CN100507038C - Preparation method of tungsten carbide-inhibitor composite powder and ultrafine cemented carbide - Google Patents

Abstract

The invention relates to a preparation method of tungsten carbide-inhibitor composite powder and ultrafine hard alloy thereof. First prepare the oxide powder containing carbon and inhibitor, then synthesize tungsten carbide-inhibitor composite powder by direct reduction carbonization method, add metal powder and then carry out ball mill mixing, drying, forming, heat treatment after vacuum sintering or hydrogen sintering, or direct low pressure Sintering to obtain ultrafine or nanometer tungsten carbide-based hard alloy. The invention solves the defects of the prior art that the inhibitors are added unevenly in the later stage or that the inhibitors with low carbonization temperature can only be used when the inhibitors are added in the early stage, so that various inhibitors can be introduced in the early stage and ensure that they are in the tungsten carbide matrix The uniform dispersion, the raw materials used are all environmentally friendly compounds, the preparation temperature is lower than the traditional preparation method, the process is simple and safe, the production cost is low, and it is easy to realize industrialization.

Description

Preparation method of tungsten carbide-inhibitor composite powder and ultrafine cemented carbide

technical field

The invention belongs to a preparation method of tungsten carbide-based ultrafine hard alloy.

Background technique

Ultra-fine-grained tungsten carbide (hereinafter referred to as "WC")-based cemented carbide has the "double high" performance of high strength and high hardness, and can be applied to the production of micro-drills for printed circuit boards, printing needles for dot-matrix printers, precision molds, difficult Processing materials, knives, etc. When the grain size of WC is reduced and the distribution of cobalt in the binder phase is highly uniform, the number and size of defects will be reduced or even zero, and the mechanical properties of the alloy can be much higher than that of ordinary cemented carbide. There are two key processes in the preparation of ultrafine-grained WC-based cemented carbide: one is the preparation of WC or WC-Co raw material powder with fine grains and uniform particle size distribution; the other is the growth inhibition of WC grains during sintering.

At present, the preparation of ultrafine or nanocrystalline WC powder or WC-based composite powder is mainly realized by gas and liquid phase synthesis technology and low-temperature rapid carbonization process in the world (S.D.Dunmead, et al., Method for making submicrometer carbides, submicrometer solid solution carbides, and the material resulting therefrom, US Pat.5380688, Jan.10, 1995; L.E.McCandlish et al., Spray conversion process for the production of nanophase composite powders, World Pat.WO 91/07244, May30, 1991).

For the growth inhibition of WC grains during the sintering process, the researchers mainly synthesized WC-based composite powders in the liquid phase or when WC powders were mixed with metal powders such as cobalt (Co), nickel (Ni), and iron (Fe). Add grain growth inhibitors (such as vanadium carbide (VC), chromium carbide (Cr ₃ C ₂ ), tantalum carbide (TaC), niobium carbide (NbC), etc.) to achieve. like:

(1) Ultrafine or nanometer WC powder plus metal powder (Co powder, or Ni powder, or Fe powder) and inhibitor ball milling, molding, heat treatment after sintering, or direct low-pressure sintering to obtain ultrafine WC-based cemented carbide ( A. Grearson, et al., Method of making ultrafine WC-Co alloys, US Pat.6413293, July2, 2002). This method is currently widely used in the production of cemented carbide. The outstanding problem is that it is difficult to achieve a high degree of uniform dispersion in the WC matrix by ball milling when a small amount of inhibitor is added in the later stage;

(2) Ultrafine or nanometer WC-Co composite powder plus inhibitor ball milling, molding, heat treatment after sintering, or direct low-pressure sintering to obtain ultrafine WC-based cemented carbide (Seung I..Cha et al., Mechanical properties of WC-10 Cocemented carbides sintered from nanocrystalline spray conversion processed powders, International Journal of Refractory Metals and Hard Materials, 2001, 19(4-6): 397-403). This method is a new method for preparing ultra-fine WC-Co cemented carbide developed in the past ten years. The advanced method lies in the use of composite powder, but the inhibitor is still added in the later stage, which has not fundamentally solved the problem that it is difficult to uniformly disperse. .

(3) The composite powder of ultrafine or nano WC-Co (containing inhibitor) is subjected to ball milling, molding, heat treatment after sintering, or direct low-pressure sintering to obtain ultrafine/nano WC-Co cemented carbide (Shao Gangqin et al., without η phase Industrial preparation method of tungsten carbide-cobalt nanocomposite powder, Chinese invention patent ZL 99 1 16597.7, August 13, 1999; GQShao, et al., Properties of superfine tungsten carbide sintered from nanocrystalline powder by spraypyrogenation-continuous reduction carburization process, Proceedings of ^16th International Plansee Seminar, Reutte, Austria, pp.519-526, 2005). The advancement of this method lies in the introduction of soluble salts of inhibitors in the early stage, but because the presence of cobalt limits the subsequent carbonization temperature, it is more suitable for the introduction of inhibitors with low carbonization temperatures (such as vanadium carbide, etc.), while for chromium, tantalum It is difficult to completely carbonize, and there will still be a small amount of oxide or carbon-deficient phase in the WC matrix, so other methods must be used.

Contents of the invention

The purpose of the present invention is to propose a preparation method of WC-inhibitor composite powder and its ultrafine hard alloy aiming at the deficiencies of the prior art. The method uses tungsten oxide (or salt) and inhibitor oxide (or salt) as raw materials to reduce and carbonize WC-inhibitor composite powder in one step, and the products are all carbides, and the process is easy to control and is not limited by the type of raw materials.

The above method is described in detail below:

This method first prepares the oxide powder containing carbon and inhibitor, and then adopts the direct reduction carbonization method (Shao Gangqin et al., the direct reduction carbonization preparation method of tungsten carbide-cobalt nanocomposite powder, Chinese invention patent 200410012902.3, applied on March 26, 2004 ) Synthesize WC-inhibitor composite powder, add metal powder (Co powder, or Ni powder, or Fe powder) and then carry out ball milling, drying, molding, vacuum sintering or hydrogen sintering and heat treatment, or direct low-pressure sintering to obtain ultrafine or Nano WC-based cemented carbide.

Oxide powders containing carbon and inhibitors can be obtained by one of the following three methods: (1) directly using commercial oxide powders and carbon powders for ball milling; (2) mixing soluble tungsten salts and inhibitor salts in proportion Dissolve, spray pyrolysis or spray drying plus calcination to obtain inhibitor-containing oxide powder, and then mix with carbon powder ball mill; (3) Dissolve soluble tungsten salt, inhibitor salt, and carbon source in proportion, and spray Pyrolysis or spray drying plus calcination to produce oxide powders containing carbon and inhibitors.

The preparation method of WC-inhibitor composite powder and ultrafine cemented carbide thereof of the present invention comprises:

1. Preparation method of WC-inhibitor composite powder

Put the oxide powder containing carbon and inhibitor into the atmosphere furnace or vacuum furnace for direct reduction carbonization. in:

(1) ratio

The oxide powder containing carbon and inhibitor and the raw material ratio of WC-inhibitor composite powder are as follows: 91.26-93.39wt% tungsten, 6.17-6.50wt% carbon, and 0.44-6.50wt% metal element of the inhibitor 2.25 wt%.

Tungsten compound can choose one of the following: ammonium metatungstate AMT ((NH ₄ ) ₆ (H ₂ W ₁₂ O ₄₀ )·4H ₂ O), ammonium paratungstate APT ((NH ₄ ) ₁₀ (H ₂ W ₁₂ O ₄₂ )·4H ₂ O), ammonium orthotungstate (NH ₄ ) ₂ WO ₄ , tungstic acid H ₂ WO ₄ , metatungstic acid H ₆ (H ₂ W ₁₂ O ₄₀ ), yellow tungsten WO ₃ , blue tungsten WO _2.9 , Violet tungsten WO _2.72 , brown tungsten WO ₂ and other tungsten oxides or tungsten-containing salts;

Inhibitor raw materials can choose one or more of the following: vanadium (V), chromium (Cr), molybdenum (Mo), tantalum (Ta), niobium (Nb), titanium (Ti) and other acids, ammonium salts, nitric acid Salts, acetates, chlorides, sulfates, oxalates, oxides;

Soluble carbon source can choose one or more of the following: ethylene diammonium (en), fiber, pulp, polypropylene, syrup, sucrose;

(2) The ball milling process, spray pyrolysis, spray drying, and calcination processes are based on the "direct reduction carbonization preparation method of tungsten carbide-cobalt nanocomposite powder" (Shao Gangqin et al., Chinese invention patent 200410012902.3, applied on March 26, 2004);

(3) Synthesis of WC-inhibitor composite powder:

The reaction is carried out in an ordinary heating furnace, or a microwave oven, or a tube furnace, or a fixed bed, or a rotary furnace, or a fluidized furnace, or an atmosphere furnace, or a vacuum furnace, and the ambient atmosphere is an inert gas, or hydrogen, or a carbon-containing gas , or inert gas and hydrogen, or inert gas and carbon-containing gas, or hydrogen and carbon-containing gas, or a mixture of several carbon-containing gases, or vacuum, the temperature is controlled at 1000-1350 ° C, and the reaction time is 0.5-12 hours ;

2. Preparation method of ultrafine WC-based cemented carbide

The prepared WC-inhibitor composite powder and metal powder (Co powder, or Ni powder, or Fe powder) with a particle size of not more than 1.0 μm are ball milled and mixed, dried and granulated, shaped, vacuum sintered or hydrogen sintered, and then heat treated, or Direct low pressure sintering.

(1) ratio:

The proportion of ultra-fine WC-based hard alloy is as follows: 70-97wt% of WC-inhibitor composite powder, 3-30wt% of metal powder; 0.5-12wt% externally added, 0.1-0.3wt% surfactant externally added;

Forming agent:

One or more of the following can be selected: solid paraffin, liquid paraffin, vaseline, synthetic rubber, polyethylene glycol, polyvinyl alcohol;

Surfactant:

You can choose stearic acid or oleic acid;

(2) Ball milling process

Use one or more of ethanol, acetone, and hexane as a medium for wet grinding, material: ball: liquid (mass ratio) = 1: 2～20: 0.5～10; or dry grinding, material: ball (mass ratio )=1:2～20, the ball milling time is 1～72 hours, and the ambient atmosphere is inert gas or vacuum;

(3) Sintering process

The sintering temperature is 1300-1500°C, the holding time is 1-3 hours, and the sintering method is vacuum sintering, hydrogen sintering, or low-pressure sintering. The pressure during vacuum sintering is 1×10 ^-5 ~ 1×10 ^-6 MPa; the pressure during hydrogen sintering is normal pressure, the water content of hydrogen is 0-0.5g/m ³ , and the concentration is 10-100% vol (residual gas argon, or nitrogen); during low-pressure sintering, the pressure in the vacuum stage is 1×10 ^-5 ~ 1×10 ^-6 MPa, and the pressure in the pressurized stage is 3 ~ 7MPa, and the gas is argon or nitrogen;

(4) heat treatment process

The heat treatment method is hot isostatic pressing or low pressure, wherein the atmosphere of hot isostatic pressing treatment is argon or nitrogen, the temperature is 1200-1350 ° C, and the pressure is 100-200 MPa; the atmosphere of low-pressure heat treatment is argon or nitrogen, The temperature is 1250-1400°C, and the pressure is 3-7MPa.

The invention solves the defects of the prior art that the inhibitors are added unevenly in the later stage or that the inhibitors with low carbonization temperature can only be used when the inhibitors are added in the early stage. Evenly dispersed, the raw materials used are all environmentally friendly compounds, the preparation temperature is lower than the traditional preparation method, the process is simple and safe, the production cost is low, and it is easy to realize industrialization. The invention can be extended to the research and production fields of preparing various compound carbides, titanium carbide-based hard alloys, cermets and the like.

Description of drawings

Figure 1: Process flow chart of the preparation method of WC-inhibitor composite powder and its ultrafine cemented carbide.

Fig. 2: XRD pattern of the carbide powder prepared in Example 1.

Among them: (a) WO ₃ /V ₂ O ₅ /Cr ₂ O ₃ +C raw material;

(b) WO ₃ +C raw material;

(c) V ₂ O ₅ +C raw material;

(d) Cr ₂ O ₃ +C raw material;

  

●—WC;★—VC;

Fig. 3: the SEM photograph of the powder gained in embodiment 1;

Fig. 4: the TEM photograph of the powder gained in embodiment 1;

Fig. 5: the SEM photograph of the alloy obtained in embodiment 1;

Fig. 6: the TEM photograph of the alloy obtained in embodiment 1;

Fig. 7: TEM photo of the alloy obtained in Example 2.

specific implementation plan

Example 1: Ammonium metatungstate AMT ((NH ₄ ) ₆ (H ₂ W ₁₂ O ₄₀ )·4H ₂ O), ammonium metavanadate (NH ₄ VO ₃ ), ammonium dichromate ((NH ₄ ) ₂ Cr ₂ O ₇ ) is miscible in distilled water at a mass ratio of 100:0.66:0.74, and is made into oxide powder by spray pyrolysis. The oxide powder and carbon powder were weighed according to the mass ratio W: C=3.83:1, V: C=1.21:1, Cr: C=2.00:1, and put into a roller mill for dry grinding for 72 hours (material: ball =1:2), the resulting mixed powder was carbonized in a tube furnace in an argon atmosphere at 1350°C for 0.5 hours, and then cooled to room temperature in argon. At the same time, a comparative experiment was carried out in this furnace: using WO ₃ +C, V ₂ O ₅ +C, and Cr ₂ O ₃ +C three additional raw materials, in which the proportions of tungsten, vanadium, chromium and carbon all follow this implementation example ratio. The XRD diagram of the powder after carbonization is shown in the accompanying drawing 2 of the specification. The results show that: at the carbonization temperature of 1350 ° C, the inhibitor oxide raw materials can be carbonized into the desired inhibitor carbide; compared with the prepared WC-inhibitor compound The characteristic peaks of the powder and pure WC powder are exactly the same, but the inhibitor cannot be detected due to the small amount. The characteristic parameters of the prepared WC-inhibitor composite powder are: tungsten content W=92.86wt%, total carbon _Ct =6.18wt%, free carbon _Cf =0.04wt%, oxygen content O=0.11wt%, other Metal element content = 0.81wt%, specific surface area BET = 2.52m ² /g. The scanning electron microscope (SEM) and transmission electron microscope (TEM) photos of the powder are shown in Fig. 3 and Fig. 4, respectively. It can be seen that the particle size of the powder is uniform, and the size is about 100-200nm. Add cobalt powder (Fess=0.8μm, by 12wt%) and appropriate amount of carbon powder and forming agent to the WC-inhibitor composite powder for ball milling, drying, molding, vacuum sintering (1400°C, 1h), low-pressure heat treatment ( 1400°C, 1h, 5MPa), thus producing ultra-fine WC-12Co-0.4VC-0.4Cr ₃ C ₂ cemented carbide, and its SEM and TEM photos are shown in Figure 5 and Figure 6, respectively. It can be seen that the grain size in the cemented carbide is uniform, there are no macropores, cobalt pools, carbon deficiency or carburized areas, and the cross-section of most grains is a matrix with a length of 0.3-0.5 μm and a width of 0.1-0.2 μm. shape.

Example 2: Ammonium paratungstate APT ((NH ₄ ) ₁₀ (H ₂ W ₁₂ O ₄₂ )·4H ₂ O), ammonium metavanadate (NH ₄ VO ₃ ), ammonium dichromate ((NH ₄ ) ₂ Cr ₂ O ₇ ) Miscible in distilled water at a mass ratio of 100:0.44:0.50, spray-dried by centrifugal pressure to make oxide powder, put it in a vacuum furnace at 250°C for 8 hours, and mix the oxide powder and carbon powder by mass Ratio W:C=3.83:1, V:C=1.21:1, Cr:C=2.00:1 weighed, put into roller ball mill, wet mill with absolute alcohol as medium for 48 hours (material: ball: liquid = 1:3:0.8), the mixed powder obtained after drying was carbonized at 1000°C for 12 hours in a rotary furnace in a nitrogen atmosphere, and then cooled to room temperature in a nitrogen atmosphere. The characteristic parameters of the prepared WC-inhibitor composite powder are: tungsten content W=93.27wt%, C _t =6.15wt%, _Cf =0.05wt%, O=0.10wt%, other metal element content=0.43wt %, BET=2.62m ² /g. Add cobalt powder (Fess=0.6 μm, 10wt%) and appropriate amount of carbon powder and forming agent to the WC-inhibitor composite powder for ball milling, drying, molding, hydrogen sintering (1500 ° C, 1 h), hot isostatic pressing heat treatment ( 1350°C, 1h, 100MPa), thus producing ultra-fine WC-10Co-0.3VC-0.3Cr ₃ C ₂ cemented carbide. The TEM photo of the obtained alloy is shown in Fig. 7 of the specification, and it can be seen from the figure that most of the crystal grains have a rectangular cross-section with a length of 0.3-0.5 μm and a width of 0.1-0.2 μm. The measured mechanical performance parameters are: Rockwell hardness HRA=92.5, bending strength TRS=4080MPa.

Example 3: Ammonium metatungstate AMT ((NH ₄ ) ₆ (H ₂ W ₁₂ O ₄₀ )·4H ₂ O) and ammonium metavanadate (NH ₄ VO ₃ ) are miscible in distilled water at a mass ratio of 100:1.03 , through centrifugal pressure spray drying to make oxide powder, put it in a microwave oven at 600°C for 10 minutes and calcinate, then mix the oxide powder and carbon powder according to the mass ratio W:C=3.83:1, V:C=1.21:1 Weigh it, put it into a ball mill, and use acetone as a medium for wet grinding for 48 hours (material: ball: liquid = 1:4:0.8), and the mixed powder obtained after drying is carbonized in a vacuum furnace at 1300 ° C for 2 hours, and then the Cool to room temperature. The characteristic parameters of the prepared WC-inhibitor composite powder are: tungsten content W=91.23wt%, Ct=6.45wt%, _Cf =0.04wt%, O=0.13wt%, other metal element content=2.15wt% , BET=2.66m ² /g. Add cobalt powder (Fess=1.0μtm, 30wt%) and appropriate amount of carbon powder and molding agent to WC-inhibitor composite powder for ball milling, drying, molding, vacuum sintering (1250°C, 3h), hot isostatic pressing ( 1200°C, 1h, 200MPa), thus producing ultra-fine WC-30Co-2VC cemented carbide.

Example 4: Ammonium metatungstate AMT ((NH ₄ ) ₆ (H ₂ W ₁₂ O ₄₀ )·4H ₂ O), ammonium dichromate ((NH ₄ ) ₂ Cr ₂ O ₇ ), glucose (C ₆ H ₁₂ O ₆ ) raw materials are miscible in distilled water at a mass ratio of 100:0.84:48.00, and are sprayed and pyrolyzed to produce carbon-containing oxide powder. ) in a rotary furnace at 1350°C for 3 hours, and then cooled with the furnace in argon. The characteristic parameters of the prepared WC-inhibitor composite powder are: tungsten content W=93.32wt%, C _t =6.13wt%, _Cf =0.06wt%, O=0.10wt%, other metal element content=0.39wt %, BET=2.56m ² /g. Add cobalt powder (Fess=0.8μm, 3wt%) and forming agent to the WC-inhibitor composite powder for ball milling, drying, molding, vacuum sintering (1450°C, 1h), low-pressure heat treatment (1400°C, 1h, 7MPa), In this way, ultra-fine WC-3Co-0.5Cr ₃ C ₂ cemented carbide is obtained.

Example 5: WO ₃ , V ₂ O ₅ , and Cr ₂ O ₃ raw materials were formulated into a suspension in distilled water at a mass ratio of 100:0.41:0.59, and were spray-dried by centrifugal pressure to make oxide powder, which was then placed in a drying oven After drying at 200°C for 2 hours, weigh the powder and carbon powder according to the mass ratio W:C=3.83:1, V:C=1.21:1, Cr:C=2.00:1, put them into a ball mill, and Alkane was used as a medium for wet milling for 48 hours (material:ball:liquid=1:3.5:0.8), and the mixed powder obtained after drying was carbonized in a vacuum furnace at 1300°C for 2 hours, and then cooled to room temperature with the furnace. The characteristic parameters of the prepared WC-inhibitor composite powder are: tungsten content W=92.98wt%, C _t =6.19wt%, _Cf =0.05wt%, O=0.09wt%, other metal element content=0.69wt %, BET=2.68m ² /g. Add cobalt powder (Fess=0.6μm, 10wt%) and forming agent to the WC-inhibitor composite powder for ball milling, drying, molding, vacuum sintering (1380°C, 1h), low-pressure heat treatment (1250°C, 1h, 3MPa), In this way, ultra-fine WC-10Co-0.3VC-0.5Cr ₃ C ₂ cemented carbide was prepared. The measured mechanical performance parameters are: Rockwell hardness HRA=93.0, flexural strength TRS=3910MPa.

Claims (2)

1. A preparation method of tungsten carbide-inhibitor composite powder, characterized in that the oxide powder containing carbon and inhibitor is put into an atmosphere furnace or a vacuum furnace for direct reduction carbonization, wherein: tungsten carbide-inhibitor composite powder The composition of the raw material ratio is as follows: 91.26-93.39wt% tungsten, 6.17-6.50wt% carbon, 0.44-2.25wt% inhibitor metal elements; the synthesis temperature of the tungsten carbide-inhibitor composite powder is controlled at 1000～1350℃, the reaction time is 0.5～12 hours; Oxide powders containing carbon and inhibitors are obtained by one of three methods: (1) Directly adopt commercial oxide powder and carbon powder ball milling; (2) dissolving the soluble tungsten salt and the salt of the inhibitor in proportion, spray pyrolysis or spray drying and calcining to obtain the oxide powder containing the inhibitor, and then mix it with carbon powder; (3) Dissolve soluble tungsten salt, inhibitor salt, and carbon source in proportion, and prepare oxide powder containing carbon and inhibitor through spray pyrolysis or spray drying plus calcination. 2. A preparation method of ultrafine tungsten carbide-based cemented carbide, characterized in that the tungsten carbide-inhibitor composite powder and particle diameter are no more than 1.0 μm of cobalt, nickel or iron prepared according to the method claimed in claim 1 Metal powder ball milling, drying granulation, molding, heat treatment after vacuum sintering or hydrogen sintering, or direct low-pressure sintering, of which: (1) The ratio of ultra-fine tungsten carbide-based cemented carbide is by weight percentage: tungsten carbide-inhibitor composite powder is 70-97wt%, metal powder is 3-30wt%; agent, wherein 0.5 to 12 wt% of the forming agent is added, and 0.1 to 0.3 wt% of the surfactant is added; The molding agent is selected from one or more of the following: solid paraffin, liquid paraffin, vaseline, synthetic rubber, polyethylene glycol, polyvinyl alcohol; Surfactant selects stearic acid or oleic acid; (2) The ball milling process is: use one or more of ethanol, acetone, and hexane as a medium for wet milling, and the mass ratio is material: ball: liquid=1: 2～20: 0.5～10; or dry milling, The mass ratio is material:ball=1:2～20, the ball milling time is 1～72 hours, and the ambient atmosphere is inert gas or vacuum; (3) The sintering process is as follows: the sintering temperature is 1300-1500°C, the holding time is 1-3 hours, the sintering method is one of vacuum sintering, hydrogen sintering, and low-pressure sintering, and the pressure during vacuum sintering is 1×10 ^-5 ～1×10 ^-6 MPa; the pressure during hydrogen sintering is normal pressure, the water content of hydrogen is 0～0.5g/m ³ , the concentration is 10～100% vol, and the remaining gas is argon or nitrogen; vacuum stage during low pressure sintering The pressure is 1×10 ^-5 ~ 1×10 ^-6 MPa, the pressure in the pressurization stage is 3 ~ 7MPa, and the gas is argon or nitrogen; (4) The heat treatment process is: the heat treatment method is hot isostatic pressing or low pressure, wherein the atmosphere of hot isostatic pressing treatment is argon or nitrogen, the temperature is 1200-1350 ° C, and the pressure is 100-200 MPa; the atmosphere of low-pressure heat treatment is argon gas or nitrogen, the temperature is 1250-1400°C, and the pressure is 3-7MPa.

Images