Gradient nanocrystalline self-lubricating cemented carbide and preparation method thereof
By using a gradient nanocrystalline self-lubricating cemented carbide preparation method, the problems of interface peeling and brittleness of traditional tungsten carbide cemented carbide in high-frequency servo transmission were solved, and a gradient structure that balances hardness and toughness was achieved, thus improving fatigue resistance and friction stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZIGONG CEMENTED CARBIDE CORP
- Filing Date
- 2025-11-28
- Publication Date
- 2026-05-12
AI Technical Summary
In the process of preparing multilayer structures, traditional tungsten carbide cemented carbide can lead to interfacial delamination and the formation of brittle η phase due to the difference in thermal expansion coefficients of WC and Co, which affects the interfacial strength and makes it difficult to meet the requirements of high hardness and high toughness at the same time. In particular, it is prone to interlayer stress concentration and fatigue cracking in high-frequency servo drives.
A gradient nanocrystalline self-lubricating cemented carbide preparation method was adopted. Through the component design and sintering process of the surface layer, transition layer and core, combined with metal powder ball milling, pre-sintering and multi-step sintering, a gradient change in WC grain size and binder phase content was formed. Components such as VC and NbC were added to adjust the grain size and interfacial bonding strength. Low-temperature nitriding treatment was performed using Cu-Zn-Cr alloy structure to improve the surface hardness and toughness.
This invention achieves a gradient structure in high-frequency servo drives, characterized by high surface hardness, smooth transition of the transition layer, and high core toughness of cemented carbide. This avoids stress concentration between layers, improves fatigue resistance and friction stability, and meets the requirements for low wear and dimensional stability.
Smart Images
Figure CN121289470B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of metal powder processing technology, specifically to a gradient nanocrystalline self-lubricating cemented carbide for high-frequency servo transmission and its preparation method. Background Technology
[0002] Tungsten carbide (WC), with its hexagonal crystal structure formed by WC covalent bonds, possesses excellent properties such as a Mohs hardness of 8.5-9.0 and a melting point of 2870℃. When combined with binder phases such as Co, it has become a core material in fields such as machinery manufacturing, mining, and aerospace. Currently, diversified preparation systems have been established both domestically and internationally to improve its performance. However, traditional tungsten carbide cemented carbides face a severe performance paradox: increasing hardness (increasing WC content / refining grains) reduces toughness, while enhancing toughness (increasing the Co content of the binder phase) sacrifices hardness, limiting the application of this cemented carbide under specific working conditions.
[0003] Based on this, multilayered cemented carbide structures have emerged in existing technologies, achieving an ideal combination of external hardness and internal toughness through a high-hardness, wear-resistant outer layer and a high-toughness, impact-resistant inner layer. However, during the fabrication of multilayer structures, the large difference in the thermal expansion coefficients of WC and Co generates significant residual stress during cooling, leading to interfacial delamination. Furthermore, brittle η phases are easily formed during high-temperature sintering, reducing interfacial strength.
[0004] To address the aforementioned issues, a transition layer can be added to alleviate them. However, it is difficult to adjust the grain size variation of WC during the preparation process, and the uniformity of grain growth is uncontrollable, leading to unstable performance. Summary of the Invention
[0005] The purpose of this invention is to provide a gradient nanocrystalline self-lubricating cemented carbide for high-frequency servo transmission.
[0006] Another objective of this invention is to provide a method for preparing the gradient nanocrystalline self-lubricating cemented carbide for the above-mentioned high-frequency servo drive.
[0007] The objective of this invention is achieved through the following technical solution:
[0008] A gradient nanocrystalline self-lubricating cemented carbide, characterized in that it is composed of a surface layer, a transition layer, and a core. By mass percentage, the surface layer is made of WC 88-90wt%, Co 4-8wt%, pore-forming agent (graphite) 1.2-1.8wt%, Cr3C2 0.3-0.6wt%, h-BN 0.5-0.7wt%, VC 0.4-0.6wt%, TaC 0.5wt%, and TiC 1-2wt%. The transition layer is made of WC 84-86wt%, Co 10-12wt%, Ni 2wt%, NbC 1-1.5wt%, and Cr3C2 0.8-1.2wt%. The core is made of WC 84-86wt%, Co 10-14wt%, Ni 2wt%, and NbC 1.5-2.5wt%.
[0009] Furthermore, the gradient nanocrystalline self-lubricating cemented carbide has a surface layer thickness of 10~50μm, a WC grain size of 50~200nm, a transition layer thickness of 150~300μm, a WC grain size of 0.5~0.5μm, and a core WC grain size of 0.3~0.8μm.
[0010] A method for preparing gradient nanocrystalline self-lubricating cemented carbide for high-frequency servo transmission is characterized by: ball milling the surface layer, transition layer and core powders respectively to obtain surface powder, transition layer powder and core powder, feeding and pressing the core powder, transition layer powder and surface powder in sequence, pressing and pre-firing to form the powder, and then performing sintering treatment and surface control.
[0011] Furthermore, by mass percentage, the surface powder is made from WC 88~90wt%, Co 4~8wt%, pore-forming agent (graphite) 1.2~1.8wt%, Cr3C2 0.3~0.6wt%, h-BN 0.5~0.7wt%, VC 0.4~0.6wt%, TaC 0.5wt%, and TiC 1~2wt%, the transition layer powder is made from WC 84~86wt%, Co 10~12wt%, Ni 2wt%, NbC 1~1.5wt%, and Cr3C2 0.8~1.2wt%, and the core powder is made from WC 84~86wt%, Co 10~14wt%, Ni 2wt%, and NbC 1.5~2.5wt%.
[0012] Furthermore, the surface material ball milling is carried out using anhydrous ethanol medium and ZrO2 balls, with a ball-to-material ratio of 12~15:1, a ball milling speed of 300~350 rpm, and a ball milling time of 12~18 h. After ball milling, the material is vacuum dried and passed through a 200-mesh sieve.
[0013] Furthermore, the ball milling of the transition layer is carried out using kerosene as the medium and WC-Co balls, with a ball-to-material ratio of 10~12:1, a ball milling speed of 250~300 rpm, a ball milling time of 6~10 h, and then dried and passed through a 200-mesh sieve.
[0014] Furthermore, the core material ball milling is carried out using kerosene as the medium and WC-Co balls, with a ball-to-material ratio of 8~10:1, a ball milling speed of 200~250 rpm, a ball milling time of 6~10 h, and then dried and passed through a 200-mesh sieve.
[0015] Furthermore, the pressing and pre-firing molding process involves filling the ball-milled powder of each layer into a mold in the order of core, transition layer and surface layer, pre-forming under a pressure of 160~280Mpa, and then holding at 700~900℃ for 30~90min.
[0016] Furthermore, the sintering process is a two-step sintering process, specifically, first holding at 1350~1450℃ for 20~60min, and then cooling down to 1250~1350℃ and holding for another 30~90min.
[0017] For the surface layer: During the first sintering stage, rapid densification occurs, and the abnormal growth of WC is suppressed at low temperatures, reducing the damage to the alloy's toughness caused by sintering. For the transition layer, high temperature promotes the diffusion of Cr3C2 with the binder phase to form a solid solution, improving the interfacial bonding strength. The low temperature stage homogenizes the composition of the transition region formed between the transition layer and the core. For the core, high temperature promotes the formation of a solid solution between NbC and WC, causing the core hardness to recover and improving its resistance to deformation. Low temperature eliminates residual stress.
[0018] Furthermore, the surface conditioning involves using a composite powder obtained by ball milling a mixture of Cu powder, Zn powder, and Cr powder to embed the alloy powder, and then introducing NH3 at a flow rate of 5-7 L / min at 560-620℃, applying a pressure of 0.1-0.3 MPa, and holding for 3-4 hours.
[0019] Furthermore, the composite powder contains 5-6 wt% Zn, 1-2 wt% Cr powder, and the remainder is Cu powder. The ball milling is performed using anhydrous ethanol as the medium and WC balls, with a ball-to-material ratio of 3-4:1, a ball milling speed of 200-250 rpm, and a ball milling time of 1-1.5 h. After ball milling, the composite powder is dried to obtain the final product.
[0020] Existing technologies have addressed the common dilemma of balancing hardness and toughness by combining high surface hardness with high internal toughness. However, during high-frequency reciprocating motion, the abrupt change in hardness from surface to toughness between the two layers can easily lead to stress concentration between the layers, causing fatigue cracking. Relying solely on a single gradient in composition or grain size cannot simultaneously meet the three major requirements of "low wear, dimensional stability, and precision machining".
[0021] This invention incorporates vitamin C (VC) into the surface layer to refine grain size. VC adsorbs at grain boundaries, inhibiting grain growth and laying the foundation for surface hardness. The addition of graphite, which oxidizes and decomposes during pre-firing, reacts with WC decarburization products during high-temperature sintering, preventing the enrichment of brittle W2C phases on the surface and thus improving surface hardness. The addition of graphite replenishes carbon, stabilizing WC grain boundaries and allowing for refined and controlled WC grain size on the surface. During sintering, the decomposition of graphite forms a highly interconnected microporous structure on the surface, providing favorable conditions for subsequent surface control.
[0022] A transition layer was added between the surface layer and the core, and NbC and Cr3C2 were introduced into the transition layer to adjust the grain size and build a bridge for the gradual change in hardness, avoiding the risk of cracking caused by abrupt changes in hardness. In addition, NbC is distributed at the interface between the transition layer and the core, which improves the interfacial bonding strength, adjusts the gradual change in the coefficient of thermal expansion, and enhances the stress absorption capacity.
[0023] Adding NbC to the core achieves interface strengthening and solid solution. Some NbC dissolves into the WC lattice, forming a (W,Nb)C solid solution, thereby improving the core's hardness and stability and avoiding insufficient hardness caused by excessively coarse WC grains. Undissolved NbN particles accumulate at the interface between WC and the binder phase, forming a WC-NbC-Co-Ni interface strengthening layer, which enhances the interfacial bonding strength and stabilizes toughness.
[0024] A method for preparing a gradient nanocrystalline self-lubricating cemented carbide, characterized by comprising the following steps:
[0025] S1. Ingredient Ball Milling
[0026] Surface layer ingredients: WC 88~90wt%, Co 4~8wt%, pore-forming agent (graphite) 1.2~1.8wt%, Cr3C2 0.3~0.6wt%, h-BN 0.5~0.7wt%, VC 0.4~0.6wt%, TaC 0.5wt%, and TiC 1~2wt%. The mixture was ball-milled with ZrO2 balls in anhydrous ethanol medium at a ball-to-material ratio of 12~15:1, at a milling speed of 300~350 rpm, for 12~18 hours. After milling, the mixture was vacuum-dried and passed through a 200-mesh sieve to obtain the surface layer powder.
[0027] Transition layer ingredients: WC 84~86wt%, Co 10~12wt%, Ni 2wt%, NbC 1~1.5wt%, Cr3C 20.8~1.2wt%. The mixture was ball-milled with WC-Co balls using kerosene as the medium, with a ball-to-material ratio of 10~12:1, a ball milling speed of 250~300rpm, and a ball milling time of 6~10h. After ball milling, the mixture was vacuum dried and passed through a 200-mesh sieve to obtain the transition layer powder.
[0028] Core components: 84~86wt% WC, 10~14wt% Co, 2wt% Ni, 1.5~2.5wt% NbC. The mixture is ball-milled with WC-Co balls using kerosene as the medium, with a ball-to-material ratio of 8~10:1, a ball milling speed of 200~250 rpm, and a ball milling time of 6~10 h. After ball milling, the mixture is vacuum dried and passed through a 200-mesh sieve to obtain the core powder.
[0029] S2. Layered filling preforming
[0030] The ball-milled powders are filled into the mold in the order of core powder, transition layer powder and surface powder, pre-formed under a pressure of 160~280Mpa, and then kept at 700~900℃ for 30~90min. The surface layer thickness is 10~50μm and the transition layer thickness is 150~300μm.
[0031] S3. Sintering treatment
[0032] First, keep it at 1350~1450℃ for 20~60 minutes, then cool it down to 1250~1350℃ and keep it at that temperature for 30~90 minutes.
[0033] S4. Surface regulation
[0034] A composite powder obtained by ball milling a mixture of Cu powder, Zn powder, and Cr powder was used to embed the alloy powder. NH3 was introduced at 560-620℃ with a flow rate of 5-7 L / min, and a pressure of 0.1-0.3 MPa was applied for 3-4 hours. The composite powder contained 5-6 wt% Zn, 1-2 wt% Cr powder, and the remainder was Cu powder. Ball milling was performed using anhydrous ethanol as the medium and WC balls with a ball-to-powder ratio of 3-4:1. The milling speed was 200-250 rpm, and the milling time was 1-1.5 hours. After milling, the composite powder was dried to obtain the final product.
[0035] In this invention, due to the differences in composition of each layer during sintering, there is a certain temperature difference. This allows for rapid heating of the surface layer to inhibit WC grain growth, while slow heating of the core promotes uniform diffusion of NbC, thereby regulating the uniform transition of the overall WC grain size.
[0036] In this invention, at a specific temperature, Cu, Zn, and Cr in the composite powder form a Cu-Zn-Cr alloy structure, which significantly lowers the melting point of the composite powder, allowing it to form a molten state at low temperatures. This enables simultaneous infiltration and nitriding. During low-temperature nitriding, active nitrogen atoms generated by the decomposition of NH3 diffuse to the surface, forming a WC-N solid solution with WC (lattice distortion strengthening) and metal nitrides with Co / Ni (such as Co4N and Ni3N, second-phase strengthening), thereby increasing the surface hardness. The modified composite powder forms a Cu-WC-Cr structure during infiltration, filling the surface pores and working synergistically with the WC-N solid solution to resist wear. The Cu matrix acts as a "bonding agent for wear-resistant particles," preventing the hard phase from detaching, while its plasticity can buffer some impact loads.
[0037] The diffusion coefficient of Ni binder relative to Cu increases exponentially with increasing temperature, causing Cu to migrate towards the core and thus reducing core toughness. This invention achieves multi-dimensional gradient regulation: a gradient transition in grain size from the surface layer to the core; gradient changes in the binder phase content of the surface layer, transition layer, and core; and a transition layer of a specific thickness further suppress the problem of wear-resistant components diffusing into the core during surface conditioning, which leads to a decrease in toughness.
[0038] The present invention has the following technical effects:
[0039] In this invention, cemented carbide is prepared into a gradient structure of surface, transition layer and core by using different metal powders. This achieves a gradient change in WC grain size from the surface to the core, a gradient change in the content of binder phase in the cemented carbide, and a three-dimensional gradient transition through the partitioning of functional components. This forms a core structure with high hardness and high internal toughness, while avoiding interlayer stress concentration and stabilizing the core hardness, making the alloy suitable for the fatigue resistance requirements of high-frequency reciprocating motion. Attached Figure Description
[0040] Figure 1 : Schematic diagram of the structure of each layer of cemented carbide in this invention.
[0041] Figure 2 Scanning electron microscope image of the cross section of the cemented carbide prepared in Example 1 of this invention.
[0042] Figure 3 The hardness variation curves of the cemented carbide prepared in Example 1 of this invention at different distances from the surface.
[0043] Figure 4 The binder phase curves of the cemented carbide prepared in Example 1 of this invention at different positions from the surface layer.
[0044] Figure 5 The lubrication phase curves of the cemented carbide at different positions from the surface layer prepared in Example 1 of this invention. Detailed Implementation
[0045] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.
[0046] Example 1
[0047] A method for preparing a gradient nanocrystalline self-lubricating cemented carbide includes the following steps:
[0048] S1. Ingredient Ball Milling
[0049] Surface ingredients: WC 89wt%, Co 5.8wt%, graphite 1.6wt%, Cr3C2 0.4wt%, h-BN 0.6wt%, VC 0.5wt%, TaC 0.5wt%, and TiC 1.6wt%. The mixture was ball-milled with ZrO2 balls in anhydrous ethanol medium at a ball-to-material ratio of 14:1, at a milling speed of 330 rpm, for 16 hours. After milling, the mixture was vacuum dried and passed through a 200-mesh sieve.
[0050] The transition layer materials consist of 85.5 wt% WC, 10 wt% Co, 2 wt% Ni, 1.4 wt% NbC, and 21.1 wt% Cr3C. The mixture is ball-milled with WC-Co balls using kerosene as the medium at a ball-to-material ratio of 12:1. The ball milling speed is 280 rpm, and the ball milling time is 8 hours. After ball milling, the mixture is vacuum dried and passed through a 200-mesh sieve to obtain the transition layer powder.
[0051] Core ingredients: WC 85.5wt%, Co 10.7wt%, Ni 2wt%, NbC 1.8wt%. The mixture was ball-milled with WC-Co balls using kerosene as the medium at a ball-to-material ratio of 10:1. The ball milling speed was 240 rpm and the ball milling time was 8 hours. After ball milling, the mixture was vacuum dried and passed through a 200-mesh sieve to obtain the core powder.
[0052] S2. Layered filling preforming
[0053] The ball milled powder was filled into the mold in the order of core, transition layer and surface layer, pre-formed under 200 MPa pressure, and then kept at 800℃ for 60 min. The thickness of the prepared cemented carbide was 40 μm for the surface layer and 150 μm for the transition layer.
[0054] S3. Sintering treatment
[0055] First, keep it at 1400℃ for 50 minutes, then cool it down to 1300℃ and keep it at that temperature for another 60 minutes.
[0056] S4. Surface regulation
[0057] A composite powder was obtained by ball milling a mixture of Cu powder, Zn powder, and Cr powder to embed the alloy. NH3 was introduced at 580℃ with a flow rate of 6 L / min, and a pressure of 0.2 MPa was applied for 3.5 h. The composite powder contained 5.5 wt% Zn, 1.5 wt% Cr powder, and the remainder was Cu powder. Ball milling was performed using anhydrous ethanol as the medium and WC balls at a ball-to-powder ratio of 3.5:1. The milling speed was 220 rpm, and the milling time was 1 h. After milling, the composite powder was dried to obtain the final product.
[0058] Figure 1 This is a schematic diagram of the cemented carbide structure prepared according to the present invention, and a cross-sectional morphology diagram of the alloy after sintering treatment in Example 1. Figure 2 As shown.
[0059] During the design process of the material distribution for each layer, we tried adding different components and the effects on the performance of each layer. The specific test groups are shown in Table 1.
[0060] Table 1:
[0061]
[0062] Following the ingredient ratios of the above experimental groups, different cemented carbides were prepared according to the preparation process of Example 1. The cemented carbides without any surface conditioning treatment served as a control group. The relevant performance tests of each group of cemented carbides are as follows:
[0063] (1) Hardness test:
[0064] According to GB / T 3851-2015, a Vickers hardness tester was used to apply a load of 30 kgf and hold the pressure for 15 seconds. Five points were measured on the surface layer, transition layer, and core, and the average value was taken.
[0065] (2) Bending strength test:
[0066] According to GB / T 6569-2006, the three-point bending method is used, with a sample size of 10mm×4mm×3mm, a span of 8mm, and a loading speed of 0.5mm / min, in MPa.
[0067] (3) Fracture toughness test: According to GB / T 4161-2007, single-sided notched beam method (SENB), sample 10mm×5mm×50mm, notch depth 2mm (notch tip radius ≤0.1mm), unit MPa m¹ / ².
[0068] (4) Coefficient of friction:
[0069] According to GB / T 3960-2016, reciprocating friction testing machine, mating parts GCr15 steel, load 5N, speed 0.1m / s, stroke 5mm, duration 60min.
[0070] (5) Wear rate:
[0071] According to GB / T 12444-2006, the mass loss is measured by an electronic balance (accuracy 0.0001g). The calculation formula is: wear rate = (mass loss / material density) / (load × sliding distance), unit mm³ / (N·m).
[0072] (6) Reciprocating friction gap stability test:
[0073] Under the same friction coefficient test conditions, the maximum change in gap within 60 minutes was recorded using a displacement sensor, in μm.
[0074] The test results are shown in Table 2.
[0075] Table 2:
[0076]
[0077] In Experiment 1 (Example 1), the surface layer exhibited high hardness, while the core hardness and toughness were both ideal, with a bending strength as high as 2960 MPa. This effectively ensured the high hardness of the cemented carbide surface layer and the high toughness of the core, while also maintaining high strength and hardness in the core, which is beneficial for the application of the alloy in high-frequency servo drive applications. In Experiment 2, the surface layer lacked TaC and was replaced with an equal amount of TiC, resulting in a lower overall hardness improvement compared to Experiment 1. Experiment 3 had no graphite added, and the surface layer did not form a microporous structure, leading to poor subsequent surface layer control and a significant decrease in surface hardness and wear resistance. In Experiment 4, graphite was replaced with PMMA. The different pore-forming agent resulted in differences in the uniformity and connectivity of the micropores, and PMMA could not supplement carbon to improve surface hardness, leading to a decrease in the final surface hardness and wear resistance. In experimental group 5, the proportion of NbC in the transition layer exceeded that in the core. NbC has a significant impact on the interfacial bonding strength between the transition layer and the core, and can also cause changes in grain size. When the proportion of NbC in the transition layer is higher than that in the core, the gradient of grain size will change, the interfacial strength will decrease, and the performance of the core will also be affected.
[0078] Figure 3The curves showing the hardness change of the cemented carbide prepared in Example 1 from the surface to the core with increasing test depth show that the surface layer maintains a high hardness, which then slowly decreases, leading to a transition layer. This transition layer effectively provides a smooth transition, with its hardness gradually decreasing before rising again to connect with the core. Finally, the core hardness returns to a relatively stable level. During this process, the hardness first decreases and then increases, effectively alleviating interlayer stress. Figure 4 It can be seen that as the testing depth increases, the binder phase in the alloy gradually increases, showing a gradient change, which effectively regulates the strength and toughness of the alloy. Figure 5 The lubricating phase is mainly present in the surface layer, with a small amount in the transition layer near the surface. As the test depth increases, the content of the lubricating phase decreases, and the core is completely free of lubricating phase. This indicates that the presence of the transition layer prevents the lubricating phase from migrating and ensures the stability of the core performance.
[0079] Comparative Example 1:
[0080] Compared with Example 1, no NH3 was introduced in the surface control step, while the remaining steps were the same as in Example 1.
[0081] The prepared cemented carbide surface layer has a hardness of 1760 HV30 and a fracture toughness of 7.4 MPa·m. 1 / 2 The coefficient of friction is 0.24, and the volumetric wear rate is 3.2 × 10⁻⁴. -7 mm³ / (N·m), the performance of the transition layer and the core did not change significantly.
[0082] Comparative Example 2
[0083] Compared to Example 1, ball-milled Cu powder was directly used for impregnation in the surface conditioning process, while the remaining steps were the same as in Example 1.
[0084] The prepared cemented carbide surface layer has a hardness of 1730 HV30 and a fracture toughness of 8.9 MPa·m. 1 / 2 The coefficient of friction is 0.28, and the volumetric wear rate is 4.3 × 10⁻⁶. -7 mm³ / (N·m), the performance of the transition layer and the core did not change significantly.
[0085] Comparative Example 3
[0086] Compared with Example 1, in the surface conditioning step, after NH3 was introduced and kept at 580°C for 3.5h, the sintered alloy was soaked in an impregnation solution prepared with MoS2@Ni, and the pressure was maintained at 0.2 MPa for 1-2h under vacuum, followed by drying and curing at 150°C. The MoS2@Ni ratio was 1:1, the particle size was 1-3 μm, and it accounted for 25% of the mass of the impregnation solution. The binder was phenolic resin, accounting for 12% of the impregnation solution, and the solvent was anhydrous ethanol.
[0087] Because MoS2@Ni has a low decomposition temperature, MoS2 oxidizes to MoO3 at around 320℃, losing its lubricating function. Furthermore, the phenolic resin completely decomposes, losing its binding effect on MoS2@Ni. Therefore, simultaneous nitriding and impregnation are not possible. During the initial nitriding process, a dense nitrogen-containing hardened layer forms on the surface, hindering subsequent MoS2@Ni impregnation and preventing the filling of deep pores. Ultimately, surface control is unsatisfactory, and the presence of deep pores negatively impacts surface hardness and wear resistance.
[0088] The cemented carbide surface layer prepared by this method has an average surface hardness of 1690 HV30, a friction coefficient of 0.39, and a wear rate of 2.3 × 10⁻⁶. -6 The hardness of the transition layer is significantly higher than that of the core, reaching a minimum of 1300 HV30, while the average core hardness reaches 1700 HV30. The high surface hardness is not achieved in either the surface layer or the core. High core toughness is expected, with a core fracture toughness of 15.0 MPa·m. 1 / 2 The average core bending strength is 2920 MPa. After 60 minutes and 10 hours of testing... 6 Reciprocating motion, with a gap change ≥2.0μm.
[0089] Example 2
[0090] A method for preparing a gradient nanocrystalline self-lubricating cemented carbide includes the following steps:
[0091] S1. Ingredient Ball Milling
[0092] Surface material composition: WC 88wt%, Co 7wt%, graphite 1.5wt%, Cr3C2 0.3wt%, h-BN 0.5wt%, VC 0.4wt%, TaC 0.5wt%, and TiC 1.8wt%. It was ball-milled with ZrO2 balls in anhydrous ethanol medium at a ball-to-material ratio of 12:1, at a ball milling speed of 300 rpm, and for 18 hours. After ball milling, it was vacuum dried and passed through a 200-mesh sieve to obtain the surface powder.
[0093] Transition layer ingredients: WC 84wt%, Co 12wt%, Ni 2wt%, NbC 1wt%, Cr3C 21wt%. The mixture was ball-milled with WC-Co balls using kerosene as the medium at a ball-to-material ratio of 10:1. The ball milling speed was 250 rpm and the ball milling time was 6 h. After ball milling, the mixture was vacuum dried and passed through a 200-mesh sieve to obtain the transition layer powder.
[0094] Core components: 84wt% WC, 10wt% Co, 2wt% Ni, 2wt% NbC. The mixture was ball-milled with WC-Co balls using kerosene as the medium at a ball-to-material ratio of 8:1. The ball milling speed was 200 rpm and the milling time was 10 h. After the ball milling was completed, the mixture was vacuum dried and passed through a 200-mesh sieve to obtain the core powder.
[0095] S2. Layered filling preforming
[0096] The ball milled powder was filled into the mold in the order of core, transition layer and surface layer, pre-formed under 280 MPa pressure, and then kept at 700℃ for 90 min. The thickness of the prepared cemented carbide was 10 μm for the surface layer and 200 μm for the transition layer.
[0097] S3. Sintering treatment
[0098] First, keep it at 1350℃ for 60 minutes, then cool it down to 1250℃ and keep it at that temperature for another 90 minutes.
[0099] S4. Surface regulation
[0100] A composite powder was obtained by ball milling a mixture of Cu powder, Zn powder, and Cr powder to embed the alloy. NH3 was introduced at 620℃ with a flow rate of 5 L / min, and a pressure of 0.1 MPa was applied for 4 hours. The composite powder contained 6 wt% Zn, 1 wt% Cr powder, and the remainder was Cu powder. Ball milling was performed using anhydrous ethanol as the medium and WC balls with a ball-to-material ratio of 4:1. The milling speed was 200 rpm, and the milling time was 1 hour. After ball milling, the composite powder was dried to obtain the final product.
[0101] The cemented carbide surface layer prepared in this embodiment has a hardness of 1960 HV30, a friction coefficient of 0.14, and a wear rate of 2.9 × 10⁻⁶. -7 mm³ / (N·m), the average core hardness reaches 1700HV30, and the core fracture toughness is 14.9 MPa·m. 1 / 2 The core bending strength reaches 2920 MPa, and after 60 minutes and 10 seconds... 6 Reciprocating motion, with a gap variation ≤1.0μm.
[0102] Example 3
[0103] A method for preparing a gradient nanocrystalline self-lubricating cemented carbide includes the following steps:
[0104] S1. Ingredient Ball Milling
[0105] Surface material composition: WC 90wt%, Co 4wt%, graphite 1.8wt%, Cr3C2 0.6wt%, h-BN 0.7wt%, VC 0.5wt%, TaC 0.5wt%, and TiC 1.9wt%. It was ball-milled with ZrO2 balls in anhydrous ethanol medium at a ball-to-material ratio of 15:1, at a ball milling speed of 300~350 rpm, and for 12~18 h. After ball milling, it was vacuum dried and passed through a 200-mesh sieve to obtain surface powder.
[0106] The transition layer materials are: WC 86wt%, Co 10wt%, Ni 2wt%, NbC 1.2wt%, Cr3C 20.8wt%. The materials are ball-milled with WC-Co balls using kerosene as the medium, with a ball-to-material ratio of 11:1, a ball milling speed of 300 rpm, and a ball milling time of 10 h. After ball milling, the materials are vacuum dried and passed through a 200-mesh sieve to obtain the transition layer powder.
[0107] Core components: 86wt% WC, 10.5wt% Co, 2wt% Ni, 1.5wt% NbC. The mixture was ball-milled with WC-Co balls using kerosene as the medium at a ball-to-material ratio of 9:1. The ball milling speed was 250 rpm and the ball milling time was 10 h. After ball milling, the mixture was vacuum dried and passed through a 200-mesh sieve to obtain the core powder.
[0108] S2. Layered filling preforming
[0109] The ball milled powder was filled into the mold in the order of core, transition layer and surface layer, pre-formed under 280 MPa pressure, and then kept at 900℃ for 30 min. The thickness of the prepared cemented carbide was 50 μm for the surface layer and 300 μm for the transition layer.
[0110] S3. Sintering treatment
[0111] First, keep it at 1450℃ for 20 minutes, then cool it down to 1350℃ and keep it at that temperature for another 30 minutes.
[0112] S4. Surface regulation
[0113] A composite powder was obtained by ball milling a mixture of Cu powder, Zn powder, and Cr powder to embed the alloy. NH3 was introduced at 560℃ with a flow rate of 7 L / min, and a pressure of 0.3 MPa was applied for 4 hours. The composite powder contained 5 wt% Zn, 1 wt% Cr powder, and the remainder was Cu powder. Ball milling was performed using anhydrous ethanol as the medium and WC balls with a ball-to-material ratio of 3:1. The ball milling speed was 250 rpm, and the milling time was 1.5 hours. After ball milling, the composite powder was dried to obtain the final product.
[0114] The cemented carbide surface layer prepared in this embodiment has a hardness of 2010HV30, a friction coefficient of 0.14, and a wear rate of 2.5×10⁻⁶.-7 The core hardness is 1720 HV30 with a thickness of mm³ / (N·m) and an average core fracture toughness of 14.7 MPa·m. 1 / 2 The core bending strength reaches 2880 MPa, and after 60 minutes and 10 seconds... 6 The reciprocating motion has a gap variation of ≤1.2μm.
Claims
1. A method for preparing gradient nanocrystalline self-lubricating cemented carbide for high-frequency servo transmission, characterized in that: The surface, transition layer, and core powders were ball-milled separately to obtain surface powder, transition layer powder, and core powder. These powders were then added sequentially in the order of core powder, transition layer powder, and surface powder, pressed, and pre-fired. Sintering and surface conditioning were then performed. By mass percentage, the surface powder was made from WC 88-90wt%, Co 4-8wt%, graphite 1.2-1.8wt%, Cr3C2 0.3-0.6wt%, h-BN 0.5-0.7wt%, VC 0.4-0.6wt%, TaC 0.5wt%, and TiC 1-2wt%; the transition layer powder was made from WC 84-86wt%, Co 10-12wt%, Ni 2wt%, NbC 1-1.5wt%, and Cr3C2 0.8-1.2wt%; and the core powder was made from WC 84-86wt%, Co 10-14wt%, Ni... The alloy is made from 2wt% and NbC 1.5~2.5wt%. The surface conditioning is carried out by ball milling a mixture of Cu powder, Zn powder and Cr powder to obtain a composite powder for embedding the powder. NH3 is introduced at 560~620℃, with a flow rate of 5~7 L / min, and a pressure of 0.1~0.3 MPa is applied for 3~4h.
2. The method for preparing a gradient nanocrystalline self-lubricating cemented carbide for high-frequency servo transmission as described in claim 1, characterized in that: The surface material ball milling is performed using anhydrous ethanol as the medium and ZrO2 balls. The ball-to-material ratio is 12-15:1, the ball milling speed is 300-350 rpm, and the ball milling time is 12-18 hours. After ball milling, the powder is vacuum dried and passed through a 200-mesh sieve to obtain the surface powder.
3. The method for preparing a gradient nanocrystalline self-lubricating cemented carbide for high-frequency servo transmission as described in claim 2, characterized in that: The transition layer material ball milling is carried out using kerosene as the medium and WC-Co balls, with a ball-to-material ratio of 10~12:1, a ball milling speed of 250~300 rpm, and a ball milling time of 6~10 h. After drying, the transition layer powder is obtained by passing it through a 200-mesh sieve.
4. The method for preparing a gradient nanocrystalline self-lubricating cemented carbide for high-frequency servo transmission as described in claim 3, characterized in that: The core material ball milling is performed using kerosene as the medium and WC-Co balls. The ball-to-material ratio is 8~10:1, the ball milling speed is 200~250 rpm, and the ball milling time is 6~10 hours. After drying, the core powder is obtained by passing it through a 200-mesh sieve.
5. The method for preparing a gradient nanocrystalline self-lubricating cemented carbide for high-frequency servo transmission as described in claim 4, characterized in that: The pressing and pre-firing molding process involves filling the ball-milled powder of each layer into a mold in the order of core, transition layer and surface layer, pre-forming under a pressure of 160~280MPa, and then holding at 700~900℃ for 30~90min.
6. The method for preparing a gradient nanocrystalline self-lubricating cemented carbide for high-frequency servo transmission as described in claim 5, characterized in that: The sintering process is a two-step sintering process, specifically, first holding at 1350~1450℃ for 20~60 minutes, and then cooling down to 1250~1350℃ and holding for another 30~90 minutes.
7. A method for preparing a gradient nanocrystalline self-lubricating cemented carbide, characterized in that, Includes the following steps: S1. Ingredient Ball Milling Surface material composition: WC 88~90wt%, Co 4~8wt%, graphite 1.2~1.8wt%, Cr3C2 0.3~0.6wt%, h-BN 0.5~0.7wt%, VC 0.4~0.6wt%, TaC 0.5wt%, and TiC 1~2wt%. The mixture was ball-milled using ZrO2 balls with anhydrous ethanol as the medium. The ball-to-material ratio was 12~15:1, the ball milling speed was 300~350 rpm, and the ball milling time was 12~18 h. After ball milling, the mixture was vacuum dried and passed through a 200-mesh sieve to obtain the surface powder. Transition layer ingredients: WC 84~86wt%, Co 10~12wt%, Ni 2wt%, NbC 1~1.5wt%, Cr3C2 0.8~1.2wt%. Using kerosene as the medium, WC-Co balls were used for ball milling at a ball-to-material ratio of 10~12:1, a ball milling speed of 250~300rpm, and a ball milling time of 6~10h. After ball milling, the mixture was vacuum dried and passed through a 200-mesh sieve to obtain the transition layer powder. Core components: WC 84~86wt%, Co 10~14wt%, Ni 2wt%, NbC 1.5~2.5wt%. Using kerosene as the medium, WC-Co balls are used for ball milling at a ball-to-material ratio of 8~10:1, a milling speed of 200~250rpm, and a milling time of 6~10h. After milling, the core powder is obtained by vacuum drying and passing through a 200-mesh sieve. S2. Layered filling preforming The ball-milled powders are filled into the mold in the order of core powder, transition layer powder and surface powder, pre-formed under a pressure of 160~280MPa, and then kept at 700~900℃ for 30~90min. S3. Sintering treatment First, keep it at 1350~1450℃ for 20~60 minutes, then cool it down to 1250~1350℃ and keep it at that temperature for 30~90 minutes. S4. Surface regulation A composite powder was obtained by ball milling a mixture of Cu powder, Zn powder, and Cr powder to embed the alloy. NH3 was introduced at 560–620°C with a flow rate of 5–7 L / min, and a pressure of 0.1–0.3 MPa was applied. The mixture was held at this temperature for 3–4 hours. The composite powder contained 5–6 wt% Zn, 1–2 wt% Cr powder, and the remainder was Cu powder. Ball milling was performed using anhydrous ethanol as the medium and WC balls with a ball-to-powder ratio of 3–4:
1. The milling speed was 200–250 rpm, and the milling time was 1–1.5 hours. After milling, the composite powder was dried to obtain the final product.