Method for preparing titanium alloy product based on binder spraying additive manufacturing process

Abstract

The invention discloses a method for preparing a titanium alloy product based on a binder spraying additive manufacturing process, which comprises the following steps: (1) preparing titanium alloy powder with the oxygen content of less than or equal to 100ppm, carrying out vibration screening on the obtained titanium alloy powder, and selecting particles with the particle size range of 5-25 microns; (2) the surfaces of titanium alloy powder particles are coated with nano oxide coatings, the titanium alloy powder coated with the nano oxide coatings is subjected to vacuum drying and then transferred into binder spraying additive manufacturing equipment, a green body is printed by controlling the binder spraying technology, and the strength of the green body is made to be larger than or equal to 5 MPa; and (3) the green body is subjected to degreasing, microwave sintering and hot isostatic pressing treatment, and the oxide dispersion enhanced titanium alloy product is obtained. According to the method, the oxygen content in the titanium alloy powder is reduced, meanwhile, the surface of the titanium alloy powder is coated with the nanometer oxide coating, and microwave sintering and hot isostatic pressing treatment are cooperated under specific conditions, so that micro cracks and micro holes in the titanium alloy component can be effectively eliminated, and the density of the titanium alloy component is greatly improved; therefore, the mechanical property is improved.

Description

Technical Field

[0001] The invention relates to a method for preparing a titanium alloy product based on a binder jetting additive manufacturing process. Background Art

[0002] Titanium alloys, due to their excellent specific strength, corrosion resistance, and biocompatibility, have important application value in aerospace, medical implants, national defense, and other fields. However, traditional titanium alloy manufacturing processes (such as forging, casting, and machining) have problems such as low material utilization, long processing cycles, and high costs. Especially for complex structural parts, traditional processes often require multiple steps and even rely on expensive five-axis machining equipment, which greatly limits the widespread application of titanium alloys.

[0003] In recent years, additive manufacturing technology has provided new solutions for the forming of titanium alloys. Among them, powder bed fusion technology (such as SLM and EBM) has been successfully applied to the direct manufacturing of titanium alloy parts, but its equipment cost is high, printing efficiency is low, and residual stress is large. In contrast, binder jet additive manufacturing technology has the advantages of fast printing speed, low cost, the ability to form complex structures, and no need for support. It is especially suitable for the mass production of small and medium-sized precision parts. However, this technology is relatively mature in the process research of preparing steel and copper materials. In the preparation of titanium alloy products, there are problems such as poor sintering density and low mechanical properties of the products. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for preparing titanium alloy products with high density and good mechanical properties by using a binder jet printing process.

[0005] Technical solution: The method for preparing titanium alloy products based on the binder jet additive manufacturing process of the present invention comprises the following steps:

[0006] (1) preparing a titanium alloy powder with an oxygen content of ≤100 ppm, vibrating and screening the obtained titanium alloy powder to select particles with a particle size range of 5 to 25 μm; selecting the particle size within this range is to improve the capillary force of the powder, facilitate the subsequent penetration of the binder, and thus improve the green strength; and on the other hand, it can improve the subsequent printing accuracy and sintering driving force;

[0007] (2) coating the surface of titanium alloy powder particles with a nano-oxide coating, drying the titanium alloy powder coated with the nano-oxide coating, and then transferring the titanium alloy powder to a binder jetting additive manufacturing device, and printing a green body by controlling the binder jetting process so that the green body strength is ≥5 MPa; wherein, during the binder jetting process, the laying thickness of the titanium alloy powder is 30 to 40 μm, the laying speed of the titanium alloy powder is 5 to 6 mm / s, and the drying time after the binder jetting is 12 to 15 seconds;

[0008] (3) The green body is subjected to degreasing, microwave sintering and hot isostatic pressing to obtain a titanium alloy component with oxide dispersion enhancement.

[0009] Wherein, in step (1), the preparation method of titanium alloy powder with an oxygen content of ≤100ppm is as follows: the titanium alloy powder is prepared by electrode induction melting gas atomization, the molten titanium alloy is broken into fine droplets by high-purity argon gas, and spherical titanium alloy powder is formed after rapid solidification; the flowability of the titanium alloy powder is ≤25s / 50g, and the tap density is ≥4.2g / cm 3 , oxygen content ≤100ppm; in this method, high-purity argon (purity>99.999%) is used, the jet pressure in the crushing process is 5-6.5MPa, and the speed at which the titanium alloy electrode rod rotates downward is 0.5-0.8mm / s.

[0010] In step (2), the oxide is one of Y2O3, Al2O3, SiO2 or ZrO2, and the coating amount of the nano-oxide coating on the surface of the titanium alloy powder is 0.3-0.5% of the mass of the titanium alloy powder.

[0011] In step (2), the drying conditions are: vacuum insulation in a drying furnace at 100-105° C. for 2-2.5 hours to ensure the dryness and fluidity of the titanium alloy powder.

[0012] In step (3), the adhesive is a water-based adhesive. The water-based adhesive is easy to volatilize during the subsequent degreasing process. The water-based adhesive includes a polyacrylic acid-based adhesive (polyacrylic acid (10wt%), ethylene glycol (5wt%), ethylene glycol monobutyl ether (5wt%), water (80wt%)).

[0013] In step (3), the degreasing treatment is as follows: the green body is placed in a tubular heating furnace, an inert gas is introduced, the heating rate is 3-5°C / min, the temperature is raised to 350-400°C, and the temperature is kept at 1-2 hours to remove the binder. The degreased sample is transferred to a microwave sintering device, the microwave sintering device is vacuumed, the microwave frequency is set to 4.5-5GHz, and a segmented temperature control strategy is adopted: in the first stage, the temperature is raised to 850-900°C at a heating rate of 6-8°C / min and kept at 0.5 hours; in the second stage, the temperature is raised to 1250-1450°C at a heating rate of 12-15°C / min, kept at 2 hours, and cooled with the furnace. The sample after microwave sintering is transferred to a hot isostatic pressing device, the argon pressure is set to 120-150MPa, the temperature is 1250-1450°C, and kept at 2-3 hours.

[0014] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the method of the present invention can effectively eliminate microcracks and micropores inside titanium alloy components by reducing the oxygen content in titanium alloy powder and coating the surface of titanium alloy powder with nano-oxide coating, and cooperate with microwave sintering and hot isostatic pressing under specific conditions, thereby greatly improving the density of titanium alloy components and thus improving their mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Flowchart of the method of the present invention. DETAILED DESCRIPTION

[0016] Example 1

[0017] The present invention provides a method for preparing a titanium alloy product based on a binder jet additive manufacturing process, comprising the following steps:

[0018] (1) TC4 titanium alloy (Ti-6Al-4V) was selected, and a TC4 titanium alloy electrode rod (the constant feed speed of the titanium alloy electrode rod was 0.5 mm / s) was placed in an electrode induction melting gas atomization device. High-purity argon (purity ≥ 99.999%) was used as the atomizing gas. The titanium alloy electrode rod was melted using an alternating magnetic field. High-pressure inert gas (pressure of 6.5 MPa) was used to break the molten titanium alloy into fine droplets. After rapid solidification, spherical TC4 titanium alloy powder was obtained. The flowability of the obtained powder was 23 s / 50 g, and the tap density was 4.3 g / cm 3 , oxygen content is 100ppm;

[0019] (2) 5-25 μm particles were selected by vibration screening, and a 0.5 wt% Y2O3 nano-coating was coated on the surface of the titanium alloy powder by physical vapor deposition, and the coating was kept in a vacuum oven at 100°C for 2 h;

[0020] (3) The TC4 titanium alloy powder coated with the Y2O3 nano-coating was transferred to a binder jetting additive device, and a water-based binder was used to print the green body. The green body strength was 5.3±0.1MPa by controlling the binder jetting process. During the binder jetting process, the titanium alloy powder was laid at a thickness of 30μm, the spreading speed of the titanium alloy powder was 5mm / s, and the drying time after the binder jetting was 15s.

[0021] (4) The debinding stage takes place in a tubular heating furnace, where the temperature is raised to 400°C at a rate of 3°C / min and kept at that temperature for 2 hours under argon protection; the microwave sintering stage takes place in a microwave sintering device, which is equipped with a multi-mode resonant cavity and a temperature sensor. An array of auxiliary heating bodies arranged horizontally and vertically is set at the upper end of the cavity, and the spacing between adjacent heating bodies is 15 mm. The microwave frequency is set to 5 GHz. The temperature is first raised to 900°C at a rate of 8°C / min and kept at that temperature for 0.5 hours, and then raised to 1450°C at a rate of 15°C / min and kept at that temperature for 2 hours, and then cooled with the furnace; finally, hot isostatic pressing is performed at 1450°C and 150 MPa argon for 3 hours to obtain titanium alloy components.

[0022] The tensile strength of the component prepared in Example 1 is 1150±18 MPa and the density is 99.95%, which meets the performance requirements of structural parts used in the aerospace field.

[0023] Example 2

[0024] The present invention provides a method for preparing a titanium alloy product based on a binder jet additive manufacturing process, comprising the following steps:

[0025] (1) Titanium alloy (Ti-6Al-7Nb) was selected, and a Ti-6Al-7Nb titanium alloy electrode rod (the constant feed speed of the titanium alloy electrode rod was 0.5 mm / s) was placed in an electrode induction melting gas atomization device. High-purity argon (purity ≥ 99.999%) was used as the atomizing gas. The titanium alloy electrode rod was melted using an alternating magnetic field. High-pressure inert gas (the injection pressure was 6.5 MPa) was used to break the molten titanium alloy into fine droplets. After rapid solidification, spherical titanium alloy powder was obtained. The flowability of the obtained powder was 22 s / 50 g, and the tap density was 4.25 g / cm 3 , oxygen content is 100ppm;

[0026] (2) selecting particles of 5 to 25 μm by vibration screening, coating the surface of the titanium alloy powder with a 0.3 wt% ZrO2 nanocoating by a sol-gel method, and then keeping the coating in a vacuum oven at 100°C for 2 h;

[0027] (3) The titanium alloy powder coated with the ZrO2 nano-coating was transferred to a binder jetting additive device, and a water-based binder was used to print a green body. The green body strength was 5.2±0.12MPa by controlling the binder jetting process. During the binder jetting process, the titanium alloy powder was laid at a thickness of 40μm, a spreading speed of 6mm / s, and a drying time of 12s after the binder jetting.

[0028] (4) The debinding stage takes place in a tubular heating furnace, where the temperature is raised to 350°C at a rate of 5°C / min and kept at that temperature for 2 hours under argon protection; the microwave sintering stage takes place in a microwave sintering device, which is equipped with a multi-mode resonant cavity and a temperature sensor. An array of auxiliary heating bodies arranged horizontally and vertically is set at the upper end of the cavity, and the spacing between adjacent heating bodies is 15 mm. The microwave frequency is set to 4.5 GHz. The temperature is first raised to 850°C at a rate of 6°C / min and kept at that temperature for 0.5 hours, then raised to 1250°C at a rate of 12°C / min and kept at that temperature for 2 hours, and then cooled with the furnace; finally, hot isostatic pressing is performed at 1250°C and 120 MPa argon for 2 hours to obtain titanium alloy components.

[0029] The tensile strength of the component prepared in Example 2 is 950±12 MPa and the density is 99.92%, which meets the performance requirements of biomedical structural components.

[0030] Comparative Example 1

[0031] The method of Comparative Example 1 is basically the same as that of Example 1, with the only difference being that in step (1), argon with a purity of less than 99% is used as the atomizing gas to obtain spherical titanium alloy powder with an oxygen content greater than 100 ppm (150-180 ppm).

[0032] The tensile strength of the component prepared in Comparative Example 1 is 983±4.5 MPa, and the density is 98.54%.

[0033] Comparative Example 2

[0034] The method of Comparative Example 2 is basically the same as that of Example 1, with the only difference being that in step (2), the 5-25 μm particles after screening are not coated with a nano-oxide coating.

[0035] The tensile strength of the component prepared in Comparative Example 2 is 896±7.2 MPa, and the density is 98.12%.

[0036] Comparative Example 3

[0037] The method of Comparative Example 3 is basically the same as that of Example 1, with the only difference being that in step (2), during the binder spraying process, the laying thickness of the titanium alloy powder is 30 μm, the laying speed of the titanium alloy powder is 5 mm / s, and the drying time after the binder spraying is 8 s, so that the green strength is 4.63 MPa.

[0038] The tensile strength of the component prepared in Comparative Example 3 is 945±3.8 MPa, and the density is 98.37%.

[0039] Comparative Example 4

[0040] The method of Comparative Example 4 is basically the same as that of Example 1, with the only difference being that no hot isostatic pressing treatment is performed in step (4).

[0041] The tensile strength of the component prepared in Comparative Example 4 is 812±6.4 MPa, and the density is 96.23%.

[0042] Comparative Example 5

[0043] The method of Comparative Example 5 is basically the same as that of Example 1, with the only difference being that in step (4), conventional heat treatment process is adopted for sintering, and a tubular furnace resistance wire is used for heating, placed in the middle of the furnace, and inert gas is introduced for protection. The temperature is raised to 1450°C at 5°C / min and kept for 2h, and then cooled with the furnace.

[0044] The tensile strength of the component prepared in Comparative Example 5 is 1017±5.6 MPa, and the density is 99.12%.

[0045] By comparing Example 1 and Comparative Examples 1 to 5, it can be seen that the present invention prepares titanium alloy powder with high sphericity and low oxygen content by electrode induction melting gas atomization method, combines it with nano-oxide coating coating, introduces oxide reinforcement phase into the titanium alloy structure in situ during degreasing and sintering, utilizes high-frequency electromagnetic field to achieve rapid and uniform heating of the material, utilizes hot isostatic pressing technology to eliminate internal pores and microcracks, and further improves density and mechanical properties.

Claims

1. A method for preparing titanium alloy products based on a binder jet additive manufacturing process, characterized in that: The steps include: (1) preparing a titanium alloy powder having an oxygen content of ≤100 ppm, and vibrating and screening the obtained titanium alloy powder to select particles with a particle size range of 5 to 25 μm; (2) coating the surface of the titanium alloy powder particles with a nano-oxide coating, vacuum drying the titanium alloy powder coated with the nano-oxide coating, and then transferring the titanium alloy powder to a binder jet additive manufacturing device, and printing a green body by controlling the binder jet process to make the green body strength ≥5 MPa; (3) The green body is subjected to degreasing, microwave sintering and hot isostatic pressing to obtain a titanium alloy product with oxide dispersion enhancement.

2. The method according to claim 1, wherein: In step (1), the titanium alloy powder is prepared by electrode induction melting gas atomization method, and the molten titanium alloy is crushed into fine droplets using high-purity argon gas, which is then rapidly solidified to form spherical titanium alloy powder; the purity of the high-purity argon gas is greater than 99.999%, and the jet pressure during the crushing process is 5 to 6.5 MPa.

3. The method according to claim 1, wherein: In step (2), the oxide is one of Y2O3, Al2O3, SiO2 or ZrO2.

4. The method according to claim 3, wherein: The coating amount of the nano-oxide coating on the surface of the titanium alloy powder is 0.3-0.5% of the mass of the titanium alloy powder.

5. The method according to claim 1, wherein: In step (2), the drying conditions are: vacuum insulation in a drying oven at 100-105° C. for 2-2.5 hours.

6. The method according to claim 1, wherein: In step (2), during the binder spraying process, the laying thickness of the titanium alloy powder is 30 to 40 μm, the spreading speed of the titanium alloy powder is 5 to 6 mm / s, and the drying time after the binder spraying is 12 to 15 s.

7. The method according to claim 1, wherein: In step (3), the adhesive is a water-based adhesive.

8. The method according to claim 1, wherein: In step (3), the degreasing treatment is as follows: placing the green body in a tubular heating furnace, introducing inert gas, heating at a rate of 3 to 5°C / min to 350 to 400°C, and keeping the temperature for 1 to 2 hours to remove the binder.

9. The method according to claim 1, wherein: In step (3), the microwave sintering treatment is as follows: the microwave sintering equipment is vacuumed, the microwave frequency is set to 4.5-5 GHz, and segmented temperature control is adopted: in the first stage, the temperature is increased to 850-900°C at a heating rate of 6-8°C / min and kept warm for 0.5h; in the second stage, the temperature is increased to 1250-1450°C at a heating rate of 12-15°C / min, kept warm for 2h, and cooled with the furnace.

10. The method according to claim 1, wherein: In step (3), the hot isostatic pressing treatment is as follows: argon pressure is 120-150 MPa, temperature is 1250-1450° C., and heat preservation is carried out for 2-3 hours.

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