CN1082551C - Smelting method and equipment for nanometer hard tungsten-cobalt carbide alloy - Google Patents

Abstract

A method and equipment for manufacturing nano-tungsten carbide-cobalt cemented carbide, which is characterized in that the mixed powder of WO ₃ and CoO nanoparticles is directly reduced-carbonized into WC-Co nano-particles in an H ₂ /C ₂ H ₂ atmosphere. Cemented carbide powder, the alloy powder contains a small amount of carbon nanotubes. Compared with the prior art, the present invention has the outstanding advantages of reduced manufacturing cost, the crystal grain size of the alloy is less than 100nm, and the highest microhardness of the alloy reaches 28GPa. Its mechanical strength, wear resistance and other technical performance indicators are superior to the existing technology, and can be widely used in the production of cutting tools, molds, measuring tools, mining drilling tools and various wear-resistant parts.

Description

Nano tungsten carbide-cobalt cemented carbide manufacturing method and equipment

The invention relates to a tungsten carbide alloy, in particular to a method and equipment for manufacturing nanometer tungsten carbide-cobalt hard alloy.

Tungsten carbide has excellent properties such as high hardness and high wear resistance, and is widely used in the production of cutting tools, molds, measuring tools, mining drilling tools and wear-resistant parts. U.S. Patent 5651808 provides a method for manufacturing nano-WC-Co cemented carbide powder. The method is to mix tungstate H ₂ WO ₄ or ammonium tungstate (NH ₄ ) ₆ (HW ₁₂ O ₄₀ )·4H ₂ O and cobalt Salt CoCl ₂ 6H ₂ O or Co(NO ₃ ) 6H ₂ O or Co(CH ₃ COO) ₂ 4H ₂ O generates W and Co composite powder through thermochemical reaction, and realizes its industrial production by spray drying technology; Use CO/CO ₂ mixed gas at 700-850°C to carbonize W and Co composite powders into nano WC-Co composite powders. The grain size of the powders is less than 100nm. Fluidized bed technology is used to realize the industrialization of the carbonization process.

The purpose _of the present invention is to provide a new manufacturing method and equipment for nano-WC-Co hard alloy, which uses acetylene _C2H2 gas to carbonize metal W nanoparticles to produce nano-WC-Co composite powder, the crystal size of which is less than 100nm. The invention has the advantages of low production cost, a small amount of carbon nanotubes are contained in the prepared nano-hard alloy, and the carbon nanotube has a dispersion strengthening effect on the nano-hard alloy, so that the hardness and bending strength of the nano-hard alloy of the present invention are improved. It exceeds the corresponding value of the existing similar nano-hard alloy.

A method for manufacturing nanometer tungsten carbide-cobalt hard alloy, comprising hydrogen reduction reaction and carbonization reaction, characterized in that the following process steps are adopted:

a) According to the set composition of nano-WC-Co cemented carbide, the weight percentage of WC component is 70-97, and the weight percentage of Co component is 3-30. Take the corresponding W-containing ammonium tungstate aqueous solution, Cobalt nitrate aqueous solution containing Co content, mixed with ammonia water, add appropriate amount of polyethylene glycol and ethylenediamine, and mix well;

b) adding nitric acid to adjust the pH value to 1.6-2.0, and precipitate a mixture of WO ₃ and CoO particles;

c) Remove the ammonia water, put the above paste mixture in a container, and calcinate at 600-800° C. for 1-3 hours to form a mixed powder of WO ₃ and CoO particles;

d) placing the above-mentioned mixed powder in a quartz boat in a quartz tube, and evacuating the oxygen in the quartz tube;

e) Passing hydrogen for reduction, the purity of hydrogen is 99.99%, and the time of passing hydrogen is 1 to 3 hours to obtain a mixed powder of metal W and Co nanoparticles;

f) Turn off the hydrogen gas, fill the quartz tube with high-purity acetylene C ₂ H ₂ gas to carbonize metal W nanopowder, the carbonization temperature is 500-950°C, and the carbonization time is 0.5-3 hours; the preferred carbonization temperature is 600-900 ℃, the carbonization time is 1-2 hours, and the WC-Co nanoparticle composite powder is obtained; the carbonization process can be carried out in a fluidized bed;

g) Vacuum hot pressing and sintering processes are used to make WC-Co nano-tungsten carbide bulk materials.

A special device for implementing the above method, characterized in that the device is composed of a quartz tube 1, a quartz boat 2, an electric heater 3, a thermocouple 4, a temperature controller 5, an air charging channel 6, and an exhaust pipe 7, wherein the quartz tube 1 is arranged in the electric heater 3, the quartz boat 2 containing the mixed powder of WO ₃ and CoO is placed in the quartz tube 1, the thermocouple 4 is arranged outside the quartz tube 1, and connected to the temperature controller 5, the quartz tube 1 One end of it is connected with an inflatable channel 6, which is respectively connected with a hydrogen source and a _C2H2 gas source through a valve and a flow meter, _and the other end is connected with an exhaust pipe 7.

Compared with the prior art, the present invention has the following outstanding advantages:

1. The cemented carbide of the present invention contains a small amount of carbon nanotubes, which have super high strength, toughness and Young's modulus. "American Science" magazine prepares nano-devices from carbon nanotubes, and has super strong mechanical properties Listed as one of the world's top ten science and technology news in 1997. Although carbon nanotubes have potential industrial application prospects, there has been no report on the practical application of carbon nanotubes in the cemented carbide manufacturing industry so far. For references on the basic research on the super-mechanical properties of carbon nanotubes, see:

① M.M.J. Treacy, et.al, Nature, 381(1996) 678.

②E.W.Wong, et.al, Science, 277(1997)1971.

2, the microhardness maximum value of nanometer WC-Co cemented carbide of the present invention reaches 28GPa, surpasses the highest value (22GPa) of existing similar nanometer cemented carbide microhardness, this and contain carbon in the cemented carbide of the present invention related to nanotubes.

3. Metal W nanopowder is carbonized with acetylene C ₂ H ₂ to form tungsten carbide nanopowder with an average grain size of less than 100nm. Since the price of acetylene C ₂ H ₂ gas is cheaper than carbon monoxide CO gas, the manufacturing cost is reduced.

Figure 1 is a schematic diagram of the special equipment for manufacturing nano-WC-Co cemented carbide.

Fig. 2 is a TEM morphology image of carbon nanotubes in the nanometer WC-Co cemented carbide of the present invention.

Fig. 3 is an electron diffraction image of carbon nanotubes in the nanometer WC-Co cemented carbide of the present invention.

Example:

A method for manufacturing nanometer WC-Co cemented carbide, the preparation process of direct reduction-carbonization in H ₂ /C ₂ H ₂ atmosphere:

·In the WC-Co alloy, the weight percentage of the WC component is 90, and the weight percentage of the Co component is 10. Take the corresponding ammonium tungstate aqueous solution and cobalt nitrate aqueous solution and mix them into ammonia water, and add appropriate amount of polyethylene glycol and ethyl alcohol. Diamine, to prevent the precipitated particles from becoming thicker, stir and mix;

Add nitric acid to the above mixture to adjust the pH value to 1.8, and precipitate a mixture of WO ₃ and CoO particles;

Remove the ammonia water, put the above paste mixture in a container, and calcinate at 700°C for 2 hours to form a mixed powder of WO ₃ and CoO particles;

Put the above-mentioned WO ₃ , CoO mixed powder in the quartz boat 2, and place the quartz boat 2 in the quartz tube 1, seal it and then vacuumize it to remove the oxygen in the quartz tube 1;

Slowly raise the temperature of the quartz tube to 700°C, pass hydrogen for reduction, the purity of hydrogen is 99.99%, and the hydrogen flow time is 2 hours to obtain a mixed powder of metal W and Co nanoparticles.

Turn off the hydrogen gas, fill the quartz tube with high-purity acetylene C ₂ H ₂ gas to carbonize the metal W nanopowder, the carbonization temperature is 900°C, and the carbonization time is 1 hour to obtain the composite powder of WC-Co nanoparticle; Except for a small amount of carbon nanotubes, the metal W nanopowders were all carbonized into WC nanopowders, and no other free carbon was found;

After the carbonization reaction is completed, hydrogen gas is introduced to rapidly cool the powder;

·Using vacuum hot pressing (vacuum degree of 10 ^-5 Pa, temperature of 500 ° C, hot pressing pressure of 1 GPa) technology to press the above WC-Co nano powder into shape, and sintering at 1320 ° C in a nitrogen protective atmosphere A bulk cemented carbide of nanometer WC-Co is obtained.

Carbide performance of the present invention is described as follows according to actual measurement and analysis result: After testing, in above-mentioned cemented carbide, the weight percent of WC component is 89.9, and the weight percent of Co component is 10, and average grain size is 80nm, The highest value of its microhardness Hv is 28GPa (2800kg/mm ² ), exceeding the highest value of the microhardness of nano-hard alloys currently reported in the world; it was observed with a transmission electron microscope (TEM) that the above-mentioned WC-Co nanopowder contains A small amount of carbon nanotubes (shown in Figure 2, Figure 3). In the process of carbonizing metal W nanoparticles with acetylene C ₂ H ₂ gas, due to the catalytic effect of metal Co nanoparticles, carbon nanotubes are simultaneously formed during the carbonization process.

Claims (4)

1. A manufacturing method of nanometer tungsten carbide-cobalt cemented carbide, comprising hydrogen reduction reaction and carbonization reaction, characterized in that the following process steps are adopted: a) According to the set composition of nano-WC-Co cemented carbide, the weight percentage of WC component is 70-97, and the weight percentage of Co component is 3-30. Take the corresponding W-containing ammonium tungstate aqueous solution, Cobalt nitrate aqueous solution containing Co content, mixed with ammonia water, add appropriate amount of polyethylene glycol and ethylenediamine and mix well; b) adding nitric acid to adjust the pH value to 1.6-2.0, and precipitate a mixture of WO ₃ and CoO particles; c) Remove the ammonia water, put the above paste mixture in a container, and calcinate at 600-800° C. for 1-3 hours to form a mixed powder of WO ₃ and CoO particles; d) placing the above-mentioned mixed powder in a quartz boat in a quartz tube, and evacuating the oxygen in the quartz tube; e) reducing by introducing hydrogen gas, the purity of hydrogen gas is 99.99%, and the time of passing hydrogen gas is 1 to 3 hours to obtain metal W and Co nanopowders; f) Turn off the hydrogen gas, fill the quartz tube with high-purity acetylene C ₂ H ₂ gas to carbonize metal W nanopowder, the carbonization temperature is 500-950°C, and the carbonization time is 0.5-3 hours to obtain WC-Co nanoparticle composite powder body; g) Vacuum hot pressing and sintering processes are used to make WC-Co nano-tungsten carbide bulk materials. 2. The method according to claim 1, characterized in that the quartz tube is filled with high-purity acetylene C ₂ H ₂ gas to carbonize metal W nanopowder, the carbonization temperature is 600-900°C, and the carbonization time is 1-2 Hour. 3. The method according to claim 1 or 2, characterized in that the hydrogen reduction reaction can be carried out by spray drying technology, and the carbonization reaction can be carried out in a fluidized bed. 4. A special device for implementing the method of claim 1, characterized in that the device consists of a quartz tube (1), a quartz boat (2), an electric heater (3), a thermocouple (4), a temperature controller (5 ), an air-filling channel (6), and an exhaust pipe (7), in which the quartz tube (1) is arranged in the electric heater (3), and the quartz boat (2) containing WO ₃ and CoO mixed powder is placed in the quartz Inside the tube (1), the thermocouple (4) is arranged on the outside of the quartz tube (1) and connected to the temperature controller (5). One end of the quartz tube (1) is connected to an air-filling channel (6), which passes through the valve, The flow meter is connected to the hydrogen source and _{the C2H2} gas source, and the other end thereof is connected to the exhaust pipe (7).

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