A solid solution change distribution gradient cemented carbide and a method for manufacturing the same

Abstract

The application discloses a gradient cemented carbide with solid solution change distribution and a preparation method thereof. The gradient cemented carbide comprises a poor-FCC high-toughness area, a rich-FCC high-hardness area and a core area from outside to inside. The thickness of the poor-FCC high-toughness area is denoted as L1, the thickness of the rich-FCC high-hardness area is denoted as L2, the ratio of L2 to L1 is 1.1-5:1, and the ratio of the EBSD calibration area of the rich-FCC high-hardness area to the core area is 1.1-3:1. The preparation method comprises preparing raw materials according to the elements and proportions of the gradient cemented carbide, pressing forming and alloy sintering. The gradient cemented carbide can realize the double high characteristics of the high-toughness surface layer and the high-hardness subsurface layer at the same time without changing the alloy matrix component system and the hard phase particle size system, thereby significantly improving the high-temperature plastic deformation resistance of the cutter.

Description

Technical Field

[0001] This invention belongs to the field of CVD coated gradient cemented carbide cutting tool technology, and relates to a gradient cemented carbide with varying solid solution distribution, specifically a gradient cemented carbide with varying cubic solid solution distribution. Background Technology

[0002] CVD-coated gradient cemented carbide WC-Co-(W,Ti,Ta,Nb)CN ((W,Ti,Ta,Nb)CN is represented by FCC) forms a high-toughness zone (typically 5-50 μm thick) near the surface of the substrate, rich in cobalt and poor in FCC. This effectively prevents the rapid propagation of CVD coating cracks into the substrate during machining, significantly improving the machining life of CVD-coated tools. Therefore, gradient cemented carbide has always been a core technology and research hotspot in the field of steel turning CVD CNC inserts. Toughness and hardness are crucial factors that need to be balanced in cemented carbide material research. Excessive hardness reduces toughness, making the material less impact-resistant; conversely, increased toughness leads to decreased hardness, weakening resistance to plastic deformation under high-temperature machining conditions. Adding a cubic solid solution (W,Ti,Ta,Nb)CN phase to the WC-Co system in gradient cemented carbide can improve the room temperature and high-temperature hardness of the cemented carbide matrix, thereby enhancing the tool's resistance to plastic deformation under high-temperature machining conditions. However, the cubic solid solution (W,Ti,Ta,Nb)CN is a brittle and hard phase, and an excessively high proportion will greatly reduce the toughness and strength of the alloy. Therefore, it needs to be controlled within a suitable range.

[0003] In recent years, with the gradual improvement of the properties of processed materials and the increasing complexity of working conditions, the processing speed has become higher and higher, which has placed higher demands on the gradient cemented carbide substrate of CVD coated CNC tools. At high speeds, the processing temperature is getting higher and higher, and the situation of tool failure due to plastic deformation of the substrate during processing is becoming more and more significant. Therefore, it is very important to continue to improve the resistance to plastic deformation of gradient cemented carbide substrate at high temperatures without changing the high toughness gradient structure and with a reasonable cubic solid solution ratio.

[0004] The following compares three representative gradient structure cemented carbides. In the paper "Effect of initial WC particle size on grain growth behavior and gradient structure formation of bilayer functionally graded cemented carbides[J], Materials Chemistry and Physics, 271(2021)124919", Chen Jian prepared a bigradation cemented carbide WC-TiC-Co by adjusting the sintering N2 atmosphere pressure. The outermost layer is a layer rich in FCC phase, and the second layer is a layer rich in Co. The outermost layer of this structure is rich in FCC phase and has high hardness, but it cannot effectively absorb the hot cracks of CVD coating.

[0005] Zhang Weibin disclosed a dual-gradient cemented carbide in Chinese patent document CN106048360A. The principle behind this dual-gradient structure is to add ZrC / HfC to a conventional gradient cemented carbide formulation, utilizing the interstitial dissolution between Ti-rich cubic solid solutions and Zr / Hf-rich cubic solid solutions during a denitrification process to form the dual-gradient structure. This method requires adding ZrC / HfC to the raw materials and combining it with a nitrogen-removing sintering process. ZrC readily forms ZrO2 defects in powder metallurgy, distributed throughout the gradient alloy, significantly reducing its bending strength and shortening the lifespan of CVD CNC tools.

[0006] Chinese patent document CN109161711B discloses a method for preparing an ultrafine-grained gradient cemented carbide with a dual-gradient structure, which has the following characteristics: ① The dual-gradient cemented carbide is an ultrafine-grained gradient cemented carbide with a WC grain size of 0.1-0.5μm, which is different from the alloy matrix system of CVD-coated gradient cemented carbide tools (EBSD average grain size is 0.7-1.5μm). The significantly reduced average grain size will reduce the toughness of the alloy; ② The process of forming the dual-gradient structure involves first low-pressure sintering into a dense, gradient-free ultrafine-grained cemented carbide block, and then subjecting the alloy block to a secondary vacuum gradient re-sintering treatment, i.e., by superimposing two sintering processes, the process is complex, the cost is doubled, and it is not suitable for industrial production; ③ Its purpose is to solve the problem of low alloy strength and hardness caused by large cemented carbide grain size, with the focus on achieving an ultrafine-grained structure.

[0007] In summary, meeting the ever-increasing demand from the steel market for CVD-coated gradient carbide cutting tools has become an urgent problem to be solved. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a gradient cemented carbide and its preparation method that simultaneously achieves the dual characteristics of "high toughness surface layer - high hardness sub-surface layer" and can meet the needs of high-speed and high-efficiency processing without changing the matrix composition system and hard phase particle size system of the gradient cemented carbide.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0010] A gradient cemented carbide with varying solid solution distribution, wherein the gradient cemented carbide, from the outside to the inside (i.e., from the outer surface to the core), consists of a high-toughness region depleted by FCC, a high-hardness region rich in FCC, and a core region. FCC refers to a cubic solid solution phase composed of refractory compounds, wherein the refractory compounds are one or more of refractory carbides, refractory carbonitrides, and refractory nitrides. The refractory carbides include Ti-containing carbides, which include TiC and / or (W,Ti)C; the refractory carbonitrides include TiCN; and the refractory nitrides include TiN. The FCC-depleted high-toughness region includes WC and Co, or WC, Co, and FCC, with a thickness denoted as L1. The FCC-rich high-hardness region includes WC, Co, and FCC, with a thickness denoted as L2. The core region includes WC, Co, and FCC. The ratio of L2 to L1 is 1.1 to 5:1. The ratio of the EBSD area of ​​FCC in the FCC-rich high-hardness region to the EBSD area of ​​the core FCC is 1.1 to 3:1. The average Co content is highest in the FCC-depleted high-toughness region, and lowest in the FCC-rich high-hardness region. Preferably, the refractory compound is one or more of refractory carbides, refractory carbonitrides, and refractory nitrides, more preferably one or a combination of refractory carbonitrides and refractory nitrides with refractory carbides.

[0011] In the aforementioned gradient cemented carbide with varying solid solution distribution, preferably, based on the total mass of each region, the average FCC content in the FCC-depleted high-toughness region, the FCC-rich high-hardness region, and the core region is denoted as FCC1, FCC2, and FCC3, respectively. Then, FCC1 < 1%, FCC2 is the highest, and the FCC2 / FCC3 ratio is 1.1–2. For example: FCC2 = mass of FCC in the FCC-rich high-hardness region / total mass of the FCC-rich high-hardness region.

[0012] In the aforementioned gradient cemented carbide with varying solid solution distribution, preferably, based on the total mass of each region, the average Co content in the FCC-depleted high-toughness region, the FCC-rich high-hardness region, and the core region is denoted as Co1, Co2, and Co3, respectively. Co1, Co2, and Co3 satisfy the following conditions: Co1 / Co2 is 1.5 to 2.2, Co1 / Co3 is 1.2 to 2, and (Co1 / Co2) - (Co1 / Co3) ≥ 0.2.

[0013] In the aforementioned gradient cemented carbide with varying solid solution distribution, preferably, the thickness L1 of the FCC-depleted high-toughness region is 10 μm to 50 μm, and the thickness L2 of the FCC-rich high-hardness region is 20 μm to 150 μm.

[0014] In the aforementioned gradient cemented carbide with varying solid solution distribution, preferably, the refractory carbides further include one or more of TaC, NbC, and (Ta,Nb)C.

[0015] As a general technical concept, the present invention also provides a method for preparing the above-mentioned gradient cemented carbide with varying solid solution distribution, comprising the following steps:

[0016] (1) Prepare raw materials according to the required elements and proportions of gradient cemented carbide: Based on the total mass of the raw materials, the following percentages are calculated by mass: Co is 5% to 10%, Ta is 0% to 5%, Nb is 0% to 5%, Ti is 2% to 8%, N is 0.06% to 1%, C is 6.2% to 6.9%, and the balance is W.

[0017] (2) Pressing and molding: The above raw materials, molding agent, ball milling rod and alcohol are mixed and wet milled. The resulting slurry is dried and sieved to obtain a mixture, which is then pressed into a green embryo.

[0018] (3) Alloy sintering: The above green blank is heated to 300℃~450℃ for H2 sintering, the forming agent is removed by Towack process at 400℃~500℃, and then heated to 1330℃~1360℃ under vacuum conditions, 20mbar~100mbar of inert gas Ar is introduced and sintered at the temperature for 20min~60min, then heated to 1420℃~1480℃ and sintered at the temperature for 30min~90min, then 30bar~100bar of Ar is introduced and sintered under pressure for 10min~30min, then cooled to 1000℃~1200℃ and cooled to room temperature under H2 conditions to obtain a gradient hard alloy with a solid solution distribution.

[0019] In the preferred method for preparing the gradient cemented carbide with varying solid solution distribution described above, in step (1), based on the total mass of the raw materials, the following percentages are used: Co is 5%–10%, Ta is 0.5%–5%, Nb is 0.5%–5%, Ti is 2%–8%, N is 0.06%–1%, C is 6.2%–6.9%, and the balance is W.

[0020] In the preferred embodiment of the above-mentioned method for preparing gradient cemented carbide with varying solid solution distribution, in step (1), the raw material sources for the W element include WC powder and / or (W,Ti)C solid solution powder; the raw material sources for the Ti element include one or more of TiC powder, TiCN powder, (W,Ti)C solid solution powder, and TiN powder; the raw material sources for the Ta element include TaC powder and / or (Ta,Nb)C solid solution powder; the raw material sources for the Nb element include NbC powder and / or (Ta,Nb)C solid solution powder; the raw material sources for the N element include TiCN powder and / or TiN powder; and the raw material sources for the Co element include Co powder.

[0021] In the preferred embodiment of the above-mentioned method for preparing gradient cemented carbide with varying solid solution distribution, the FSSS particle size of the Co powder is 1.2 μm to 1.5 μm, the FSSS particle size of the (W,Ti)C solid solution powder is 1.5 μm to 2.0 μm, the FSSS particle size of the TiCN powder is 0.8 μm to 1.2 μm, the FSSS particle size of the (Ta,Nb)C solid solution powder is 1.0 μm to 1.5 μm, the FSSS particle size of the TiC powder, TiN powder, TaC powder, and NbC powder is 1.0 μm to 2.0 μm, and the FSSS particle size of the WC powder is 3.0 μm to 4.0 μm.

[0022] In the preferred method for preparing the gradient cemented carbide with varying solid solution distribution described above, in step (2), the forming agent is PEG, the mass of the forming agent is 1.5% to 2.5% of the total mass of the raw materials in step (1), the mass of the ball milling rod is 4 to 6 times the total mass of the raw materials in step (1), the amount of alcohol added is 200 mL to 300 mL of alcohol per kilogram of raw materials, and the wet milling time is 25 h to 35 h.

[0023] In the preferred method for preparing gradient cemented carbide with varying solid solution distribution, in step (2), the drying temperature is 60℃~120℃, the drying time is 2h~3h, and the sieving is 60 mesh~80 mesh.

[0024] In this invention, the gradient cemented carbide consists of an FCC-poor high-toughness region, an FCC-rich high-hardness region, and a core region from the outside to the inside. That is, from the outer surface to the core, the regions are FCC-poor high-toughness region, FCC-rich high-hardness region, and core region.

[0025] In this invention, EBSD refers to electron backscatter diffraction, an advanced material structure characterization technique. EBSD allows us to determine the phase distribution and area percentage of a sample. Hardness is characterized using Vickers hardness (HV); a higher HV indicates higher material hardness. Toughness is characterized by fracture toughness (K).1C Characterization K 1C The higher the value, the better the material's toughness.

[0026] Compared with the prior art, the advantages of the present invention are as follows:

[0027] 1. This invention proposes and achieves the superposition of "high toughness and high hardness zones" in the near-surface (0-120μm) layer of cemented carbide through process control. The surface layer forms a high-toughness zone rich in Co and low in FCC, while the subsurface layer forms a high-hardness zone rich in cubic phase and low in Co. The core maintains a macroscopically uniform WC-Co-(W,Ti,Ta,Nb)CN structure with no significant enrichment or depletion of components, achieving a synergistic effect of "high toughness surface layer - high hardness subsurface layer". This invention prepares a gradient cemented carbide with varying cubic solid solution FCC content without altering the WC-Co-(W,Ti,Ta,Nb)CN system, resulting in a "dual-high" characteristic of superimposed high toughness in the surface layer and high hardness in the subsurface layer.

[0028] 2. The hardness of the dual-high advantage gradient cemented carbide of this invention first increases from the lowest to the highest value from the surface to the core, and then decreases to an intermediate value, which is positively correlated with the FCC content; fracture toughness K 1C The hardness decreases from a maximum to a minimum, then rises to an intermediate value, positively correlated with Co content. This structure helps prevent hot cracks in the CVD coating from propagating into the alloy interior. Simultaneously, the high-hardness subsurface region improves the tool's resistance to high-temperature plastic deformation. In terms of preparation, the thickness and composition of the FCC-depleted high-toughness and FCC-rich high-hardness regions can be flexibly controlled by adjusting element ratios and sintering processes to meet the toughness and hardness requirements of the gradient cemented carbide of this invention under machining conditions. Attached Figure Description

[0029] Figure 1 This is a SEM image of the near-surface microstructure of the gradient cemented carbide in Example 1 of the present invention.

[0030] Figure 2 This is an EBSD phase distribution diagram of the FCC-poor high-toughness region, the FCC-rich high-hardness region, and the core region of the gradient cemented carbide in Embodiment 1 of the present invention.

[0031] Figure 3 This is the EDS elemental distribution diagram of the near-surface layer (0-240 μm) of the gradient cemented carbide in Example 1 of this invention.

[0032] Figure 4 This is a Vickers hardness curve (0-120μm, load 2kg) from the surface to the core of the gradient cemented carbide in Embodiment 1 of the present invention.

[0033] Figure 5 This is a SEM image of the near-surface microstructure of the gradient cemented carbide in Comparative Example 1.

[0034] Figure 6 This is the room temperature hardness (HV) curve of the near-surface layer (0-90μm) of the gradient cemented carbide in Comparative Example 1.

[0035] Figure 7 These are the HT-HV curves of the near-surface layer (0-120μm) of the present invention in Embodiment 1 and Comparative Example 1. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0037] In the following examples and comparative examples, the characterization method was as follows: Gradient carbide was cut to expose the core cross-section. The cross-section was then metallographically ground and polished using a Struer metallographic sample preparation instrument until it was flat, smooth, and free of obvious scratches. A Zeiss Supra 55 field emission scanning electron microscope and an Oxford X-MAX 50mm energy dispersive spectrometer were used. 2 The microstructure and composition of the alloy core were analyzed. Data acquisition and analysis were performed on the FCC-poor high-toughness region, the FCC-rich high-hardness region, and the core of the sample using an Oxford Instruments Nordlys EBSD system. Microhardness testing of the sample surface layer (0-120 μm) was conducted using an AFFRI microhardness tester.

[0038] Example 1

[0039] A gradient cemented carbide with varying solid solution distribution according to the present invention comprises, from the outside to the inside (from the outer surface to the core), a sequentially arranged FCC-depleted high-toughness region, an FCC-rich high-hardness region, and a core region. The FCC is a cubic solid solution phase made of (W,Ti)C, TiCN, (Ta,Nb)C, and TaC. The FCC-depleted high-toughness region includes WC and Co, with a thickness denoted as L1; the FCC-rich high-hardness region includes WC, Co, and FCC, with a thickness denoted as L2; ​​and the core region contains WC, Co, and FCC. The average FCC content and average Co content within the three regions exhibit a varying distribution, as shown below. Figure 1 As shown, the thickness L1 of the FCC-poor high-toughness region is 28 μm, and the thickness L2 of the FCC-rich high-hardness region is 45 μm, with an L2 / L1 ratio of 1.61. Figure 2 As shown, the EBSD calibration area of ​​the FCC phase in the FCC-rich, high-hardness region, Area2, is 26.4%, while the EBSD calibration area of ​​the FCC phase in the core region, Area3, is 16%, and the ratio of Area2 to Area3 is 1.65.

[0040] In this embodiment, the average FCC content in the FCC-poor, high-toughness region is denoted as FCC1, the average FCC content in the FCC-rich, high-hardness region is denoted as FCC2, and the average FCC content in the core is denoted as FCC3. FCC1, FCC2, and FCC3 satisfy the following conditions: FCC1 is the lowest (0), FCC2 is the highest, and the ratio of FCC2 / FCC3 is 1.26. Figure 3 As shown.

[0041] In this embodiment, the average Co content in the FCC-poor high-toughness region is denoted as Co1, the average Co content in the FCC-rich high-hardness region is denoted as Co2, and the average Co content in the core region is denoted as Co3. Co1, Co2, and Co3 satisfy the following conditions: Co1 is the highest; Co2 is the lowest; Co1 / Co2 is 1.96, Co1 / Co3 is 1.71, and (Co1 / Co2)-(Co1 / Co3) is 0.25. Figure 3 As shown.

[0042] A method for preparing a gradient hard alloy with varying solid solution distribution according to the present invention includes the following steps:

[0043] (1) Prepare raw materials according to the elements and proportions of gradient cemented carbide: Based on the total mass of the raw materials, the mass percentages are as follows: Co is 7.5%, Ta is 2.8%, Nb is 0.75%, Ti is 3%, N is 0.2%, C is 6.32%, and the remainder is W;

[0044] (2) Pressing and molding: The above raw materials, molding agent, ball milling rod and alcohol are mixed and wet milled. The resulting slurry is dried and sieved to obtain a mixture, which is then pressed into a green embryo.

[0045] (3) Alloy sintering: The above green blanks are first sintered at 370℃ in H2 atmosphere, then heated to 450℃ to remove the forming agent by Towack process, then heated to 1350℃ under vacuum, filled with 60mbar inert gas Ar and sintered at the temperature for 30min, then heated to 1450℃ and sintered at the temperature for 50min, then filled with 40bar Ar atmosphere and sintered under pressure for 20min, then cooled to 1000℃~1200℃ and cooled to room temperature under H2 conditions.

[0046] In step (1), the raw materials for W element are WC powder and (W,Ti)C solid solution powder, the raw materials for Ti element are TiCN powder and (W,Ti)C solid solution powder, the raw materials for Ta element are (Ta,Nb)C solid solution powder and TaC powder, the raw materials for Nb element are (Ta,Nb)C solid solution powder, the raw materials for N element are TiCN powder, the raw materials for Co element are Co powder, and the raw materials for C element are carbides of the above elements.

[0047] The FSSS particle sizes of the raw materials are as follows: Co powder 1.3 μm, (W,Ti)C solid solution powder 1.63 μm, TiCN powder 1.1 μm, (Ta,Nb)C solid solution powder 1.3 μm, TaC powder 1.1 μm, and WC powder 3.7 μm.

[0048] In step (2), the molding agent is PEG, the mass of the molding agent is 2% of the total mass of the raw materials in step (1), the mass of the ball milling rod is 5 times the total mass of the raw materials in step (1), the amount of alcohol added is 200 mL of alcohol per kilogram of raw materials, and the wet milling time is 28 h.

[0049] In step (2), the drying temperature is 120℃, the drying time is 3h, and the sieve is 80 mesh.

[0050] Upon testing, the Vickers hardness HV curves (at room temperature) of the gradient cemented carbide in this embodiment, from the outer surface to the core (0-120μm), in each region are as follows: Figure 4 As shown, the surface FCC-poor, high-toughness region has the lowest hardness, the subsurface FCC-rich, high-hardness region has the highest hardness, and the core has intermediate hardness. The average HV and average fracture toughness K of the FCC-poor, high-toughness region are also shown. 1C The value is 1343 N / mm. 2 and 12.52 MPa·m 1 / 2 The average HV and average fracture toughness K in the FCC-rich high-hardness region 1C 1630 N / mm 2 and 9.8 MPa·m 1 / 2 The average HV and average fracture toughness K in the core region 1C 1560 N / mm 2 and 10.27 MPa·m 1 / 2 This structure helps prevent hot cracks in the CVD coating from propagating into the alloy interior. At the same time, the high hardness of the subsurface layer improves the tool's resistance to high-temperature plastic deformation.

[0051] Example 2

[0052] A gradient cemented carbide with varying solid solution distribution according to the present invention comprises, from the outside to the inside, a sequentially arranged FCC-depleted high-toughness region, an FCC-rich high-hardness region, and a core region. The FCC is a cubic solid solution phase composed of (W,Ti)C, TiCN, (Ta,Nb)C, and NbC. The FCC-depleted high-toughness region includes WC, Co, and FCC, with a thickness denoted as L1; the FCC-rich high-hardness region includes WC, Co, and FCC, with a thickness denoted as L2; ​​and the core region contains WC, Co, and FCC. The average FCC content and average Co content within the three regions exhibit varying distributions. The thickness L1 of the FCC-depleted high-toughness region is 30 μm, the thickness L2 of the FCC-rich high-hardness region is 75 μm, and the L2 / L1 ratio is 2.5. The EBSD-calibrated area (Area2) of the FCC phase in the FCC-rich high-hardness region is 28.5%, and the EBSD-calibrated area (Area3) of the FCC phase in the core region is 22.02%, with an Area2 / Area3 ratio of 1.29.

[0053] In this embodiment, the average FCC content in the FCC-poor, high-toughness region is denoted as FCC1, the average FCC content in the FCC-rich, high-hardness region is denoted as FCC2, and the average FCC content in the core region is denoted as FCC3. FCC1, FCC2, and FCC3 satisfy the following conditions: FCC1 is the lowest, FCC2 is the highest, FCC1 is 0.12%, and the ratio of FCC2 to FCC3 is 1.21.

[0054] In this embodiment, the average Co content in the FCC-poor high-toughness region is denoted as Co1, the average Co content in the FCC-rich high-hardness region is denoted as Co2, and the average Co content in the core region is denoted as Co3. Co1, Co2, and Co3 satisfy the following conditions: Co1 is the highest; Co2 is the lowest; Co1 / Co2 is 2.0, Co1 / Co3 is 1.69, and (Co1 / Co2)-(Co1 / Co3) is 0.31.

[0055] A method for preparing a gradient cemented carbide with varying solid solution distribution according to this embodiment includes the following steps:

[0056] (1) Prepare raw materials according to the elements and proportions of gradient cemented carbide: Based on the total mass of the raw materials, by mass percentage, Co is 7.5%, Ta is 1.32%, Nb is 1%, Ti is 4.4%, N is 0.32%, C is 6.35%, and the remainder is W;

[0057] (2) Pressing and molding: The above raw materials, molding agent, ball milling rod and alcohol are mixed and wet milled. The resulting slurry is dried and sieved to obtain a mixture, which is then pressed into a green embryo.

[0058] (3) Alloy sintering: The above green blank is first sintered at 370℃ in H2 atmosphere, then heated to 450℃ to remove the forming agent by Towack process, then heated to 1350℃ under vacuum, filled with 60mbar inert gas Ar and sintered for 30min, then heated to 1450℃ and sintered for 50min, then filled with 40bar Ar atmosphere and sintered for 20min, then cooled to 1000℃~1200℃ and cooled to room temperature under H2 conditions.

[0059] In step (1) of this embodiment, the raw material sources for W element include WC powder and (W,Ti)C solid solution powder, the raw material sources for Ti element are TiCN powder and (W,Ti)C solid solution powder, the raw material sources for Ta element include (Ta,Nb)C solid solution powder, the raw material sources for Nb element are (Ta,Nb)C solid solution powder and NbC powder, the raw material source for N element is TiCN powder, the raw material source for Co element is Co powder, and the raw material source for C element is the carbides of the above elements.

[0060] The FSSS particle sizes of the raw materials are as follows: Co powder 1.3 μm, (W,Ti)C solid solution powder 1.63 μm, TiCN powder 1.1 μm, (Ta,Nb)C solid solution powder 1.3 μm, TaC powder 1.1 μm, and WC powder 3.7 μm.

[0061] In step (2) of this embodiment, the molding agent is PEG, the mass of the molding agent is 2% of the total mass of the raw materials in step (1), the mass of the ball milling rod is 5 times the total mass of the raw materials in step (1), the amount of alcohol added is 200 mL of alcohol per kilogram of raw materials, and the wet milling time is 28 h.

[0062] In step (2) of this embodiment, the drying temperature is 120°C, the drying time is 3 hours, and the sieve is 80 mesh.

[0063] Testing revealed that in the gradient cemented carbide of this embodiment, the average HV and average fracture toughness K in the FCC-depleted, high-toughness region were... 1C 1305 N / mm 2 and 12.8 MPa·mm 1 / 2 The average HV and average fracture toughness K in the FCC-rich high-hardness region 1C 1646 N / mm 2 and 9.68 MPa·mm 1 / 2 The average HV and average fracture toughness K in the core 1C 1580 N / mm 2 and 10.36 MPa·mm 1 / 2 .

[0064] Comparative Example 1

[0065] To better demonstrate the structural features and performance advantages of the gradient cemented carbide of this invention, Comparative Example 1 uses a conventional gradient cemented carbide product from our company, whose near-surface microstructure is as follows: Figure 5 As shown, FCC is a cubic solid solution phase formed by refractory carbides TaC, (W,Ti)C, (TaNb)C, and TiNC. The cross-sectional SEM morphology includes a surface FCC-poor, high-toughness region and a core homogeneous region. The high-toughness region contains only WC and Co areas, with its thickness and average Co content denoted as L1 and Co1, respectively. The core contains WC, Co, and FCC phases, with its average Co content and FCC content denoted as Co3 and FCC3, respectively. The comparative sample lacks an FCC-rich, high-hardness region. To better reveal the structural characteristics of different solid solution distributions in this invention and the advantages of this structure, the region in the Comparative Example 1 sample with the same geometric depth as the FCC-rich, high-hardness region in Example 1 is used as an analogy region, and the average Co content and average FCC content of this analogy region are denoted as Co2 and FCC2, respectively.

[0066] In Comparative Example 1, the thickness L1 of the high-toughness region of the lean FCC is 25 μm. The Co content is highest in the high-toughness region of the lean FCC, and the Co content changes little as it extends further into the core. The ratio of the average Co content in the high-toughness region of the lean FCC to the average Co content in the analog region is Co1 / Co2 = 1.48 and Co1 / Co3 = 1.47, with a difference of 0.01. The ratio of FCC2 / FCC3 is 1.04, and the ratio of Area2 / Area3 is 1.07.

[0067] After testing, such as Figure 6 As shown, the comparative sample exhibits the lowest hardness in the FCC-poor high-toughness region, while the hardness variation is not significant in the analog region and the core. The average HV and average fracture toughness K in the FCC-poor high-toughness region are... 1C 1320 N / mm 2 and 12.9 MPa·m 1 / 2 The average HV and average fracture toughness K in the core 1C 1530 N / mm 2 and 10.88 MPa·m 1 / 2 .

[0068] In comparison, firstly, the hardness and fracture toughness of the embodiment are similar to those of the comparative sample in the FCC-poor high-toughness region. From the sample surface to the core, this region exhibits the lowest hardness and highest fracture toughness, ensuring the high toughness characteristic of the outermost layer of the sample. In the low-Co, FCC-rich high-hardness region, the embodiment sample shows the highest hardness and lowest fracture toughness, ensuring the highest resistance to plastic deformation in the subsurface layer. In the core region, the embodiment sample exhibits higher hardness and fracture toughness than the FCC-poor high-toughness region, and its core resistance to plastic deformation is significantly better than that of the comparative sample. Therefore, it can be concluded that the comparative sample cannot achieve the structural and performance characteristics of the present invention, and the gradient cemented carbide of the present invention has a significantly higher resistance to plastic deformation than the comparative sample.

[0069] like Figure 7 As shown, Example 1 and Comparative Example 1 were tested online at 800℃ using the Vickers hardness test (HT-HV). The results showed that, compared with the Comparative Example, Example 1 exhibited significantly higher high-temperature hardness in the FCC-rich high-hardness region of the subsurface layer, thus achieving the purpose of this invention to improve the high-temperature hardness of the matrix under high-temperature conditions and thereby enhance its resistance to plastic deformation.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A gradient hard alloy with varying solid solution distribution, characterized in that, The gradient cemented carbide consists of, from the outside to the inside, a FCC-depleted high-toughness region, an FCC-rich high-hardness region, and a core region. FCC refers to a cubic solid solution phase made of refractory compounds. These refractory compounds are one or more of refractory carbides, refractory carbonitrides, and refractory nitrides. The refractory carbides include Ti-containing carbides, which include TiC and / or (W,Ti)C. The refractory carbonitrides include TiCN, and the refractory nitrides include TiN. The FCC-depleted high-toughness region includes WC. The thickness of the FCC-rich high-hardness region is denoted as L1, and the thickness of the FCC-rich high-hardness region is denoted as L2, and the thickness of the core ...

2. The gradient cemented carbide with varying solid solution distribution according to claim 1, characterized in that, The average FCC content in the FCC-poor high-toughness region, FCC-rich high-hardness region, and core region is denoted as FCC1, FCC2, and FCC3, respectively. FCC1 < 1%, FCC2 is the highest, and the ratio of FCC2 to FCC3 is 1.1 to 2.

3. The gradient cemented carbide with varying solid solution distribution according to claim 1, characterized in that, The average Co content in the FCC-poor high-toughness region, FCC-rich high-hardness region, and core region is denoted as Co1, Co2, and Co3, respectively. Co1, Co2, and Co3 satisfy the following conditions: Co1 / Co2 is 1.5 to 2.2, Co1 / Co3 is 1.2 to 2, and (Co1 / Co2) - (Co1 / Co3) ≥ 0.

2.

4. The gradient cemented carbide with varying solid solution distribution according to any one of claims 1 to 3, characterized in that, The thickness L1 of the FCC-poor high-toughness region is 10μm to 50μm, and the thickness L2 of the FCC-rich high-hardness region is 20μm to 150μm.

5. The gradient cemented carbide with varying solid solution distribution according to any one of claims 1 to 3, characterized in that, The refractory carbides also include one or more of TaC, NbC, and (Ta,Nb)C.

6. A method for preparing a gradient cemented carbide with varying solid solution distribution as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Prepare raw materials according to the required elements and proportions of gradient cemented carbide: Based on the total mass of the raw materials, the following percentages are calculated by mass: Co is 5% to 10%, Ta is 0% to 5%, Nb is 0% to 5%, Ti is 2% to 8%, N is 0.06% to 1%, C is 6.2% to 6.9%, and the balance is W. (2) Pressing and molding: The above raw materials, molding agent, ball milling rod and alcohol are mixed and wet milled. The resulting slurry is dried and sieved to obtain a mixture, which is then pressed into a green embryo. (3) Alloy sintering: The above green blank is heated to 300℃~450℃ for H2 sintering, the forming agent is removed by Towack process at 400℃~500℃, and then heated to 1330℃~1360℃ under vacuum conditions, 20mbar~100mbar of inert gas Ar is introduced and sintered at the temperature for 20min~60min, then heated to 1420℃~1480℃ and sintered at the temperature for 30min~90min, then 30bar~100bar of Ar is introduced and sintered under pressure for 10min~30min, then cooled to 1000℃~1200℃ and cooled to room temperature under H2 conditions to obtain a gradient hard alloy with a solid solution distribution.

7. The method for preparing gradient cemented carbide with varying solid solution distribution according to claim 6, characterized in that, In step (1), based on the total mass of the raw materials, the percentage of Co is 5% to 10%, Ta is 0.5% to 5%, Nb is 0.5% to 5%, Ti is 2% to 8%, N is 0.06% to 1%, C is 6.2% to 6.9%, and the remainder is W.

8. The method for preparing gradient cemented carbide with varying solid solution distribution according to claim 6 or 7, characterized in that, In step (1), the raw material sources for the W element include WC powder and / or (W,Ti)C solid solution powder; the raw material sources for the Ti element include one or more of TiC powder, TiCN powder, (W,Ti)C solid solution powder, and TiN powder; the raw material sources for the Ta element include TaC powder and / or (Ta,Nb)C solid solution powder; the raw material sources for the Nb element include NbC powder and / or (Ta,Nb)C solid solution powder; the raw material sources for the N element include TiCN powder and / or TiN powder; and the raw material sources for the Co element include Co powder.

9. The method for preparing gradient cemented carbide with varying solid solution distribution according to claim 8, characterized in that, The FSSS particle size of the Co powder is 1.2 μm to 1.5 μm, the FSSS particle size of the (W,Ti)C solid solution powder is 1.5 μm to 2.0 μm, the FSSS particle size of the TiCN powder is 0.8 μm to 1.2 μm, the FSSS particle size of the (Ta,Nb)C solid solution powder is 1.0 μm to 1.5 μm, the FSSS particle size of the TiC powder, TiN powder, TaC powder, and NbC powder is 1.0 μm to 2.0 μm, and the FSSS particle size of the WC powder is 3.0 μm to 4.0 μm.

10. The method for preparing a gradient hard alloy with varying solid solution distribution according to claim 6 or 7, characterized in that, In step (2), the molding agent is PEG, the mass of the molding agent is 1.5% to 2.5% of the total mass of the raw materials in step (1), the mass of the ball milling rod is 4 to 6 times the total mass of the raw materials in step (1), the amount of alcohol added is 200 mL to 300 mL of alcohol per kilogram of raw materials, and the wet milling time is 25 h to 35 h.

11. The method for preparing a gradient hard alloy with varying solid solution distribution according to claim 6 or 7, characterized in that, In step (2), the drying temperature is 60℃~120℃, the drying time is 2h~3h, and the sieving is through a 60-80 mesh sieve.

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