Gradient functional composite wire drawing die and preparation method

Abstract

The application provides a gradient functional composite wire drawing die and a preparation method. The die comprises, from outside to inside in the radial direction, a modified hard alloy base, a diamond sintering layer and a diamond deposition layer. TiH2 with a mass fraction of 0.2% to 0.8% is added to the modified hard alloy base. The diamond sintering layer comprises a transition layer and a main body layer arranged from outside to inside in the radial direction. The diamond particles on the surfaces of the transition layer and the main body layer are both coated with MoSi2, and the binder phases of the two are both silanized Ni powder. The diamond deposition layer is formed on the inner hole working surface of the diamond sintering layer. During preparation, the modified base is prepared through secondary ball milling, the base is formed through zoned cold pressing, the base is sintered through gradient vacuum hot pressing, and the thin CVD diamond deposition process is used to realize integrated preparation. The application solves the problems of low CVD diamond coating deposition efficiency, easy high-temperature graphitization and falling off, and rapid failure of the die after the coating is exhausted.

Description

Technical Field

[0001] This invention relates to the field of wire drawing dies, and in particular to a gradient functional composite wire drawing die and its preparation method. Background Technology

[0002] Currently, the mainstream technology for microscale wire drawing dies involves using CVD to prepare a diamond coating on a cemented carbide substrate. However, due to the small pore size and large aspect ratio of the pores within the die, the reactant gas easily forms a concentration gradient within the narrow channels, leading to uneven coating deposition and negatively impacting product yield and production efficiency. Furthermore, the instantaneous high temperatures generated by friction during the drawing process promote the diffusion of Co from the substrate into the coating, catalyzing the formation of a graphitized brittle phase at the diamond-substrate interface, causing the coating to detach. Once the surface CVD coating is worn away, the underlying cemented carbide substrate lacks sufficient wear resistance, causing the die to fail rapidly and failing to meet the long-life requirements of microscale wire drawing applications. Summary of the Invention

[0003] The main objective of this invention is to provide a gradient functional composite wire drawing die and its preparation method, which solves the problems of low CVD diamond coating deposition efficiency, easy high-temperature graphitization and peeling off, and rapid die failure after coating depletion in microscale wire drawing dies.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A gradient functional composite wire drawing die, the die comprising, from the outside to the inside, a modified cemented carbide matrix, a diamond sintered layer and a diamond deposited layer in the radial direction; The modified cemented carbide matrix contains 0.2% to 0.8% TiH2 by mass. The diamond sintered layer includes a transition layer and a main layer arranged radially from the outside to the inside. The diamond particles in both the transition layer and the main layer are coated with MoSi2, and the binder phase of both is silanized Ni powder. The diamond deposition layer is formed on the inner working surface of the diamond sintered layer.

[0005] In some embodiments of this application, the modified cemented carbide matrix further includes the following components by mass fraction: 3% to 5% Co, 0.5% to 1.2% TaC, and 93% to 96.3% WC.

[0006] In some embodiments of this application, TiH2 is added to the modified cemented carbide matrix powder by a secondary ball milling doping method.

[0007] In some embodiments of this application, the coating amount of MoSi2 on the surface of the diamond particles is 0.6wt% to 0.8wt%.

[0008] In some embodiments of this application, the diamond particles include coarse diamond powder and fine diamond powder, with a mass ratio of 1:2 to 3. The coarse diamond powder has a particle size of 25 μm to 35 μm, and the fine diamond powder has a particle size of 1 μm to 15 μm.

[0009] In some embodiments of this application, the transition layer comprises the following components by mass fraction: 25%–30% WC, 15%–20% SiC, 10%–15% silanized Ni powder, and 35%–50% diamond particles; The main body layer contains the following components by mass fraction: WC 2%–4%, SiC 1%–4%, silanized Ni powder 3.5%–5.5%, hexagonal boron nitride powder 0.5%–1.5%, and diamond particles 85%–93%.

[0010] In some embodiments of this application, the silanized Ni powder is Ni powder obtained by drying after pretreatment with a silane coupling agent, wherein the silane coupling agent is one or more of KH-550, KH-560 and KH-570.

[0011] In some embodiments of this application, the thickness of the diamond sintered layer is 1 mm to 3 mm.

[0012] In some embodiments of this application, the thickness of the diamond deposition layer is 3 μm to 5 μm.

[0013] A second aspect of the present invention provides a method for preparing a gradient functional composite drawing die, comprising the following steps: Step 1: Preparation of modified cemented carbide matrix powder: WC, Co, and TaC are placed in a ball mill jar for a first ball milling according to the set mass ratio; then TiH2 with a mass fraction of 0.2% to 0.8% is added for a second ball milling, which takes 1 to 2 hours. After that, the powder is dried and sieved. Step 2, Preparation of diamond sintered layer powder: After coating the surface of diamond particles with MoSi2, the raw materials of the transition layer and the main layer are ball-milled according to a preset ratio. Step 3, partitioned filling and cold pressing: Partitioned filling of the modified cemented carbide matrix, the transition layer and the main layer in the diamond sintered layer, and cold pressing under a pressure of 10MPa to 20MPa for 30s to 60s. Step 4, sintering the mold blank and laser hole making: A gradient heating and vacuum hot pressing sintering process is adopted. First, the temperature is raised from room temperature to 600℃ and held for 30 minutes. Then, the temperature is raised to 800℃ and the pressure is slowly increased to 30MPa while holding for 30 minutes. Then, the temperature is raised to 1100℃ and held for 30 minutes. Finally, the temperature is raised to 1400℃ and held for 3 hours for cooling. With the center of the mold blank as the reference, the laser is perpendicularly incident to form the hole diameter. Then, the inner hole wall is processed and shaped. Step 5: Prepare a diamond deposition layer on the inner surface of the pore using hot-wire CVD: The mixed gas is CH4, H2, and Ar, with a volume concentration ratio of CH4:H2:Ar = 3~5:93~95:0~4, and the total gas flow rate is 200 sccm. The tantalum wire is heated to 2200℃, and the deposition time is 2h~4h. A diamond deposition layer is formed on the inner working surface of the diamond sintered layer.

[0014] This invention provides a gradient functional composite drawing die and its preparation method, which has the following beneficial effects: 1. The coating preparation effect in micro-scale channels was optimized. By using a composite structure of millimeter-scale diamond sintered layer and 3~5μm thin CVD diamond deposition layer, the deposition time was significantly shortened, effectively avoiding the problem of uneven coating thickness caused by the concentration difference of reactive gas in micro-channels. At the same time, the thin deposition layer has lower residual internal stress, and the homogeneous substrate deposition greatly improves the interlayer bonding strength, avoiding coating peeling failure, and significantly improving product yield and production efficiency.

[0015] 2. The graphitization problem of diamond is curbed at its root. By adding TiH2 to the cemented carbide matrix, the Ti atoms decomposed during sintering are used to capture the diffused Co elements in situ. Combined with the MoSi2 coating layer on the surface of diamond particles and the silanized Ni binder phase, multiple barriers are blocked and passivated to enhance the catalytic activity of the metal. This effectively solves the defect of Co migration-induced diamond graphitization in the existing technology, and significantly improves the wear resistance of the diamond layer and the service life of the mold.

[0016] 3. It alleviates the interface matching problem in the co-sintering of heterogeneous materials. By designing a gradient diamond sintering layer containing a transition layer and a main layer, the composition of each layer is controlled to achieve a gradient transition of the coefficient of thermal expansion, which effectively alleviates the thermal mismatch stress between heterogeneous materials and avoids defects such as mold cracking and interface delamination. At the same time, MoSi2 coating and silanization treatment improve the wettability of diamond and metal binder phase, and significantly improve the interfacial bonding strength and sintering density.

[0017] 4. It takes into account both the high wear resistance and high precision surface quality of the mold. The high diamond content of the main body layer provides ultra-high wear resistance and load-bearing capacity. Combined with the CVD diamond deposition layer on the inner hole surface and the hexagonal boron nitride lubricating phase in the main body layer, it effectively smooths the micropores and rough surface of the sintered layer, realizes an ultra-smooth and low-friction drawing working surface, avoids surface scratches on the metal wire during the drawing process, and meets the quality requirements of high precision drawing of micro-wires. Detailed Implementation

[0018] The embodiments of this application are described below. These embodiments are exemplary and intended to explain this application, and should not be construed as limiting this application. It should be noted that any modifications and improvements made by those skilled in the art without departing from the concept of this invention are within the scope of protection of this invention.

[0019] This application is based on the inventor's discoveries and understanding of the following facts and problems: For the development of microscale wire drawing dies ranging from 0.2 mm to 2 mm, existing methods typically employ hot-wire chemical vapor deposition to deposit a 10 μm to 15 μm nanodiamond coating on a cemented carbide substrate. However, this approach suffers from numerous intractable technical problems: For molds with micro-apertures and large pore aspect ratios, preparing CVD diamond coatings with a thickness exceeding 10 μm requires significantly extended deposition time. Prolonged aeration creates concentration differences in the reactant gases at the inlet and outlet of the narrow pores, preventing uniform distribution and resulting in uneven coating thickness and poor density. This drastically reduces product yield and impacts production efficiency. Furthermore, thick CVD diamond coatings exhibit significant residual internal stress, making them highly susceptible to coating detachment and failure during service. Secondly, the instantaneous high temperatures generated during mold drawing due to friction cause Co binder phases in the cemented carbide matrix to easily migrate to the surface diamond layer through grain boundaries. Co, as a strong graphitization catalyst, induces graphitization transformation in diamond, significantly reducing the wear resistance and lifespan of the diamond layer. Existing technologies using TiN and TiC transition layers are merely simple physical barrier layers, unable to effectively inhibit Co grain boundary diffusion. This fails to address the root cause of Co migration catalyzing diamond graphitization, which leads to embrittlement between the diamond and the substrate.

[0020] The significant differences in thermal expansion coefficients between diamond, ceramic phase, and cemented carbide matrix make direct co-sintering highly susceptible to interfacial thermal stress due to thermal mismatch, leading to defects such as die cracking and interfacial delamination. Furthermore, the intrinsic inertness of diamond results in extremely poor wettability with the metal binder phase, making it difficult to achieve high-strength interfacial bonding between diamond and the binder phase using conventional sintering processes. Additionally, the metal binder phase is prone to catalyzing diamond graphitization under high-temperature sintering conditions. Using a single sintered diamond layer as the working layer results in excessive frictional resistance during drawing due to its micropores and high surface roughness, easily causing scratches on the wire surface and failing to meet the surface quality requirements for high-precision micro-wire drawing. Conversely, using only a CVD diamond coating cannot provide a sufficiently thick, high-wear-resistant support layer. Once the surface diamond film is consumed, the wear resistance and strength of the cemented carbide substrate drop sharply, limiting the overall lifespan of the die.

[0021] Based on this, the first aspect of this application provides a gradient functional composite wire drawing die, wherein the die radially from the outside to the inside includes a modified cemented carbide matrix, a diamond sintered layer and a diamond deposited layer. The modified cemented carbide matrix contains 0.2% to 0.8% TiH2 by mass. The diamond sintered layer includes a transition layer and a main layer arranged radially from the outside to the inside. The diamond particles in both the transition layer and the main layer are coated with MoSi2, and the binder phase of both is silanized Ni powder. The diamond deposition layer is formed on the inner working surface of the diamond sintered layer.

[0022] This invention creatively proposes a composite solution combining CVD diamond deposition and diamond sintering processes: a millimeter-scale diamond sintered layer provides a sufficiently thick, highly wear-resistant support layer, while simultaneously thinning the CVD deposited layer to 3–5 μm, significantly shortening the deposition time and mitigating or avoiding the problem of uneven coating within micropores. Furthermore, the micron-thin diamond layer is deposited directly on the diamond sintered layer; due to its homogeneity, the bonding strength is far superior to solutions using various complex transition layers, and the residual internal stress of the thin diamond deposited layer is lower. In addition, unlike methods that add TiN or TiC to physically block and compress Co diffusion, this invention adds TiH2 to the cemented carbide matrix. The Ti atoms released during sintering from the TiH2 matrix capture free Co elements diffused from the matrix in situ, fundamentally inhibiting Co migration to the surface. To address the interface problem between diamond and the binder phase, diamond particles are coated with MoSi2. This improves the wettability of the diamond and the metal binder phase, enhances the interfacial bonding strength, and isolates the direct contact between metal atoms and diamond through the MoSi2 barrier layer, inhibiting diamond graphitization. The binder phase uses silanized Ni powder. Compared to traditional Co binders, Ni has a slower diffusion rate, and silanization effectively inhibits its catalytic graphitization activity. It also enhances the affinity of the Ni phase with other ceramic sintering phases, improving the densification effect during sintering. The diamond sintering layer is designed as a gradient structure including a transition layer and a main body layer. The transition layer, by controlling the ratio of WC, SiC, and diamond, matches the thermal expansion coefficient with the outer cemented carbide matrix, alleviating interfacial thermal stress. The main body layer features a high diamond content, providing excellent wear resistance. This gradient structure solves the cracking and interfacial bonding problems associated with co-sintering different materials, ultimately achieving high performance and long lifespan for the micro-drawing die.

[0023] In some embodiments of this application, the modified cemented carbide matrix further includes the following components by mass fraction: Co 3%–5%, TaC 0.5%–1.2%, and WC 93%–96.3%. WC and Co are the main components of the cemented carbide; WC provides wear resistance and structural strength to the matrix, while Co acts as a binder phase to ensure sintering densification and toughness. The specific mass fraction of TaC is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, or any combination thereof. TaC within this range helps refine WC grains, inhibits abnormal WC grain growth at high temperatures, and ensures a uniform microstructure.

[0024] In some embodiments of this application, TiH2 is added to the modified cemented carbide matrix powder using a secondary ball milling doping method. The secondary ball milling of TiH2, combined with the addition of the milling agent PEG, allows TiH2 to accurately coat the grain boundaries. TiH2 chemically binds free Co at the grain boundaries in situ, and the secondary ball milling helps prevent premature decomposition of TiH2.

[0025] In some embodiments of this application, the MoSi2 coating amount on the diamond particle surface is 0.6–0.8 wt%. This coating amount helps to form a continuous, complete, and moderately thick coating film on the diamond surface. On the one hand, it significantly improves the wettability of the diamond and enhances the bonding strength of the sintering interface; on the other hand, it effectively isolates the direct contact between the binder phase metal atoms and the diamond, suppressing diamond graphitization at high temperatures. If the coating amount is less than 0.6 wt%, failure occurs due to insufficient coating sites; if the coating amount is greater than 0.8 wt%, the high hardness and high wear resistance of the diamond itself are weakened, and the thick coating layer reduces the bonding force between the diamond and the sintering layer, leading to weaker interlayer bonding and increased susceptibility to cracking during cooling.

[0026] In some embodiments of this application, the diamond particles include coarse diamond powder and fine diamond powder, with a mass ratio of 1:2 to 3. The particle size of the coarse diamond powder is 25 μm to 35 μm, specifically 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm or any two of these ranges. The coarse diamond powder within this particle size range is used to construct the wear-resistant load-bearing skeleton of the diamond sintered layer, ensuring the strength and wear resistance of the layer. The particle size of the fine diamond powder is 1 μm to 15 μm. Specifically, diamond powder within the range of 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or any two of these ranges helps fill the gaps between coarse and fine powders, achieving dense packing, significantly improving sintering density, and reducing porosity. This compounding scheme enables the diamond sintered layer to simultaneously possess high density and high wear resistance, meeting the long life requirements of 0.2–2mm microscale wire drawing dies.

[0027] In some embodiments of this application, the transition layer comprises the following components by mass fraction: 25%–30% WC, 15%–20% SiC, 10%–15% silanized Ni powder, and 35%–50% diamond particles. This ratio makes the thermal expansion coefficient of the transition layer match that of the modified cemented carbide matrix, improves the interfacial bonding strength, and alleviates thermal mismatch stress. At the same time, an appropriate amount of diamond particles is introduced to achieve a performance gradient transition from the matrix to the transition layer.

[0028] The main body layer comprises the following components by mass fraction: 2%–4% WC, 1%–4% SiC, 3.5%–5.5% silanized Ni powder, 0.5%–1.5% hexagonal boron nitride powder, and 85%–93% diamond particles. The 85%–93% diamond particle content ensures ultra-high hardness and wear resistance of the mold's inner working surface, and also enhances the homogeneous bonding force for CVD deposition. The 3.5%–5.5% silanized Ni powder content achieves sintering densification with the lowest effective bonding amount. Small amounts of WC and SiC are used for micro-reinforcement and densification, while 0.5%–1.5% hexagonal boron nitride powder provides solid lubrication and improves surface finish. This gradient formulation gives the mold high interfacial bonding strength, high structural stability, high wear resistance, and a low coefficient of friction.

[0029] In some embodiments of this application, the silanized Ni powder is Ni powder obtained by drying after pretreatment with a silane coupling agent, wherein the silane coupling agent is one or more of KH-550, KH-560, and KH-570. Through silanization treatment, a stable modified layer can be formed on the surface of the Ni powder: on the one hand, it passivates the surface catalytic activity of the Ni powder, significantly reducing its graphitization catalytic effect on diamond; on the other hand, it constructs a molecular bridge structure, greatly improving the wettability and interfacial bonding strength between the Ni powder and MoSi2-coated diamond, SiC, and WC, thereby enhancing the density and structural stability of the diamond sintered layer and ensuring that the mold does not delaminate or fail during high-temperature sintering and high-load drawing.

[0030] In some embodiments of this application, the thickness of the diamond sintered layer is 1 mm to 3 mm. The millimeter-level sintering thickness can provide sufficient structural strength to ensure the efficiency of the mold under high load drawing; it can also avoid problems such as insufficient effective space of the inner hole, excessive sintering thermal stress, and increased difficulty of laser hole making due to excessive thickness; at the same time, it can provide a stable and highly rigid support substrate for surface CVD diamond deposition, making the interlayer bonding of the composite layer stronger and the overall performance more stable.

[0031] In some embodiments of this application, the thickness of the diamond deposition layer is between 3 μm and 5 μm. This thickness effectively avoids problems such as uneven gas concentration distribution within the pores, large coating thickness deviations, and cracking and detachment due to excessive internal stress caused by prolonged deposition time. Simultaneously, it allows for precise leveling of the inner pore surface of the diamond sintered layer, forming an ultra-smooth, low-friction, and highly wear-resistant wire-drawing working surface. The CVD deposition thickness should not be too thin, as a uniform film layer is not effectively formed in the early stages of seed crystal nucleation.

[0032] A second aspect of the present invention provides a method for preparing a gradient functional composite drawing die, comprising the following steps: Step 1: Preparation of modified cemented carbide matrix powder: WC, Co, and TaC are placed in a ball mill jar for a first ball milling according to the set mass ratio; then TiH2 with a mass fraction of 0.2% to 0.8% is added for a second ball milling, which takes 1 to 2 hours. After that, the powder is dried and sieved. Step 2, Preparation of diamond sintered layer powder: After coating the surface of diamond particles with MoSi2, the raw materials of the transition layer and the main layer are ball-milled according to a preset ratio. Step 3, partitioned filling and cold pressing: Partitioned filling of the modified cemented carbide matrix, the transition layer and the main layer in the diamond sintered layer, and cold pressing under a pressure of 10MPa to 20MPa for 30s to 60s. Step 4, sintering the mold blank and laser hole making: A gradient heating and vacuum hot pressing sintering process is adopted. First, the temperature is raised from room temperature to 600℃ and held for 30 minutes. Then, the temperature is raised to 800℃ and the pressure is slowly increased to 30MPa while holding for 30 minutes. Then, the temperature is raised to 1100℃ and held for 30 minutes. Finally, the temperature is raised to 1400℃ and held for 3 hours for cooling. With the center of the mold blank as the reference, the laser is perpendicularly incident to form the hole diameter. Then, the inner hole wall is processed and shaped. Step 5: Prepare a diamond deposition layer on the inner surface of the pore using hot-wire CVD: The mixed gas is CH4, H2, and Ar, with a volume concentration ratio of CH4:H2:Ar = 3~5:93~95:0~4, and the total gas flow rate is 200 sccm. The tantalum wire is heated to 2200℃, and the deposition time is 2h~4h. A diamond deposition layer is formed on the inner working surface of the diamond sintered layer.

[0033] The gradient functional composite wire drawing die preparation method provided in this application achieves an integrated gradient composite of a cemented carbide matrix, a diamond sintered layer, and a CVD diamond layer through a synergistic preparation process involving secondary ball milling modification of the matrix, diamond particle surface coating, gradient layering cold pressing, vacuum hot pressing gradient sintering, and hot-wire CVD thinning deposition. This method can precisely control the structure and interface bonding state of each layer, effectively suppress metal element migration and diamond graphitization, improve interlayer bonding strength and sintering density, and solve the problems of uneven CVD deposition and high internal stress under microscale pore size. Ultimately, it produces a gradient functional composite wire drawing die with stable structure, excellent wear resistance, and long service life.

[0034] The embodiments of this application are described in detail below: Example 1 A method for preparing a gradient functional composite wire drawing die includes the following steps: Step 1: Preparation of modified cemented carbide matrix powder: According to the following mass composition, Co: 3%, TaC: 0.5%, WC: 96.3%, TiH2: 0.2%, first put WC, Co, and TaC into a ball mill jar, add zinc stearate as a grinding aid, and ball mill once for 4 hours; then add TiH2 and a small amount of PEG, and ball mill a second time for 2 hours, dry and sieve. Step 2, Preparation of diamond sintered layer powder: After ball milling diamond particles and 0.6wt% MoSi2 for coating, the raw materials for the transition layer and the main layer are ball milled separately according to the mass fraction ratio. The transition layer composition is: WC 25%, SiC 15%, silanized Ni powder 10%, and diamond particles 50%; the main layer composition is: WC 2%, SiC 1%, silanized Ni powder 3.5%, hexagonal boron nitride powder 0.5%, and diamond particles 93%. Step 3, partitioned filling and cold pressing: A radial three-layer composite mold is used to partition the modified cemented carbide matrix, the transition layer and the main body layer in the diamond sintered layer, and cold press it under a pressure of 20MPa for 30s. Step 4, sintering the mold blank and laser hole making: Gradient heating and vacuum hot pressing sintering are adopted. The temperature is raised from room temperature to 600℃ and held for 30 minutes. Then, when the temperature is raised to 800℃, the pressure is slowly increased to 30MPa and held for 30 minutes. Then, the temperature is raised to 1100℃ and held for 30 minutes. Finally, the temperature is raised to 1400℃ and held for 3 hours for cooling. With the center of the mold blank as the reference, the laser is incident vertically to form the hole diameter. Then, the inner hole wall is machined and shaped. Step 5: A diamond deposition layer is prepared on the surface of the inner hole using hot-wire CVD: the mixed gas is CH4, H2 and Ar, the volume concentration ratio of the three is CH4:H2:Ar=4:95:1, the total gas flow rate is 200sccm, the tantalum wire is heated to 2200℃, and a diamond deposition layer with a thickness of 3μm is deposited on the diamond sintered layer.

[0035] Example 2 This embodiment 2 is based on embodiment 1, but the difference lies in adjusting the composition ratio of the diamond sintered layer powder. The transition layer composition is: WC 27%, SiC 20%, silanized Ni powder 13%, and diamond particles 40%; the main layer composition is: WC 4%, SiC 3%, silanized Ni powder 4.5%, hexagonal boron nitride powder 1.5%, and diamond particles 87%.

[0036] Comparative Example 1 Based on Example 1, the difference in Comparative Example 1 is that TiH2 is replaced with an equal amount of TiN.

[0037] Comparative Example 2 Based on Example 1, the difference in Comparative Example 2 is that the diamond particles are not coated with MoSi2.

[0038] Comparative Example 3 Based on Example 1, the difference in Comparative Example 3 is that the binder phase silanized Ni powder in the diamond sintered layer is replaced with an equal amount of Co.

[0039] Comparative Example 4 Based on Example 1, the difference in Comparative Example 4 is that the Ni powder binder phase in the diamond sintered layer did not undergo silanization pretreatment.

[0040] Comparative Example 5 Based on Example 2, the thickness of the diamond deposition layer is 1 μm.

[0041] Using steel wire of the same specification, the die hole diameter was measured at regular intervals using a laser aperture measuring instrument. The total drawn wire length was recorded when the cumulative wear of the die hole diameter relative to the initial value reached 0.1 μm. The coating adhesion was tested using the scratch method with a multi-functional scratch tester. A diamond indenter was used to apply a uniform load at a rate of 100 N / min, with a load range of 0–100 N. The critical load at which the coating first peeled off or cracked was taken as the adhesion. Three test sections were taken along the die hole axis to measure the surface roughness, and the average value was taken as the die hole surface roughness.

[0042] The parameters of the above embodiments and comparative examples are shown in Table 1.

[0043] Table 1

[0044] As shown in Table 1, comparing Comparative Example 1 and Example 1 reveals that TiH2 chemically captures free Co, while TiN forms a solid solution barrier layer to block Co diffusion. During high-temperature sintering of the raw materials or mold service, Co diffusion ultimately affects the service life of the wire drawing die; adding TiN to the cemented carbide substrate results in a shorter service life. Comparing Comparative Example 2 and Example 1 shows that when the diamond particles are not coated with MoSi2, the affinity between diamond and silanized Ni powder and the ceramic phase decreases, leading to densification and coating cracking during sintering, thus reducing coating adhesion. Comparing Comparative Examples 3, 4, and 1, it can be seen that compared with the binder phase Co, the Ni powder phase, with its sintered layer, catalyzes graphitization, significantly reducing the working life of the diamond coating and the bonding force between the coating and the substrate. The Ni powder treated with silanization has better overall performance. This is because the silane coupling agent hydrolyzes and condenses on the surface of the Ni powder to form a covalently bonded siloxane modified layer. Through molecular bridging, it connects the Ni powder with the diamond, MoSi2, WC, and SiC ceramic phases, greatly improving wettability and interfacial bonding strength, and passivating the catalytic activity of Ni, thus inhibiting diamond graphitization.

[0045] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the invention.

Claims

1. A gradient functional composite wire drawing die, characterized in that, The mold consists of a modified cemented carbide matrix, a diamond sintered layer, and a diamond deposited layer, arranged radially from the outside to the inside. The modified cemented carbide matrix contains 0.2% to 0.8% TiH2 by mass. The diamond sintered layer includes a transition layer and a main layer arranged radially from the outside to the inside. The diamond particles in both the transition layer and the main layer are coated with MoSi2, and the binder phase of both is silanized Ni powder. The diamond deposition layer is formed on the inner working surface of the diamond sintered layer.

2. The gradient functional composite wire drawing die according to claim 1, characterized in that, The modified cemented carbide matrix also includes the following components by mass fraction: Co 3%–5%, TaC 0.5%–1.2%, and WC 93%–96.3%.

3. The gradient functional composite wire drawing die according to claim 1, characterized in that, TiH2 was added to the modified cemented carbide matrix powder using a secondary ball milling doping method.

4. The gradient functional composite wire drawing die according to claim 1, characterized in that, The MoSi2 coating on the surface of the diamond particles is 0.6wt% to 0.8wt%.

5. The gradient functional composite wire drawing die according to claim 4, characterized in that, Diamond particles include coarse diamond powder and fine diamond powder, with a mass ratio of 1:2 to 3. The particle size of the coarse diamond powder is 25 μm to 35 μm, and the particle size of the fine diamond powder is 1 μm to 15 μm.

6. The gradient functional composite wire drawing die according to claim 1, characterized in that, The transition layer comprises the following components by mass fraction: 25%–30% WC, 15%–20% SiC, 10%–15% silanized Ni powder, and 35%–50% diamond particles; The main body layer contains the following components by mass fraction: 2%–4% WC, 1%–4% SiC, 3.5%–5.5% silanized Ni powder, 0.5%–1.5% hexagonal boron nitride powder, and 85%–93% diamond particles.

7. The gradient functional composite wire drawing die according to claim 6, characterized in that, Silanized Ni powder is Ni powder obtained by drying after pretreatment with a silane coupling agent. The silane coupling agent is one or more of KH-550, KH-560 and KH-570.

8. The gradient functional composite wire drawing die according to claim 1, characterized in that, The thickness of the diamond sintered layer is 1mm to 3mm.

9. The gradient functional composite wire drawing die according to any one of claims 1 to 8, characterized in that, The thickness of the diamond deposition layer is 3μm to 5μm.

10. A method for preparing a gradient functional composite wire drawing die according to any one of claims 1 to 9, characterized in that, Includes the following steps: Step 1: Preparation of modified cemented carbide matrix powder: WC, Co, and TaC are placed in a ball mill jar for a first ball milling according to the set mass ratio; then TiH2 with a mass fraction of 0.2% to 0.8% is added for a second ball milling, which takes 1 to 2 hours. After that, the powder is dried and sieved. Step 2, Preparation of diamond sintered layer powder: After coating the surface of diamond particles with MoSi2, the raw materials of the transition layer and the main layer are ball-milled according to a preset ratio. Step 3, partitioned filling and cold pressing: Partitioned filling of the modified cemented carbide matrix, the transition layer and the main layer in the diamond sintered layer, and cold pressing under a pressure of 10MPa to 20MPa for 30s to 60s. Step 4, sintering the mold blank and laser hole making: A gradient heating and vacuum hot pressing sintering process is adopted. First, the temperature is raised from room temperature to 600℃ and held for 30 minutes. Then, the temperature is raised to 800℃ and the pressure is slowly increased to 30MPa while holding for 30 minutes. Then, the temperature is raised to 1100℃ and held for 30 minutes. Finally, the temperature is raised to 1400℃ and held for 3 hours for cooling. With the center of the mold blank as the reference, the laser is perpendicularly incident to form the hole diameter. Then, the inner hole wall is processed and shaped. Step 5: Prepare a diamond deposition layer on the inner surface of the pore using hot-wire CVD: The mixed gas is CH4, H2, and Ar, with a volume concentration ratio of CH4:H2:Ar = 3~5:93~95:0~4, and the total gas flow rate is 200 sccm. The tantalum wire is heated to 2200℃, and the deposition time is 2h~4h. A diamond deposition layer is formed on the inner working surface of the diamond sintered layer.

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