Method for preparing high-density low-carbon-oxygen titanium alloy

Abstract

The invention discloses a method for preparing a high-density and low-carbon-oxygen titanium alloy. The method comprises the following steps: weighing a certain mass of spherical TC4 powder and a binder; the spherical TC4 powder and a binder are put into an internal mixer to be mixed; putting the mixed feed into a granulator, and extruding and granulating to obtain granular injection feed; putting the granular injection feed into an injection stock bin, and injecting into a mold to obtain a TC4 green body; the TC4 green body is subjected to degreasing treatment; and the TC4 degreased blank is sintered, the first stage is a thermal degreasing stage, the TC4 degreased blank is cooled to the room temperature along with a furnace, then the second stage is sintered, the TC4 degreased blank is cooled to the room temperature along with the furnace, and a TC4 sintered part is obtained. According to the method for preparing the high-density and low-carbon-oxygen titanium alloy, an optimized two-section type sintering process is adopted for the blank, a binder can be fully volatilized and discharged at the low temperature, the content of C and O in a titanium alloy sintered part is reduced, and the method has the advantages that atomic diffusion and rearrangement of the titanium alloy blank are more orderly, the density is effectively improved, and the service life of the titanium alloy blank is prolonged. And the cracking and deformation risks are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of metal injection molding, and particularly to a method for preparing a high-density, low-carbon and low-oxygen titanium alloy. Background Art

[0002] As the crystallization of the deep integration of plastic industry injection molding technology and powder metallurgy, MIM is a new powder metallurgy near-net-shape forming technology. With its outstanding product performance, obvious cost advantages, and the ability to fabricate complex-shaped parts, it has attracted much attention in the industry and won the title of "one of the most popular component forming technologies today". The process flow of MIM mainly includes several key links such as the mixing of powder and binder, injection molding, debinding, and sintering. In the raw material system of MIM, the binder plays a crucial role. On the one hand, its core function is to tightly bond metal powder particles together to form a feedstock with specific strength, laying the foundation for the subsequent injection molding process. On the other hand, during the sintering process, the binder serves as a medium that needs to be completely removed. Only by completely removing it can the purity of the final product be ensured. Therefore, the proportion of the binder must be precisely designed to ensure both sufficient bonding strength to meet the molding requirements and ease of subsequent processing, minimizing residues to the greatest extent.

[0003] Traditional plastic-based binders for titanium alloys are composed of various organic components such as main binders, surfactants, dispersants, and lubricants, and their molecular structures contain various functional groups such as ether bonds, methylene groups, methyl groups, and carboxyl groups. These organic components are prone to gas residues and uneven shrinkage during debinding and sintering, resulting in pores in the final product and failing to achieve the desired high-density state, thereby affecting the mechanical properties of the material. At the same time, during the debinding stage, it is difficult for the binder to effectively avoid the introduction of C and O impurities. On the one hand, when the organic components in the binder are not completely debound, C elements will remain, increasing the C content in the alloy; on the other hand, during the high-temperature sintering process, titanium alloys are extremely prone to react with O in the environment, resulting in an increase in O content. Excessive C and O contents will significantly reduce the mechanical properties of titanium alloys. These problems existing in the binders greatly restrict the wide application of titanium alloys in high-end fields. Therefore, the design and optimization of titanium alloy binders have become an urgent task. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: To solve the above technical problem, the technical solution adopted by the present invention is: A method for preparing a high-density, low-carbon and low-oxygen titanium alloy, comprising the following steps: Step 1, weigh a certain mass of spherical TC4 powder and binder; Step 2, put the spherical TC4 powder and the binder into a mixer for mixing to obtain a feedstock; Step 3: Put the feedstock obtained after kneading into a granulator for extrusion granulation to obtain granular injection feedstock; Step 4: Put the granular injection feedstock into an injection agent bin and inject it into a mold to obtain a green TC4 blank; Step 5: Subject the green TC4 blank to debinding treatment to obtain a debound TC4 blank; Step 6: Sinter the debound TC4 blank. The first stage is the thermal debinding stage, and it is cooled to room temperature with the furnace. Then, the second-stage sintering process is carried out, and it is cooled to room temperature with the furnace to obtain a sintered TC4 part.

[0005] The beneficial effects of the present invention are as follows: The method for preparing a high-density and low-carbon-oxygen titanium alloy optimizes the two-stage sintering process for the blank, enabling the binder to fully volatilize and be discharged at a lower temperature, reducing the C and O contents in the sintered titanium alloy part, and promoting more orderly atomic diffusion and rearrangement of the titanium alloy blank, effectively reducing the risks of cracking and deformation. It has significant advantages such as enhancing the thoroughness of impurity removal, increasing the density, improving the tissue uniformity, and reducing the process risks. Description of the Drawings

[0006] Figure 1 It is the metallographic diagram of the sintered TC4 part 1 prepared in Example 1 of the present invention; Figure 2 It is the metallographic diagram of the sintered TC4 part 2 prepared in Example 2 of the present invention; Figure 3 It is the metallographic diagram of the sintered TC4 part 3 prepared in Comparative Example 1; Figure 4 It is the metallographic diagram of the sintered TC4 part 4 prepared in Comparative Example 2. Detailed Embodiments

[0007] To describe the technical content, the achieved objectives and effects of the present invention in detail, the following is described in conjunction with the embodiments and accompanied by the drawings.

[0008] A method for preparing a high-density and low-carbon-oxygen titanium alloy includes the following steps: Step 1: Weigh a certain mass of spherical TC4 powder and binder; Step 2: Put the spherical TC4 powder and binder into a mixer for kneading to obtain a feedstock; Step 3: Put the feedstock obtained after kneading into a granulator for extrusion granulation to obtain granular injection feedstock; Step 4: Put the granular injection feedstock into an injection agent bin and inject it into a mold to obtain a green TC4 blank; Step 5: Subject the green TC4 blank to debinding treatment to obtain a debound TC4 blank; Step 6: Sinter the TC4 degreased blank. The first stage is the thermal degreasing stage, followed by furnace cooling to room temperature. Then, the second-stage sintering process is carried out, followed by furnace cooling to room temperature to obtain the TC4 sintered part.

[0009] As can be seen from the above description, the beneficial effects of the present invention are as follows: The method for preparing a high-density and low-carbon oxygen titanium alloy adopts an optimized two-stage sintering process for the blank, which can enable the binder to volatilize and discharge fully at a lower temperature, reduce the C and O contents in the titanium alloy sintered part, and has the advantages of promoting the atomic diffusion and rearrangement of the titanium alloy blank to be more orderly, effectively reducing the risks of cracking and deformation, and having remarkable advantages such as enhancing the thoroughness of impurity removal, increasing the density, improving the tissue uniformity, and reducing the process risks.

[0010] Further, the loading amount of the spherical TC4 powder is 55 vol% - 60 vol%, and the loading amount of the binder is 40 vol% - 45 vol%.

[0011] Further, the particle size of the spherical TC4 powder is less than or equal to 25 μm, and D50 is 12 μm - 15 μm.

[0012] Further, in the spherical TC4 powder, the weight percentage of Al is 6 wt% - 6.5 wt%, the weight percentage of V is 3.75 wt% - 4.25 wt%, the weight percentage of Fe ≤ 0.3 wt%, the weight percentage of C ≤ 0.08 wt%, the weight percentage of O ≤ 0.18 wt%, and the balance is Ti.

[0013] Further, the binder includes: 83% - 87% polyoxymethylene, 2% - 4% stearic acid, 5% - 7% high-density polyethylene, 2% - 4% ethylene-vinyl acetate copolymer, 1% - 3% polyethylene, and 1% - 2% B215 antioxidant.

[0014] As can be seen from the above description, stearic acid can improve the bonding strength and flexibility of the blank, polyethylene, high-density polyethylene, and ethylene-vinyl acetate copolymer can enhance the fluidity and uniformity of the blank, and B215 antioxidant can protect the easily oxidized organic polymers.

[0015] Further, the mixer in Step 2 is an atmosphere mixer, the rotation speed of the mixer rotor is 40 rpm - 50 rpm, the mixing time is 2 h - 3 h, and the mixing temperature is 160°C - 200°C.

[0016] Further, the granulation temperature in Step 3 is 175°C - 185°C, the extrusion speed is 10 Hz - 20 Hz, the feeding speed is 5 Hz - 10 Hz, the cutting speed is 5 Hz - 10 Hz, the particle size of the granular injection feed is 3 mm, and the particle size length of the granular injection feed is 2 mm - 4 mm.

[0017] Furthermore, the injection mold in Step 4 is a stretching rod mold. The temperature of the injection mold is 80°C - 120°C, the feeding heating temperature is 160°C - 200°C, the injection pressure is 100 MPa - 140 MPa, and the holding pressure time is 5 s - 15 s.

[0018] Furthermore, the debinding method in Step 5 adopts oxalic acid catalytic debinding. The debinding temperature is 110°C - 140°C, and the debinding time is 8 h - 14 h.

[0019] Furthermore, in the thermal debinding stage of Step 6, the heating rate is 3°C / min - 10°C / min, the sintering temperature is 550°C - 600°C, and the heat preservation time is 2 h - 3 h; in the second-stage sintering process, the heating rate is 5°C / min - 15°C / min, the sintering temperature is 1030°C - 1080°C, and the heat preservation time is 3 h - 6 h.

[0020] Example 1 of the present invention is: a method for preparing a high-density and low-carbon oxygen titanium alloy, including the following steps: Step 1, weigh a certain mass of spherical TC4 powder prepared by the commercially available gas atomization method and a plastic-based binder; wherein the loading amount of the spherical TC4 powder is 57 vol%, and the loading amount of the plastic-based binder is 43 vol%; the particle size of the spherical TC4 powder is less than or equal to 25 μm, and D 50 is 13 μm; in the spherical TC4 powder, the weight percentage of Al is 6.2 wt%, the weight percentage of V is 4 wt%, the weight percentage of Fe is 0.1 wt%, the weight percentage of C is 0.03 wt%, the weight percentage of O is 0.08 wt%, and the balance is Ti; the components of the plastic-based binder include: 85% polyoxymethylene as the main binder, 3% stearic acid, 7% high-density polyethylene, 2% ethylene-vinyl acetate copolymer, 2% polyethylene, and 1% B215 antioxidant.

[0021] Step 2, put the spherical TC4 powder and the plastic-based binder into an atmosphere type internal mixer according to the specified loading amount and mix to obtain a feed; the rotor speed of the internal mixer is 45 rpm, the mixing time is 3 h, and the mixing temperature is 180°C.

[0022] Step 3, put the mixed feed into a granulator to extrude and granulate to obtain granular injection feed; the granulation temperature is 180°C, the extrusion speed is 15 Hz, the feeding speed is 8 Hz, the cutting speed is 8 Hz, the particle size of the granular injection feed is 3 mm, and the particle size length of the granular injection feed is 3 mm.

[0023] Step 4, put the granular injection feed into an injection material bin and inject it into a mold to obtain a TC4 green body; wherein the injection mold is a stretching rod mold, the temperature of the injection mold is 110°C, the feeding heating temperature is 180°C, the injection pressure is 120 MPa, and the holding pressure time is 10 s.

[0024] Step 5: Degrease the green TC4 compact to obtain a degreased TC4 compact. The degreasing method uses oxalic acid-catalyzed degreasing at a degreasing temperature of 120°C and a degreasing time of 9 h.

[0025] Step 6: Sinter the degreased TC4 compact. The first stage is the thermal degreasing stage with a heating rate of 5°C / min, a sintering temperature of 580°C, a holding time of 3 h, and furnace cooling to room temperature. Then, carry out the second-stage sintering process with a heating rate of 10°C / min, a sintering temperature of 1060°C, a holding time of 5 h, and furnace cooling to room temperature to obtain TC4 sintered part 1.

[0026] Figure 1 This is the metallographic diagram of TC4 sintered part 1 in Example 1.

[0027] Example 2 of the present invention is: A method for preparing a high-density, low-carbon and low-oxygen titanium alloy, comprising the following steps: Step 1: Weigh a certain mass of spherical TC4 powder prepared by commercially available gas atomization method and a plastic-based binder. The loading amount of the spherical TC4 powder is 57 vol%, and the loading amount of the plastic-based binder is 43 vol%. The particle size of the spherical TC4 powder is less than or equal to 25 μm, and D 50 is 13 μm. In the spherical TC4 powder, the weight percentage of Al is 6.2 wt%, the weight percentage of V is 4 wt%, the weight percentage of Fe is 0.1 wt%, the weight percentage of C is 0.03 wt%, the weight percentage of O is 0.08 wt%, and the balance is Ti. The composition of the plastic-based binder includes: 86% polyoxymethylene as the main binder, 3% stearic acid, 5% high-density polyethylene, 3% ethylene-vinyl acetate copolymer, 2% polyethylene, and 1% B215 antioxidant.

[0028] Step 2: Put the spherical TC4 powder and the plastic-based binder into an atmospheric kneader according to the specified loading amounts and knead to obtain a feedstock. The rotor speed of the kneader is 45 rpm, the kneading time is 3 h, and the kneading temperature is 180°C.

[0029] Step 3: Put the kneaded feedstock into a granulator and extrude and granulate to obtain granular injection feedstock. The granulation temperature is 180°C, the extrusion speed is 15 Hz, the feeding speed is 8 Hz, the cutting speed is 8 Hz, the particle size of the granular injection feedstock is 3 mm, and the particle size length of the granular injection feedstock is 3 mm.

[0030] Step 4: Put the granular injection feedstock into an injection hopper and inject it into a mold to obtain a green TC4 compact. The injection mold is a tensile rod mold, the injection mold temperature is 110°C, the feedstock heating temperature is 180°C, the injection pressure is 120 MPa, and the holding pressure time is 10 s.

[0031] Step Five: Degrease the green TC4 body to obtain a degreased TC4 body. The degreasing method uses oxalic acid-catalyzed degreasing, with a degreasing temperature of 120°C and a degreasing time of 10 h.

[0032] Step Six: Sinter the degreased TC4 body. The first stage is the thermal degreasing stage, with a heating rate of 5°C / min, a sintering temperature of 580°C, a holding time of 3 h, and furnace cooling to room temperature. Then, carry out the second-stage sintering process, with a heating rate of 10°C / min, a sintering temperature of 1050°C, a holding time of 6 h, and furnace cooling to room temperature to obtain the TC4 sintered part 2.

[0033] Figure 2 This is the metallographic diagram of the TC4 sintered part 2 of Example Two.

[0034] Comparative Example One: A method for preparing a titanium alloy, including the following steps: Step One: Weigh a certain mass of spherical TC4 powder prepared by the commercially available gas atomization method and a plastic-based binder. The loading amount of the spherical TC4 powder is 70 vol%, and the loading amount of the plastic-based binder is 30 vol%. The particle size of the spherical TC4 powder is less than or equal to 25 μm, and D 50 is 13 μm. In the spherical TC4 powder, the weight percentage of Al is 6.2 wt%, the weight percentage of V is 4 wt%, the weight percentage of Fe is 0.1 wt%, the weight percentage of C is 0.03 wt%, the weight percentage of O is 0.08 wt%, and the balance is Ti. The composition of the plastic-based binder includes: 90% polyoxymethylene as the main binder, 5% stearic acid, 2% high-density polyethylene, 2% ethylene-vinyl acetate copolymer, and 1% B215 antioxidant.

[0035] Step Two: Put the spherical TC4 powder and the plastic-based binder into an atmosphere-type internal mixer according to the specified loading amounts for mixing to obtain a feedstock. The rotor speed of the internal mixer is 45 rpm, the mixing time is 3 h, and the mixing temperature is 180°C.

[0036] Step Three: Put the mixed feedstock into a granulator for extrusion granulation to obtain granular injection feedstock. The granulation temperature is 180°C, the extrusion speed is 15 Hz, the feeding speed is 8 Hz, the cutting speed is 8 Hz, the particle size of the granular injection feedstock is 3 mm, and the particle size length of the granular injection feedstock is 3 mm.

[0037] Step Four: Put the granular injection feedstock into an injection hopper and inject it into a mold to obtain a green TC4 body. The injection mold is a tensile rod mold, the injection mold temperature is 110°C, the feedstock heating temperature is 180°C, the injection pressure is 120 MPa, and the holding pressure time is 10 s.

[0038] Step 5: Degrease the TC4 green compact to obtain a degreased TC4 blank. The degreasing method uses oxalic acid-catalyzed degreasing at a degreasing temperature of 120°C and a degreasing time of 7 h.

[0039] Step 6: Sinter the degreased TC4 blank. The first stage is the thermal degreasing stage with a heating rate of 8°C / min, a sintering temperature of 500°C, a holding time of 1 h, and furnace cooling to room temperature. Then, carry out the second-stage sintering process with a heating rate of 8°C / min, a sintering temperature of 1100°C, a holding time of 4 h, and furnace cooling to room temperature to obtain the TC4 sintered part 3.

[0040] Figure 3 It is the metallographic diagram of the TC4 sintered part 3 of Comparative Example 1.

[0041] Comparative Example 2: A method for preparing a titanium alloy, comprising the following steps: Step 1: Weigh a certain mass of spherical TC4 powder prepared by the commercially available gas atomization method and a plastic-based binder. Among them, the loading amount of the spherical TC4 powder is 50 vol%, and the loading amount of the plastic-based binder is 50 vol%. The particle size of the spherical TC4 powder is less than or equal to 25 μm, and D 50 is 13 μm. In the spherical TC4 powder, the weight percentage of Al is 6.2 wt%, the weight percentage of V is 4 wt%, the weight percentage of Fe is 0.1 wt%, the weight percentage of C is 0.03 wt%, the weight percentage of O is 0.08 wt%, and the balance is Ti. The components of the plastic-based binder include: 89% polyoxymethylene as the main binder, 5% stearic acid, 2% high-density polyethylene, 3% ethylene-vinyl acetate copolymer, and 1% B215 antioxidant.

[0042] Step 2: Put the spherical TC4 powder and the plastic-based binder into an atmosphere-type internal mixer according to the specified loading amounts to obtain a feedstock. The rotor speed of the internal mixer is 45 rpm, the mixing time is 3 h, and the mixing temperature is 180°C.

[0043] Step 3: Put the feedstock obtained after mixing into a granulator to extrude and granulate to obtain a granular injection feedstock. The granulation temperature is 180°C, the extrusion speed is 15 Hz, the feeding speed is 8 Hz, the cutting speed is 8 Hz, the particle size of the granular injection feedstock is 3 mm, and the particle size length of the granular injection feedstock is 3 mm.

[0044] Step 4: Put the granular injection feedstock into an injection hopper and inject it into a mold to obtain a TC4 green compact. Among them, the injection mold is a tensile rod mold, the injection mold temperature is 110°C, the feedstock heating temperature is 180°C, the injection pressure is 120 MPa, and the holding pressure time is 10 s.

[0045] Step 5: Degrease the TC4 green body to obtain a degreased TC4 blank. The degreasing method uses oxalic acid-catalyzed degreasing, with a degreasing temperature of 120 °C and a degreasing time of 5 h.

[0046] Step 6: Sinter the degreased TC4 blank. The first stage is the thermal degreasing stage, with a heating rate of 5 °C / min, a sintering temperature of 580 °C, and a holding time of 3 h. Cool it in the furnace to room temperature, and then carry out the second-stage sintering process. The heating rate is 10 °C / min, the sintering temperature is 1060 °C, and the holding time is 5 h. Cool it in the furnace to room temperature to obtain the TC4 sintered part 4.

[0047] Figure 4 It is the metallographic diagram of the TC4 sintered part 4 of Comparative Example 2.

[0048] Perform performance tests on the above-mentioned TC4 sintered parts 1, TC4 sintered parts 2, TC4 sintered parts 3, and TC4 sintered parts 4, and the results are shown in Table 1 below:

[0049] Table 1 In summary, the method for preparing a high-density and low-carbon-oxygen titanium alloy provided by the present invention uses an optimized two-stage sintering process for the blank, which can enable the binder to volatilize and discharge fully at a lower temperature, reduce the C and O contents in the titanium alloy sintered part, and has the advantages of promoting the atomic diffusion and rearrangement of the titanium alloy blank to be more orderly, effectively reducing the risks of cracking and deformation, enhancing the thoroughness of impurity removal, improving the density, improving the tissue uniformity, and reducing the process risks.

[0050] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in the relevant technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A method for preparing a high-density and low-carbon and oxygen titanium alloy, characterized in that, It includes the following steps: Step 1: Weigh a certain mass of spherical TC4 powder and binder; Step 2: Put the spherical TC4 powder and binder into a mixer to mix and obtain a feedstock; Step 3: Put the feedstock obtained after mixing into a granulator to extrude and granulate, obtaining a granular injection feedstock; Step 4: Put the granular injection feedstock into an injection hopper and inject it into a mold to obtain a green TC4 blank; Step 5: Perform debinding treatment on the green TC4 blank to obtain a debound TC4 blank; Step 6: Sinter the debound TC4 blank. The first stage is the thermal debinding stage, cool it to room temperature with the furnace, and then carry out the second-stage sintering process, cool it to room temperature with the furnace, obtaining a sintered TC4 part.

2. The method for preparing a high-density and low-carbon oxygen titanium alloy according to claim 1, wherein: The loading amount of the spherical TC4 powder is 55 vol% - 60 vol%, and the loading amount of the binder is 40 vol% - 45 vol%.

3. The method for preparing a high-density and low carbon-oxygen titanium alloy according to claim 1, characterized in that: The particle size of the spherical TC4 powder is less than or equal to 25 μm, and D 50 is 12 μm - 15 μm.

4. The method for preparing a high-density, low-carbon and low-oxygen titanium alloy according to claim 1, wherein: In the spherical TC4 powder, the weight percentage of Al is 6 wt% - 6.5 wt%, the weight percentage of V is 3.75 wt% - 4.25 wt%, the weight percentage of Fe ≤ 0.3 wt%, the weight percentage of C ≤ 0.08 wt%, the weight percentage of O ≤ 0.18 wt%, and the balance is Ti.

5. The method for preparing a high-density and low carbon-oxygen titanium alloy according to claim 1, characterized in that, The binder includes 83% - 87% polyoxymethylene, 2% - 4% stearic acid, 5% - 7% high-density polyethylene, 2% - 4% ethylene-vinyl acetate copolymer, 1% - 3% polyethylene, and 1% - 2% B215 antioxidant.

6. The method for preparing a high-density, low-carbon and low-oxygen titanium alloy according to claim 1, wherein: The mixer in Step 2 is an atmosphere mixer. The rotation speed of the mixer rotor is 40 rpm - 50 rpm, the mixing time is 2 h - 3 h, and the mixing temperature is 160 °C - 200 °C.

7. The method for preparing a high-density, low-carbon and low-oxygen titanium alloy according to claim 1, wherein: The granulation temperature in Step 3 is 175 °C - 185 °C, the extrusion speed is 10 Hz - 20 Hz, the feeding speed is 5 Hz - 10 Hz, the cutting speed is 5 Hz - 10 Hz, the particle size of the granular injection feedstock is 3 mm, and the particle size length of the granular injection feedstock is 2 mm - 4 mm.

8. The method for preparing a high-density and low-carbon oxygen titanium alloy according to claim 1, characterized in that: The injection mold in Step 4 is a tensile bar mold. The temperature of the injection mold is 80 °C - 120 °C, the feeding heating temperature is 160 °C - 200 °C, the injection pressure is 100 MPa - 140 MPa, and the holding pressure time is 5 s - 15 s.

9. The method for preparing a high-density and low-carbon oxygen titanium alloy according to claim 1, characterized in that: The debinding method in Step 5 adopts oxalic acid catalytic debinding. The debinding temperature is 110 °C - 140 °C, and the debinding time is 8 h - 14 h.

10. The method for preparing a high-density and low-carbon oxygen titanium alloy according to claim 1, characterized in that: The heating rate in the thermal debinding stage of Step 6 is 3 °C / min - 10 °C / min, the sintering temperature is 550 °C - 600 °C, and the holding time is 2 h - 3 h; the heating rate of the second-stage sintering process is 5 °C / min - 15 °C / min, the sintering temperature is 1030 °C - 1080 °C, and the holding time is 3 h - 6 h.

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