Two-step oscillating hot-press sintering method of WC-Co cemented carbide
By employing a two-step oscillating hot pressing sintering method, combined with dynamic pressure treatment during the low-temperature solid-phase and high-temperature liquid-phase sintering stages, the problems of densification and grain uniformity in cemented carbide sintering were solved, and high-performance WC-Co cemented carbide was prepared.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SOUTHWEST JIAOTONG UNIV
- Filing Date
- 2026-04-29
- Publication Date
- 2026-06-26
AI Technical Summary
In existing cemented carbide liquid phase sintering processes, it is difficult to simultaneously achieve high densification, uniform distribution of the binder phase, and absence of abnormal grain growth. Traditional methods suffer from problems such as high equipment requirements, complex processes, or performance degradation.
A two-step oscillating hot-pressing sintering method is adopted, including low-temperature solid-phase sintering and high-temperature liquid-phase sintering stages. Dynamic pressure is used to promote particle rearrangement and atomic diffusion, ensuring uniform distribution of the binder phase and inhibiting abnormal grain growth.
The WC-Co cemented carbide has achieved a high degree of densification, uniform distribution of binder phase and no abnormal grain growth, and has excellent strength and toughness properties, with a relative density ≥99.0%, HV30 ≥2000 and fracture toughness ≥9 MPa·m1/2.
Smart Images
Figure CN122274181A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of cemented carbide technology, and particularly relates to a two-step oscillating hot pressing sintering method for WC-Co cemented carbide. Background Technology
[0002] Cemented carbide is a composite material prepared by powder metallurgy, using refractory metal carbides (such as WC and TiC) as the hard phase and ferrous metals (such as Co, Fe, and Ni) as the binder phase. Due to its high hardness, excellent wear resistance, and good strength, cemented carbide is widely used in metal cutting tools, mining and rock drilling tools, wear-resistant parts, and molds. Among them, WC-Co cemented carbide is the most produced and widely used cemented carbide system.
[0003] In the preparation of WC-Co cemented carbide, sintering is a crucial step that determines its final microstructure and mechanical properties. Traditional liquid-phase sintering involves heating the compact to a temperature higher than the melting point of the binder phase (typically 1280℃~1500℃), causing the cobalt phase to melt and form a liquid phase. Densification is achieved through capillary forces driving particle rearrangement, dissolution-precipitation, and solid-state framework sintering. However, traditional liquid-phase sintering has two prominent problems: first, the liquid cobalt phase is prone to uneven distribution under gravity and capillary action, forming macroscopic "cobalt pools" or cobalt-depleted regions, causing localized differences in material properties and affecting service reliability; second, in the later stages of liquid phase formation, WC grains are prone to abnormal growth through the dissolution-precipitation mechanism, leading to a significant decrease in alloy hardness.
[0004] To suppress abnormal grain growth in WC, industrial methods typically involve adding grain inhibitors (such as VC, Cr3C2, etc.) or lowering the sintering temperature. However, excessive addition of inhibitors can introduce brittle phases and reduce alloy toughness; lowering the sintering temperature often leads to incomplete densification, with residual pores becoming stress concentration sources and impairing strength.
[0005] In recent years, oscillating pressure sintering technology has attracted attention in the field of materials preparation. Unlike traditional hot pressing sintering that applies constant pressure, oscillating pressure sintering, by introducing dynamic pressure with a certain frequency and amplitude, can effectively promote particle rearrangement, accelerate the elimination of pores, and inhibit grain growth. For example, CN121320771A discloses a method for preparing gradient cemented carbide, which combines vacuum sintering with oscillating hot pressing. However, this method requires the introduction of oscillating pressure as high as 250~400 MPa at high temperature, placing extremely stringent requirements on equipment and molds. CN121320772A discloses a method for preparing gradient cemented carbide with a removed β layer, which achieves surface β removal through two-stage oscillating hot pressing treatment (nitriding stage and gradient sintering stage). However, its process involves nitrogen partial pressure control and multi-step atmosphere switching, making process control relatively complex. In addition, the above methods focus on the construction of gradient structures, and still lack targeted solutions on how to achieve uniform distribution of the binder phase and inhibit abnormal grain growth in the matrix while achieving complete densification.
[0006] Therefore, it is necessary to develop a cemented carbide sintering method with a wide process window, low equipment requirements, and the ability to simultaneously achieve high densification, uniform distribution of binder phase, and no abnormal grain growth. Summary of the Invention
[0007] This invention aims to solve the technical problem that it is difficult to simultaneously achieve high densification, uniform distribution of binder phase and no abnormal grain growth in the existing cemented carbide liquid phase sintering process. It provides a two-step oscillatory hot pressing sintering method for cemented carbide with a wide process window, low equipment requirements and strong operational controllability.
[0008] This invention provides a two-step oscillatory hot pressing sintering method for WC-Co cemented carbide, comprising the following steps:
[0009] Step 1: Load the uniformly mixed WC-Co cemented carbide powder into a graphite mold and perform powder pre-pressing.
[0010] Step 2: Transfer the pre-pressed billet together with the graphite mold to the vibrating hot pressing sintering furnace. Keep the pre-pressed billet at 800℃ in a vacuum environment to complete degassing and pre-sintering, so that the relative density of the billet reaches more than 60%.
[0011] Step 3: Apply unidirectional oscillating pressure to the billet through the mold and heat it to 1100℃ for solid sintering. Use dynamic pressure to rearrange WC particles and cause Co particles to undergo severe plastic deformation under the extrusion of WC particles, so that the relative density of the billet is further increased to more than 80%.
[0012] Step 4: Continue heating to 1300-1350℃ to form a WC-Co eutectic liquid phase. Dynamic pressure drives further rearrangement and atomic diffusion of WC particles, and the eutectic liquid phase uniformly fills the gaps between WC particles to complete the sintering process. Then, the furnace is cooled to room temperature.
[0013] Furthermore, in step 1, the Co content in the WC-Co cemented carbide powder is 1-15% by mass, and the grain size of WC is 20-800 nm.
[0014] Furthermore, in step 2, the heating rate is 15℃ / min; the holding time at 800℃ is 30-90 min, and the vacuum degree is ≤10 Pa.
[0015] Furthermore, in step 3, the heating rate is 5-10 ℃ / min; the holding time at 1100℃ is 30-120 min; and the median value of the oscillation pressure is 20 MPa.
[0016] Furthermore, in step 3, the amplitude of the oscillating pressure is 1-5 MPa, and the frequency is 1-10 Hz.
[0017] Furthermore, in step 4, the heating rate is 2-10 ℃ / min, the cooling rate is 10-30 ℃ / min, the holding time at 1300-1350 ℃ is 5-60 min, and the median value of the oscillation pressure is 25-75 MPa.
[0018] Furthermore, in step 4, the amplitude of the oscillating pressure is 1-50 MPa, and the frequency is 1-10 Hz.
[0019] This invention produces a WC-Co cemented carbide using the aforementioned two-step oscillating hot pressing sintering method. The WC-Co cemented carbide exhibits a uniform microstructure, with the Co phase dispersed throughout the WC matrix and no abnormally large WC grains. The WC-Co cemented carbide has a relative density ≥99.0%, HV30 ≥2000, and fracture toughness ≥9 MPa•m. 1 / 2 .
[0020] The beneficial technical effects of this invention compared to the prior art are as follows:
[0021] This invention improves the three-dimensional spatial distribution uniformity of the binder phase and eliminates residual pores through a two-step oscillating hot pressing sintering process of "low-temperature solid-phase sintering - high-temperature liquid-phase sintering". This effectively inhibits the abnormal growth of WC grains and produces a cemented carbide with excellent strength and toughness. Attached Figure Description
[0022] Figure 1 SEM image of the WC-6Co cemented carbide prepared in Example 1;
[0023] Figure 2 SEM image of the WC-6Co cemented carbide prepared in Example 2;
[0024] Figure 3 SEM image of the WC-3Co cemented carbide prepared in Example 3;
[0025] Figure 4 The image shows a SEM image of the WC-9Co cemented carbide prepared in Example 4. Detailed Implementation
[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.
[0027] The present invention provides a two-step oscillatory hot pressing sintering method for WC-Co cemented carbide, comprising the following steps:
[0028] Step 1: Load the uniformly mixed WC-Co cemented carbide powder into a graphite mold and perform powder pre-pressing.
[0029] Step 2: Transfer the pre-pressed billet together with the graphite mold to the vibrating hot pressing sintering furnace. Keep the pre-pressed billet at 800℃ in a vacuum environment to complete degassing and pre-sintering, so that the relative density of the billet reaches more than 60%.
[0030] Step 3: Apply unidirectional oscillating pressure to the billet through the mold and heat it to 1100℃ for solid sintering. Use dynamic pressure to rearrange WC particles and cause Co particles to undergo severe plastic deformation under the extrusion of WC particles, so that the relative density of the billet is further increased to more than 80%.
[0031] Step 4: Continue heating to 1300-1350℃ to form a WC-Co eutectic liquid phase. Dynamic pressure drives further rearrangement and atomic diffusion of WC particles, and the eutectic liquid phase uniformly fills the gaps between WC particles to complete the sintering process. Then, the furnace is cooled to room temperature.
[0032] The core innovation of this invention lies in proposing a two-step oscillating hot pressing sintering process of "low-temperature solid-phase sintering - high-temperature liquid-phase sintering". The working mechanism of each stage is explained in detail below:
[0033] Pressureless pre-firing stage: The main purpose of this stage is to remove adsorbed gases and residual moisture from the powder surface and to initially form a metallurgical bond between the cobalt powder particles and the WC particles. At 800℃, the Co phase has not yet melted but has already undergone significant diffusion, laying the foundation for subsequent densification. No pressure is applied during this stage to avoid prematurely closing the exhaust channels.
[0034] Low-temperature solid-state sintering stage: The plastic flowability of the cobalt phase is significantly enhanced in this stage. The mechanism of applying a low median oscillating pressure is reflected in two aspects: First, dynamic pressure can effectively break up the agglomerates between WC powder particles, eliminate the arching effect formed during powder pre-compression, and promote the rearrangement of WC particles; Second, dynamic pressure causes Co particles to undergo severe plastic deformation under the compression of WC particles, enabling the mixed powder to complete most of the volume shrinkage in the solid state, laying the foundation for rapid densification in subsequent liquid-phase sintering.
[0035] High-temperature liquid phase sintering stage: The sintering temperature in this stage is 1300-1350℃, which is adjusted appropriately according to the material composition. In this stage, the cobalt phase fully melts and forms a eutectic liquid phase with WC, while a relatively high median oscillating pressure is applied to achieve rapid densification. The mechanism of the oscillating pressure includes: First, the dynamic pressure generates periodically changing shear stress in the eutectic liquid phase, forcibly driving the eutectic liquid phase to flow between WC particle skeletons, eliminating macroscopic segregation such as cobalt-depleted regions and cobalt pools, and achieving a uniform distribution of the Co phase in three-dimensional space; Second, the dynamic pressure can further promote the rearrangement of WC particles with the help of the eutectic liquid phase, and at the same time accelerate the discharge of residual pores by filling the pore channels through the liquid phase; Third, the dynamic pressure can effectively promote atomic diffusion, improve the strength of the skeleton in cemented carbide, and achieve rapid densification; Fourth, the dynamic pressure can effectively inhibit the abnormal growth of WC grains through the liquid phase dissolution-precipitation mechanism, maintaining the fineness and uniformity of the grains.
[0036] The present invention achieves the following beneficial effects through the synergistic cooperation of the above two-step oscillating pressure system: (1) The density of the green body is greatly improved by the rearrangement of WC particles and the plastic deformation of Co phase in the low-temperature solid-phase sintering stage, laying the foundation for rapid densification in the subsequent liquid-phase sintering; (2) The eutectic liquid phase is uniformly filled in the WC skeleton by dynamic pressure in the high-temperature liquid-phase sintering stage, eliminating Co phase segregation and residual pores; (3) The progressive design of the amplitude of the two-step oscillating pressure avoids the formation of a large number of closed pores by applying excessive pressure in the low-temperature stage, and also avoids liquid phase extrusion caused by applying excessive pressure at one time in the high-temperature stage, thus improving the controllability and practicality of the process.
[0037] As a preferred option:
[0038] In step 2, the holding time at 800℃ is 30 min, and the vacuum degree is ≤10 Pa.
[0039] In step 3, the holding time at 1100℃ is 30 min, the median oscillation pressure is 20 MPa, the amplitude is 5 MPa, and the frequency is 2 Hz.
[0040] In step 4, the holding time at 1330℃ is 15 min, the median oscillation pressure is 25 MPa, the amplitude is 5 MPa, and the frequency is 2 Hz.
[0041] Example 1:
[0042] A two-step oscillatory hot pressing sintering method for WC-6Co cemented carbide includes the following steps:
[0043] Step 1: Load the WC-6Co cemented carbide mixed powder into a graphite mold and pre-press the powder at room temperature with a pre-pressing pressure of 15 MPa to obtain a compact.
[0044] Step 2: Place the pressed billet in a vibrating hot pressing sintering furnace, evacuate the furnace to control the vacuum level ≤10Pa, and sinter according to the following procedure:
[0045] (1) Pressureless pre-firing stage: The temperature is raised to 800℃ at a rate of 15℃ / min and held for 30 min to allow the compact to complete degassing and preliminary solid-phase sintering.
[0046] (2) Low-temperature solid-state sintering stage: The temperature is increased to 1100℃ at a rate of 10℃ / min, and an oscillating pressure is applied (the median pressure is 20 MPa, the amplitude is 5 MPa, and the frequency is 2 Hz), and the temperature is held for 30 min.
[0047] (3) High-temperature liquid phase sintering stage: The temperature is increased to 1330℃ at a rate of 10℃ / min, and an oscillating pressure is applied (the median pressure is 25 MPa, the amplitude is 5 MPa, and the frequency is 2 Hz), and the temperature is held for 15 min.
[0048] Step 3: Cooling treatment. Stop heating and pressurizing, and allow the sintered sample to cool to room temperature in the furnace to obtain cemented carbide.
[0049] Example 2:
[0050] A two-step oscillatory hot pressing sintering method for WC-6Co cemented carbide includes the following steps:
[0051] Step 1: Load the WC-6Co cemented carbide mixed powder into a graphite mold and pre-press the powder at room temperature with a pre-pressing pressure of 15 MPa to obtain a compact.
[0052] Step 2: Place the pressed billet in a vibrating hot pressing sintering furnace, evacuate the furnace to control the vacuum level ≤10Pa, and sinter according to the following procedure:
[0053] (1) Pressureless pre-firing stage: The temperature is raised to 800℃ at a rate of 15℃ / min and held for 30 min to allow the compact to complete degassing and preliminary solid-phase sintering.
[0054] (2) Low-temperature solid-state sintering stage: The temperature is increased to 1100℃ at a rate of 10℃ / min, and an oscillating pressure is applied (the median pressure is 20 MPa, the amplitude is 5 MPa, and the frequency is 2 Hz), and the temperature is held for 30 min.
[0055] (3) High-temperature liquid phase sintering stage: The temperature is increased to 1300℃ at a rate of 10℃ / min, and an oscillating pressure is applied (the median pressure is 45 MPa, the amplitude is 5 MPa, and the frequency is 2 Hz), and the temperature is held for 60 min.
[0056] Step 3: Cooling treatment. Stop heating and pressurizing, and cool the furnace to room temperature at a rate of 25°C / min to obtain cemented carbide.
[0057] Example 3:
[0058] A two-step oscillatory hot pressing sintering method for WC-3Co cemented carbide includes the following steps:
[0059] Step 1: Load the WC-3Co cemented carbide mixed powder into a graphite mold and pre-press the powder at room temperature with a pre-pressing pressure of 15 MPa to obtain a compact.
[0060] Step 2: Place the pressed billet in a vibrating hot pressing sintering furnace, evacuate the furnace to control the vacuum level ≤10Pa, and sinter according to the following procedure:
[0061] (1) Pressureless pre-firing stage: The temperature is raised to 800℃ at a rate of 15℃ / min and held for 30 min to allow the compact to complete degassing and preliminary solid-phase sintering.
[0062] (2) Low-temperature solid-state sintering stage: The temperature is increased to 1100℃ at a rate of 10℃ / min, and an oscillating pressure is applied (the median pressure is 20 MPa, the amplitude is 5 MPa, and the frequency is 2 Hz), and the temperature is held for 30 min.
[0063] (3) High-temperature liquid phase sintering stage: Heat to 1350℃ at a rate of 10℃ / min, apply oscillation pressure (median pressure value of 25 MPa, amplitude of 5 MPa, frequency of 2 Hz), and hold for 15 min.
[0064] Step 3: Cooling treatment. Stop heating and pressurizing, and cool the furnace to room temperature at a rate of 25°C / min to obtain cemented carbide.
[0065] Example 3:
[0066] A two-step oscillatory hot pressing sintering method for WC-9Co cemented carbide includes the following steps:
[0067] Step 1: Load the WC-9Co cemented carbide mixed powder into a graphite mold and pre-press the powder at room temperature with a pre-pressing pressure of 15 MPa to obtain a compact.
[0068] Step 2: Place the pressed billet in a vibrating hot pressing sintering furnace, evacuate the furnace to control the vacuum level ≤10Pa, and sinter according to the following procedure:
[0069] (1) Pressureless pre-firing stage: The temperature is raised to 800℃ at a rate of 15℃ / min and held for 30 min to allow the compact to complete degassing and preliminary solid-phase sintering.
[0070] (2) Low-temperature solid-state sintering stage: The temperature is increased to 1100℃ at a rate of 10℃ / min, and an oscillating pressure is applied (the median pressure is 20 MPa, the amplitude is 5 MPa, and the frequency is 2 Hz), and the temperature is held for 30 min.
[0071] (3) High-temperature liquid phase sintering stage: Heat to 1300℃ at a rate of 10℃ / min, apply oscillation pressure (median pressure value of 25 MPa, amplitude of 5 MPa, frequency of 2 Hz), and hold for 15 min.
[0072] Step 3: Cooling treatment. Stop heating and pressurizing, and cool the furnace to room temperature at a rate of 25°C / min to obtain cemented carbide.
[0073] SEM images of the WC-Co cemented carbides prepared in Examples 1-4 are shown below. Figure 1-4 As shown, the alloy exhibits a uniform microstructure, with no observed defects such as pores or cobalt pools. The cemented carbides prepared through Examples 1-4 of this invention achieve a density of over 99% and an HV30 (Vickers hardness) of up to 2000.
[0074] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A two-step oscillatory hot pressing sintering method for WC-Co cemented carbide, characterized in that, Includes the following steps: Step 1: Load the uniformly mixed WC-Co cemented carbide powder into a graphite mold for powder pre-pressing; Step 2: Transfer the pre-pressed billet together with the graphite mold to the vibrating hot pressing sintering furnace. Keep the pre-pressed billet in a vacuum environment at 800℃ to complete degassing and pre-sintering, so that the relative density of the billet reaches more than 60%. Step 3: Apply unidirectional oscillating pressure to the billet through the mold and heat it to 1100℃ for solid sintering. Use dynamic pressure to rearrange WC particles and cause Co particles to undergo severe plastic deformation under the extrusion of WC particles, so that the relative density of the billet can be further increased to more than 80%. Step 4: Continue heating to 1300-1350℃ to form a WC-Co eutectic liquid phase. Dynamic pressure drives further rearrangement and atomic diffusion of WC particles, and the eutectic liquid phase uniformly fills the gaps between WC particles to complete the sintering process. Then, the furnace is cooled to room temperature.
2. The two-step oscillatory hot pressing sintering method for WC-Co cemented carbide according to claim 1, characterized in that, In step 1, the Co content in the WC-Co cemented carbide powder is 1-15% by mass, and the grain size of WC is 20-800 nm.
3. The two-step oscillatory hot pressing sintering method for WC-Co cemented carbide according to claim 1, characterized in that, In step 2, the heating rate is 15℃ / min; the holding time at 800℃ is 30-90 min; and the vacuum degree is ≤10 Pa.
4. The two-step oscillatory hot pressing sintering method for WC-Co cemented carbide according to claim 1, characterized in that, In step 3, the heating rate is 5-10℃ / min; the holding time at 1100℃ is 30-120 min; and the median value of the oscillation pressure is 20 MPa.
5. The two-step oscillatory hot pressing sintering method for WC-Co cemented carbide according to claim 4, characterized in that, In step 3, the amplitude of the oscillation pressure is 1-5 MPa and the frequency is 1-10 Hz.
6. The two-step oscillatory hot pressing sintering method for WC-Co cemented carbide according to claim 1, characterized in that, In step 4, the heating rate is 2-10℃ / min, the cooling rate is 10-30℃ / min, the holding time at 1300-1350℃ is 5-60 min, and the median value of the oscillation pressure is 25-75 MPa.
7. The two-step oscillatory hot pressing sintering method for WC-Co cemented carbide according to claim 1, characterized in that, In step 4, the amplitude of the oscillation pressure is 1-50 MPa and the frequency is 1-10 Hz.
8. A WC-Co cemented carbide, characterized in that, It is made by the two-step oscillating hot pressing sintering method according to any one of claims 1-7.
9. A WC-Co cemented carbide, characterized in that, WC-Co cemented carbide has a uniform microstructure with the Co phase dispersed in the WC matrix and no abnormally grown WC grains. WC-Co cemented carbide has a relative density ≥99.0%, HV30 ≥2000, and fracture toughness ≥9 MPa•m. 1 / 2 .