Preparation of high specific gravity tungsten-nickel-cobalt nanopowder and alloy with uniform element distribution and fine particle size

Abstract

The invention discloses a preparation method of a high specific gravity tungsten-nickel-cobalt nanopowder and alloy with uniform element distribution and fine particle size, belonging to the technical field of shielding materials and powder metallurgy. The method comprises the following steps: dissolving tungsten trioxide, cobalt chloride and nickel chloride in deionized water, mixing and stirring evenly, heating and stirring to evaporate the liquid, and then drying in an oven, grinding the dried agglomerates with a mortar and sieving to obtain a precursor powder. Subsequently, the precursor powder is sent into an argon plasma torch through a carrier gas hydrogen, and the powders from various parts are collected after the reaction is completed. The powders are loaded into a stainless steel mold, cold pressed and sintered in a tubular furnace under a hydrogen atmosphere to obtain a tungsten-nickel-cobalt heavy alloy block. The particle size of the tungsten-nickel-cobalt nanopowder prepared by the present invention is about 25nm, and the relative density of the tungsten-based heavy alloy after sintering is >99%. The shielding test results show that the linear absorption coefficient is 1.31 times that of lead.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy, and relates to a preparation method of a high-density tungsten-nickel-cobalt nano powder and an alloy thereof with uniform element distribution and fine particle size. Background Art

[0002] Tungsten-based high-density alloy is a two-phase composite material composed of tungsten as the matrix and nickel, cobalt, iron, copper, etc. as the main bonding phase. It has high strength, good plasticity, strong impact resistance and penetration ability, good corrosion resistance and high-temperature oxidation resistance, small thermal expansion coefficient, good electrical and thermal conductivity, and strong radiation absorption ability. It can not only be machined by turning, milling, grinding, planing, drilling, tapping, etc., but also can be subjected to large deformation strengthening treatments such as rolling, rotary forging and forging. Tungsten-based high-density alloy has been widely used in modern military industry and civilian industry, such as armor-piercing and armor-piercing projectiles in the weapons industry, gyroscope outer rotors of navigation instruments in aerospace, and radiation shielding materials and anvil materials in the nuclear industry.

[0003] With the development of science and technology, higher performance requirements are placed on tungsten-based high-density alloys, such as higher density, better mechanical properties, and the ability to shield radiation. At present, there are problems of coarse tungsten grains and uneven organization. Studies have shown that the probability of brittle phase precipitation in tungsten-nickel-cobalt alloys is lower than that of traditional tungsten-nickel-iron alloys, and replacing iron with cobalt can reduce the sintering wetting angle and increase the sintering densification rate. Nickel and cobalt can play a synergistic strengthening role, which is conducive to obtaining fine-grained tungsten-based high-density alloys after sintering. Therefore, providing a method for preparing tungsten-nickel-cobalt nanopowders and alloys thereof with uniform element distribution and fine particle size can be beneficial to improving the performance of tungsten-based high-density alloys.

[0004] At present, the traditional methods for preparing tungsten-based high-density alloy powders mainly include mechanical alloying, chemical coprecipitation, and sol-gel methods. Due to the easy wear of the spherical tank and pellets in the mechanical alloying method, impurity elements are easily introduced, which reduces the performance of the alloy material after sintering. Although the chemical coprecipitation method has a simple process, the powder agglomeration is serious, which slows down the sintering densification rate and makes it difficult for the material to achieve density. The sol-gel method takes a long time and is simple to operate, but it is difficult to mass produce. Compared with the traditional preparation method, the high-frequency induction thermal plasma reduction technology can be used to synthesize tungsten-nickel-cobalt nanopowders in one step. The powder has good element dispersion, uniform structure, fine particle size, higher sintering reaction activity, and is more conducive to obtaining a high-density tungsten-nickel-cobalt alloy with uniform density and excellent performance. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing high-density tungsten-nickel-cobalt nanopowder and its alloy with uniform element distribution and fine particle size, so as to solve the problem of uneven particle size distribution and easy agglomeration of powder prepared by traditional methods. High-frequency induction thermal plasma technology is adopted, tungsten oxide, cobalt salt and nickel salt are used as raw materials, and high-density tungsten-nickel-cobalt nanopowder with uniform element distribution and fine particle size is prepared by high-frequency induction thermal plasma equipment, and tungsten-nickel-cobalt heavy alloy with excellent performance is obtained by traditional sintering.

[0006] The method for preparing a high-density tungsten-nickel-cobalt nanopowder and an alloy thereof with uniform element distribution and fine particle size described in the present invention is characterized by comprising the following steps:

[0007] (1) A certain amount of tungsten oxide, cobalt salt, and nickel salt are mechanically mixed in a certain ratio, and the mixed powder is sieved through an 80-mesh sieve to obtain a precursor powder.

[0008] (2) The precursor powder obtained in step (1) is fed into an argon plasma torch through a carrier gas of hydrogen. After the reaction is completed and the entire system is completely cooled, the powder is collected from various parts. The entire system is maintained in a slightly negative pressure state by adjusting the induced air negative pressure during the feeding process to ensure the stability of the equipment parameters and the plasma arc. After the reaction is completed and the entire system is completely cooled, the powder is collected from various parts, and the powder particle size is about 25 nm.

[0009] (3) The powder obtained in step (2) is placed in a stainless steel mold and cold pressed.

[0010] (4) The pressed green sheet obtained in step (3) is heated to a certain temperature in a hydrogen atmosphere and kept at this temperature for a certain period of time, and then cooled in the furnace or cooled to room temperature at a certain rate to obtain a tungsten-nickel-cobalt alloy.

[0011] In step (1), the tungsten oxide is selected from tungsten dioxide, tungsten trioxide, etc., and the cobalt salt and the nickel salt can be sulfates, nitrates, chlorides, etc. of cobalt and nickel. The sum of the mass of nickel and cobalt elements in the three raw materials accounts for 0-20% of the total mass of tungsten, nickel and cobalt, and the content of nickel and cobalt is not 0 at the same time.

[0012] In step (2), the power of the plasma device is 30KW, the hydrogen flow rate is 0.5-5L / h, the argon flow rate is 20-30L / h, and the powder feeding rate is 1-40g / min.

[0013] In step (3), the cold pressing pressure is 200-600 MPa, the holding time is 0.5-10 min, the optimal pressing pressure is 400 MPa, and the optimal holding time is 5 min.

[0014] In step (4), the hydrogen flow rate is 50-300 ml / min, the heating rate is 1-20°C / min, the holding time is 0.5-3h, the sintering temperature is 1300-1550°C, and the cooling rate is 1-20°C / min.

[0015] The beneficial effects of the present invention are embodied in:

[0016] The present invention provides a method for preparing a high-density tungsten-nickel-cobalt nanopowder with uniform element distribution and fine particle size. The particle size of the prepared nano-scale powder is about 25nm, and the sintered tungsten-based high-density alloy has high density, fine grains, and uniform distribution of tungsten matrix phase and bonding phase. The relative density of the sintered tungsten-based heavy alloy is >99%, and the shielding test results show that the line absorption coefficient is 1.31 times that of lead. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a scanning electron microscope image of tungsten-nickel-cobalt powder.

[0018] Figure 2 This is the X-ray diffraction pattern of tungsten-nickel-cobalt powder.

[0019] Figure 3 It is a transmission electron microscope image and element distribution map of tungsten-nickel-cobalt powder.

[0020] Figure 4 This is a scanning electron microscope image of the fracture of the sintered tungsten-nickel-cobalt heavy alloy. DETAILED DESCRIPTION

[0021] In order to further illustrate the present invention, the following examples are given. These examples are only for illustration of the present invention, and are not intended to limit the scope of protection claimed by the present invention.

[0022] Example 1

[0023] (1) The raw materials of tungsten trioxide, cobalt chloride and nickel chloride are mechanically mixed uniformly according to the mass fraction W:Ni:Co=90:7:3, and sieved with a sieve of 80 meshes to obtain a precursor powder.

[0024] (2) The precursor powder obtained in step (1) is fed into an argon plasma torch through a carrier gas of hydrogen. The power of the plasma device is 30 kW, the hydrogen flow rate is 2 L / h, the argon flow rate is 20 L / h, and the powder feeding rate is 10 g / min. After the reaction is completed and the entire system is completely cooled, the powders at various locations are collected.

[0025] (3) The powder obtained in step (2) is placed in a stainless steel mold and cold pressed at a pressing pressure of 400 MPa for 5 min.

[0026] (4) The compact obtained in step (3) is placed in a sintering boat and then sent into a tubular furnace for sintering in a hydrogen atmosphere with a hydrogen flow rate of 250 ml / min. The temperature is increased to 1400°C at a heating rate of 5°C / min and kept at that temperature for 60 min. After the insulation, the temperature is decreased to 600°C at a rate of 10°C / min and then cooled to room temperature in the furnace to obtain a tungsten-based heavy alloy block.

[0027] Example 2

[0028] (1) The raw materials of tungsten trioxide, cobalt nitrate and nickel nitrate were mechanically mixed uniformly according to the mass fraction of W:Ni:Co=93:5:2, and sieved with a 140-mesh sieve to obtain a precursor powder.

[0029] (2) The precursor powder obtained in step (1) is fed into an argon plasma torch through a carrier gas of hydrogen. The power of the plasma device is 30 kW, the hydrogen flow rate is 3 L / h, the argon flow rate is 25 L / h, and the powder feeding rate is 20 g / min. After the reaction is completed and the entire system is completely cooled, the powders at various locations are collected.

[0030] (3) The powder obtained in step (2) is placed in a stainless steel mold and cold pressed at a pressing pressure of 200 MPa for 5 min.

[0031] (4) The compact obtained in step (3) is placed in a sintering boat and then sent into a tubular furnace for sintering in a hydrogen atmosphere with a hydrogen flow rate of 300 ml / min. The temperature is increased to 1450°C at a heating rate of 5°C / min and kept at this temperature for 60 min. After the holding period, the temperature is decreased to 600°C at a rate of 5°C / min and then cooled to room temperature in the furnace to obtain a tungsten-based heavy alloy block.

Claims

1. A method for preparing high-density tungsten-nickel-cobalt nanopowder with uniform element distribution and fine particle size, characterized in that: The steps include: (1) mechanically mixing raw materials of tungsten trioxide, cobalt nitrate, and nickel nitrate according to a mass fraction of W:Ni:Co=90:7:3, or W:Ni:Co=93:5:2, and sieving the mixed powder through a sieve of 80 meshes to obtain a precursor powder; (2) The precursor powder obtained in step (1) is fed into an argon plasma torch through a carrier gas of hydrogen, and the powders at various locations are collected after the reaction is completed and the entire system is completely cooled; the entire system is maintained in a slightly negative pressure state by adjusting the induced draft negative pressure during the feeding process to ensure the stability of the equipment parameters and the plasma arc; the powders at various locations are collected after the reaction is completed and the entire system is completely cooled; In step (2), the power of the plasma device is 30KW, the hydrogen flow rate is 0.5-5L / h, the argon flow rate is 20-30L / h, and the powder feeding rate is 1-40g / min; The particle size of the nano-scale powder is 25nm. The sintered tungsten-based high-density alloy has high density, fine grains, and uniform distribution of tungsten matrix phase and bonding phase. The relative density of the sintered tungsten-based heavy alloy is >99%, and the shielding test results show that the linear absorption coefficient is 1.31 times that of lead.

2. A method for preparing a high specific gravity tungsten-nickel-cobalt alloy, characterized in that: The high specific gravity tungsten-nickel-cobalt nanopowder with uniform element distribution and fine particle size prepared by the method described in claim 1 specifically comprises the following steps: loading the powder into a stainless steel mold for cold pressing; heating and keeping the obtained pressed blank in a hydrogen atmosphere, and then cooling it with the furnace to obtain a tungsten-nickel-cobalt alloy.

3. The method according to claim 2, characterized in that The cold pressing pressure is 200-600Mpa, and the holding time is 0.5-10min.

4. The method according to claim 3, characterized in that The pressing pressure is 400 MPa and the holding time is 5 min.

5. The method according to claim 2, characterized in that The hydrogen flow rate is 50-300 ml / min, the heating rate is 1-20°C / min, the holding time is 0.5-3h, the sintering temperature is 1300-1550°C, and the cooling rate is 1-20°C / min.

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