A method for producing a tungsten-copper composite material by plastic-binder injection molding

Abstract

The application relates to a method for preparing a tungsten-copper composite material by adopting plastic-based binder injection molding, relates to the fields of preparation of tungsten-copper composite materials and metal injection molding technology. In order to solve the problem that existing superfine tungsten-copper composite powder is difficult to be injection molded, the superfine tungsten-copper composite powder in the form of tungsten-coated copper is prepared by adopting spray drying and hydrogen reduction, the agglomeration phenomenon among powders is improved by adopting airflow milling crushing technology, the loose bulk density and the tap density of the powder are greatly improved, and the powder particle size distribution is obviously narrowed. The treated tungsten-copper composite powder is mixed and densified into a feed material with a plastic-based binder, and a tungsten-copper composite material with a complex shape and good size stability is successfully prepared by injection molding, has the advantages of high compactness, high thermal conductivity, good air tightness, low thermal expansion coefficient and the like, and meets the performance requirements of electronic packaging materials.

Description

Technical Field

[0001] This invention relates to the field of tungsten-copper composite material preparation and metal injection molding technology, specifically to a method for preparing tungsten-copper composite materials using injection molding with a plastic binder. Background Technology

[0002] With the rapid development of high-tech fields such as microelectronics, aerospace, and military engineering, the upgrading of electronic devices has accelerated, driving electronic packaging materials towards high quality, low power consumption, and complex miniaturization. Tungsten-copper composites combine the unique performance advantages of tungsten and copper, exhibiting excellent thermal and electrical properties, as well as high strength and high hardness. Based on the excellent electrical and thermal conductivity and low coefficient of thermal expansion of tungsten-copper composites, they are widely used in the field of microelectronics and information technology as substrates, connectors, and heat dissipation components in large-scale integrated circuits and microwave communication devices. Considering the significant differences in the basic properties of tungsten and copper, and their poor wettability, traditional preparation techniques mainly employ melt infiltration and liquid-phase sintering. While melt infiltration has a simple production process, it is difficult to obtain a tungsten framework structure with uniform openings, leading to coarse microstructure in the tungsten-copper material. Prolonged high-temperature liquid-phase sintering easily causes tungsten grain growth, resulting in tungsten-copper materials with uneven composition. Furthermore, for complex-shaped parts, machining is often required, which undoubtedly increases production costs.

[0003] Metal injection molding combines the rapid production of plastic injection molding with the characteristics of powder metallurgy, making it a near-net-shape forming process capable of mass-producing small to medium-sized complex-shaped parts. Currently, the preparation of tungsten-copper composite powders is mainly divided into physical and chemical methods. During mechanical alloying, the powder collides with alloy spheres for a long time, easily introducing impurities such as iron, which affects the electrical and thermal conductivity of the tungsten-copper composite material to some extent. Furthermore, mechanical alloying is time-consuming and difficult to produce large quantities of powder in a short period. Chemical methods such as sol-gel, co-precipitation, and spray drying can successfully prepare ultrafine tungsten-copper composite powders with uniform composition. Among these, spray drying and hydrogen reduction processes are simple and low-cost, enabling rapid, large-scale production of tungsten-copper composite powders. However, smaller powder particle sizes are more prone to agglomeration, resulting in lower powder loading during injection molding and problems such as sample cracking and uncontrollable dimensional shrinkage during sintering. Air jet milling technology, utilizing high-pressure nitrogen impact grinding, effectively improves powder agglomeration, narrows the powder particle size distribution, and facilitates higher powder loading. Plastic-based binders are widely used in metal injection molding binders due to their high debinding efficiency and small deformation of sintered samples. Summary of the Invention

[0004] The purpose of this invention is to provide a preparation method using modified tungsten-coated copper composite powder for injection molding, solving the problem of difficulty in injection molding ultrafine tungsten-copper composite powder. Ultrafine tungsten-copper composite powder in the form of tungsten-coated copper is prepared by spray drying and hydrogen reduction. Air jet milling technology improves the agglomeration of the powder, significantly increasing the loose density and tap density, and narrowing the particle size distribution. The treated tungsten-copper composite powder is mixed with a plastic binder and kneaded to form a feedstock. Injection molding successfully prepares tungsten-copper composite materials with complex shapes and good dimensional stability, exhibiting advantages such as high density, high thermal conductivity, good airtightness, and low coefficient of thermal expansion, meeting the performance requirements of electronic packaging materials.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing tungsten-copper composite materials by injection molding using a plastic-based binder includes the following steps:

[0007] Step 1: Spray drying and hydrogen reduction

[0008] Ammonium metatungstate (AMT, Aladdin, purity ≥99.95%), copper nitrate trihydrate (AMT, Aladdin, purity ≥99.95%), and oxalic acid dihydrate (C2H2O4·2H2O, analytical grade) were dissolved together in deionized water in a reaction vessel and heated and stirred for a certain period of time to form a mixed solution. The mixed solution was fed into a spray drying tower through a feed pipe and dried under hot air to form a tungsten-copper precursor. The obtained tungsten-copper precursor was then loaded into a ceramic sintering boat and pushed into a pusher-type reduction furnace for reduction to prepare an ultrafine tungsten-copper composite powder, which exists in the form of tungsten-copper coating.

[0009] Step 2: Grinding with an air jet mill

[0010] The tungsten-copper composite powder obtained in step 1 is added to an air jet mill. Under high-purity, high-pressure nitrogen, the powder particles impact and collide with each other, achieving a grinding effect and dispersing the agglomerated powder. The dispersed powder is then carried by the air jet to a turbine for classification. Powder that meets the particle size requirements is collected by a cyclone separator, while the remaining coarse particles are carried to the grinding chamber for further grinding until they meet the requirements and are separated. Finally, tungsten-copper composite powder with good dispersibility and narrow particle size distribution is collected.

[0011] Step 3: Mixing and Injection Molding

[0012] Weigh the tungsten-copper composite powder and plastic binder obtained from the air jet mill in step 2 according to a certain component ratio, mix them evenly in a mixer until they reach a dough-like state, and then crush them into feed material using a crusher. Pour the feed material into the barrel of the injection molding machine, and inject it into the shape of the mold under the action of temperature and pressure. The injection tail material can be recycled for multiple injections after being crushed.

[0013] Step 4: Oxalic acid-catalyzed degreasing and hydrogen sintering

[0014] The injection-molded parts obtained in step 3, which have no obvious defects on a macroscopic scale, are placed on ceramic sheets. The ceramic sheets are then pushed into an oxalic acid degreasing furnace for catalytic degreasing under a nitrogen atmosphere and acidic environment. The degreasing rate is calculated by weighing the samples before and after degreasing. The qualified degreased green body is placed in a high-temperature hydrogen furnace, where residual binder is removed by low-temperature heat degreasing and high-temperature sintering densification is performed to obtain tungsten-copper composite material.

[0015] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0016] In step 1, according to stoichiometry, if the designed mass ratio is W-(10-30)Cu, then the masses of copper nitrate trihydrate and oxalic acid dihydrate are 32%-120% and 30%-45% of the mass of ammonium metatungstate, respectively. During the mixed solution reaction stage, the oil bath temperature is controlled at 110-130℃, the reaction time is 4-6 hours, and the rotation speed is 180-250 r / min. During the spray drying stage, the inlet air temperature is 240-260℃, the peristaltic pump feed rate is 2-4 L / h, and the atomizer rotation speed is 22000-25000 r / min. During the hydrogen reduction stage, the maximum reduction temperature is controlled at 880-920℃, the boat loading is 1-1.5 kg / boat, the boat pushing speed is 0.5-1 h / boat, and the hydrogen flow rate is 8-16 m³ / min. 3 / h.

[0017] In step 2, in order to ensure that the tungsten-copper composite powder can be effectively dispersed, the grinding pressure of the air jet mill is 0.3-0.7 MPa, the grinding time is 2-4 h, and the classifier wheel speed is 3000-6000 r / min.

[0018] In step 3, the plastic binder comprises, by mass ratio, 75-85 wt.% polyoxymethylene (POM), 8-12 wt.% high-density polyethylene (HDPE), 3-8 wt.% ethylene bis-stearamide (EBS), and 3-8 wt.% stearic acid (SA). The total mass ratio of all components is 100%. The mass ratio of the tungsten-copper composite powder after air jet milling to the plastic binder is (88-92):(8-12), which translates to a powder volume loading of 40-47.5%. During the internal mixing stage, the mixing temperature is 170-190℃, the mixing speed is 30-50 r / min, and the mixing time is 40-80 min. During the injection stage, the injection temperature is 160-170℃, the injection pressure is 80-100 bar, the injection speed is 40-80%, the mold temperature is 90-110℃, and the injection cycle can be repeated 8-12 times.

[0019] In step 4, during the oxalic acid catalytic degreasing stage, the degreasing temperature is 100-150℃, the acid injection rate is 0.1-0.3 g / min, and the degreasing time depends on the thickness of the part, generally controlled at 6-10 hours, with a degreasing rate of 5.8-8%. During the hydrogen sintering stage, the low-temperature section temperature is controlled at 480-550℃, with a heating rate of 2-4℃ / min and a holding time of 1-2 hours to remove residual binder. The maximum temperature depends on the copper content; the higher the copper content, the lower the maximum temperature, generally 1200-1350℃, with a heating rate of 5-7℃ / min and a holding time of 2-4 hours to promote material densification. The cooling rate is controlled at 4-6℃ / min to ensure the material does not bend due to thermal stress.

[0020] The present invention has the following advantages:

[0021] (1) Tungsten-copper composite powder pulverized by air jet milling is easy to injection mold. The ultrafine tungsten-copper composite powder prepared by spray drying and hydrogen reduction exists in the form of tungsten-coated copper, which has the characteristics of uniform distribution of tungsten and copper phases, high sintering activity, and reduced copper phase loss during sintering. However, the smaller the particle size of the ultrafine tungsten-copper composite powder, the more serious the spontaneous agglomeration, which leads to an increase in the amount of binder required and a large shrinkage of the sample size during debinding and sintering. By pulverizing the tungsten-copper composite powder by air jet milling, the powder particles impact and break each other, thereby achieving the purpose of powder grinding, so that the obtained tungsten-copper composite powder particles are dispersed, the loose density and tap density are greatly improved, and the particle size distribution is narrowed, which meets the requirements of injection molding for the performance of metal powder.

[0022] (2) Tungsten-copper parts injected using plastic-based binders exhibit good shape retention, high degreasing efficiency, and low residual carbon content. The plastic-based binder proposed in this invention, which is kneaded with tungsten-copper composite powder, has an optimized formulation, ensuring good flowability of the feedstock during injection and giving the injected parts sufficient strength to prevent collapse. During the degreasing process, polyoxymethylene is catalyzed into formaldehyde in an acidic environment, and then converted into carbon dioxide and nitrogen in a heating chamber. The entire process ensures high degreasing efficiency and low residual binder, making it environmentally friendly and pollution-free.

[0023] (3) The sintered tungsten-copper product exhibits excellent performance. The sintered tungsten-copper composite material has controllable dimensional shrinkage, high density, good thermal properties, and an airtightness of less than 1×10⁻⁶. -9 Pa·m 3 ·s -1 This meets the performance requirements of electronic packaging materials. Therefore, it has significant practical production value in industrialization. Attached Figure Description

[0024] Figure 1 This is a cross-sectional SEM image of the W-15Cu composite powder in Example 1.

[0025] Figure 2 These are SEM images of the surface morphology of W-15Cu composite powder before and after air jet milling in Example 1.

[0026] Figure 3 This is a laser particle size distribution diagram of the W-15Cu composite powder before and after air jet milling in Example 1.

[0027] Figure 4 These are SEM images of the fracture surfaces of the injection molded part before and after degreasing with oxalic acid in Example 3.

[0028] Figure 5 These are SEM images of the surface and fracture surface of W-15Cu after sintering in Example 3. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0030] Example 1

[0031] In this embodiment, the preparation of W-15Cu composite powder by mass ratio is taken as an example. The specific preparation method is as follows:

[0032] Step 1: Spray drying and hydrogen reduction

[0033] Ammonium metatungstate (AMT, Aladdin, purity ≥99.95%), copper nitrate trihydrate (AMT, Aladdin, purity ≥99.95%), and oxalic acid dihydrate (C2H2O4·2H2O, analytical grade) were dissolved together in deionized water in a reactor. The mixture was heated in an oil bath at 120°C and stirred at 220 rpm for 5 hours to obtain a mixed solution. The mass percentages of copper nitrate trihydrate and oxalic acid dihydrate were 50% and 40% of the mass of ammonium metatungstate, respectively. The mixed solution was fed to a spray drying tower at a feed rate of 2 L / h and dried to obtain a tungsten-copper precursor at an inlet air temperature of 250°C and an atomizer speed of 24000 rpm. The obtained tungsten-copper precursor was then loaded into ceramic sintering boats, with 1 kg of precursor per boat, and pushed into a pusher-type reduction furnace at a rate of 0.5 h / boat for a maximum temperature of 880°C and a hydrogen flow rate of 8 m³ / h. 3 / h reduction was used to prepare ultrafine tungsten-copper composite powder.

[0034] Figure 1This is a cross-sectional SEM image of the W-15Cu composite powder in Example 1. The contrast clearly shows that the black particles are coated with a white phase; the black particles are copper, and the white phase is tungsten, clearly revealing that the tungsten-copper composite powder exists in a tungsten-coated copper form. This coating form of the tungsten-copper composite powder itself can achieve a uniform distribution of the tungsten and copper phases, and can significantly reduce the evaporation and overflow of the copper phase during subsequent high-temperature sintering, thereby effectively controlling the composition ratio of the material.

[0035] Step 2: Grinding with an air jet mill

[0036] The tungsten-copper composite powder obtained in step 1 was added to an air jet mill. Under high-purity nitrogen and a grinding pressure of 0.5 MPa, the powder particles impacted and collided with each other. The powder was then classified at a turbine speed of 6000 r / min for 2 hours. The final result was tungsten-copper composite powder after air jet milling.

[0037] Figure 2 Figure 1 shows the surface SEM images of the W-15Cu composite powder before and after air jet milling in Example 1. Figure (a) shows the surface SEM image of the powder before air jet milling, exhibiting an irregular polygonal shape and severe agglomeration, primarily in the form of secondary particles. Since these secondary particles often contain tiny voids, more binder is required during the mixing process. Figure (b) shows the surface SEM image of the powder before air jet milling, where the particles are clearly dispersed, mainly existing as single or primary particles. Due to the air jet milling process, the powder morphology tends to be near-spherical, which is beneficial for improving powder flowability.

[0038] Figure 3 This is a laser particle size distribution diagram of the W-15Cu composite powder before and after air jet milling in Example 1. It can be clearly seen that the particle sizes of D10, D50 and D90 of the powder are smaller and the particle size distribution is narrower after treatment, which is beneficial to increasing the powder loading during the internal mixing process.

[0039] Example 2

[0040] In this embodiment, the preparation of W-30Cu composite powder by mass ratio is taken as an example. The specific preparation method is as follows:

[0041] Step 1: Spray drying and hydrogen reduction

[0042] Ammonium metatungstate (AMT, Aladdin, purity ≥99.95%), copper nitrate trihydrate (AMT, Aladdin, purity ≥99.95%), and oxalic acid dihydrate (C2H2O4·2H2O, analytical grade) were dissolved together in deionized water in a reactor. The mixture was heated in an oil bath at 130°C and stirred at 250 rpm for 6 hours to obtain a mixed solution. The mass percentages of copper nitrate trihydrate and oxalic acid dihydrate were 120% and 45% of the mass of ammonium metatungstate, respectively. The mixed solution was fed to a spray drying tower at a feed rate of 4 L / h and dried to obtain a tungsten-copper precursor at an inlet air temperature of 260°C and an atomizer speed of 25000 rpm. The obtained tungsten-copper precursor was then loaded into ceramic sintering boats, with 1.5 kg of precursor per boat, and pushed into a pusher-type reduction furnace at a rate of 1 h / boat for a maximum temperature of 920°C and a hydrogen flow rate of 16 m³ / h. 3 / h reduction was used to prepare ultrafine tungsten-copper composite powder.

[0043] Step 2: Grinding with an air jet mill

[0044] The tungsten-copper composite powder obtained in step 1 was added to an air jet mill. Under high-purity nitrogen and a grinding pressure of 0.7 MPa, the powder particles impacted and collided with each other. The powder was then classified at a turbine speed of 3000 r / min for 4 hours. Finally, the tungsten-copper composite powder after air jet milling was obtained.

[0045] Table 1 lists the loose packing density and tapped density of W-15Cu in Example 1 and W-30Cu in Example 2 before and after air jet milling. It can be seen that after air jet milling, the loose packing density and tapped density of the powder increased by about three times, directly reflecting the high density of the tungsten-copper composite powder after air jet milling.

[0046] Table 1

[0047]

[0048] Example 3

[0049] In this embodiment, the W-15Cu composite material is prepared by injection molding as follows:

[0050] Step 1: Secret Refining

[0051] The W-15Cu composite powder and plastic binder treated by air jet milling in Example 1 were weighed at a mass ratio of 90:10, which translates to a powder volume loading of 45%. The plastic binder comprises, by mass ratio, 80 wt.% polyoxymethylene (POM), 10 wt.% high-density polyethylene (HDPE), 5 wt.% ethylene bis-stearamide (EBS), and 5 wt.% stearic acid (SA). The above raw materials were uniformly mixed in an internal mixer at a mixing temperature of 180°C and a rotation speed of 40 r / min for 60 min until a dough-like consistency was achieved. This dough was then crushed into feedstock using a crusher. The feedstock had a relative density of 99.3% and a melt flow rate of 320 g / 10 min at a temperature of 165°C and a load of 5 kg.

[0052] Step 2: Injection Molding

[0053] The feed material obtained in step 1 is poured into the barrel of the injection molding machine. At this time, the injection screw temperature is 170℃ and the mold temperature is 100℃. The molten feed material is injected into the mold at an injection pressure of 90 bar and an injection speed of 60%, resulting in an injection-molded part with the mold shape. Excess injection tail material is crushed and reused for injection, allowing for up to 10 cycles.

[0054] Step 3: Oxalic acid-catalyzed degreasing

[0055] The injection-molded parts obtained in step 2, which showed no obvious macroscopic defects, were placed on ceramic sheets. The ceramic sheets were then pushed into an oxalic acid degreasing furnace for catalytic degreasing under a nitrogen atmosphere and acidic environment. The degreasing temperature was 130℃, and the acid inlet rate was 0.2 g / min. The total degreasing time was 8 hours. The samples before and after degreasing were weighed to calculate the degreasing rate. Degreased green parts with a degreasing rate greater than 6.3% were selected, and unqualified parts underwent further degreasing.

[0056] Figure 4 Figure 3 shows the fracture surface SEM images of the injection molded part before and after degreasing with oxalic acid in Example 3. Figure (a) is the fracture surface SEM image of the injection molded part, which clearly shows that the plastic binder coats the tungsten copper powder particles like glue, with virtually no pores between the binder and the powder, and both are evenly distributed. Figure (b) is the fracture surface SEM image of the injection molded part after degreasing with oxalic acid, indicating that the main component of the plastic binder, polyoxymethylene, has been basically removed, and continuous degreasing channels have been formed in the green body, which facilitates the removal of residual binder by thermal degreasing during sintering. At this time, the powder particles are mainly connected by high-density polyethylene as a skeleton agent, giving the degreased green body a certain strength and preventing cracking of the degreased green body during the transfer process before sintering.

[0057] Step 4: Hydrogen sintering

[0058] Qualified degreased green blanks were placed in a high-temperature hydrogen furnace and subjected to two-step sintering processes: hot degreasing at 500℃ for 1.5 hours to remove residual binder, and sintering at a maximum temperature of 1350℃ for 2 hours to densify, yielding W-15Cu composite material. The heating rate was controlled at 3℃ / min in the low-temperature stage, 6℃ / min in the densification stage, and 5℃ / min in the cooling stage. The W-15Cu composite material exhibited a dimensional shrinkage ratio of 1.3, with a shrinkage range controlled within ±0.05 mm, a density of 98.5%, a thermal conductivity of 212 W / (m·K), a coefficient of thermal expansion of 7.01 ppm / ℃, and an airtightness of 4 × 10⁻⁶. -10 Pa·m 3 ·s -1 .

[0059] Figure 5 These are SEM images of the surface and fracture surface of W-15Cu after sintering in Example 3. Figure (a) is a surface morphology image of W-15Cu taken in SEM backscatter mode. The tungsten and copper phases can be clearly distinguished by the difference in contrast; the white particles are tungsten, and the black matrix is ​​copper. Figure (b) is a SEM image of the fracture surface of W-15Cu. This structure shows a network of copper encapsulating tungsten particles with virtually no pores, demonstrating the material's excellent thermal properties.

[0060] Example 4

[0061] In this embodiment, the W-15Cu composite material is prepared by injection molding as follows:

[0062] Step 1: Secret Refining

[0063] The W-15Cu composite powder and plastic binder treated by air jet milling in Example 1 were weighed at a mass ratio of 92:8, resulting in a powder volume loading of 47.5%. The plastic binder consisted of 75 wt.% polyoxymethylene (POM), 10 wt.% high-density polyethylene (HDPE), 7.5 wt.% ethylene bis-stearamide (EBS), and 7.5 wt.% stearic acid (SA) by mass ratio. The raw materials were uniformly mixed in an internal mixer at 170°C and 30 rpm for 80 minutes until a dough-like consistency was achieved. This dough was then crushed into feedstock using a crusher. The feedstock had a relative density of 98.9% and a melt flow rate of 260 g / 10 min at 165°C and a load of 5 kg.

[0064] Step 2: Injection Molding

[0065] The feed material obtained in step 1 is poured into the barrel of the injection molding machine. At this time, the injection screw temperature is 160℃ and the mold temperature is 90℃. The molten feed material is injected into the mold at an injection pressure of 80 bar and an injection speed of 40%, resulting in an injection-molded part with the mold shape. Excess injection tail material is crushed and reused for injection, allowing for up to 8 cycles of injection.

[0066] Step 3: Oxalic acid-catalyzed degreasing

[0067] The injection-molded parts obtained in step 2, which showed no obvious macroscopic defects, were placed on ceramic sheets. The ceramic sheets were then pushed into an oxalic acid degreasing furnace for catalytic degreasing under a nitrogen atmosphere and acidic environment. The degreasing temperature was 100℃, and the acid inlet rate was 0.1 g / min. The total degreasing time was 6 hours. The samples before and after degreasing were weighed to calculate the degreasing rate. Degreased green parts with a degreasing rate greater than 5.8% were selected, and unqualified parts underwent further degreasing.

[0068] Step 4: Hydrogen sintering

[0069] The qualified degreased green compact was placed in a high-temperature hydrogen furnace and sintered in two steps: a low-temperature section at 480℃ for 1 hour to remove residual binder, and a high-temperature section at 1300℃ for 2 hours for densification, to obtain the W-15Cu composite material. The heating rate was controlled at 2℃ / min in the low-temperature section, 5℃ / min in the densification stage, and 4℃ / min in the cooling rate. The W-15Cu composite material exhibited a dimensional shrinkage ratio of 1.27, with a shrinkage range controlled within ±0.05 mm, a density of 98.7%, a thermal conductivity of 215 W / (m·K), a coefficient of thermal expansion of 7.01 ppm / ℃, and an airtightness of 3 × 10⁻⁶. -10 Pa·m 3 ·s -1 .

[0070] Example 5

[0071] In this embodiment, the W-30Cu composite material is prepared by injection molding as follows:

[0072] Step 1: Secret Refining

[0073] The W-30Cu composite powder and plastic binder treated by air jet milling in Example 2 were weighed at a mass ratio of 88:12, which is equivalent to a powder volume loading of 40%. The plastic binder components, by mass ratio, include 85 wt.% polyoxymethylene (POM), 8 wt.% high-density polyethylene (HDPE), 3.5 wt.% ethylene bis-stearamide (EBS), and 3.5 wt.% stearic acid (SA). The above raw materials were uniformly mixed in an internal mixer at a mixing temperature of 190°C and a rotation speed of 50 r / min for 40 minutes until a dough-like consistency was achieved. This dough was then crushed into feedstock using a crusher.

[0074] Step 2: Injection Molding

[0075] The feedstock obtained in step 1 is poured into the barrel of the injection molding machine. At this time, the injection screw temperature is 165℃ and the mold temperature is 110℃. The molten feedstock is injected into the mold at an injection pressure of 100 bar and an injection speed of 80%, resulting in an injection-molded part with the mold shape. Excess injection tail material is crushed and reused for injection, allowing for up to 12 cycles. The feedstock has a relative density of 99.6% and a melt flow rate of 480 g / 10 min at a temperature of 165℃ and a load of 5 kg.

[0076] Step 3: Oxalic acid-catalyzed degreasing

[0077] The injection-molded parts obtained in step 2, which showed no obvious macroscopic defects, were placed on ceramic sheets. The ceramic sheets were then pushed into an oxalic acid degreasing furnace for catalytic degreasing under a nitrogen atmosphere and acidic environment. The degreasing temperature was 150℃, and the acid inlet rate was 0.3 g / min. The total degreasing time was 10 hours. The samples before and after degreasing were weighed to calculate the degreasing rate. Degreased green parts with a degreasing rate greater than 8% were selected, and the unqualified parts underwent further degreasing.

[0078] Step 4: Hydrogen sintering

[0079] Qualified degreased green blanks were placed in a high-temperature hydrogen furnace and subjected to two-step sintering processes: a low-temperature degreasing process at 550℃ for 2 hours to remove residual binder, followed by a high-temperature densification process at 1200℃ for 4 hours to obtain W-30Cu composite material. The heating rate was controlled at 4℃ / min in the low-temperature stage and 7℃ / min in the densification stage, with a cooling rate of 6℃ / min. The W-30Cu composite material exhibited a dimensional shrinkage ratio of 1.35, a shrinkage range controlled within ±0.08 mm, a density of 98.1%, a thermal conductivity of 232 W / (m·K), a coefficient of thermal expansion of 9.58 ppm / ℃, and an airtightness of 7 × 10⁻⁶. -10 Pa·m 3 ·s -1 .

[0080] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing tungsten-copper composite materials by injection molding using a plastic-based binder, characterized in that, The steps are as follows: Step 1: Spray drying and hydrogen reduction Ammonium metatungstate, copper nitrate trihydrate, and oxalic acid dihydrate were dissolved together in deionized water in a reactor. The mass of copper nitrate trihydrate and oxalic acid dihydrate were 32%-120% and 30%-45% of the mass of ammonium metatungstate, respectively. After heating and stirring for a certain period of time, a mixed solution was formed. The mixed solution was sent to a spray drying tower through a feed pipe and dried into a tungsten-copper precursor under hot air. The inlet air temperature during the spray drying stage was 240-260℃, the peristaltic pump feed rate was 2-4L / h, and the atomizer speed was 22000-25000r / min. Then, the obtained tungsten-copper precursor was loaded into a ceramic sintering boat and pushed into a pusher-type reduction furnace for reduction. The reduction temperature during the hydrogen reduction stage was 880-920℃, thus preparing an ultrafine tungsten-copper composite powder in the form of tungsten-copper coating. Step 2: Grinding with an air jet mill The tungsten-copper composite powder obtained in step 1 is added to an air jet mill. Under high-purity and high-pressure nitrogen, the powder particles impact and collide with each other, achieving a grinding effect and dispersing the agglomerated powder. The dispersed powder is then carried by the air jet to the turbine for classification. Powder that meets the particle size requirements is collected by a cyclone separator, while the remaining coarse particles are carried to the grinding chamber for further grinding until they meet the requirements and are separated. Finally, tungsten-copper composite powder with good dispersibility and narrow particle size distribution is collected. Step 3: Mixing and Injection Molding Weigh the tungsten-copper composite powder and plastic binder after air jet milling in step 2 according to a mass ratio of (88-92):(8-12), mix them evenly in a mixer until they reach a dough-like state, and then crush them into feed material by a crusher; the components of the plastic binder include 75-85wt.% polyoxymethylene (POM), 8-12wt.% high-density polyethylene (HDPE), 3-8wt.% ethylene bis-stearamide (EBS), and 3-8wt.% stearic acid (SA) according to a mass ratio; pour the feed material into the barrel of the injection molding machine, and inject it into the shape of the mold under the action of temperature and pressure; the injection tail material is crushed and then injected repeatedly; Step 4: Oxalic acid-catalyzed degreasing and hydrogen sintering The injection molded parts obtained in step 3, which have no obvious defects on a macroscopic scale, are placed on ceramic sheets. The ceramic sheets are then pushed into an oxalic acid degreasing furnace for catalytic degreasing in a nitrogen atmosphere and acidic environment. The degreasing rate is calculated by weighing the samples before and after degreasing. The qualified degreased green body is placed in a high-temperature hydrogen furnace and undergoes low-temperature heat degreasing to remove residual binder and high-temperature sintering to densify, thus obtaining tungsten-copper composite material.

2. The method as described in claim 1, characterized in that, In step 1, during the mixed solution reaction stage, the oil bath temperature is 110-130℃, and the reaction time is 4-6 hours.

3. The method as described in claim 1, characterized in that, In step 2, the grinding pressure of the air jet mill is 0.3-0.7 MPa, the grinding time is 2-4 hours, and the speed of the classifying wheel is 3000-6000 r / min.

4. The method as described in claim 1, characterized in that, Step 3: During the mixing stage, the mixing temperature is 170-190℃ and the mixing time is 40-80 minutes; during the injection stage, the injection temperature is 160-170℃, the injection pressure is 80-100 bar, the injection speed is 40-80%, and the mold temperature is 90-110℃.

5. The method as described in claim 1, characterized in that, Step 4: In the oxalic acid catalytic degreasing stage, the degreasing temperature is 100-150℃, the acid feed rate is 0.1-0.3g / min, the degreasing time is 6-10h, and the degreasing rate is 5.8-8%. In the hydrogen sintering stage, the low-temperature section temperature is 480-550℃, the heating rate is 2-4℃ / min, and the holding time is 1-2h. The high-temperature sintering temperature is 1200-1350℃, the heating rate is 5-7℃ / min, and the holding time is 2-4h. After completion, the cooling rate is 4-6℃ / min.

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