GB2506287A

GB2506287A - Tungsten carbide composite material comprising aluminium oxide particles and silicon nitride whiskers and preparation process thereof

Info

Publication number: GB2506287A
Application number: GB1320481.3A
Authority: GB
Inventors: Yuanyuan Li; Xiaoqiang Li; Dong-Hai Zheng; sheng-guan Qu; Chao Yang; Ming Shao; Zhiyu Xiao
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2011-08-05
Filing date: 2011-09-08
Publication date: 2014-03-26
Anticipated expiration: 2031-09-08
Also published as: CN102390998A; GB201320481D0; WO2013020317A1; GB2506287B; CN102390998B

Abstract

Disclosed in the present invention are a tungsten carbide composite material comprising aluminium oxide particles and silicon nitride whiskers and a preparation process thereof. The tungsten carbide composite material comprises 0.5-3% aluminium oxide particles by mass percent, and 0.4-10% silicon nitride whiskers by mass percent, and the balance is tungsten carbide and an inevitable impurity phase; the silicon nitride whiskers are authigenic Î²-Si3N4 whiskers. The WC composite material prepared in the present invention does not contain any metal bonding phase, has good hardness, abrasion resistance and mechanical performance at high temperatures, and medium toughness; the present invention can not only reduce the costs of preparing the WC composite material, but also effectively expand the scope of application thereof; and the material is suitable as a cutter such as a indexable blade, etc., a plastic machining tool such as a wire-drawing die, etc., and is also suitable as a shearing tool, such as a punching and shearing die, etc.

Description

DESCRIPTION

TUNGSTEN CARBIDE COMPOSITE

CONTAINNG ALUMINA GRAINS AND SILICON NITRIDE WHISKERS

AND THE PREPARATION METHOD THEREOF

FIELD OF THE INVENTION

The present invention relates to a tungsten carbide (WC) material and the preparation method thereof, specifically to the tungsten carbide composite containing alumina (A12O3) grains and silicon nitride (f3-Si3N4) whiskers and the preparation method thereof.

BACKGROUND OF THE INVENTION

The traditional cemented carbide is composed of a hard WC phase and a low-melting-point metallic adhesive phase, wherein WC possesses very high hardness as well as excellent oxidation resistance and corrosion resistance; however, the addition of metallic adhesive may inevitably weaken hardness, wear resistance, oxidation resistance, corrosion resistance and other properties of the alloy, and be also very likely to reduce wear resistance of the alloy, especially such characteristics of the metallic adhesive as being easily softened and oxidized at high temperatures. which all may make the WC cemented carbide quick to fail, thus limiting the application of the WC cemented carbide. For this, researchers have been making an effort to overcome the limitation caused by metallic adhesive.

Besides, the WC-Co alloy is the most common alloy for the traditional cemented carbide, while both scarcity and strategic position of the Co resource require that it is reduced or avoided as far as possible for Co to be used as the adhesive phase in the WC cemented carbide, The Chinese patent 200410068022.8 disclosed a method of sintering pure ultrafine-grained tungsten carbide, by which the spark plasma sintering technology is used for preparing the pure WC material without any adhesive phase, with the resulting dense pure WC material having very high hardness and excellent wear resistance; however, due to the low fracture toughness, application of this material is seriously obstnicted. The chemical boild of WC is mainly a covalent bond, making WC have inherent brittleness of the ceramic materials. For a long time, the research of toughening WC by making use of the toughening method for the traditiollal ceramic materials (such as grains or whiskers toughening) has been seriously lagging behind the research of WC-Co, and rarely reported. In the general ceramic materials, the materials are toughened by the addition of whiskers, which can effectively improve strength and toughness of the materials. However, this method of adding whiskers usually has such problems as the whiskers being easily intertwined and agglomerated, and difficult to be dispersed; besides, the operator may suffer health hazards due to direct contact with the whiskers, making the operability greatly reduced. The Chinese patent 200610011114.1 disclosed a Si3N4-based ceramics toughening by in-situ f3-Si3N4 whiskers and a method thereof, in which in-situ fi-Si3N4 whiskers in the matrix form through the transformation of u-Si3N4 grains to f3-Si3N4 at high temperatures. This method of generating whiskers in situ can not only toughen the ceramic matrix, but also avoid the problems with the addition of ceramic whiskers such as the whiskers being easily intertwined and agglomerated, and difficult to be dispersed, and moreover the health hazards that the operator may stiffer due to direct contact with the whiskers can also be avoided.

However, this method is currently applied to few materials such as A1203-based and Si3N4-based materials. with its application needing further development and re search.

it is an R&D hotspot in this field to further improve toughness of the WC materials and iltilize the high hardness characteristic of the pure WC as much as possible under the premise of adding no metallic adhesive.

CONTENTS OF THE INVENTION

A purpose of the present invention is to overcome the shortcomings of the prior technology by providing a tungsten carbide composite containing alumina grains and silicon nitride whiskers without metallic adhesive.

Another purpose of the present invention is to provide a method of preparing the tungsten carbide composite containing aluminum grains and silicon nitride whiskers by making use of the synergistic toughening of grains and in-situ whiskers.

The purposes of the present invention can be achieved through the following measures: A tungsten carbide composite containing alumina grains and silicon nitride whiskers is provided, having the following features: The tungsten carbide composite contains alumina grains and silicon nitride whiskers, with the rest being tungsten carbide and unavoidable impurities; the mass percentage of the alumina grain is 0.5%-3%; the silicon nitride whiskers are in-situ!3-Si3N4 whiskers, having a mass percentage of O.4%-l0%.

The in-situ -Si3N4 whisker has an aspect ratio 3.

A method of preparing the tungsten carbide composite containing alumina grains and silicon nitride whiskers is provided, having the following features: The preparation method includes the following steps and process conditions: Step 1: Materials preparing The raw material powder is prepared with WC, A1203, and a-Si3N4 powder in the following mass percentage ratio: WC 87%-99%, A1202 0.5%-3%, aSi N4 0,5%-l0% having a grain size of 0.5-10 jim, with the rest being unavoidable trace impurities.

Step 2: Powder dispersing and fluxing Putting the above raw material powder in an organic or inorganic solvent, dispersing the agglomerated powder by a coercive measure, and then subjecting the resulting slurry to the low-energy ball milling, thus obtaining the mixed slurry.

Step 3: Powder drying and sieving Putting the above mixed sluny into a dry stove and drying it to an extent where the solvent residue C 1%, and then crushing and sieving, thus obtaining a mixed powder having a grain size C 250 pim.

Step 4: Sintering Sintering the above mixed powder by spark plasma sintering or hot pressing.

The mass ratio of Al,O3to a-Si3N4 is 1/10.

The organic solvent is ethanol, and the inorganic solvent is water; the coercive measure means that the agglomerated powder is dispersed under the synergistic effect of ultrasonic vibration and mechanical stirring.

The spark plasma sintering process is a one-step or a two-step sinterrng process. The one-step sintering process has the following conditions: The sintering current is a DC pulse current; sintering pressure: 30-70 Mpa; heating rate: 50°C-300°C/min; sintering temperature: 1550°C -1900°C; holding time: 0-20 mm; and sintering vacuum degree; «= 4 Pa.

The two-step sintering process has the following conditions: Step 1: The sintering current is a DC pulse current: sintering pressure; 30-70 Mpa; heating rate: 50°C-300°CImin; sintering temperature: 1550°C -1900°C; holding time: 0-20 mm; and sintering vacuum degree: «= 4 Pa.

Step 2: The sintering current is a DC pulse current: sintering pressure; 30-70 Mpa; cooling rate: 50°C-300°C/min; sintering temperature: 1350°C -1550°C; holding time: 0-20 mm; and sintering vacuum degree: «= 4 Pa.

The hot pressing sintering process is a one-step or a two-step sintering process.

The one-step sintering process has the following conditions: sintering pressure: 30-70 Mpa; heating rate: 5°C-20°CImin; sintering temperature: 1550°C -1900°C; holding time: 0-120 mm; and sintering atmosphere: N2 protective atmosphere with 0.1 MPa or vacuum with a degree 4 Pa.

The two-step sintering process has the following conditions: Step 1: sintering pressure: 30-70 Mpa; heating rate: 5°C-20°Clmin; sintering temperature: 1550°C -1900°C; holding time: 0-120 mm; and sintering atmosphere: N, protective atmosphere with 0.1 MPa or vacuum with a degree «=4Pa.

Step 2: sintering pressure: 30-70 Mpa; cooling rate: 5°C -20°C 1mm; sintering temperature: 1350 C -1550 C; holding time: 0-120 mm; and sintering atmosphere: N2 protective atmosphere with 0.1 MPa or vacuum with a degree Pa.

The present invention has die following outstanding advantages compared to the prior technology: 1. The WC composite prepared by the present invention is a WC composite toughened synergistically by A1703 grains and in-situ f3-Si3N4 whiskers without any metallic adhesive, and has good hardness, wear resistance and high-temperature mechanical properties. as well as moderate toughness, suitable as cuttillg tools such as indexable inserts, and plastic processing tools such as drawing dies, as well as cropping tool such as punching molds.

2. The WC composite prepared by the present invention, containing no Co, can not only reduce costs but also save the scarce and strategic Co resource compared with the traditional WC-Co cemented carbide.

3. The WC composite prepared by the present invention does not contain any metallic adhesive, and thus has higher hardness and better wear resistance than the WC-based cemented carbide with metallic adhesive, especially at higher operating temperatures when the hardness of the material will not be reduced substantially due to softening of the metal; therefore, this material is more suitable for application under conditions where there is a higher requirement on hardness and wear resistance or there is a higher operating temperature, e.g., it can be used as a high-speed cutting tool or used for cutting high-strength alloys and a drawing die, etc.. Besides, its oxidation resistance and corrosion resistance are also significantly improved, and thus it is also more applicable to various corrosive environments, such as being used as a special seal material, thereby expanding the application scope of die WC material.

4. The WC composite prepared by the present invention contains Al2O grains and I)-SiN4 whiskers; because of synergistic toughening by the A1103 grains and the j3-Si3N4 whiskers, the WC material without adhesive can be obtained, having higher toughness than the pure WC or the WC material toughened by a single ceramic component.

5. The preparation method of the present invention introduced the 13-Si3N4 whiskers into the WC matrix by in-situ growing, making use of the characteristics that a-Si3N4 transforms into f3-Si3N4 at high temperatures and die f3-Si3N4 grain incline to grow along a specific crystal face. In preparation of the starting material powder, simply by mixing die a-Si3N4 powder and other powder sufficiently uniformly, can the uniformly distributed f3-Si3N4 whiskers be formed between the WC grains in the subsequent sintering process; it was found by the X-ray diffraction analysis that the final conversion rate of a-SiN4 into j3-Si3t4 was 80%. For this, the present invention not only solves the problems with the addition of the ceramic whiskers such as the whiskers being easily intertwined and agglomerated, and difficult to be dispersed, but also avoids the health hazards that the operator may suffer due to direct contact with the whiskers.

6. The present invention uses the relatively inexpensive M203 and a-Si3N4 powder as the raw materials, which can reduce the production costs of the WC-based hard material. The added A1203 is used not only as the sintering aids for transformation of a-Si3N4 into fi-Si3N4, but also as a grain toughening phase to be dispersed in the WC matrix.

7. The a-Si3N4 powder used by the present invention inevitably involves a trace amount of Sift on the surface; in the sintering process, Sift has eutectic reaction with A1203 at about 1587°C to form a liquid phase, thereby promoting densification of the material, making it possible to prepare the dense WC material without adhesive at a relatively low sintering temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a scanning electron microscope (SEM) image of the fracture morphology of the tungsten carbide composite containing alumina grains and silicon nitride whiskers obtained in Example 1; Fig. 2 is an SEM image of the microstructure of the tungsten carbide composite containing alumina grains and silicon nitride whiskers obtained in

Example 1;

Fig. 3 is an SEM image of the fracture morphology of the tungsten carbide composite containing alumina grains and silicon nitride whiskers obtained in

Example 2;

Fig. 4 is an SEM image of the microstructure of the tungsten carbide composite containing aiumina grains and silicon nitride whiskers obtained in

Example 2;

Fig. 5 is an SEM image of the fracture morphology of the tungsten carbide composite containing alumina grains and silicon nitride whiskers obtained in

Example 3; and

Fig. 6 is an SEM image of the microstructure of the tungsten carbide composite containing alumina grains and silicon nitride whiskers obtained in

Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will further be described with reference to the following examples, but the embodiments of the present invention are not limited to these.

Example I

The method of preparing the tungsten carbide composite containing alumina grains and silicon nitride whiskers includes the following steps and the process conditions: Step it: Materials preparing The WC, A1203, and a-Si3N4 powder are mixed in the following mass percentage ratio: WC 96%, A1203 1%, a-Si3N4 3%, with the rest being unavoidable trace impurities; the WC powder has a purity 98.7% and a grain size about 100 nm, the A1103 powder has a purity ? 99.9% and a grain size of 1-2 pm, and the u-Si3N4 powder has a surface oxygen content of 3-5 wt.% and a grain size of 0.8-i jim.

Step 2: Powder dispersing and mixing Immersing the above raw material powder in ethanol, subjecting it to ultrasonic vibration and mechanical agitation so as to make the agglomerated powder dispersed, and then subjecting the resulting slurry to the low-energy ball milling; the ball mill is of a planetary type, the vials (500 mL) and the milling balls are made of A1103 ceramic, and the ball-to-powder ratio is 2:1, with the mixed slurry obtained under the work condition of milling at a speed of 200 r/rnin for 30 hours.

Step 3: Powder drying and sieving Putting the above mixed slurry into a dry stove and drying it to an extent where the solvent residue 1%, and then crushing and sieving, thus obtaining a mixed powder having a grain size 250 jim.

Step 4: Sintering Weighing 60 g of the mixed powder obtained in Step 3 and putting it into a graphite mold having an inner diameter of (1)30 mm for the one-step spark plasma sintering; the sintering current is a DC pulse current, wherein the sintering pressure is 70 MPa, the sintering temperature is 1800t, the heating rate is 1OCYC/min, the hoMing time is 5 mm, and the vacuum degree is 4 Pa.

Through preparation by the above method, the resulting tungsten carbide composite contains the alumina grains at a mass percentage of about 1%, and the in-situ f3-Si3N4 whiskers at a mass percentage of about 2.5%. The above binderless tungsten carbide composite with alumina grains and silicon nitride whiskers has the hardness of HV10 i8.65 OPa and the fracture toughness of 7.25 MPam"2 (the fracture toughness was measured by the Vickers hardness indentation method (Anstis (3 R, Chantikul P, Lawn B R, et a!., A critical-evaluation of indentation techniques for measuring fracture toughness.1. direct crack ineasurements'JJ.

Journal of/he American Ceramic Society, 1981. 64(9): 533-538)), with the fracture morphology and the microstructure morphology shown in Figs. 1 and 2, respectively. The grain size of the material matrix is estimated to be 200-800 nm according to the fracture morphology as shown in Fig. 1; and the aspect ratio of the f3-Si3N4 whisker in the material as shown in Fig. 2 is 5-6.

Example 2 1]

The method of preparing the tungsten carbide composite containing alumina grains and silicon nitride whiskers includes the following steps and the process conditions: Step 1: Materials preparing The WC, AJ703, and a-Si3N4 powder are mixed in the following mass percentage ratio: WC 94 %, Al,03 1%, a-Si3N4 5%, with the rest being unavoidable trace impurities; the WC powder has a purity 98.7% and a grain size about 100 nm, the A1203 powder has a purity ? 99.9% and a grain size of 1-2 pm, and the u-Si3N4 powder has a surface oxygen content of 3-5 wt.% and a grain size of 0.8-1 jim.

Step 2: Powder dispersing and mixing Immersing the above raw material powder in ethanol, subjecting it to ultrasonic vibration and mechamcal agitation so as to make the agglomerated powder dispersed, and then subjecting the resulting slurry to the low-energy ball milling; the bail mill is of a planetary type, the vials (500 rnL) and the milling ball are made of M203 ceramic, and the ball-to-powder ratio is 2: I, with the mixed slurry obtained under the work condition of mining at a speed of 200 rJmin for 30 hours.

Step 3: Powder drying and sieving Putting the above mixed stuny into a dry stove and drying it to an extent where the solvent residue 1%, and then crushing and sieving, thus obtaining a mixed powder having a grain size 250 pin.

Step 4: Sintering Weighing 60 g of the mixed powder obtained in Step 3 and putting it into a graphite mold having an inner diameter of (1)30 mm for the two-step spark plasma sintering; the sintering current is a DC pulse current, wherein the sintering pressure is 70 MPa, and the vacuum degree is 4 Pa. The following two steps are needed for sintering: First the temperature is increased to 1550°C at a heating rate of 100°C 1mm, which is followed by holding for 10 mm; and then the temperature is reduced to 1450°C at a cooling rate of 50°C/mm, which is again followed by holding for 10 nun, thus completing the sintering process.

Through preparation by the above steps, the resulting tungsten carbide composite material contains the alumina grains at a mass percentage of about 1%, and the in-situ autogenous f3-Si3N4 whiskers at a mass percentage of about 4.5%.

The above binderless tungsten carbide composite material with alumina grains and silicon nitride whiskers has the hardness of 11V10 21.42 UPa and the fracture toughness of 5.94 MPa.nlIC, with the fracture morphology and the microstructure morphology shown in Figs. 3 and 4, respectively. The grain size of the material matrix is estimated to be 100-300 nm according to the fracture morphology as shown in Fig. 3; and the aspect ratio of the j3-Si3N4 whisker in the material as shown in Fig. 4 is 3-5.

Example 3

The method of preparing the tungsten carbide composite containing alumina grains and silicon nitride whiskers includes the following steps and the process conditions: Step 1: Materials preparing The WC, M203, and ct-Si3N4 powder are mixed in the following mass percentage ratio: WC 97 %, A1203 1%, a-Si3N4 2%, with the rest being unavoidable trace impurities; the WC powder has a purity 98.7% and a grain size about 100 nm, the A1203 powder has a purity 99.9% and a grain size of 1-2 pm, and the u-Si3N4 powder has a surface oxygen content of 3-5 wt.% and a grain size of 0.8-1 pm.

Step 2: Powder dispersing and mixing immersing the above raw material powder in ethanol, subjecting it to ultrasonic vibration and mechanical agitation so as to make the agglomerated powder dispersed, and then subjecting the resulting slurry to the low-energy ball milling; the ball mill is of a planetary type, the vials (500 mL) and the milling balls are made of A1203 ceramic, and the ball-to-powder ratio is 2:1, with the mixed slurry obtained under the work condition of mining at a speed of 200 r/min for 30 hours.

Step 3: Powder drying and sieving Putting the above mixed stuny into a dry stove and drying it to an extent where the solvent residue C 1%, and then crushing and sieving, thus obtaining a mixed powder having a grain size C 250 pm.

Step 4: Sintering Weighing 60 g of the mixed powder obtained in Step 3 and putting it into a graphite mold having an inner diameter of 4)30 mm for the two-step hot pressing sintering, wherein the sintering pressure is 70 MPa, and the sintering atmosphere is N2 (0.1 MPa). The following two steps are needed for sintering: First the temperature is increased to 1550°C at a heating rate of 20 °C 1mm, which is followed by heat preservation for 60 mm; and then the temperature is reduced to 1450°C at a cooling rate of 10°C/mm, which is again followed by holding for 60 mm, thus completing the sintering process.

Through preparation by the above steps, the resulting tungsten carbide composite material contains the alumina grains at a mass percentage of about 1%, and the in-situ autogenous f3-Si3N4 whiskers at a mass percentage of about 1.7%.

The above binderless tungsten carbide composite material with alumina grains and silicon nitride whiskers has the hardness of flY10 22.87 CPa and the fracture toughness of 5.64 MPa*m', with the fracture morphology and the microstructure morphology shown in Figs. 5 and 6, respectively. The grain size of the material matrix is estimated to be 100-200 nm according to the fracture morphology as shown in Fig. 5; and the aspect ratio of the -Si3N4 whisker in the material as shown in Fig. 6 is 3-4.

Example 4

The method of preparing the tungsten carbide composite containing alumina grains and silicon nitride whiskers includes the following steps and the process conditions: Step 1: Materials preparing The WC, A1203, and ct-Si3N4 powder are mixed in the following mass percentage ratio: WC 99 %. A1203 0.5%, u-Si3N4 0.5%, with the rest being unavoidable trace impurities; the WC powder has a purity 99.9% and a grain size about 800 nm, the A1203 powder has a purity ? 99.9% and a grain size of 1-2 jim, and the a-Si3N4 powder has a surface oxygen content of 3-5 wt.% and a grain size of 8-10 jim.

Step 2: Powder dispersing and mixing immersing the above raw material powder in ethanol, subjecting it to ultrasonic vibration and mechanical agitation so as to make the agglomerated powder dispersed, and then subjecting the resulting slurry to the low-energy ball milling; the ball mill is of a planetary type, the vials (500 mL) and the milling balls are made of Al203 ceramic, and the ball-to-powder ratio is 2:1, with the mixed slurry obtained under the work condition of milling at a speed of 200 r/niin for 30 hours, Step 3: Powder drying and sieving Putting the above mixed slurry into a dry stove and drying it to an extent where the solvent residue C 1%, and thea crushing and sieving, thus obtaining a mixed powder having a grain size C 250 jim.

Step 4: Sintering Weighing 60 g of the mixed powder obtained in Step 3 and putting it into a graphite mold having an inner diameter of (1)30 mm for the one-step spark plasma sintering; the sintering current is a DC pulse current, wherein the sintering pressure is 30 MPa. the sintering temperature is 1900t, the heating rate is SOC 1mm, there is no holding time in the sintering process, and the vacuum degree is 4 Pa.

Through preparation by the above method, the resulting tungsten carbide composite contains the alumina grains at a mass percentage of about 0.5%, and the in-situ f3-Si3N14 whiskers at a mass percentage of about 0.4%. The above binderless tungsten carbide composite with alumina grains and silicon nitride whiskers has the hardness of HV10 23.20 (liPa and the fracture toughness of 5.45 MPa*m", with the grain size of the material matrix being 800-1000 nm; and the aspect ratio of the fI-Si3N4 whisker in the material is 4-5.

Example 5

The method of preparing the tungsten carbide composite containing alumina grains and silicon nitride whiskers includes the following steps and the process conditions: Step 1: Materials preparing The WC, AJ703, and a-Si3N4 powder are mixed in the following mass percentage ratio: WC 87 %, A12O 3%, a-Si3N4 10%, with the rest being unavoidable trace impurities; the WC powder has a purity 99.9% and a grain size about 600 nm, the A1203 powder has a purity? 99.9% and a grain size of 1-2 pm, and the a-Si3N4 powder has a surface oxygen content of 3-5 wt.% and a grain size of 6-8 jani.

Step 2: Powder dispersing and mixing Immersing the above raw material powder in water, subjecting it to ultrasonic vibration and mechanical agitation so as to make the agglomerated powder dispersed, and then subjecting the resulting slurry to the low-energy ball milling; the ball mill is of a planetary type, the vials (500 mL) and the milling balls are made of A1103 ceramic, and the ball-to-powder ratio is 2:1, with the mixed slurry obtained under the work condition of milling at a speed of 200 rfmin for 30 hours.

Step 3: Powder drying and sieving Putting the above mixed slurry into a dry stove and drying it to an extent where the solvent residue 1%, and then crushing and sieving, thus obtaining a mixed powder having a grain size 250 jam.

Step 4: Sintering Weighing 60 g of the mixed powder obtained in Step 3 and putting it into a graphite mold having an inner diameter of (1)30 mm for the one-step spark phtsnia sintering; the sintering cunent is a DC pulse current, wherein the sintering pressure is 50 MPa, the sintering temperature is 1550°C, the heating rate is 300°C/nun, the holding tinie is 20 mm, and the vacuum degree is 3 Pa.

Through preparation by the above method, the resulting tungsten carbide composite contains the alumina grains at a mass percentage of about 3%, and the in-situ -SiIN4 whiskers at a mass percentage of about 10%. The above binderless tungsten carbide composite material with alumina grains and silicon nitride whiskers has the hardness of HV10 17.56 GPa and the fracture toughness of 7.62 MPa* ni"2, with the grain size of the material matrix being 600-800 nrn; and the aspect ratio of the -Si3N4wluisker in the material is 5-6.

Example 6

The method of preparing the tungsten carbide composite containing alumina grains and silicon nitride whiskers includes the following steps and the process conditions: Step 1: Materials preparing The WC, A1203, and a-Si3N4 powder are mixed in the fouowing mass percentage ratio: WC 90 %, Al,03 2%, a-Si3N4 8%, with the rest being unavoidable trace impurities; the WC powder has a purity 98.7% and a grain size about 100 nm, the A1203 powder has a purity ? 99.9% and a grain size of 1-2 pm, and the cz-Si3N4 powder has a surface oxygen content of 3-5 wt.% and a grain size of 0,5-0.8 jim.

Step 2: Powder dispersing and mixing immersing the above raw material powder in water, subjecting it to ultrasonic vibration and mechanical agitation so as to make the agglomerated powder dispersed, and then subjecting the resulting slurry to the low-energy ball milling; the ball mill is of a planetary type, the vials (500 mL) and the milling balls are made of A1203 ceramic, and the ball-to-powder ratio is 2:1, with the mixed slurry obtained under the work condition of milling at a speed of 200 nun for 30 hours.

Step 3: Powder drying and sieving Putting the above mixed slurry into a dry stove and drying it to an extent where the solvent residue 1%, and then crushing and sieving, thus obtaining a mixed powder having a grain size ( 250 jim.

Step 4: Sintering Weighing 60 g of the mixed powder obtained in Step 3 and putting it into a graphite mold having an inner diameter of 30 nun for the one-step hot pressing sintering, wherein the sintening pressure is 30 MPa, the sintering temperature is 1550°C, the heating rate is 5°C/mm, the holding time is 120 mm, and the vacuum degree is 4 Pa.

Through preparation by the above method, the resulting tungsten carbide composite contains the alumina grains at a mass percentage of about 2%, and the in-situ f3-Si3N4 whiskers at a mass percentage of about 7%. The above binderless tungsten carbide composite with alumina grains and silicon nitride whiskers has the hardness of HV10 18.20 CPa and the fracture toughness of 6.58 MPa*m"2, with the grain size of the material matrix being 200-1000 nm; and the aspect ratio of the f3-Si3N4whisker in the material is 4-5.

Claims

CLAIMSWhat is claimed is: 1. A tungsten carbide composite containing alumina grains and silicon nitride whiskers, characterized in that: the tungsten carbide composite contains alumina grains and silicon nitride whiskers, with the rest being tungsten carbide and unavoidable impurities; the mass percentage of the alumina grains is O.5%-3%; and the silicon nitride whiskers are in-situ f3-Si3N4 whiskers, having a mass percentage of 0.4%-10%.
2. The tungsten carbide composite containing alumina grains and silicon nitride whiskers according to claim I, characterized in that: the in-situf3-Si3N4 whisker has an aspect ratio 3.
3. A method of preparing the tungsten carbide composite containing alumina grains and silicon nitride whiskers, characterized in that: the preparation method includes the following steps and process conditions: Step 1: materials preparing the raw material powder is prepared with WC, A1203, and u-S13N4 powder in the following mass percentage ratio: WC 87%-99%, A1203 0.5%-3%, a-Si3N4 0.5%-10% having a grain size of 0.5-10 tm, with the rest being unavoidable trace impurities; Step 2: powder dispersing and mixing put the above raw material powder in ai organic or inorganic solvent, dispersing the agglomerated powder by a coercive measure, and then subjecting the resulting slurry to the low-energy ball milling; obtaining the mixed slurry; Step 3: powder drying and sieving putting the above mixed slurry into a dry stove and drying it to an extent where the solvent residue C 1%, and then crushing and sieving, thus obtaining a mixed powder having a grain size C 250 xm; Step 4: sintering sintering the above mixed powder by spark plasma sintering or hot pressing
4. The method of preparing die tungsten carbide composite containing alumina grains and silicon nitride whiskers according to claim 3, characterized in that: the mass ratio of A1203to a-Si3N4 is 1/10.
5. The method of preparing the tungsten carbide composite containing a'umina grains and silicon nitride whiskers according to claim 3, characterized in that: the organic solvent is ethanol, and the inorganic solvent is water; the coercive measure means that the agglomerated powder is dispersed tinder the synergistic effect of ultrasonic vibration and mechanical stirring.
6. The method of preparing the tungsten carbide composite material containing alumina grains and silicon nitride whiskers according to claim 3, characterized in that: the spark plasma sintering process is a one-step or a two-step sintering process; the one-step sintering process has the foflowing conditions: the sintering current is a direct current pulse current: sintering pressure: 30-70 Mpa; sintering heating rate: 50°C -300 C 1mm; sintering temperature: 1550 C -1900 C; sintering heat preservation time: 0-20 mm; and sintering vacuum degree: «= 4 Pa; the two-step sintering process has the following conditions: Step 1: the sintering current is a direct current pulse current: sintering pressure: 30-70 Mpa; sintering heating rate: 50°C-300°Clmin; sintering temperature: 1550°C -1900°C; sintering heat preservation time: 0-20 mm; and sintering vacuum degree: «= 4 Pa; Step 2: the sintering current is a direct current pulse current: sintering pressure: 30-70 Mpa; cooling rate: 50°C-300°CInimn; sintering temperature: 1350°C -1550°C; sintering heat preservation time: 0-20 mm; and sintering vacuum degree: «= 4 Pa.
7. The method of preparing the tungsten carbide composite materiffi containing alumina grains and silicon nitride whiskers according to c'aim 3, characterized in that: the hot pressing sintering process is a one-step or a two-step sintering process; the one-step sintering process has the following conditions: sintering pressure: 30-70 Mpa; sintering heating rate: 5°C -20°C frnin; sintering temperature: 1550°C -1900°C; sintering heat preservation time: 0-120 mm; and sintering atmosphere: N2 protective atmosphere having a vacuum degree «= 4 Pa or 0.1 MPa; the two-step sinterillg process has the following conditions: Step 1: sintering pressure: 30-70 Mpa; sintering heating rate: 500-20°C 1mm; sintering temperature: 1550°C -1900°C; sintering heat preservation time: 0-120 mm; and sintering atmosphere: N2 protective atmosphere having a vacuum degree «= 4 Pa or 0.1 MPa; Step 2: sintering pressure: 30-70 Mpa; cooling rate: 5°C-20°Clmin; sintering temperature: 1350°C -1550°C; sintering heat preservation time: 0-120 mm; and sintering atmosphere: N2 protective atmosphere having a vacuum degree «= 4 Pa or 0.1 MPa.