Low-cobalt tough nano gradient hard alloy as well as preparation method and application thereof

Abstract

The invention discloses a low-cobalt tough nano gradient hard alloy and a preparation method and application thereof, and relates to the technical field of hard alloy materials, the hard alloy comprises a WC hard phase and a Co-based binding phase, and a surface layer, a transition layer and a core layer are sequentially arranged in the thickness direction of a product; the mass fraction of Co in the surface layer is 0.5 wt%-3.0 wt%, the mass fraction of Co in the transition layer is 3.0 wt%-5.0 wt%, and the mass fraction of Co in the core layer is 5.0 wt%-7.0 wt%; the hard alloy contains Cr3Si nano precipitated phases, the average particle size of the Cr3Si nano precipitated phases is 2-20 nm, the density of the Cr3Si nano precipitated phases is not lower than 1 * 10 < m-3 >, and the Cr3Si nano precipitated phases are in interface enrichment distribution. A more stable comprehensive strengthening and toughening effect is achieved in a low-cobalt system, and the service consistency and the service life stability of the material under the working condition of precision machining are improved.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide materials technology, and in particular to a low-cobalt, high-strength, and tough nano-gradient cemented carbide, its preparation method, and its applications. Background Technology

[0002] In recent years, WC-based cemented carbide has continued to evolve in applications such as high-precision electronic molds, semiconductor packaging, and precision connector processing. Research and industry have conducted systematic explorations in areas such as grain refinement, cobalt reduction, functional gradient, and interface strengthening. By controlling the content and distribution of the cobalt-based binder phase, optimizing the sintering thermal field and atmosphere conditions, and introducing nanoscale dispersed phases, the material's hardness retention, wear resistance, and service consistency have been continuously improved. Meanwhile, for the localized load concentration and thermomechanical coupling conditions in the processing of fine features, interface structure design and nanoprecipitation control have gradually become important means to improve overall performance.

[0003] Under low-cobalt conditions, the performance of cemented carbide is more sensitively constrained by the structural stability and load transfer capacity of the interface between WC and the cobalt-based binder phase. Interfacial microcracks are prone to initiation and propagation under cyclic stress and localized thermal effects, thereby weakening crack resistance reliability and lifespan stability. Although existing technologies can improve hardness and wear resistance by reducing the surface cobalt content or introducing dispersed phases, if the interfacial strengthening is insufficient or the location of the precipitated phase is uncontrollable, the strengthening contribution cannot effectively act on the critical areas of the interface. This limits the synergistic improvement of strength and toughness in low-cobalt systems, making it difficult to meet the requirements of high-precision molds that emphasize both wear resistance and crack resistance. Summary of the Invention

[0004] In view of this, this application provides a low-cobalt, high-strength nanogradient cemented carbide, its preparation method, and its application.

[0005] According to one aspect of this disclosure, a low-cobalt, high-strength nanogradient cemented carbide is provided, comprising a WC hard phase and a Co-based binder phase, and a surface layer, a transition layer and a core layer are sequentially disposed along the thickness direction of the article. The surface layer contains 0.5 wt% to 3.0 wt% Co, the transition layer contains 3.0 wt% to 5.0 wt% Co, and the core layer contains 5.0 wt% to 7.0 wt% Co. The cemented carbide contains Cr3Si nano-precipitates, the average particle size of which is 2 nm to 20 nm and the density is not less than 1 × 10²² m³. -3 It also exhibits an interface-enriched distribution.

[0006] According to one aspect of this disclosure, a method for preparing a low-cobalt, high-strength nanogradient cemented carbide is provided, comprising the following steps: Step 1: Provide WC powder, perform a composite coating operation of Cr-containing precursor and Si-containing precursor on the WC powder to form a Cr / Si-rich precursor coating layer with a thickness of 5nm to 50nm on the surface of WC particles, and obtain coated WC powder. Step 2: The coated WC powder is processed into a carbon nanostructure and mixed with Co powder according to the target composition ratio. The mixture is then uniformly mixed by ball milling to obtain the composite raw material powder. Step 3: Granulate the composite raw material powder and press the granulated powder into shape by cold isostatic pressing to obtain a shaped green body; Step 4: The interior of the formed green body is sintered into a preliminary sintered neck structure through pre-sintering treatment to obtain a pre-sintered body; Step 5: Gradient sintering is performed on the pre-sintered body. Multi-zone temperature control is adopted and the temperature difference between the core and the surface of the product is monitored and adjusted in real time to ΔT≤50℃. At the same time, the dew point of the sintering atmosphere is controlled to ≤-40℃ and the carbon potential is maintained within the carbon potential window that inhibits the formation of η phase and the precipitation of free graphite by adjusting the atmosphere ratio, so as to form a Co-based binder phase gradient structure. Step 6: In the high-temperature heat preservation stage of the Co-based binder phase gradient structure, a segmented heat preservation treatment is carried out in the range of 1420℃~1450℃. The Cr / Si rich precursor coating layer reacts at the interface between WC and the binder phase and generates Cr3Si nano-precipitates in situ, thus obtaining cemented carbide.

[0007] According to one aspect of this disclosure, an application of a low-cobalt, high-toughness nanogradient cemented carbide in high-precision electronic molds is provided, the high-precision electronic molds including semiconductor packaging molds and precision connector molds.

[0008] The beneficial effects of this invention are as follows: By using Cr-containing and Si-containing precursors to composite-coat WC powder, a stable Cr / Si-rich precursor coating layer is formed on the surface of WC particles. During the subsequent high-temperature holding stage, Cr3Si nano-precipitates are generated in situ at the interface between WC and the cobalt-based binder phase. This allows for the construction of high-density nanoscale reinforcing units in the interface neighborhood, improving interface load transfer and structural stability. This interface-oriented precipitation method makes the size and distribution of the precipitates more controllable, reducing the risk of embrittlement caused by coarse second phases. Simultaneously, under external load, it promotes crack deflection and energy-dissipating propagation in the interface region, achieving a more stable overall strengthening and toughening effect in a low-cobalt system, and improving the service consistency and lifespan stability of the material under precision machining conditions. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram showing the line scan enrichment characteristics of Cr and Si elements at the WC / Co interface.

[0011] Figure 2 This is a bar chart comparing surface hardness.

[0012] Figure 3 This is a gradient distribution diagram of the Co-based binder phase along the thickness direction.

[0013] Figure 4 This is a schematic diagram of the temperature program for multi-zone temperature-controlled sintering. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0015] This invention aims to construct a low-cobalt, strong, and tough nano-gradient cemented carbide. In the embodiments of this application, the cemented carbide comprises a WC hard phase and a Co-based binder phase, and a surface layer, a transition layer, and a core layer are sequentially arranged along the thickness direction of the product. The surface layer contains 0.5 wt% to 3.0 wt% Co, the transition layer contains 3.0 wt% to 5.0 wt% Co, and the core layer contains 5.0 wt% to 7.0 wt% Co. The cemented carbide contains Cr3Si nano-precipitates, the average particle size of which is 2 nm to 20 nm and the density is not less than 1 × 10²² m³. -3 It also exhibits an interface-enriched distribution.

[0016] In some embodiments of this application, the average grain size of the WC hard phase is 0.2 μm to 0.6 μm.

[0017] In some embodiments of this application, the thickness of the surface layer is 0.1 mm to 1.0 mm, and the thickness of the transition layer is 0.2 mm to 2.0 mm.

[0018] In some embodiments of this application, the cemented carbide further comprises a grain inhibitor NbC, wherein the mass fraction of NbC is 0.05wt% to 0.50wt%; and a Nb-rich carbide segregation layer is formed at the interface between WC and the Co-based binder phase, and coexists with the Cr3Si nanoprecipitates near the interface.

[0019] This application embodiment also provides a method for preparing a low-cobalt strong and tough nano-gradient hard alloy, which includes: step 1, providing WC powder, performing a composite coating operation of a Cr-containing precursor and a Si-containing precursor on the WC powder, forming a Cr / Si-rich precursor coating layer with a thickness of 5nm to 50nm on the surface of the WC particles, and obtaining coated WC powder. Step 2: The coated WC powder is processed into a carbon nanostructure and mixed with Co powder according to the target composition ratio. The mixture is then uniformly mixed by ball milling to obtain the composite raw material powder. Step 3: Granulate the composite raw material powder and press the granulated powder into shape by cold isostatic pressing to obtain a shaped green body; Step 4: The interior of the formed green body is sintered into a preliminary sintered neck structure through pre-sintering treatment to obtain a pre-sintered body; Step 5: Gradient sintering is performed on the pre-sintered body. Multi-zone temperature control is adopted and the temperature difference between the core and the surface of the product is monitored and adjusted in real time to ΔT≤50℃. At the same time, the dew point of the sintering atmosphere is controlled to ≤-40℃ and the carbon potential is maintained within the carbon potential window that inhibits the formation of η phase and the precipitation of free graphite by adjusting the atmosphere ratio, so as to form a Co-based binder phase gradient structure. Step 6: In the high-temperature heat preservation stage of the Co-based binder phase gradient structure, a segmented heat preservation treatment is carried out in the range of 1420℃~1450℃. The Cr / Si rich precursor coating layer reacts at the interface between WC and the binder phase and generates Cr3Si nano-precipitates in situ, thus obtaining cemented carbide.

[0020] In some embodiments of this application, the composite coating operation involves contacting WC powder with a Cr-containing salt solution and a Si-containing sol or silicon source precursor and depositing it into a film, followed by drying and heat treatment in a reducing atmosphere to solidify and stabilize the Cr / Si-rich precursor coating layer.

[0021] In some embodiments of this application, the carbon potential window is constrained based on a dew point of ≤-40℃. One of the CO / CO2 atmosphere system or CH4 / H2 atmosphere system is selected as the carbon-regulating gas source. The carbon potential in the furnace is kept stable within the effective carbon potential control window by adjusting the volume fraction ratio of the two components in the atmosphere system online. The effective carbon potential control window is defined as the carbon balance condition of "no η phase generated and no free graphite precipitated" being met simultaneously throughout the entire sintering cycle.

[0022] In some embodiments of this application, when uniformly mixing by ball milling, grain inhibitor NbC is added simultaneously. Through mechanical shearing and collision, the grain inhibitor NbC preferentially adheres to and distributes on the surface of WC particles.

[0023] In some embodiments of this application, the process of coating WC powder into carbon nanostructure involves performing in-situ vapor deposition on the coated WC powder to deposit a carbon source on the surface of the WC powder to form a carbon nanostructure, and then mixing the WC powder with Co powder to form the carbon nanostructure. The total content of the carbon nanostructures is 0.03wt% to 0.30wt%, and after sintering, some of them will be converted and retained as carbon nano-derived bridging structures.

[0024] This application also provides an application of low-cobalt strong and tough nano-gradient cemented carbide in high-precision electronic molds, which includes semiconductor packaging processing molds and precision connector processing molds.

[0025] Example 1: Using fine-grained WC as the hard phase, a bonding phase gradient was constructed along the thickness direction, consisting of a surface layer, a transition layer, and a core layer. The Co mass fractions in the surface layer, transition layer, and core layer were set to 0.9wt% / 3.3wt% / 5.5wt%, and the thicknesses of the surface layer and transition layer were controlled within the commonly used ranges of 0.1mm–1.0mm and 0.2mm–2.0mm, respectively. Simultaneously, 0.18wt% NbC was added to stabilize the crystals. To introduce a reaction source at the interface, a Cr / Si precursor composite coating layer (thickness controlled between 5nm and 50nm) was first formed on the WC surface, and a low-content carbon nanostructure was introduced. After forming, a preliminary sintering neck is established through pre-sintering, followed by multi-zone temperature-controlled sintering: the core-to-surface temperature difference is controlled to be no greater than 50℃, the dew point is controlled below -40℃, and the carbon potential in the furnace is adjusted by CO / CO2 or CH2 / H2 to ensure a stable window where neither the η-phase nor free graphite is precipitated; segmented holding is used between 1420℃ and 1450℃ to allow the coating layer to react in situ at the WC / Co interface to generate Cr3Si nano-precipitates. TEM shows dispersed nanoparticles near the interface, with a particle size distribution of 2nm to 20nm and a particle number density of 10²²m. -3 The sample exhibits a high degree of enrichment in Cr / Si at the interface, as indicated by EDS line scanning. Simultaneously, Nb forms continuous or semi-continuous segregation bands near the interface, coexisting adjacent to the Cr3Si enriched region. XRD and metallographic / SEM analyses did not reveal any η phase or free graphite. The sample shows enhanced surface hardness and corrosion resistance, while the core layer retains good toughness and load-bearing capacity, demonstrating a combined effect of gradient structure and interfacial nano-reinforcement.

[0026] Example 2: Fine-grained WC was still used as the hard phase, and the gradient binder phase adopted a surface / transition layer / core layer Co ratio of 1.3wt% / 4.1wt% / 6.2wt% to further emphasize the balanced combination of "surface hardness / corrosion resistance - core toughness / bending resistance"; the NbC content was adjusted to 0.22wt%. A Cr / Si precursor composite coating layer (5nm~50nm) was also introduced onto the WC surface, and a medium content of carbon nanostructures was added. The sintering approach was consistent with Example 1, but with greater emphasis on "interfacial reaction stability" at high temperatures: under the premise of maintaining ΔT no greater than 50℃, dew point below -40℃, and a stable carbon potential window, segmented holding at 1420℃~1450℃ was performed to enhance the controllability of the in-situ interfacial reaction, such as... Figure 4 The sintering temperature program shown has a segmented holding range of 1420℃ to 1450℃ after entering the high-temperature section. The curve shows that the temperature undergoes multiple plateau / inflection point changes within this range, connecting with the preceding and following heating and cooling stages. Characterization results show that the Cr3Si nanoprecipitates still have a particle size of 2nm to 20nm and a number density of 10²²m. -3 The sample exhibits a more continuous Cr / Si enrichment band at the interface, a more complete Nb segregated layer, and no η phase or free graphite was observed. It also demonstrates a more balanced overall performance in terms of hardness, toughness, bending strength, and corrosion resistance.

[0027] Example 3: Considering the core load-bearing requirements, the surface layer's Co content is set to 2.6 wt%, the transition layer to 4.8 wt%, and the core layer's Co content to 6.8 wt%. This ensures a high Co level in the core layer to highlight toughness and bending load-bearing capacity, while maintaining a low cobalt content in the surface layer to balance hardness and corrosion resistance. Figure 3 As shown, the Co content increases in layers from the surface to the core along the thickness direction. The curves correspond to approximately 2.6 wt%, 4.8 wt%, and 6.8 wt% in the surface layer, transition layer, and core layer, respectively, with transitional changes between layers, describing the gradient distribution characteristics of the binder phase set in this embodiment. The NbC content is set to 0.15 wt% to reduce the sensitivity of the hard second phase. A Cr / Si precursor composite coating layer (5 nm to 50 nm) is constructed on the WC surface, and a low-content carbon nanostructure is introduced. During sintering, a multi-zone temperature control method is used to limit the core-to-surface temperature difference to within 50 °C, and the dew point is controlled below -40 °C. The carbon potential window is stabilized by atmosphere ratio. Subsequently, segmented holding at 1420 °C to 1450 °C triggers in-situ precipitation of Cr3Si at the interface. TEM / EDS confirms the presence of Cr3Si nanoparticles (2 nm to 20 nm, 10²² m) near the interface. -3 The sample exhibits a high degree of toughness and flexural strength, with significant interface enrichment. XRD and metallographic / SEM analyses also show no η phase or free graphite. This sample demonstrates enhanced toughness and flexural strength, while its hardness shows a slight decrease, consistent with the reasonable trade-off resulting from the "high toughness" formulation.

[0028] Example 4: To investigate the influence of the lower limit of crystal stabilization capability, the surface layer was set to 1.6 wt%, the transition layer to 3.7 wt%, and the core layer Co to 5.9 wt%, while NbC was reduced to 0.06 wt%. A Cr / Si precursor composite coating layer (5 nm–50 nm, leaning towards medium to thick to ensure reaction supply) was still applied to the WC surface, and the carbon nanostructure content was set to medium to low. During the sintering stage, ΔT was maintained at no more than 50°C, the dew point at less than -40°C, and the carbon potential window remained stable. The temperature was maintained in stages from 1420°C to 1450°C to allow Cr3Si nanoprecipitates to form in situ at the interface. Characterization showed that the Cr3Si particle size was between 2 nm and 20 nm, and the number density reached 10²² m. -3 The sample exhibits good hardness and corrosion resistance, but the strength improvement is somewhat limited, highlighting the boundary effect of NbC in the "stabilizing crystal + interfacial synergy".

[0029] Example 5: The surface layer was set to 1.0 wt%, the transition layer to 4.6 wt%, and the core layer to 6.6 wt% Co, with NbC increased to 0.45 wt% to enhance grain boundary pinning and fine grain stability. A Cr / Si precursor composite coating layer (5 nm–50 nm) was also provided on the WC surface, with a lower carbon nanostructure content to reduce variable coupling. During mixing, ball milling was used to promote NbC adhesion to the WC surface, followed by gradient sintering: maintaining a core-to-surface temperature difference of no more than 50°C, a dew point below -40°C, and a stable carbon potential window, segmented temperature holding at 1420°C–1450°C resulted in in-situ nanoprecipitations of Cr3Si at the interface. TEM / EDS confirmed the enrichment of Cr / Si at the interface and the presence of Cr3Si nanoparticles (2 nm–20 nm, 10²² m²). -3 (In terms of magnitude), Nb shows a more pronounced clustering near the interface, such as... Figure 1 As shown, along the line scan path spanning from the WC side to the Co side, the Cr and Si signals show synchronous enhancement near the interface. The curves form a peak at the interface and gradually decline towards both sides. The interface location marked in the figure corresponds to the Cr / Si peak region, reflecting the enrichment distribution characteristics of Cr / Si near the interface; and no η phase or free graphite was observed. The sample shows a more significant increase in hardness, but the toughness gain tends to plateau, exhibiting the engineering boundary characteristics common at the high NbC end.

[0030] Example 6: For the gradient binder phase, a ratio of 1.2 wt% for the surface layer, 3.9 wt% for the transition layer, and 6.1 wt% for the core layer Co was used, with NbC set at 0.20 wt%. A Cr / Si precursor composite coating layer (5 nm to 50 nm) was still constructed on the WC surface. The carbon nanostructure content was controlled within the high range of 0.03 wt% to 0.30 wt% to increase the probability of retaining the "carbon nano-derived bridging structure" after sintering. Sintering was more sensitive to atmosphere and temperature control: the dew point was stabilized below -40℃, the carbon potential was always within a window that suppressed both the η phase and free graphite, and the core-to-surface temperature difference was no greater than 50℃; the high-temperature stage involved segmented holding at 1420℃ to 1450℃ to simultaneously promote in-situ Cr3Si nano-precipitation at the interface and partial conversion / retention of the carbon structure. TEM / EDS showed that the Cr3Si nanoparticles at the interface met the requirements of a particle size of 2 nm to 20 nm and a thickness of 10²² m. -3 The number density is on the order of magnitude and is enriched at the interface; at the same time, a small number of carbon-derived bridging morphologies spanning adjacent hard phases can be observed under SEM / TEM, such as... Figure 2 As shown, the surface hardness of Examples 1-6 and Comparative Examples 1-3 are listed in a columnar format, with each column corresponding to a sample number and HRA value, facilitating comparison of the surface hardness levels and their range of differences between different samples on the same coordinate system. This sample maintains high levels of hardness and corrosion resistance while exhibiting significantly improved toughness and flexural strength, highlighting the combined contribution of bridging toughening and interfacial nano-reinforcement.

[0031] Comparative Example 1: A conventional homogeneous WC–Co system was used, with Co uniformly distributed throughout the thickness and no NbC added (0 wt%). No Cr / Si precursor coating was applied to the WC, nor were carbon nanostructures introduced. Sintering employed a standard isothermal process, lacking a multi-zone temperature-controlled gradient formation process, windowing stabilization of dew point and carbon potential, and no segmented holding at 1420℃–1450℃ to trigger in-situ interfacial reactions. Microscopic and compositional analyses showed no interfacial Cr / Si enrichment bands, no Cr3Si nanoprecipitates, and no Nb-rich interfacial segregated layers. The system typically exhibited acceptable toughness but low hardness and poor corrosion resistance, consistent with typical characteristics of high-Co homogeneous systems.

[0032] Comparative Example 2: A homogeneous low-Co system was used, with Co content of 6.0wt% / 6.0wt% / 6.0wt%, and no NbC added (0wt%). Only traditional Cr carbide additives were added for conventional crystal stabilization or corrosion resistance improvement. Since no Si source was introduced into the system, no Cr3Si nanoprecipitates appeared. Sintering was carried out according to the conventional isotropic route, without multi-zone temperature-controlled gradient sintering, windowing of dew point and carbon potential for online stabilization, or segmented holding at 1420℃~1450℃ to promote in-situ interfacial reactions. Characterization showed that Cr existed mainly in solid solution or carbide form, and TEM / EDS did not exhibit interfacial Cr3Si nanoprecipitates. While the hardness of this comparative system could be improved, its toughness and flexural load-bearing capacity were more easily limited, and the improvement in corrosion resistance was also relatively limited.

[0033] Comparative Example 3: Co layering was performed and NbC was added, with the surface layer set at 1.1 wt%, the transition layer at 4.0 wt%, and the core layer at 6.0 wt% Co and 0.20 wt% NbC. However, the WC surface was not coated with Cr / Si precursors (lacking Si source), and no carbon nanostructures were introduced. During sintering, multi-zone temperature control was lacking, making it difficult to stabilize the core-surface temperature difference below 50℃; the dew point was also difficult to maintain below -40℃ for extended periods, and the carbon potential failed to consistently fall within the window of "simultaneously suppressing the η phase and free graphite." Furthermore, segmented holding at 1420℃–1450℃ was not used to achieve controllable in-situ interfacial reactions. Phase composition and microstructure observation revealed η phase-related characteristics, while metallographic / SEM showed brittle phases or free carbon defects, making crack propagation along these defects more likely. Even if the surface hardness approached that of graded materials, fracture toughness and flexural strength still decreased, leading to poorer reliability.

[0034] Table 1. Comparison of overall performance between the embodiments and comparative examples.

[0035] As shown in Table 1, compared with the comparative examples, the embodiments of the present invention, while reducing the overall Co content and introducing a Co gradient structure, still achieve high surface hardness, superior fracture toughness, and good flexural strength and corrosion resistance. In particular, all embodiments, under low-cobalt surface conditions, achieved a synergistic improvement in hardness, strength, and toughness by forming Cr3Si nano-precipitates in situ at the WC / Co interface, combined with NbC grain suppression and gradient sintering processes. In contrast, while Comparative Examples 1 and 2 show advantages in local performance indicators, they exhibit deficiencies in hardness or significantly insufficient toughness and corrosion resistance due to the lack of a gradient structure and interface nano-reinforcement mechanism. Comparative Example 3, lacking key process control conditions, easily generates the η phase, leading to a decrease in fracture toughness and flexural strength. This demonstrates that the present invention, through the synergistic effect of low-cobalt gradient design and in-situ Cr3Si nano-precipitation reinforcement at the interface, exhibits significantly superior technical effects in terms of comprehensive mechanical properties and corrosion resistance compared to existing technologies.

[0036] The above description is only a specific embodiment of this disclosure, but the protection scope of this disclosure is not limited thereto. The protection scope of this disclosure should be determined by the protection scope of the claims.

Claims

1. A low-cobalt, high-strength, nano-gradient cemented carbide, characterized in that: The cemented carbide comprises a WC hard phase and a Co-based binder phase, and a surface layer, a transition layer, and a core layer are sequentially formed along the thickness direction of the product. The surface layer contains 0.5 wt% to 3.0 wt% Co, the transition layer contains 3.0 wt% to 5.0 wt% Co, and the core layer contains 5.0 wt% to 7.0 wt% Co. The cemented carbide contains Cr3Si nano-precipitates, the average particle size of which is 2 nm to 20 nm and the density is not less than 1 × 10²² m³. -3 It also exhibits an interface-enriched distribution.

2. The low-cobalt, high-strength nanogradient cemented carbide as described in claim 1, characterized in that: The average grain size of the WC hard phase is 0.2 μm to 0.6 μm.

3. The low-cobalt, high-strength nanogradient cemented carbide as described in claim 1, characterized in that: The thickness of the surface layer is 0.1 mm to 1.0 mm, and the thickness of the transition layer is 0.2 mm to 2.0 mm.

4. The low-cobalt, high-strength nanogradient cemented carbide as described in claim 1, characterized in that: The cemented carbide further comprises a grain inhibitor NbC, wherein the mass fraction of NbC is 0.05wt% to 0.50wt%; and a Nb-rich carbide segregation layer is formed at the interface between WC and the Co-based binder phase, and coexists with the Cr3Si nanoprecipitates near the interface.

5. The method for preparing a low-cobalt, high-strength nanogradient cemented carbide as described in any one of claims 1 to 4, characterized in that: Includes the following steps: Step 1: Provide WC powder, perform a composite coating operation of Cr-containing precursor and Si-containing precursor on the WC powder to form a Cr / Si-rich precursor coating layer with a thickness of 5nm to 50nm on the surface of WC particles, and obtain coated WC powder. Step 2: The coated WC powder is processed into a carbon nanostructure and mixed with Co powder according to the target composition ratio. The mixture is then uniformly mixed by ball milling to obtain the composite raw material powder. Step 3: Granulate the composite raw material powder and press the granulated powder into shape by cold isostatic pressing to obtain a shaped green body; Step 4: The interior of the formed green body is sintered into a preliminary sintered neck structure through pre-sintering treatment to obtain a pre-sintered body; Step 5: Gradient sintering is performed on the pre-sintered body. Multi-zone temperature control is adopted and the temperature difference between the core and the surface of the product is monitored and adjusted in real time to ΔT≤50℃. At the same time, the dew point of the sintering atmosphere is controlled to ≤-40℃ and the carbon potential is maintained within the carbon potential window that inhibits the formation of η phase and the precipitation of free graphite by adjusting the atmosphere ratio, so as to form a Co-based binder phase gradient structure. Step 6: In the high-temperature heat preservation stage of the Co-based binder phase gradient structure, a segmented heat preservation treatment is carried out in the range of 1420℃~1450℃. The Cr / Si rich precursor coating layer reacts at the interface between WC and the binder phase and generates Cr3Si nano-precipitates in situ, thus obtaining cemented carbide.

6. The method for preparing low-cobalt, high-strength, nano-gradient cemented carbide as described in claim 5, characterized in that: The composite coating process involves contacting WC powder with a Cr-containing salt solution and a Si-containing sol or silicon source precursor and depositing it into a film, followed by drying and heat treatment in a reducing atmosphere to solidify and stabilize the Cr / Si-rich precursor coating layer.

7. The method for preparing low-cobalt, high-strength nanogradient cemented carbide as described in claim 5, characterized in that: The carbon potential window is constrained by a dew point of ≤-40℃. One of the CO / CO2 atmosphere system or CH4 / H2 atmosphere system is selected as the carbon control gas source. The carbon potential in the furnace is kept stable within the effective carbon potential control window by adjusting the volume fraction ratio of the two components in the atmosphere system online. The effective carbon potential control window is defined as the carbon balance condition of "no η phase generated and no free graphite precipitated" being met simultaneously throughout the entire sintering cycle.

8. The method for preparing low-cobalt, high-strength, nano-gradient cemented carbide as described in claim 5, characterized in that: During the uniform mixing process via ball milling, the grain inhibitor NbC is added simultaneously. Through mechanical shearing and collision, the grain inhibitor NbC preferentially adheres to and distributes on the surface of WC particles.

9. The method for preparing low-cobalt, high-strength, nano-gradient cemented carbide as described in claim 5, characterized in that: The process of processing the coated WC powder into a carbon nanostructure involves performing in-situ vapor deposition on the coated WC powder to deposit a carbon source on the surface of the WC powder to form a carbon nanostructure, and then mixing the WC powder with the carbon nanostructure with Co powder. The total content of the carbon nanostructures is 0.03wt% to 0.30wt%, and after sintering, some of them will be converted and retained as carbon nano-derived bridging structures.

10. The application of a low-cobalt, high-toughness nanogradient cemented carbide according to any one of claims 1 to 4 in high-precision electronic molds, characterized in that, High-precision electronic molds include semiconductor packaging molds and precision connector molds.

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