Fine beta-crystal titanium alloy and laser three-dimensional forming method

Abstract

The invention discloses a fine beta-crystal titanium alloy and a laser three-dimensional forming method, and belongs to the technical field of additive manufacturing. According to the forming method, a terbium (Tb) element is added in titanium alloy powder. As a very strong segregation element in the titanium alloy, the terbium element can segregate at the grain boundary at the final stage of solidification to generate an alpha-Tb phase, the pinning effect is achieved, and rapid growth of grains is limited. In addition, in the laser three-dimensional forming process, the laser energy density is reduced to reduce heat input, the cooling speed in the forming process is increased, and grain coarsening caused by heat influence in the forming process is avoided. According to the method, grain coarsening is limited under the combined action of reducing laser three-dimensional forming heat input and increasing a grain boundary segregation alpha-Tb phase, and finally grain refinement is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and particularly relates to a fine β-grained titanium alloy and a laser solid forming method. Background Art

[0002] In recent years, additive manufacturing technology has received extensive attention and rapid development. This technology integrates the functions of forming and performance regulation, and can realize the efficient manufacturing of complex metal components, and has become an important manufacturing means for high-performance complex metal components. Especially in the field of biomedicine, additive manufacturing technology is widely used in customized services for human bones, such as ribs, leg bones, and teeth.

[0003] Compared with other metal materials, titanium alloy has good formability and biocompatibility. However, existing research shows that there are significant differences in the mechanical properties, especially fatigue properties, between additively manufactured titanium alloy human bones and natural human bones, which are difficult to meet the current requirements of biomedicine for additively manufactured titanium alloys. This problem has greatly restricted the further popularization and application of additively manufactured titanium alloys.

[0004] Analysis shows that the fatigue performance of titanium alloy is mainly affected by the grain size of β-phase crystals. The β-phase crystals of additively manufactured titanium alloys are often extremely coarse, and the grain size can range from several hundred micrometers to several millimeters. However, current methods are difficult to effectively regulate it. On the one hand, the coarse β-phase crystals reduce the material's ability to coordinate deformation and easily induce cracks; on the other hand, the grain boundary α-phase (continuous straight shape) caused by the coarse grains significantly increases the crack propagation rate, resulting in insufficient fatigue performance. Therefore, grain refinement is of great significance for improving the fatigue performance of titanium alloys.

[0005] Chinese invention application with the publication number CN 1013114826 A discloses a titanium-nickel-aluminum-rare earth superalloy material and its preparation method. The technical solution is to add a series of rare earth elements (including terbium) to the titanium-nickel-aluminum-rare earth superalloy material to refine the grains, thereby improving the fatigue performance of the superalloy material. In this technical solution, the reason for adding rare earth elements to the superalloy is that rare earth elements have extremely high affinity with oxygen, can reduce the oxygen content in the superalloy material and generate rare earth oxides. The rare earth oxides can increase the nucleation sites during solidification, thereby promoting grain refinement, which is one of the traditional grain refinement methods. Different from superalloy materials, limited by the process characteristics and basic physical properties of titanium alloys, the grain growth activation energy of titanium alloys is extremely low, and the grains are prone to coarsening and growing, resulting in the inability to quickly and efficiently prepare fine β-phase crystals through currently widely used methods. Therefore, realizing the refinement of β-phase crystals during the additive manufacturing of titanium alloys has become an important research direction and key technical bottleneck in the current additive manufacturing of titanium alloys. Summary of the Invention

[0006] The object of the present invention is to overcome the disadvantages of the above-mentioned prior art, and to provide a fine β-grained titanium alloy and a laser solid forming method, aiming to effectively refine the β grains of the additive manufactured titanium alloy and avoid the performance problems caused by coarse grains.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A laser solid forming method for a fine β-grained titanium alloy, comprising the following steps: S1, adding terbium metal powder or titanium-terbium intermetallic compound to titanium alloy powder to obtain forming powder; S2, preparing a fine β-grained titanium alloy by laser solid forming the forming powder. After forming one layer, if the molten pool temperature is less than 2000 °C, stay for 2 s - 60 s for the laser solid forming of the next layer; if the molten pool temperature is greater than or equal to 2000 °C, stay until the molten pool temperature is less than 800 °C for the laser solid forming of the next layer. After preparing the set number of layers, a specimen is obtained. During the laser solid forming process, the laser energy density is 25 (W·s) / mm - 200 (W·s) / mm, and the ambient oxygen content ≤ 500 ppm; S3, after the forming is completed, naturally cool to room temperature to obtain a fine β-grained titanium alloy, and α-Tb phase is pinned at the grain boundaries of the fine β-grained titanium alloy.

[0008] A further improvement of the present invention lies in: Preferably, in S1, the content of terbium element in the forming powder < 10 wt.%.

[0009] Preferably, in S1, the particle size of the terbium metal powder or titanium-terbium intermetallic compound is 15 μm - 200 μm.

[0010] Preferably, in S1, adding a titanium-terbium intermetallic compound to titanium alloy powder to obtain forming powder; the structural formula of the titanium-terbium intermetallic compound is Ti (1-x） -Tb x , where 0 < x < 1, and x is the atomic number of terbium element.

[0011] Preferably, in S1, the titanium-terbium intermetallic compound and titanium alloy powder are mixed by ball milling, or the terbium metal powder and titanium alloy powder are mixed by ball milling, and the ball milling tank is sealed during the ball milling process.

[0012] Preferably, during the ball milling process, the rotation speed is 20 Hz - 30 Hz, and the time is 3 h - 6 h.

[0013] Preferably, in S2, during the laser solid forming process, the laser power is 380W - 2000W, the laser scanning speed is 10mm / s - 60mm / s, the laser spot diameter is 3mm - 5mm, the powder feeding rate is 12g / min - 20g / min, the lifting amount is 0.2mm - 1.0mm, and the overlapping rate is 30% - 60%.

[0014] Preferably, before S2, the process parameter determination process of the laser solid forming process is as follows: conduct metallographic observation on the specimen obtained by laser solid forming. When the grains are equiaxed grains and the porosity ≥ 99.5%, reduce the laser energy density, repeat the laser solid forming to obtain a specimen, observe the specimen and judge whether the grains and porosity meet the preset requirements. If not, reduce the laser energy density again until the grains or porosity of the specimen obtained in the nth time meet the preset requirements. Then, the process parameters of the laser solid forming process in the (n - 1)th time are the final process parameters; where n is the number of cycles and is a natural number, and the preset requirements are specifically: the grains of the specimen are columnar grains or the porosity is less than 99.5%.

[0015] Preferably, in S2, the temperature of the molten pool is monitored by an infrared thermometer.

[0016] A fine β-grained titanium alloy prepared by the laser solid forming method according to any one of the above, the grain size of the fine β-grained titanium alloy is 10μm - 50μm, and α-Tb phases are pinned at the grain boundaries of the fine β-grained titanium alloy.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a laser solid forming method for a fine β-grained titanium alloy. During the laser solid forming process, due to the heat dissipation of the molten pool to the formed specimen during the forming process, the deposited layer is prone to being strongly thermally affected, resulting in the formation of a titanium alloy with coarse grains. The method of the present invention mainly refines grains through two means. Firstly, terbium (Tb) element is added to the titanium alloy powder. As a very strong segregation element in the titanium alloy, terbium can segregate at the grain boundaries to form α-Tb phase at the end of solidification of each layer, restricting the rapid coarsening of grains and playing a pinning role. And because terbium element is very active, during the entire laser solid forming process, the oxygen content is strictly controlled to avoid reducing the formation of α-Tb phase at the grain boundaries due to the formation of terbium oxide, thereby reducing the pinning effect. Secondly, an extremely low laser energy density is adopted. Reducing the laser energy density can reduce the heat input, restrict the grain growth under thermal action, significantly reduce the in-situ thermal influence, and avoid the coarsening and growth of β grains. Therefore, during the laser solid forming process, the temperature of the molten pool is observed in-situ. Once it is found that the temperature is too high, exceeding 2000 °C, the corresponding interlayer dwell time will be increased to reduce the temperature of the specimen. Further, by limiting the laser energy density, the heat accumulation of the specimen is reduced, thereby increasing the cooling rate during the forming process, making more α-Tb phase segregate at the grain boundaries, further pinning the grain boundaries and restricting grain growth, realizing grain refinement.

[0018] The second aspect of the present invention discloses a fine β-grained titanium alloy prepared by the above method. The grain size of this fine β-grained titanium alloy is 10 μm - 50 μm, which is much smaller than the grain size of conventional titanium alloys. Brief Description of the Drawings

[0019] Figure 1 Microstructure of the Ti-5Al-5Mo-5V-3Cr-1Zr-4Tb-0.1B alloy prepared in Example 1; Figure 2 Microstructure of the Ti-9Mo-6Tb-0.1B alloy prepared in Example 2; Figure 3 Microstructure of the Ti-7Mo-3Cr-3Nb-3Al-4.5Tb-0.1B alloy prepared in Example 3; Figure 4 Microstructure of the Ti-24Nb-4Zr-8Sn-6Tb-0.1B alloy prepared in Example 4; Figure 5 Microstructure of the Ti-12Zr-5Nb-3Ta-6Tb-0.1B alloy prepared in Example 5; Figure 6 Microstructure of the Ti-24Nb-4Zr-8Sn-4.5Tb-0.1B alloy prepared in Example 6; Figure 7The microstructure of the Ti-9Mo-3.8Tb-0.1B alloy prepared in Example 7. Detailed implementation manners

[0020] The present invention will be further described in detail below with reference to the accompanying drawings: To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meanings understood by those skilled in the art with respect to the present invention. In case of conflicts, the definitions in this specification shall prevail.

[0021] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar expressions cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0022] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0023] Conventional instruments and equipment in the art are used in the following embodiments. For the experimental methods without specific conditions indicated in the following embodiments, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are the conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratios represent weight ratios.

[0024] The metal elements involved in the present invention and their corresponding abbreviations are shown in Table 1 below.

[0025] Table 1 Correspondence table of element Chinese names and abbreviations

[0026] The first aspect of the present invention discloses a laser solid forming method for a fine β-grained titanium alloy, comprising the following steps: S1, adding terbium metal powder or titanium-terbium intermetallic compound to titanium alloy powder to obtain forming powder; S2. Prepare a fine β-grained titanium alloy from the formed powder by laser solid forming. After forming one layer, if the molten pool temperature is less than 2000 °C, pause for 2 s - 60 s for the next layer of laser solid forming; if the molten pool temperature is greater than or equal to 2000 °C, pause until the molten pool temperature is less than 800 °C for the next layer of laser solid forming. After completing the set number of layers, obtain a specimen. During the laser solid forming process, the laser energy density is 25 (W·s) / mm - 200 (W·s) / mm, and the environmental oxygen content ≤ 500 ppm. S3. After the forming is completed, cool naturally to room temperature to obtain a fine β-grained titanium alloy. At the grain boundaries of the fine β-grained titanium alloy, α-Tb phases are pinned.

[0027] The present invention realizes grain refinement by introducing terbium elements into the titanium alloy and matching laser solid forming process parameters. During the laser solid forming process of the titanium alloy, terbium elements are added. Utilizing the characteristics that terbium elements can strongly segregate in the titanium alloy, combined with controlling the laser solid forming process parameters, more segregation phases, α-Tb phases, are generated at the grain boundaries of the titanium alloy, restricting the growth of β grains during the in-situ thermal cycle at the end of solidification and after solidification, thereby realizing the refinement of the entire grains and obtaining a fine β-grained titanium alloy. In terms of controlling the laser solid forming process, it includes low laser energy density, high cooling rate, and low molten pool temperature. The laser energy density during the forming process under this process is extremely low, only 25 (W·s) / mm - 200 (W·s) / mm, which is significantly lower than the current conventional laser energy density, and the conventional one is above 600 (W·s) / mm. The low laser energy density has two functions. Firstly, it can reduce the heat accumulation of the formed specimen, thereby increasing the temperature gradient during the rapid solidification process, realizing extremely rapid cooling, and promoting grain refinement. Secondly, it can reduce the heat accumulation effect and reduce the in-situ coarsening of grains under the influence of heat. In terms of specific process control, in the present invention, after each layer is formed during the laser solid forming process, a pause is made for a certain period of time to avoid excessive heat accumulation, reduce heat input, and avoid the specimen temperature being too high, resulting in the growth of grain size.

[0028] It should be noted that in the present invention, it is defined that the grain size of β grains in the fine β-grained titanium alloy is less than 50 μm.

[0029] In some embodiments of the present invention, in S1, the content of terbium elements in the obtained formed powder is < 10 wt.%, which enables the terbium elements to play a role while avoiding excessive content from affecting other properties of the titanium alloy.

[0030] In some embodiments of the present invention, in S1, compared with directly adding terbium metal powder to the titanium alloy powder, it is preferred to add terbium elements by adding titanium-terbium intermetallic compounds to the titanium alloy powder; the structural formula of the titanium-terbium intermetallic compound is Ti (1-x） -Tbx , where 0 < x < 1 and x is the atomic number of terbium. Since terbium is an active element and is easily oxidized, in order to improve the stability of terbium, terbium and titanium elements are mixed and added to the titanium alloy powder in the form of a binary alloy. While ensuring the stability of terbium, terbium can play a role in the laser solid forming process. The formed powder containing terbium can in-situ generate eutectic phases β-Ti and α-Tb phases during the additive manufacturing process. The α-Tb phase is mainly distributed at the grain boundaries, in the form of spheres or continuous long strips at the grain boundaries, pinning the grain boundaries and restricting the growth of grains.

[0031] In some embodiments of the present invention, in S1, the particle size of the titanium-terbium intermetallic compound or terbium metal powder is 15 μm - 200 μm; this particle size can facilitate the uniform distribution of the titanium-terbium intermetallic compound or terbium metal powder in the titanium alloy powder when subsequently mixed with titanium alloy powder with a particle size of 45 μm - 300 μm, and at the same time can meet the requirements of laser solid forming for the powder particle size.

[0032] Specifically, if a titanium-terbium intermetallic compound is added to the titanium alloy powder, when selecting the corresponding intermetallic compound powder, different ratios of titanium-terbium intermetallic compounds need to be selected according to the set composition. Exemplarily, TiTb can be used, where the atomic ratio of Ti to Tb is 1:1.

[0033] In some embodiments of the present invention, in S1, the powdered titanium-terbium intermetallic compound and titanium alloy powder are mixed by ball milling, or terbium metal powder and titanium alloy powder are mixed by ball milling. During the ball milling process, the ball milling tank is sealed to isolate oxygen and prevent the oxidation of terbium and titanium elements, which may affect the powder quality.

[0034] Furthermore, the parameter range during the ball milling process is set as follows: the rotation speed is 20 Hz - 30 Hz, and the time is 3 h - 6 h; controlling the ball milling process within this parameter range can ensure the uniform mixing of the titanium-terbium intermetallic compound and titanium alloy powder, or ensure the uniform mixing of terbium metal powder and titanium alloy powder.

[0035] Furthermore, after the powder mixing in S1, the formed powder is quickly transferred to a vacuum bag, and the vacuum bag is immediately evacuated to avoid the oxidation of the formed powder.

[0036] In some embodiments of the present invention, in S1, the titanium alloy powder is any one of Ti-5Al-5Mo-5V-3Cr-1Zr-0.1B, Ti-9Mo-0.1B, Ti-7Mo-3Cr-3Nb-3Al-0.1B, Ti-24Nb-4Zr-8Sn-0.1B or Ti-12Zr-5Nb-3Ta-0.1B. It can be seen that the method of the present invention is applicable to multiple types of titanium alloys.

[0037] In some embodiments of the present invention, in S2, before laser solid forming, the inside of the laser solid forming device cavity is filled with argon, and the inflation time is at least 20 minutes, so that the oxygen content in the laser solid forming device cavity is less than 500 ppm. Excessive oxygen content will cause great harm to the final mechanical properties of the material.

[0038] In some embodiments of the present invention, in S2, during the laser solid forming process, the laser power is 380W - 2000W, the laser scanning speed is 10mm / s - 60mm / s, the laser spot diameter is 3mm - 5mm, the powder feeding rate is 12g / min - 20g / min, the lifting amount is 0.2 mm - 1.0mm, and the overlapping rate is 30% - 60%; this laser power is suitable for most titanium alloys and can obtain good metallurgical quality of titanium alloys. It should be understood that for different titanium alloys, these process parameters can be adjusted within the corresponding ranges.

[0039] In some embodiments of the present invention, for titanium alloys with different substrates, although terbium elements are introduced, due to the differences in their physical and chemical properties, it is difficult to prepare the smallest β grains with a set of the same process parameters. To enhance the adaptability of the solution, the following method for determining the process parameters of the laser solid forming process is set.

[0040] Specifically, before S2, for various titanium alloys, the process of determining the process parameters of the laser solid forming process is as follows: The specimens obtained by laser solid forming are observed metallographically. When the grains are equiaxed grains and the porosity ≥ 99.5%, the laser energy density is reduced, and laser solid forming is repeated to obtain specimens. Observe the specimens and judge whether the grains and porosity meet the preset requirements. If not, reduce the laser energy density again until the grains or porosity of the specimens obtained for the nth time meet the preset requirements. Then, the process parameters of the laser solid forming process for the (n - 1)th time are the final process parameters; where n is the number of cycles, which is a natural number, and the preset requirements are specifically: the grains of the specimens are columnar grains or the porosity is less than 99.5%. This process hopes to finally obtain equiaxed grains with a small porosity. Therefore, by using this method, the process parameters of the previous time that meet the preset requirements are used as the final process parameters.

[0041] In a specific example, the determination process is as follows: The specimen is observed by metallographic SEM (Scanning Electron Microscope), and the grain size and porosity are characterized. When the observed grains are equiaxed grains and the porosity is greater than or equal to 99.5%, the laser energy density is reduced by 5% by adjusting the laser power or the laser scanning speed, and laser solid forming is repeated for specimen forming. After cycling n times (n≥2), when SEM observation of the specimen shows that the grains have transformed into columnar grains or the porosity is less than 99.5%, the forming experiment stops. At this time, the process parameters of the (n - 1)th time are the process parameters suitable for the titanium alloy of this composition, and the equiaxed grain structure obtained at the (n - 1)th time is the minimum-size microstructure of the titanium alloy of this composition. This method can adopt a cyclic verification method in the subsequent forming process to further highlight this effect, and finally obtain β grains with the minimum grain size.

[0042] It should be understood that the value of the reduction in the laser energy density can be adjusted. The smaller the value of each reduction, the more accurate the final obtained process parameters, but the number of repeated cycles is too high.

[0043] It should be understood that the laser energy density is the ratio of the laser power to the laser scanning speed. In the actual laser solid forming process, the laser energy density is changed by adjusting the laser power or the laser scanning speed, so that the laser energy density finally falls within the range of 25 (W·s) / mm - 200 (W·s) / mm.

[0044] In some embodiments of the present invention, in S2, since heat accumulation gradually intensifies with the increase of the forming height during the laser solid forming process, an infrared thermometer is installed outside the forming chamber, and the infrared thermometer is used to in-situ record and monitor the temperature of the molten pool during the forming process, and the interlayer residence process is always protected by high-purity argon gas.

[0045] In some embodiments of the present invention, during the cooling process of S3, argon gas is continuously filled for protection until the specimen is cooled to room temperature, and finally a fine β-grain titanium alloy is obtained.

[0046] The present invention also discloses a fine β-grain titanium alloy. The grains finally formed by this titanium alloy are equiaxed grains, and the grain size is 10μm - 50μm.

[0047] The following is further illustrated with specific examples: Example 1 (1) Weigh 4 g of terbium metal powder according to the mass ratio converted from the atomic ratio. The average particle size of the terbium metal powder is 50μm.

[0048] (2) Add the terbium metal powder from step (1) and 996 g of titanium alloy powder Ti-5Al-5Mo-5V-3Cr-1Zr-0.1B to a ball mill and mix at a rotation speed of 30 Hz for 6 hours to obtain a uniformly mixed forming powder. After mixing, quickly transfer the forming powder to a vacuum bag and immediately evacuate the vacuum bag using a vacuum machine.

[0049] (3) Fill the forming chamber with argon gas with a purity of 99%. The inflation time is 20 minutes. After inflation, use an additive manufacturing device to form the uniformly mixed forming powder.

[0050] (4) The specific process parameters are as follows: laser power 420 W, laser scanning speed 10 mm / s, laser spot diameter 4 mm, powder feeding rate 18 g / min, lift amount 0.75 mm, overlap rate 50%; the forming path is single-pass reciprocating. Finally, a block with a length of 60 mm, a height of 45 mm, and a width of 2 mm is obtained. During the forming process, the forming chamber is filled with argon gas with a purity of 99% throughout.

[0051] (5) During the forming process, use an infrared thermometer to observe the molten pool. The temperature of the molten pool in the first five layers is less than 2000 °C, and there is a 2-s pause between each layer. The temperature in the 6th - 10th layers is higher than 2000 °C, and after staying for 4 s, 8 s, 13 s, 19 s, and 27 s respectively, the temperature drops below 800 °C.

[0052] (6) After forming, continue to fill the forming chamber with argon gas with a purity of 99%. Stop inflation after standing for 60 minutes. Take out the block that has cooled to room temperature 30 minutes after stopping inflation.

[0053] (7) According to the microstructure characterization, the grains are equiaxed grains with an average grain size of about 20 μm, and the porosity is 99.6%.

[0054] (8) Adjust the process parameters to: laser power 400 W, laser scanning speed 10 mm / s, and keep other process parameters unchanged. Repeat steps (3) - (6).

[0055] (9) According to the microstructure characterization, the grains are equiaxed grains with an average grain size of about 10 μm, and the porosity is 99.5%.

[0056] (10) Adjust the process parameters to: laser power 380 W, laser scanning speed 10 mm / s, and repeat steps (3) - (6) with other process parameters unchanged.

[0057] (11) According to the tissue characterization, the grains are equiaxed grains with an average grain size of about 10 μm, the porosity is 99.0%, the cyclic forming process stops, and the tissue in step (9) is the optimal tissue for the grain size of this alloy. The final titanium alloy obtained is Ti-5Al-5Mo-5V-3Cr-1Zr-4Tb-0.1B, and its finest equiaxed grain structure is as Figure 1 shown. It can also be found through the above adjustment process that the method of the present invention can finally control the grain size and porosity of the formed aluminum alloy by adjusting the laser power and the laser scanning speed.

[0058] Example 2 (1) Weigh 8 g of titanium terbium intermetallic compound powder TiTb (atomic ratio 1:1), and its average powder particle size is 75 μm.

[0059] (2) Add the titanium terbium intermetallic compound powder obtained in step (1) and 992 g of titanium alloy powder Ti-9Mo-0.1B into a ball mill, and mix them at a rotation speed of 20 Hz for 4 hours to obtain a uniformly mixed forming powder.

[0060] (3) After mixing, quickly transfer the forming powder into a vacuum bag, and immediately use a vacuum machine to evacuate the vacuum bag.

[0061] (4) Fill the forming chamber with argon with a purity of 99%, and the filling time is 20 minutes. After filling, use an additive manufacturing device to form the uniformly mixed forming powder.

[0062] (5) The specific process parameters are: laser power 600 W, laser scanning speed 15 mm / s, laser spot diameter 4 mm, powder feeding rate 18 g / min, lifting amount 0.75 mm, overlapping rate 50%, and the forming path is single-pass reciprocating. Finally, a block with a length of 60 mm, a height of 45 mm, and a width of 2 mm is obtained. During the forming process, the forming chamber is filled with argon with a purity of 99% throughout the process.

[0063] (6) During the forming process, use an infrared thermometer to observe the molten pool. The temperature of the molten pool in the first 8 layers is less than 2000 °C, and there is a 30 s pause between each layer. The temperature of the 9th - 10th layers is higher than 2000 °C, and after staying for 8 s and 27 s respectively, the temperature drops below 800 °C.

[0064] (7) After forming, continue to fill the forming chamber with argon with a purity of 99%. After standing for 60 minutes, stop filling. 30 minutes after stopping filling, take out the block that has cooled to room temperature.

[0065] (8) According to the tissue characterization, at this time, the grains are equiaxed grains with an average grain size of about 20 μm, and the porosity is 99.9%.

[0066] (9) Adjust the process parameters as follows: laser power 570 W, laser scanning speed 15 mm / s, repeat steps (4) - (7) with other process parameters unchanged.

[0067] (10) According to the tissue characterization, the grains are columnar crystals at this time, the cyclic forming process stops, the structure in step (8) is the optimal structure for the grain size of this alloy, and the final process parameters adopt the process parameters of step (5) to obtain the final titanium alloy Ti-9Mo-6Tb-0.1B, and its finest equiaxed crystal structure is as Figure 2 shown.

[0068] Example 3 (1) Weigh 6 g of terbium intermetallic compound powder TiTb (atomic ratio 1:1), and its average powder particle size is 75 μm.

[0069] (2) Add the titanium-terbium intermetallic compound powder obtained in step (1) and 994 g of titanium alloy powder Ti-7Mo-3Cr-3Nb-3Al-0.1B to a ball mill and mix them at a rotation speed of 20 Hz for 4 hours to obtain uniformly mixed forming powder.

[0070] (3) After mixing, quickly transfer the forming powder to a vacuum bag and immediately evacuate the vacuum bag using a vacuum machine.

[0071] (4) Fill the forming chamber with argon with a purity of 99%, and the filling time is 20 minutes. After filling, use an additive manufacturing device to form the uniformly mixed forming powder.

[0072] (5) The specific process parameters are as follows: laser power 2000 W, laser scanning speed 10 mm / s, laser spot diameter 4 mm, powder feeding rate 18 g / min, lift amount 0.75 mm, overlap rate 50%; the forming path is single-pass reciprocating, and finally a block with a length of 60 mm, a height of 60 mm, and a width of 2 mm is obtained. During the forming process, the forming chamber is filled with argon with a purity of 99% throughout.

[0073] (6) During the forming process, use an infrared thermometer to observe the molten pool. The temperature of the molten pool in the first 5 layers is less than 2000 °C, and a 60 s pause is made between each layer. The temperature in the 6th - 10th layers is higher than 2000 °C, and after staying for 8 s, 27 s, 56 s, 72 s, and 108 s respectively, the temperature drops below 800 °C.

[0074] (7) After forming, continue to fill the forming chamber with argon with a purity of 99%, stop filling after standing for 60 minutes, and take out the block that has cooled to room temperature 30 minutes after stopping filling.

[0075] (8) For tissue characterization, the grains are equiaxed crystals with an average grain size of about 56 μm, and the porosity is 99.8%.

[0076] (9) Adjust the process parameters as follows: laser power 1800 W, laser scanning speed 10 mm / s, repeat steps (4)-(7) with other process parameters unchanged.

[0077] (10) According to the microstructure characterization, the grains are equiaxed grains with an average grain size of about 21 μm, and the porosity is 99.6%.

[0078] (11) Adjust the process parameters as follows: laser power 1600 W, laser scanning speed 10 mm / s, repeat steps (4)-(7) with other process parameters unchanged.

[0079] (12) According to the microstructure characterization, the porosity is 99.2% at this time, and the cyclic forming process stops. The microstructure in step (10) is the optimal microstructure of the grain size of this alloy. The final process parameters adopt the process parameters of step (9) to obtain the final titanium alloy Ti-7Mo-3Cr-3Nb-3Al-4.5Tb-0.1B, and its finest equiaxed grain microstructure is as Figure 3 shown.

[0080] Example 4 (1) Weigh 8 g of titanium-terbium intermetallic compound powder TiTb (atomic ratio 1:1), and its average powder particle size is 75 μm.

[0081] (2) Add the titanium-terbium intermetallic compound powder obtained in step (1) and 992 g of titanium alloy powder Ti-24Nb-4Zr-8Sn-0.1B into a ball mill and mix for 4 hours at a rotation speed of 20 Hz to obtain a uniformly mixed forming powder.

[0082] (3) After mixing, quickly transfer the forming powder into a vacuum bag, and immediately use a vacuum machine to evacuate the vacuum bag.

[0083] (4) Fill the forming chamber with argon with a purity of 99% for 20 minutes. After filling, use an additive manufacturing device to form the uniformly mixed forming powder.

[0084] (5) The specific process parameters are as follows: laser power 1000 W, laser scanning speed 10 mm / s, laser spot diameter 4 mm, powder feeding rate 18 g / min, lift amount 0.75 mm, overlap rate 50%; the forming path is single-pass reciprocating. Finally, a block with a length of 60 mm, a height of 30 mm, and a width of 2 mm is obtained. During the forming process, the forming chamber is filled with argon with a purity of 99% throughout the process.

[0085] During the forming process, an infrared thermometer was used to observe the molten pool. The temperature of the molten pool in the first 11 layers was less than 2000 °C, and a 10-s pause was made between each layer. The temperature of the 12th - 14th layers was higher than 2000 °C, and after pauses of 5 s, 17 s, and 36 s respectively, the temperature dropped below 800 °C.

[0086] (7)After the forming was completed, argon with a purity of 99% was continuously filled into the forming chamber. The inflation was ended after 60 minutes of standing, and the block that had cooled to room temperature was taken out 30 minutes after the inflation ended.

[0087] (8)According to the microstructure characterization, the grains were equiaxed grains with an average grain size of about 28 μm, and the porosity was 99.7%.

[0088] (9)The process parameters were adjusted to: laser power 950 W, laser scanning speed 10 mm / s. Steps (4) - (7) were repeated with other process parameters unchanged.

[0089] (10)According to the microstructure characterization, the grains were columnar grains at this time, and the cyclic forming process stopped. The microstructure in step (8) was the optimal microstructure of the grain size of this alloy. The final process parameters adopted the process parameters in step (5), and the final titanium alloy obtained was Ti - 24Nb - 4Zr - 8Sn - 6Tb - 0.1B, and its finest equiaxed grain microstructure was as Figure 4 shown.

[0090] Example 5 (1)8 g of titanium terbium intermetallic compound powder TiTb (atomic ratio 1:1) with an average powder particle size of 75 μm was weighed.

[0091] (2)The titanium terbium intermetallic compound powder obtained in step (1) and 992 g of titanium alloy powder Ti - 12Zr - 5Nb - 3Ta - 0.1B were added to a ball mill and mixed at a rotation speed of 20 Hz for 4 hours to obtain a uniformly mixed forming powder.

[0092] (3)After mixing, the forming powder was quickly transferred to a vacuum bag, and the vacuum bag was immediately evacuated using a vacuum machine.

[0093] (4)Argon with a purity of 99% was filled into the forming chamber for 20 minutes. After the inflation was completed, an additive manufacturing device was used to form the uniformly mixed forming powder.

[0094] (5)The specific process parameters were: laser power 500 W, laser scanning speed 15 mm / s, laser spot diameter 4 mm, powder feeding rate 18 g / min, lifting amount 0.75 mm, overlapping rate 50%; the forming path was single - pass reciprocating. Finally, a block with a length of 60 mm, a height of 45 mm, and a width of 2 mm was obtained. During the forming process, argon with a purity of 99% was continuously filled into the forming chamber.

[0095] (6) During the forming process, an infrared thermometer was used to observe the molten pool. The temperature of the molten pool in the first 16 layers was less than 2000 °C, and a 5-second pause was made between each layer. The temperature of the 17th - 18th layers was higher than 2000 °C, and after pausing for 4 seconds and 11 seconds respectively, the temperature dropped below 800 °C.

[0096] (7) After the forming was completed, argon with a purity of 99% was continuously filled into the forming chamber. The inflation ended after standing for 60 minutes. The block that had cooled to room temperature was taken out 30 minutes after the inflation ended.

[0097] (8) According to the microstructure characterization, the grains were equiaxed grains with an average grain size of about 26 μm, and the porosity was 99.9%.

[0098] (9) The process parameters were adjusted as follows: laser power 480 W, laser scanning speed 15 mm / s. Steps (4) - (7) were repeated.

[0099] (10) According to the microstructure characterization, the grains were equiaxed grains with an average grain size of about 17 μm, and the porosity was 99.7%.

[0100] (11) The process parameters were adjusted as follows: laser power 460 W, laser scanning speed 15 mm / s. Steps (4) - (7) were repeated with other process parameters remaining unchanged.

[0101] (12) According to the microstructure characterization, the grains were equiaxed grains with an average grain size of about 15 μm, and the porosity was 99.5%.

[0102] (13) The process parameters were adjusted as follows: laser power 440 W, laser scanning speed 15 mm / s. Steps (4) - (7) were repeated.

[0103] (14) According to the microstructure characterization, the porosity was 99.3% at this time, and the cyclic forming process stopped. The microstructure in step (12) was the optimal microstructure for the grain size of this alloy. The final process parameters were those in step (11), and the final titanium alloy obtained was Ti - 12Zr - 5Nb - 3Ta - 6Tb - 0.1B, and its finest equiaxed grain microstructure was as Figure 5 shown.

[0104] Example 6 (1) Weigh 6 g of titanium - terbium intermetallic compound powder TiTb (atomic ratio 1:1), and its average powder particle size is 15 μm.

[0105] (2) The titanium - terbium intermetallic compound powder obtained in step (1) and 994 g of titanium alloy powder Ti - 24Nb - 4Zr - 8Sn - 0.1B were added to a ball mill and mixed at a rotation speed of 25 Hz for 5 hours to obtain a uniformly mixed forming powder.

[0106] (3) After mixing, quickly transfer the formed powder into a vacuum bag, and immediately evacuate the vacuum bag using a vacuum machine.

[0107] (4) Fill the forming chamber with argon gas with a purity of 99%. The inflation time is 20 minutes. After inflation, use an additive manufacturing device to form the uniformly mixed formed powder.

[0108] (5) The specific process parameters are: laser power 2000W, laser scanning speed 60mm / s, laser spot diameter 3mm, powder feeding rate 12g / min, lifting amount 0.2mm, overlapping rate 30%; the forming path is single-pass reciprocating. Finally, a block with a length of 50mm, a height of 20mm, and a width of 2mm is obtained. During the forming process, the forming chamber is filled with argon gas with a purity of 99% throughout.

[0109] (6) During the forming process, use an infrared thermometer to observe the molten pool. The temperature of the molten pool in the first 11 layers is less than 2000°C, and a 30s pause is made between each layer. The temperature of the 12th - 14th layers is higher than 2000°C, and after staying for 5s, 17s, and 36s respectively, the temperature drops below 800°C.

[0110] (7) After forming, continue to fill the forming chamber with argon gas with a purity of 99%. After standing for 60 minutes, stop the inflation. After 30 minutes of stopping the inflation, take out the block that has cooled to room temperature.

[0111] (8) According to the microstructure characterization, the grains are equiaxed grains with an average grain size of about 25μm, and the porosity is 99.7%.

[0112] (9) Adjust the process parameters to: laser power 1500W, laser scanning speed 60mm / s, and repeat steps (4) - (7) with other process parameters unchanged.

[0113] (10) According to the microstructure characterization, the grains are columnar grains at this time, and the cyclic forming process stops. The microstructure in step (8) is the optimal microstructure of the grain size of this alloy. The final process parameters adopt the process parameters of step (5) to obtain the final titanium alloy Ti-24Nb-4Zr-8Sn-4.5Tb-0.1B, and its finest equiaxed grain microstructure is as Figure 6 shown.

[0114] Example 7 (1) Weigh 5g of titanium terbium intermetallic compound powder TiTb (atomic ratio 1:1), and its average powder particle size is 200μm.

[0115] (2) Add the titanium-terbium intermetallic compound powder obtained in step (1) and 995 g of titanium alloy powder Ti-9Mo-0.1B to a ball mill and mix them at a rotation speed of 30 Hz for 6 hours to obtain uniformly mixed forming powder.

[0116] (3) After mixing, quickly transfer the forming powder to a vacuum bag and immediately evacuate the vacuum bag using a vacuum machine.

[0117] (4) Fill the forming chamber with argon with a purity of 99%. After 20 minutes of inflation, use an additive manufacturing device to form the uniformly mixed forming powder.

[0118] (5) The specific process parameters are as follows: laser power 1500 W, laser scanning speed 20 mm / s, laser spot diameter 5 mm, powder feeding rate 20 g / min, lifting amount 1 mm, overlapping rate 60%, and the forming path is single-pass reciprocating. Finally, a block with a length of 70 mm, a height of 30 mm, and a width of 2 mm is obtained. During the forming process, the forming chamber is filled with argon with a purity of 99% throughout.

[0119] (6) During the forming process, use an infrared thermometer to observe the molten pool. The temperature of the molten pool in the first 11 layers is less than 2000 °C, and it stops for 40 s between each layer. The temperature of the 12th - 14th layers is higher than 2000 °C, and after staying for 5 s, 17 s, and 36 s respectively, the temperature drops below 800 °C.

[0120] (7) After forming, continue to fill the forming chamber with argon with a purity of 99%. After standing for 60 minutes, stop the inflation. After 30 minutes of stopping the inflation, take out the block that has cooled to room temperature.

[0121] (8) According to the microstructure characterization, the grains are equiaxed grains with an average grain size of about 28 μm, and the porosity is 99.7%.

[0122] (9) Adjust the process parameters to: laser power 1200 W, laser scanning speed 20 mm / s, and repeat steps (4) - (7) with other process parameters unchanged.

[0123] (10) According to the microstructure characterization, the grains are columnar grains at this time, and the cyclic forming process stops. The microstructure in step (8) is the optimal microstructure of the grain size of this alloy. Finally, the process parameters in step (5) are adopted to prepare Ti-9Mo-3.8Tb-0.1B, and its finest equiaxed grain microstructure is as Figure 7 shown.

Claims

1. A laser solid forming method for a fine β-phase titanium alloy, characterized in that, It includes the following steps: S1. Add terbium metal powder or titanium-terbium intermetallic compound to titanium alloy powder to obtain formed powder; S2. Prepare fine β-grained titanium alloy by laser solid forming with the formed powder. After forming one layer, if the molten pool temperature is less than 2000 °C, stay for 2 s - 60 s for the next layer of laser solid forming; if the molten pool temperature is greater than or equal to 2000 °C, stay until the molten pool temperature is less than 800 °C for the next layer of laser solid forming. After preparing the set number of layers, obtain a specimen. During the laser solid forming process, the laser energy density is 25 (W·s) / mm - 200 (W·s) / mm, and the environmental oxygen content ≤ 500 ppm; S3. After forming, cool naturally to room temperature to obtain fine β-grained titanium alloy. At the grain boundaries of the fine β-grained titanium alloy, α-Tb phase is pinned.

2. The laser solid forming method of a fine β crystal titanium alloy according to claim 1, characterized in that In S1, the content of terbium element in the formed powder < 10 wt.%.

3. The laser solid forming method of a fine β crystal titanium alloy according to claim 1, characterized in that, In S1, the particle size of the terbium metal powder or titanium-terbium intermetallic compound is 15 μm - 200 μm.

4. The laser solid forming method of a fine β crystal titanium alloy according to claim 1, characterized in that, In S1, a titanium-terbium intermetallic compound is added to titanium alloy powder to obtain formed powder; the structural formula of the titanium-terbium intermetallic compound is Ti (1-x） -Tb x , where 0 < x < 1 and x is the number of atoms of terbium element.

5. The laser solid forming method of a fine β crystal titanium alloy according to claim 1, characterized in that In S1, mix the titanium-terbium intermetallic compound with titanium alloy powder by ball milling, or mix the terbium metal powder with titanium alloy powder by ball milling. Seal the ball milling tank during the ball milling process.

6. The laser solid forming method of a fine β crystal titanium alloy according to claim 5, characterized in that, During the ball milling process, the rotation speed is 20 Hz - 30 Hz, and the time is 3 h - 6 h.

7. A laser solid forming method for a fine β-phase titanium alloy according to claim 1, characterized in that, In S2, during the laser solid forming process, the laser power is 380 W - 2000 W, the laser scanning speed is 10 mm / s - 60 mm / s, the laser spot diameter is 3 mm - 5 mm, the powder feeding rate is 12 g / min - 20 g / min, the lifting amount is 0.2 mm - 1.0 mm, and the overlapping rate is 30% - 60%.

8. The laser solid forming method of a fine β crystal titanium alloy according to claim 7, characterized in that, Before S2, the process parameter determination process of the laser solid forming process is: conduct metallographic observation on the specimen obtained by laser solid forming. When the grains are equiaxed crystals and the porosity ≥ 99.5%, reduce the laser energy density, repeat the laser solid forming to obtain a specimen, observe the specimen and judge whether the grains and porosity meet the preset requirements. If not, reduce the laser energy density again until the grains or porosity of the specimen obtained for the nth time meet the preset requirements. Then the process parameters of the laser solid forming process for the (n - 1)th time are the final process parameters; where n is the number of cycles, which is a natural number, and the preset requirements are specifically: the grains of the specimen are columnar crystals or the porosity is less than 99.5%.

9. The laser solid forming method of a fine β crystal titanium alloy according to claim 1, characterized in that, In S2, monitor the molten pool temperature with an infrared thermometer.

10. A fine β-grained titanium alloy prepared by the laser solid forming method according to any one of claims 1-9, characterized in that, The grain size of the fine β-grained titanium alloy is 10 μm - 50 μm. At the grain boundaries of the fine β-grained titanium alloy, α-Tb phase is pinned.

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