A method for sintering TC4 titanium alloy using a graphite furnace

Abstract

The present invention discloses a method for sintering TC4 titanium alloy using a graphite furnace. The graphite furnace includes an outer shell, a carbon felt layer, and a graphite furnace body, which are sequentially arranged from the outside to the inside. The graphite furnace body and the carbon felt layer form an intermediate region, and the graphite furnace body has a graphite cavity. The method is as follows: a degreased TC4 titanium alloy green body is placed in the graphite cavity for sintering to obtain a TC4 titanium alloy sintered part. The sintering process sequentially includes a hot degreasing stage, a vacuum sintering stage, a first cooling stage, and a second cooling stage. During the hot degreasing stage, high-purity argon gas is introduced into the graphite cavity to maintain an argon atmosphere. During the vacuum sintering stage and the first cooling stage, high-purity argon gas is introduced into both the graphite cavity and the intermediate region to maintain an argon atmosphere. This method solves the problem of carbon and oxygen contamination in existing graphite furnace sintering of TC4 titanium alloy.

Description

[0001] Technology Leader

[0002] The invention relates to the technical field of powder metallurgy materials, in particular to a method for sintering TC4 titanium alloy using a graphite furnace. Background Art

[0003] Currently, powder metallurgy generally uses sintering furnaces to sinter metal products. Sintering is a critical step in powder metallurgy manufacturing. Common sintering furnaces on the market include graphite furnaces and metal furnaces. For TC4 titanium alloy products, excessive carbon and oxygen content during the sintering process can easily lead to poor elongation, thus affecting product performance. Compared to graphite furnaces, metal furnaces are carbon-free, but their construction and maintenance costs are higher, hindering production cost reduction. Summary of the Invention

[0004] In view of the above defects in the prior art, the present invention provides a method for sintering TC4 titanium alloy using a graphite furnace to solve the defects of carbon pollution and oxygen pollution in the existing graphite furnace.

[0005] The present invention is achieved by adopting the following technical solutions:

[0006] A method for sintering a TC4 titanium alloy using a graphite furnace, the graphite furnace comprising an outer shell, a carbon felt layer, and a graphite furnace body, which are sequentially arranged from the outside inward. An intermediate region is formed between the graphite furnace body and the carbon felt layer, and a graphite cavity is provided in the graphite furnace body. The method is as follows: a degreased TC4 titanium alloy green body is placed in the graphite cavity for sintering to obtain a TC4 titanium alloy sintered part, wherein the sintering process sequentially comprises a thermal degreasing stage, a vacuum sintering stage, a first cooling stage, and a second cooling stage; in the thermal degreasing stage, high-purity argon gas is introduced into the graphite cavity to maintain an argon atmosphere in the graphite cavity; and in the vacuum sintering stage and the first cooling stage, high-purity argon gas is introduced into both the graphite cavity and the intermediate region to maintain an argon atmosphere in the graphite cavity and the intermediate region.

[0007] Furthermore, during the vacuum sintering stage and the first cooling stage, the air pressure in the graphite cavity is greater than the air pressure in the middle area.

[0008] Furthermore, during the vacuum sintering stage and the first cooling stage, the air pressure in the graphite cavity is maintained at 1±0.3 KPa, and the air pressure difference between the middle area and the graphite cavity is maintained at 0.3 KPa-0.5 KPa.

[0009] Furthermore, in the thermal degreasing stage, the temperature of the graphite cavity is raised from 30°C to 600°C and then kept warm for 60-90 minutes; in the vacuum sintering stage, the temperature of the graphite cavity is raised from 600°C to 1200°C and then kept warm for 2 hours; in the first cooling stage, the temperature of the graphite cavity is reduced from 1200°C to 500°C, and the middle area and the graphite cavity are both maintained in a high-purity argon atmosphere; in the second cooling stage, the high-purity argon atmosphere is maintained, and the insulation door of the graphite cavity is opened until the temperature of the graphite cavity drops from 500°C to room temperature.

[0010] Furthermore, during the vacuum sintering stage and the first cooling stage, high-purity argon gas is continuously introduced into the graphite cavity and continuously discharged to maintain an argon atmosphere in the graphite cavity; high-purity argon gas is continuously introduced into the middle area and continuously discharged to maintain an argon atmosphere in the middle area.

[0011] Furthermore, the method of introducing high-purity argon gas and continuously exhausting high-purity argon gas includes: the graphite cavity and the middle area respectively use independent air intake devices to introduce high-purity argon gas, and the graphite cavity and the middle area use the same exhaust device to pump gas out.

[0012] Furthermore, the method of introducing high-purity argon gas and continuously exhausting high-purity argon gas includes: the graphite cavity and the middle area are both introduced with high-purity argon gas through independent air intake devices and are both exhausted through independent exhaust devices.

[0013] Furthermore, the air intake method of the middle area is: the output end of the air intake device in the middle area directly extends into the middle area; or the output end of the air intake device in the middle area extends to the area between the carbon felt layer and the outer shell, and the gas enters the middle area from the pores of the carbon felt layer.

[0014] Furthermore, in the thermal degreasing stage, the high-purity argon gas is introduced in the following manner: firstly, the high-purity argon gas is heated to 90-130° C. outside the furnace, and then the high-purity argon gas is introduced into the graphite cavity.

[0015] Furthermore, the process of degreasing the TC4 titanium alloy green body includes: the TC4 titanium alloy green body is acid degreased in an oxalic acid degreasing furnace, high-purity argon is used as a protective gas during the degreasing process, wherein the degreasing temperature is 110-135° C., and the degreasing time is 6-8 hours.

[0016] Compared with the prior art, the beneficial effects of the present invention include at least:

[0017] When the TC4 titanium alloy of the present invention is sintered in a graphite furnace, during the hot degreasing stage, high-purity argon gas is introduced into the graphite cavity to maintain an argon atmosphere in the graphite cavity, thereby preventing the TC4 titanium alloy part from being contaminated by impurities; and during the vacuum sintering stage and the first cooling stage, high-purity argon gas is introduced into the interior and middle area of the graphite cavity to maintain an argon atmosphere in the graphite cavity and the middle area. The argon atmosphere in the graphite cavity can protect the TC4 titanium alloy part from being contaminated by impurities during the sintering process, and the argon atmosphere in the middle area can discharge carbon and oxygen in the middle area, thereby preventing carbon and oxygen outside the graphite cavity from penetrating into the graphite cavity and contaminating the TC4 titanium alloy part, thereby overcoming the defects of carbon pollution and oxygen pollution in existing graphite furnaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is one of the structural schematic diagrams of a graphite furnace according to an embodiment of the present invention;

[0019] Figure 2 This is the second structural schematic diagram of a graphite furnace according to an embodiment of the present invention;

[0020] Figure 3 This is the third structural diagram of a graphite furnace according to an embodiment of the present invention;

[0021] Figure 4 This is a table of experimental data on the effect of the pressure difference between inside and outside the graphite cavity on the physical properties of the present invention;

[0022] Figure 5 This is a table of experimental data on the effect of gas pressure in the graphite cavity on density of the present invention;

[0023] In the figure: 1. outer shell; 2. carbon felt layer; 3. graphite furnace body; 31. graphite cavity; 4. middle area; 5. first air inlet pipe; 6. second air inlet pipe; 7. first exhaust pipe; 71. exhaust branch 1; 72. exhaust branch 2; 8. second exhaust pipe; 9. third exhaust pipe. DETAILED DESCRIPTION

[0024] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concepts of the example embodiments to those skilled in the art. Identical reference numerals in the drawings represent identical or similar structures, and thus repeated descriptions thereof will be omitted.

[0025] The words expressing positions and directions described in the present invention are all explained with reference to the accompanying drawings as examples, but can be modified as needed, and all such modifications are within the scope of protection of the present invention.

[0026] like Figures 1 to 3As shown, a graphite furnace provided by the present invention comprises, from the outside to the inside, an outer shell 1, a carbon felt layer 2, and a graphite furnace body 3 having a graphite cavity 31. An intermediate area 4 is formed between the graphite furnace body 3 and the carbon felt layer 2. The graphite furnace body 3 has a graphite cavity 31, wherein the graphite cavity 31 is used for sintering TC4 titanium alloy.

[0027] Also, see Figure 1 The carbon felt layer 2 has a hollow square structure, and the graphite furnace body 3 is suspended inside the carbon felt layer 2 by a bracket, so that the outer wall of the graphite furnace body 3 and the inner wall of the carbon felt layer 2 define a middle area 4. Of course, in other embodiments, the carbon felt layer 2 can also be cylindrical with both ends open, with one end abutting the inner end wall of the outer shell 1 and the other end abutting the inner end wall of the furnace door of the outer shell 1. The graphite furnace body 3 is suspended inside the carbon felt layer 2 by a bracket, so that the outer wall of the graphite furnace body 3 and the inner wall of the carbon felt layer 2 define a middle area 4.

[0028] The present invention provides a method for sintering TC4 titanium alloy using a graphite furnace. The method is as follows: a degreased TC4 titanium alloy green body is placed in a graphite cavity 31 for sintering to obtain a TC4 titanium alloy sintered part, wherein the sintering process sequentially includes a hot degreasing stage, a vacuum sintering stage, a first cooling stage, and a second cooling stage. In the hot degreasing stage, high-purity argon gas is introduced into the graphite cavity 31 to maintain an argon atmosphere in the graphite cavity 31; in the vacuum sintering stage and the first cooling stage, high-purity argon gas is introduced into the graphite cavity 31 and the middle area 4 to maintain an argon atmosphere in the graphite cavity 31 and the middle area 4.

[0029] In the present embodiment, before sintering, earlier adopt injection molding process to make TC4 titanium alloy green compact, then TC4 titanium alloy green compact is put into oxalic acid degreasing furnace and carry out acid degreasing, to promote binding agent decomposition, use high purity argon as shielding gas in the degreasing process, wherein, degreasing temperature is 110-135 ℃, degreasing time 6-8 hour.After acid degreasing finishes, take out the degreasing part, calculate the weight loss rate of degreasing part and do destructive test, survey the weight loss rate purpose: see whether binding agent removes cleanly, measuring method is: measure the weight change before degreasing and after degreasing, and variation range is qualified between 12-14%.Destructive test adopts physical method to judge whether degreasing fully completes, concrete, after crushing with hands, see whether hard core occurs, occurred, and explanation binding agent is removed not thoroughly.After the qualified test, degreasing part is put into graphite cavity 31 again and carries out sintering.

[0030] During the thermal debinding stage, high-purity argon (99.999%) is used as a heat transfer and shielding gas to remove the binder from the product. The thermal debinding parameters are as follows: the temperature of the graphite cavity 31 is raised from 30°C to 600°C at a heating rate of 2-3°C / min, with a holding time of 60-90 minutes. Preferably, the high-purity argon is introduced during the thermal debinding stage by first heating the argon outside the furnace to 90-130°C before introducing it into the graphite cavity 31. This shortens the subsequent heating time and improves efficiency to a certain extent.

[0031] During the vacuum sintering stage, the temperature of the graphite cavity 31 is increased from 600°C to 1200°C at a heating rate of 3-5°C / min. This process primarily reduces the metal oxides and densifies the metal particles. During this stage, the atmosphere is required to be vacuum-evacuated. Specifically, high-purity argon (99.999%) is introduced into the interior of the graphite cavity 31 and the intermediate region 4, maintaining an argon atmosphere in both the graphite cavity 31 and the intermediate region 4. The argon atmosphere in the graphite cavity 31 protects the TC4 titanium alloy from contamination during the sintering process. In actual application scenarios, the carbon felt layer (2) will generate C (i.e., carbon source) when heated, and C will diffuse into the middle region 4. In addition, the middle region 4 also carries O (i.e., oxygen) in the air. C and O penetrate into the graphite cavity 31 from the side wall or port gap of the graphite cavity 31, contaminating the TC4 titanium alloy part. Therefore, in this embodiment, high-purity argon gas is introduced into the middle region 4 to maintain an argon atmosphere in the middle region 4, thereby discharging C and O in the middle region 4 and preventing C and O outside the graphite cavity 31 from penetrating into the graphite cavity 31 and contaminating the TC4 titanium alloy part.

[0032] In the first cooling stage, the temperature of the graphite cavity 31 is reduced from 1200°C to 500°C, and the middle area 4 and the graphite cavity 31 continue to maintain a high-purity argon (99.999%) atmosphere. In the second cooling stage, the temperature inside the graphite cavity 31 is reduced from 500°C to room temperature, maintaining a high-purity argon (99.999%) atmosphere, and the insulation door of the graphite cavity 31 is opened. Specifically, the process of opening the insulation door of the graphite cavity 31 includes: the insulation door is an electrically controlled door, and the insulation door at one end of the graphite cavity 31 is opened electrically, while the interior of the furnace body (i.e., the outer shell 1) remains closed; of course, the process of opening the insulation door of the graphite cavity 31 can also be achieved by electrically controlling only the gas valve on the insulation door to enable gas exchange between the inside and outside of the graphite cavity 31 to assist in cooling the interior of the graphite cavity 31. Furthermore, in the second cooling stage, the pressure in the furnace (referring to the pressure in the inner cavity of the shell 1) is maintained at 84.5 kPa±1.5 kPa until the temperature in the furnace drops to room temperature.

[0033] Furthermore, in the second cooling stage, during the process of dropping the temperature from 500°C to 60°C, the fan (which is installed on the inner door at one end of the graphite felt layer) can be turned on to form an air circulation inside the furnace body (referring to the inner cavity of the outer shell 1) to assist in cooling. Of course, during the process of dropping the temperature from 500°C to room temperature, the air intake device of the middle area 4 can be closed, and argon gas can be filled only through the air intake device of the graphite cavity 31, saving argon gas consumption and thus reducing costs. Preferably, the furnace door (referring to the door of the outer shell 1) is opened to take out the TC4 titanium alloy sintered parts when the temperature of the graphite cavity 31 drops below 60°C. If the furnace is opened when the temperature of the graphite cavity 31 is higher than 60°C, the TC4 titanium alloy sintered parts will be exposed to air and oxidized, affecting the appearance of the product.

[0034] In addition, the present invention can perform solution heat treatment on the sintered TC4 titanium alloy sintered part to obtain a titanium alloy with a uniform TC4 dual-phase ratio. Of course, according to actual needs, the TC4 titanium alloy sintered part can also be heat treated.

[0035] As a preferred embodiment, during the vacuum sintering stage and the first cooling stage, the gas pressure in the graphite cavity 31 is greater than the gas pressure in the middle region 4. This prevents the gas in the middle region 4 from penetrating into the graphite cavity 31 and bringing in C and O impurities, further reducing the probability of C and O penetrating into the graphite cavity 31.

[0036] As a preferred embodiment, during the vacuum sintering stage and the first cooling stage, the air pressure in the graphite cavity 31 is maintained at 1±0.3 KPa, and the air pressure difference between the middle area 4 and the graphite cavity 31 is maintained at 0.3 KPa-0.5 KPa.

[0037] The present invention controls the air pressure in the following way: the air pressure of the middle area 4 and the graphite cavity 31 is controlled by the air intake and exhaust flow rates of the two areas, so that the air pressure in the middle area 4 is lower than that in the graphite cavity 31. Specifically, intermittent air intake can be adopted into the graphite cavity 31, and the air pressure in the graphite cavity 31 is maintained at 1KPA by controlling the flow difference between the air intake and the air pumping amount. In the same principle, the air pressure in the middle area 4 is lower than that in the graphite cavity 31 by controlling the flow difference between the air intake and the air pumping amount. When the air pressure difference between the middle area 4 and the graphite cavity 31 is greater than 0.5KPA, the middle area 4 stops intake, and when it is lower than 0.3KPA, the middle area 4 is inflated. The inflation and exhaust processes are controlled by PLC. Specifically, the air intake device and the exhaust device are provided with corresponding valves. The PLC controller (or other applicable microcomputer controller) is electrically connected to the corresponding valves, and the gas flow is controlled by controlling the opening of the valves, so that the air pumping and inflation can be controlled. In other embodiments, the PLC controller directly controls the air intake device or the air exhaust device to switch between the working state and the non-working state to realize inflation and exhaust; preferably, a pressure gauge can be set on each pipeline, and the air pressure in the corresponding area can be sensed by the pressure gauge on the pipeline. The PLC controller is connected to the corresponding pressure gauge, so that the corresponding valve opening can be controlled according to the signal fed back by the pressure gauge, thereby controlling the gas flow in real time to control the air pressure.

[0038] In this embodiment, refer to Figure 5 Table 2 shows that as the gas pressure in the graphite cavity 31 increases, the sintering density and the thickness of the surface dense layer of the TC4 titanium alloy sintered part also increase. However, as the gas pressure in the graphite cavity 31 continues to increase, the increase in the thickness of the surface dense layer of the TC4 titanium alloy sintered part will gradually decrease. Since the gas pressure difference between the middle area 4 and the graphite cavity 31 will affect the material properties of the TC4 titanium alloy sintered part, the gas pressure in the graphite cavity 31 cannot be increased indefinitely. Experiments have shown that maintaining the gas pressure in the graphite cavity 31 at 1±0.3KPa is more conducive to improving the density of TC4 titanium alloy sintering (the thicker the density layer thickness, the better the physical properties, and the easier it is to polish later, the higher the polishing quality, and thus obtain good physical properties). If the gas pressure difference is too low, carbon and oxygen impurities outside the graphite cavity 31 will enter the graphite cavity 31, increasing the carbon and oxygen content of TC4 and reducing the physical properties. If the gas pressure difference is too high, the service life of the furnace will be reduced. Figure 4Table 1 shows the measured data. As the pressure differential between the middle region 4 and the graphite cavity 31 increases from 0.2 kPa to 0.6 kPa, the carbon and oxygen contents gradually decrease, and material properties such as yield strength, tensile strength, and elongation gradually increase, while hardness gradually decreases. Tests have shown that when the pressure differential between the middle region 4 and the graphite cavity 31 is maintained between 0.3 kPa and 0.5 kPa, the carbon content in the graphite cavity 31 is ≤ 0.11%, the oxygen content is ≤ 0.33%, and the elongation of the sintered TC4 titanium alloy is ≥ 5%, which further extends the service life of the graphite furnace.

[0039] As a preferred embodiment, during the vacuum sintering stage, high-purity argon gas is continuously introduced into the graphite cavity 31 and continuously discharged to maintain an argon atmosphere in the graphite cavity 31; high-purity argon gas is continuously introduced into the middle area 4 and continuously discharged to maintain an argon atmosphere in the middle area 4.

[0040] The present invention adopts the method of continuously introducing and continuously discharging high-purity argon gas to ensure that the graphite cavity 31 and the middle area 4 maintain an argon atmosphere, which can always and effectively protect the TC4 titanium alloy sintering process from being contaminated by impurities, and has the advantages of low implementation cost, simple implementation plan, safety and reliability; in addition, using argon gas as a protective atmosphere can reduce the production cost of TC4 titanium alloy, so that the graphite furnace can also be suitable for sintering titanium alloy.

[0041] As a preferred embodiment, the method of continuously introducing high-purity argon gas and continuously exhausting high-purity argon gas is as follows: the graphite cavity 31 and the middle area 4 respectively use independent air intake devices to introduce high-purity argon gas, and the graphite cavity 31 and the middle area 4 use the same exhaust device to extract gas out.

[0042] In this embodiment, refer to Figure 1 and Figure 3 The air inlet device includes a first air inlet pipe 5 extending directly into the graphite cavity 31, a delivery mechanism (not shown) for delivering argon through the first air inlet pipe 5, and a second air inlet pipe 6 for ventilating the middle area 4. The delivery mechanism can be a blower, an air compressor, etc.

[0043] The exhaust device includes a first exhaust pipe 7 for exhausting the graphite cavity 31 and an exhaust mechanism for exhausting the first exhaust pipe 7. The exhaust mechanism can be an exhaust fan, a Roots blower, or the like. The first exhaust pipe 7 has an exhaust branch 1 71 connected to the intermediate region 4 and an exhaust branch 2 72 connected to the graphite cavity 31. The exhaust mechanism exhausts the graphite cavity 31 and the intermediate region 4 through the first exhaust pipe 7.

[0044] In the prior art, existing graphite furnaces introduce high-purity argon gas between the carbon felt layer 2 and the outer shell 1 and evacuate the graphite cavity 31, allowing the high-purity argon gas to pass through the carbon felt layer 2 and the outer wall of the graphite furnace body 3 and enter the graphite cavity 31. This can carry carbon and oxygen impurities from the carbon felt layer 2 and the intermediate region 4 into the graphite cavity 31, resulting in carbon and oxygen contamination defects in the sintered parts. Compared to the prior art, this embodiment directly connects the graphite cavity 31 via a first air inlet pipe 5, which directly introduces high-purity argon gas into the graphite cavity 31. This eliminates the need for the high-purity argon gas to pass through the carbon felt layer 2 and the intermediate region 4, effectively preventing the high-purity argon gas from carrying carbon and oxygen impurities from the carbon felt layer 2 and the intermediate region 4 into the graphite cavity 31. High-purity argon gas is introduced into the middle area 4 through the second air inlet pipe 6 and is exhausted through the first exhaust pipe 7. This can discharge C and O in the middle area 4 and prevent C and O outside the graphite cavity 31 from penetrating into the graphite cavity 31 and contaminating the sintered part. The graphite cavity 31 and the middle area 4 are exhausted only through one first exhaust pipe 7, reducing the number of pipes connected to the outer shell 1, so as to control the airtightness of the outer shell 1.

[0045] Specifically, see Figure 1 and Figure 3 In this embodiment, two first air inlet pipes 5 and two second air inlet pipes 6 are respectively provided, and both are evenly arranged along the length direction of the furnace body. Three exhaust branch lines 72 are provided, and two exhaust branch lines 71 are provided. Inert gas enters from the two first air inlet pipes 5 above, and is then drawn into the first exhaust pipe 7 from the three exhaust branch lines 72 below. The first exhaust pipe 7 draws the gas out, so that the high-purity argon gas in the graphite cavity 31 is evenly distributed, so that the products placed at various positions in the graphite cavity 31 can be fully protected by the atmosphere.

[0046] In another embodiment, the method of continuously introducing high-purity argon gas and continuously exhausting high-purity argon gas can also be: high-purity argon gas is introduced into the graphite cavity 31 and the middle area 4 through independent air intake devices and is exhausted through independent exhaust devices.

[0047] In this embodiment, see Figure 2 The air intake device includes a second air intake pipe 6 for ventilating the intermediate region 4 and a first air intake pipe 5 for ventilating the graphite cavity 31. The exhaust device includes a second exhaust pipe 8 for independently exhausting the intermediate region 4 and a third exhaust pipe 9 for independently exhausting the graphite cavity 31. The graphite cavity 31 is independently provided with the first air intake pipe 5 and the third exhaust pipe 9, and the intermediate region 4 is independently provided with the second air intake pipe 6 and the second exhaust pipe 8. This allows the intermediate region 4 and the graphite cavity 31 to independently intake and exhaust air without interfering with each other. Furthermore, the pipes between the intermediate region 4 and the graphite cavity 31 are not interconnected, which prevents impurities outside the graphite furnace body 3 from entering the graphite cavity 31, thereby reducing contamination.

[0048] As a preferred embodiment, the air intake mode of the middle area 4 is as follows: the output end of the air intake device of the middle area 4 directly extends into the middle area 4 .

[0049] See Figure 1 and Figure 2 In this embodiment, the air intake device of the middle area 4 is a second air intake pipe 6, and the output end of the second air intake pipe 6 extends into the middle area 4. In this way, gas can be directly introduced into the middle area 4 through the second air intake pipe 6, so that the middle area 4 is quickly filled with high-purity argon gas, thereby improving ventilation efficiency.

[0050] In another embodiment, see Figure 3 The air intake method of the middle area 4 can also be: the output end of the air intake device of the middle area 4 extends to the area between the carbon felt layer 2 and the shell 1, and the gas enters the middle area 4 from the pores of the carbon felt layer 2.

[0051] In this embodiment, the air intake device of the middle area 4 is the second air intake pipe 6. In order to uniformly fill the middle area 4 with gas, the air intake method of the middle area 4 of this embodiment is: the second air intake pipe 6 first passes high-purity argon into the area between the carbon felt layer 2 and the outer shell 1, and then the high-purity argon penetrates into the middle area 4 from the pores of the carbon felt layer 2. Under the dispersing effect of the carbon felt layer 2, the high-purity argon can be evenly dispersed in the middle area 4, making the high-purity argon atmosphere better, thereby more effectively protecting the TC4 titanium alloy parts from being contaminated by impurities during the sintering process.

[0052] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limiting the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the invention without departing from the principles and purpose of the present invention. All such changes shall fall within the scope of protection of the claims of the present invention.

Claims

1. A method for sintering TC4 titanium alloy using a graphite furnace, wherein the graphite furnace comprises a shell (1), a carbon felt layer (2), and a graphite furnace body (3) arranged in sequence from the outside to the inside, an intermediate region (4) is formed between the graphite furnace body (3) and the carbon felt layer (2), and a graphite cavity (31) is provided in the graphite furnace body (3); characterized in that: The method is as follows: placing a degreased TC4 titanium alloy green body into a graphite cavity (31) for sintering to obtain a TC4 titanium alloy sintered part, wherein the sintering process sequentially includes a thermal degreasing stage, a vacuum sintering stage, a first cooling stage, and a second cooling stage; During the thermal degreasing stage: high-purity argon gas is introduced into the graphite cavity (31) to maintain an argon atmosphere in the graphite cavity (31); During the vacuum sintering stage and the first cooling stage: high-purity argon gas is introduced into the graphite cavity (31) and the middle area (4) so that the graphite cavity (31) and the middle area (4) are both kept in an argon atmosphere; During the vacuum sintering stage and the first cooling stage, the gas pressure of the graphite cavity (31) is greater than the gas pressure of the middle area (4); During the vacuum sintering stage and the first cooling stage, the air pressure in the graphite cavity (31) is maintained at 1±0.3 KPa, and the air pressure difference between the middle area (4) and the graphite cavity (31) is maintained at 0.3 KPa-0.5 KPa; During the vacuum sintering stage and the first cooling stage, high-purity argon gas is continuously introduced into the graphite cavity (31) and continuously discharged, so that the graphite cavity (31) maintains an argon atmosphere, and high-purity argon gas is continuously introduced into the middle area (4) and continuously discharged, so that the middle area (4) maintains an argon atmosphere; The method of introducing high-purity argon gas and continuously exhausting high-purity argon gas includes: the graphite cavity (31) and the middle area (4) respectively use independent air intake devices to introduce high-purity argon gas, and the graphite cavity (31) and the middle area (4) use the same exhaust device to pump gas out.

2. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 1, characterized in that: In the thermal degreasing stage, the temperature of the graphite cavity (31) is raised from 30°C to 600°C and then kept warm for 60-90 minutes; in the vacuum sintering stage, the temperature of the graphite cavity (31) is raised from 600°C to 1200°C and then kept warm for 2 hours; in the first cooling stage, the temperature of the graphite cavity (31) is reduced from 1200°C to 500°C; in the second cooling stage, a high-purity argon atmosphere is maintained, and the insulation door of the graphite cavity (31) is opened until the temperature of the graphite cavity (31) is reduced from 500°C to room temperature.

3. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 1, characterized in that: The method of introducing high-purity argon gas and continuously exhausting high-purity argon gas includes: the graphite cavity (31) and the middle area (4) are both introduced with high-purity argon gas through independent air intake devices and are both exhausted through independent exhaust devices.

4. The method for sintering TC4 titanium alloy using a graphite furnace according to any one of claims 1 or 3, characterized in that: The air intake method of the middle area (4) is as follows: the output end of the air intake device of the middle area (4) directly extends into the middle area (4); or the output end of the air intake device of the middle area (4) extends to the area between the carbon felt layer (2) and the outer shell (1), and the gas enters the middle area (4) from the pores of the carbon felt layer (2).

5. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 1, characterized in that: During the thermal degreasing stage, the high-purity argon is introduced in the following manner: first, the high-purity argon is heated outside the furnace to 90-130° C., and then the high-purity argon is introduced into the graphite cavity (31).

6. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 1, characterized in that: The process of degreasing the TC4 titanium alloy green body includes: the TC4 titanium alloy green body is acid degreased in an oxalic acid degreasing furnace, high-purity argon is used as a protective gas during the degreasing process, wherein the degreasing temperature is 110-135° C., and the degreasing time is 6-8 hours.

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