5~2.5m / s, focusing current -7mA~7mA, melt pool spacing 0.1~0.3mm; 5) Set the part scanning parameters: scanning current 10~12mA, scanning rate 1.1~1.3m / s, scanning interval 0.09~0.11mm, focusing current -7mA~7mA; 6) Set the scanning strategy for the parts; 7) Load the mixed powder described in step 1) into the hopper of the electron beam selective melting equipment, level the substrate, and evacuate the vacuum. 8) Stack the materials cyclically in steps 2) to 6) to obtain WC-Co cemented carbide.

[0022] The present invention does not have any special limitation on the source of the tungsten carbide (WC) powder and cobalt (Co) powder, and conventional commercially available products in the art can be used.

[0023] In this invention, the particle size of the WC powder is preferably 10-100 μm, the particle size of the Co powder is preferably 50-150 μm, and the purity of the above raw materials is preferably ≥99.9%.

[0024] In this invention, the mass percentage of tungsten carbide powder to cobalt powder is preferably (90-94):(6-10), and more preferably 92:8.

[0025] In this invention, it is preferable to load the mixed powder into the hopper of the electron beam selective melting equipment, level the substrate, and evacuate it to 10°C. -5 Pa.

[0026] In this invention, preferably according to the parameters set in steps 2) to 6), the EBM device cyclically stacks materials by descending the worktable by one layer thickness, spreading powder with a scraper, preheating the powder bed, scanning the outline, and scanning the selected area, and finally forms the required print.

[0027] In this invention, after printing is completed, the printed part is preferably cooled in a vacuum furnace for 10 minutes, then cooled with helium protective gas, the powder bed is sandblasted to remove the printed part, the printed part is wire cut and surface treated to finally form the desired printed part.

[0028] The present invention preferably uses the above-mentioned cut sample to perform coarse grinding and polishing in stages using different grades of sandpaper and polishing liquid, and observes the tissue characteristics using a scanning electron microscope.

[0029] The present invention preferably uses the above-mentioned cut sample to perform coarse grinding and polishing in stages using different grades of sandpaper and polishing liquid, and conducts room temperature wear test.

[0030] In this invention, the preferred conditions for the room temperature friction and wear test are: room temperature (20–25℃), load 5N, rotation speed 200r / min, rotation radius 2mm, and test time 120min.

[0031] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1 The method for preparing WC-Co alloy by electron beam selective melting 3D printing includes the following steps: (1) Model the components to be printed, slice them using slicing software, and import the sliced ​​files into the EBM device; (2) Set the substrate preheating parameters: preheating temperature 1000℃, scanning current 40mA, scanning speed 20m / s, focusing current 50mA; (3) Set the contour scanning parameters: scanning current 18mA, scanning rate 2m / s, focusing current 0mA, and melt pool spacing 0.2mm; (4) Set the part scanning parameters: scanning current 11mA, scanning rate 1.2m / s, scanning interval 0.1mm, focusing current 5mA; (5) Set the scanning strategy for the part: starting angle 45°, rotation angle 90°, and rotation layer 1; (6) Load a total of 10 kg of mixed powder, consisting of 9.2 kg of WC powder and 0.8 kg of Co powder, into the EBM equipment hopper, level the substrate, and evacuate to 10°C. -5 Pa; (7) According to the parameters set in steps (1) to (6), the EBM equipment stacks the powder in a cycle by descending the worktable by one layer thickness, spreading the powder with a scraper, preheating the powder bed, scanning the outline, and scanning the selected area, and finally forms the required print. (8) After printing, the printed parts are cooled in the vacuum furnace for 10 minutes, then helium protective gas is introduced for cooling. The printed parts are then wire-cut and surface-treated to finally form the required printed parts. (9) The alloy sample was coarsely ground with different grades of sandpaper: 80 mesh, 600 mesh, 1000 mesh, and 2000 mesh. Then, it was mechanically polished for coarse and fine polishing until the alloy surface was free of obvious scratches and had a bright mirror finish. The microstructure was observed using X-ray diffraction and scanning electron microscopy. The average size of WC grains in the microstructure was 50-60 μm, and the Co phase was uniformly distributed. (10) The alloy prepared by the above method is prepared into a room temperature friction and wear test specimen and the room temperature friction and wear performance is tested. The room temperature friction and wear test conditions are: room temperature (20–25℃), load 5N, rotation speed 200r / min, rotation radius 2mm, test time 120min, and the friction coefficient at room temperature is measured to be 0.55–0.65.

[0034] Experimental results: SEM observations were performed on the powder used in the above-mentioned selective electron beam fusion 3D printing. The observation results are as follows: Figure 1 As shown in (A) and (B), the powder is mixed evenly.

[0035] The process steps of the above-mentioned selective electron beam melting 3D printing were recorded, such as... Figure 2 As shown in (A), (B), (C), and (D), the entire process is stable, the powder bed surface is uniform, the powder bed sintering degree is moderate, and the powder bed recycling rate is high. The printed samples are as follows... Figure 3 As shown in (A) and (B), the printed parts have a high degree of reproduction of the model, low surface roughness, and present an overall complete state.

[0036] The WC-8Co cemented carbide prepared above was characterized and tested. The alloy sample was separated from the substrate by wire cutting. The printed part was smoothed and polished using 80-2000 grit diamond sandpaper. The alloy sample was then subjected to room temperature tribological testing using a tribological testing machine. The test results are as follows: Figure 4 As shown in the figure. Experimental results show that the coefficient of friction of the WC-8Co alloy is 0.55-0.65 when deformed at room temperature. Under these conditions, the WC-8Co alloy manufactured by EBM exhibits excellent wear resistance at room temperature.

[0037] The crystal structure of the WC-8Co alloy was analyzed using XRD, such as... Figure 5As shown in (A), WC phase and Co3W3C phase were observed, which is basically consistent with the WC-8Co alloy produced by conventional methods.

[0038] The microstructure of the WC-8Co alloy was observed using BSD, such as... Figure 5 As shown in (B), (C), and (D), the Co phase is observed to be uniformly distributed between the WC hard phases, which is basically consistent with the WC-8Co alloy produced by the conventional method.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing WC-Co cemented carbide based on electron beam selective melting, characterized in that, Includes the following steps: 1) Tungsten carbide powder and cobalt powder are mixed to obtain a mixed powder; 2) Model the components to be printed, slice them using slicing software, and import the sliced ​​files into the electron beam selective melting equipment; 3) Set the substrate preheating parameters: preheating temperature 950~1050℃, scanning current 38~42mA, scanning rate 18~22m / s, focusing current 48~52mA; 4) Set the contour scanning parameters: scanning current 15~20mA, scanning rate 1.5~2.5m / s, focusing current -7mA~7mA, melt pool spacing 0.1~0.3mm; 5) Set the part scanning parameters: scanning current 10~12mA, scanning rate 1.1~1.3m / s, scanning interval 0.09~0.11mm, focusing current -7mA~7mA; 6) Set the scanning strategy for the parts; 7) Load the mixed powder described in step 1) into the hopper of the electron beam selective melting equipment, level the substrate, and evacuate the vacuum. 8) Stack the materials in a cyclic manner according to steps 2) to 6) to obtain WC-Co cemented carbide.

2. The preparation method of WC-Co cemented carbide based on electron beam selective melting according to claim 1, characterized in that, In step 1), the mass percentage of tungsten carbide powder to cobalt powder is (90-94): (6-10).

3. The method for preparing WC-Co cemented carbide based on electron beam selective melting according to claim 1, characterized in that, In step 1), the mass percentage of tungsten carbide powder to cobalt powder is 92:

8.

4. The method for preparing WC-Co cemented carbide based on electron beam selective melting according to claim 1, characterized in that, The particle size of the tungsten carbide powder in step 1) is 10-100 μm.

5. The method for preparing WC-Co cemented carbide based on electron beam selective melting according to claim 1, characterized in that, The cobalt powder in step 1) has a particle size of 50-150 μm.

6. The method for preparing WC-Co cemented carbide based on electron beam selective melting according to claim 1, characterized in that, In step 3), the substrate preheating parameters are: preheating temperature 1000℃, scanning current 40mA, scanning rate 20m / s, and focusing current 50mA.

7. The method for preparing WC-Co cemented carbide based on electron beam selective melting according to claim 1, characterized in that, In step 5), the part scanning parameters are: scanning current 11mA, scanning rate 1.2m / s, scanning spacing 0.1mm, and focusing current 5mA.

8. The method for preparing WC-Co cemented carbide based on electron beam selective melting according to claim 1, characterized in that, In step 6), the scanning strategy for the part is a starting angle of 45°, a rotation angle of 90°, and a rotation layer of 1.

9. A WC-Co cemented carbide prepared by the preparation method according to any one of claims 1 to 8 based on electron beam selective melting.

10. The application of the electron beam selective melting method for WC-Co cemented carbide as described in claim 9 in the fabrication of complex structural parts in the fields of aerospace, mineral exploration, and precision cutting tools.

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