CN109778046B - Preparation method of low-cost high-performance WC-Co hard alloy with mixed crystal structure - Google Patents
Preparation method of low-cost high-performance WC-Co hard alloy with mixed crystal structure Download PDFInfo
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- 239000000956 alloy Substances 0.000 title claims abstract description 49
- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 47
- 239000013078 crystal Substances 0.000 title claims abstract description 44
- 229910009043 WC-Co Inorganic materials 0.000 title claims abstract description 27
- 238000002360 preparation method Methods 0.000 title claims abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 56
- 238000005245 sintering Methods 0.000 claims abstract description 44
- 230000008569 process Effects 0.000 claims abstract description 26
- 239000000843 powder Substances 0.000 claims abstract description 25
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 24
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 claims abstract description 22
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 21
- 239000000203 mixture Substances 0.000 claims abstract description 20
- 238000001354 calcination Methods 0.000 claims abstract description 19
- 239000011812 mixed powder Substances 0.000 claims abstract description 17
- 239000008367 deionised water Substances 0.000 claims abstract description 16
- 229910021641 deionized water Inorganic materials 0.000 claims abstract description 16
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 16
- 238000000498 ball milling Methods 0.000 claims abstract description 14
- 238000005238 degreasing Methods 0.000 claims abstract description 13
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims abstract description 11
- 238000002156 mixing Methods 0.000 claims abstract description 11
- 239000002994 raw material Substances 0.000 claims abstract description 9
- 238000000748 compression moulding Methods 0.000 claims abstract description 4
- 239000000463 material Substances 0.000 claims description 24
- 238000010438 heat treatment Methods 0.000 claims description 18
- 238000003825 pressing Methods 0.000 claims description 7
- 229910052760 oxygen Inorganic materials 0.000 claims description 6
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 5
- 239000007864 aqueous solution Substances 0.000 claims description 5
- 238000001816 cooling Methods 0.000 claims description 5
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 5
- 238000005452 bending Methods 0.000 abstract description 6
- 238000004519 manufacturing process Methods 0.000 abstract description 5
- 239000007789 gas Substances 0.000 description 17
- 239000012071 phase Substances 0.000 description 17
- 229910052799 carbon Inorganic materials 0.000 description 6
- 238000006722 reduction reaction Methods 0.000 description 5
- ZNOKGRXACCSDPY-UHFFFAOYSA-N tungsten(VI) oxide Inorganic materials O=[W](=O)=O ZNOKGRXACCSDPY-UHFFFAOYSA-N 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 3
- 230000002950 deficient Effects 0.000 description 3
- 239000007791 liquid phase Substances 0.000 description 3
- 150000001247 metal acetylides Chemical class 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 238000005054 agglomeration Methods 0.000 description 2
- 230000002776 aggregation Effects 0.000 description 2
- 230000002902 bimodal effect Effects 0.000 description 2
- 238000003763 carbonization Methods 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000005034 decoration Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 238000011065 in-situ storage Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 230000005501 phase interface Effects 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 1
- FFBHFFJDDLITSX-UHFFFAOYSA-N benzyl N-[2-hydroxy-4-(3-oxomorpholin-4-yl)phenyl]carbamate Chemical compound OC1=C(NC(=O)OCC2=CC=CC=C2)C=CC(=C1)N1CCOCC1=O FFBHFFJDDLITSX-UHFFFAOYSA-N 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- UBEWDCMIDFGDOO-UHFFFAOYSA-N cobalt(II,III) oxide Inorganic materials [O-2].[O-2].[O-2].[O-2].[Co+2].[Co+3].[Co+3] UBEWDCMIDFGDOO-UHFFFAOYSA-N 0.000 description 1
- 230000008094 contradictory effect Effects 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 238000009472 formulation Methods 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 239000013067 intermediate product Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 238000004663 powder metallurgy Methods 0.000 description 1
- 238000011946 reduction process Methods 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- UONOETXJSWQNOL-UHFFFAOYSA-N tungsten carbide Chemical compound [W+]#[C-] UONOETXJSWQNOL-UHFFFAOYSA-N 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
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Abstract
The invention discloses a preparation method of WC-Co hard alloy with a low-cost high-performance mixed crystal structure, which comprises the steps of preparing mixed powder by taking ammonium metatungstate, WC powder, graphite powder and cobalt powder as raw materials; adding deionized water; and performing ball milling and mixing on the mixture, adding a forming agent, performing compression molding, degreasing and calcining, and sintering to obtain the WC-Co hard alloy with the mixed crystal structure. The WC-Co hard alloy prepared by the method has high hardness, bending strength and fracture toughness, and has good comprehensive mechanical properties. The preparation method has the advantages of simple process, no special requirements on production equipment, low production cost and wide application prospect.
Description
Technical Field
The invention relates to a preparation method of low-cost high-performance WC-Co hard alloy with a mixed crystal structure, belonging to the technical field of powder metallurgy.
Background
The WC-Co hard alloy has a series of excellent characteristics of high hardness, good wear resistance, high red hardness, good chemical stability and the like, is widely used as a cutting tool, a geological mine tool, a die, a structural part, a wear-resistant part, a high-temperature resistant structural part and the like, and is known as a tooth in the modern industry. However, in cemented carbide materials, there is a contradictory relationship between hardness and toughness. Under the condition of the same Co content, when WC crystal grains of the material are finer, the hard alloy has higher hardness and better wear resistance, but the toughness is obviously lower and the brittleness is larger; when the WC crystal grains of the material are thicker, the toughness is better, but the hardness and the wear resistance are obviously reduced. However, with the appearance of difficult-to-machine materials and the increase of complex and severe working conditions, higher requirements are provided for the comprehensive mechanical properties of hard alloy materials, and obviously, the traditional hard alloy cannot meet the requirements, which restricts the development of the hard alloy industry.
To solve the contradiction between the hardness and the toughness of the hard alloy and prepare the comprehensive mechanical propertyExcellent hard alloy material, scientific research personnel provide mixed crystal structure hard alloy with hard phase grain size in bimodal distribution, and the advantages of coarse crystal hard alloy and fine crystal hard alloy can be integrated. Liu super et al (preparation and performance research of mixed crystal WC-8Co hard alloy, university of Central and south, 2014) prepares the mixed crystal structure hard alloy with the hard phase particle size in bimodal distribution by adding a certain proportion of coarse WC powder into fine WC powder, and improves the comprehensive mechanical properties of the material. However, the hardness of the coarse WC particles in the mixed crystal structure hard alloy is obviously reduced relative to that of the fine crystal hard alloy while the toughness is improved. Chinese patent CN102212731A discloses 'an industrial preparation method of a bicrystal hard alloy with high strength and high toughness', which uses WO2.9，Co3O4Firstly, preparing WC-Co mixed powder in a vacuum furnace by using carbon black as a raw material, then carrying out agglomeration pretreatment under the protection of argon, and finally carrying out compression molding and final liquid phase sintering on the powder subjected to the agglomeration pretreatment to prepare the hard alloy with the twin-crystal structure. However, the preparation method has complex process flow, complicated operation, easy introduction of impurities and large mechanical property fluctuation. Chinese patent CN 106756391A discloses 'a method for preparing WC-Co hard alloy with mixed crystal structure', which is based on in-situ carbothermic reduction of WO3The hard alloy with the mixed crystal structure is prepared, but because the carbon-deficient phase of the intermediate product is difficult to carbonize completely, a brittle third phase often exists in a final sintered body, the toughness of the material is reduced, and the performance fluctuation of the material is large.
In view of the above circumstances, in order to make WC — Co cemented carbide be better applied in more fields, further research on the material is necessary, and a new method for preparing WC — Co cemented carbide with a mixed crystal structure is developed, so that the WC — Co cemented carbide not only has higher hardness and strength, but also has higher fracture toughness, and is suitable for industrial production.
Disclosure of Invention
The invention aims to provide a preparation method of WC-Co hard alloy with a mixed crystal structure, which is low in cost and high in performance, so as to prepare WC-Co hard alloy with high hardness and strength and high fracture toughness, and is simple in process and low in manufacturing cost.
In order to achieve the purpose, the invention adopts the technical scheme that:
a preparation method of low-cost high-performance mixed crystal structure WC-Co hard alloy comprises the following steps:
step 1, preparing mixed powder by taking ammonium metatungstate, WC powder, graphite powder and cobalt powder as raw materials; the WC-Co hard alloy consists of the following elements in parts by mass: n is 0.58 to 0.61, H is 0.18 to 0.19, O is 4.41 to 4.68, W is 76.01 to 80.68, C is 7.78 to 8.35, and Co is 5.49 to 11.04; wherein N, H and O are introduced by ammonium metatungstate; part of W is introduced by ammonium metatungstate, and part of W is introduced by WC; part of C is introduced by graphite powder, and part of C is introduced by WC; co is introduced from cobalt powder;
step 2, adding deionized water into the mixed powder obtained in the step 1;
step 3, performing ball milling and mixing on the mixture obtained in the step 2, adding a forming agent, performing compression molding, degreasing and calcining, and sintering to obtain WC-Co hard alloy with a mixed crystal structure;
the sintering process is completed in a complete thermal cycle and comprises the following four stages:
(1) firstly, continuously heating the degreased and calcined pressed blank to 800 ℃ at a speed of 0.4-0.8 ℃/min;
(2) then heating to 1180-1220 ℃ at the speed of 4 ℃/min, and preserving the heat for 90-150 min at the temperature;
(3) then heating to 1380-1420 ℃ at the speed of 3 ℃/min, carrying out vacuum sintering for 20min, and then introducing CH4Mixing the obtained product with Ar mixed gas, keeping the pressure at 500-1000 Pa, and keeping the temperature for 20-60 min;
(4) then the temperature is reduced to 1300 ℃ at the speed of 3 ℃/min, and CH is introduced4Mixing with Ar mixed gas, keeping the pressure at 500-1000 Pa for 20-60 min, and then cooling along with the furnace;
in the above sintering process, except for the gas-permeable sintering stage, the rest of temperature raising and sintering stages are all performed at vacuum degree higher than 1.0 × 10-1Pa, and the like.
According to a preferable technical scheme, in the step 1, the granularity of WC powder is 0.5-0.8 μm, the granularity of graphite powder is 3-4 μm, and the granularity of cobalt powder is 1-2 μm.
In the degreasing and calcining process, under the condition that the forming agent is completely removed, the ammonium metatungstate is also completely decomposed into WO3 through calcination, therefore, as a preferred technical scheme, in the step 1, after the added C completely removes O in the system and generates WC through carbonization, the residual total C content in the sintered body is also between (6.13% -0.085 multiplied by Co%) and (6.13% -0.080 multiplied by Co%) so as to ensure that the microstructure of the alloy obtained after final sintering is in a normal two-phase region and a residual graphite phase or a harmful brittle η phase cannot appear, wherein the Co% is the mass fraction of Co in the corresponding component system.
As a preferred technical scheme, in the step 2, the weight ratio of the deionized water to the mixed powder is 1:1 to 2.
In the step 3, the ball milling and mixing process is carried out in a roller ball mill with the rotation speed of 30-50 rpm, the ball-to-material ratio of 5:1 and the ball milling time of 36-48 h.
As a preferable technical scheme, in the step 3, the forming agent is a polyvinyl alcohol aqueous solution with a concentration of 7 wt.%, and the adding proportion is 4-6 wt% of the mixture.
Preferably, in the step 3, the pressure applied in the press molding process is 120 to 180 MPa.
Preferably, in the step 3, the degreasing and calcining step is performed in a vacuum/atmosphere furnace with a vacuum degree higher than 10Pa, and the temperature is slowly raised from room temperature to 600 ℃, wherein the temperature raising rate is 0.2-0.4 ℃/min between 200-600 ℃.
Preferably, in step 3, the CH is charged in the (3) th stage of the sintering process4And CH in Ar mixed gas4Volume ratio to Ar 1: 1-2, and adopting a pendulum type inflation method, wherein the pendulum type period is 20 min;
as a preferred technical scheme, in the step 3, the (4) th stage of the sintering process is filled with the powderIn CH4And CH in Ar mixed gas4Volume ratio to Ar 1: 1-2, and a pendulum type inflation method is adopted, wherein the pendulum type period is 20 min.
The principle of the invention is as follows:
oxygen has been regarded as a harmful impurity in cemented carbide, and since it increases the wetting angle between the hard phase and the binder phase during liquid phase sintering, decreases the wettability thereof, and thus deteriorates the texture and properties of the material, the oxygen content in the powder is currently reduced as much as possible when cemented carbide is produced. Although a large amount of O is introduced while part of W is introduced in the form of ammonium metatungstate, the ammonium metatungstate can be completely decomposed into WO while degreasing is carried out at 200-600 ℃ by reasonably controlling the process3And the corresponding content of graphite powder is introduced and the sintering process is controlled to ensure that O reacts at the temperature of 600-800 ℃ through WO3+3C → W +3CO is completely removed, and WO is added3Reducing the product into W in situ. At this time, the sintered body is still in the early solid phase sintering stage, the relative density is low, the pores are in an open pore state, and the gas generated by the reaction can smoothly escape under the vacuum condition. In the subsequent sintering stage, as the temperature continues to rise, the reduced W powder continues to react with the remaining graphite powder and Co powder in the following order: xW + yC + zCo → CoxWyCz，CoxWyCz+C→WC+Co，CoxWyCzThe phases form twins during reaction with carbon, forming plate-like coarse WC grains. On one hand, the plate-shaped coarse WC crystal grains enable the crack propagation path of the material to deflect when the material bears external load, so that the fracture toughness of the material is effectively improved. On the other hand, WC crystal grains are of a close-packed hexagonal system, and the (0001) basal plane hardness thereof is close to that of the system
2 times the cylinder hardness. Since the plate-like WC crystal grains preferentially grow along the (0001) basal plane, the proportion of the (0001) basal plane increases, and therefore a large number of plate-like coarse WC crystal grainsIs beneficial to improving the hardness of the material. And the reducing gas CO released in the carbothermic reduction process can thoroughly remove the adsorbed oxygen on the surfaces of other original powder WC powder and Co powder, purify the interface between a ceramic phase and a metal bonding phase, and enhance the bonding strength of the phase interface, thereby achieving the purpose of improving the obdurability of the ceramic phase.
The invention has the following characteristics: deionized water is used as a ball milling medium, and ammonium metatungstate can be dissolved in the deionized water to form a stable solution, so that the distribution uniformity of the ammonium metatungstate in the mixture is improved, and on the other hand, the deionized water is used for replacing alcohol, so that the cost can be saved, and the environment is protected. Degreasing and calcining are carried out in a vacuum/atmosphere integrated furnace with the vacuum degree higher than 10Pa, the temperature of a pressed blank is raised to 600 ℃ at the speed of 0.2-0.4 ℃/min, and the aim is to calcine and completely decompose ammonium metatungstate into WO while degreasing3. Sintering is carried out in a vacuum/atmosphere integrated furnace, comprising four stages: firstly, continuously heating the degreased and calcined pressed blank to 800 ℃ at a speed of 0.4-0.8 ℃/min, so as to perform a carbothermic reduction reaction, fully removing oxygen contained in tungsten trioxide, and enabling generated gas to smoothly escape from a sintered body through an opening; then heating to 1180-1220 ℃ at the speed of 4 ℃/min, and preserving heat for 90-150 min at the temperature, so as to further completely carbonize the tungsten powder obtained by carbothermic reduction into tungsten carbide; then heating to a final sintering temperature of 1380-1420 ℃ at the speed of 3 ℃/min, preserving heat for 20min to perform final liquid phase sintering and obtain a compact mixed crystal structure sintered body, and then filling CH4Mixing the obtained product with Ar mixed gas, keeping the pressure at 500-1000 Pa, and keeping the temperature for 20-60 min; finally, the temperature is reduced to 1300 ℃ at the speed of 3 ℃/min, and CH is introduced into the temperature4And Ar mixed gas, the pressure is 500-1000 Pa, the temperature is kept for 20-60 min, and then the mixture is cooled along with the furnace. Filling CH in two stages after sintering4The purpose of the Ar mixed gas is to ensure that carbon-deficient phases possibly remaining in the hard alloy react with carbon to form twin crystals and further form tabular WC crystal grains, thereby ensuring that harmful carbon-deficient phases do not exist in a final sintered body and improving the mechanical property and the performance stability of the hard alloy.
The invention has the beneficial effects that:
(1) according to the mixed crystal structure WC-Co hard alloy provided by the invention, the plate-shaped coarse WC crystal grains can effectively improve the toughness of the material and also can improve the hardness of the material, and the fine WC crystal grains can ensure the hardness and the bending strength of the material. Therefore, the material has higher comprehensive mechanical property.
(2) According to the invention, the ammonium metatungstate with low price is used as a main raw material, and the deionized water is used as a ball milling medium instead of alcohol, so that on one hand, the ammonium metatungstate can be dissolved in the deionized water to form a stable solution, thereby improving the distribution uniformity of the ammonium metatungstate in a mixture, and on the other hand, the ammonium metatungstate is cost-saving and environment-friendly.
(3) Completely generating WO after calcination and decomposition of ammonium metatungstate3And the carbon thermal reduction reaction is further carried out on the graphite powder to generate reducing gas CO, so that the interface between a WC hard phase and a Co binding phase can be purified, the binding strength of the phase interface is enhanced, and the toughness of the material is favorably improved.
(4) The invention has simple process and complete process in a complete thermal cycle, and can obviously save energy consumption, reduce production cost and improve productivity.
(5) The invention has no special requirements on production equipment, only needs conventional equipment, and is beneficial to industrial popularization and application.
Detailed Description
The present invention will be further explained with reference to examples.
The present invention will be better understood from the following examples. However, those skilled in the art will readily appreciate that the specific material ratios, process conditions and results thereof described in the examples are illustrative only and should not be taken as limiting the invention as detailed in the claims.
The raw materials used in the following examples were WC powder, ammonium metatungstate, Co powder and graphite powder.
Table 1 is a blend of 4 ingredient formulations used in the examples below. 3 different process parameters in the examples 1-3 are adopted to prepare the mixed crystal structure hard alloy, and the bending strength, the hardness and the palmqvist fracture toughness of the mixed crystal structure hard alloy are respectively measured.
TABLE 1 mixing of the components in the four cases
| Composition (I) | N | H | O | W | C | Co |
| 1# | 0.61 | 0.19 | 4.68 | 80.68 | 8.35 | 5.49 |
| 2# | 0.60 | 0.19 | 4.59 | 79.13 | 8.16 | 7.33 |
| 3# | 0.59 | 0.18 | 4.50 | 77.58 | 7.97 | 9.18 |
| 4# | 0.58 | 0.18 | 4.41 | 76.01 | 7.78 | 11.04 |
Wherein, the proportion of each element in parts by mass is shown in table 1.
Example 1:
(1) preparing 4 kinds of mixed powder according to the table 1, wherein the used raw materials are ammonium metatungstate, WC powder, graphite powder and Co powder, the granularity of the WC powder is 0.5-0.8 mu m, the granularity of the graphite powder is 3-4 mu m, and the granularity of the cobalt powder is 1-2 mu m;
(2) adding deionized water into the mixed powder, wherein the weight ratio of the deionized water to the mixed powder is 1: 1;
(3) placing the mixture obtained in the step (2) into a roller ball mill for ball milling at the rotating speed of 30rpm, the ball-to-material ratio of 5:1 and the ball milling time of 48 h;
(4) adding a forming agent, wherein the forming agent is a polyvinyl alcohol aqueous solution with the concentration of 7 wt.%, and the adding amount of the forming agent is 4 wt% of the mixture;
(5) pressing and forming, wherein the pressure for pressing and forming is 120 MPa;
(6) removing the forming agent and calcining, wherein the removing of the forming agent and the calcining are carried out in a vacuum/atmosphere integrated furnace, the vacuum degree is higher than 10Pa, the temperature is slowly increased from room temperature to 600 ℃, degreasing and calcining are carried out, and the temperature increase speed is 0.2 ℃/min between 200 ℃ and 600 ℃;
(7) sintering is carried out in a vacuum/atmosphere integrated furnace. Firstly, the degreased and calcined pressed compactContinuously heating to 800 ℃ at the speed of 0.4 ℃/min; then heating to 1180 ℃ at the speed of 4 ℃/min, and preserving the heat for 150min at the temperature; then heating to 1380 ℃ at the speed of 3 ℃/min, vacuum sintering for 20min, and then introducing CH4And Ar mixed gas with the volume ratio of 1:1 and the pressure of 500Pa, and keeping the temperature for 20 min; then the temperature is reduced to 1300 ℃ at the speed of 3 ℃/min, and CH is introduced into the temperature4And Ar mixed gas with the volume ratio of 1:1 and the pressure of 1000Pa, preserving the heat for 60min, and then cooling along with the furnace. In the above sintering process, except for the stage of gas-permeable sintering, the rest of temperature raising and sintering stages are all performed at vacuum degree higher than 1.0 × 10-1Pa, and the like.
The mechanical properties of the cemented carbide with different component ratios under the above preparation process conditions are shown in table 2.
TABLE 2 mechanical Properties of different cemented carbides prepared by Process 1
| Composition (I) | 1# | 2# | 3# | 4# |
| Bending strength sigmab(MPa) | 2369 | 2574 | 2662 | 2866 |
| Hardness (HRA) | 91.3 | 90.6 | 89.7 | 88.3 |
| Fracture toughness (MPa. m)1/2) | 14.6 | 16.7 | 20.4 | 24.3 |
Example 2:
(1) preparing 4 kinds of mixed powder according to the table 1, wherein the used raw materials are ammonium metatungstate, WC powder, graphite powder and Co powder, the granularity of the WC powder is 0.5-0.8 mu m, the granularity of the graphite powder is 3-4 mu m, and the granularity of the cobalt powder is 1-2 mu m;
(2) adding deionized water into the mixed powder, wherein the weight ratio of the deionized water to the mixed powder is 1: 1.5;
(3) placing the mixture obtained in the step (2) into a roller ball mill for ball milling at the rotating speed of 40rpm, the ball-to-material ratio of 5:1 and the ball milling time of 42 h;
(4) adding a forming agent, wherein the forming agent is a polyvinyl alcohol aqueous solution with the concentration of 7 wt.%, and the adding amount of the forming agent is 5 wt% of the mixture;
(5) pressing and forming, wherein the pressure for pressing and forming is 150 MPa;
(6) removing the forming agent and calcining, wherein the removing of the forming agent and the calcining are carried out in a vacuum/atmosphere integrated furnace, the vacuum degree is higher than 10Pa, the temperature is slowly increased from room temperature to 600 ℃, degreasing and calcining are carried out, and the temperature increase speed is 0.3 ℃/min between 200 ℃ and 600 ℃;
(7) sintering is carried out in a vacuum/atmosphere integrated furnace. Firstly, continuously heating the degreased and calcined pressed blank to 800 ℃ at the speed of 0.6 ℃/min; then heating to 1200 ℃ at the speed of 4 ℃/min, and preserving the heat for 120min at the temperature; then heating to 1400 ℃ at the speed of 3 ℃/min, sintering in vacuum for 20min, and then introducing CH4And Ar mixed gas with the volume ratio of 1:1.5 and the pressure of 800Pa, and keeping the temperature for 40 min; then the temperature is reduced to 1300 ℃ at the speed of 3 ℃/min, and CH is introduced into the temperature4And Ar mixed gas with the volume ratio of 1:1.5 and the pressure of 800Pa, preserving the heat for 40min, and then cooling along with the furnace. In the above sintering process, except for the stage of gas-permeable sintering, the rest of temperature raising and sintering stages are all performed at vacuum degree higher than 1.0 × 10-1Pa, and the like.
The mechanical properties of the cemented carbide with different component ratios under the above preparation process conditions are shown in table 3.
TABLE 3 mechanical Properties of different cemented carbides prepared by Process 2
| Composition (I) | 1# | 2# | 3# | 4# |
| Bending strength sigmab(MPa) | 2456 | 2578 | 2703 | 2857 |
| Hardness (HRA) | 91.1 | 90.4 | 89.4 | 88.1 |
| Fracture toughness (MPa. m)1/2) | 14.4 | 17.3 | 21.6 | 25.3 |
Example 3:
(1) preparing 4 kinds of mixed powder according to the table 1, wherein the used raw materials are ammonium metatungstate, WC powder, graphite powder and Co powder, the granularity of the WC powder is 0.5-0.8 mu m, the granularity of the graphite powder is 3-4 mu m, and the granularity of the cobalt powder is 1-2 mu m;
(2) adding deionized water into the mixed powder, wherein the weight ratio of the deionized water to the mixed powder is 1: 2;
(3) and (3) placing the mixture obtained in the step (2) into a roller ball mill for ball milling at the rotating speed of 50rpm and the ball-material ratio of 5:1 for 36 h.
(4) Adding a forming agent, wherein the forming agent is a polyvinyl alcohol aqueous solution with the concentration of 7 wt.%, and the adding amount of the forming agent is 6 wt% of the mixture;
(5) pressing and forming, wherein the pressure for pressing and forming is 180 MPa;
(6) removing the forming agent and calcining, wherein the removing of the forming agent and the calcining are carried out in a vacuum/atmosphere integrated furnace, the vacuum degree is higher than 10Pa, the temperature is slowly increased from room temperature to 600 ℃, degreasing and calcining are carried out, and the temperature increase speed is 0.4 ℃/min between 200 ℃ and 600 ℃;
(7) sintering is carried out in a vacuum/atmosphere integrated furnace. Firstly, continuously heating the degreased and calcined pressed blank to 800 ℃ at the speed of 0.8 ℃/min; then heating to 1220 ℃ at the speed of 4 ℃/min, and preserving the temperature for 90 min; then heating to 1420 deg.C at 3 deg.C/min, vacuum sintering for 20min, and introducing CH4And Ar mixed gas with the volume ratio of 1:2 and the pressure of 1000Pa, and keeping the temperature for 60 min; then the temperature is reduced to 1300 ℃ at the speed of 3 ℃/min, and CH is introduced into the temperature4And Ar mixed gas in a volume ratio of1:2, keeping the pressure at 500Pa, preserving the heat for 20min, and then cooling along with the furnace. In the above sintering process, except for the stage of gas-permeable sintering, the rest of temperature raising and sintering stages are all performed at vacuum degree higher than 1.0 × 10-1Pa, and the like.
The mechanical properties of the cemented carbide with different component ratios under the above preparation process conditions are shown in table 4.
TABLE 4 mechanical Properties of different cemented carbides prepared by Process 3
| Composition (I) | 1# | 2# | 3# | 4# |
| Bending strength sigmab(MPa) | 2412 | 2558 | 2673 | 2862 |
| Hardness (HRA) | 91.2 | 90.5 | 89.5 | 88.2 |
| Fracture toughness (MPa. m)1/2) | 15.0 | 16.9 | 21.7 | 26.5 |
Within the value range of the invention, the technological parameters of the first two stages of the sintering process have relatively large influence on the mechanical properties, and the hard alloy with the formula of each component can obtain relatively good comprehensive mechanical properties only when the carbothermic reduction and carbonization processes of the stage are completely carried out. In summary, within the value range of the present invention, there is a limited impact on the properties of the cemented carbide.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A preparation method of WC-Co hard alloy with a low-cost high-performance mixed crystal structure is characterized by comprising the following steps: the method comprises the following steps:
step 1, preparing mixed powder by taking ammonium metatungstate, WC powder, graphite powder and cobalt powder as raw materials; the WC-Co hard alloy consists of the following elements in parts by mass: n is 0.58 to 0.61, H is 0.18 to 0.19, O is 4.41 to 4.68, W is 76.01 to 80.68, C is 7.78 to 8.35, and Co is 5.49 to 11.04; wherein N, H and O are introduced by ammonium metatungstate; part of W is introduced by ammonium metatungstate, and part of W is introduced by WC; part of C is introduced by graphite powder, and part of C is introduced by WC; co is introduced from cobalt powder;
step 2, adding deionized water into the mixed powder obtained in the step 1;
step 3, performing ball milling and mixing on the mixture obtained in the step 2, adding a forming agent, performing compression molding, degreasing and calcining, and sintering to obtain WC-Co hard alloy with a mixed crystal structure;
the sintering process is completed in a complete thermal cycle and comprises the following four stages:
(1) firstly, continuously heating the degreased and calcined pressed blank to 800 ℃ at a speed of 0.4-0.8 ℃/min;
(2) then heating to 1180-1220 ℃ at the speed of 4 ℃/min, and preserving the heat for 90-150 min at the temperature;
(3) then heating to 1380-1420 ℃ at the speed of 3 ℃/min, carrying out vacuum sintering for 20min, and then introducing CH4Mixing the obtained product with Ar mixed gas, keeping the pressure at 500-1000 Pa, and keeping the temperature for 20-60 min;
(4) then the temperature is reduced to 1300 ℃ at the speed of 3 ℃/min, and CH is introduced4Mixing with Ar mixed gas, keeping the pressure at 500-1000 Pa for 20-60 min, and then cooling along with the furnace;
in the above sintering process, except for the gas-permeable sintering stage, the rest of temperature raising and sintering stages are all performed at vacuum degree higher than 1.0 × 10-1Pa, and the like.
2. The method for preparing the WC-Co hard alloy with the low cost and the high performance mixed crystal structure according to claim 1, wherein the method comprises the following steps: in the step 1, the granularity of WC powder is 0.5-0.8 μm, the granularity of graphite powder is 3-4 μm, and the granularity of cobalt powder is 1-2 μm.
3. The method for preparing the WC-Co hard alloy with the low cost and the high performance mixed crystal structure according to claim 1, wherein the method comprises the following steps: in the step 1, after the added C is completely removed of O in the system and carbonized to generate WC, the content of the remaining total C in the sintered body is between (6.13% -0.085 multiplied by Co%) and (6.13% -0.080 multiplied by Co%) so as to ensure that the microstructure of the alloy obtained after final sintering is in a normal two-phase region, wherein Co% is the mass fraction of Co in the corresponding component system.
4. The method for preparing the WC-Co hard alloy with the low cost and the high performance mixed crystal structure according to claim 1, wherein the method comprises the following steps: in the step 2, the weight ratio of the deionized water to the mixed powder is 1:1 to 2.
5. The method for preparing the WC-Co hard alloy with the low cost and the high performance mixed crystal structure according to claim 1, wherein the method comprises the following steps: in the step 3, the ball milling and mixing process is carried out in a roller ball mill with the rotating speed of 30-50 rpm, the ball-material ratio of 5:1 and the ball milling time of 36-48 h.
6. The method for preparing the WC-Co hard alloy with the low cost and the high performance mixed crystal structure according to claim 1, wherein the method comprises the following steps: in the step 3, the forming agent is a polyvinyl alcohol aqueous solution with the concentration of 7 wt.%, and the adding proportion is 4-6 wt% of the mixture.
7. The method for preparing the WC-Co hard alloy with the low cost and the high performance mixed crystal structure according to claim 1, wherein the method comprises the following steps: in the step 3, the pressure applied in the pressing and forming process is 120-180 MPa.
8. The method for preparing the WC-Co hard alloy with the low cost and the high performance mixed crystal structure according to claim 1, wherein the method comprises the following steps: in the step 3, the degreasing and calcining processes are carried out in a vacuum/atmosphere integrated furnace with the vacuum degree higher than 10Pa, the temperature is raised from room temperature to 600 ℃, and degreasing and calcining are carried out, wherein the temperature raising speed is 0.2-0.4 ℃/min between 200 ℃ and 600 ℃.
9. The method for preparing the WC-Co hard alloy with the low cost and the high performance mixed crystal structure according to claim 1, wherein the method comprises the following steps: in the step 3, CH is charged in the (3) stage of the sintering process4And CH in Ar mixed gas4Volume ratio to Ar 1: 1-2, and a pendulum type inflation method is adopted, wherein the pendulum type period is 20 min.
10. The method for preparing the WC-Co hard alloy with the low cost and the high performance mixed crystal structure according to claim 1, wherein the method comprises the following steps: in the step 3, CH is charged in the (4) th stage of the sintering process4And CH in Ar mixed gas4Volume ratio to Ar 1: 1-2, and a pendulum type inflation method is adopted, wherein the pendulum type period is 20 min.
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