A method for continuous vacuum powder preparation of nano-WC-Co cemented carbide

Abstract

This invention belongs to the field of vacuum powder forming technology, specifically relating to a continuous vacuum powder preparation system and method for nano-WC-Co cemented carbide. The system includes: a central chamber, a powder loading chamber, a hot pressing chamber, a heat treatment chamber, an inlet / outlet chamber, and a vacuum control system. The central chamber is connected to the powder loading chamber, the hot pressing chamber, the heat treatment chamber, and the inlet / outlet chamber, and is separated from each of these chambers by valves. A robotic arm is installed in the central chamber to transfer the mold between the powder loading chamber, the hot pressing chamber, the heat treatment chamber, and the inlet / outlet chamber. The nano-WC-Co cemented carbide prepared by this invention has high dimensional accuracy, high density, uniform microstructure, and excellent mechanical properties, enabling high-efficiency, low-cost production of high-performance nano-WC-Co cemented carbide.

Description

Technical Field

[0001] This invention belongs to the field of vacuum powder forming technology, specifically relating to a vacuum powder continuous preparation system and method for nano-WC-Co cemented carbide. Background Technology

[0002] Nano-WC-Co cemented carbide is widely used in precision machining due to its high hardness, wear resistance, and high-temperature resistance. Traditional manufacturing processes typically involve a step-by-step production process of molding followed by vacuum sintering, which suffers from problems such as cumbersome procedures, low efficiency, and uneven density.

[0003] In existing technologies, attempts have been made to integrate processes such as powder loading, sintering, and demolding to improve production efficiency. However, due to limitations in mold material properties, vacuum environment stability, and high-temperature fine grain protection technology, the product density and dimensional accuracy are difficult to meet the requirements of high-performance cutting tools.

[0004] Furthermore, the agglomeration of nano-WC powder and the uneven distribution of the Co phase also limit the improvement of mechanical properties. Therefore, there is an urgent need to develop a nano-WC-Co cemented carbide preparation technology that enables continuous production and efficient shape and property control. Summary of the Invention

[0005] This invention provides a vacuum powder continuous preparation system and method for nano-WC-Co cemented carbide. The prepared nano-WC-Co cemented carbide has the characteristics of high dimensional accuracy, high density, uniform structure and excellent mechanical properties, and can realize the high-efficiency and low-cost production of high-performance nano-WC-Co cemented carbide.

[0006] Specifically, the present invention adopts the following technical solution:

[0007] A vacuum powder continuous preparation system for nano-WC-Co cemented carbide includes: a central chamber, a powder filling chamber, a hot pressing chamber, a heat treatment chamber, a material feeding and discharging chamber, and a vacuum control system;

[0008] The central chamber is connected to the powder filling chamber, the hot pressing chamber, the heat treatment chamber, and the inlet / outlet chamber, respectively, and the central chamber is separated from the powder filling chamber, the hot pressing chamber, the heat treatment chamber, and the inlet / outlet chamber by valves.

[0009] A robotic arm is installed in the central chamber, which is used to transfer the mold between the powder filling chamber, the hot pressing chamber, the heat treatment chamber, and the material inlet and outlet chamber.

[0010] The vacuum control system is connected to the central chamber, the powder filling chamber, the hot pressing chamber, the heat treatment chamber, and the inlet and outlet chamber, respectively.

[0011] Preferably, the powder filling chamber is equipped with an automatic powder filling device and a horizontal oscillation platform.

[0012] A continuous vacuum powder preparation method for nano-WC-Co cemented carbide, applied to the above-mentioned preparation system, includes the following steps:

[0013] (1) Mix nano WC powder with a high-temperature fine-grained protective phase to obtain nano WC powder doped with a high-temperature fine-grained protective phase; attach Co powder to the surface of the obtained nano WC powder by high-temperature spray granulation to obtain WC-Co cemented carbide mixed powder.

[0014] (2) After evacuation, protective gas is introduced to maintain the temperature in the central chamber, hot pressing chamber, heat treatment chamber, and discharge chamber at 10°C. -3 ~10 -1 Under a negative pressure protective atmosphere (i.e., an absolute pressure of 10 Pa), -3 ~10 -1 Pa);

[0015] (3) Open the door of the powder filling chamber, put the WC-Co hard alloy mixed powder and the mold into the powder filling chamber; close the door, and maintain the temperature in the powder filling chamber at 10℃ again by evacuating and then purging with protective gas. -3 ~10 -1 Under a negative pressure protective atmosphere of Pa; then WC-Co hard alloy mixed powder is filled into the mold and compacted;

[0016] (4) Open the valve between the powder filling chamber and the central chamber, insert the robot into the powder filling chamber, grab the mold and then exit, and close the valve between the two chambers; open the valve between the central chamber and the hot pressing chamber, insert the robot into the hot pressing chamber, place the mold and then exit, and close the valve between the two chambers.

[0017] (5) In the hot pressing chamber, the WC-Co cemented carbide mixed powder in the mold is hot-pressed and sintered. The sintering pressure is set to 50~300MPa, the sintering temperature is set to 1100~1450℃, and the heat and pressure are maintained for 0.5~3 h. Then the heating and pressurization are stopped to obtain the WC-Co cemented carbide billet.

[0018] (6) Open the valve between the hot pressing chamber and the central chamber, insert the robot into the hot pressing chamber, grab the mold and then exit, and close the valve between the two chambers; open the valve between the central chamber and the heat treatment chamber, insert the robot into the heat treatment chamber, place the mold and then exit, and close the valve between the two chambers.

[0019] (7) Anneal the WC-Co cemented carbide billet in the mold in the heat treatment chamber;

[0020] (8) Open the valve between the heat treatment chamber and the central chamber, insert the robot into the hot pressing chamber, grab the mold and then exit, and close the valve between the two chambers; open the valve between the central chamber and the discharge chamber, insert the robot into the discharge chamber, place the mold and then exit, and close the valve between the two chambers.

[0021] (9) In the discharge chamber, the WC-Co cemented carbide billet is cooled to below 100°C. The door of the discharge chamber is opened, the mold is removed, and nano-WC-Co cemented carbide is obtained after demolding. The door is closed, and the temperature in the powder filling chamber is maintained at 10°C again by evacuating and then purging with protective gas. -3 ~10 -1 Under a negative pressure protective atmosphere of Pa;

[0022] (10) Demolding to obtain nano WC-Co cemented carbide.

[0023] Preferably, the high-temperature fine-grained protective phase is carbide particles and / or rare earth oxide particles; wherein the carbide particles are selected from at least one of Cr3C2 and VC, and the rare earth oxide particles are selected from at least one of Y2O3 and ZrO2.

[0024] Preferably, in step (1), the nano WC powder and the high-temperature fine-grained protective phase are subjected to wet milling followed by vacuum drying to obtain nano WC powder doped with the high-temperature fine-grained protective phase.

[0025] Preferably, in step (1), the mass ratio of the nano WC powder, the high-temperature fine-grained protective phase, and the Co powder is 80~95:0.1~3:5~20.

[0026] Preferably, in step (3), the mold is a high-strength isostatic graphite mold with multiple parts in one mold, which can prepare multiple nano WC-Co hard alloys at one time.

[0027] Preferably, in step (3), the WC-Co cemented carbide mixed powder is filled into the mold by an automatic powder filling device;

[0028] The WC-Co cemented carbide mixed powder was compacted using a horizontal oscillation platform.

[0029] Preferably, in step (4), before opening the valve between the powder filling chamber and the central chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system; before opening the valve between the central chamber and the hot pressing chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system.

[0030] And / or, in step (6), before opening the valve between the hot pressing chamber and the central chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system; before opening the valve between the central chamber and the heat treatment chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system.

[0031] And / or, in step (8), before opening the valve between the heat treatment chamber and the central chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system; before opening the valve between the central chamber and the discharge chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system.

[0032] In a preferred embodiment, each chamber is equipped with a vacuum gauge to monitor real-time changes in the chamber's vacuum level. When it is necessary to open the valve between the chambers to connect them, the central control system sends a signal, and the vacuum system checks whether the vacuum difference between the two chambers is within 0.1 Pa (this pressure difference meets the opening condition). If the pressure difference exceeds 0.1 Pa, the vacuum pumping or gas replenishment function is activated in the chamber where the material is not located to achieve pressure balance, and then the valve is opened to transfer the material.

[0033] Preferably, in step (7), the annealing temperature is 600~1000℃ and the time is 0.5~3 h.

[0034] The beneficial effects achieved by this invention are as follows:

[0035] (1) The present invention adds trace amounts of carbide particles such as Cr3C2 and VC or rare earth oxide particles such as Y2O3 and ZrO2 as a high-temperature fine-grained protective phase. The purpose is that during the high-temperature sintering process, the protective phase will preferentially react with the precipitated W and C to form a shell on the surface of the WC hard phase, which prevents W and C from entering the liquid Co phase, or the W and C phases in the Co phase from entering the WC hard phase, thereby avoiding the growth phenomenon of the WC hard phase at high temperature.

[0036] (2) In this invention, Co powder is attached to the surface of nano-WC powder by high-temperature spray granulation. The high-temperature spray granulation utilizes the difference in melting points between Co and WC, melting the lower-melting-point Co element into a liquid state and spraying it uniformly onto the surface of WC particles in a misting manner with high-pressure air, thereby achieving a microstructure in which WC particles are uniformly coated with Co. Studies have found that the WC-Co cemented carbide mixed powder prepared by this process has the characteristic of uniform Co phase distribution. During hot pressing, it is easier to form an ideal microstructure in which the hard WC phase is coated with the metallic toughness Co phase, which is beneficial to improving the strength of WC-Co cemented carbide materials, while saving the amount of Co used, and is more suitable for achieving efficient and highly uniform continuous production.

[0037] (3) The existing compaction process is not carried out under a negative pressure protective atmosphere. Due to bridging and other phenomena between particles, the powder flow is affected and closed pores are easily generated. Even under vacuum conditions, the gas in the closed pores is difficult to escape, resulting in a loose internal structure or even oxidation, which is not conducive to the uniform microstructure and high performance of the product. The present invention first maintains the powder filling chamber under a negative pressure protective atmosphere, and then fills the WC-Co hard alloy mixed powder into the mold for compaction, thus overcoming the above-mentioned drawbacks.

[0038] (4) The multiple processes from powder filling to final cooling, as well as the mold transfer between different processes, are all carried out under a continuous negative pressure protective atmosphere, which avoids the formation of an oxide layer on the surface of Co phase particles in WC-Co hard alloy powder, so that the final product's microstructure and properties reach the most ideal effect. Attached Figure Description

[0039] Figure 1 A schematic diagram of the preparation system according to Example 1 is shown; in the figure, 1-central chamber, 2-powder filling chamber, 3-hot pressing chamber, 4-heat treatment chamber, 5-inlet / outlet chamber, 6-valve, 7-robotic arm.

[0040] Figure 2 The microstructure of the nano-WC-Co cemented carbide prepared according to the preparation system of Example 1 is shown. Detailed Implementation

[0041] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques or conditions described in the literature in the field, or in accordance with the product manual.

[0042] In the following embodiments, all instruments and equipment used, unless otherwise specified, are conventional products that can be purchased through legitimate channels. Unless otherwise stated, all methods described are conventional methods, and all raw materials are available from publicly available commercial sources.

[0043] Example 1

[0044] Example 1 first provides a preparation system for nano-WC-Co cemented carbide tool blanks, such as... Figure 1 As shown, it includes: a central chamber 1, a powder filling chamber 2, a hot pressing chamber 3, a heat treatment chamber 4, a material inlet and outlet chamber 5, and a vacuum control system;

[0045] The central chamber 1 is connected to the powder filling chamber 2, the hot pressing chamber 3, the heat treatment chamber 4, and the inlet and outlet chamber 5, respectively, and the central chamber 1 is separated from the powder filling chamber 2, the hot pressing chamber 3, the heat treatment chamber 4, and the inlet and outlet chamber 5 by valves 6.

[0046] The central chamber 1 is equipped with a robotic arm 7, which is used to transfer the mold between the powder filling chamber 2, the hot pressing chamber 3, the heat treatment chamber 4 and the material inlet and outlet chamber 5.

[0047] The vacuum control system is connected to the central chamber 1, the powder filling chamber 2, the hot pressing chamber 3, the heat treatment chamber 4, and the inlet and outlet chamber 5, respectively.

[0048] The powder filling chamber 2 is equipped with an automatic powder filling device and a horizontal oscillation platform.

[0049] Example 1 also provides a method for preparing nano-WC-Co cemented carbide applied to the above preparation system, the steps of which are as follows:

[0050] Step 1: Nano WC powder is used as the matrix powder, Co powder is used as the metal binder, and trace amounts of VC are added as a high-temperature fine-grained protective phase. The mass ratio is WC:VC:Co = 88%:0.7%:11.3%.

[0051] Step 2: The high-temperature fine-grained protective phase is uniformly mixed with WC powder by wet grinding and powder mixing. After vacuum drying, the Co phase is attached to the surface of WC particles by high-temperature spray granulation to obtain WC-Co cemented carbide composite powder.

[0052] Step 3: After evacuation, a protective gas is introduced to maintain the temperature in the central chamber, hot pressing chamber, heat treatment chamber, and discharge chamber at 5×10⁻⁶℃ respectively. -2 Under a negative pressure protective atmosphere of Pa.

[0053] Step 4: Open the door of the powder filling chamber, load the WC-Co cemented carbide composite powder into the powder hopper of the automatic powder filling device, close the door, and perform three cycles of vacuuming and purging with protective atmosphere (ensuring the oxygen content in the chamber is ≤0.05%) to maintain an atmosphere of 5×10⁻⁶ within the powder filling chamber. -2 Under a negative pressure protective atmosphere of Pa, powder is filled into a high-strength isostatic graphite mold with multiple parts by an automatic powder filling device, and the horizontal oscillation platform is started to compact the powder blank.

[0054] Step 5: (1) Simultaneously fill the powder chamber and central chamber vacuum level → open the connecting valve; (2) The robot grabs the mold and transfers it to the central chamber → close the valve; (3) Simultaneously fill the central chamber and hot pressing chamber vacuum level → open the valve; (4) The robot accurately places the mold into the mold seat in the hot pressing chamber and then exits → close the valve.

[0055] Step 6: After the mold automatically locks, the heating system is started. At the same time, the forming system begins to apply pressure to the mold. Heating process: heat from room temperature to 800℃ for 75 minutes, hold for 10 minutes, and continue heating for 60 minutes to the target temperature of 1250℃. Pressurization process: pressurize from 0 MPa to 10 MPa for 75 minutes, hold for 10 minutes, and continue pressurizing for 60 minutes to the target pressure of 60 MPa. After holding the temperature and pressure for 1 hour, heating is stopped, and pressure is continued until the product temperature is <900℃, then pressurization is stopped.

[0056] Step 7: (1) Synchronize the vacuum levels of the hot pressing chamber and the central chamber → open the valve; (2) The robot grabs the blank mold and enters the central chamber → close the valve; (3) Synchronize the vacuum levels of the central chamber and the heat treatment chamber → open the valve; (4) The robot places the mold on the constant temperature heat treatment rack in the heat treatment chamber and then exits → close the valve.

[0057] Step 8: Start the automatic temperature compensation system of the heat treatment chamber, control the target temperature to 1000℃±5℃, and anneal at a constant temperature for 1.5 h.

[0058] Step 9: (1) Simulate the vacuum level of the heat treatment chamber and the central chamber → open the valve; (2) The robot grabs the blank mold and enters the central chamber → close the valve; (3) Simulate the vacuum level of the central chamber and the discharge chamber → open the valve; (4) The robot places the mold in the shelf in the discharge chamber and then exits → close the valve.

[0059] Step 10: Activate the cooling system to bring the billet temperature to ≤100℃, open the door of the powder filling chamber, remove the mold, close the door, and perform three cycles of vacuuming and purging with a protective atmosphere (ensuring the oxygen content in the chamber is ≤0.05%) to restore the temperature in the powder filling chamber to 5×10⁻⁶. -2 Under a negative pressure protective atmosphere of Pa, the carbide blank is removed from the mold, and the mold surface is quickly cleaned before use.

[0060] Repeat steps 4-10 to form a continuous production of nano-WC-Co cemented carbide tool blanks.

[0061] Figure 2 The image shows the microstructure of the WC-Co cemented carbide sample prepared in Example 1. Table 1 shows the mechanical properties.

[0062] Table 1

[0063]

[0064] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for continuous vacuum powder preparation of nano-WC-Co cemented carbide, characterized in that, A vacuum powder continuous preparation system for a nano-WC-Co cemented carbide is provided. The preparation system includes: a central chamber, a powder filling chamber, a hot pressing chamber, a heat treatment chamber, a material feeding and discharging chamber, and a vacuum control system. The central chamber is connected to the powder filling chamber, the hot pressing chamber, the heat treatment chamber, and the inlet / outlet chamber, respectively, and the central chamber is separated from the powder filling chamber, the hot pressing chamber, the heat treatment chamber, and the inlet / outlet chamber by valves. A robotic arm is installed in the central chamber, which is used to transfer the mold between the powder filling chamber, the hot pressing chamber, the heat treatment chamber, and the material inlet and outlet chamber. The vacuum control system is connected to the central chamber, the powder filling chamber, the hot pressing chamber, the heat treatment chamber, and the inlet and outlet chamber, respectively. The preparation method includes the following steps: (1) Mix nano WC powder with a high-temperature fine-grained protective phase to obtain nano WC powder doped with a high-temperature fine-grained protective phase; attach Co powder to the surface of the obtained nano WC powder by high-temperature spray granulation to obtain WC-Co cemented carbide mixed powder. (2) After evacuation, protective gas is introduced to maintain the temperature in the central chamber, hot pressing chamber, heat treatment chamber, and discharge chamber at 10°C. -3 ~10 -1 Under a negative pressure protective atmosphere of Pa; (3) Open the door of the powder filling chamber, put the WC-Co hard alloy mixed powder and the mold into the powder filling chamber; close the door, and maintain the temperature in the powder filling chamber at 10℃ again by evacuating and then purging with protective gas. -3 ~10 -1 Under a negative pressure protective atmosphere of Pa; then WC-Co hard alloy mixed powder is filled into the mold and compacted; (4) Open the valve between the powder filling chamber and the central chamber, insert the robot into the powder filling chamber, grab the mold and then exit, and close the valve between the two chambers; open the valve between the central chamber and the hot pressing chamber, insert the robot into the hot pressing chamber, place the mold and then exit, and close the valve between the two chambers. (5) In the hot pressing chamber, the WC-Co cemented carbide mixed powder in the mold is hot-pressed and sintered. The sintering pressure is set to 30~300 MPa, the sintering temperature is set to 1100~1450 ℃, and the heat and pressure are maintained for 0.5~3 h. Then the heating and pressurization are stopped to obtain the WC-Co cemented carbide billet. (6) Open the valve between the hot pressing chamber and the central chamber, insert the robot into the hot pressing chamber, grab the mold and then exit, and close the valve between the two chambers; open the valve between the central chamber and the heat treatment chamber, insert the robot into the heat treatment chamber, place the mold and then exit, and close the valve between the two chambers. (7) Anneal the WC-Co cemented carbide billet in the mold in the heat treatment chamber; (8) Open the valve between the heat treatment chamber and the central chamber, insert the robot into the hot pressing chamber, grab the mold and then exit, and close the valve between the two chambers; open the valve between the central chamber and the discharge chamber, insert the robot into the discharge chamber, place the mold and then exit, and close the valve between the two chambers. (9) In the discharge chamber, cool the WC-Co cemented carbide billet to below 100°C, open the door of the discharge chamber, and remove the mold; close the door, and after evacuating, circulate protective gas to restore the temperature in the powder filling chamber to 10°C. -3 ~10 -1 Under a negative pressure protective atmosphere of Pa; (10) Demolding to obtain nano WC-Co cemented carbide.

2. The preparation method according to claim 1, characterized in that, In step (1), the high-temperature fine-grained protective phase is carbide particles and / or rare earth oxide particles; wherein the carbide particles are selected from at least one of Cr3C2 and VC, and the rare earth oxide particles are selected from at least one of Y2O3 and ZrO2.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the nano WC powder and the high-temperature fine-grained protective phase are subjected to wet milling followed by vacuum drying to obtain nano WC powder doped with the high-temperature fine-grained protective phase.

4. The preparation method according to claim 1 or 2, characterized in that, In step (1), the mass ratio of the nano WC powder, the high-temperature fine-grained protective phase, and the Co powder is 80~95:0.1~3:5~20.

5. The preparation method according to claim 1 or 2, characterized in that, In step (3), the mold is a high-strength isostatic graphite mold with multiple parts in one mold.

6. The preparation method according to claim 1 or 2, characterized in that, In step (3), the WC-Co cemented carbide mixed powder is filled into the mold by an automatic powder filling device; The WC-Co cemented carbide mixed powder was compacted using a horizontal oscillation platform.

7. The preparation method according to claim 1 or 2, characterized in that, In step (4), before opening the valve between the powder filling chamber and the central chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system; before opening the valve between the central chamber and the hot pressing chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system. And / or, in step (6), before opening the valve between the hot pressing chamber and the central chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system; before opening the valve between the central chamber and the heat treatment chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system. And / or, in step (8), before opening the valve between the heat treatment chamber and the central chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system; before opening the valve between the central chamber and the discharge chamber, the vacuum level of the two chambers is adjusted to be consistent through the vacuum control system.

8. The preparation method according to claim 1 or 2, characterized in that, In step (7), the annealing temperature is 600~1000℃ and the time is 0.5~3 h.

9. The preparation method according to claim 1, characterized in that, The powder filling chamber is equipped with an automatic powder filling device and a horizontal oscillation platform.

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