A method for preparing high-density cemented carbide based on a binder jetting additive manufacturing technique

Abstract

The application discloses a method for preparing high-density cemented carbide based on a binder jetting additive manufacturing technology, and the method adopts WC-12Co alloy powder to print the powder by using a binder jetting printing device, the saturation of the binder and the jetting voltage are accurately and cooperatively controlled, the weight of the ink drop of single ink jetting is highly matched with the weight required by the theoretical saturation, and thus the green body with extremely uniform internal binder distribution can be directly solidified and sintered. The high-density cemented carbide with the density of more than 99% and the hardness of 1295.3 HV 30 is prepared by omitting the independent debinding process in the traditional BJ process through the three-step process of "printing-solidifying-sintering", the problems of low density (<98%) and complex process of the traditional BJ printed cemented carbide are solved, an efficient and reliable near-net forming scheme is provided for high-performance and complex-structure cemented carbide parts, the process is simple and easy to implement, and the application has a good popularization prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing high-density cemented carbide, and more particularly to a method for preparing high-density cemented carbide based on binder spraying additive manufacturing technology. Background Technology

[0002] Carbide is an alloy material made from hard compounds of refractory metals (such as WC) and binder metals (such as Co) through powder metallurgy. It possesses extremely high hardness, strength, and wear resistance, and is widely used in cutting tools, molds, and wear-resistant parts. However, traditional carbide tool manufacturing processes have limitations when producing tools with complex structures, such as difficulty in forming, low material utilization, and long manufacturing cycles, making it difficult to meet the growing demands for high precision and personalization.

[0003] Additive manufacturing, commonly known as 3D printing, is a disruptive technology that allows for the layer-by-layer accumulation of material based on CAD design files to form parts with complex shapes. Additive manufacturing technology can easily produce parts with complex geometries, and is expected to reduce production costs in the production and application of cemented carbide. Binder jetting (BJ), as a type of 3D printing, is a "cold forming" process based on a powder bed. It selectively jets binder to bond powder layer by layer, followed by debinding and sintering to obtain the final part. It offers advantages such as low cost, no need for supports, ability to form complex structures, high material utilization, and suitability for mass production, providing a new technological path for the forming of cemented carbide.

[0004] However, existing technologies using binder jet additive manufacturing (BJ) to prepare cemented carbides face numerous challenges in achieving high density. Sintered bodies often exhibit low density (typically below 98%), abnormal grain growth, and uneven mechanical properties, hindering their application in high-end fields. Existing documents (such as patent CN115026301A) employ a complex multi-material layered printing strategy (printing WC and Co green blanks separately, then stacking and infiltrating them). While aiming to improve Co phase distribution, this approach is cumbersome, requiring precise control of debinding and infiltrating processes, and making shape preservation and compositional uniformity control difficult. On the other hand, the conventional route of directly using WC-Co composite powder for binder jet printing and sintering generally suffers from insufficient sintering density (typically below 98%), high shrinkage and significant anisotropy, and susceptibility to decarburization or abnormal grain growth. This results in the final product's mechanical properties (such as hardness and toughness) failing to reach the levels of traditional processes, limiting its application in high-performance scenarios.

[0005] Furthermore, in the existing understanding of binder jet additive manufacturing (BJ) for preparing cemented carbide, there is a widely accepted technical bias: due to the high content and potentially uneven distribution of organic binder in BJ-printed green blanks, a separate, slowly heated debinding process is considered an essential safety step to prevent cracking, blistering, or even collapse of the green blank due to rapid pyrolysis of the binder during subsequent sintering. This has resulted in the BJ process remaining stuck in a lengthy "print-curing-debinding-sintering" process, hindering the realization of its efficiency advantages.

[0006] Therefore, the key bottleneck hindering the large-scale, high-quality mass production application of this technology lies in how to achieve one-step forming and sintering of WC-Co composite powder without a separate debinding process, by systematically optimizing the core process parameters of binder jet printing while simplifying the process flow and reducing production costs. This will ultimately result in cemented carbide parts with a density exceeding 99%, uniform microstructure, and excellent mechanical properties. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to overcome the shortcomings of the prior art and provide a simple and efficient method for preparing high-density cemented carbide based on binder spraying additive manufacturing technology, which does not require an independent debinding process.

[0008] Technical solution: The present invention discloses a method for preparing high-density cemented carbide based on binder spraying additive manufacturing technology, comprising the following steps:

[0009] (1) WC-12Co cemented carbide powder was used to prepare WC-12Co cemented carbide green blanks using binder jet printing technology. During the preparation process, the binder saturation and jetting voltage were controlled in a coordinated manner.

[0010] (2) Heat and solidify the WC-12Co cemented carbide green blank, remove excess powder from the surface, and obtain a shaped green blank;

[0011] (3) Take the solidified green body and sinter it.

[0012] In step (1), the WC-12Co cemented carbide powder has a particle size of 5-30 μm, a loose packing density of 5.43±0.03 g / cm³, a loose relative density of 37%-38%, a flowability of 22.13±0.20 s / 50g, and a carbon content of 5.20±0.02%. The binder includes polyvinylpyrrolidone, ethylene glycol, ethylene glycol monobutyl ether, 2-pyrrolidone, and water. The TG-DSC curve of the binder shows that it no longer volatilizes or volatilizes only in very small amounts after reaching 440 ℃. During the preparation process, the binder saturation is synergistically controlled at 77.5%-80%, and the spraying voltage is 95-96 V. By coordinating the control of binder saturation and jetting voltage, the actual single-jet ink droplet weight is 0.4166-0.4295 g, and the deviation between this actual droplet weight and the theoretical droplet weight calculated based on binder saturation is less than or equal to ±0.5%. When the matching relationship between binder saturation and jetting voltage deviates from this limit, causing the deviation between the actual droplet weight and the theoretical value to exceed ±0.5%, the density of the resulting cemented carbide is less than 99%, and the density decreases significantly. The powder fall time for binder jet printing is 2500-3000 ms, with 18-20 layers of pre-powder, and the penetration time is 25000-30000 ms. In step (2), the heating and curing temperature is 180-200 ℃, the heating and curing time is 4-5 h, and the density of the green body is 39%-42%. In step (3), the solidified green blank is directly sintered without a separate degreasing process. The sintering process is hydrogen positive pressure sintering, with a total sintering time of 17-19 h. The sintering temperature is first increased from room temperature to 495-600 ℃ at a rate of 1.1-1.3 ℃ / min and held for 2-3 h, then increased to 1345-1360 ℃ at a rate of 3.4-3.6 ℃ / min and held for 1-2 h, and finally increased to above 1430 ℃ at a rate of 0.9-1.1 ℃ / min and held for 1-2 h, followed by water cooling to obtain a cemented carbide with a density ≥99%. The sintering shrinkage rate of the cemented carbide is 25%-26%, 25%-27%, and 19%-24% in the X, Y, and Z directions, respectively, and the average density of the cemented carbide is 14.20-14.24 g / cm³. 3 The average density is 99.1%-99.4%.

[0013] Invention Principle: This invention is based on a method for preparing high-density cemented carbide using binder jet additive manufacturing technology. It employs WC-12Co cemented carbide powder with a particle size of 5-30 μm as the printing material, and combines specific printing parameters (binder saturation 77.5%-80%, jetting voltage 95-96 V) and a sintering process to obtain high-density, high-performance cemented carbide products. In binder jet printing, "binder saturation" is a theoretically calculated value that determines the ideal binder volume required to fill the pores of the powder at a preset green density. The "jet voltage" directly affects the driving waveform of the piezoelectric printhead, determining the actual weight of a single jetted binder droplet (ink droplet weight). Through systematic experiments, a precise jetting voltage of 95 V was determined to make the actual single-jet ink droplet weight (0.4166 g) infinitely close to the theoretical value. This precise matching of "saturation-voltage" (deviation < ±0.5%) is the physical basis for obtaining high-quality green bodies with uniform internal binder distribution and regular pore structure, creating important precursor conditions for subsequent efficient densification sintering.

[0014] Traditional BJ (Browser-Jet) processes typically employ a multi-step heat treatment process of "printing-curing-debinding-sintering," with a separate debinding step designed to slowly remove the organic binder and prevent cracking of the green body. This invention, based on the aforementioned principles, yields a green body with a highly uniform internal structure, uniform internal stress distribution, and good bonding between the organic binder and powder particles. Furthermore, the separate debinding step is omitted, and the cured green body is directly sintered. During the low-temperature heating stage of the sintering process (typically below 600°C), the binder components can be gently thermally decomposed and removed in a protective atmosphere. Due to the good uniformity of the green body, decomposition gases can escape smoothly, avoiding cracking or deformation caused by localized rapid gas generation or stress concentration. In the subsequent high-temperature sintering stage, the uniform green body structure ensures the uniform formation and spreading of the liquid phase (Co phase), with uniform capillary force distribution, thereby driving efficient rearrangement and dissolution-precipitation of WC particles, ultimately achieving near-fully dense sintering.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The process of preparing cemented carbide products by the present invention is significantly simplified, the cost is reduced and the effect is synergistically improved. The most prominent effect is that by matching specific parameters (binder saturation 77.5%-80%, spraying voltage 95-96 V), an extremely uniform green blank is obtained. It was unexpectedly found that this uniform green blank can safely skip the independent degreasing process required in the traditional BJ process. Compared with the lengthy process of complex WC / Co layer printing, stacking, degreasing, and melting sintering in the existing technology, the present invention simplifies the traditional four-step process (printing-curing-degreasing-sintering) to three steps (printing-curing-sintering), which greatly reduces energy consumption, time and equipment costs. Moreover, under this simplified process, the density of the final product not only does not decrease, but is actually increased to more than 99%, breaking through the bottleneck that the density of direct BJ printing of composite powder in the existing technology is generally lower than 98%; (2) The present invention found that the binder saturation and jet voltage are not independently adjustable parameters. The two must be precisely matched within a specific range (saturation 77.5%-80%, voltage 95-96 V) in order to make the actual ink drop weight (0.4166-0.4295 g) deviate from the theoretical required weight by less than ±0.5%. This matching is the physical basis for obtaining a uniform green body and is the premise for subsequent high-density sintering and omitting the degreasing process. By matching these parameters, the density of the sintered body can be successfully and stably increased to over 99%, exceeding the general level of direct BJ printing of composite powders in the prior art (usually <98%); (3) The cemented carbide products obtained by this invention not only have high density, but also high hardness (up to 1295.3 HV). 30 (3) The phase is pure and there is no decarburization, which proves the reliability of the simplified process route; (4) The “saturation-voltage” matching optimization principle provided by this invention can be directly extended to the optimization of BJ printing parameters in other material systems, providing a general parameter determination method for high density BJ printing. Attached Figure Description

[0016] Figure 1 SEM micrograph of the WC-12Co cemented carbide powder used in Example 1;

[0017] Figure 2 The image shows a physical sample of the high-density cemented carbide prepared using binder spraying additive manufacturing technology in Example 1.

[0018] Figure 3 The image shows the microstructure of the high-density cemented carbide prepared by binder spraying additive manufacturing technology in Example 1 under a scanning electron microscope.

[0019] Figure 4 A graph showing the relationship between different binder saturation, printing voltage, and single inkjet weight;

[0020] Figure 5 A bar chart showing the density and hardness of high-density cemented carbides prepared by binder spraying additive manufacturing technology at different binder saturation levels. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the embodiments. The test materials used in the embodiments can all be purchased through conventional means.

[0022] Example 1

[0023] (1) WC-12Co cemented carbide powder with a particle size of 5-30 μm (e.g. Figure 1 (As shown) The powder is placed in the powder storage bin of the binder jet printing equipment, and a WC-12Co cemented carbide green blank is prepared using the printing equipment according to specific printing parameters. The loose packing density of the cemented carbide powder is 5.43 g / cm³. 3 The bulk density was 38%, the flowability was 22.13 s / 50 g, and the carbon content was 5.20%. The binder, by weight, consisted of polyvinylpyrrolidone (12%), ethylene glycol (6%), ethylene glycol monobutyl ether (7%), 2-pyrrolidone (7%), and water (68%). The binder ceased to volatilize or volatilized only in very small amounts after reaching 440 °C. Specific printing parameters were: layer thickness 50 μm, jet voltage 95 V, binder saturation 77.5%, and single-droplet weight 0.4166 g. The binder jet printing process had a powder settling time of 3000 ms, a pre-lay of 20 layers, and a penetration time of 30000 ms. A WC-12Co cemented carbide green blank was obtained.

[0024] (2) After printing, the WC-12Co cemented carbide green blank is placed in an oven. After vacuuming, it is cured at 180 ℃ for 4 h. After removing it, excess powder on the surface is swept away to obtain the shaped green blank. The mass of the green blank is measured. The actual density is calculated by dividing the mass by the volume. Then, the actual density is divided by the theoretical density to obtain the density of the green blank after curing, which is 39%.

[0025] (3) The solidified green blank is directly placed into the sintering furnace without a separate degreasing process. The conventional WC-12Co cemented carbide sintering process is performed under a protective atmosphere, and then cooled with the furnace to obtain cemented carbide products with a density of ≥99%. The sintering process was hydrogen positive pressure sintering, using a horizontal sintering furnace that integrated debinding and sintering. The total sintering time was 18 hours. The sintering temperature was first increased from room temperature to 500℃ at a rate of 1.2℃ / min and held for 3 hours, then increased to 1350℃ at a rate of 3.5℃ / min and held for 2 hours, and finally increased to above 1435℃ at a rate of 1℃ / min and held for 1 hour, followed by water cooling. The dimensions of the sintered cemented carbide product in three directions were measured with vernier calipers and compared with the dimensions of the printed green blank. The shrinkage rates of the sintered sample in the X, Y, and Z directions were calculated to be 25%, 26%, and 21%, respectively. The average density of the sample was 14.23 g / cm³, the average compactness was 99.3%, and the average hardness was 1230.9 HV. 30 .

[0026] An appearance photograph of the high-density cemented carbide sample prepared in Example 1 is shown below. Figure 2 As shown, the microstructure is as follows Figure 3 As shown, the obtained high-density cemented carbide sample exhibits a dense overall microstructure with an average density of 14.23 g / cm³. The phases are pure with no decarburization, and the sample density reaches over 99%, specifically 99.3%. The average hardness is 1230.9 HV. 30 It performs well. Figure 3 The image shows the microstructure of the high-density cemented carbide prepared by binder spraying additive manufacturing technology in Example 1 under a scanning electron microscope. It can be seen that the structure is composed of granular WC and fillers, and the whole structure is very dense with almost no defects such as pores or cracks, which is consistent with its density of over 99%.

[0027] Example 2

[0028] The preparation process is the same as in Example 1, except that the printing voltage and adhesive saturation are adjusted, including the following steps:

[0029] (1) WC-12Co cemented carbide powder with a particle size of 5-30 μm was placed in the powder storage bin of a binder jet printing equipment, and WC-12Co cemented carbide green blanks were prepared using the printing equipment according to specific printing parameters. The loose packing density of the cemented carbide powder was 5.43 g / cm³. 3The loose relative density is 38%, the flowability is 22.13 s / 50 g, and the carbon content is 5.20%. The binder, based on a 100% mass fraction, consists of polyvinylpyrrolidone (12%), ethylene glycol (6%), ethylene glycol monobutyl ether (7%), 2-pyrrolidone (7%), and water (68%). The binder stops volatile or volatilizes only in very small amounts after reaching a temperature of 440 °C. The difference from Example 1 is that the layer thickness of 50 μm remains unchanged in the specific printing parameters, and the binder saturation is set to 80%. At this time, the theoretical single inkjet droplet weight is 0.4292 g. Through multiple weighing experiments, it was found that when the jetting voltage is adjusted to 96 V, the actual single inkjet droplet weight is 0.4295 g, which is closest to the theoretical value. Therefore, the jetting voltage is set to 96 V. The powder fall time of the binder jetting printing process is 3000 ms, the pre-powder layer is 20 layers, and the penetration time is 30000 ms.

[0030] (2) After printing, the WC-12Co cemented carbide green blank was placed in an oven, and after vacuuming, it was cured at 180 ℃ for 4 h. After that, it was taken out and the excess powder on the surface was swept off to obtain the shaped green blank. The density of the obtained WC-12Co cemented carbide shaped green blank was 42% after testing.

[0031] (3) The solidified green blank is directly placed into the sintering furnace without a separate degreasing process. The conventional WC-12Co cemented carbide sintering process is performed under a protective atmosphere, and then cooled with the furnace to obtain cemented carbide products with a density of ≥99%. The sintering process was hydrogen positive pressure sintering, using a horizontal sintering furnace that integrated debinding and sintering. The total sintering time was 18 hours. The sintering temperature was first increased from room temperature to 500℃ at a rate of 1.2℃ / min and held for 3 hours, then increased to 1350℃ at a rate of 3.5℃ / min and held for 2 hours, and finally increased to above 1435℃ at a rate of 1℃ / min and held for 1 hour, followed by water cooling. Tests showed that the sintering shrinkage of the cemented carbide products was 26%, 27%, and 24% in the X, Y, and Z directions, respectively. The average density of the samples was 14.24 g / cm³, the average compactness was 99.4%, and the average hardness was 1295.3 HV. 30 .

[0032] The high-density cemented carbide sample obtained in Example 2 has a similar morphology to that in Example 1. The sample exhibits a dense overall microstructure with an average density of 14.24 g / cm³, achieving a density of over 99%, and an average hardness of 1295.3 HV. 30 It performs well.

[0033] Example 3

[0034] The preparation process is the same as in Example 1, except that the printing voltage is adjusted to 94.5 V and the adhesive saturation is 75%, including the following steps:

[0035] (1) Use the exact same WC-12Co powder as in the same example, wherein the powder particle size is 5-30 μm and the loose packing density is 5.43 g / cm³. 3 The loose relative density is 38%, the flowability is 22.13 s / 50 g, and the carbon content is 5.20%. It is placed in the toner storage hopper for binder jet printing. The binder, by mass fraction (100%), consists of polyvinylpyrrolidone (12%), ethylene glycol (6%), ethylene glycol monobutyl ether (7%), 2-pyrrolidone (7%), and water (68%). The binder stops evaporating or evaporates only in very small amounts after the temperature reaches 440 °C. Unlike the previous example, while keeping the layer thickness constant at 50 μm, the binder saturation is set to 75%. At this point, the theoretical single-droplet weight is 0.4024 g. Through multiple droplet weighing experiments, the actual single-droplet weight of 0.4085 g was found to be closest when the jetting voltage is 94.5 V (with a deviation of approximately ±1.5% to ±2%). Therefore, the jetting voltage is set to 94.5 V. The toner settling time for the binder jet printing process is 3000 seconds. The pre-coated powder layer is 20 layers, and the penetration time is 30,000 ms.

[0036] (2) After printing, the WC-12Co cemented carbide green blank was placed in an oven, vacuumed, and cured at 180 ℃ for 4 h. After that, it was taken out and the excess powder on the surface was swept away to obtain the shaped green blank. The density of the obtained WC-12Co cemented carbide shaped green blank was tested to be 38%.

[0037] (3) The solidified green blank is placed directly into the sintering furnace without a separate degreasing process. The conventional WC-12Co cemented carbide sintering process is performed under a protective atmosphere, and then cooled with the furnace to obtain cemented carbide products with a density ≥98%. The sintering process was hydrogen positive pressure sintering, using a horizontal sintering furnace that integrated debinding and sintering. The total sintering time was 18 hours. The sintering temperature was first increased from room temperature to 500℃ at a rate of 1.2℃ / min and held for 3 hours, then increased to 1350℃ at a rate of 3.5℃ / min and held for 2 hours, and finally increased to above 1435℃ at a rate of 1℃ / min and held for 1 hour, followed by water cooling. Tests showed that the sintering shrinkage of the cemented carbide products was 27%, 28%, and 26% in the X, Y, and Z directions, respectively. The average density of the samples was 14.07 g / cm³, the average compactness was 98.2%, and the average hardness was 1203.8 HV. 30 .

[0038] The appearance of the high-density cemented carbide sample obtained in this embodiment is similar to that in Example 1. However, in this embodiment, because the binder saturation is set to 75%, when the ink droplet weighing experiment is conducted, the actual single ink droplet weight measured when the jetting voltage is set to 94.5 V is closest to the theoretically calculated optimal ink droplet weight, but there is a certain deviation (the deviation is calculated to be between ±1.5% and ±2%). This ultimately leads to insufficient uniformity of the green blank. Even if the degreasing step is omitted, the density of the sintered sample cannot reach more than 99%, and the dimensional accuracy control deteriorates, resulting in reduced performance.

[0039] The relationship between different binder saturation, printing voltage, and single inkjet weight is plotted based on the results of Examples 1-3, as shown in the figure. Figure 4 As shown, the density and hardness of high-density cemented carbides prepared by binder spraying additive manufacturing technology under different binder saturation levels in Examples 1-3 are plotted as follows. Figure 5 As shown; combined with Figure 4-5 It is evident that binder saturation and jetting voltage are not independently adjustable parameters. They must achieve a precise match within a specific range (saturation 77.5%-80%, voltage 95-96V) to ensure that the actual droplet weight (0.4166-0.4295 g) deviates from the theoretically required weight by less than ±0.5%. This guarantees that the sintered cemented carbide product achieves a density of over 99% and good hardness, reaching 1295.3 HV. 30 above.

Claims

1. A method for preparing high-density cemented carbide based on binder spraying, characterized in that, Includes the following steps: (1) WC-12Co cemented carbide powder was used to prepare WC-12Co cemented carbide green blanks using binder jet printing technology. During the preparation process, the binder saturation and jetting voltage were controlled in a coordinated manner to obtain WC-12Co cemented carbide green blanks. (2) Heat and solidify the WC-12Co cemented carbide green blank, remove excess powder from the surface, and obtain a shaped green blank; (3) Take the solidified green blank and sinter it.

2. The preparation method according to claim 1, characterized in that, In step (1), the particle size of WC-12Co cemented carbide powder is 5-30 μm, the loose packing density of WC-12Co cemented carbide powder is 5.43±0.03 g / cm³, the loose packing relative density is 37%-38%, the flowability is 22.13±0.20 s / 50 g, and the carbon content is 5.20±0.02%.

3. The preparation method according to claim 1, characterized in that, In step (1), the adhesive includes polyvinylpyrrolidone, ethylene glycol, ethylene glycol monobutyl ether, 2-pyrrolidone and water.

4. The preparation method according to claim 1, characterized in that, During the preparation process, the binder saturation is controlled to be 77.5%-80% and the spraying voltage is 95-96 V.

5. The preparation method according to claim 4, characterized in that, By coordinating the control of binder saturation and jet voltage, the actual single-jet ink droplet weight is 0.4166-0.4295 g, and the deviation between the actual ink droplet weight and the theoretical ink droplet weight calculated based on binder saturation is less than or equal to ±0.5%.

6. The preparation method according to claim 1, characterized in that, In step (1), the powder drop time for adhesive jet printing is 2500-3000 ms, the pre-powder layer is 18-20 layers, and the penetration time is 25000-30000 ms.

7. The method according to claim 1, characterized in that, In step (2), the heating and curing temperature is 180-200℃, the heating and curing time is 4-5 h, and the density of the green body is 39%-42%.

8. The preparation method according to claim 1, characterized in that, In step (3), the solidified green blank is directly sintered without going through a separate degreasing process.

9. The preparation method according to claim 8, characterized in that, The sintering process is hydrogen positive pressure sintering, with a total sintering time of 17-19 h. The sintering temperature is first raised from room temperature to 495-600 ℃ at a rate of 1.1-1.3 ℃ / min and held for 2-3 h, then raised to 1345-1360 ℃ at a rate of 3.4-3.6 ℃ / min and held for 1-2 h, and finally raised to above 1430 ℃ at a rate of 0.9-1.1 ℃ / min and held for 1-2 h, followed by water cooling to obtain a cemented carbide with a density ≥99%.

10. The preparation method according to claim 9, characterized in that, The sintering shrinkage rates of cemented carbide are 25%-26%, 25%-27%, and 19%-24% in the X, Y, and Z directions, respectively, and the average density of cemented carbide is 14.20-14.24 g / cm³. 3 The average density is 99.1%-99.4%.

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