CN106350721B - A kind of preparation method of plate crystal structure high-performance WC-Co hard alloy - Google Patents

Abstract

The invention relates to a preparation method of a high-performance WC-Co cemented carbide with a plate crystal structure, belonging to the field of cemented carbide materials and preparations. The preparation method is as follows: using W/Co/C composite powder with dispersed and evenly distributed components as raw material, carbonization and sintering at 1380-1460°C to obtain plate-shaped crystals Structural high-performance WC-Co cemented carbide; the W/Co/C composite powder contains nano W powder and plate crystal W. The present invention can be sintered at a lower temperature for a shorter time to obtain a new type of high-performance WC-Co cemented carbide with a fully dense plate crystal structure that is almost completely densified and has excellent comprehensive properties, and can be used in various processing fields such as turning, drilling, and milling. And it has important industrial application prospects in terms of being used as a coated cemented carbide substrate.

Description

A preparation method of high-performance WC-Co cemented carbide with plate crystal structure

technical field

The invention relates to a preparation method of a high-performance WC-Co hard alloy with a plate crystal structure, belonging to the field of hard alloy materials and preparation.

Background technique

The hard phase WC in WC-Co cemented carbide is an anisotropic crystal belonging to the hexagonal crystal system. If the bottom (001) surface with higher hardness grows preferentially, it is usually in the shape of a triangular or polygonal prism. The grains will transform into plate-shaped WC grains, which will improve the overall hardness of the WC-Co cemented carbide and at the same time help to improve the fracture toughness of the alloy. Generally, the fracture toughness KIC of low-cobalt two-phase WC-Co cemented carbide mainly depends on the volume fraction of γ phase and its mean free path and composition, and its micro-cracks are at the weaker WC/WC crystal interface and WC/Co phase interface. Formation and propagation or fracture through the binder phase, while in platy grained cemented carbide, microcracks can propagate through various ways such as crack deflection, bridging or pulling out, and transgranular fracture. Plate grain cemented carbide has comprehensive properties such as high hardness, strong wear resistance and plastic deformation resistance, high toughness and good thermal shock resistance. The matrix and other aspects show excellent results, and it is a new development direction in the field of cemented carbide.

At present, by adding other substances (such as TiC, Y ₂ O ₃ , plate-shaped WC seed crystals, etc.) These preparation methods generally have the disadvantages of difficult control of the number and size of plate-shaped WC grains, a small proportion of plate-shaped grains or poor grain orientation, and the need for special sintering equipment, which makes the comprehensive properties of cemented carbide such as hardness and toughness unsatisfactory. It has been effectively improved, but its application is limited. Using W powder and graphite with plate-like morphology as raw materials, chemically synthesizing plate-like WC grains is an effective way to prepare plate-shaped cemented carbide, but the alloy is difficult to sinter and densify.

Contents of the invention

The purpose of the present invention is to provide a novel method for preparing high-performance WC-Co cemented carbide with a full-dense plate crystal structure, aiming at the shortcomings of the existing preparation technology.

A kind of preparation method of high-performance WC-Co cemented carbide with plate crystal structure of the present invention comprises the following steps:

Using W/Co/C composite powder with dispersed and evenly distributed components as raw material, carbonization and sintering at 1380-1460°C after carbon adjustment, wet grinding, drying, and compression molding to obtain high-performance WC-Co with plate-like crystal structure Cemented carbide: the W/Co/C composite powder contains nano W powder and plate crystal W.

As a preferred solution; the W/Co/C composite powders in which the components are dispersed and uniformly distributed are prepared by the following scheme:

Using water-soluble tungsten-containing salt as nano-tungsten source and water-soluble cobalt-containing salt as cobalt source, dissolve nano-tungsten source, cobalt source, and carbon source in alcoholic aqueous solution and mix evenly to obtain mixture A; then flake W powder Add to Mix A, mix evenly and dry to obtain dry Mixture B; Mixture B is reduced at 560-820°C under a reducing atmosphere to obtain a W/Co/C composite powder in which the components are dispersed and evenly distributed; the flake The aspect ratio of the shape W powder is: 5:1-20:1 and the diameter is 5-30 microns; the mass ratio of the flake W powder to the nanopowder C is 4:1-9:1, and the powder C It is the theoretical value of reducing the nano-tungsten source to tungsten.

As a further preferred option,

Using water-soluble tungsten-containing salt as the nano-tungsten source and water-soluble cobalt-containing salt as the cobalt source, dissolve the nano-tungsten source, cobalt source, carbon source, and additives in an alcoholic aqueous solution and mix evenly to obtain a mixture E; Add W powder to mixture E, mix well and then dry to obtain dry mixture D; mixture D is reduced at 560-820°C for 120-300min under reducing atmosphere to obtain W/Co/C composite with dispersed and uniform distribution of components Powder; the aspect ratio of the flaky W powder is: 5:1-20:1 and the diameter is 5-30 microns; the mass ratio of the flaky W powder to the nanopowder C is 4:1-9:1 , the powder C is the theoretical value of reducing the nano-tungsten source to tungsten; the additive is a water-soluble vanadium-containing salt. The water-soluble vanadium-containing salt is ammonium metavanadate or chromium nitrate. In order to further enhance the effect, in the mixture E, in terms of mass ratio, water-soluble tungsten-containing salt: water-soluble carbon source: water-soluble vanadium-containing salt=10-20:15-30:30-60:1-2.5. The mass percent content of alcohol in the alcohol aqueous solution is 10-30%. The mass ratio of solute to solvent in the mixture E is 10:8-10:6.

As a further preferred solution, the water-soluble tungsten-containing salt is ammonium metatungstate.

As a further preferred solution, the water-soluble cobalt-containing salt is cobalt nitrate.

As a further preferred solution, the carbon source is reducing sugar. The reducing sugar is more preferably glucose or sucrose.

In industrial application, the flake-shaped W powder is added to mixture E or mixture A, mixed evenly, and evaporated or spray-dried by vacuum heating.

In industrial application, the mixture B or mixture D is ball milled and then reduced at 560-820° C. for 120-300 minutes in a reducing atmosphere to obtain a W/Co/C composite powder in which the components are dispersed and uniformly distributed. The condition of described ball milling is: rotating speed (rev/min, D is the diameter of the grinding cylinder/m), that is, 0.5-1.1m/s, and the mass ratio of ball to material is 5:1-10:1.

As a further preferred solution, mixture B or mixture D is put into a five-belt temperature-controlled continuous four-tube atmosphere muffle reduction furnace after ball milling for in-situ carbon-assisted hydrogen reduction, and the reduction temperature is divided into five stages in turn; The temperature of the five stages is controlled at 560°C-600°C, 600°C-640°C, 640°C-680°C, 700°C-760°C, 760°C-820°C, the reduction time is 300min, and nitrogen gas is used before the furnace is released Inert gas passivation treatment. During reduction, excess hydrogen is present.

As a preferred solution; the carbon adjustment is: adding powdered paraffin to the W/Co/C composite powder in which the components are dispersed and uniformly distributed; the quality of the added powdered paraffin is that the components are dispersed and uniformly distributed W/ 2.0-3.0% of the mass of Co/C composite powder.

As a preferred version; during the wet grinding, the control speed is: (rev/min, D is the diameter of the grinding cylinder/meter) that is 0.5-1.1m/s, the mass ratio of the ball to material is controlled to be 4:1-6:1, and the ball milling time is controlled to be 24-60 hours; the ball milling medium used in wet milling It is preferably alcohol, and the amount of alcohol added per kilogram of powder is 300-400 milliliters.

As a preferred solution; the pressure of the compression molding is 130-180MPa.

As a preferred solution; the time for primary carbonization and sintering at 1380-1460° C. is 90-120 minutes. As a further preferred solution, the primary carbonization and sintering temperature is 1410-1440°C. For primary carbonization and sintering, hydrogen molybdenum wire furnace is preferred.

The invention discloses a method for preparing a high-performance WC-Co cemented carbide with a plate-like crystal structure. The properties of the prepared WC-Co cemented carbide with a cobalt mass percentage of 8.5-10.5% are:

The relative density is greater than or equal to 98.77%, preferably 98.77-99.15%, the coercive force is greater than or equal to 18.25KA·m ^-1 , preferably 18.25-19.25KA·m ^-1 , the fracture toughness KIC is greater than or equal to 14.17MPa·m ^1/2 , Preferably it is 14.17-14.34 MPa·m ^1/2 , HV30 is greater than or equal to 1500 kgf·mm ^-2 , more preferably 1500-1550 kgf·mm ^-2 .

Principles and advantages

The above method can be used to prepare nano-tungsten-doped plate-like W/Co/C composite powder with uniform distribution of components. A new high-performance WC-Co cemented carbide with almost complete densification and excellent comprehensive performance can be obtained in a short time. Its hardness is equivalent to that of submicron alloy grades, and it shows obvious anisotropy. The fracture toughness is obviously better than the performance of the corresponding submicron grade alloys, and has important industrial application prospects in various processing fields such as turning, drilling, milling, and as a coated cemented carbide substrate.

The sintering shrinkage and densification of the WC-Co cemented carbide of the present invention, in addition to the sharp shrinkage caused by the plastic flow of the bonding metal in the solid phase sintering stage at a higher temperature, the key to obtaining a fully dense structure alloy is the WC under the liquid phase sintering stage. Particles undergo sufficient re-densification and shrinkage due to dissolution elution mechanisms. As the main raw material of WC-Co cemented carbide, it is usually required that the particle size distribution of WC powder is narrow and normally distributed. The particle size distribution will affect the grain coarsening, the wider the distribution range, the more serious the grain coarsening. The present invention generates nano W particles in situ. During the carbonization and sintering process, due to its high specific surface energy, the internal energy of the alloy system is significantly increased, and it may have been first carbonized to form nano W particles in the solid phase sintering stage at a lower temperature WC, and promotes the liquid phase to appear earlier, effectively promotes the shrinkage and densification of the alloy during sintering, and at the same time, due to the dissolution-precipitation mechanism, the finer nano-WC grains are preferentially dissolved and preferentially precipitated on the larger plate-shaped grains, Prompting WC grains to further undergo two-dimensional nucleation and growth, resulting in more coarse plate-like WC grains.

Description of drawings

FIG. 1 is an SEM photo of the nano-tungsten-doped plate-like crystal W/Co/C composite powder prepared in Example 1.

Fig. 2 is the SEM photo of the novel plate grain WC-Co structured cemented carbide prepared in Example 1.

FIG. 3 is an SEM photo of the novel plate-like WC-Co structured cemented carbide prepared in Comparative Example 1. FIG.

Detailed ways

The present invention will be further illustrated by the following examples, but the protection scope of the present invention is not limited thereto.

Example 1

Weigh 24 grams of ammonium metatungstate, 27 grams of anhydrous glucose, 50 grams of cobalt nitrate and 2.0 grams of chromium nitrate, dissolve them in alcohol, and after fully mixing, add 70 grams of flaky W powder induced by ball milling, and mix them by ball milling After uniformity (ball milling time 2h, ball-to-material ratio 10:1), the precursor mixed powder for reduction was prepared by ball milling after vacuum heating and evaporation. Put the precursor powder into a five-zone temperature-controlled continuous four-tube atmosphere muffle reduction furnace for in-situ carbon-assisted hydrogen reduction. The reduction temperature is 560-600-640-700-760°C, the reduction time is 300 minutes, and the excess hydrogen flow rate is large. Passivation treatment with inert gas such as nitrogen before being released from the furnace. The obtained composite powder, after testing and re-adjusting the carbon ingredients, added 2.5% by weight of powdered paraffin and an appropriate amount of alcohol, continued ball milling for 48 hours, obtained the mixture after vacuum drying, and then pressed it and put it on a hydrogen-molybdenum wire. In the furnace at 1410 ° C, carbonization and sintering for 90 minutes at a time to prepare a new type of high-performance WC-Co cemented carbide with a plate-like crystal structure. The scanning electron microscope photos of the prepared nano-tungsten-doped plate-like crystal W/Co/C composite powder and its new plate-shaped crystal WC-10wt% Co structure cemented carbide obtained by primary carbonization and sintering are shown in Figure 1 and Figure 2 respectively , as can be seen from Figures 1 and 2: Nano-tungsten, cobalt and carbon black are closely adhered to the surface of flat tungsten particles, and are uniformly dispersed; different from traditional WC-Co alloys, WC grains are triangular or polygonal prisms shape, the new plate-shaped WC-10wt% Co cemented carbide has a uniform structure, and its WC grains are composed of a large number of flat plate-shaped WC grains and a very small amount of ultra-fine WC grains. The test results of the obtained cemented carbide performance are shown in attached table 1.

Example 2

Weigh 20 grams of ammonium metatungstate, 27 grams of anhydrous glucose, 50 grams of cobalt nitrate and 2.0 grams of chromium nitrate, dissolve them in alcohol, and after fully mixing, add 73 grams of flaky W powder induced by ball milling, and mix them by ball milling After uniformity (ball milling time 2h, ball-to-material ratio 10:1), the precursor mixed powder for reduction was prepared by ball milling after vacuum heating and evaporation. Put the precursor powder into a five-zone temperature-controlled continuous four-tube atmosphere muffle reduction furnace for in-situ carbon-assisted hydrogen reduction. The reduction temperature is 600-640-680-760-820°C, the reduction time is 300 minutes, and the excess hydrogen flow rate is large. Passivation treatment with inert gas such as nitrogen before being released from the furnace. The obtained composite powder, after testing and re-adjusting the carbon ingredients, added 2.5% by weight of powdered paraffin and an appropriate amount of alcohol, continued ball milling for 48 hours, obtained the mixture after vacuum drying, and then pressed it and put it on a hydrogen-molybdenum wire. In the furnace at 1410 ° C, carbonization and sintering for 90 minutes at a time to prepare a new type of high-performance WC-Co cemented carbide with a plate-like crystal structure. The test results of the obtained cemented carbide performance are shown in attached table 1.

Example 3

Weigh 17 grams of ammonium metatungstate, 27 grams of anhydrous glucose, 50 grams of cobalt nitrate and 2.0 grams of chromium nitrate, dissolve them in alcohol, and after fully mixing, add 75 grams of flaky W powder induced by ball milling, and mix them by ball milling After uniformity (ball milling time 2h, ball-to-material ratio 10:1), the precursor mixed powder for reduction was prepared by ball milling after vacuum heating and evaporation. Put the precursor powder into a five-zone temperature-controlled continuous four-tube atmosphere muffle reduction furnace for in-situ carbon-assisted hydrogen reduction. The reduction temperature is 560-600-640-700-760°C, the reduction time is 300 minutes, and the excess hydrogen flow rate is large. Passivation treatment with inert gas such as nitrogen before being released from the furnace. The obtained composite powder, after testing and re-adjusting the carbon ingredients, added 2.5% by weight powdered paraffin and appropriate amount of alcohol, continued ball milling for 48 hours, obtained the mixture after vacuum drying, then pressed it, and put it on a hydrogen-molybdenum wire In the furnace at 1410 ° C, carbonization and sintering for 120 minutes at a time to prepare a new type of high-performance WC-Co cemented carbide with a plate-like crystal structure. The test results of the obtained cemented carbide properties are shown in Attached Table 1.

Example 4

Weigh 13 grams of ammonium metatungstate, 27 grams of anhydrous glucose, 50 grams of cobalt nitrate and 2.0 grams of chromium nitrate, dissolve them in alcohol, and after fully mixing, add 78 grams of flaky W powder induced by ball milling, and mix by ball milling After uniformity (ball milling time 2h, ball-to-material ratio 10:1), the precursor mixed powder for reduction was prepared by ball milling after vacuum heating and evaporation. Put the precursor powder into a five-zone temperature-controlled continuous four-tube atmosphere muffle reduction furnace for in-situ carbon-assisted hydrogen reduction. The reduction temperature is 560-600-640-700-760°C, the reduction time is 300 minutes, and the excess hydrogen flow rate is large. Passivation treatment with inert gas such as nitrogen before being released from the furnace. The obtained composite powder, after testing and re-adjusting the carbon ingredients, added 2.5% by weight of powdered paraffin and an appropriate amount of alcohol, continued ball milling for 48 hours, obtained the mixture after vacuum drying, and then pressed it and put it on a hydrogen-molybdenum wire. In the furnace at 1440 ° C, carbonization and sintering for 90 minutes at a time to prepare a new type of high-performance WC-Co cemented carbide with a plate-like crystal structure. The test results of the obtained cemented carbide performance are shown in attached table 1.

Comparative example 1

Weigh 0 g of ammonium metatungstate, 27 g of anhydrous glucose, 50 g of cobalt nitrate and 2.0 g of chromium nitrate, dissolve them in alcohol, and after fully mixing, add 87.30 g of flaky W powder induced by ball milling, and mix by ball milling After uniformity (ball milling time 2h, ball-to-material ratio 10:1), the precursor mixed powder for reduction was prepared by ball milling after vacuum heating and evaporation. Put the precursor powder into a five-zone temperature-controlled continuous four-tube atmosphere muffle reduction furnace for in-situ carbon-assisted hydrogen reduction. The reduction temperature is 560-600-640-700-760°C, the reduction time is 300 minutes, and the excess hydrogen flow rate is large. Passivation treatment with inert gas such as nitrogen before being released from the furnace. The obtained composite powder, after testing and re-adjusting the carbon ingredients, added 2.5% by weight of powdered paraffin and an appropriate amount of alcohol, continued ball milling for 48 hours, obtained the mixture after vacuum drying, and then pressed it and put it on a hydrogen-molybdenum wire. In the furnace at 1410 ° C, carbonization and sintering for 90 minutes at a time to prepare a new type of high-performance WC-Co cemented carbide with a plate-like crystal structure. The test results of the obtained cemented carbide performance are shown in attached table 1.

Table 1 Performance test results of WC-10wt% Co sintered body prepared in different examples

P: pressing surface; V: vertical pressing surface.

Claims (9)

1. A preparation method of high-performance WC-Co cemented carbide with plate crystal structure, characterized in that it comprises the following steps: Using W/Co/C composite powder with dispersed and evenly distributed components as raw material, carbonization and sintering at 1380-1460°C after carbon adjustment, wet grinding, drying, and compression molding to obtain high-performance WC-Co with plate-like crystal structure Cemented carbide; the W/Co/C composite powder contains nano W powder and plate crystal W; The W/Co/C composite powder in which the components are dispersed and uniformly distributed is prepared by the following scheme: Using water-soluble tungsten-containing salt as nano-tungsten source and water-soluble cobalt-containing salt as cobalt source, dissolve nano-tungsten source, cobalt source, and carbon source in alcoholic aqueous solution and mix evenly to obtain mixture A; then flake W powder Add to Mix A, mix evenly and dry to obtain dry Mixture B; Mixture B is reduced at 560-820°C under a reducing atmosphere to obtain a W/Co/C composite powder in which the components are dispersed and evenly distributed; the flake The aspect ratio of the shape W powder is: 5:1-20:1 and the diameter is 5-30 microns; the mass ratio of the flake W powder to the nano powder C is 4:1-9:1, and the nano powder C is the theoretical value of reducing the nano-tungsten source to tungsten. 2. the preparation method of a kind of high-performance WC-Co cemented carbide with plate grain structure according to claim 1, is characterized in that: Using water-soluble tungsten-containing salt as the nano-tungsten source and water-soluble cobalt-containing salt as the cobalt source, dissolve the nano-tungsten source, cobalt source, carbon source, and additives in an alcoholic aqueous solution and mix evenly to obtain a mixture E; Add W powder to mixture E, mix well and then dry to obtain dry mixture D; mixture D is reduced at 560-820°C for 120-300 min under a reducing atmosphere to obtain W/Co/C with dispersed and uniform distribution of components Composite powder; the aspect ratio of the flake W powder is: 5:1-20:1 and a diameter of 5-30 microns; the mass ratio of the flake W powder to nanopowder C is 4:1-9: 1. The nano-powder C is the theoretical value of reducing the nano-tungsten source to tungsten; the additive is a water-soluble chromium-containing salt. 3. the preparation method of a kind of high-performance WC-Co cemented carbide with plate grain structure according to claim 2, is characterized in that; In the mixture E, in terms of mass ratio, water-soluble tungsten-containing salt: water-soluble carbon source: water-soluble chromium-containing salt=10-20:15-30:30-60:1-2.5; The water-soluble tungsten-containing salt is ammonium metatungstate; The water-soluble cobalt-containing salt is cobalt nitrate; The carbon source is reducing sugar; the reducing sugar is glucose or sucrose. 4. the preparation method of a kind of high-performance WC-Co cemented carbide with plate grain structure according to claim 1 or 2, is characterized in that; After mixture B or mixture D is ball milled, it is reduced under a reducing atmosphere at 560-820°C for 120-300 min to obtain a W/Co/C composite powder in which the components are dispersed and evenly distributed; the conditions of the ball milling are: 0.5-1.1m/s, mass ratio of ball to material 5:1-10:1, control ball milling time to 32-60 hours. 5. The preparation method of a high-performance WC-Co cemented carbide with plate grain structure according to claim 1 or 2, characterized in that; After ball milling, the mixture B or mixture D is put into a five-belt temperature-controlled continuous four-tube atmosphere muffle reduction furnace for in-situ carbon-assisted hydrogen reduction. The reduction temperature is divided into five stages in turn; the temperatures of the five stages are controlled separately. 560°C-600°C, 600°C-640°C, 640°C-680°C, 700°C-760°C, 760°C-820°C, the reduction time is 300 min, and nitrogen passivation treatment is used before being released from the furnace. 6. The preparation method of a high-performance WC-Co cemented carbide with plate grain structure according to claim 1, characterized in that the carbon adjustment is: W/Co/C dispersed and evenly distributed to each component Powdery paraffin is added to the composite powder; the mass of the added powdery paraffin is 2.0-3.0% of the mass of the W/Co/C composite powder in which the components are dispersed and evenly distributed. 7. the preparation method of a kind of high-performance WC-Co cemented carbide with plate grain structure according to claim 1, is characterized in that: During wet grinding, the control speed is 0.5-1.1m/s, the ball-to-material mass ratio is 4:1-6:1, and the ball-milling time is 24-60 hours; During compression molding, the control pressure is 130-180MPa. 8. The preparation method of a high-performance WC-Co cemented carbide with a plate-shaped grain structure according to claim 1, characterized in that: the time for primary carbonization and sintering at 1380-1460°C is 90-120 min; primary carbonization and sintering , the sintering furnace used is a hydrogen-molybdenum wire furnace. 9. According to any one of claims 1, 2, 3, 7, 8, a method for preparing a high-performance WC-Co cemented carbide with a plate crystal structure, it is characterized in that: the prepared cobalt has a mass of 100% The properties of WC-Co cemented carbide with a content of 8.5-10.5% are: The relative density is greater than or equal to 98.77%; The coercive force is greater than or equal to 18.25 KA·m ^-1 ; Fracture toughness K _IC greater than or equal to 14.17 MPa·m ^1/2 ; HV30 is greater than or equal to 1500 kgf•mm ^-2 .