Method for sintering TC4 titanium alloy by using graphite furnace

Abstract

The graphite furnace comprises a shell, a carbon felt layer and a graphite furnace body which are sequentially arranged from outside to inside, a middle area is formed between the graphite furnace body and the carbon felt layer, and a graphite cavity is formed in the graphite furnace body. The method comprises the following steps that a degreased part obtained after a TC4 titanium alloy green body is degreased is put into a graphite cavity to be sintered, so that a TC4 titanium alloy sintered part is obtained, and 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 is introduced into the graphite cavity so that the graphite cavity can keep the argon atmosphere; in the vacuum sintering stage and the first cooling stage, high-purity argon is introduced into the graphite cavity and the middle area so that the graphite cavity and the middle area can keep the argon atmosphere. The problem that carbon pollution and oxygen pollution exist when TC4 titanium alloy is sintered in an existing graphite furnace is solved.

Description

[0001] Technology

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

[0003] At present, the field of powder metallurgy technology generally uses sintering furnaces to sinter metal products, and sintering is a key link in the manufacture of powder metallurgy products. Common sintering furnaces on the market include graphite furnaces and metal furnaces. For TC4 titanium alloy products, during the sintering process, if the C and O content is too high, it is easy to cause the elongation of the titanium alloy to deteriorate, thereby affecting the performance of the product. Compared with graphite furnaces, metal furnaces have no carbon pollution, but their construction and maintenance costs are higher than graphite furnaces, which is not conducive to reducing production costs. Summary of the invention

[0004] In view of the defects of the above 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 implemented by the following technical solutions:

[0006] A method for sintering 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 to the inside, an intermediate area being formed between the graphite furnace body and the carbon felt layer, and a graphite cavity being provided in the graphite furnace body. The method is as follows: a degreased TC4 titanium alloy green body is placed in a graphite cavity for sintering to obtain a TC4 titanium alloy sintered part, wherein the sintering process sequentially comprises 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 is introduced into the graphite cavity so that the graphite cavity maintains an argon atmosphere; in the vacuum sintering stage and the first cooling stage: high-purity argon is introduced into both the graphite cavity and the intermediate area so that both the graphite cavity and the intermediate area maintain an argon atmosphere.

[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 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 exhaust 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: the high-purity argon gas is first 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 using 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, in the hot degreasing stage: high-purity argon gas is introduced into the graphite cavity so that the graphite cavity maintains an argon atmosphere, thereby preventing the TC4 titanium alloy part from being contaminated by impurities; and in the vacuum sintering stage and the first cooling stage, high-purity argon gas is introduced into the inside and middle area of ​​the graphite cavity so that the graphite cavity and the middle area both maintain an argon atmosphere. The argon atmosphere in the graphite cavity can protect the TC4 titanium alloy part from being contaminated by impurities during the sintering process. The argon atmosphere in the middle area can discharge C and O in the middle area, thereby preventing C and O outside the graphite cavity from penetrating into the graphite cavity to contaminate the TC4 titanium alloy part, thereby overcoming the defects of carbon pollution and oxygen pollution in the existing graphite furnace. 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 a third structural schematic diagram of a graphite furnace according to an embodiment of the present invention;

[0021] Figure 4 It is a test data table of the influence of the pressure difference inside and outside the graphite cavity on the physical properties of the present invention;

[0022] Figure 5 It is a test data table of the effect of gas pressure in the graphite cavity on compactness 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 one; 72. exhaust branch two; 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 a variety of forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to make the present invention more comprehensive and complete and to fully convey the concepts of example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar structures, and thus their repeated description 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 they can be changed as needed, and all such changes are included in the protection scope of the present invention.

[0026] like Figures 1 to 3As shown, a graphite furnace provided by the present invention comprises, from outside to 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, and 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 is 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, one end of the two ends abutting against the inner end wall of the shell 1, and the other end abutting against the inner end wall of the furnace door of the shell 1, 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.

[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, first adopt injection molding process to make TC4 titanium alloy green compact, then put TC4 titanium alloy green compact into oxalic acid degreasing furnace and carry out acid degreasing, to promote the decomposition of binder, use high purity argon as shielding gas in the degreasing process, wherein, the degreasing temperature is 110-135 ℃, degreasing time is 6-8 hours.After acid degreasing finishes, take out the degreased piece, calculate the weight loss rate of the degreased piece and do destructive test, measure the weight loss rate purpose: see whether binder is removed cleanly, the measuring method is: measure the weight change before and after degreasing, and the variation range is qualified between 12-14%.Destructive test adopts physical method to judge whether degreasing is fully completed, specifically, after crushing with hands, see whether hard core appears, appears, explanation binder is not thoroughly removed.After qualified test, degreased piece is put into graphite cavity 31 again and sintered.

[0030] In the thermal degreasing stage, high-purity argon (99.999%) is used as a heat transfer and protective gas to perform thermal degreasing on the degreased parts to remove the skeleton binder in the product, wherein the thermal degreasing parameters are: the temperature of the graphite cavity 31 is increased from 30°C to 600°C at a heating rate of 2-3°C / min, and the heat preservation time is 60-90min. Preferably, the high-purity argon is introduced in the thermal degreasing stage by first heating the argon to 90-130°C outside the furnace, and then introducing the argon into the graphite cavity 31, which can shorten the subsequent heating time and improve the 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 mainly reduces metal oxides and densifies metal particles. In this stage, the atmosphere is required to be sintered in a vacuum. Specifically, high-purity argon (99.999%) 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 maintained in an argon atmosphere. The argon atmosphere of the graphite cavity 31 can protect the TC4 titanium alloy part from being contaminated by impurities 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. For this reason, in this embodiment, high-purity argon gas is introduced into the middle region 4 to maintain an argon atmosphere in the middle region 4, so that the C and O in the middle region 4 can be discharged, thereby 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 electric control door, and the insulation door at one end of the graphite cavity 31 is opened by electric control, while the inside of the furnace body (i.e., the shell 1) remains closed; of course, the process of opening the insulation door of the graphite cavity 31 can also be to open and close the gas valve on the insulation door by electric control, so that the inside of the graphite cavity 31 and the outside of the graphite cavity 31 can exchange gas to assist in cooling the inside of the graphite cavity 31. Furthermore, in the second temperature-lowering 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 decreasing 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 decreasing 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, when the temperature of the graphite cavity 31 drops below 60°C, the furnace door (referring to the door of the outer shell 1) is opened to take out the TC4 titanium alloy sintered parts. 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 structure. 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 of the graphite cavity 31 is greater than the gas pressure of the middle region 4. This can prevent 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 manner: 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 middle area 4 and the graphite cavity 31, so that the air pressure of the middle area 4 is lower than that of the graphite cavity 31. Specifically, intermittent air intake into the graphite cavity 31 can be adopted, 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 extraction. In the same principle, the air pressure in the middle area 4 is lower than the air pressure in the graphite cavity 31 by controlling the flow difference between the air intake and the air extraction. 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, and 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 valve, so that the exhaust 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, 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 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 show that maintaining the gas pressure in the graphite cavity 31 at 1±0.3KPa is more conducive to improving the density of the sintered TC4 titanium alloy (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); too low a pressure difference will cause carbon and oxygen impurities outside the graphite cavity 31 to enter the graphite cavity 31, increase the carbon and oxygen content of TC4, and reduce the physical properties. If the pressure difference is too high, the service life of the furnace will be reduced. Figure 4Table 1 shows that the pressure difference between the middle area 4 and the graphite cavity 31 increases from 0.2Kpa to 0.6Kpa, and the carbon and oxygen contents gradually decrease. The material properties such as yield strength, tensile strength and elongation gradually increase, while the hardness gradually decreases. The test shows that the pressure difference between the middle area 4 and the graphite cavity 31 is maintained at 0.3KPa-0.5KPa, 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 is beneficial to extend 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 the graphite cavity 31 in an argon atmosphere; high-purity argon gas is continuously introduced into the middle area 4 and continuously discharged to maintain the middle area 4 in an argon atmosphere.

[0040] The present invention adopts the method of continuously introducing high-purity argon gas and continuously exhausting 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 the 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 exhaust gas out.

[0042] In this embodiment, refer to Figure 1 and Figure 3 The air intake device includes a first air intake pipe 5 directly extending into the graphite cavity 31, a delivery mechanism (not shown) for delivering argon gas through the first air intake pipe 5, and a second air intake 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, etc. The first exhaust pipe 7 has an exhaust branch 1 71 connected to the middle area 4 and an exhaust branch 2 72 connected to the graphite cavity 31. Under the action of the exhaust mechanism, the graphite cavity 31 and the middle area 4 are exhausted by the same first exhaust pipe 7.

[0044] In the prior art, the existing graphite furnace introduces high-purity argon gas between the carbon felt layer 2 and the shell 1, and evacuates the graphite cavity 31, so that the high-purity argon gas passes through the carbon felt layer 2 and the outer wall of the graphite furnace body 3 and enters the graphite cavity 31. In this way, the high-purity argon gas will bring the carbon and oxygen impurities in the carbon felt layer 2 and the middle area 4 into the graphite cavity 31, resulting in the defects of carbon pollution and oxygen pollution in the sintered parts. Compared with the prior art, this embodiment is directly connected to the graphite cavity 31 through the first air inlet pipe 5, and the first air inlet pipe 5 directly introduces high-purity argon gas into the graphite cavity 31. In this way, the high-purity argon gas does not need to pass through the carbon felt layer 2 and the middle area 4, effectively preventing the high-purity argon gas from bringing the carbon and oxygen impurities in the carbon felt layer 2 and the middle area 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 the gas is pumped out through the first exhaust pipe 7, so that C and O in the middle area 4 can be discharged, preventing C and O outside the graphite cavity 31 from penetrating into the graphite cavity 31 and contaminating the sintered parts; the graphite cavity 31 and the middle area 4 are evacuated 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 1 71 are provided. Inert gas enters from the two first air inlet pipes 5 above, and then is 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 at each placement position 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: 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.

[0047] In this embodiment, see Figure 2 The air intake device includes a second air intake pipe 6 for ventilating the middle area 4 and a first air intake pipe 5 for ventilating the graphite cavity 31, and the exhaust device includes a second exhaust pipe 8 for independently exhausting the middle area 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 middle area 4 is independently provided with the second air intake pipe 6 and the second exhaust pipe 8, so that the middle area 4 and the graphite cavity 31 are independently air intake and independently exhausted, and the two will not interfere with each other; and the pipelines of the middle area 4 and the graphite cavity 31 are not connected to each other, which can prevent impurities outside the graphite furnace body 3 from entering the graphite cavity 31 to reduce pollution.

[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 also 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 outer shell 1, and the gas enters the middle area 4 from the pores of the carbon felt layer 2.

[0051] In the present embodiment, the air intake device of the middle area 4 is the second air intake pipe 6. In order to evenly fill the middle area 4 with gas, the air intake method of the middle area 4 of the present embodiment is as follows: the second air intake pipe 6 first passes high-purity argon gas into the area between the carbon felt layer 2 and the outer shell 1, and then the high-purity argon gas 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 gas can be evenly dispersed in the middle area 4, so that the high-purity argon gas atmosphere is 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 is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, substitute 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 should 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 area (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: a degreased TC4 titanium alloy green body is placed in a graphite cavity (31) for sintering to obtain a TC4 titanium alloy sintered piece, 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 (31) so that the graphite cavity (31) maintains an argon atmosphere; During the vacuum sintering stage and the first temperature reduction 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.

2. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 1, characterized in that: During the vacuum sintering stage and the first temperature reduction stage, the gas pressure in the graphite cavity (31) is greater than the gas pressure in the middle area (4).

3. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 2, characterized in that: 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.

4. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 3, 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.

5. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 1, characterized in that: 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.

6. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 5, characterized in that: The method of introducing high-purity argon gas and continuously exhausting high-purity argon gas comprises: the graphite cavity (31) and the middle area (4) are respectively introduced with independent air intake devices, and the graphite cavity (31) and the middle area (4) are exhausted with the same exhaust device.

7. The method for sintering TC4 titanium alloy using a graphite furnace according to claim 5, 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) both introduce high-purity argon gas through independent air intake devices and both exhaust gas through independent exhaust devices.

8. The method for sintering TC4 titanium alloy using a graphite furnace according to any one of claims 6 or 7, 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).

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

10. 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 comprises: 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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