CN117778851A - Preparation method of high-performance tungsten carbide nanocrystalline hard alloy - Google Patents
Preparation method of high-performance tungsten carbide nanocrystalline hard alloy Download PDFInfo
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Abstract
The invention discloses a preparation method of a high-performance tungsten carbide nanocrystalline hard alloy, which comprises the following steps: 1. VC powder, cr 3 C 2 Wet milling the powder and Co powder with nano WC powder, adding paraffin and paraffin emulsifier for ball milling, and spray drying to obtain composite powder B; 2. cold-pressing and preforming to obtain a pressed blank; 3. and (3) vacuum degreasing, hydrogen pretreatment and vacuum hot-pressing sintering of the pressed compact. The invention combines binder phase Co powder, grain growth inhibitor VC powder and Cr 3 C 2 Powder high-energy ball milling is mixed to form a composite structure, and then the composite structure is integrally added into nano WC powder, and the VC powder and Cr are mixed 3 C 2 The powder granularity is reduced to nano-scale, the uniform distribution of the powder in the WC matrix is improved, the carbide with uniform grains is obtained, the growth of WC grains is inhibited, the compactness of the carbide is improved, and the comprehensive performance of the carbide is improved, so that the carbide is suitable for the fields of metal processing, electronic industry, wood processing, biomedicine and the like.
Description
Technical Field
The invention belongs to the technical field of novel powder metallurgy, and particularly relates to a preparation method of a high-performance tungsten carbide nanocrystalline hard alloy.
Background
Cemented carbide is an indispensable key material in almost all industrial and new technical fields, and particularly has wide application in the fields of aerospace, automobiles, electronics, ships, mining, petroleum drilling, war industry and the like, is known as industrial teeth, and is a key material for promoting the development of manufacturing and processing levels in the fields. WC-Co cemented carbide is currently the most widely used cemented carbide.
With the rapid development of the high and new technology industry and aerospace, the performance of WC-Co hard alloy with common grain size can not meet the requirements. In general, the smaller the grain size of WC in the cemented carbide, the smaller the mean free path of the binder phase Co, and the higher the hardness of the cemented carbide. When the grain size of WC is reduced to the nanometer level (< 200 nm), various mechanical properties of the hard alloy material such as hardness, strength, fracture toughness, wear resistance and the like are greatly improved.
The nanocrystalline WC-Co hard alloy (WC average grain size is less than 200 nm) has the advantages of high wear resistance, high fracture toughness, high transverse fracture strength, high hardness and the like, and has urgent demands in the fields of metal processing, electronic industry, wood processing, biomedicine and the like. However, one of the core technical difficulties in the preparation of nanocrystalline cemented carbide is the control of WC grains during sintering. The nano WC powder used for sintering the nano-crystalline hard alloy has large surface energy, high particle activity, van der Waals force and various chemical bonds between particles, active chemical property, higher sensitivity to temperature than micron powder and easy growth in a high-temperature environment.
The research shows that the grain growth inhibitor is added into the WC-Co composite powder, so that the growth of WC grains can be effectively inhibited, and the hard alloy with fine grains can be easily obtained. Currently, transition metal carbides are mainly used as grain growth inhibitors, such as VC, cr 3 C 2 NbC, taC and TiC, among others, wherein VC and Cr 3 C 2 Is the most effective grain growth inhibitor at present.
Because the grain size of the grain growth inhibitor is small, the addition amount is not more than 4 wt%, the grain growth inhibitor is difficult to uniformly distribute in the composite powder, the component segregation is extremely easy to cause, the inhibition effect is insufficient, the problem of abnormal growth of grains in a local area exists, the material shows unstable mechanical properties, and the service performance of the hard alloy is finally affected. In addition, currently nanoscale VC and Cr 3 C 2 The powder is expensive and easy to agglomerate, and the micron or submicron grade VC and Cr 3 C 2 Although the powder has the price advantage, the size of the nano WC powder added into the nano WC powder is generally larger than that of surrounding WC powder, the inhibition effect on grain growth is limited, and a large part of the nano WC powder exists in the hard alloy in the form of impurity phases, so that the mechanical property of the hard alloy is damaged to some extent. Meanwhile, the grain growth inhibitor blocks the densification process of the hard alloy, so that the density of the hard alloy is reduced, and the density of the sintered hard alloy under the condition of no pressure is relatively low, thereby further affecting the properties of hardness, fracture toughness and the like of the material. In the hot-pressing sintering process, co in a liquid phase state is easier to flow under the action of pressure, so that the Co is more uniformly distributed, gaps among particles are easier to fill, and the preparation of nanocrystalline hard alloy with high density, fine grains and excellent comprehensive performance is facilitated.
Disclosure of Invention
The invention aims to solve the technical problem of providing a preparation method of high-performance tungsten carbide nanocrystalline hard alloy aiming at the defects of the prior art. The invention is prepared by mixing binding phase Co powder, grain growth inhibitor VC powder and Cr 3 C 2 Powder high-energy ball milling and mixing to form a composite structure, and then integrally adding the composite structure into nano WC powderVC powder and Cr 3 C 2 The powder granularity is reduced to the nanometer level, the uniform distribution of the powder granularity in the WC matrix is improved, the tungsten carbide nanocrystalline hard alloy with uniform grains is obtained, the growth of WC grains is restrained, the density of the hard alloy is improved by combining hydrogen pretreatment and vacuum hot-pressing sintering, the comprehensive performance of the hard alloy is improved, and the problems of nonuniform grain size, low density, poor comprehensive performance and the like of the existing nanocrystalline hard alloy are solved.
In order to solve the technical problems, the invention adopts the following technical scheme: the preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized by comprising the following steps of:
step one, mixing powder: VC powder, cr 3 C 2 The powder and Co powder are mechanically alloyed by high-energy ball milling under the protection of argon atmosphere, and Co-VC-Cr is prepared 3 C 2 The composite powder, namely composite powder A, is prepared by loading nano WC powder and composite powder A into a zirconia ball milling tank, adding absolute ethyl alcohol, wet milling on a planetary ball mill, adding forming agent paraffin and paraffin emulsifier, continuously ball milling, and spray drying to obtain micron-sized spherical WC-Co-VC-Cr 3 C 2 Composite particles, namely composite powder B;
step two, molding: putting the composite powder B obtained in the step one into a stainless steel mold for cold pressing preforming to obtain a pressed blank;
step three, sintering: and (3) sequentially carrying out vacuum degreasing, hydrogen pretreatment and vacuum hot-pressing sintering on the pressed compact prepared in the step (II) to obtain the tungsten carbide nanocrystalline hard alloy.
The invention uses high energy ball milling to make Co powder, grain growth inhibitor VC powder and Cr 3 C 2 Uniformly mixing the powder into small particles, namely composite powder A, adding the composite powder A into nano WC powder for wet grinding, adding forming agent paraffin and paraffin emulsifier for continuous ball milling, spray drying to obtain micron-sized spherical powder, namely composite powder B, cold pressing and preforming to obtain a pressed blank, and sequentially carrying out vacuum degreasing, hydrogen pretreatment and vacuum hot pressing sintering to obtain the tungsten carbide nanocrystalline hard alloy with uniform grain size, high density and excellent comprehensive performance. The invention is realized byImproving the powder mixing process to lead the grain growth inhibitor VC and Cr 3 C 2 Evenly distributed in the hard alloy, fully plays the role of inhibiting the growth of WC crystal grains, ensures the uniformity of the crystal grain size, and improves the comprehensive performance of the tungsten carbide nanocrystalline hard alloy. Meanwhile, the invention performs vacuum degreasing on the pressed compact to avoid the influence of the residual forming agent on the performance of the hard alloy, and removes oxygen on the surface of cobalt in the pressed compact through hydrogen pretreatment, thereby improving the mobility of a cobalt binding phase, reducing the porosity of the hard alloy, and obtaining the tungsten carbide nanocrystalline hard alloy with high density and fine grains through vacuum hot-pressing sintering.
The preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized in that the VC powder and the Cr in the first step 3 C 2 The granularity of the powder is 0.3-1 mu m, the granularity of the Co powder is 0.3-0.8 mu m, and the mass ratio of Co to VC to Cr is calculated 3 C 2 ＝40～120:1～20:1～20。
The preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized in that the rotating speed of the high-energy ball milling in the first step is 350-500 r/min, and the ball milling time is 24-72 h. By limiting the rotating speed and the ball milling time of high-energy ball milling, co powder, VC powder and Cr powder are ensured 3 C 2 After the powder is subjected to agglomeration, cold welding, plastic deformation, agglomeration dispersion and other processes, composite particles with smaller size and better dispersibility are formed.
The preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized in that BET granularity of the nano WC powder in the first step is 100-200 nm; the mass percentage of Co powder in the composite powder B is 4-12%, the mass percentage of VC powder is 0.1-2.0%, and Cr 3 C 2 The mass percentage of the powder is 0.1-2.0%, and the balance is WC powder.
BET particle size refers to the particle size of the powder obtained by the specific surface area test method.
The preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized in that in the first step, the addition mass of the paraffin wax forming agent accounts for 0.5% -3% of the total mass of the nano WC powder and the composite powder A, the mass of the paraffin wax emulsifying agent accounts for 30% of the mass of the forming agent, and the addition process is as follows: melting paraffin in a water bath at 70-90 ℃, adding paraffin emulsifier, stirring uniformly, and pouring into a ball mill tank after the paraffin is fully emulsified. The forming agent added in a molten state and a fully emulsified state ensures that the forming agent is uniformly distributed in the composite powder; in addition, the paraffin and paraffin emulsifier have low evaporation temperature, are easy to remove in the low-temperature sintering stage, and are not easy to cause carbon residue.
The preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized in that the rotating speed of wet milling in the first step is 150-300 r/min, the ball milling time is 24-36 h, the rotating speed of continuous ball milling is 120-200 r/min, and the ball milling time is 6-12 h. In the wet milling stage before paraffin wax and paraffin wax emulsifier as forming agents are not added, the method adopts a slightly high ball milling rotating speed and a longer ball milling time to promote nano WC powder and Co-VC-Cr 3 C 2 The composite powder is fully and uniformly mixed, so that the tungsten carbide nanocrystalline hard alloy is obtained by sintering, and in the continuous ball milling stage after the forming agent paraffin and the paraffin emulsifier are added, the paraffin is fully emulsified, the rotational speed is reduced, the ball milling time is shortened, the tungsten carbide nanocrystalline hard alloy is fully and uniformly mixed with powder in a ball milling tank, and the powder mixing efficiency is effectively improved.
The preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized in that the spray drying process in the first step is as follows: filtering the mixed slurry obtained after the continuous ball milling to remove grinding balls, and then performing spray drying to obtain 1-5 mu m micron-sized spherical WC-Co-VC-Cr 3 C 2 Composite particles. By adopting a spray drying mode, the mixed slurry is dispersed into fog drops and then forms a sphere due to surface tension, the fog drops in a drying tower are directly contacted with hot air and instantly evaporated to take away absolute ethyl alcohol in the fog drops, and spherical particles are obtained through granulation, so that the problem of low bulk density of the nano powder and low bulk density caused by poor fluidity is solved.
The preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized in that the pressure of cold pressing preforming in the second step is 50-100 MPa, and the pressure maintaining time is 5-30 min. The invention is beneficial to improving the density of the pressed compact by controlling the pressure and the pressure maintaining time of cold pressing preforming, and further is beneficial to obtaining the tungsten carbide nanocrystalline hard alloy with high density through sintering in the later period.
The preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized in that the specific processes of vacuum degreasing, hydrogen pretreatment and vacuum hot-pressing sintering in the third step are as follows: heating to 250-400 ℃ under vacuum condition, preserving heat for 30-150 min for degreasing, and removing paraffin and paraffin emulsifier; then introducing hydrogen, heating to 450-500 ℃ and preserving heat for 30-60 min, and removing residual oxygen on the surface of cobalt powder in the pressed compact; then put into a hot-pressing sintering furnace, vacuumized to 10 -2 And (3) carrying out stage heating sintering after Pa, namely firstly heating to 1150-1250 ℃ from room temperature at a speed of 10 ℃/min and preserving heat for 30-90 min, then heating to 1410-1450 ℃ at a speed of 5 ℃/min-10 ℃/min and preserving heat for 5-15 min, applying pressure of 15-25 MPa in the heating and preserving heat process, cooling to 1350-1400 ℃ at a speed of 3 ℃/min-5 ℃/min and preserving heat for 30-180 min, applying pressure of 20-30 MPa in the cooling and preserving heat process, then cooling to 800 ℃ at a speed of 5 ℃/min, applying pressure of 20-30 MPa in the cooling process, then removing the pressure, and cooling along with a furnace.
According to the invention, the paraffin wax forming agent and the paraffin wax emulsifying agent are completely removed by heating to a lower temperature in a vacuum state and properly preserving heat; the temperature is continuously increased and kept at the temperature in the hydrogen atmosphere, so that the cobalt oxide layer on the surface of the cobalt powder in the pressed compact is completely reduced into a cobalt simple substance, the fluidity of the bonding phase Co in the subsequent sintering process is improved, and the density of the hard alloy is improved; by adopting stage heating sintering, the temperature is firstly increased to 1150-1250 ℃ at a relatively high speed and is kept at a temperature, so that Co phases are melted, flow and fill gaps among WC, and the Co phases are continuously heated at a relatively low speed and are kept at a temperature and are applied with pressure, thus promoting Co, VC and Cr 3 C 2 The WC grains are restrained from growing up while being uniformly distributed, and pressure is applied under the condition that a small amount of liquid phase exists by pressurizing and pressure maintaining after cooling, so that the tungsten carbide nanometer is further improvedThe compactness of the crystal hard alloy.
In addition, the invention also discloses a high-performance tungsten carbide nanocrystalline hard alloy prepared by the method, which is characterized in that the high-performance tungsten carbide nanocrystalline hard alloy comprises a WC matrix, a Co bonding phase, VC and Cr which are uniformly distributed 3 C 2 Grain growth inhibitor, the density of the high-performance tungsten carbide nanocrystalline hard alloy is more than 99.3%, the average grain size is 130 nm-200 nm, the hardness is 92.0 HRA-93.8 HRA, and the fracture toughness is 11.0 MPa.m 1/2 ～13.5MPa·m 1/2 。
Compared with the prior art, the invention has the following advantages:
1. compared with the conventional method of binding phase Co powder, grain growth inhibitor VC powder and Cr 3 C 2 The powder and the nano WC powder are directly subjected to ball milling and powder mixing, and mechanical alloying is carried out by high-energy ball milling in the powder mixing process, so that binding phase Co powder, grain growth inhibitor VC powder and Cr powder are obtained 3 C 2 The powder is fully mixed to form a composite structure, and then is integrally added into nano WC powder, and the powder mixing process firstly mixes VC powder and Cr powder 3 C 2 The granularity of the powder is reduced to nano-scale, the size difference between the powder and WC powder is reduced, the inhibition effect on grain growth is improved, the powder cannot exist in hard alloy in a heterogeneous form, and on the other hand, the VC powder and the Cr powder 3 C 2 The powder and Co powder form a whole, so that the powder is easy to disperse, and the grain growth inhibitor VC powder and Cr are improved 3 C 2 The uniform distribution of the powder in the WC matrix is beneficial to obtaining tungsten carbide nanocrystalline hard alloy with uniform grains, thereby improving the comprehensive performance, especially the mechanical performance.
2. Compared with the conventional method that the forming agent is directly added into the raw materials, the method has the advantages that the forming agent paraffin and the paraffin emulsifying agent are simultaneously added in the powder mixing process, so that paraffin components are melted and emulsified and then added into the raw material mixed powder, the dispersion uniformity of the paraffin is obviously improved, the formability of a pressed compact is improved, and the condition of edge and corner falling is avoided; in addition, the forming agent paraffin and paraffin emulsifier have low evaporation temperature, are easy to remove in the low-temperature sintering stage, are not easy to cause carbon residue, and avoid adverse effects on the performance of the tungsten carbide nanocrystalline hard alloy.
3. Compared with the conventional method that the composite powder is obtained by directly drying in a drying oven, the method adopts a spray drying method to dry the composite powder B into spherical particles with the particle diameter of 1-5 mu m, improves the fluidity of the composite powder B, overcomes the problem of low bulk density caused by low bulk density and poor fluidity of nano powder, is beneficial to improving the density of tungsten carbide nanocrystalline hard alloy, and further improves the performances such as hardness, fracture toughness and the like.
4. Compared with the conventional low-temperature degreasing combined segmented pressureless sintering process, the method sequentially performs vacuum degreasing, hydrogen pretreatment and vacuum hot-pressing sintering on the pressed compact, reduces cobalt oxide on the surface of cobalt in the pressed compact into Co by adding hydrogen pretreatment, improves the mobility of a cobalt binding phase, and promotes Co, VC and Cr 3 C 2 Is uniformly distributed, and simultaneously utilizes the pressure applied in the vacuum hot-pressing sintering process to ensure Co, VC and Cr 3 C 2 The tungsten carbide nanocrystalline hard alloy contacts with WC matrix components, inhibits the growth of WC grains, improves the density of the tungsten carbide nanocrystalline hard alloy, and is favorable for obtaining nanocrystalline hard alloy with uniform grain size and high density.
5. The high-performance tungsten carbide nanocrystalline hard alloy prepared by the invention comprises a WC matrix, a Co bonding phase which is uniformly distributed, VC and Cr 3 C 2 Grain growth inhibitor, the density of the high-performance tungsten carbide nanocrystalline hard alloy is more than 99.3%, the average grain size is 130 nm-200 nm, the hardness is 92.0 HRA-93.8 HRA, and the fracture toughness is 11.0 MPa.m 1/2 ～13.5MPa·m 1/2 Has excellent comprehensive mechanical properties and wide application prospect in the fields of metal processing, electronic industry, wood processing, biomedicine and the like.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
FIG. 1a is a microstructure morphology of nano WC powder in example 1 of the present invention.
FIG. 1b is a microstructure morphology of Co powder in example 1 of the present invention.
FIG. 2 is a microstructure morphology of composite powder A prepared in example 1 of the present invention.
Fig. 3 is a microstructure morphology diagram of the tungsten carbide nanocrystalline cemented carbide prepared in example 1 of the present invention.
Fig. 4 is a microstructure morphology diagram of the tungsten carbide nanocrystalline cemented carbide prepared in comparative example 1 of the present invention.
Fig. 5 is a microstructure morphology diagram of the tungsten carbide nanocrystalline cemented carbide prepared in comparative example 2 of the present invention.
Fig. 6 is a microstructure morphology diagram of the tungsten carbide nanocrystalline cemented carbide prepared in example 2 of the present invention.
Fig. 7 is a microstructure morphology diagram of the tungsten carbide nanocrystalline cemented carbide prepared in example 3 of the present invention.
Detailed Description
Example 1
The embodiment comprises the following steps:
step one, mixing powder: 1g of VC powder with granularity of 0.7-1 mu m and 1g of Cr with granularity of 0.7-1 mu m 3 C 2 Mechanically alloying the powder with 40g Co powder with granularity of 0.5-0.8 μm under the protection of argon atmosphere and under the condition of rotating speed of 500r/min for 24h by high-energy ball milling to prepare Co-VC-Cr 3 C 2 The composite powder, namely composite powder A, is prepared by loading 95.8g of nano WC powder with the BET granularity of 100-200 nm and 4.2g of composite powder A into a zirconia ball milling tank, loading zirconia grinding balls and absolute ethyl alcohol into a planetary ball mill, carrying out wet milling for 36h under the conditions of 150r/min rotating speed and 3:1 ball material ratio, carrying out wet milling in a positive and negative alternate mode, reversing once every 2h, melting 0.5g of forming agent paraffin in a water bath kettle at 70-90 ℃, adding 0.15g of paraffin emulsifier, stirring uniformly, fully emulsifying the paraffin, pouring into a ball milling tank, continuously carrying out ball milling for 12h under the condition of 120r/min rotating speed, filtering the obtained mixed slurry, removing the grinding balls, and carrying out spray drying to obtain micron-sized spherical WC-Co-VC-Cr with the granularity of 1-5 mu m 3 C 2 Composite particles, namely composite powder B;
step two, molding: putting the composite powder B obtained in the step one into a stainless steel mold for cold pressing preforming to obtain a pressed blank; the pressure of the cold pressing preforming is 50MPa, and the pressure maintaining time is 30min;
step three, sintering: heating the pressed compact prepared in the second step to 250 ℃ under vacuum condition, preserving heat for 150min for degreasing, removing paraffin and paraffin emulsifier, then introducing hydrogen, heating to 450 ℃ and preserving heat for 60min, removing residual oxygen on the surface of cobalt powder in the pressed compact, then placing into a hot-pressing sintering furnace, and vacuumizing to 10 DEG C -2 And (3) carrying out stage heating sintering after Pa, namely firstly heating to 1150 ℃ from room temperature at a speed of 10 ℃/min and preserving heat for 90min, then heating to 1410 ℃ at a speed of 5 ℃/min and preserving heat for 15min, applying pressure of 25MPa in the heating and preserving heat process, cooling to 1350 ℃ at a speed of 3 ℃/min and preserving heat for 180min, applying pressure of 30MPa in the cooling and preserving heat process, cooling to 800 ℃ at a speed of 10 ℃/min, applying pressure of 30MPa in the cooling process, removing the pressure, and cooling along with a furnace to obtain the tungsten carbide nanocrystalline hard alloy.
The density (average value is obtained by measuring three times) and converting the density of the tungsten carbide nanocrystalline hard alloy prepared in the embodiment, observing the microstructure of the tungsten carbide nanocrystalline hard alloy, counting the average grain size, measuring the Rockwell hardness (HRA, at least measuring 5 different positions and obtaining the average value) and fracture toughness, and the result shows that: the density of the tungsten carbide nanocrystalline hard alloy prepared in the embodiment is 99.8%, the average grain size is 150 nm-200 nm, the Rockwell hardness is 93.0 HRA-93.8 HRA, and the fracture toughness is 11.0 MPa.m 1/2 ～12.1MPa·m 1/2 。
FIG. 1a is a microstructure chart of the nano WC powder in the embodiment, and as can be seen from FIG. 1a, the average particle size of the WC powder is 100 nm-200 nm.
FIG. 1b is a microstructure of Co powder according to the embodiment of the present invention, and it can be seen from FIG. 1b that the particle size of Co powder is 0.5 μm to 0.8. Mu.m.
FIG. 2 is a microstructure of composite powder A prepared in this example, and it can be seen from FIG. 2 that Co powder, VC powder and Cr powder are contained in composite powder A 3 C 2 The powder is mixed uniformly.
Fig. 3 is a microstructure morphology diagram, i.e., a back-scattering SEM diagram, of the tungsten carbide nanocrystalline cemented carbide prepared in this example, and as can be seen from fig. 3, the cemented carbide grains are fine and uniformly distributed, and most of the grains have a size of less than 200nm.
Comparative example 1
The comparative example comprises the following steps:
step one, mixing powder: 0.1g of VC powder with granularity of 0.7-1 mu m and 0.1g of Cr with granularity of 0.7-1 mu m 3 C 2 Powder, 4g of Co powder with the granularity of 0.5-0.8 mu m and 95.8g of nano WC powder with the BET granularity of 100-200 nm are filled into a zirconia ball milling tank, zirconia grinding balls and absolute ethyl alcohol are filled into the zirconia ball milling tank, wet milling is carried out on a planetary ball mill for 36 hours under the conditions of the rotating speed of 150r/min and the ball-material ratio of 3:1, the wet milling adopts a positive and negative alternate mode, reversing is carried out once every 2 hours, 0.5g of forming agent paraffin is melted in a water bath kettle at 70-90 ℃, then 0.15g of paraffin emulsifier is added, the mixture is stirred uniformly, after the paraffin is fully emulsified, the mixture is poured into the ball milling tank, ball milling is continued for 12 hours under the rotating speed of 120r/min, and the obtained mixed slurry is filtered to remove the grinding balls and then spray-dried, so as to obtain composite powder;
step two, molding: putting the composite powder obtained in the first step into a stainless steel mold for cold pressing preforming to obtain a pressed blank; the pressure of the cold pressing preforming is 50MPa, and the pressure maintaining time is 30min;
step three, sintering: heating the pressed compact prepared in the second step to 250 ℃ under vacuum condition, preserving heat for 150min for degreasing, removing paraffin and paraffin emulsifier, then introducing hydrogen, heating to 450 ℃ and preserving heat for 60min, removing residual oxygen on the surface of cobalt powder in the pressed compact, then placing into a hot-pressing sintering furnace, and vacuumizing to 10 DEG C -2 And (3) carrying out stage heating sintering after Pa, namely firstly heating to 1150 ℃ from room temperature at a speed of 10 ℃/min and preserving heat for 90min, then heating to 1410 ℃ at a speed of 5 ℃/min and preserving heat for 15min, applying pressure of 25MPa in the heating and preserving heat process, cooling to 1350 ℃ at a speed of 3 ℃/min and preserving heat for 180min, applying pressure of 30MPa in the cooling and preserving heat process, cooling to 800 ℃ at a speed of 10 ℃/min, applying pressure of 30MPa in the cooling process, removing the pressure, and cooling along with a furnace to obtain the tungsten carbide nanocrystalline hard alloy.
The density (average value is obtained by three times of measurement) and the converted density of the tungsten carbide nanocrystalline hard alloy prepared in the comparative example are measured, the microstructure is observed, the average grain size is counted, the Rockwell hardness (HRA, at least 5 different positions are measured and the average value is obtained) and the fracture toughness are measured, and the result shows that: the density of the tungsten carbide nanocrystalline hard alloy prepared in the embodiment is 98.7%, the average grain size is 360 nm-420 nm, the Rockwell hardness is 90.3 HRA-91.4 HRA, and the fracture toughness is 9.8 MPa.m 1/2 ～10.5MPa·m 1/2 。
Fig. 4 is a back-scattering SEM image which is a microstructure morphology image of the tungsten carbide nanocrystalline cemented carbide prepared in this comparative example, and it can be seen from fig. 4 that the cemented carbide grains are unevenly distributed, and large grains of 1 μm to 3 μm are present in addition to a very small number of grains of 200nm or less.
Comparative example 2
The comparative example comprises the following steps:
step one, mixing powder: 1g of VC powder with granularity of 0.7-1 mu m and 1g of Cr with granularity of 0.7-1 mu m 3 C 2 Mechanically alloying the powder with 40g Co powder with granularity of 0.5-0.8 μm under the protection of argon atmosphere and under the condition of rotating speed of 500r/min for 24h by high-energy ball milling to prepare Co-VC-Cr 3 C 2 The composite powder, namely composite powder A, is prepared by loading 95.8g of nano WC powder with the BET granularity of 100-200 nm and 4.2g of composite powder A into a zirconia ball milling tank, loading zirconia grinding balls and absolute ethyl alcohol into a planetary ball mill, carrying out wet milling for 36h under the conditions of 150r/min rotating speed and 3:1 ball material ratio, carrying out wet milling in a positive and negative alternate mode, reversing once every 2h, melting 0.5g of forming agent paraffin in a water bath kettle at 70-90 ℃, adding 0.15g of paraffin emulsifier, stirring uniformly, fully emulsifying the paraffin, pouring into a ball milling tank, continuously carrying out ball milling for 12h under the condition of 120r/min rotating speed, filtering the obtained mixed slurry, removing the grinding balls, and carrying out spray drying to obtain micron-sized spherical WC-Co-VC-Cr with the granularity of 1-5 mu m 3 C 2 Composite particles, namely composite powder B;
step two, molding: putting the composite powder B obtained in the step one into a stainless steel mold for cold pressing preforming to obtain a pressed blank; the pressure of the cold pressing preforming is 50MPa, and the pressure maintaining time is 30min;
step three, sintering: heating the pressed compact prepared in the second step to 250 ℃ under vacuum condition, preserving heat for 150min for degreasing, removing paraffin and paraffin emulsifying agent, then placing into a hot-pressing sintering furnace, and vacuumizing to 10 DEG C -2 And (3) after Pa, carrying out stage heating sintering, namely firstly heating to 1150 ℃ from room temperature at a speed of 10 ℃/min and preserving heat for 90mi, then heating to 1410 ℃ at a speed of 5 ℃/min and preserving heat for 15min, then cooling to 1350 at a speed of 3 ℃/min and preserving heat for 180min, then cooling to 800 ℃ at a speed of 10 ℃/min, then removing the pressure, and cooling along with a furnace to obtain the tungsten carbide nanocrystalline hard alloy.
The density (average value is obtained by three times of measurement) and the converted density of the tungsten carbide nanocrystalline hard alloy prepared in the comparative example are measured, the microstructure is observed, the average grain size is counted, the Rockwell hardness (HRA, at least 5 different positions are measured and the average value is obtained) and the fracture toughness are measured, and the result shows that: the density of the tungsten carbide nanocrystalline hard alloy prepared in the embodiment is 97.0%, the average grain size is 300 nm-360 nm, the Rockwell hardness is 88.5 HRA-89.3 HRA, and the fracture toughness is 8.0 MPa.m 1/2 ～9.7MPa·m 1/2 。
Fig. 5 is a microstructure morphology diagram, i.e., a back-scattering SEM diagram, of the tungsten carbide nanocrystalline cemented carbide prepared in this comparative example, and as can be seen from fig. 5, the cemented carbide grains are relatively uniformly distributed, and no significantly abnormally grown grains are observed.
As can be seen from a comparison of example 1 with comparative example 1 and comparative example 2, the binder phase Co powder, grain growth inhibitor VC powder and Cr powder were obtained in comparison with comparative example 1 3 C 2 The four powders of the powder and the nano WC powder are directly subjected to ball milling and powder mixing, and the hard alloy prepared by the embodiment is prepared from Co powder, VC powder and Cr powder 3 C 2 The powder is mixed with nano WC powder in the form of composite powder after mechanical alloying, so that VC and Cr are improved 3 C 2 The grain inhibition effect of the alloy is uniformly distributed in the hard alloy, so that the grain uniformity, rockwell hardness and fracture toughness of the alloy are improved; compared with the comparisonIn example 2, the hydrogen reduction and hot press sintering process was not used, and in this example, the hydrogen reduction process was used to improve the fluidity of Co powder at high temperature in the subsequent sintering process, thereby promoting Co, VC and Cr 3 C 2 Evenly distributed, and then adopting a sectional hot-pressing sintering process to inhibit the growth of WC crystal grains and improve the density of the hard alloy, so that the hard alloy prepared by the embodiment has finer crystal grains and higher density, rockwell hardness and fracture toughness.
In conclusion, the invention adopts high-energy ball milling to form Co, VC and Cr 3 C 2 The method of mixing the composite powder with nano WC powder, molding and sintering reduces VC and Cr 3 C 2 The size of the alloy is improved and the distribution uniformity of the alloy in the hard alloy is improved, thereby fully exerting the functions of VC and Cr 3 C 2 Is a suppression effect of (a); sintering under hot pressing to make Co, VC and Cr 3 C 2 The four powders of WC are fully contacted, the growth of WC crystal grains is restrained, the density of the hard alloy is improved, and finally the comprehensive performance of the hard alloy is improved.
Example 2
The embodiment comprises the following steps:
step one, mixing powder: 5g of VC powder with granularity of 0.3-0.6 mu m and 20g of Cr with granularity of 0.3-0.6 mu m 3 C 2 Mechanically alloying the powder with 80g Co powder with granularity of 0.3-0.5 μm under the protection of argon atmosphere and under the condition of rotating speed of 400r/min for 48h by high-energy ball milling to prepare Co-VC-Cr 3 C 2 The composite powder, namely composite powder A, is prepared by loading 89.5g of nano WC powder with BET granularity of 100-200 nm and 10.5g of composite powder A into a zirconia ball milling tank, loading zirconia grinding balls and absolute ethyl alcohol on a planetary ball mill, carrying out wet milling for 30 hours under the conditions of 240r/min rotating speed and 3:1 ball material ratio, carrying out wet milling in a positive and negative transfer mode, reversing once every 2 hours, melting 3g of forming agent paraffin in a water bath kettle at 70-90 ℃, adding 0.9g of paraffin emulsifier, stirring uniformly, fully emulsifying the paraffin, pouring the paraffin into a ball milling tank, continuously carrying out ball milling for 9 hours under the condition of 160r/min rotating speed, filtering and removing the grinding balls from the obtained mixed slurry, and carrying out spray drying to obtain the 1 mu m thick slurryMicron-sized spherical WC-Co-VC-Cr with a size of 5 mu m 3 C 2 Composite particles, namely composite powder B;
step two, molding: putting the composite powder B obtained in the step one into a stainless steel mold for cold pressing preforming to obtain a pressed blank; the pressure of the cold pressing preforming is 75MPa, and the pressure maintaining time is 15min;
step three, sintering: heating the pressed compact prepared in the second step to 300 ℃ under vacuum condition, preserving heat for 60min for degreasing, removing paraffin and paraffin emulsifier, then introducing hydrogen, heating to 475 ℃ and preserving heat for 45min, removing residual oxygen on the surface of cobalt powder in the pressed compact, then placing into a hot-pressing sintering furnace, and vacuumizing to 10 DEG C -2 And (3) carrying out stage heating sintering after Pa, namely firstly heating to 1200 ℃ from room temperature at a speed of 10 ℃/min and preserving heat for 60min, then heating to 1430 ℃ at a speed of 7 ℃/min and preserving heat for 10min, applying 20MPa of pressure in the heating and preserving heat process, cooling to 1370 ℃ at a speed of 5 ℃/min and preserving heat for 90min, applying 25MPa of pressure in the cooling and preserving heat process, then cooling to 800 ℃ at a speed of 10 ℃/min, applying 25MPa of pressure in the cooling process, removing the pressure, and cooling along with a furnace to obtain the tungsten carbide nanocrystalline hard alloy.
The density (average value is obtained by measuring three times) and converting the density of the tungsten carbide nanocrystalline hard alloy prepared in the embodiment, observing the microstructure of the tungsten carbide nanocrystalline hard alloy, counting the average grain size, measuring the Rockwell hardness (HRA, at least measuring 5 different positions and obtaining the average value) and fracture toughness, and the result shows that: the density of the tungsten carbide nanocrystalline hard alloy prepared in the embodiment is 99.3%, the average grain size is 130 nm-170 nm, the Rockwell hardness is 92.6 HRA-93.3 HRA, and the fracture toughness is 12.3 MPa.m 1/2 ～13.0MPa·m 1/2 。
Fig. 6 is a microstructure morphology diagram, i.e., a back-scattering SEM diagram, of the tungsten carbide nanocrystalline cemented carbide prepared in this example, and as can be seen from fig. 6, the cemented carbide grains are fine and uniformly distributed, and most of the grains have a size of less than 200nm.
Example 3
The embodiment comprises the following steps:
step oneMixing: 20g of VC powder with granularity of 0.5-0.8 mu m and 10g of Cr with granularity of 0.5-0.8 mu m 3 C 2 Mechanically alloying the powder with 120g Co powder with granularity of 0.4-0.7 μm under the protection of argon atmosphere and under the condition of rotating speed of 350r/min for 72h by high-energy ball milling, and preparing the Co-VC-Cr 3 C 2 The composite powder, namely composite powder A, is prepared by loading 85.0g of nano WC powder with BET granularity of 100-200 nm and 15g of composite powder A into a zirconia ball milling tank, loading zirconia grinding balls and absolute ethyl alcohol into a planetary ball mill, carrying out wet milling on the zirconia grinding balls and absolute ethyl alcohol for 24 hours under the conditions of rotating speed of 300r/min and ball material ratio of 3:1, carrying out wet milling in a positive and negative transfer mode, reversing once every 2 hours, melting 1.5g of forming agent paraffin in a water bath kettle at 70-90 ℃, adding 0.45g of paraffin emulsifier, stirring uniformly, fully emulsifying the paraffin, pouring the paraffin into a ball milling tank, continuously carrying out ball milling for 6 hours under the condition of rotating speed of 200r/min, filtering and removing the grinding balls from the obtained mixed slurry, and carrying out spray drying to obtain micron-sized spherical WC-Co-VC-Cr with the granularity of 1-5 mu m 3 C 2 Composite particles, namely composite powder B;
step two, molding: putting the composite powder B obtained in the step one into a stainless steel mold for cold pressing preforming to obtain a pressed blank; the pressure of the cold pressing preforming is 100MPa, and the pressure maintaining time is 5min;
step three, sintering: heating the pressed compact prepared in the second step to 400 ℃ under vacuum condition, preserving heat for 30min for degreasing, removing paraffin and paraffin emulsifier, then introducing hydrogen, heating to 500 ℃ and preserving heat for 30min, removing residual oxygen on the surface of cobalt powder in the pressed compact, then placing into a hot-pressing sintering furnace, and vacuumizing to 10 DEG C -2 And (3) carrying out stage heating sintering after Pa, namely firstly heating to 1250 ℃ from room temperature at a speed of 10 ℃/min and preserving heat for 30min, then heating to 1450 ℃ at a speed of 10 ℃/min and preserving heat for 5min, applying 15MPa pressure in the heating and preserving heat process, cooling to 1400 ℃ at a speed of 5 ℃/min and preserving heat for 30min, applying 20MPa pressure in the cooling and preserving heat process, cooling to 800 ℃ at a speed of 10 ℃/min, applying 20MPa pressure in the cooling process, removing the pressure, and cooling along with a furnace to obtain the tungsten carbide nanocrystalline hard alloy.
The density (average value is obtained by measuring three times) and converting the density of the tungsten carbide nanocrystalline hard alloy prepared in the embodiment, observing the microstructure of the tungsten carbide nanocrystalline hard alloy, counting the average grain size, measuring the Rockwell hardness (HRA, at least measuring 5 different positions and obtaining the average value) and fracture toughness, and the result shows that: the density of the tungsten carbide nanocrystalline hard alloy prepared in the embodiment is 99.5%, the average grain size is 140 nm-190 nm, the Rockwell hardness is 92.0 HRA-92.7 HRA, and the fracture toughness is 12.8 MPa.m 1/2 ～13.5MPa·m 1/2 。
Fig. 7 is a microstructure morphology diagram, i.e., a back-scattering SEM diagram, of the tungsten carbide nanocrystalline cemented carbide prepared in this example, and as can be seen from fig. 7, the cemented carbide grains are fine and uniformly distributed, and most of the grains have a size of less than 200nm.
The above description is only of the preferred embodiments of the present invention, and is not intended to limit the present invention. Any simple modification, variation and equivalent variation of the above embodiments according to the technical substance of the invention still fall within the scope of the technical solution of the invention.
Claims (10)
1. The preparation method of the high-performance tungsten carbide nanocrystalline hard alloy is characterized by comprising the following steps of:
step one, mixing powder: VC powder, cr 3 C 2 The powder and Co powder are mechanically alloyed by high-energy ball milling under the protection of argon atmosphere, and Co-VC-Cr is prepared 3 C 2 The composite powder, namely composite powder A, is prepared by loading nano WC powder and composite powder A into a zirconia ball milling tank, adding absolute ethyl alcohol, wet milling on a planetary ball mill, adding forming agent paraffin and paraffin emulsifier, continuously ball milling, and spray drying to obtain micron-sized spherical WC-Co-VC-Cr 3 C 2 Composite particles, namely composite powder B;
step two, molding: putting the composite powder B obtained in the step one into a stainless steel mold for cold pressing preforming to obtain a pressed blank;
step three, sintering: and (3) sequentially carrying out vacuum degreasing, hydrogen pretreatment and vacuum hot-pressing sintering on the pressed compact prepared in the step (II) to obtain the tungsten carbide nanocrystalline hard alloy.
2. The method for preparing high-performance tungsten carbide nanocrystalline hard alloy according to claim 1, wherein in the first step, the VC powder and Cr powder are as follows 3 C 2 The granularity of the powder is 0.3-1 mu m, the granularity of the Co powder is 0.3-0.8 mu m, and the mass ratio of Co to VC to Cr is calculated 3 C 2 ＝40～120:1～20:1～20。
3. The method for preparing high-performance tungsten carbide nanocrystalline hard alloy according to claim 1, wherein the rotation speed of the high-energy ball milling in the first step is 350-500 r/min, and the ball milling time is 24-72 h.
4. The method for preparing a high-performance tungsten carbide nanocrystalline hard alloy according to claim 1, wherein the BET particle size of the nano WC powder in the first step is 100 nm-200 nm; the mass percentage of Co powder in the composite powder B is 4-12%, the mass percentage of VC powder is 0.1-2.0%, and Cr 3 C 2 The mass percentage of the powder is 0.1-2.0%, and the balance is WC powder.
5. The method for preparing high-performance tungsten carbide nanocrystalline hard alloy according to claim 1, wherein in the first step, the addition mass of paraffin wax as a forming agent accounts for 0.5% -3% of the total mass of nano WC powder and composite powder A, the mass of paraffin wax emulsifying agent is 30% of the mass of the forming agent, and the addition process is as follows: melting paraffin in a water bath at 70-90 ℃, adding paraffin emulsifier, stirring uniformly, and pouring into a ball mill tank after the paraffin is fully emulsified.
6. The method for preparing the high-performance tungsten carbide nanocrystalline hard alloy according to claim 1, wherein the rotational speed of wet milling in the first step is 150-300 r/min, the ball milling time is 24-36 h, the rotational speed of continuous ball milling is 120-200 r/min, and the ball milling time is 6-12 h.
7. The method for preparing a high-performance tungsten carbide nanocrystalline cemented carbide according to claim 1, wherein the spray drying in the step one is: filtering the mixed slurry obtained after the continuous ball milling to remove grinding balls, and then performing spray drying to obtain 1-5 mu m micron-sized spherical WC-Co-VC-Cr 3 C 2 Composite particles.
8. The method for preparing a high-performance tungsten carbide nanocrystalline hard alloy according to claim 1, wherein the pressure of the cold pressing preforming in the second step is 50-100 MPa, and the dwell time is 5-30 min.
9. The method for preparing high-performance tungsten carbide nanocrystalline hard alloy according to claim 1, wherein the specific processes of vacuum degreasing, hydrogen pretreatment and vacuum hot-press sintering in the third step are as follows: heating to 250-400 ℃ under vacuum condition, preserving heat for 30-150 min for degreasing, and removing paraffin and paraffin emulsifier; then introducing hydrogen, heating to 450-500 ℃ and preserving heat for 30-60 min, and removing residual oxygen on the surface of cobalt powder in the pressed compact; then put into a hot-pressing sintering furnace, vacuumized to 10 -2 And (3) carrying out stage heating sintering after Pa, namely firstly heating to 1150-1250 ℃ from room temperature at a speed of 10 ℃/min and preserving heat for 30-90 min, then heating to 1410-1450 ℃ at a speed of 5 ℃/min-10 ℃/min and preserving heat for 5-15 min, applying pressure of 15-25 MPa in the heating and preserving heat process, cooling to 1350-1400 ℃ at a speed of 3 ℃/min-5 ℃/min and preserving heat for 30-180 min, applying pressure of 20-30 MPa in the cooling and preserving heat process, then cooling to 800 ℃ at a speed of 5 ℃/min, applying pressure of 20-30 MPa in the cooling process, then removing the pressure, and cooling along with a furnace.
10. A high performance tungsten carbide nanocrystalline cemented carbide produced by the method of any one of claims 1 to 9, characterized in that the high propertiesThe tungsten carbide nanocrystalline hard alloy comprises a WC matrix, a Co bonding phase which is uniformly distributed, VC and Cr 3 C 2 Grain growth inhibitor, the density of the high-performance tungsten carbide nanocrystalline hard alloy is more than 99.3%, the average grain size is 130 nm-200 nm, the hardness is 92.0 HRA-93.8 HRA, and the fracture toughness is 11.0 MPa.m 1/2 ～13.5MPa·m 1/2 。
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| CN118497583A (en) * | 2024-05-06 | 2024-08-16 | 株洲硬质合金集团有限公司 | A high-strength, corrosion-resistant ultrafine-grained WC-Ni-based cemented carbide and its preparation method |
| CN120174227A (en) * | 2025-05-19 | 2025-06-20 | 崇义章源钨业股份有限公司 | Platy crystal reinforced YT hard alloy and preparation method and application thereof |
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| CN118497583A (en) * | 2024-05-06 | 2024-08-16 | 株洲硬质合金集团有限公司 | A high-strength, corrosion-resistant ultrafine-grained WC-Ni-based cemented carbide and its preparation method |
| CN120174227A (en) * | 2025-05-19 | 2025-06-20 | 崇义章源钨业股份有限公司 | Platy crystal reinforced YT hard alloy and preparation method and application thereof |
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