Method for producing a metal ceramic working die reinforced in situ with platelet-shaped tungsten carbide and a metal ceramic working die material

Abstract

The present application relates to cermet material preparation technology, belongs to other hard alloy technical field, especially a kind of plate-shaped crystal tungsten carbide in situ reinforced cermet tooling preparation method and cermet tooling material.The method includes: solid solution powder, powder, carbide powder, carbon black powder and metal binder powder are mixed, ball milled and granulated, after compaction forming, carry out degreasing treatment, deoxidation and impurity removal treatment, nitrogen atmosphere negative pressure solid phase sintering treatment and high-temperature liquid phase sintering treatment, make solid solution of tungsten-containing solid solution and nitrogen-containing carbonitride occur solid solution reaction and promote WC in situ precipitation, form plate-shaped crystal tungsten carbide in high-temperature liquid phase sintering stage, obtain densification cermet tooling material.The method does not need to add expensive plate-shaped crystal powder, can realize the uniform distribution of plate-shaped crystal tungsten carbide, and the obtained material has higher bending strength, hardness and fracture toughness.

Description

Technical Field

[0001] This invention relates to the preparation technology of cermet materials, belonging to the field of other cemented carbide technology, and particularly to a method for preparing plate-shaped tungsten carbide in-situ reinforced cermet tools and dies, as well as the cermet tool and die material. This technical solution uses tungsten-containing titanium carbide solid solution powder and nitrogen-containing titanium carbonitride powder as reaction precursors, and controls the in-situ precipitation and growth of plate-shaped tungsten carbide through staged sintering. It can be used to prepare cermet cutting tool materials and die materials with high bending strength, high hardness, and high fracture toughness. Background Technology

[0002] Titanium carbide-based and titanium carbonitride-based cermets combine the high hardness, high wear resistance, and high chemical stability of the ceramic phase with the toughness and machinability of the metallic binder phase, and have been widely used in cutting tools, wear-resistant tools, and mold materials. Under conditions such as high-speed cutting, wear-resistant forming, and high-temperature processing, these materials exhibit good wear resistance and thermal stability, thus occupying an important position in modern manufacturing.

[0003] In existing technologies, common improvement directions for Ti(C,N)-based cermets mainly focus on composition adjustment, core-shell structure control, gradient structure design, and sintering atmosphere regulation. For example, Chinese patent document CN100371299C (hereinafter referred to as Document 1) discloses a functionally graded nanocomposite Ti(C,N)-based cermet and its preparation method. This method involves preparing a mixture of TiC, TiN, WC, Ni, Mo, VC, Cr3C2, and C powders, followed by mixing, adding a forming agent, pressing, debinding, vacuum sintering, and then nitriding at 1100℃ to 1250℃ in a nitrogen atmosphere of 0.08MPa to 6MPa to obtain Ti(C,N)-based cermet materials with high flexural strength and surface hardness. This document indicates that in the field of Ti(C,N)-based cermets, there already exists a technical route to improve material properties by adding W-related components, vacuum sintering, and subsequent nitriding treatment.

[0004] For example, Japanese patent document JP4172754B2 discloses TiCN-based cermets and their preparation methods, focusing on improving hardness and toughness by constructing a hard dispersed phase with a dual or triple core structure. This document indicates that improvements in the strength and toughness of existing TiCN-based cermets mainly focus on the design of the hard phase microstructure and conventional microstructure control.

[0005] However, while existing technologies can improve the hardness and toughness of Ti(C,N)-based cermets to some extent, they still have the following shortcomings: First, existing solutions mostly improve performance by directly adding WC or other hard phase powders, adjusting the proportion of metal binder phases, or controlling the core structure. They have not yet provided a clear technical path for how to utilize the solid solution reaction between tungsten-containing solid solutions and nitrogen-containing carbonitrides to induce the precipitation and growth of plate-shaped tungsten carbide in situ during sintering. Second, existing solutions usually do not solve the problem of low-cost and uniform dispersion of plate-shaped crystalline reinforcements. Third, existing Ti(C,N)-based cermets are still prone to chipping and cracking under complex stress conditions, indicating that there is still room for further improvement in their strength and toughness.

[0006] Therefore, existing technologies still require a new method for preparing metal-ceramic molds to form a uniformly distributed plate-shaped tungsten carbide structure in situ during sintering, based on the metallurgical reaction rules of tungsten-containing solid solutions, nitrogen-containing carbonitrides, and staged sintering processes, without relying on expensive external plate-shaped crystalline powders or whisker powders. This would improve the bending strength, hardness, and fracture toughness of the metal-ceramic mold material. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing plate-shaped tungsten carbide in-situ reinforced metal ceramic molds and a metal ceramic mold material, so as to solve the problems of insufficient strength and toughness, high cost of reinforcing body introduction, and uneven dispersion of plate-shaped crystalline reinforcing body in existing titanium carbide-based metal ceramics or titanium carbonitride-based metal ceramics.

[0008] A method for preparing a plate-shaped crystalline tungsten carbide in-situ reinforced cermet mold includes the following steps: Powder mixing and granulation steps: Tungsten-containing titanium carbide solid solution powder, nitrogen-containing titanium carbonitride powder, carbide powder, carbon black powder, and metal binder powder are mixed and then ball-milled, dried, and granulated to obtain a metal-ceramic mixed powder. The tungsten-containing titanium carbide solid solution powder is... Solid solution powder, wherein the nitrogen-containing titanium carbonitride powder is powder.

[0009] Pressing and forming step: The metal-ceramic mixed powder is pressed and formed to obtain a metal-ceramic blank.

[0010] The phased sintering process involves sequentially subjecting the metal-ceramic green body to degreasing, deoxidation and impurity removal, solid-state sintering, and high-temperature liquid-phase sintering. The solid-state sintering is performed under a nitrogen atmosphere and negative pressure to ensure that the green body... solid solution powder and the The powder undergoes a solid solution reaction to form a nitrogen-containing solid solution, which simultaneously reduces the solid solubility of W in the nitrogen-containing solid solution and promotes the precipitation of WC. The high-temperature liquid phase sintering treatment is used to grow the precipitated WC into plate-shaped crystalline tungsten carbide and to densify the metal ceramic green body.

[0011] Cooling and sampling step: The metal-ceramic preform after the high-temperature liquid phase sintering treatment is cooled to obtain a metal-ceramic mold material containing plate-shaped tungsten carbide in its microstructure.

[0012] Preferably, the Parameters in solid solution powder The value is 0.20 to 0.45, preferably 0.30 to 0.40; The particle size of the solid solution powder is from 0.1 micrometers to 5.0 micrometers, preferably from 0.5 micrometers to 2.0 micrometers. The purpose of adopting the above composition and particle size range is to ensure that the initial raw materials have a sufficient concentration of W element and to make the powder have a high specific surface area, so as to promote the reaction between the tungsten-containing titanium carbide solid solution powder, the nitrogen-containing carbonitride powder, and the carbide powder during sintering, thereby facilitating the precipitation amount and size control of plate-shaped tungsten carbide.

[0013] Preferably, the Powder parameters The value is between 0.5 and 1.0. The powder has a particle size of 0.05 micrometers to 2.0 micrometers. The powder is used to provide nitrogen and form a nitrogen-containing solid solution with the tungsten-containing titanium carbide solid solution powder, which is one of the necessary raw materials for inducing the precipitation of plate-shaped tungsten carbide.

[0014] Preferably, the carbide powder is at least one selected from molybdenum carbide, tantalum carbide, and niobium carbide, and the particle size of the carbide powder is from 0.1 micrometers to 5.0 micrometers. The carbide powder is used to improve the wettability between the titanium-containing carbonitride grains and the metal binder phase after sintering, or to improve the thermal shock resistance and other properties of the cermet material.

[0015] Preferably, the carbon black powder has a particle size of 0.05 micrometers to 0.5 micrometers, which is used to ensure the total carbon content of the sintered cermet material and to compensate for decarburization caused by the oxygen content on the surface of the ultrafine powder during sintering, as well as denitrification of the nitrogen-containing titanium carbonitride powder during the solid-phase reaction stage. The metal binder powder is at least one of nickel and cobalt, and the particle size of the metal binder powder is 1.0 micrometers to 5.0 micrometers. The metal binder powder forms a liquid phase during sintering and accelerates the solid solution reaction between the carbide and carbonitride powders through the dissolution process.

[0016] Preferably, the mass parts of the tungsten-containing titanium carbide solid solution powder, the nitrogen-containing titanium carbonitride powder, the carbide powder, the carbon black powder, and the metal binder powder are 50 to 75 parts, 10 to 20 parts, 0 to 8 parts, 0.1 to 1.0 parts, and 5 to 25 parts, respectively.

[0017] Preferably, in the powder mixing and granulation step, wet ball milling is used for 20 to 60 hours, with a ball-to-powder ratio of 3:1 to 10:1. A forming agent is added during the ball milling process, accounting for 1.0% to 3.0% of the total powder mass. Anhydrous ethanol is used as the grinding medium. The spray drying temperature is 80°C to 120°C, and the particle size of the metal-ceramic mixed powder after spray drying is 20 micrometers to 200 micrometers. This process helps ensure thorough mixing and refinement of the raw materials, forming spherical powder with good flowability, thereby improving the uniformity of subsequent pressing and forming and the density of the green body.

[0018] Preferably, the pressing pressure in the pressing and forming step is 100 MPa to 200 MPa.

[0019] Preferably, the degreasing treatment is vacuum degreasing, with a vacuum degree of 0.1 Pa to 10 Pa, a degreasing temperature of 350°C to 500°C, a holding time of 2 hours to 4 hours, and a heating rate of 1°C / min to 3°C / min; the deoxidation and impurity removal treatment has a temperature of 800°C to 1000°C, a holding time of 0.5 hours to 1 hour, and a heating rate of 2°C / min to 5°C / min.

[0020] Preferably, the solid-state sintering treatment employs nitrogen atmosphere negative pressure sintering, with a nitrogen pressure of 2000 Pa to 5000 Pa, a sintering temperature of 1200 °C to 1350 °C, a holding time of 0.5 hours to 1 hour, and a heating rate of 1 °C / min to 3 °C / min. This stage primarily promotes the solid solution reaction between tungsten-containing titanium carbide solid solution powder, nitrogen-containing titanium carbonitride powder, and carbide powder, and creates conditions for the precipitation of WC.

[0021] Preferably, the high-temperature liquid-phase sintering treatment is vacuum sintering or gas pressure sintering; when vacuum sintering, the vacuum degree is 1 Pa to 10 Pa, the sintering temperature is 1450℃ to 1550℃, and the holding time is 1 hour to 3 hours; when gas pressure sintering, the atmosphere is argon, the gas pressure is 0.5 MPa to 10 MPa, the sintering temperature is 1420℃ to 1500℃, and the holding time is 1 hour to 2 hours. This stage is a key stage for the densification of the metal-ceramic preform, and also a stage for the rapid growth of plate-like tungsten carbide.

[0022] Preferably, the cooling rate in the cooling sampling step is 5°C / min to 10°C / min, and the sample is removed from the furnace after cooling to below 100°C.

[0023] The metal-ceramic mold material prepared by the above method contains a plate-like tungsten carbide volume fraction of 10 vol% to 30 vol%, a length of 5 μm to 20 μm, and a thickness of 0.2 μm to 2 μm. The metal-ceramic mold material exhibits a three-point bending strength of 2300 MPa to 2800 MPa, a Vickers hardness of 1500 HV30 to 1700 HV30, and a fracture toughness of [missing information]. to .

[0024] The beneficial effects of this invention are: This invention does not employ direct addition of plate-like or whisker-like powders for reinforcement. Instead, it combines tungsten-containing titanium carbide solid solution powder with nitrogen-containing titanium carbonitride powder, and utilizes a staged control of nitrogen atmosphere negative pressure solid-state sintering and high-temperature liquid-phase sintering. This allows the W element to transition from a solid solution state to a precipitated state during sintering, thereby forming a plate-like tungsten carbide structure in situ within the cermet matrix. Compared to the technique in Reference 1, which directly uses WC powder and undergoes vacuum sintering and subsequent nitriding, this invention does not simply incorporate WC as an external raw material. Instead, through the control of the reaction precursor system and sintering path, WC is formed in situ during sintering, resulting in a tighter bond between the reinforcing phase and the matrix, and is more conducive to the homogenization of the microstructure.

[0025] This invention further divides the sintering process into degreasing treatment, deoxidation and impurity removal treatment, nitrogen atmosphere negative pressure solid-state sintering treatment, and high-temperature liquid-phase sintering treatment. The nitrogen atmosphere negative pressure solid-state sintering stage is mainly used to promote the solid solution reaction between the tungsten-containing solid solution and the nitrogen-containing carbonitrides, and to induce the precipitation of WC. The high-temperature liquid-phase sintering stage is mainly used to rapidly grow the precipitated WC to form plate-like tungsten carbide, while simultaneously densifying the green body. This division of labor between the two stages fundamentally differs the microstructure formation path of this invention from existing Ti(C,N)-based cermets that rely solely on conventional sintering or subsequent nitriding treatments.

[0026] Because the present invention ultimately yields a uniformly distributed plate-like tungsten carbide microstructure, cracks are more prone to deflection, bridging, and pinning during propagation, thus improving the fracture toughness of the material. Simultaneously, the synergistic effect of the plate-like and densified microstructure allows the material to maintain high hardness while still achieving high flexural strength. According to the data from the embodiments, the resulting cermet mold material can achieve a three-point flexural strength of 2300 MPa to 2800 MPa, a Vickers hardness of 1500 HV30 to 1700 HV30, and... to The fracture toughness can effectively overcome the bottleneck of insufficient strength and toughness in traditional Ti(C,N)-based cermets.

[0027] Furthermore, this invention does not rely on the addition of expensive plate-shaped crystal powder or whisker powder, but utilizes the metallurgical reaction of conventional powder particles during the sintering process to achieve the formation of plate-shaped crystal reinforcement structure. Therefore, it also has the effects of reducing the cost of reinforcement raw materials, alleviating the problem of uneven dispersion of added reinforcement, and improving the feasibility of industrialization. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the microstructure of the metal ceramic prepared in Example 1 of the present invention.

[0029] Figure 2 This is a schematic diagram of the microstructure of the metal ceramic prepared in Comparative Example 1. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Example 1

[0031] In this embodiment, the raw material ratio is 65 parts. Solid solution powder, 15 parts The metal binder powder was prepared by mixing 3 parts molybdenum carbide powder, 0.5 parts carbon black powder, and 16.5 parts nickel-cobalt powder in a 1:1 ratio. The preparation process involved 40 hours of wet ball milling at a ball-to-powder ratio of 6:1, with 2% paraffin wax added as a forming agent and anhydrous ethanol as the grinding medium. Spray drying was carried out at 100℃ to obtain spherical metal-ceramic powder with a particle size of 80 to 120 micrometers. The pressing pressure was 150 MPa. Sintering was performed under gas pressure at 1480℃ for 1.5 hours under 5 MPa argon gas pressure, with a cooling rate of 8℃ / min. The final metal-ceramic exhibited a three-point flexural strength of 2650 MPa, a Vickers hardness of 1620 HV30, and a fracture toughness of [missing information]. The volume fraction of plate-shaped tungsten carbide is 18%, the average aspect ratio is 8:1, and the porosity grade reaches A04B00. Example 2

[0032] In this embodiment, the raw material ratio is 70 parts. Solid solution powder, 12 parts The mixture consisted of powder, 4 parts of tantalum carbide and niobium carbide mixed in a 1:1 ratio (carbide powder), 0.8 parts of carbon black powder, and 13.2 parts of nickel metal binder powder. Ball milling was performed for 50 hours at a ball-to-powder ratio of 7:1, using polyethylene glycol as a forming agent at a content of 2.5%. After spray drying, the powder particle size ranged from 60 to 150 micrometers. The pressing pressure was 180 MPa. Vacuum sintering was used at a vacuum degree of 5 Pa, a sintering temperature of 1520℃, and a holding time of 2 hours. Testing showed that the cermet's three-point flexural strength was 2480 MPa, its Vickers hardness was 1680 HV30, and its fracture toughness was... The volume fraction of plate-shaped tungsten carbide is 25%, the average aspect ratio is 10:1, and the porosity grade is A04B00. Example 3

[0033] This embodiment uses 55 portions. Solid solution powder, 20 parts The mixture consisted of powder, 5 parts molybdenum carbide powder, 0.6 parts carbon black powder, and 19.4 parts cobalt metal binder powder. Ball milling time was 30 hours, ball-to-powder ratio was 5:1, paraffin wax was used as a forming agent, accounting for 1.8% of the total composition; pressing pressure was 120 MPa; sintering was performed using 8 MPa argon pressure at 1450℃ for 2 hours. The final product exhibited a three-point flexural strength of 2780 MPa, a Vickers hardness of 1550 HV30, and a fracture toughness of [missing information]. The volume fraction of plate-shaped tungsten carbide is 12%, the average aspect ratio is 6:1, and the porosity grade is A04B00.

[0034] Comparative Example 1 The raw material ratio in Comparative Example 1 is 65 parts. Solid solution powder, 15 parts The metal binder powder, consisting of 3 parts molybdenum carbide powder, 0.5 parts carbon black powder, and 16.5 parts nickel-cobalt mixed in a 1:1 ratio, was prepared using the same process as in Example 1. Due to the low W content and insufficient precipitation of plate-like tungsten carbide, the final cermet exhibited a three-point flexural strength of 1850 MPa, a Vickers hardness of 1420 HV30, and a fracture toughness of [missing information]. The volume fraction of plate-like tungsten carbide is less than 5%, and no obvious plate-like structure is formed. The porosity grade is A10B03.

[0035] Comparative Example 2 Comparative Example 2 used 65 samples The product is a 1:1 mixture of solid solution powder, 15 parts TiC powder, 3 parts molybdenum carbide powder, 0.5 parts carbon black powder, and 16.5 parts nickel-cobalt metal binder powder, without the addition of nitrogen-containing titanium carbonitride powder; all other processes remain consistent. Due to the lack of nitrogen, titanium dioxide (W) is difficult to effectively precipitate from the solid solution. The resulting product has a three-point flexural strength of 2020 MPa, a Vickers hardness of 1580 HV30, and a fracture toughness of [missing information]. The volume fraction of plate-shaped tungsten carbide is less than 8%, and the size distribution is uneven, with a porosity grade of A06B01.

[0036] Comparative Example 3 In Comparative Example 3, the raw material ratio was the same as in Example 1, but the sintering process used was vacuum sintering with a vacuum degree of 50 Pa, and the temperature and holding time were the same as in Example 1. Due to insufficient densification, the resulting product had a three-point flexural strength of 2210 MPa, a Vickers hardness of 1520 HV30, and a fracture toughness of [missing information]. The porosity grade is A08B02, and the overall performance is lower than that of Example 1.

[0037] The performance test results of each embodiment and comparative example are shown in Table 1.

[0038] Table 1 Performance data for each embodiment and comparative example As shown in Table 1, Examples 1 to 3 of this invention all achieved high flexural strength, high Vickers hardness, and high fracture toughness, and the porosity grade reached A04B00. This indicates that the proposed solution does not only improve a single property locally, but achieves a good comprehensive balance among strength, hardness, toughness, and density. Specifically, Example 1 has a flexural strength of 2650 MPa, a hardness of 1620 HV30, and a fracture toughness of [missing information]. Example 2 further improved the hardness to 1680 HV30 while maintaining a flexural strength of 2480 MPa. The fracture toughness; Example 3, while maintaining a hardness of 1550HV30, increases the flexural strength to 2780MPa and the fracture toughness to The above results indicate that by adjusting the composition ratios of tungsten-containing titanium carbide solid solution powder, nitrogen-containing titanium carbonitride powder, and metal binder powder, and by controlling the sintering process, a tunable performance distribution between high hardness and high toughness can be achieved. However, their common feature is the formation of a plate-like tungsten carbide-reinforced structure and the attainment of low porosity.

[0039] Compared to the embodiments, the performance of Comparative Examples 1 to 3 all showed a significant decline, further proving that the key technical features in the technical solution of this case cannot be arbitrarily replaced. In Comparative Example 1, because... The W content in the solid solution powder is reduced to The volume fraction of plate-like tungsten carbide is less than 5%, and no obvious plate-like structure is formed. Its bending strength is only 1850 MPa, and its fracture toughness is only [missing information]. The porosity grade deteriorated to A10B03. This result indicates that when the concentration of W in the initial raw material is insufficient, W is more likely to continue to dissolve in the solution. In the matrix, there is insufficient precipitate to form an effective plate-like tungsten carbide reinforcing phase, resulting in a significant weakening of the reinforcing and toughening effect.

[0040] In Comparative Example 2, although it still adopts The solid solution powder was replaced with TiC powder, resulting in a lack of necessary nitrogen source in the system. The volume fraction of plate-like tungsten carbide was less than 8%, and the size distribution was uneven. Its flexural strength decreased to 2020 MPa, and its fracture toughness decreased to [missing value]. This result indicates that nitrogen is not a dispensable byproduct, but rather a key condition for altering the solid solution state of titanium (W) in titanium-containing solid solutions and triggering WC precipitation. In other words, only when both tungsten-containing titanium carbide solid solution powder and nitrogen-containing titanium carbonitride powder are present can the reaction basis for the in-situ formation of plate-like tungsten carbide be established during subsequent sintering.

[0041] In Comparative Example 3, the raw material composition was the same as in Example 1, but the sintering conditions were changed to vacuum sintering at a vacuum level of 50 Pa. The flexural strength decreased to 2210 MPa, the hardness decreased to 1520 HV30, and the porosity grade changed to A08B02. This result demonstrates that even if the raw material system meets the material conditions for the precipitation of plate-like tungsten carbide, if sufficient densification conditions are not provided during the sintering stage, it is difficult to obtain the same microstructure integrity and comprehensive mechanical properties as in the example. In other words, the high-performance results in this case are not determined solely by the formulation, but rather by the synergistic effect of the raw material system and the sintering regime.

[0042] Therefore, the conclusions reflected in Table 1 can be summarized as follows: In this scheme, the initial W solid solution concentration, the introduction of nitrogen source, and the staged sintering conditions together constitute the necessary technical chain for the in-situ formation and performance improvement of plate-shaped tungsten carbide; the absence or deviation of any key link will lead to insufficient formation of plate-shaped crystals, increased porosity, and simultaneous decrease in strength and toughness.

[0043] See Figure 1 and Figure 2 , Figure 1 This is a microstructure image of the metal-ceramic material prepared in Example 1. Figure 2The image shows the microstructure of the metal-ceramic mixture obtained in Comparative Example 1. Combining the image morphology characteristics with the performance data in Table 1, it can be seen that there are significant differences between the two in terms of the morphology, distribution, and structural integrity of the reinforcing phase. These differences are directly correlated with the changes in their mechanical properties.

[0044] from Figure 1 As can be seen, the cermet matrix of Example 1 contains a large number of bright, elongated, plate-like, and needle-like structures. These bright white structures exhibit a large aspect ratio, with the length significantly greater than the width, and are distributed relatively fully and uniformly throughout the field of view, displaying typical plate-like tungsten carbide morphology characteristics. Most of the plate-like crystals are dispersed among each other in the figure; although there are local overlaps, there is no large-area agglomeration or severe local segregation. Meanwhile, the dark gray matrix region is relatively continuous, indicating that the plate-like tungsten carbide is formed and distributed in a relatively dense cermet matrix, rather than randomly precipitated in a porous structure with many defects. This morphology shows that, through the synergistic effect of tungsten-containing titanium carbide solid solution powder, nitrogen-containing titanium carbonitride powder, and the staged sintering process, Example 1 has been able to stably induce a large number of large-sized and uniformly distributed plate-like tungsten carbide reinforcing phases. Based on the performance data of Example 1 in Table 1, its flexural strength reaches 2650 MPa, Vickers hardness reaches 1620 HV30, fracture toughness reaches 12.8 MPa·m^0.5, and porosity grade reaches A04B00, which indicates that... Figure 1 The structure shown does indeed correspond to a superior overall mechanical performance state.

[0045] Further analysis Figure 1 The strengthening mechanism can be attributed to the fact that these plate-like tungsten carbide crystals distributed in the matrix can significantly hinder the crack front during material loading or crack propagation. Due to the large aspect ratio and orientation of the plate-like crystals, cracks encountering this structure are less likely to penetrate directly along their original path, but are more prone to diffraction, deflection, or bifurcation. Simultaneously, some plate-like crystals may also form bridging effects on both sides of the crack, thereby lengthening the crack propagation path and increasing crack propagation resistance. Therefore, Figure 1 The corresponding structure not only indicates that the scheme of this case has achieved in-situ precipitation of plate-shaped tungsten carbide, but also that the plate-shaped crystals have reached a morphology and distribution level that is sufficient to have a substantial impact on fracture behavior. This is also the main microstructure basis for Example 1 to obtain high bending strength and high fracture toughness while maintaining high hardness.

[0046] In comparison, Figure 2 The microstructure differences in Comparative Example 1 are very obvious. Figure 2Although a small number of bright white second-phase particles or short rod-shaped tissues can be observed, their number is significantly reduced, their size is significantly shorter, and their aspect ratio is significantly decreased. Most of them exhibit short columnar, irregular blocky, or nearly granular morphologies, lacking... Figure 1 It exhibits the large-sized, elongated, and plate-like characteristics of typical plate-like crystals. Simultaneously, these bright white structures are sparsely distributed in the field of view, failing to form the high-density and strongly anisotropic reinforcing network seen in Example 1. In other words, Figure 2 Although there are some precipitates in the structure shown, their morphology and quantity are insufficient to constitute an effective plate-like crystal reinforcement structure.

[0047] This Figure 2 The observed tissue state is highly consistent with the formulation and performance results of Comparative Example 1. In Comparative Example 1, The W content of the solid solution powder decreased to (x=0.15). The document clearly states that due to the excessively low W content, effective precipitation of WC plate-like crystals was impossible. Ultimately, the WC plate-like crystal fraction was less than 5%, and there was no obvious plate-like structure. Its flexural strength was only 1850 MPa, its Vickers hardness was only 1420 HV30, its fracture toughness was only 8.2 MPa·m^0.5, and its porosity grade dropped to A10B03. In other words… Figure 2 It doesn't simply indicate "less reinforcing phase," but rather directly reflects the difficulty in forming the system when the initial raw materials lack sufficient reserves of W element available for precipitation. Figure 1 Such a large quantity of plate-shaped tungsten carbide with suitable size and a large aspect ratio ultimately resulted in insufficient reinforcement and toughening effects.

[0048] Will Figure 1 and Figure 2 By making a comparison, the key technical mechanism of this case can be explained more clearly. Figure 1 This corresponds to the organizational results after the effective implementation of the technical solution in this case, namely, under suitable W solid solution concentration, nitrogen source conditions and staged sintering conditions, WC can precipitate in situ and further grow to form a large number of plate-shaped tungsten carbide. Figure 2 This corresponds to the microstructure resulting from the disruption of key conditions. Specifically, when the W content is too low, although a small amount of second phase may still form, it is difficult to form a sufficiently abundant and typically morphologically typical plate-like tungsten carbide-reinforced microstructure. Therefore, Figure 1 and Figure 2 The comparison actually provides a direct verification of the effectiveness of the technical route of "sufficient W element reserves + nitrogen element participation in regulation + sintering process-induced growth" at the microstructure level.

[0049] From an engineering application perspective Figure 1 The microstructure it represents is more suitable for use as a material for cermet cutting tools and molds. The reason is that... Figure 1The plate-like tungsten carbide in the material is abundant and evenly distributed, enabling it to more effectively undertake crack deflection, bridging, and pinning effects during material service, thereby reducing the risk of chipping and brittle fracture; Figure 2 Due to insufficient lamellar crystals and inadequate reinforcing phase morphology, the material is more prone to rapid cracking along continuous regions of the matrix under impact or stress concentration, resulting in significantly lower flexural strength and fracture toughness compared to other materials. Figure 1 The corresponding example is Example 1.

[0050] therefore, Figure 1 and Figure 2 The analysis combining text and images can be summarized as follows: Figure 1 The diagram visually demonstrates the in-situ formation and uniform distribution of a large number of plate-shaped tungsten carbide crystals in the metal-ceramic matrix under the proposed scheme. This structure corresponds to higher flexural strength, higher hardness, higher fracture toughness, and lower porosity. Figure 2 This shows that when the W content is insufficient, the amount of reinforcing phase decreases, the aspect ratio decreases, and the plate-like characteristics are not obvious, resulting in a microstructure with poor overall mechanical properties. The comparison proves that this case is not a simple improvement of the formula, but rather a substantial change in the morphology and distribution of the reinforcing phase by controlling the raw material system and sintering reaction path, thereby achieving the preparation of high-strength and high-toughness metal-ceramic mold materials.

[0051] The technical principle of this case is not simply to add pre-existing plate-shaped crystalline powder to the cermet system to achieve reinforcement, but rather to control the raw material system and sintering reaction path to enable the in-situ precipitation and growth of plate-shaped tungsten carbide during the sintering process. Specifically, this case firstly uses... The solid solution powder serves as the initial carrier for W. A sufficient concentration of W must be pre-dissolved in the solid solution powder because if the W content is too low, it will more easily remain stably dissolved in the solution during subsequent reactions. Within the matrix, it is difficult to precipitate and form an independent plate-like tungsten carbide phase. At the same time, the powder needs to be controlled within a certain particle size range to increase the specific surface area and reactivity, thereby promoting element diffusion and phase transformation reactions during the sintering process.

[0052] Based on this, this case introduces Powder is used as a nitrogen source. The role of nitrogen is not merely to supplement other components, but rather to participate in the formation of... A nitrogen-containing solid solution was used, and by altering the solid solution state of W in the solid solution, the tendency of W to continue to remain in a stable solid solution was reduced, thereby creating thermodynamic and microstructural conditions for WC precipitation. In other words, this case established a precursor system capable of triggering WC precipitation during sintering through a combination of "tungsten-containing titanium carbide solid solution powder + nitrogen-containing titanium carbonitride powder".

[0053] From the perspective of sintering mechanism, this project employs staged sintering rather than single sintering. The first two stages, thermal degreasing and deoxidation, are mainly used to remove forming agents, volatile impurities, and unfavorable factors such as oxygen, creating a more stable reaction environment for subsequent solid-state reactions and liquid-state densification. The third stage is a nitrogen atmosphere negative pressure solid-state sintering stage. The core function of this stage is not final densification, but rather to promote... solid solution powder, The solid solution reaction between the powder and other carbide powders, under nitrogen atmosphere, accelerates the establishment of a nitrogen-containing solid solution system, thus providing conditions for WC precipitation. The fourth stage is the high-temperature liquid-phase sintering stage, which is the key stage for the densification and shrinkage of the green body, and also the key stage for the rapid growth and evolution of the precipitated WC into plate-like tungsten carbide. In other words, the third stage is more inclined to "promote precipitation", while the fourth stage is more inclined to "promote growth and densification", with a clear division of labor and seamless connection between the two.

[0054] From the perspective of microstructural evolution, the final structure formed in this case is a uniformly distributed plate-like tungsten carbide-reinforced structure, rather than a randomly coarsened granular structure. Plate-like tungsten carbide exhibits a more pronounced aspect ratio and geometric anisotropy within the matrix. Therefore, when cracks propagate within the material, they are more easily blocked by the plate-like crystals, resulting in crack deflection, crack bridging, and crack pinning. It is precisely due to this unique crack propagation hindering mechanism that the fracture toughness of the material can be significantly improved. Simultaneously, because the cermet matrix maintains high density and strong hard phase support, toughness is not sacrificed for hardness; rather, a synergistic improvement in strength, hardness, and toughness is achieved.

[0055] Therefore, the overall mechanism of this case can be summarized as follows: First, a reserve of W element that can be precipitated is provided by tungsten-containing titanium carbide solid solution powder. Then, nitrogen element is introduced by nitrogen-containing titanium carbonitride powder and the solid solution state of W element is changed. Subsequently, in-situ precipitation of WC is triggered in the nitrogen atmosphere negative pressure solid phase sintering stage. In the high temperature liquid phase sintering stage, the precipitated WC is promoted to grow rapidly to form plate-shaped tungsten carbide and achieve uniform distribution in the densified structure. Finally, through the crack deflection, bridging and pinning effect of plate-shaped crystals and the bearing effect of low porosity structure, a high-strength and tough metal ceramic mold material is obtained.

[0056] The overall beneficial effect of this case should not be understood in isolation as "performance improvement," but rather as an overall technical effect comprised of organizational formation mechanisms, process synergy mechanisms, and final service performance.

[0057] Firstly, at the microstructure level, this project achieves in-situ precipitation and growth of plate-like tungsten carbide in a cermet matrix through the synergistic reaction between tungsten-containing titanium carbide solid solution powder and nitrogen-containing titanium carbonitride powder, combined with process control of nitrogen atmosphere negative pressure solid-state sintering and high-temperature liquid-phase sintering. Compared with the route of directly adding plate-like or whisker powders, this project does not rely on expensive irregularly shaped reinforcement materials, and the reinforcement phase is not dispersed by mechanical mixing, but formed within the matrix through metallurgical reactions, thus being more conducive to achieving uniform distribution and stable interfacial bonding. Its direct effect is to reduce the cost of the reinforcement and simultaneously reduce the risk of microstructural defects caused by agglomeration and uneven dispersion of the added reinforcement.

[0058] Secondly, in terms of material properties, the plate-like tungsten carbide microstructure formed in this study effectively hinders crack propagation and improves fracture toughness through crack deflection, bridging, and pinning mechanisms. Simultaneously, because the matrix maintains a high proportion of hard phase and high density, the material retains high hardness and high flexural strength. In other words, this study does not simply increase the content of the metallic binder phase to gain toughness, but achieves toughening without significantly sacrificing hardness. Therefore, it overcomes the performance bottleneck of traditional Ti(C,N)-based cermets, which are characterized by "high hardness but brittleness" and "toughening but reducing hardness." Example data shows that the material can achieve flexural strengths of 2300 MPa to 2800 MPa, Vickers hardness of 1500 HV30 to 1700 HV30, and... to Its fracture toughness, a comprehensive property, is a significant advantage for cermet cutting tools and die materials.

[0059] Secondly, at the process implementation level, this project improves the uniformity of raw material mixing and powder flowability through wet ball milling and spray granulation. A more uniform green body is obtained through pressing. Through multi-stage synergistic control of hot degreasing, deoxidation and impurity removal, nitrogen atmosphere negative pressure solid-state sintering, high-temperature liquid-phase sintering, and controlled cooling, multiple objectives are achieved, including forming agent removal, impurity purification, solid solution reaction promotion, plate-like crystal precipitation, plate-like crystal growth, green body densification, and microstructure stabilization. In other words, this project does not merely propose a new formula, but establishes a complete preparation process path suitable for industrial implementation, making the formation of plate-like crystal-reinforced microstructure repeatable and controllable.

[0060] Finally, in practical applications, because the material in this case possesses high flexural strength, high hardness, high fracture toughness, and low porosity, it can reduce the risk of chipping, cracking, and brittle failure under high-load cutting, mold forming, and wear-resistant conditions, thereby extending the service life of tools and dies, reducing replacement frequency, and improving processing stability and economy. Therefore, this case not only has innovative significance in terms of material preparation but also has high engineering application value and industrialization prospects.

[0061] Finally, it should be noted that the above description is only 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 plate-shaped crystalline tungsten carbide in-situ reinforced cermet mold, characterized in that, The steps include the following: Mixing and granulation steps: Tungsten-containing titanium carbide solid solution powder, nitrogen-containing titanium carbonitride powder, carbide powder, carbon black powder, and metal binder powder are mixed and then ball-milled, dried, and granulated to obtain a metal-ceramic mixed powder; the tungsten-containing titanium carbide solid solution powder is (Ti 1-x W x Ti(C) solid solution powder, wherein the nitrogen-containing titanium carbonitride powder is Ti(C) 1-y N y ) powder; the (Ti 1-x W x In the Ti(C) solid solution powder, parameter x is from 0.20 to 0.45, and parameter y is from 0.5 to 1.

0. 1-y N y The particle size of the powder is 0.05 micrometers to 2.0 micrometers; the mass parts of the tungsten-containing titanium carbide solid solution powder, the nitrogen-containing titanium carbonitride powder, the carbide powder, the carbon black powder, and the metal binder powder are 50 to 75 parts, 10 to 20 parts, 0 to 8 parts, 0.1 to 1.0 parts, and 5 to 25 parts, respectively; the ball milling is wet ball milling, the ball milling time is 20 to 60 hours, the ball-to-material ratio is 3:1 to 10:1, a forming agent is added during the ball milling process, the forming agent accounts for 1.0% to 3.0% of the total mass of the powder, the grinding medium is anhydrous ethanol, the spray drying temperature is 80°C to 120°C, and the particle size of the metal-ceramic mixed powder after spray drying is 20 micrometers to 200 micrometers; Pressing and forming step: The metal-ceramic mixed powder is pressed and formed to obtain a metal-ceramic green body; the pressing pressure is 100MPa to 200MPa; The sintering process involves several stages: the metal-ceramic green body is sequentially subjected to degreasing, deoxidation and impurity removal, solid-state sintering, and high-temperature liquid-state sintering. The solid-state sintering is performed under nitrogen atmosphere negative pressure, with a nitrogen pressure of 2000 Pa to 5000 Pa, a sintering temperature of 1200°C to 1350°C, a holding time of 0.5 hours to 1 hour, and a heating rate of 1°C / min to 3°C / min, to ensure the (Ti) 1-x W x )C solid solution powder and the Ti(C) 1-y N y The powder undergoes a solid solution reaction to form a nitrogen-containing solid solution, while simultaneously reducing the solid solubility of W in the nitrogen-containing solid solution, thus promoting the precipitation of WC. The high-temperature liquid phase sintering treatment is used to grow the precipitated WC into plate-shaped crystalline tungsten carbide and to densify the metal-ceramic green body. The high-temperature liquid phase sintering treatment is either vacuum sintering or gas pressure sintering. When vacuum sintering is used, the vacuum degree is 1 Pa to 10 Pa, the sintering temperature is 1450℃ to 1550℃, and the holding time is 1 hour to 3 hours. When gas pressure sintering is used, the atmosphere is argon, the gas pressure is 0.5 MPa to 10 MPa, the sintering temperature is 1420℃ to 1500℃, and the holding time is 1 hour to 2 hours. Cooling and sampling step: The metal-ceramic preform after the high-temperature liquid phase sintering treatment is cooled to obtain a metal-ceramic mold material containing plate-shaped tungsten carbide in its microstructure; the cooling rate is 5℃ / min to 10℃ / min.

2. The method for preparing plate-shaped tungsten carbide in-situ reinforced cermet molds according to claim 1, characterized in that, The parameter x is between 0.30 and 0.40, and the (Ti) 1-x W x The particle size of the C solid solution powder is 0.5 micrometers to 2.0 micrometers.

3. The method for preparing plate-shaped tungsten carbide in-situ reinforced cermet molds according to claim 2, characterized in that, The carbide powder is at least one of molybdenum carbide, tantalum carbide, and niobium carbide, and the particle size of the carbide powder is from 0.1 micrometers to 5.0 micrometers; The carbon black powder has a particle size of 0.05 micrometers to 0.5 micrometers, and the metal binder powder is at least one of nickel and cobalt, with a particle size of 1.0 micrometers to 5.0 micrometers.

4. The method for preparing plate-shaped tungsten carbide in-situ reinforced cermet molds according to claim 3, characterized in that, The degreasing process is vacuum degreasing, with a vacuum degree of 0.1 Pa to 10 Pa, a degreasing temperature of 350°C to 500°C, a holding time of 2 hours to 4 hours, and a heating rate of 1°C / min to 3°C / min; the deoxidation and impurity removal process is carried out at a temperature of 800°C to 1000°C, with a holding time of 0.5 hours to 1 hour, and a heating rate of 2°C / min to 5°C / min.

5. A plate-shaped tungsten carbide reinforced cermet mold material, characterized in that, The metal-ceramic mold material is prepared by any one of claims 1 to 4. The matrix of the metal-ceramic mold material is a titanium-containing carbonitride-based metal-ceramic matrix. The titanium-containing carbonitride-based metal-ceramic matrix contains plate-shaped tungsten carbide, the volume fraction of which is 10 vol% to 30 vol%, the length of which is 5 micrometers to 20 micrometers, and the thickness of which is 0.2 micrometers to 2 micrometers.

6. The plate-like tungsten carbide reinforced cermet tooling material according to claim 5, characterized in that, The metal-ceramic mold material has a three-point bending strength of 2300 MPa to 2800 MPa, a Vickers hardness of 1500 HV30 to 1700 HV30, and a fracture toughness of 10 MPa·m. 0.5 Up to 15 MPa·m 0.5 .

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