CN109175387B - Method for preparing nanocrystalline WC-Co hard alloy by amorphous crystallization - Google Patents
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- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 68
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- 238000000034 method Methods 0.000 title claims abstract description 29
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- 239000000463 material Substances 0.000 claims abstract description 17
- 150000001875 compounds Chemical class 0.000 claims abstract description 15
- 238000000280 densification Methods 0.000 claims abstract description 10
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- 239000002131 composite material Substances 0.000 claims abstract description 4
- 239000002159 nanocrystal Substances 0.000 claims abstract description 3
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- 238000004321 preservation Methods 0.000 claims description 8
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- 230000001681 protective effect Effects 0.000 claims description 7
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical group CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 6
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Abstract
A method for preparing nanocrystalline WC-Co hard alloy by amorphous crystallization belongs to the field of hard alloy material preparation. Firstly, ternary compound Co is prepared6W6C powder is subjected to high-energy ball milling to obtain amorphous Co6W6C powder, then under the condition of spark plasma sintering making amorphous Co6W6And C, performing crystallization reaction on the powder C to generate nano polycrystalline WC-Co two-phase composite powder in one step, and further performing sintering densification to obtain the compact WC-Co hard alloy block material with a nano crystal structure. The method can ensure amorphous Co6W6The C powder is completely crystallized and fully reacted to obtain pure WC and Co, and meanwhile, obvious grain growth does not occur, so that the average grain size of WC in the block body is kept in a nanometer scale.
Description
Technical Field
The invention belongs to the field of hard alloy material preparation, and particularly relates to a method for preparing a nanocrystalline WC-Co hard alloy block material by using a ternary compound as a precursor.
Background
WC-Co hard alloy is widely applied to the industrial fields of cutting tools, dies, mining tools, wear-resistant parts and the like due to the unique properties of high hardness, wear resistance, high bending strength, good fracture toughness and the like. When the WC grain size is refined to superfine or even nanometer size, the hard alloy can have higher hardness and strength. The traditional method is to add refractory metal carbide (VC, Cr) into WC-Co powder3C2NbC, etc.) as grain growth inhibitor, controlling grain coarsening in the sintering process so as to obtain the hard alloy block material with nano grain structure. However, because of the difficulty in solving the contradiction between the control of grain growth and the achievement of sintering compactness close to theoretical density, the average WC grain size of the existing hard alloy block materials prepared at home and abroad is mostly in submicron scale, and few nanocrystalline hard alloy blocks in the true sense that the average WC grain size is reduced to below 100nmThe research of the bulk material is reported.
The amorphous crystallization method is an effective method for preparing metal or alloy with nanocrystalline structure in the field of metal materials. However, this method has never been applied in the field of ceramic materials or ceramic matrix composite materials, and the fundamental reason is that the preparation of ceramic matrix amorphous precursor materials is extremely difficult. Therefore, no report of preparing the nanocrystalline hard alloy by an amorphous crystallization mode is available at home and abroad. In order to break through the international technical problem, the invention selects a special ternary compound as an indirect precursor, firstly prepares an amorphous structure, and then obtains the WC-Co composite material block with the nanocrystalline structure through the processes of synchronously generating amorphous crystallization and in-situ reaction.
Disclosure of Invention
The invention firstly prepares ternary compound Co in batches6W6C powder, preferably using the technology of the patent granted by the applicant (granted patent No. CN 201510491451.4); co to be prepared6W6C powder is ball milled by high energy to obtain amorphous Co6W6C powder, then making use of the unique condition of spark plasma sintering to make amorphous Co6W6And C, synchronously performing crystallization reaction on the powder to generate nano polycrystalline WC-Co composite powder, and further performing sintering densification to obtain the compact WC-Co hard alloy block material with a nano crystal structure. The invention is characterized by comprising the following steps:
(1) preparing ternary compound Co with average grain diameter not more than 500nm in batch6W6C powder (the technology of the patent granted by the applicant (the granted patent number: CN201510491451.4)) is taken as a raw material and added into a hard alloy ball milling tank together with hard alloy balls, four kinds of hard alloy grinding balls with the diameters of 4mm, 5mm, 8mm and 10mm are respectively filled into each tank, the mass ratio of the four kinds of hard alloy grinding balls is 2:2:4:2, argon is taken as protective atmosphere, and the hard alloy grinding balls and a ternary compound Co are mixed according to the proportion of 2:2:4:26W6The weight ratio of C is (18-25): 1, ball milling time is 55-70 hours, ball milling rotating speed is 500-600 r/min, and amorphous Co is obtained after ball milling6W6C, powder;
(2) for the prepared amorphous Co6W6C powder is subjected to carbon content detection, and the carbon content and the reactive Co are combined6W6Adding corresponding carbon black into C + 5C-6 WC +6Co to ensure that the content of carbon element in the mixed powder is 6.00-6.90 wt%;
(3) adding the mixed powder obtained in the step (2) and a hard alloy grinding ball with the diameter of 8mm into a hard alloy ball milling tank, wherein the ball milling medium is absolute ethyl alcohol, and the weight ratio of the hard alloy grinding ball to the mixed powder is (3-5): 1, ball milling for 10-15 hours at a ball milling speed of 250-300 r/min to obtain mixed powder with uniformly dispersed carbon powder;
(4) and (3) drying the mixed powder obtained in the step (3), putting a certain amount of the dried mixed powder into a hot-pressing mold for prepressing at the pressure of 1-2 MPa, then putting the mold filled with the mixed powder into a discharge plasma sintering system for crystallization reaction and sintering densification, wherein the pressure is 30-40 MPa, the heating rate is 100-140 ℃/min, the temperature is 870-1000 ℃/min, and the heat preservation time is 2-5 min, and finally obtaining the compact WC-Co hard alloy block material with pure phase and average grain size smaller than 100 nm. The invention has the technical advantages and effects that:
(1) the ball milling mode and action in the step (1) are different from the conventional wet milling mode in the preparation of hard alloy, and the method does not add any ball milling medium, adopts argon as protective atmosphere and simultaneously adopts higher ball-to-material ratio. The argon gas is used as the protective atmosphere in the dry milling process, so that the oxidation of the powder in the ball milling process can be effectively prevented. The balls with smaller diameters in the grinding balls can ensure that the powder can be fully ball-milled, and the balls with larger diameters provide larger impact energy in the ball-milling process. Grinding balls with different diameters are matched for use, and the high ball-to-material ratio is combined, so that Co can be ensured6W6The C powder obtains high enough energy in the ball milling process, so that a large number of crystal defects are generated in a polycrystal, and finally, the lattice is caused to collapse, and the powder in an amorphous structure state is obtained.
(2) The phase purity of the WC-Co hard alloy block material is very sensitive to the carbon content, the optimal carbon addition amount adopted in the method is obtained through massive calculation analysis and experimental exploration, firstly, the stoichiometric ratio required by the generation of a pure phase is ensured to be met, and secondly, the initial carbon addition amount is accurately adjusted by combining the influence of various parameter combinations of a ball milling process and a discharge plasma sintering process on the change of the combined carbon content, the carbon distribution and the like. And (3) comprehensively considering and combining the carbon content in the powder detected in the step (2) to match carbon, so that the finally prepared cemented carbide sintered block has no other impurity phases except WC and Co, and no redundant free carbon exists in reaction products.
(3) In the step (3), absolute ethyl alcohol is used as a ball milling medium, carbon powder is added for wet milling, which is beneficial to the dispersion and the elimination of agglomeration of the powder, and is beneficial to the lubrication of the carbon powder6W6And C, fully mixing the powder C and the carbon powder. The step is also characterized in that the weight ratio of the grinding balls to the powder is low, and the ball milling time is short. The process aims to achieve uniform mixing, avoids phase change of amorphous powder caused by high-energy ball milling, and ensures smooth subsequent sintering process.
(4) In the step (4), the amorphous powder is crystallized by using the unique advantages of the spark plasma sintering technology, and is synthesized and sintered and densified along with reaction, which is different from the processes of vacuum reaction, vacuum sintering or low-pressure sintering and densification and the like. In this step, amorphous Co6W6And C, synchronously performing crystallization and reaction to generate nanocrystalline WC and Co biphase, and then performing sintering densification to obtain the nanocrystalline WC-Co hard alloy block material.
(5) The determination of the technological parameters in the discharge plasma sintering process needs to combine raw material components, reaction heat preservation temperature and the like to determine the heating rate and the heat preservation time so as to obtain the WC-Co bulk material which has sufficient reaction, pure phase and no obvious growth of crystal grains. Excessive pressure is not favorable for crystallization and reaction processes, and excessive temperature and excessive heat preservation time can cause large grain size. The optimal determination of the process parameter combination in the spark plasma sintering process in the method is obtained by a large number of experimental searches and trials, and can ensure that the amorphous Co6W6The C powder is completely crystallized, pure WC and Co are obtained from reaction components, and simultaneously, no obvious grain growth occurs to ensure that W in the block bodyThe average grain size of C is kept in a nanometer scale, and the average grain size of WC of the invention is reduced to be below 100 nm.
Drawings
In FIG. 1, (a) is Co6W6An X-ray diffraction pattern of the initial state of the powder C, (b) is the amorphous Co prepared in example 16W6X-ray diffraction pattern of C powder, (C) amorphous Co prepared in example 26W6X-ray diffraction pattern of C powder.
FIG. 2(a) shows the amorphous Co prepared in example 16W6The microscopic morphology of the powder C by scanning electron microscope, and (b) the amorphous Co prepared in example 26W6And C, the scanning electron microscope microscopic morphology of the powder.
Figure 3 is an X-ray diffraction pattern of the nanocrystalline WC-Co cemented carbide mass prepared in example 2.
Fig. 4(a) is a nano-indentation measurement of hardness for the nanocrystalline WC-Co cemented carbide bulk prepared in example 2, and (b) is a nano-indentation measurement of elastic modulus for the nanocrystalline WC-Co cemented carbide bulk prepared in example 2.
Fig. 5(a) shows the nano-indentation measurement of hardness of the nanocrystalline WC-Co cemented carbide bulk prepared in example 3, and (b) shows the nano-indentation measurement of elastic modulus of the nanocrystalline WC-Co cemented carbide bulk prepared in example 3.
Detailed Description
The present invention will be further illustrated with reference to the following examples, but the present invention is not limited to the following examples.
Example 1
The ternary compound Co with the average grain diameter of about 300nm is prepared in batches by the prior patented technology (granted patent number: CN201510491451.4) of the applicant6W6C powder is taken as a raw material and is added into a hard alloy ball milling tank together with hard alloy balls, four hard alloy grinding balls with the diameters of 4mm, 5mm, 8mm and 10mm are respectively filled into each tank, the mass ratio of the four hard alloy grinding balls to the hard alloy grinding balls is 2:2:4:2, argon is taken as protective atmosphere, and the hard alloy grinding balls and a ternary compound Co are mixed6W6The weight ratio of C is 18: 1, the ball milling time is 70 hours, and the ball milling rotating speed is 600r/min, obtaining amorphous Co after ball milling6W6C, powder; for the prepared amorphous Co6W6C powder is subjected to carbon content detection, the carbon content is measured to be 1.10 wt.%, and the carbon content is measured according to a reaction formula Co6W6C +5C ═ 6WC +6Co add the corresponding carbon black 4.90 wt.%, so that the carbon content in the mixed powder is 6.00%; adding the obtained mixed powder and a hard alloy grinding ball with the diameter of 8mm into a hard alloy ball milling tank, wherein the ball milling medium is absolute ethyl alcohol, and the weight ratio of the hard alloy grinding ball to the mixed powder is 3: 1, ball milling for 15 hours at the ball milling speed of 300r/min to obtain mixed powder with uniformly dispersed carbon powder; drying the mixed powder, putting a certain amount of the dried mixed powder into a hot-pressing mold for prepressing under the pressure of 1MPa, then putting the mold filled with the mixed powder into a discharge plasma sintering system for crystallization reaction and sintering densification, wherein the pressure is 40MPa, the heating rate is 100 ℃/min, the temperature is 870 ℃, and the heat preservation time is 5min, and finally obtaining the compact WC-Co hard alloy block material with pure phase and average grain size less than 100 nm.
Amorphous Co prepared in this example6W6The X-ray diffraction pattern of the C powder is shown in FIG. 1(a), and the scanning electron micrograph thereof is shown in FIG. 2 (a).
Example 2
The ternary compound Co with the average grain diameter of about 500nm is prepared in batches by the prior patented technology (granted patent number: CN201510491451.4) of the applicant6W6C powder is taken as a raw material and is added into a hard alloy ball milling tank together with hard alloy balls, four hard alloy grinding balls with the diameters of 4mm, 5mm, 8mm and 10mm are respectively filled into each tank, the mass ratio of the four hard alloy grinding balls to the hard alloy grinding balls is 2:2:4:2, argon is taken as protective atmosphere, and the hard alloy grinding balls and a ternary compound Co are mixed6W6The weight ratio of C is 22: 1, ball milling time is 65 hours, ball milling rotating speed is 550r/min, and amorphous Co is obtained after ball milling6W6C, powder; for the prepared amorphous Co6W6C powder is subjected to carbon content detection, the carbon content is measured to be 1.20 wt.%, and the carbon content is measured according to a reaction formula Co6W6C +5C + 6WC +6Co add 5.30 wt.% of the corresponding carbon black,so that the carbon content in the mixed powder was 6.50%; adding the obtained mixed powder and a hard alloy grinding ball with the diameter of 8mm into a hard alloy ball milling tank, wherein the ball milling medium is absolute ethyl alcohol, and the weight ratio of the hard alloy grinding ball to the mixed powder is 4: 1, ball milling for 12 hours at a ball milling speed of 280r/min to obtain mixed powder with uniformly dispersed carbon powder; drying the mixed powder, putting a certain amount of the dried mixed powder into a hot-pressing die for prepressing under the pressure of 1.5MPa, and then putting the die filled with the mixed powder into a discharge plasma sintering system for crystallization reaction and sintering densification, wherein the pressure is 40MPa, the heating rate is 140 ℃/min, the temperature is 930 ℃, the heat preservation time is 3min, and finally the compact WC-Co hard alloy block material with pure phase and the average grain size less than 100nm is obtained.
Amorphous Co prepared in this example6W6The X-ray diffraction pattern of the C powder is shown in fig. 1(b), the scanning electron microscope microscopic morphology thereof is shown in fig. 2(b), the X-ray diffraction pattern of the prepared nanocrystalline WC-Co cemented carbide bulk is shown in fig. 3, and the hardness and elastic modulus measured by the nanoindentation method are shown in fig. 4.
Example 3
The ternary compound Co with the average grain diameter of about 400nm is prepared in batches by the prior patented technology (granted patent number: CN201510491451.4) of the applicant6W6C powder is taken as a raw material and is added into a hard alloy ball milling tank together with hard alloy balls, four hard alloy grinding balls with the diameters of 4mm, 5mm, 8mm and 10mm are respectively filled into each tank, the mass ratio of the four hard alloy grinding balls to the hard alloy grinding balls is 2:2:4:2, argon is taken as protective atmosphere, and the hard alloy grinding balls and a ternary compound Co are mixed6W6The weight ratio of C is 25: 1, ball milling time is 55 hours, ball milling rotating speed is 500r/min, and amorphous Co is obtained after ball milling6W6C, powder; for the prepared amorphous Co6W6C powder is subjected to carbon content detection, the carbon content is measured to be 1.50 wt.%, and the carbon content is measured according to a reaction formula Co6W6C +5C ═ 6WC +6Co add 5.40 wt.% of the corresponding carbon black, making the carbon content in the mixed powder 6.90%; adding the obtained mixed powder and a hard alloy grinding ball with the diameter of 8mm into a hard alloy ball milling tankIn the method, the ball milling medium is absolute ethyl alcohol, and the weight ratio of the hard alloy grinding balls to the mixed powder is 5: 1, ball milling for 10 hours at a ball milling speed of 250r/min to obtain mixed powder with uniformly dispersed carbon powder; drying the mixed powder, putting a certain amount of the dried mixed powder into a hot-pressing mold for prepressing under the pressure of 2MPa, then putting the mold filled with the mixed powder into a discharge plasma sintering system for crystallization reaction and sintering densification, wherein the pressure is 35MPa, the heating rate is 120 ℃/min, the temperature is 1000 ℃, the heat preservation time is 2min, and finally obtaining the compact WC-Co hard alloy block material with pure phase and the average grain size smaller than 100 nm.
Hardness and elastic modulus of the nanocrystalline WC-Co hard alloy block prepared in this example measured by nanoindentation are shown in FIG. 5.
Claims (1)
1. The method for preparing the nanocrystalline WC-Co hard alloy by amorphous crystallization is characterized by firstly preparing a ternary compound Co6W6C powder, Co to be prepared6W6C powder is ball milled by high energy to obtain amorphous Co6W6C powder, then under the condition of spark plasma sintering making amorphous Co6W6C, performing crystallization reaction on the powder to generate nano polycrystalline WC-Co two-phase composite powder in one step, and further performing sintering densification to obtain a compact WC-Co hard alloy block material with a nano crystal structure; the method specifically comprises the following steps:
(1) preparing ternary compound Co with average grain diameter not more than 500nm in batch6W6C powder is taken as a raw material and is added into a hard alloy ball milling tank together with hard alloy balls, four hard alloy grinding balls with the diameters of 4mm, 5mm, 8mm and 10mm are respectively filled into each tank, the mass ratio of the four hard alloy grinding balls to the hard alloy grinding balls is 2:2:4:2, argon is taken as protective atmosphere, and the hard alloy grinding balls and a ternary compound Co are mixed6W6The weight ratio of C is (18-25): 1, ball milling time is 55-70 hours, ball milling rotating speed is 500-600 r/min, and amorphous Co is obtained after ball milling6W6C, powder;
(2) for the prepared amorphous Co6W6C powder is subjected to carbon content detection, and the carbon content and the reactive Co are combined6W6Adding corresponding carbon black into C + 5C-6 WC +6Co to ensure that the content of carbon element in the mixed powder is 6.00-6.90 wt%;
(3) adding the mixed powder obtained in the step (2) and a hard alloy grinding ball with the diameter of 8mm into a hard alloy ball milling tank, wherein the ball milling medium is absolute ethyl alcohol, and the weight ratio of the hard alloy grinding ball to the mixed powder is (3-5): 1, ball milling for 10-15 hours at a ball milling speed of 250-300 r/min to obtain mixed powder with uniformly dispersed carbon powder;
(4) and (3) drying the mixed powder obtained in the step (3), putting a certain amount of the dried mixed powder into a hot-pressing mold for prepressing under the pressure of 1-2 MPa, and then putting the mold filled with the mixed powder into a discharge plasma sintering system for crystallization reaction and sintering densification, wherein the pressure is 30-40 MPa, the heating rate is 100-140 ℃/min, the temperature is 870-1000 ℃, the heat preservation time is 2-5 min, and finally the compact WC-Co hard alloy block material with a pure phase and an average grain size smaller than 100nm is obtained.
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