A nanocrystalline tungsten-copper composite material with both excellent thermal stability and mechanical properties

Abstract

A nanocrystalline tungsten copper composite material with excellent thermal stability and mechanical properties belongs to the fields of W-Cu composite materials and powder metallurgy. It specifically includes the following steps: preparing W-Mn nanocrystalline single-phase alloy powder and Cu-Mn nanocrystalline single-phase alloy powder respectively, and ball-milling and mixing the two powders evenly; after loading the mixed and ball-milled powder into a graphite mold, sintering is completed in a rapid hot-pressing sintering furnace. The addition of Mn element is beneficial to segregate at the interface, forming fine and dispersed nanoscale particle phases, further hindering the interface migration, obtaining a stable W phase and the nanocrystalline structure inside it, and at the same time being beneficial to improving the interface strength. A nanocrystalline W-Cu-Mn composite material is prepared by sintering, and this composite material exhibits excellent comprehensive properties in terms of high-temperature stability, compressive strength, and plastic deformation.

Description

Technical Field

[0001] The present invention relates to a novel tungsten - copper (W - Cu) - based composite material prepared by mechanical alloying and rapid hot - press sintering. The prepared W - Cu - Mn composite material takes into account the stability of nanocrystalline structure and the interfacial mechanical properties, belonging to the fields of W - Cu composite materials and powder metallurgy. Background Art

[0002] The W - Cu composite material is a bimetallic material composed of two metals, W and Cu. Since the two - phase metals are neither mutually soluble nor form intermetallic compounds, it is called a "pseudo - alloy". The W - Cu composite material retains the comprehensive physical and chemical properties of the W phase and the Cu phase. For example, the high strength, hardness, wear and corrosion resistance, low coefficient of thermal expansion of metal W and the good electrical and thermal conductivity of Cu. By adjusting the composition of the W phase and the Cu phase in the composite material, W - Cu composite materials with different comprehensive properties can be obtained to meet the requirements in different working environments. The controllable performance of the W - Cu composite material makes it widely used in high - voltage electrical contact materials, electronic packaging materials, aerospace and other fields. The grain size of the W phase has a significant impact on the mechanical properties of the W - Cu composite material. The strength of the W - Cu composite material with a nanocrystalline structure of the W phase can be significantly improved compared with the traditional coarse - grained W - Cu composite material. However, the nanocrystalline structure is prone to thermal instability and rapid grain growth in a high - temperature service environment, which seriously affects the excellent mechanical properties that the nanostructured W - Cu composite material should have. Therefore, improving the stability of the W - phase grain size is the key to obtaining a W - Cu - based composite material with excellent mechanical properties.

[0003] Existing research has shown that the addition of solute elements can improve the stability of grain size. For example, the Ti element added to the W matrix is prone to segregate to the W grain boundary, and a stable W nanocrystalline structure can be obtained by reducing the grain - boundary energy; adding Cr element to the W matrix can form a W - Cr duplex nanocrystalline structure with the Cr - phase size close to the W - phase grain size. Although adding alloying elements can stabilize the nanocrystalline structure, the addition of alloying elements will also lead to a reduction in the plasticity of the composite material. On the one hand, since it is more difficult to generate dislocations inside the grains as the grain size decreases to the nanoscale, plastic deformation is difficult to occur; on the other hand, most of the added elements have an adverse effect on the grain - boundary strength. Therefore, it is urgent to select a suitable solute element, and the addition of this solute element can take into account the stability of the nanocrystalline structure and the interfacial mechanical properties, so as to synergistically improve the high - temperature stability, strength and plasticity of the W - Cu - based composite material. Summary of the Invention

[0004] The present invention obtains a novel W-Cu-Mn composite material with synergistically improved nanocrystalline tissue stability and mechanical properties. The addition of Mn element is conducive to segregation at the interface, forming fine and dispersed nanoscale particle phases, hindering interface migration, obtaining a stable W phase and the nanocrystalline tissue inside it, and at the same time being beneficial to enhancing the interface strength. The composite material prepared by adding Mn element takes into account both the nanocrystalline tissue stability and the interface strength, solving the problems that the addition of other elements is prone to embrittling the interface, reducing the interface strength, and resulting in a decrease in plasticity while the strength of the composite material is increased. The nanocrystalline W-Cu-Mn composite material is obtained by sintering, and this composite material exhibits excellent comprehensive properties in terms of high-temperature stability, compressive strength, and plastic deformation.

[0005] The method for preparing the W-Cu-Mn composite material provided by the present invention is characterized by comprising the following steps:

[0006] (1) Using micron-scale W powder and Mn powder as raw materials, mechanical alloying is carried out using a planetary ball mill, with a cemented carbide ball mill pot and grinding balls, a ball-to-powder ratio of 15:1, a rotation speed of 580 - 620 rpm, and a ball milling time of 36 h to obtain W-Mn nanocrystalline single-phase alloy powder.

[0007] (2) Using micron-scale Cu powder and Mn powder as raw materials, mechanical alloying is carried out in a vibration ball milling manner, with a stainless steel pot and grinding balls, a ball-to-powder ratio of 20:1, a rotation speed of 350 - 380 rpm, and ball milling for 5 h to obtain Cu-Mn nanocrystalline single-phase alloy powder.

[0008] In the above steps (1) and (2), the content of Mn in both the W-Mn nanocrystalline single-phase alloy powder and the Cu-Mn nanocrystalline single-phase alloy powder is 4 - 10 at.%, having a relatively wide adjustable range.

[0009] (3) Mix the W-Mn and Cu-Mn single-phase alloy powders obtained by ball milling in steps (1) and (2) evenly. The rotation speed of the planetary ball mill used is 260 rpm, the ball-to-powder ratio is 10:1, and after ball milling for 6 h, nanocrystalline W-Cu-Mn composite powder is obtained; wherein the mass ratio of the W-Mn single-phase alloy powder to the Cu-Mn single-phase alloy powder is (6 - 8):(2 - 4);

[0010] (4) After loading the powder mixed evenly in step (3) into a graphite mold, sintering is carried out in a rapid thermal pressing sintering furnace. When the vacuum degree in the furnace cavity reaches below 2×10 -2 Pa, start to pass current to heat up, with a heating rate of 80 - 100 °C / min, and increase the pressure while heating up. When the pressure reaches 100

[0011] After reaching MPa, it remains constant. When the temperature rises to 900 - 950 °C, it is held for 5 minutes. After the heat preservation ends, the sample is cooled to room temperature with the furnace, and the as-prepared W-Cu-Mn composite material is obtained after sampling and demolding. Further, the as-prepared W-Cu-Mn composite material is heat-treated with H2 in a high-temperature tube furnace at a temperature of 800 °C for 2 hours, and finally the product of the present invention is obtained.

[0012] In the above step (4), the sintering temperature needs to be adjusted according to the different Mn element contents in order to obtain a W-Cu-Mn composite material with uniform composition and structure and high density.

[0013] The features and technical advantages of the present technology are as follows:

[0014] ① In the W phase of the W-Cu-Mn composite material, the Mn element is distributed in the form of nano-particle phases at the W grain boundaries. The average size of these particle phases is several nanometers to more than ten nanometers, and the average grain size of the finally obtained W phase is dozens of nanometers. The distribution form of Mn is significantly different from that of the addition elements such as Ti and Cr used in other W-based alloys. ② The nano-particles formed by adding Mn are dispersedly distributed at the grain boundaries, playing a role in pinning the interfaces and hindering the interface migration, so the microstructure of the composite material is stabilized. ③ While stabilizing the microstructure, the distribution of the Mn element at the interfaces also inhibits interface embrittlement, which is beneficial to improving the interface strength. In summary, the W-Cu-Mn composite material prepared by the present invention has both excellent thermal stability and mechanical properties, with high compressive strength and high compressive plasticity. ④ The W-Cu-Mn composite material prepared by the present invention is expected to have higher tissue stability and strength than the existing W-Cu composite materials during high-temperature service, thereby expanding the application of W-Cu-based composite materials in the high-temperature field. Description of the Drawings

[0015] Figure 1 The microstructure of the W phase of the W-Cu-5at.%Mn composite material prepared in Example 1;

[0016] Figure 2 The microstructural morphology of the heat-treated W-Cu-5at.%Mn composite material in Example 1;

[0017] Figure 3 The microstructural morphology of the W-Cu composite material prepared in Comparative Example 1;

[0018] Figure 4 The comparison of the compression curves at room temperature between the W-Cu-5at.%Mn composite material prepared in Example 1 and the W-Cu composite material prepared in Comparative Example 1. Detailed Embodiments

[0019] The following examples further illustrate the present invention, but the present invention is not limited to the following examples.

[0020] Example 1

[0021] Using micron-sized W powder and Mn powder as raw materials, the molar ratio of Mn powder to W powder is 5:95. In a glove box under an argon atmosphere, the grinding balls and powders are placed into a ball milling jar, with a ball-to-material ratio of 15:1. Using an NM-600 type intelligent planetary ball mill, with a cemented carbide ball milling jar and grinding balls, the rotation speed is 580 rpm, and the ball milling time is 36 h, to obtain a W-Mn single-phase nanocrystalline alloy powder. After mixing Cu and Mn powders with a molar ratio of 95:5, mechanical alloying is carried out using a GN-2 type high-energy ball mill in a vibration ball milling mode, with a stainless steel jar and grinding balls, a ball-to-material ratio of 20:1, a rotation speed of 350 rpm, and ball milling for 5 h, to obtain a nanocrystalline Cu-Mn single-phase alloy powder. Then, the W-Mn and Cu-Mn powders are mixed evenly according to a mass ratio of 7:3, with a ball milling rotation speed of 260 rpm, and after ball milling for 6 h, a composite powder of W-Mn and Cu-Mn is obtained. The obtained composite powder is loaded into a graphite mold and sintered in a rapid thermal pressing sintering furnace. When the vacuum degree in the furnace cavity reaches below 2×10 -2 Pa, current is passed to increase the temperature, with a heating rate of 100℃ / min. While heating, the pressure is increased. When the pressure reaches 100 MPa, it is kept constant. When the temperature rises to 950℃, it is held for 5 min. After the holding ends, the sample is cooled to room temperature with the furnace, and after sampling and demolding, a as-prepared W-Cu-5at.%Mn composite material is obtained. The microstructure of the W phase in the composite material is as Figure 1 shown. It can be seen that the W phase has a nanocrystalline structure, and the average grain size is about 36 nm. The as-prepared composite material is heat-treated in a high-temperature tube furnace at 800℃ for 2 h, and finally the product is obtained. Its microstructure is as Figure 2 shown. The W phase grains are still nanocrystalline, with an average grain size of about 80 nm, indicating that the composite material has high thermal stability during the high-temperature sintering process. The compressive property of this product is tested at room temperature, and its compressive strength reaches 1551±20 MPa, and the strain is 8±0.5%.

[0022] Comparative Example 1

[0023] Using micron-sized W powder and Cu powder as raw materials, they were mixed using an NM-600 type intelligent planetary ball mill with a ball-to-material ratio of 15:1. Tungsten carbide ball milling jars and grinding balls were used, the rotational speed was 620 rpm, and the ball milling time was 36 h to obtain nanocrystalline W powder. The Cu powder was ball milled by the vibration ball milling method using a GN-2 type high-energy ball mill with a ball-to-material ratio of 20:1. Stainless steel jars and grinding balls were used, the rotational speed was 380 rpm, and ball milling was carried out for 5 h to obtain nanocrystalline Cu powder. The nanocrystalline W powder and Cu powder prepared by ball milling were mixed evenly with a ball milling rotational speed of 260 rpm and a ball milling time of 6 h to obtain nanocrystalline W-Cu composite powder. The obtained W-Cu composite powder was loaded into a graphite mold and sintered in a rapid hot pressing sintering furnace. When the vacuum degree in the furnace cavity reached below 2×10 -2 Pa, current was passed to start heating up, with a heating rate of 100°C / min. Pressure was increased while heating up. When the pressure reached 100 MPa, it was kept constant. When the temperature rose to 900°C, it was held for 5 min. After the holding ended, the sample was cooled to room temperature with the furnace, and after sampling and demolding, a W-Cu bulk composite material was obtained. The microstructure morphology of the W-Cu bulk composite material prepared in this example is as shown in Figure 3 . The average grain size of the W phase is 100 nm. Compared with Example 1, the average grain size of the W phase in the as-prepared W-Cu-Mn bulk composite material is only 36 nm, indicating that adding the Mn element can effectively inhibit the grain growth of the W phase. Room temperature compression tests show that the compressive strength of the W-Cu composite material prepared in this example is 1160 ± 20 MPa, which is significantly lower than the room temperature compressive strength of the W-Cu-5at.%Mn composite material prepared in Example 1. At the same time, the strain of the W-Cu composite material prepared in this example is 8 ± 0.5%, which is comparable to the strain of the W-Cu-5at.%Mn composite material prepared in Example 1, indicating that the W-Cu-Mn composite material prepared in Example 1 has excellent thermal stability, high compressive strength, and high compressive plasticity.

Claims

1. A preparation method of a nanocrystalline tungsten-copper (W-Cu) composite material with both excellent thermal stability and mechanical properties, characterized in that, The steps include the following: (1) Using micron-scale W powder and Mn powder as raw materials, mechanical alloying is carried out using a planetary ball mill, with a cemented carbide ball milling tank and grinding balls. The ball-to-material ratio is 15:1, and the rotation speed is 580 - 620 rpm. The ball milling time is 36 h to obtain W-Mn nanocrystalline single-phase alloy powder; (2) Using micron-scale Cu powder and Mn powder as raw materials, mechanical alloying is carried out by vibration ball milling, with a stainless steel tank and grinding balls. The ball-to-material ratio is 20:1, and the rotation speed is 350 - 380 rpm. After ball milling for 5 h, Cu-Mn nanocrystalline single-phase alloy powder is obtained; In the above steps (1) and (2), the Mn content in both the W-Mn nanocrystalline single-phase alloy powder and the Cu-Mn nanocrystalline single-phase alloy powder is 4 - 10 at.%, having a relatively wide adjustable range; (3) The W-Mn and Cu-Mn single-phase alloy powders obtained by ball milling in steps (1) and (2) are mixed evenly. The rotation speed of the planetary ball mill used is 260 rpm, and the ball-to-material ratio is 10:

1. After ball milling for 6 h, nanocrystalline W-Cu-Mn composite powder is obtained; the mass ratio of the W-Mn single-phase alloy powder to the Cu-Mn single-phase alloy powder is (6 - 8):(2 - 4); (4) After filling the powder evenly mixed in step (3) into a graphite mold, sintering is carried out in a rapid hot pressing sintering furnace. When the vacuum degree in the furnace cavity reaches below 2×10 -2 Pa, start to pass current to raise the temperature, with a heating rate of 80 - 100 °C / min. While raising the temperature, increase the pressure. When the pressure reaches 100 MPa, keep it constant. When the temperature rises to 900 - 950 °C, hold for 5 min. After the heat preservation ends, the sample is cooled to room temperature with the furnace. After sampling and demolding, the as-prepared W-Cu-Mn composite material is obtained; the as-prepared W-Cu-Mn composite material is heat-treated with H2 in a high-temperature tubular furnace at a temperature of 800 °C for 2 h to finally obtain the product of the present invention.

2. The method according to claim 1, characterized in that, In the W phase of the prepared W-Cu-Mn composite material, the Mn element is distributed in the form of nanoparticle phases at the W grain boundaries.

3. The method according to claim 1, wherein The prepared W-Cu-Mn composite material exhibits excellent comprehensive properties in terms of high-temperature stability, compressive strength, and plastic deformation. The W-phase grain size is stable within 100 nm, the room-temperature compressive strength reaches 1551 ± 20 MPa, and the compression strain rate is 8 ± 0.5%.

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