A method for synergistically toughening and strengthening cemented carbide by introducing metal nanophase into wc grains

Abstract

The application provides a method for introducing metal nanophase into WC to synergistically strengthen and toughen the hard alloy. The application first prepares WC-Co-η three-phase composite powder with uniformly distributed three phases and controllable composition and content of η phase, and uses a segmented heating process with different heating rates, holding temperatures and times in the mixing and sintering process of refractory metal carbide powder, so that the η phase first reacts with free carbon added in step (3) in situ, Co(W,C) nanometer particle phase rich in Co is generated in the process of WC grain merging and growing, and exists in the hard phase WC grain, and the nanometer metal particle phase is successfully introduced into the WC ceramic phase grain. The application uses refractory metal carbide to regulate the eutectic temperature of WC phase and Co phase at the interface, so that the Co(W,C) nanometer particle phase generated at the WC / Co interface is dissolved into the liquid phase Co and does not segregate at the WC / Co phase interface. The application obtains a new type of hard alloy with synchronous strengthening and toughening and excellent comprehensive mechanical properties.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of WC-Co type hard alloy with synergistically improved strength and toughness, and belongs to the technical field of hard alloy and powder metallurgy. BACKGROUND

[0002] WC-Co type hard alloy, as a typical tool material in the field of manufacturing and processing, plays an irreplaceable important role in industrial application. However, as a representative cermet composite material, there is a prominent repulsion and restrictive contradictory relationship between the hardness and toughness and between the strength and toughness of the WC-Co type hard alloy. The existing methods for preparing hard alloy with high hardness, high wear resistance and high strength are often realized by sacrificing the fracture toughness of the hard alloy. It is a great challenge to simultaneously improve the hardness, strength and fracture toughness of the hard alloy, and it is necessary to break through the repulsion and restrictive relationship between the hardness and toughness and between the strength and toughness of the hard alloy from the aspects of scientific mechanism and key technology. Since the hard ceramic phase WC in the hard alloy is combined in the form of covalent bond between W and C atoms, the chemical property is stable, the bond energy is large, and the bonding strength is high, and it is difficult to break the bond, therefore, in the atomic lattice structure of the WC crystal, it is very difficult to realize solid solution strengthening, precipitation strengthening and the like in metal and alloy. On the other hand, WC is a covalent bond crystal with close-packed hexagonal structure, and the slip system is less, and the toughening effect caused by dislocation movement is much weaker than that of metal and alloy material system. Therefore, the strengthening and toughening approach for the ceramic phase WC grain is very limited, and it is a great challenge and urgent need in the field of hard alloy and powder metallurgy to develop a preparation method for simultaneously improving the strength and toughness of the hard alloy and being controllable. SUMMARY

[0003] The application aims to introduce nanoscale metal phase particles into the WC ceramic grain of the hard alloy, and controllably regulate the particle size, content and distribution of the nanoscale metal phase, so that the ceramic grain is significantly strengthened, and the fracture toughness is also synergistically improved, thereby breaking the repulsion and restrictive contradictory relationship between the hardness and toughness and between the strength and toughness of the WC-Co type hard alloy, and obtaining a new hard alloy material with excellent comprehensive performance of high strength and high toughness.

[0004] The application provides a preparation method of synergistically strengthened and toughened hard alloy, and the method is characterized in that the following steps are included.

[0005] (1) WO 2.9Co3O4 and carbon black as raw materials, according to the requirement of Co mass percentage in the final prepared WC-Co cemented carbide of 6% to 12%, the mass percentage of added carbon black is determined to be 16.70% to 16.85%. The three raw materials are ball-mixed with anhydrous ethanol as the grinding medium, the mass ratio of powder to grinding ball is 1:3 to 1:6, the rotation speed of the ball mill is 500 to 700 r / min, and the ball-milling time is 30 to 60 hours. The ball-mixed powder is cold-pressed into a compact which is sent into a vacuum furnace for reaction synthesis by using the following process: the heating rate is 20℃ / min, the temperature is raised to 780℃ and then kept for 2 to 3 hours, then the temperature is raised to 900 to 1100℃ at a heating rate of 10℃ / min, and kept for 1 to 2 hours, thus obtaining WC-Co-η composite powder, wherein η is Co3W3C or Co2W4C or Co6W6C. The WC-Co-η composite powder is ground with the mass ratio of powder to grinding ball being 1:2 to 1:5, the rotation speed of the ball mill is 200 to 400 r / min, and the ball-milling time is 5 to 10 hours, thus obtaining WC-Co-η composite powder with an average particle diameter of 800 nm or less;

[0006] (2) using a planetary ball mill to ball-mill the refractory metal carbide (referring to TaC or NbC or Cr3C2 or TiC) powder to reduce the average particle diameter to 100 nm or less, the ball-milling process is as follows: inert protective gas is filled in the ball mill tank, the mass ratio of metal carbide powder to hard alloy grinding ball is 1:30 to 1:60, the rotation speed of the ball mill is 500 to 700 r / min, a 300-mesh sieve is used to sieve the powder every 5 to 10 hours, and the total ball-milling time is 30 to 40 hours;

[0007] (3) ball-mixing the WC-Co-η composite powder obtained in step (1) and the metal carbide powder obtained in step (2) with carbon black powder, wherein the mass of the metal carbide powder is 0.2 to 1.0% of the mass of the WC-Co-η composite powder, and the mass of the carbon black powder is 0.05% to 0.20% of the mass of the WC-Co-η composite powder. The ball-mixing process is as follows: using anhydrous ethanol as the grinding medium, the mass ratio of powder to grinding ball is 1:3 to 1:5, the rotation speed of the ball mill is 500 to 700 r / min, and the ball-milling time is 10 to 20 hours;

[0008] (4) The mixed powder obtained in step (3) is cold-pressed and then sintered and densified in a low-pressure sintering furnace, first heated to 300-400℃, and kept for 1-2 hours; then heated to 900-1100℃ at a heating rate of 20-30℃ / min, and kept for 1-2 hours; then heated to 1320-1350℃ at a heating rate of 10-20℃ / min, and kept for 0.5-1 hour; then heated to 1390-1430℃ at a heating rate of 5-10℃ / min, and kept for 1-2 hours, and then filled with 3-6 MPa nitrogen or argon, and kept for 1-2 hours, and then cooled to room temperature in the furnace after sintering; and finally a cemented carbide bulk material with a metal nanophase with an average particle diameter of less than 10 nm in the WC grains is prepared.

[0009] The features and technical advantages of the present technology are as follows:

[0010] (1) Compared with the existing preparation of WC and Co mixed powder and in-situ reaction synthesis method for preparing WC-Co composite powder, the first step of the present application is to prepare a WC-Co-η (η is one of Co3W3C or Co2W4C or Co6W6C three compounds) three-phase composite powder. In order to obtain a composite powder with uniform distribution among the three phases and controllable composition and content of η phase, the present application determines the accurate amount of carbon black required to meet the Co content and η phase composition and content in the three-phase composite powder through systematic research and a large number of exploratory experiments, as well as the reaction synthesis process steps and parameter combinations to achieve uniform distribution among the three phases and not produce additional impurities. This is a key technology and scientific principle that has not been used in the past in the preparation of WC-Co cemented carbide powder.

[0011] (2) During the sintering and densification of the mixed powder, the present application uses different heating rates, holding temperatures and holding times for segmented heating and holding process, which can make the η phase first react with the free carbon added in step (3) to produce Co(W,C) nanoparticles phase rich in Co and exist in the interior of the hard phase WC grains during the growth of WC grain, thereby successfully introducing the nanometer metal particle phase into the interior of the WC ceramic phase grain.

[0012] (3) The present application also mixes the WC-Co-η three-phase composite powder after ball milling with 100 nm or less refractory metal carbide (TaC or NbC or Cr3C2 or TiC) powder to prepare a mixed powder for sintering, which is also a key process step. The present application uses nanoscale refractory metal carbide to control the eutectic temperature at the interface between the WC phase and the Co phase during the liquid phase sintering of the mixed powder, so that the Co(W,C) nanoparticles phase produced by reaction at the edge of the WC grain near the WC / Co phase interface during sintering can dissolve into the liquid phase Co without segregation at the WC / Co interface.

[0013] (4) The present application can accurately adjust the amount of Co(W,C) nanoparticle phase in the WC grains of the final prepared cemented carbide by controlling the carbon content in the raw powder, the refractory metal carbide content and the carbon content added in the subsequent steps, and combining with suitable ball milling process, heating and sintering process, and control the average diameter of the nanoparticle phase below 10 nm, thereby affecting the combination relationship and crystallographic orientation relationship between the Co(W,C) nanoparticle phase and the WC matrix, further affecting the hardness, strength and toughness of the cemented carbide. This characteristic controllable Co(W,C) nanoparticle phase distributed in the WC grains can disperse the WC grains at the same time, and by using its own deformable characteristics, it can be deformed with WC, release the local stress and strain concentration in the WC grains, eliminate the hidden danger of microcrack nucleation and growth and transgranular fracture of WC, thereby playing a prominent toughening effect on the cemented carbide, and thus obtaining a new type of cemented carbide with synchronous strengthening and toughening and excellent comprehensive mechanical properties. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 A microstructure diagram of WC-10wt.%Co cemented carbide prepared in Example 1, in which the volume fraction of Co(W,C) nanoparticle phase in the WC grains is 4% and the average particle diameter is 6.35 nm.

[0015] Figure 2 A microstructure diagram of WC-10wt.%Co cemented carbide prepared in Example 2, in which the volume fraction of Co(W,C) nanoparticle phase in the WC grains is 3% and the average particle diameter is 6.46 nm.

[0016] Figure 3 A microstructure diagram of WC-10wt.%Co cemented carbide prepared in Example 3, in which the volume fraction of Co(W,C) nanoparticle phase in the WC grains is 5% and the average particle diameter is 5.88 nm.

[0017] Figure 4 A microstructure diagram of WC-6wt.%Co cemented carbide prepared in Example 4, in which the volume fraction of Co(W,C) nanoparticle phase in the WC grains is 8% and the average particle diameter is 6.68 nm.

[0018] Figure 5 A microstructure diagram of WC-10wt.%Co cemented carbide prepared in Comparative Example 1, in which there is no nanoparticle phase in the WC grains, and only WC and Co phases in the structure. DETAILED DESCRIPTION

[0019] The following examples further illustrate the present application, but the present application is not limited to the following examples.

[0020] Example 1

[0021] (1) Using WO 2.9 , Co3O4 and carbon black as raw materials, and according to the target product of 10% Co in the finally prepared WC-Co cemented carbide, the mass percentage of carbon black added in the raw materials is determined to be 16.82%. The three raw materials are ball-mixed in a mass ratio of 200.12:25.76:45.67. Anhydrous ethanol is used as the grinding medium, the mass ratio of powder to grinding ball is 1:3, the rotation speed of the ball mill is 550 r / min, and the ball milling time is 40 hours. The ball-mixed powder is cold-pressed into a compact which is then sent into a vacuum furnace for reaction synthesis using the following process: the heating rate is 20℃ / min, the temperature is raised to 780℃ and then kept for 2 hours, and then the temperature is raised to 1000℃ at a heating rate of 10℃ / min and kept for 1 hour to prepare a WC-Co-η (η is Co3W3C) composite powder. The composite powder is ground, the mass ratio of powder to grinding ball is 1:2, the rotation speed of the ball mill is 300 r / min, and the ball milling time is 5 hours, thereby obtaining a WC-Co-Co3W3C composite powder with an average particle diameter of 550 nm;

[0022] (2) The TaC powder is ball-milled to an average particle diameter of 80 nm using a planetary ball mill. The ball milling process is as follows: inert gas Ar is filled into the ball milling tank as a protective gas, the mass ratio of TaC powder to hard alloy grinding ball is 1:60, the rotation speed of the ball mill is 500 r / min, a 300-mesh sieve is used to sieve the powder every 5 hours, and the total ball milling time is 35 hours;

[0023] (3) The WC-Co-Co3W3C composite powder obtained in step (1) and the TaC powder obtained in step (2) are ball-mixed with carbon black powder. The mass of TaC powder is 0.8% of the mass of WC-Co-Co3W3C composite powder, and the mass of carbon black powder is 0.1% of the mass of WC-Co-Co3W3C composite powder. The ball-mixing process is as follows: anhydrous ethanol is used as the grinding medium, the mass ratio of powder to grinding ball is 1:3, the rotation speed of the ball mill is 550 r / min, and the ball milling time is 10 hours;

[0024] (4) The mixed powder obtained in step (3) is cold-pressed and then sintered to densify, using a low-pressure sintering furnace, first heated to 350°C and kept for 1 hour; then heated to 1000°C at a heating rate of 20°C / min and kept for 1 hour; then heated to 1350°C at a heating rate of 10°C / min and kept for 0.5 hour; then heated to 1410°C at a heating rate of 5°C / min and kept for 2 hours, then filled with 5 MPa argon and kept for 2 hours; after sintering, the furnace is cooled to room temperature, and a WC grain with a metal nanophase inside is prepared. The microstructure of the hard alloy prepared in this embodiment is shown in FIG. 1, wherein the average particle diameter, volume fraction of the nanometal phase inside the WC grain, and the mechanical property data of the hard alloy are shown in Table 1. Figure 1

[0025] Example 2

[0026] (1) WO 2.9 , Co3O4 and carbon black as raw materials, according to the target product of 10% Co mass percentage in the finally prepared WC-Co hard alloy, the mass percentage of carbon black added in the raw materials is determined to be 16.82%. The three raw materials are ball-mixed according to the mass ratio of 200.12:25.76:45.67, with anhydrous ethanol as the grinding medium, the mass ratio of powder to grinding ball is 1:3, the rotation speed of the ball mill is 500 r / min, and the ball milling time is 30 hours. The ball-mixed powder is cold-pressed into a block and sent into a vacuum furnace, and the following process is used for reaction synthesis: the heating rate is 20°C / min, the temperature is raised to 780°C and kept for 2 hours, then the temperature is raised to 900°C at a rate of 10°C / min and kept for 2 hours, to prepare a WC-Co-η (η is Co3W3C) composite powder. The composite powder is ground, the mass ratio of powder to grinding ball is 1:2, the rotation speed of the ball mill is 300 r / min, and the ball milling time is 8 hours, thereby obtaining a WC-Co-Co3W3C composite powder with an average particle diameter of 600 nm;

[0027] (2) The Cr3C2 powder is ball-milled to an average particle diameter of 50 nm using a planetary ball mill, and the ball milling process is as follows: inert gas Ar is filled into the ball mill tank as a protective gas, the mass ratio of Cr3C2 powder to hard alloy grinding ball is 1:50, the rotation speed of the ball mill is 600 r / min, and the powder is sieved every 8 hours using a 300-mesh sieve, and the total ball milling time is 40 hours;

[0028] ​(3) The WC-Co-Co3W3C composite powder obtained in step (1) and the Cr3C2 powder obtained in step (2) are ball-mixed with carbon black powder, wherein the mass of the Cr3C2 powder is 1.0% of the mass of the WC-Co-Co3W3C composite powder, and the mass of the carbon black powder is 0.1% of the mass of the WC-Co-Co3W3C composite powder. The ball-mixing process is as follows: using anhydrous ethanol as the grinding medium, the mass ratio of the powder to the grinding balls is 1:3, the rotation speed of the ball mill is 500 r / min, and the ball-milling time is 10 hours;

[0029] (4) The mixed powder obtained in step (3) is cold-pressed and then sintered and densified, using a low-pressure sintering furnace, first heated to 400℃ and kept for 1 hour; then heated to 900℃ at a heating rate of 25℃ / min and kept for 2 hours; then heated to 1320℃ at a heating rate of 10℃ / min and kept for 1 hour; then heated to 1420℃ at a heating rate of 10℃ / min and kept for 2 hours, and then 6 MPa of argon is filled and kept for 2 hours; after the sintering is completed, the furnace is cooled to room temperature, and a WC grain with a metal nanophase inside is prepared. The microstructure of the hard alloy prepared in this embodiment is shown in FIG. 1, wherein the average particle diameter, the volume fraction of the nanometal phase inside the WC grain, and the mechanical property data of the hard alloy are shown in Table 1. Figure 2

[0030] Example 3

[0031] (1) WO 2.9 , Co3O4 and carbon black as raw materials, and according to the target product of 10% Co mass percentage in the finally prepared WC-Co hard alloy, the mass percentage of carbon black added in the raw materials is determined to be 16.70%. The three raw materials are ball-mixed in a mass ratio of 200.25:25.77:45.31, using anhydrous ethanol as the grinding medium, the mass ratio of the powder to the grinding balls is 1:3, the rotation speed of the ball mill is 550 r / min, and the ball-milling time is 40 hours. The ball-mixed powder is cold-pressed into a block and sent into a vacuum furnace, and the following process is used for reaction synthesis: the heating rate is 20℃ / min, the temperature is raised to 780℃ and kept for 2 hours, then the temperature is raised to 1100℃ at a heating rate of 10℃ / min, and kept for 1 hour, thereby preparing a WC-Co-η (η is Co3W3C) composite powder. The composite powder is ground, the mass ratio of the powder to the grinding balls is 1:2, the rotation speed of the ball mill is 300 r / min, and the ball-milling time is 5 hours, thereby obtaining a WC-Co-Co3W3C composite powder with an average particle diameter of 580 nm;

[0032] ​(2) using a planetary ball mill to ball mill the TaC powder to an average particle diameter of 80 nm, the ball milling process being: filling the ball mill jar with inert Ar gas as a protective gas, the mass ratio of TaC powder to hard alloy grinding ball being 1:60, the rotation speed of the ball mill being 500 r / min, sieving the powder every 5 hours using a 300-mesh sieve, and the total ball milling time being 35 hours;

[0033] (3) ball milling the WC-Co-Co3W3C composite powder obtained in step (1) and the TaC powder obtained in step (2) with carbon black powder, wherein the mass of TaC powder is 0.5% of the mass of the WC-Co-Co3W3C composite powder, and the mass of carbon black powder is 0.14% of the mass of the WC-Co-Co3W3C composite powder. The ball milling process is: using anhydrous ethanol as a grinding medium, the mass ratio of powder to grinding ball being 1:3, the rotation speed of the ball mill being 550 r / min, and the ball milling time being 10 hours;

[0034] (4) cold pressing the mixed powder obtained in step (3) and then sintering and densifying, using a low-pressure sintering furnace, first heating to 380℃ and maintaining for 1 hour, then heating to 1100℃ at a heating rate of 30℃ / min and maintaining for 1 hour, then heating to 1350℃ at a heating rate of 15℃ / min and maintaining for 1 hour, then heating to 1420℃ at a heating rate of 5℃ / min and maintaining for 2 hours, then filling with 5 MPa argon and maintaining for 2 hours, and then cooling to room temperature in the furnace after sintering, to prepare a WC grain with metal nanophase hard alloy bulk material. The microstructure of the hard alloy prepared in this embodiment is shown in FIG. 1, wherein the average particle diameter, volume fraction of the nanometal phase inside the WC grain, and the mechanical properties of the hard alloy are shown in Table 1. Figure 3

[0035] Example 4

[0036] (1) using WO 2.9 ​, Co3O4 and carbon black as raw materials, according to the target product of Co mass percentage of 6% in the finally prepared WC-Co cemented carbide, the mass percentage of carbon black added in the raw materials is determined as 16.80%. The three kinds of raw materials are ball-mixed according to the mass ratio of 200:14.8:43.3, with anhydrous ethanol as the grinding medium, the mass ratio of powder to grinding ball is 1:5, the rotation speed of the ball mill is 550 r / min, and the ball milling time is 50 hours. The powder after ball mixing is cold-pressed into a compact which is sent into a vacuum furnace, and the following process is used for reaction synthesis: the heating rate is 20 ℃ / min, the temperature is raised to 780 ℃ and then kept for 3 hours, then the temperature is raised to 1000 ℃ at a heating rate of 10 ℃ / min, and kept for 1 hour, thus WC-Co-η (η is Co2W4C) composite powder is prepared. The composite powder is ground, the mass ratio of powder to grinding ball is 1:2, the rotation speed of the ball mill is 300 r / min, and the ball milling time is 10 hours, thus WC-Co-Co2W4C composite powder with an average particle diameter of 480 nm is obtained;

[0037] (2) The TaC powder is ball-milled to an average particle diameter of 80 nm using a planetary ball mill, and the ball milling process is as follows: inert gas Ar is filled into the ball milling tank as a protective gas, the mass ratio of TaC powder to hard alloy grinding ball is 1:60, the rotation speed of the ball mill is 500 r / min, a 300-mesh sieve is used to sieve the powder every 5 hours, and the total ball milling time is 35 hours;

[0038] (3) The WC-Co-Co2W4C composite powder obtained in step (1) and the TaC powder obtained in step (2) are ball-mixed with carbon black powder, wherein the mass of the TaC powder is 0.8% of the mass of the WC-Co-Co2W4C composite powder, and the mass of the carbon black powder is 0.08% of the mass of the WC-Co-Co2W4C composite powder. The ball-mixing process is as follows: anhydrous ethanol is used as the grinding medium, the mass ratio of powder to grinding ball is 1:3, the rotation speed of the ball mill is 550 r / min, and the ball milling time is 10 hours;

[0039] (4) The mixed powder obtained in step (3) is cold-pressed and then sintered and densified, a low-pressure sintering furnace is used, first the temperature is raised to 400 ℃ and kept for 1 hour; then the temperature is raised to 1000 ℃ at a heating rate of 25 ℃ / min, and kept for 1 hour; then the temperature is raised to 1330 ℃ at a heating rate of 10 ℃ / min, and kept for 1 hour; then the temperature is raised to 1430 ℃ at a heating rate of 5 ℃ / min, and kept for 2 hours, then 6 MPa argon is filled in, and kept for 2 hours; after the sintering is completed, the furnace is cooled to room temperature, thus a hard alloy bulk material with metal nano-phase generated in WC grains is prepared. The microstructure of the hard alloy prepared in this embodiment is as shown in Figure 4The average particle diameter, volume fraction of the nanometal phase inside the WC grains and the mechanical properties of the cemented carbide are shown in Table 1.

[0040] Comparative Example 1

[0041] (1) WC powder and Co powder were used as raw materials, and the two powders were mixed in a ball mill tank at a mass ratio of 180:20 to prepare a target product with a Co mass percentage of 10% in the finally prepared WC-Co cemented carbide. Anhydrous ethanol was used as the grinding medium, the mass ratio of powder to grinding ball was 1:3, the rotation speed of the ball mill was 550 r / min, and the ball milling time was 40 hours to obtain a mixed powder of WC and Co;

[0042] (2) The TaC powder was ball milled to an average particle diameter of 80 nm using a planetary ball mill. The ball milling process was as follows: inert gas Ar was filled into the ball mill tank as a protective gas, the mass ratio of TaC powder to hard alloy grinding ball was 1:60, the rotation speed of the ball mill was 500 r / min, a 300-mesh sieve was used to sieve the powder every 5 hours, and the total ball milling time was 35 hours;

[0043] (3) The mixed powder of WC and Co obtained in step (1) and the TaC powder obtained in step (2) were ball milled and mixed, wherein the mass of TaC powder was 0.8% of the mass of WC and Co mixed powder. The ball milling and mixing process was as follows: anhydrous ethanol was used as the grinding medium, the mass ratio of powder to grinding ball was 1:3, the rotation speed of the ball mill was 550 r / min, and the ball milling time was 10 hours;

[0044] (4) The mixed powder obtained in step (3) was cold pressed and then sintered and densified. A low-pressure sintering furnace was used. First, the temperature was raised to 350°C and kept for 1 hour. Then, the temperature was raised to 1000°C at a rate of 20°C / min and kept for 1 hour. Then, the temperature was raised to 1350°C at a rate of 10°C / min and kept for 0.5 hours. Subsequently, the temperature was raised to 1410°C at a rate of 5°C / min and kept for 2 hours. Then, 5 MPa of argon gas was filled and kept for 2 hours. After sintering, the furnace was cooled to room temperature. The microstructure of the cemented carbide prepared in this example is shown in Figure 5 , and the mechanical property data are shown in Table 1.

[0045] Comparative Example 2

[0046] (1) WO 2.9, Co3O4 and carbon black as raw materials, according to the target product of Co mass percentage of 10% in the finally prepared WC-Co cemented carbide, the mass percentage of carbon black added in the raw materials is determined as the theoretical carbon content of 16.87%. The three raw materials are ball-mixed in a mass ratio of 199.50:25.68:45.71, with anhydrous ethanol as the grinding medium, the mass ratio of powder to grinding ball is 1:3, the rotation speed of the ball mill is 550 r / min, and the ball milling time is 40 hours. The powder after ball mixing is cold-pressed into a compact which is sent into a vacuum furnace, and the following process is used for reaction synthesis: the heating rate is 20 ℃ / min, the temperature is raised to 780 ℃ and then kept for 2 hours, then the temperature is raised to 1000 ℃ at a heating rate of 10 ℃ / min, and kept for 1 hour to prepare the WC-Co composite powder without η phase. The composite powder is ground, the mass ratio of powder to grinding ball is 1:2, the rotation speed of the ball mill is 300 r / min, and the ball milling time is 5 hours, thus the WC-Co composite powder with an average particle diameter of 550 nm is obtained;

[0047] (2) The TaC powder is ball-milled to an average particle diameter of 80 nm using a planetary ball mill, and the ball milling process is as follows: inert gas Ar is filled into the ball milling tank as a protective gas, the mass ratio of TaC powder to hard alloy grinding ball is 1:60, the rotation speed of the ball mill is 500 r / min, 300-mesh sieve is used to sieve the powder every 5 hours, and the total ball milling time is 35 hours;

[0048] (3) The WC-Co composite powder obtained in step (1) and the TaC powder obtained in step (2) are ball-mixed, wherein the mass of the TaC powder is 0.8% of the mass of the WC-Co composite powder. The ball-mixing process is as follows: anhydrous ethanol is used as the grinding medium, the mass ratio of powder to grinding ball is 1:3, the rotation speed of the ball mill is 550 r / min, and the ball milling time is 10 hours;

[0049] (4) The mixed powder obtained in step (3) is cold-pressed and then sintered and densified, a low-pressure sintering furnace is used, first the temperature is raised to 350 ℃ and kept for 1 hour; then the temperature is raised to 1000 ℃ at a heating rate of 20 ℃ / min, and kept for 1 hour; then the temperature is raised to 1350 ℃ at a heating rate of 10 ℃ / min, and kept for 0.5 hour; then the temperature is raised to 1410 ℃ at a heating rate of 5 ℃ / min, and kept for 2 hours, then 5 MPa argon is filled, and kept for 2 hours; after the sintering is completed, the furnace is cooled to room temperature, and the hard alloy bulk material with metal nanophase in the WC grain is prepared. The mechanical property data of the prepared hard alloy in this example is shown in Table 1.

[0050] Table 1 Average particle diameter, volume fraction of nanometal phase in WC grain, and mechanical property data of the prepared hard alloy

[0051]

Claims

1. A method of introducing metal nanophases within the WC grains for synergistically strengthening and toughening cemented carbides, characterized in that, The method comprises the following steps: (1) WO 2.9 Co3O4 and carbon black as raw materials, according to the requirement that the mass percentage of Co in the finally prepared WC-Co cemented carbide is 6% to 12%, the mass percentage of added carbon black is determined to be 16.70% to 16.85%; the three kinds of raw materials are mixed by ball milling, with anhydrous ethanol as the grinding medium, the mass ratio of powder to grinding ball being 1:3 to 1:6, the rotation speed of the ball mill being 500 to 700 r / min, and the ball milling time being 30 to 60 hours; the powder after ball milling is cold-pressed into a compact which is sent into a vacuum furnace, and the following process is adopted for reaction synthesis: the heating rate is 20 ℃ / min, the temperature is raised to 780 ℃ and then kept for 2 to 3 hours, then the temperature is raised to 900 to 1100 ℃ at a heating rate of 10 ℃ / min, and kept for 1 to 2 hours, thereby obtaining WC-Co-η composite powder, wherein η is Co3W3C or Co2W4C or Co6W6C; the WC-Co-η composite powder is ground, the mass ratio of powder to grinding ball being 1:2 to 1:5, the rotation speed of the ball mill being 200 to 400 r / min, and the ball milling time being 5 to 10 hours, thereby obtaining WC-Co-η composite powder with an average particle diameter of 800 nm or less; wherein η is one of the three compounds Co3W3C or Co2W4C or Co6W6C. (2) using a planetary ball mill to ball mill the metal carbide powder to reduce the average particle diameter to below 100 nm, the ball milling process being: filling the ball mill jar with inert protective gas, the mass ratio of the metal carbide powder to the hard alloy grinding ball being 1:30-1:60, the rotation speed of the ball mill being 500-700 r / min, sieving the powder every 5-10 hours using a 300-mesh sieve, and the total ball milling time being 30-40 hours; (3) ball milling the WC-Co-η composite powder obtained in step (1) and the metal carbide powder obtained in step (2) with carbon black powder, wherein the mass of the metal carbide powder is 0.2%-1.0% of the mass of the WC-Co-η composite powder, and the mass of the carbon black powder is 0.05%-0.20% of the mass of the WC-Co-η composite powder; the ball milling process being: using anhydrous ethanol as the grinding medium, the mass ratio of the powder to the grinding ball being 1:3-1:5, the rotation speed of the ball mill being 500-700 r / min, and the ball milling time being 10-20 hours; (4) cold pressing the mixed powder obtained in step (3) and then sintering and densifying the same using a low-pressure sintering furnace, first heating to 300-400 ℃ and maintaining the temperature for 1-2 hours, then heating to 900-1100 ℃ at a heating rate of 20-30 ℃ / min, maintaining the temperature for 1-2 hours, then heating to 1320-1350 ℃ at a heating rate of 10-20 ℃ / min, maintaining the temperature for 0.5-1 hour, then heating to 1390-1430 ℃ at a heating rate of 5-10 ℃ / min, maintaining the temperature for 1-2 hours, then filling with 3-6 MPa nitrogen or argon, maintaining the temperature and pressure for 1-2 hours, and then cooling to room temperature in the furnace after the sintering is completed; finally, a hard alloy bulk material is prepared, in which metal nanophases with an average particle diameter of below 10 nm are generated in the WC grains.

2. The method of claim 1, wherein: The metal carbide powder refers to TaC or NbC or Cr3C2 or TiC.

3. The method of claim 1, wherein: The inert protective gas is nitrogen or argon. The inert protective gas is nitrogen or argon.

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