WO2025007471A1 - High-performance nano cemented carbide product and preparation method therefor - Google Patents

Abstract

A high-performance nano cemented carbide product and a preparation method therefor. The method comprises: carrying out wet ball milling and powder mixing on 85-95% by mass of tungsten carbide powder and 5-15% by mass of cobalt powder, and drying same; loading WC-Co cemented carbide mixed powder into a mold; carrying out powder tap on the WC-Co cemented carbide mixed powder loaded into the mold; degassing the tapped WC-Co cemented carbide mixed powder by means of a vacuum environment; by means of a press, carrying out powder forming on the degassed WC-Co cemented carbide mixed powder in the vacuum environment, such that the powder is formed into a WC-Co cemented carbide primary product in the mold; separating the WC-Co cemented carbide primary product from the mold in the presence of a protective gas; and carrying out heat treatment on the demolded WC-Co cemented carbide primary product in a protective gas environment to obtain a high-performance nano cemented carbide material product. Thus, efficient batch production of the cemented carbide product is achieved, and it is ensured that all properties of the prepared product meet the requirements.

Description

High performance nano cemented carbide product and preparation method thereof Technical Field

The invention relates to the field of hard alloy material preparation, and in particular to a high-performance nano hard alloy product and a preparation method thereof.

Background Art

Cemented carbide is a multiphase composite material made of one or more refractory metal compounds with high hardness and high elastic modulus as the matrix and transition metals or their alloys as the binder, usually prepared by powder metallurgy. Among them, refractory metal compounds, especially refractory metal carbides (such as WC, TaC, TiC, NbC, etc.), have the characteristics of high melting point, high hardness, good chemical stability, good thermal stability, and small mutual dissolution effect with the bonding metal at room temperature. The transition metal used for bonding (such as Co, Ni, Fe, etc.) is required to have good wettability with the refractory metal hard compound, transform into liquid phase during the sintering process and can well wet the surface of the refractory metal hard compound, and can even partially dissolve the refractory metal hard compound, and will not chemically react with the refractory metal hard compound at the sintering temperature, and its own mechanical properties are good, and it is ensured that no liquid phase will appear at the service temperature of the cemented carbide.

Tungsten-cobalt (WC-Co) alloy is a common cemented carbide, which is mainly composed of tungsten carbide and cobalt. Compared with other cemented carbides with the same amount of cobalt, tungsten-cobalt (WC-Co) alloy has the highest transverse fracture strength, compressive strength, fracture toughness and elastic modulus. Therefore, as an important cemented carbide material, WC-Co cemented carbide has been widely used in metal cutting, metal forming tools, mining, oil drilling, national defense and military industry, stone and wood cutting, etc., and is known as the "teeth of industry".

At present, the industrial production of WC-Co cemented carbide mainly adopts the technical process of cold pressing + low-temperature degreasing treatment + high-temperature liquid phase sintering. In the cold pressing stage, the cemented carbide powder is pressed and formed; in the low-temperature degreasing treatment stage, the organic forming agent inside the compact is degreased at a relatively low heating temperature; in the liquid phase sintering stage, the fully mixed WC-Co powder is heated to a temperature higher than the WC-Co eutectic point, so that the WC powder is surrounded by the Co-rich liquid phase containing W and C. After the rotation and rearrangement of the WC powder, and the filling of the remaining pores by the Co-rich liquid phase, Reduce the porosity of the material. To achieve complete densification of the material, it is necessary to sinter at a higher temperature to obtain a sufficient amount of liquid phase and to keep the temperature for a longer period of time (usually more than 24 hours), but this method easily leads to abnormal growth of WC grains after sintering. At present, carbides of transition elements such as TaC, NbC, VC and Cr ₃ C ₂ are usually used as grain growth inhibitors to inhibit the abnormal growth of WC grains during the sintering process.

At present, my country's output of WC-Co cemented carbide products accounts for more than 40% of the global cemented carbide products market share. However, in terms of the processing capabilities of preparing high-end WC-Co cemented carbide products, especially nano WC-Co cemented carbide products, there is still a large gap with foreign industry leaders, and it does not yet have the ability to manufacture mature and stable high-performance nano WC-Co cemented carbide products. The main difficulties are as follows: 1. Abnormal growth of nano WC powder during sintering. Nano WC powder has a high activation energy on the surface, which is easy to merge with adjacent WC particles during long-term high-temperature sintering, resulting in abnormal growth. In order to avoid the abnormal growth of WC grains and obtain nano WC-Co cemented carbide with stable organizational properties, it is necessary to design a complex sintering process, which has high requirements for production line equipment and is difficult to prepare. At present, my country has not yet achieved the independent industrialization of nano WC-Co cemented carbide products. 2. The influence of Co content on the organization and performance of nano WC-Co cemented carbide. As a metal binder, Co fills the gaps between WC particles during the sintering process to prevent the merging and growth of WC particles; however, part of the WC will dissolve in the liquid phase Co during the sintering process and re-precipitate on the surface of other WC particles, which will also lead to the growth of WC particles. In addition, the increase in Co content will lead to a decrease in the hardness and wear resistance of WC-Co cemented carbide. Therefore, under the premise of ensuring the formation of a coating on WC particles, reducing the content of Co as much as possible is an important research direction in this field. 3. Incomplete dewaxing. At present, organic substances such as synthetic rubber, paraffin, and polyethylene glycol are commonly used as forming agents. They play a role in enhancing the fluidity of powders and maintaining the shape of the compacts during the cold pressing process, avoiding microcracks inside the compacts, and cracking during demolding and transportation. The forming agent must be removed during the sintering process, also known as dewaxing. Commonly used dewaxing treatments include vacuum dewaxing, nitrogen dewaxing, and hydrogen dewaxing, among which hydrogen dewaxing has a better effect. Incomplete dewaxing will lead to excessive free carbon content in WC-Co cemented carbide and generate η phase, which will reduce the hardness, fracture toughness and wear resistance of the material. In addition, since the sintering process of WC-Co cemented carbide powder metallurgy requires multiple steps, the equipment demand and production cost are relatively high.

Lin Yaojun, Xie Yongqiang, etc. invented a patent in China (CN111455206B, 2021.07.06) A method for manufacturing cemented carbide by rapid semi-solid hot pressing is disclosed in the literature. In this method, the thickness of cemented carbide powder when fully dense is first accurately calculated; then the cemented carbide powder is placed in the inner cavity of the hot pressing mold, the pressure head is inserted into the inner cavity of the hot pressing mold, the hot press working room is evacuated or filled with inert protective gas after evacuation, and the cemented carbide powder in the hot pressing mold is quickly heated to a high temperature corresponding to a certain liquid phase; finally, the pressure head is quickly moved downward to axially press the cemented carbide powder, and when the pressure head moves downward to a thickness of the cemented carbide powder that is slightly less than the thickness calculated above when fully dense, the pressure head is immediately stopped from moving downward and the pressure on the pressure head is stopped, and the heating of the cemented carbide powder is stopped at the same time, and the manufacturing of cemented carbide is completed. This method has the following shortcomings: 1) For cemented carbide powders with more components and more complex ingredients, it is difficult to obtain the accurate thickness of the product when it is fully dense by calculation, considering the volume expansion of different components at high temperature; 2) It is difficult to control a part of the cemented carbide powder to melt first, and due to the high sintering temperature, too high heating temperature can easily cause liquid elements to re-precipitate on the surface of solid cemented carbide grains, resulting in coarse grains; 3) When the method of liquefaction followed by pressurization is adopted, since the liquid phase does not appear at the same temperature point at the same time, it may cause uneven distribution of the liquid phase, thereby affecting the uniformity of the final organization; 4) The filling time of the liquid phase in the cemented carbide compact into the pores is too short, and in the absence of subsequent heat treatment, it may lead to a high porosity.

Zhu Liu, Wang Jinfang, etc. published a method for preparing WC- _Y2O3 cemented carbide without binder phase _{by cold pressing and hot pressing in a Chinese invention patent (CN111778436B, 2021.08.31). The method comprises the following steps: ball milling WC powder and Y2O3 powder to} obtain WC- _{Y2O3 powder} ; adding saturated oxalic acid solution to the WC- _{Y2O3 powder} until it is completely wetted, and cold pressing and sintering the wetted WC- _{Y2O3 powder} to obtain a sintered body; the pressure of the cold pressing and sintering is 200-400MPa; the heating program of the cold pressing and sintering is: first heating to 100-150℃ and keeping warm for 1 hour, and then heating to 200-300℃ and keeping warm for 1-2 hours; hot pressing and sintering the sintered body to obtain WC- _Y2O3 cemented _carbide without binder phase. This method has the following disadvantages: 1) the oxalic acid solution cannot achieve the micro dissolution of the Co element without affecting the main phase WC particles, and the Co element cannot be precipitated on the surface of the main phase particles at low temperature; 2 ₎ since this method uses WC- _Y2O3 non-binder phase cemented carbide powder, although a pre-sintered compact with a certain density is obtained by pre-sintering, a sintering temperature (1400-1650°C) far higher than the eutectic temperature (1280-1330°C) of the WC-Co cemented carbide is still required for the final powder forming, and due to the lack of liquid phase, the density of the final product is (97.87%) is lower than that of commercial WC-Co cemented carbide products (>99%); 3) The whole process of this method requires more steps and stations, resulting in low preparation efficiency.

He Qiushuang, Chen Haiyan, etc. published a fine-grained WC-Co cemented carbide with B ₄ C as a dispersion strengthening additive and a preparation method thereof in a Chinese invention patent (CN104630529B, 2017.09.12). The method includes the following steps: weigh WC (0.6-0.8μm, mass purity is 99.9%) and Co (0.6-0.8μm, mass purity is 99.9%) powders in proportion, and high-speed ball milling at a speed of 400-450 rpm in a ball mill for 45-50 hours (the ball milling medium is anhydrous ethanol and the grinding ball is WC ball); add B ₄ C at a certain volume fraction (5%-10%). C (0.6-0.8 μm, mass purity>99.9%) powder, uniformly mixed at a speed of 100-150 rpm for 20-24 hours; the dried raw materials are loaded into a graphite mold, placed in a hot pressing sintering furnace, heated to 1100-1200° C. at a speed of 15-20° C./min, pressurized to 5-10 MPa, then heated to 1300-1350° C. at a speed of 10-15° C./min and pressurized to 20-25 MPa, kept warm and pressurized for 1.5-2 hours, then released the pressure and cooled with the furnace. The method has the following disadvantages: 1) this method adds 5%-10% B ₄ C as a dispersion strengthening agent, and at the same time reduces the volume fraction of the metal bonding phase Co to ensure the hardness of the final product. However, the fracture toughness (<6MPa·m ^1/2 ) of the prepared alloy product is significantly lower than that of commercial WC-Co cemented carbide products (>8MPa·m ^1/2 ); 2) the WC particle size used is 0.6-0.8μm, which is larger than the WC particle size (<300nm) in nano cemented carbide specified in the internationally commonly used Sandvik company WC grain classification standard, which has a direct adverse effect on the final wear resistance, fracture toughness and bending strength of the product; 3) the single-furnace single-piece production method is adopted, the production efficiency is low, and it is not suitable for mass production.

Zhang Jiuxing, Huang Hao, and others published a SPS sintering method for large-sized pure tungsten carbide without a binder phase in a Chinese invention patent (CN108165859B, 2019.08.30). The method includes the following steps: according to the size of the required tungsten carbide sample, a graphite mold of corresponding size is set; the pure tungsten carbide powder without a binder phase is placed in the graphite mold for pre-compression, and then placed in a spark plasma sintering system, and the temperature is increased while the gradient is pressurized until the displacement of the lower pressure head of the graphite mold no longer changes. The temperature is stopped, sintered at a constant temperature, and then cooled with the furnace to obtain a large-sized pure tungsten carbide without a binder phase. The method has the following shortcomings: 1) This method requires the addition of graphite sheets, carbon paper and other additives between the upper and lower pressure heads of the graphite mold and the powder to ensure that the powder and the graphite mold do not directly diffuse with each other during the sintering process, resulting in demolding difficulties. The process is relatively complicated. It also does not mention whether the subsequent graphite sheet or carbon paper will diffuse with the cemented carbide sample to affect the material structure and element distribution, and whether a special machining process is required to remove a certain depth of the surface diffusion layer; 2) This method requires coating the outer surface of the graphite mold with multiple layers of carbon felt to ensure that the overall temperature of the graphite mold is uniform. The process is complicated and only one cemented carbide product can be prepared each time, resulting in low production efficiency; 3) In order to achieve a binder-free phase, the sintering temperature of this method is 1600-1700°C. At this temperature, only a graphite mold can be used for forming, which cannot avoid the carburizing reaction between the graphite mold and the WC-Co cemented carbide at high temperature, resulting in excessive free carbon content in the surface layer of the product, and easy generation of a brittle phase η phase, which has an adverse effect on the material structure and performance, especially the wear resistance during service; 4) The diameter of the cemented carbide product prepared by this method can reach about 100 mm, but the thickness can only reach about 5 mm. This size range limits its application in important machined parts such as cemented carbide drills and milling cutters.

Summary of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art, provide a method for preparing a high-performance nano cemented carbide material, realize efficient mass production of nano WC-Co cemented carbide products, and ensure that the various properties of the prepared nano WC-Co cemented carbide products meet the requirements.

The preparation method of the high-performance nano cemented carbide product of the present invention is characterized by comprising the following steps: wet ball milling and mixing WC powder with a mass fraction of 85-95% and Co powder with a mass fraction of 5-15%, and obtaining WC-Co cemented carbide mixed powder after drying; loading the WC-Co cemented carbide mixed powder into a mold; performing powder compaction on the WC-Co cemented carbide mixed powder loaded into the mold; degassing the compacted WC-Co cemented carbide mixed powder in a vacuum environment; powder forming the degassed WC-Co cemented carbide mixed powder by means of a press to form a WC-Co cemented carbide primary product in the mold; separating the WC-Co cemented carbide primary product from the mold under a protective gas environment; and heat treating the cooled WC-Co cemented carbide primary product under a protective gas environment to obtain a high-performance nano cemented carbide material product.

The preparation method of the present invention improves the tap density of nano cemented carbide powder by powder tapping treatment, reduces the air content in the powder, and makes the arrangement of nano cemented carbide particles It is more compact and the powder filling surface in the mold is smoother, which is beneficial to the subsequent pressing and forming, and reduces the structural defects of the final product after powder forming.

The above-mentioned preparation method of the present invention purifies the surface of nano cemented carbide powder through vacuum degassing treatment, promotes the wetting behavior between hard phase particles and metal bonding phase at high temperature, and is an important factor for the material to finally obtain dense and uniform structure. In addition, by vacuum degassing the powder before forming, the loose density of the powder is improved and better filling properties are obtained; vacuuming is continued during the powder forming process to ensure that the powder particles do not produce air gaps during the forming process; at the same time, vacuum degassing can prevent the gas adsorbed on the surface of the nano powder from reacting chemically with the powder during the high-temperature forming process and producing inclusions, which affects the final structure and performance of the material.

The above method of the present invention reduces the content of metal bonding phase in nano cemented carbide through powder forming, and improves the hardness, corrosion resistance and high temperature resistance of cemented carbide. In the powder forming process, high forming pressure is applied to nano cemented carbide powder. Since the hard phase hardly undergoes plastic deformation, the metal bonding phase distributed between the hard phases undergoes plastic deformation with the forming pressure, which on the one hand improves the coating effect of the bonding phase on the hard phase, and on the other hand reduces the thickness of the metal bonding phase between the hard phase particles. In the high temperature forming process, high forming pressure is used to reduce the pores between the hard phase particles, so that the liquid bonding phase is easier to enter the pores to complete the filling and obtain a dense structure, thereby realizing the preparation of a nano cemented carbide product with uniform and dense structure under the condition of reducing the metal bonding phase.

The above method of the present invention combines a reasonable WC-Co powder formula, powder compaction, vacuum degassing and powder forming. 1) Without using any grain growth inhibitor, the abnormal growth of WC grains is effectively inhibited, so that the average grain size of the prepared alloy product WC is less than 300nm, and the adverse effects of other undesirable elements such as additional carbon elements on the structure and performance of the cemented carbide are avoided; 2) when the content of the metal binder phase is quite low, a good coating effect of the binder phase on the hard phase is achieved; thereby, it is ensured that the various properties of the prepared nano WC-Co cemented carbide product meet the requirements or even better; 3) the common sintering temperature of WC-Co cemented carbide of 1350°C is reduced to 1200°C, which, on the one hand, relaxes the restrictions on mold materials, so that a larger forming force can be applied during powder forming, so that the various properties of the nano WC-Co cemented carbide product are better, and on the other hand, energy consumption is saved and manufacturing costs are reduced.

In one embodiment of the present invention, the powder forming comprises the following two sub-stages: Sections: a) maintaining heat and pressure at a temperature of 600-700° C. and a pressure of 20-30 MPa, and b) maintaining heat and pressure at a temperature of 1100-1200° C. and a pressure of 50-70 MPa.

Therefore, by applying pressure to sinter the prepared nano-cemented carbide at a relatively low temperature and keeping it warm and pressurized for a period of time, the friction originally generated between the hard phase (WC) powder, the metal binder phase (Co) powder and the mold wall can be effectively reduced, and the uniformity of the compact density during the forming process can be improved. Under high forming pressure, the metal binder phase undergoes plastic deformation, the contact area with the hard phase increases, and atomic interdiffusion is achieved under conditions below the eutectic point temperature. After a period of heat preservation and pressure, an interface structure with good metallurgical bonding is finally obtained, ensuring the density and high mechanical properties of the material.

In one embodiment of the present invention, in sub-stage a), the pressure is increased to 20-30 MPa at a pressurization rate of 5 MPa/min, and the temperature is increased to 600-700°C at a heating rate of 100-130°C/min; in sub-stage b), the pressure is increased to 60-70 MPa at a pressurization rate of 10 MPa/min, and the temperature is increased to 1100-1200°C at a heating rate of 100°C/min.

Therefore, the stepwise heating and pressure raising of WC-Co cemented carbide powder further helps to improve the uniformity of the final product and reduce the stress concentration between particles. At a lower forming temperature, the formability of the metal binder phase Co in the powder material is poor. By using a smaller strain rate, the pores between the powders can be reduced while reducing the stress concentration between the particles, thus achieving the preforming of the powder compact; as the forming temperature increases, the formability of the metal binder phase Co improves, and by appropriately increasing the strain rate, it can complete the rapid filling of the pores between the hard phase WC particles, thus obtaining a dense and uniform final structure.

In one embodiment of the present invention, the size of the tungsten carbide powder is in the range of 150-300 nm.

Therefore, tungsten carbide powder with a size range of 150-300nm is selected to ensure that the original particle size is smaller than the nano-tungsten carbide grain size required by the Sandvik WC grain grading standard commonly used internationally. Combined with the forming method of the present invention, the abnormal growth of tungsten carbide particles is suppressed, further ensuring that WC-Co cemented carbide products with nano-grain size are obtained.

In one embodiment of the present invention, one or more of anhydrous ethanol, acetone, and ethane are used as grinding aids in the wet ball milling. In one embodiment of the present invention, the ball-to-material ratio in the wet ball milling is 6-10:1. The liquid-to-solid ratio in the ball mill is 0.4-0.8:1.

Thus, preferably one or more of anhydrous ethanol, acetone, and ethane are used as grinding aids, which, on the one hand, help to inhibit powder agglomeration and surface oxidation, and on the other hand, are easy to achieve complete volatilization in a short time at a relatively low temperature, avoiding the introduction of excessive carbon or other undesirable elements due to the residual grinding aid, resulting in the generation of harmful phases in the subsequent liquid phase forming process of the powder, thereby reducing the uniformity of the microstructure of the final product and the mechanical properties of the material. In addition, the above-mentioned ball-to-material ratio and liquid-to-solid ratio further improve the ball milling quality, help to achieve the ideal particle size distribution of the WC-Co cemented carbide mixed powder, thereby further improving the final performance of the nano cemented carbide material product.

In one embodiment of the present invention, the vibration frequency of the powder compaction is 50-200 Hz, and the vibration duration is 1-3 minutes.

Therefore, combined with the density of WC-Co cemented carbide powder, a vibration frequency of 50-200Hz and a vibration time of 1-3 minutes are selected to achieve a more uniform filling of powder. The porosity between particles is effectively reduced by the powder compaction method. Compared with the loose packing density of traditional direct powder filling, the powder packing density can be increased by more than 30%, which is more conducive to the subsequent vacuum forming process.

In one embodiment of the present invention, the vacuum degree of the vacuum environment is 2.0-5.5×10 ^-3 Pa, and the degassing duration is 10-60 minutes.

As a result, the volatilization of the grinding aid during the low-temperature forming process is further promoted, and the air remaining in the pores of the powder particles is discharged in time, ensuring that the hard phase WC particles and the liquid phase Co do not contact the gas to generate harmful phases or cause organizational defects such as pores in the high-temperature stage, thereby reducing the uniformity of the microstructure of the final product and the mechanical properties of the material.

In one embodiment of the present invention, the heat treatment is to firstly cool the demoulded WC-Co cemented carbide primary product to room temperature by oil quenching, and then temper the cooled WC-Co cemented carbide primary product at a temperature of 400-500°C for 2-8 hours.

Therefore, through oil quenching-tempering treatment, more α-CO high-temperature phase with good plasticity is retained, and the residual thermal stress of WC-Co cemented carbide products is eliminated, so as to avoid the interaction between the preparation residual thermal stress generated in the cooling stage due to the different linear thermal expansion coefficients of the WC phase and the Co phase and the external load, thereby affecting the mechanical behavior and service performance of the material.

In one embodiment of the present invention, the protective gas environment is a high-purity nitrogen atmosphere. or high purity argon atmosphere.

This prevents air, especially oxygen, from oxidizing the WC-Co cemented carbide product during high-temperature forming, demolding and subsequent heat treatment, thereby affecting the microstructure and mechanical properties of the material.

Another object of the present invention is to provide a high-performance nano cemented carbide product, which is made by the above preparation method.

The alloy product has a relatively low metal binder phase content, and the average grain size of WC is less than 300nm, so the alloy product has excellent mechanical properties.

The above contents of the present application will be more concise and understandable in the following description of multiple embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings of the present application will be provided below. These drawings are only for embodying the present application in a more intuitive form. They are exemplary and are not intended to limit the scope of the present application.

FIG. 1 is a schematic flow diagram of a preparation method according to the present invention.

FIG. 2 is an alloy structure image of a high-performance nano-cemented carbide product prepared according to an embodiment of the preparation method of the present invention.

FIG. 3 is an alloy structure image of a high-performance nano-cemented carbide product prepared according to another embodiment of the preparation method of the present invention.

DETAILED DESCRIPTION

To make the present application easier to understand, the present application is further described below in conjunction with specific examples. The experimental methods described in this application are all conventional methods unless otherwise specified; the materials described are all commercially available unless otherwise specified. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of the present application. If there is any inconsistency, the meaning described in this specification or the meaning derived from the contents recorded in this specification shall prevail. In addition, the terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application.

In order to accurately describe the technical content of this application, and to accurately To understand the present invention, the following explanations are given to the words and terms used in this specification before describing the specific embodiments.

The words "one embodiment" or "an embodiment" as used in this specification means that a particular feature, step, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing throughout this specification do not necessarily all refer to the same embodiment, but may refer to the same embodiment. In addition, in one or more embodiments, the particular features, steps, or characteristics can be combined in any suitable manner, as will be apparent to one of ordinary skill in the art from this application.

The present invention provides a new high-performance nano cemented carbide product and a preparation method thereof, which realizes the low-temperature, high-pressure and efficient preparation of nano WC-Co cemented carbide materials under vacuum conditions through vacuum powder forming technology. In the preparation method of the present invention, high-temperature and high-strength materials including but not limited to titanium alloys, molybdenum alloys, nickel-based high-temperature alloys, high-temperature ceramic materials and high-temperature composite materials, non-graphite or graphite-based composite materials, can be selected to prepare the forming mold, and the powder compaction method is used to increase the bulk density of the powder in the powder filling stage, and vacuum degassing treatment is performed during the forming process, and the powder forming temperature is lower than 1300°C. The process flow of the preparation method of the present invention is relatively simple, and there are no special requirements for the mold, and the high-efficiency and low-cost production of nano cemented carbide materials can be achieved. In addition, in the preparation method of the present invention, without using any grain growth inhibitor, the average grain size of WC in the prepared material or product is less than 300nm, and the prepared material or product has a relatively low metal binder phase content and excellent mechanical properties.

The term "powder forming" used in the specification and claims refers to a process for heating a composite powder containing two or more phases to a temperature near the eutectic point of the two or more phases under vacuum or protective atmosphere conditions, and applying a certain forming pressure to the powder, so that the low-melting-point auxiliary phase in the powder is liquefied and comes into close contact with the surface of the main phase particles, and after a certain period of interatomic diffusion, a material with a dense and uniform structure is formed. The powder forming of the present invention combines the two processes of pressure forming and sintering, and is suitable for rapid prototyping of composite materials containing two or more phases.

The term "vacuum degassing" used in the specification and claims refers to the process of continuously evacuating the powder particles before and during powder forming to remove the gas remaining on the particle surface or enclosed between particles during the powder making process, as well as the gas adsorbed on the powder surface during the heating process. The surface of the powder particles is a gas-solid interface. When the powder is heated to a certain temperature and is in a Under high vacuum conditions, the gas adsorbed on the surface of the particles will begin to desorb and leave the powder surface. Since desorption is an endothermic reaction, the degassing rate will increase by increasing the degassing temperature and vacuum degree. For powder degassed under vacuum heating, at 200-500°C, H ₂ O gas and the like are mainly desorbed. When the temperature rises to above 700°C, H ₂ , CO ₂ and other gases can be desorbed. The method of the present invention can effectively reduce the appearance of pores and pores in the powder metallurgy preparation process through vacuum degassing.

The term "powder compaction" used in the specification and claims refers to the process of causing relative displacement and rearrangement between powders through vibration. When powder particles are freely stacked, an "arch bridge phenomenon" will occur, resulting in an increase in the pores between the powder particles. The method of the present invention can allow the powder particles to obtain a considerable alternating speed and acceleration through powder compaction. The originally stationary powder particles generate a considerable inertial force. Under the action of this inertial force, relative displacement occurs between the powder particles, destroying the arch bridge phenomenon and causing the particles to rearrange. The air in the loose powder is discharged due to the continuous movement of the particles, and the pores between the particles are gradually reduced, ultimately improving the density and uniformity of the powder.

Referring to FIG. 1 , the preparation method of the high-performance nano-hard alloy product of the present invention mainly comprises the following steps: wet ball milling and mixing tungsten carbide (WC) powder with a mass fraction of 85-95% and cobalt (Co) powder with a mass fraction of 5-15%, and drying to obtain WC-Co hard alloy mixed powder; loading the WC-Co hard alloy mixed powder into a mold; performing powder compaction on the WC-Co hard alloy mixed powder loaded into the mold; degassing the compacted WC-Co hard alloy mixed powder in a vacuum environment; performing powder forming on the degassed WC-Co hard alloy mixed powder in a vacuum environment with the help of a press to form a WC-Co hard alloy primary product in the mold; separating the WC-Co hard alloy primary product from the mold in the presence of a protective gas; and heat treating the demolded WC-Co hard alloy primary product in a protective gas environment to obtain a high-performance nano-hard alloy material product.

To facilitate implementation, exemplary embodiments of the present invention are described below.

<Example 1>

The preparation method of this embodiment is to prepare (diameter × length) nano WC-Co cemented carbide product. The size of the female mold used in the preparation method of this embodiment is (diameter × height), the mold wall thickness is 80mm. The preparation method of this embodiment adopts a two-way pressing process, and the sizes of the upper and lower pressing molds are respectively and Powder forming manufacturing is carried out in a vacuum powder forming furnace. The specific steps are as follows:

Nano WC cemented carbide powder with a particle size of 150-300nm is used: 90wt.% WC powder and 10wt.% Co powder are wet-milled and mixed in anhydrous ethanol, the ball-to-material ratio during the wet-milling process is 8:1, the liquid-to-solid ratio is 0.5:1, the ball-milling time is 48 hours, and the wet-milling is followed by drying;

The WC-Co cemented carbide powder was loaded into the mold and subjected to a powder compaction treatment at 100 Hz for 1.5 minutes;

The mold is closed and the entire mold is transferred to a vacuum powder forming furnace for vacuum degassing treatment. The vacuum degree is 3.0×10 ^-3 Pa and the vacuuming time is 20 minutes.

Continue to evacuate, first increase the temperature in the furnace to 650°C at a heating rate of 100°C/min, and at the same time increase the forming pressure to 25MPa, keep warm and keep pressure for 10 minutes, then continue to increase the temperature in the furnace to 1200°C at a heating rate of 100°C/min, and at the same time increase the pressure to 50MPa, and then keep warm and keep pressure for 10 minutes;

After the heat preservation and pressure preservation are completed, high-purity argon is filled into the furnace as a protective gas, and the furnace is cooled to 1100°C, and the formed product is demolded and taken out of the mold;

The product is transferred to an oil quenching chamber, which is sealed, evacuated and filled with inert protective gas high-purity nitrogen, and oil quenched until the product is cooled to room temperature;

The cooled product is transferred to a heat treatment chamber, which is sealed, evacuated and filled with inert protective gas high-purity nitrogen, and tempered at 500°C for 2 hours, then quickly cooled to room temperature, and the final product is transported out of the furnace.

<Example 2>

The preparation method of this embodiment is to prepare (diameter × length) nano WC-Co cemented carbide product. The size of the female mold used in the preparation method of this embodiment is (diameter × height), the mold wall thickness is 80mm. The preparation method of this embodiment adopts a two-way pressing process, and the sizes of the upper and lower pressing molds are respectively and Powder forming manufacturing is carried out in a vacuum powder forming furnace. The specific steps are as follows:

Nano WC cemented carbide powder with a particle size of 150-300nm is used: 91wt.% WC powder and 9wt.% Co powder are wet-milled and mixed in acetone, the ball-to-material ratio during wet-milling is 8:1, the liquid-to-solid ratio is 0.7:1, the ball-milling time is 48 hours, and the powder is dried after wet-milling;

The WC-Co cemented carbide powder was loaded into the mold and subjected to a powder compaction treatment at 100 Hz for 2.5 minutes;

The mold is closed and the entire mold is transferred to a vacuum powder forming furnace for vacuum degassing treatment. The vacuum degree is 3.0×10 ^-3 Pa and the vacuuming time is 45 minutes.

Continue to evacuate, first increase the temperature in the furnace to 650°C at a heating rate of 110°C/min, and at the same time increase the forming pressure to 25MPa, keep warm and hold the pressure for 10 minutes, then continue to increase the temperature in the furnace to 1150°C at a heating rate of 100°C/min, and at the same time increase the pressure to 50MPa, and then keep warm and hold the pressure for 15 minutes;

After the heat preservation and pressure preservation are completed, high-purity argon is filled into the furnace as a protective gas, and the furnace is cooled to 1150°C, and the formed product is demolded and taken out of the mold;

The product is transferred to an oil quenching chamber, which is sealed, evacuated and filled with inert protective gas high-purity nitrogen, and oil quenched until the product is cooled to room temperature;

The cooled product is transferred to a heat treatment chamber, which is sealed, evacuated and filled with inert protective gas high-purity nitrogen, and tempered at 500°C for 3 hours, then quickly cooled to room temperature, and the final product is transported out of the furnace.

<Example 3>

The preparation method of this embodiment is to prepare (diameter × length) nano WC-Co cemented carbide product. The size of the female mold used in the preparation method of this embodiment is (diameter × height), the mold wall thickness is 80mm. The preparation method of this embodiment adopts a two-way pressing process, and the sizes of the upper and lower pressing molds are respectively and Powder forming manufacturing is carried out in a vacuum powder forming furnace. The specific steps are as follows:

Nano WC cemented carbide powder with a particle size of 150-300nm is used: 91.5wt.% WC powder and 8.5wt.% Co powder are wet-milled and mixed in acetone, the ball-to-material ratio during wet-milling is 10:1, the liquid-to-solid ratio is 0.6:1, the ball-milling time is 48 hours, and the powder is dried after wet-milling;

The WC-Co cemented carbide powder was loaded into the mold of the vacuum powder forming furnace and subjected to a powder compaction treatment at 120 Hz for 1 minute.

The mold is closed and the entire mold is transferred to a vacuum powder forming furnace for vacuum degassing treatment. The vacuum degree is 3.5×10 ^-3 Pa and the vacuuming time is 30 minutes.

Continue to evacuate, first increase the temperature in the furnace to 700°C at a heating rate of 120°C/min, and at the same time increase the forming pressure to 30MPa, keep warm and keep pressure for 10 minutes, then continue to increase the temperature in the furnace to 1200°C at a heating rate of 100°C/min, and at the same time increase the pressure to 60MPa, and then keep warm and keep pressure for 10 minutes;

After the heat preservation and pressure preservation are completed, high-purity argon is filled into the furnace as a protective gas, and the furnace is cooled to 1180°C, and the formed product is demolded and taken out of the mold;

The product is transferred to an oil quenching chamber, which is sealed, evacuated and filled with high-purity argon as an inert protective gas, and oil quenched until the product is cooled to room temperature;

The cooled product is transferred to a heat treatment chamber, which is sealed, evacuated and filled with high-purity argon as an inert protective gas, and tempered at 550°C for 4 hours, followed by rapid cooling to room temperature, and the final product is transported out of the furnace.

<Example 4>

The preparation method of this embodiment is to prepare (diameter × length) nano WC-Co cemented carbide product. The size of the female mold used in the preparation method of this embodiment is (diameter × height), the mold wall thickness is 80mm. The preparation method of this embodiment adopts a two-way pressing process, and the sizes of the upper and lower pressing molds are respectively and Powder forming manufacturing is carried out in a vacuum powder forming furnace. The specific steps are as follows:

Nano WC cemented carbide powder with a particle size of 150-300nm is used: 92.5wt.% WC powder and 7.5wt.% Co powder are wet-milled and mixed in anhydrous ethanol, the ball-to-material ratio during wet-milling is 10:1, the liquid-to-solid ratio is 0.6:1, the ball-milling time is 36 hours, and the powder is dried after wet-milling;

The WC-Co cemented carbide powder was loaded into the mold and subjected to a powder compaction treatment at 150 Hz for 2 minutes;

The mold is closed and the entire mold is transferred to a vacuum powder forming furnace for vacuum degassing treatment. The vacuum degree is 4.0×10 ^-3 Pa and the vacuuming time is 50 minutes.

Continue to evacuate, first increase the temperature in the furnace to 700°C at a heating rate of 130°C/min, and at the same time increase the forming pressure to 25MPa, keep warm and hold the pressure for 15 minutes, then continue to increase the temperature in the furnace to 1100°C at a heating rate of 100°C/min, and at the same time increase the pressure to 70MPa, and then keep warm and hold the pressure for 10 minutes;

After the heat preservation and pressure preservation are completed, high-purity nitrogen is filled into the furnace as a protective gas, and the furnace is cooled to 1120°C, and the formed product is demoulded and taken out from the mold;

The product is transferred to an oil quenching chamber, which is sealed, evacuated and filled with inert protective gas high-purity nitrogen, and oil quenched until the product is cooled to room temperature;

The cooled product is transferred to a heat treatment chamber, which is sealed, evacuated and filled with inert protective gas high-purity nitrogen, and tempered at 450°C for 5 hours, then quickly cooled to room temperature, and the final product is transported out of the furnace.

<Experimental Example 1>

The nano WC-Co cemented carbide products prepared in Example 1 and Example 2 were used as samples for metallographic observation. A sample with a thickness of 5 mm was cut from the middle part of the rod-shaped sample in the length direction by wire cutting, and hot-mounted to obtain a mounted sample, which was then ground and polished to obtain a metallographic sample.

The microstructure was observed under a Zeiss Gemini SEM 500 field emission scanning electron microscope. The magnification of Figure 2 is 2000 times, and the magnification of Figure 3 is 5000 times.

Figures 2 and 3 show the alloy structure images of the high-performance nano cemented carbide products prepared according to Examples 1 and 2, respectively. The light-colored grains in the image are the hard phase WC phase, and the dark area is the metal bonding phase Co-rich phase. It can be seen from the image that the prepared high-performance nano cemented carbide product has a small particle size, dense particles, neat arrangement, no obvious pores, and it can be seen that the Co-rich phase forms a relatively ideal coating effect on the WC phase. The WC grain size and the area fraction of each phase were statistically analyzed by image processing software. The results show that the area of the Co-rich phase in Figure 2 accounts for 11.21%, and the area of the Co-rich phase in Figure 3 accounts for 13.08%, which shows that the present invention achieves a good coating effect of the Co-rich phase on the WC phase at a lower Co content.

<Experimental Example 2>

Samples were prepared for the products in the above examples, and the hardness, compressive strength, flexural strength and fracture toughness of each sample were tested. The test results of these properties of each sample are shown in Table 1.

<Experimental Example 3>

The density of the products in the above implementation examples was measured by the “Archimedes drainage method”, and then the relative density of each product was calculated using the following formula (1-3). The results are shown in Table 1.

First, a 5×5×5 mm block sample was prepared by wire cutting and the surface was polished. Then, according to GB 3850-83 standard, the mass of the sample in the air and suspended in water was measured respectively, and the sample density was calculated according to formula (1):

Where: ρ—actual density of the sample, g/cm ³ ;

_M1 —mass of sample in air, g;

_M2 —mass of the sample in water, g;

ρ _W —density of water during measurement, 1g/cm ³ at room temperature.

Then, the theoretical density of the sample is calculated according to formula (2):

Where: ρ ₀ —theoretical density of cemented carbide, g/cm ³ ;

X—mass percentage of WC in cemented carbide (%);

Y—mass percentage of Co in cemented carbide (%);

_Zi —mass percentage (%) of grain growth inhibitor (this item is omitted in the present invention);

d _WC —density of WC, 15.6 g/cm ³ ;

d _Co —density of Co, 8.9 g/cm ³ ;

d _i —density of grain growth inhibitor, g/cm ³ (this item is omitted in the present invention).

Finally, the relative density of the sample is calculated according to formula (3):

Where: f—relative density of cemented carbide (%);

ρ—actual density of the sample, g/cm ³

ρ ₀ —Theoretical density of cemented carbide, g/cm ³ .

Table 1 Test results of various properties of the experimental products of the present invention

It can be seen from Table 1 that the high-performance nano cemented carbide product prepared by the preparation method of the present invention has relatively high hardness, compressive strength and flexural strength, and its fracture toughness and relative density are better than the corresponding parameters of commercial WC-Co cemented carbide products (fracture toughness 8MPa·m ^1/2 , relative density 99%), and the WC grain size is smaller than the WC particle size (300nm) in nano cemented carbide specified in the Sandvik company's WC grain classification standard commonly used internationally.

The above are only preferred embodiments of the present application and the technical principles used. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present application. Therefore, although the present application is described in more detail through the above embodiments, the present application is not limited to the above embodiments, and may also include more other equivalent embodiments without departing from the concept of the present application, all of which belong to the scope of protection of the present application.

Claims (10)

A method for preparing a high-performance nano-hard alloy product, characterized in that it comprises the following steps: Wet-milling 85-95% by mass tungsten carbide powder and 5-15% by mass cobalt powder to obtain WC-Co cemented carbide mixed powder after drying. The WC-Co cemented carbide mixed powder is loaded into a mold; Performing powder compaction on the WC-Co cemented carbide mixed powder loaded into the mold; Degassing the compacted WC-Co cemented carbide mixed powder in a vacuum environment; By means of a press, under a vacuum environment, the degassed WC-Co cemented carbide mixed powder is powder-formed to form a WC-Co cemented carbide primary product in the mold; Separating the WC-Co cemented carbide primary product from the mold under a protective gas environment; and The WC-Co hard alloy primary product after demoulding is heat treated in a protective gas environment to obtain a high-performance nano-hard alloy material product. The preparation method according to claim 1 is characterized in that the size range of the tungsten carbide powder is 150-300nm. The preparation method according to claim 1 is characterized in that one or more of anhydrous ethanol, acetone, and ethane are used as grinding aids in the wet ball milling, the preferred ball-to-material ratio is 6-10:1, and the preferred liquid-to-solid ratio is 0.4-0.8:1. The preparation method according to claim 1 is characterized in that the vibration frequency of the powder compaction is 50-200 Hz, and the preferred vibration duration is 1-3 minutes. The preparation method according to claim 1 is characterized in that the vacuum degree of the vacuum environment is 2.0-5.5×10 ^-3 Pa, and the preferred degassing duration is 10-60 minutes. The preparation method according to claim 1 is characterized in that the powder forming comprises the following two sub-stages: a) maintaining the temperature at 600-700°C and the pressure at 20-30MPa, and b) Maintaining the temperature at 1100-1200°C and the pressure at 50-70MPa. The preparation method according to claim 6, characterized in that In sub-stage a), the pressure is increased to 20-30 MPa at a pressurization rate of 5 MPa/min. The temperature is raised to 600-700°C at a heating rate of 100-130°C/min; In sub-stage b), the pressure is increased to 60-70 MPa at a pressurization rate of 10 MPa/min, and the temperature is increased to 1100-1200° C. at a heating rate of 100° C./min. The preparation method according to claim 1 is characterized in that the heat treatment is firstly to rapidly cool the demolded WC-Co cemented carbide primary product to room temperature by oil quenching, and then to temper the cooled WC-Co cemented carbide primary product at a temperature of 400-500°C for 2-8 hours. The preparation method according to claim 1 is characterized in that the protective gas environment is a high-purity nitrogen atmosphere or a high-purity argon atmosphere. A high-performance nano cemented carbide product, characterized in that it is made by the preparation method described in any one of claims 1 to 9.