Metal matrix composite wcu high pressure assisted flash sintering method and product

Abstract

The application belongs to the technical field of powder metallurgy, and discloses a WCu high-pressure auxiliary flash sintering method of metal matrix composite material, which comprises the following steps: firstly, uniformly mixing tungsten powder and copper powder according to a proportion to obtain tungsten-copper mixed powder; then, adding the tungsten-copper mixed powder into a mold, connecting the mold into a flash sintering device, and applying a pressure of not less than 50 MPa to the mold; further, applying a pulse current to the mold, and performing flash sintering until the temperature exceeds the melting point of copper, so as to obtain the metal matrix composite material WCu. The method can verify and explore the flash sintering of metal matrix powder by using WCu20 mixed powder which is difficult to be densified, and successfully realizes the flash sintering of metal matrix powder.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, and relates to the preparation of metal matrix composites, and particularly to the high-pressure assisted flash sintering technology of WCu20 metal matrix composite. Background Technology

[0002] Metal matrix composites have attracted widespread attention due to their superior properties of simultaneously reinforcing the second phase and the metal matrix. When the volume fraction of the reinforcing phase is high, conventional casting methods cannot produce bulk materials with a uniform distribution of the reinforcing phase; therefore, powder metallurgy is often used to prepare metal matrix composites containing a high proportion of the reinforcing phase. However, when the wettability between the reinforcing phase particles and the metal matrix is ​​poor (e.g., W-Cu, Ag-TiC, Cu-TiC), conventional powder metallurgy methods struggle to produce high-density composites, especially when the volume fraction of the reinforcing phase is high.

[0003] W / Cu composites combine the high electrical and thermal conductivity of Cu with the excellent properties of W, such as high hardness, resistance to electrolytic corrosion, high melting point, and low thermal expansion. They have important applications in electrical contact materials, electronic packaging materials, functionally graded materials, sweating materials, electromagnetic rail materials, and kinetic energy materials. However, W and Cu have poor wettability and significantly different physical properties, making it difficult to manufacture completely dense and uniformly distributed samples, especially W / Cu materials with a high W ratio. For example, high-temperature liquid-phase sintering of W / Cu composites can only achieve a density of 90-95%, and it also causes microstructure coarsening. Using alloying elements, such as Zn and Sn, can significantly promote the densification of W / Cu composites and improve interfacial strength, but the addition of alloying elements inevitably deteriorates the material's electrical and thermal conductivity. Other processes, such as SPS sintering, hot isostatic pressing, melt infiltration, severe deformation treatment, and tungsten powder copper plating, can achieve a density of 98-99% for W-Cu composites, but these all suffer from drawbacks such as complex processes and long processing times. For example, the melt infiltration method requires first sintering the W skeleton at high temperature, and then performing Cu melt infiltration on the W skeleton. The entire process takes up to 40 hours and is very energy-intensive. How to achieve rapid and complete densification of materials with poor wettability between the reinforcing phase and the metal matrix is ​​a common problem in the field of composite material preparation.

[0004] Patent CN101392335B discloses a method for preparing tungsten-copper composite packaging materials. First, tungsten powder is pressed into tungsten billets of the final product shape and size, sintered into a framework, and then copper is infiltrated followed by chemical removal of the surface copper. This method, like the traditional melt-infiltration method for preparing tungsten-copper composite materials, not only has a very long preparation time but also requires subsequent processing to remove excess copper from the material surface. The long sintering, long melt-infiltration, and subsequent processing are not only time-consuming and energy-intensive but also lead to additional tungsten and copper losses.

[0005] Patent CN114086013B discloses a high-strength, high-conductivity ultrafine-grained tungsten-copper composite material and its preparation method. The method involves plating copper onto the surface of tungsten powder to obtain a composite powder, which is then reduced in a hydrogen atmosphere. The powder is then placed in a mold and sintered at high temperature using a spark plasma sintering apparatus to obtain a tungsten-copper composite material with high mechanical and electrical properties. The sintering time is 2-20 minutes. While this method yields a tungsten-copper composite material with good performance, the copper plating process for the tungsten is very complex, and the subsequent sintering time remains relatively long.

[0006] Patent CN113584337B discloses a method and product for preparing a low-copper-content tungsten-copper composite material. The method involves mixing tungsten powder with a copper salt solution, adding a dispersant, stirring until homogeneous, and then evaporating and crystallizing the mixture to obtain a uniformly mixed powder of copper salt and tungsten powder. The powder is then calcined and reduced to obtain a uniformly mixed powder of tungsten and copper powder. Finally, the mixed powder is cold-pressed and sintered to obtain the tungsten-copper composite material. However, this method still cannot avoid the limitations of a complex preparation process and long-term high-temperature sintering.

[0007] In summary, existing tungsten-copper composite material preparation technologies mainly rely on melt infiltration and high-temperature sintering. This is primarily because tungsten and copper have poor wettability, and directly mixing and sintering tungsten and copper powders cannot achieve densification of the tungsten-copper composite material. These existing methods suffer from a series of limitations, including complex processes, time consumption, and energy consumption. Summary of the Invention

[0008] The purpose of this invention is to provide a high-pressure assisted flash sintering method for metal matrix composites (WCu), which can prepare WCu composites with a density of over 99% in a short time. The prepared WCu has excellent properties, including high electrical conductivity, high thermal conductivity, high hardness, high strength, and low coefficient of thermal expansion.

[0009] To achieve the above objectives, the present invention adopts the following technical solutions.

[0010] The high-pressure assisted flash sintering method for WCu metal matrix composites provided by this invention includes the following steps:

[0011] S1. Tungsten powder and copper powder are mixed evenly in a certain proportion to obtain tungsten-copper mixed powder;

[0012] S2 adds tungsten-copper mixed powder into a mold, then connects the mold to a flash sintering equipment and applies a pressure of not less than 50 MPa to the mold;

[0013] S3 applies a pulsed current into the mold until the temperature exceeds the melting point of copper, then performs flash sintering to obtain the metal matrix composite material WCu.

[0014] The principle of the aforementioned high-pressure assisted flash sintering method for WCu metal matrix composites is as follows: When a pulsed current flows through the sample, the sample powder compact has a high resistance, causing rapid heating. The resulting Joule heating rapidly raises the material temperature above the melting point of copper. After the copper melts, the molten copper is forced into the gaps between the tungsten particles, filling the gaps and thus achieving material densification. After densification, the material resistance decreases rapidly, the material temperature drops, and the molten copper solidifies rapidly, preventing the molten copper from being squeezed out of the mold. During the formation of the copper liquid phase, a very high pressure is applied to the sample externally, ensuring that the molten copper fully fills the gaps between the tungsten particles and that air bubbles are expelled, thereby achieving rapid densification.

[0015] In step S1 above, the mass percentage of copper powder in the mixed powder of tungsten powder and copper powder is 20%.

[0016] In step S2 above, the mold used is a thick-walled mold. The inner mold is made of alumina, titanium carbide, boron nitride, titanium nitride ceramic, or other non-conductive high-strength ceramics. The inner mold has an overall cylindrical structure (the shape of the inner hole can be adjusted according to the sample shape), and its inner hole cross-sectional shape can be circular (inner diameter 5-50mm), square (side length 5-50mm), rectangular (length 5-20mm, width 5-20mm), etc. The outer wall thickness of the inner mold is 10-50mm. The outer mold is a cylindrical steel mold with a wall thickness of 10-30mm. The ceramic mold can be completely embedded in the steel mold. The mold height is 20-100mm.

[0017] The flash sintering equipment used includes a pressure application unit, a pulse generator, and a loading unit. The pressure application unit and pulse generator employ conventional devices already disclosed in the art. The pressure application unit applies pressure to the metal powder in the mold, and the pulse generator provides a pulsed current. The loading unit includes the mold described above, an upper electrode and a lower electrode embedded within the mold, and a steel plate pad, a long copper plate, and a mica sheet placed sequentially on one side of the upper / lower electrode. The upper and lower electrodes are made of the same material and structure, and are made of high-melting-point metal rods. The high-melting-point metals used include pure tungsten, tungsten-based alloys with added rhenium, and refractory high-entropy alloys (e.g., NbMoTaWB). The diameter of the upper / lower electrode is 5-50 mm, and the electrode height is 10-50 mm. The main function of the upper / lower electrodes is to allow current to pass through and to provide high pressure to the powder during the flash sintering process at high temperatures. The upper / lower electrodes can also be square or other shapes. The steel plate gasket has a thickness of 10-50mm, a length of 10-50mm, and a width of 10-50mm. Placed between the electrode and the copper plate, the steel gasket connects the upper / lower electrode to the long copper plate to ensure current flow and also ensures rapid heat dissipation of the sample during the flash burning process. The long copper plate connects the copper wire to the pulse generator. The copper plate dimensions are: thickness 5-20mm, width 10-50mm, and length 200-500mm. The mica sheet, located at the contact point with the upper and lower pressure heads of the pressure application unit, serves as insulation and has a thickness of 5-20mm, a length of 10-50mm, and a width of 10-50mm.

[0018] In operation, the WCu2O powder to be sintered is first filled into the mold. Then, two electrode punches are inserted into the mold from both the top and bottom. Steel plate spacers are placed at both ends of the electrodes, with long copper plates placed on the steel plate spacers, and mica sheets placed on the copper plates. The upper and lower pressure heads of the pressure application unit contact the mica sheets and provide pressure to the entire system. The pressure here is not less than 50 MPa, and a constant pressure is maintained during the sintering process. The pressure is preferably 100-1000 MPa, more preferably 300-1000 Pa. Then, the two sets of long copper plates are connected to the positive and negative terminals of the pulse power supply, respectively, and the pulse power supply is turned on to start flash sintering.

[0019] In step S3 above, to ensure sufficient densification of the material, the pulse current parameters can be selected according to the sample size as follows: frequency 100Hz-320000Hz, pulse width 3μs-200μs, and current density 10A / mm². 2 -500A / mm 2 The sintering time is 5–600 s; in the preferred embodiment, the pulse current parameters are: frequency 1000 Hz–40000 Hz, pulse width 3 μs–100 μs, and current density 20 A / mm². 2 -100A / mm 2The sintering time is 5-300 seconds. The pulse processing uses various waveforms such as spikes, square waves, and sine waves. The sintering temperature can reach 1100-1800℃.

[0020] The present invention also provides WCu composite materials, especially WCu20 composite materials, prepared by the above-mentioned high-pressure assisted flash sintering method for metal matrix composite WCu.

[0021] Traditional flash sintering is mainly used in ceramic preparation: after a certain sintering incubation time, the resistivity of the powder green body decreases rapidly, and the energy applied to the powder green body rises sharply within seconds. During this rapid temperature rise, known as "thermal runaway," the powder green body undergoes intense mass transfer, achieving a very high density. Generally, the resistivity of metals gradually increases with increasing temperature, unlike ceramics; therefore, it is generally believed that flash sintering of metals is difficult. However, research has found that when metal powder is in a compacted state, the interfacial resistance makes the overall green body resistivity very high, and the resistance decreases significantly after the powder green body is densified. Utilizing the transition from the high resistivity of the metal in the compacted state to the low resistivity of the densified state, metal-based materials can undergo flash sintering similar to ceramics. The effectiveness of this method is not limited to WCu2O composites but is also applicable to other metal-based composites.

[0022] Compared with the prior art, the high-pressure assisted flash sintering method for WCu metal matrix composites provided by the present invention has the following advantages:

[0023] 1) This invention can melt the copper phase to generate a liquid phase during the sintering process. At the same time, the high pressure causes the generated copper liquid phase to fully fill the gaps between the tungsten particles, and the high pressure causes the bubbles in the liquid phase to be discharged quickly, thereby ensuring that the material reaches a very high density in a very fast sintering time.

[0024] 2) This invention can prepare WCu20 composite material with a density of over 99% in about 30 seconds. Other existing sintering technologies cannot obtain WCu20 composite material with such high density in such a short time, which has important application potential in the fields of tungsten copper electrical contact materials and tungsten copper electronic packaging materials.

[0025] 3) The method of the present invention can use WCu20 mixed powder, which is difficult to densify, to verify and explore the flash sintering of metal matrix powder, and successfully realize the flash sintering of metal matrix powder. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the flash sintering equipment provided in Embodiment 1 of the present invention; in the figure, 1-pressure application unit, 2-loading unit, 21-mold, 22-upper electrode, 23-lower electrode, 24-steel plate gasket, 25-long copper plate, 26-mica sheet.

[0027] Figure 2 The sample is a WCu20 composite material obtained by sintering in Example 5 of this invention; the sample dimensions are: length 11mm, width 7mm, and thickness 5mm. Detailed Implementation

[0028] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0029] Example 1

[0030] The schematic diagram of the flash sintering equipment provided in this embodiment is as follows: Figure 1 As shown, it includes a pressure application unit 1, a pulse generator, and a loading unit 2.

[0031] The pressure application unit 1 and the pulse generator employ conventional devices already disclosed in the art.

[0032] The loading unit 2 includes a mold 21, an upper electrode 22 and a lower electrode 23 embedded in the mold, and a steel plate pad 24, a long copper plate 25 and a mica sheet 26 placed on one side of the upper electrode 22 / lower electrode 23 in sequence.

[0033] The mold 21 used in this embodiment is a thick-walled mold. The inner mold is made of alumina ceramic; the inner mold has a cylindrical structure with an inner diameter of 11.5 mm and an outer diameter of 40 mm. The outer mold is a cylindrical steel mold with a wall thickness of 20 mm. The ceramic mold can be completely embedded in the steel mold. The mold height is 30 mm.

[0034] In this embodiment, the upper and lower electrodes are made of the same material and have the same structure, namely, NbMoTaWB high-entropy alloy electrodes. The diameter of the upper / lower electrode is 11.5 mm, and the electrode height is 15 mm.

[0035] The steel plate gasket used in this embodiment is 20mm thick, 30mm long, and 30mm wide.

[0036] The copper plate used in this embodiment is 8mm thick, 30mm wide, and 300mm long.

[0037] The mica sheet used in this embodiment is located at the contact position with the upper and lower pressure heads of the pressure application unit, and has a thickness of 10mm, a length of 40mm, and a width of 40mm.

[0038] Example 2

[0039] This embodiment uses the flash sintering equipment provided in Example 1 to prepare WCu2O (W: 80wt%; Cu: 20wt%) according to the following steps:

[0040] S1 mixes tungsten powder and copper powder in a certain proportion to obtain tungsten-copper mixed powder.

[0041] S2 adds 10g of tungsten-copper mixed powder into the mold, then inserts the upper and lower electrodes into the upper and lower ends of the mold, and places steel plate shims on the upper and lower ends of the electrodes. A long copper plate is placed on the steel plate shims and connected to the positive and negative terminals of the pulse generator. A mica sheet is inserted between the upper and lower pressure heads of the pressure application unit and the long copper plate. A pressure of 480MPa is applied to the mold through the pressure application unit.

[0042] S3 applies a pulsed current into the mold, setting the pulsed current parameters as follows: frequency 32KHz, average current 2.1kA, pulse width 3.2μs. Then, the pulsed power supply is turned on to perform flash sintering of the powder for 5s. After sintering, the mold is allowed to cool naturally, and the sintered block is taken out to obtain the metal matrix composite material WCu20.

[0043] Repeat steps S2-S3 above, and adjust the sintering time to 10s, 15s, 20s, 30s, 40s, and 50s, to prepare a total of 7 groups of samples.

[0044] The density of seven groups of samples was tested using the Archimedes displacement method. The densities of the samples sintered for 5s, 10s, 15s, 20s, 30s, 40s, and 50s were 15.02 g / cm³. 3 15.19 g / cm 3 15.40 g / cm 3 15.49 g / cm 3 15.54 g / cm 3 15.75g / cm 3 15.73 g / cm 3 The densities were 95.6%, 96.7%, 98.0%, 98.6%, 99.0%, 100%, and 100%, respectively. It can be seen that the samples gradually densify with increasing sintering time. The density of the sample sintered for 20 seconds reaches approximately 99%.

[0045] Example 3

[0046] This embodiment uses the flash sintering equipment provided in Example 1 to prepare WCu2O (W: 80wt%; Cu: 20wt%) according to the following steps:

[0047] S1 mixes tungsten powder and copper powder in a certain proportion to obtain tungsten-copper mixed powder.

[0048] S2 adds 10g of tungsten-copper mixed powder into the mold, then inserts the upper and lower electrodes into the upper and lower ends of the mold, and places steel plate shims on the upper and lower ends of the electrodes. A long copper plate is placed on the steel plate shims and connected to the positive and negative terminals of the pulse generator. A mica sheet is inserted between the upper and lower pressure heads of the pressure application unit and the long copper plate. A pressure of 480MPa is applied to the mold through the pressure application unit.

[0049] S3 applies a pulsed current into the mold, setting the pulsed current parameters as follows: frequency 32KHz, pulse width 3.2μs, average current 1.9KA. Then, the pulsed power supply is turned on to flash sinter the powder for 50s. After sintering, the mold is allowed to cool naturally, and the sintered block is taken out to obtain the metal matrix composite material WCu20.

[0050] Repeat steps S2-S3 above, and adjust the average current to 2.0KA, 2.1KA, 2.2KA, 2.3KA, and 2.4KA to prepare a total of 6 groups of samples.

[0051] The density of the samples was determined using Archimedes' displacement method. The densities of the samples sintered for 1.9 kDa, 2.0 kDa, 2.1 kDa, 2.2 kDa, 2.3 kDa, and 2.4 kDa were 14.92 g / cm³. 3 15.53 g / cm 3 15.62 g / cm 3 15.65g / cm 3 15.73 g / cm 3 15.98g / cm 3 The density values ​​were 94.9%, 98.9%, 99.5%, 99.6%, 100%, and 102%, respectively. It can be seen that when the sintering current is too high, molten copper overflows from the electrodes, leading to copper deficiency in the sample, resulting in a density greater than 100%. There is a "plateau density" before the sample density exceeds 100%, which is the highest density the sample can achieve. These results demonstrate the importance of properly controlling the sintering current.

[0052] Example 4

[0053] This embodiment uses the flash sintering equipment provided in Example 1 to prepare WCu2O (W: 80wt%; Cu: 20wt%) according to the following steps:

[0054] S1 mixes tungsten powder and copper powder in a certain proportion to obtain tungsten-copper mixed powder.

[0055] S2 adds 10g of tungsten-copper mixed powder into the mold, then inserts the upper and lower electrodes into the upper and lower ends of the mold, and places steel plate shims on the upper and lower ends of the electrodes. A long copper plate is placed on the steel plate shims and connected to the positive and negative terminals of the pulse generator. A mica sheet is inserted between the upper and lower pressure heads of the pressure application unit and the long copper plate. A pressure of 192MPa is applied to the mold through the pressure application unit.

[0056] S3 applies a pulsed current into the mold, setting the pulsed current parameters as follows: frequency 32KHz, average current 2.1kA, pulse width 3.2μs. Then, the pulsed power supply is turned on to perform flash sintering of the powder for 50s. After sintering, the mold is allowed to cool naturally, and the sintered block is removed to obtain the metal matrix composite material WCu20.

[0057] Repeat steps S2-S3 above, and adjust the applied pressure to 288MPa, 384MPa, and 480MPa to prepare a total of 4 groups of samples.

[0058] The density of the samples was determined using Archimedes' displacement method. The densities of the samples sintered at 192 MPa, 288 MPa, 384 MPa, and 480 MPa were 14.10 g / cm³. 3 15.26 g / cm 3 15.45 g / cm 3 15.65g / cm 3 The densities were 90.0%, 97.7%, 98.4%, and 99.6%, respectively. It can be seen that the sintering pressure determines the maximum density that WCu20 material can achieve during sintering; the higher the sintering pressure, the higher the maximum density.

[0059] Example 5

[0060] This embodiment uses the flash sintering equipment provided in Embodiment 1. The inner hole of the mold is 11.0 mm long, 7 mm wide, 40 mm outer diameter, and 30 mm high. The upper and lower electrodes are 11.0 mm long, 7 mm wide, and 15 mm high.

[0061] WCu2O (W: 80 wt%; Cu: 20 wt%) was prepared using the flash sintering equipment described above according to the following steps:

[0062] S1 mixes tungsten powder and copper powder in a certain proportion to obtain tungsten-copper mixed powder.

[0063] S2 adds 10g of tungsten-copper mixed powder into the mold, then inserts the upper and lower electrodes into the upper and lower ends of the mold, and places steel plate shims on the upper and lower ends of the electrodes. A long copper plate is placed on the steel plate shims and connected to the positive and negative terminals of the pulse generator. A mica sheet is inserted between the upper and lower pressure heads of the pressure application unit and the long copper plate. A pressure of 480MPa is applied to the mold through the pressure application unit.

[0064] S3 applies a pulsed current into the mold, setting the pulsed current parameters as follows: frequency 32kHz, average current 2.0kA, pulse width 3.2μs. Then, the pulsed power supply is turned on to perform flash sintering of the powder for 50s. After sintering, the mold is allowed to cool naturally, and the sintered block is removed, yielding the metal matrix composite material WCu20. Figure 2 As shown.

[0065] The sample density was determined using Archimedes' displacement method and was 15.65 g / cm³. 3 The density is 99.6%.

[0066] The thermal, electrical, and mechanical properties of the sample were tested, and the results were as follows: thermal conductivity ~225 W / m². -1 K -1 Electrical conductivity ~48% IACS, coefficient of thermal expansion 7.8×10⁻⁶ -6 K -1 Hardness ~248HV, compressive strength ~850MPa.

[0067] It can be seen that fully dense WCu20 materials can be sintered using molds of different shapes, and the prepared WCu20 samples have excellent thermal, electrical and mechanical properties.

[0068] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A high-pressure assisted flash sintering method for WCu metal matrix composites, characterized in that, Includes the following steps: S1. Tungsten powder and copper powder are mixed evenly in a certain proportion to obtain tungsten-copper mixed powder; S2. Tungsten-copper mixed powder is added to a mold, and then the mold is connected to a flash sintering equipment, and a pressure of 300-480 MPa is applied to the mold. The flash sintering equipment used includes a pressure application unit, a pulse generator, and a loading unit. The pressure application unit is used to apply pressure to the metal powder in the mold. The pulse generator is used to provide pulse current. The loading unit includes a mold, an upper electrode and a lower electrode embedded in the mold, and a steel plate pad, a long copper plate, and a mica sheet placed on one side of the upper electrode / lower electrode in sequence. S3. A pulsed current is applied into the mold, and flash sintering is performed until the temperature exceeds the melting point of copper to obtain the metal matrix composite material WCu. The applied pulsed current parameters are: frequency 1000Hz-40000Hz, pulse width 3μs-100μs, and current density 20A / mm². 2 -100A / mm 2 The sintering time is 30-50 seconds.

2. The high-pressure assisted flash sintering method for WCu metal matrix composites according to claim 1, characterized in that, In step S1, the mass percentage of copper powder in the mixed powder of tungsten powder and copper powder is 20%.

3. The WCu composite material prepared by the method of claim 1 or 2.

4. The WCu composite material according to claim 3, characterized in that... It is a WCu20 composite material.

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