A fine β-crystalline titanium alloy and laser stereo forming method

Abstract

The present invention discloses a fine β-crystalline titanium alloy and a laser stereo forming method, which belong to the field of additive manufacturing technology; the forming method adds terbium (Tb) element to the titanium alloy powder. As an extremely strong segregation element in titanium alloys, terbium element can segregate at the grain boundaries to form α-Tb phase at the end of solidification, play a pinning role, and limit the rapid growth of grains. In addition, during the laser stereo forming process, the laser energy density is reduced to reduce heat input, and the cooling rate during the forming process is increased to avoid grain coarsening caused by thermal effects during the forming process. This method limits grain coarsening under the combined effect of reducing the heat input of laser stereo forming and increasing the segregated α-Tb phase at the grain boundaries, and ultimately achieves grain refinement.

Description

Technical Field

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

[0002] Additive manufacturing technology has garnered widespread attention and rapid development in recent years. This technology integrates forming and performance control capabilities, enabling efficient manufacturing of complex metal components and becoming a key manufacturing method for high-performance, complex metal components. In the biomedical field, additive manufacturing is particularly well-suited for customized human skeletons, such as ribs, leg bones, and teeth.

[0003] Compared to other metal materials, titanium alloys offer excellent formability and biocompatibility. However, existing research indicates that the mechanical properties, particularly fatigue resistance, of additively manufactured titanium alloy human bones differ significantly from those of natural human bones, making them difficult to meet current biomedical requirements for additively manufactured titanium alloys. This limitation significantly limits the further promotion and application of additively manufactured titanium alloys.

[0004] Analysis has found that the fatigue performance of titanium alloys is primarily affected by the grain size of β crystals. The β crystals of additively manufactured titanium alloys are often particularly coarse, ranging in size from several hundred microns to several millimeters, but current methods are difficult to effectively control. Coarse β crystals reduce the material's ability to deform in a coordinated manner, making it more susceptible to cracking. Furthermore, the grain boundary α phase (continuous, straight lines) initiated by these coarse grains significantly increases the crack propagation rate, resulting in insufficient fatigue performance. Therefore, grain refinement is crucial for improving the fatigue performance of titanium alloys.

[0005] Chinese invention application publication number CN 1013114826 A discloses a titanium-nickel-aluminum rare earth superalloy and its preparation method. The technical solution involves adding a series of rare earth elements (including terbium) to the titanium-nickel-aluminum rare earth superalloy to refine the grains and thereby improve the fatigue performance of the superalloy. The reason for adding rare earth elements to the superalloy is that rare earth elements have a high affinity for oxygen, which can reduce the oxygen content in the superalloy and form rare earth oxides. Rare earth oxides increase nucleation sites during solidification, thereby promoting grain refinement and are a traditional method for grain refinement. Unlike superalloys, titanium alloys have extremely low grain growth activation energies due to processing characteristics and the basic physical properties of titanium alloys. This makes it difficult to quickly and efficiently produce fine β-crystals using currently widely used methods. Therefore, achieving β-crystal refinement during additive manufacturing of titanium alloys has become an important research direction and a key technical bottleneck in the current additive manufacturing of titanium alloys. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a fine β-crystal titanium alloy and a laser stereo forming method, aiming to achieve effective refinement of β-crystals in additively manufactured titanium alloys and avoid performance problems caused by coarse grains.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A laser stereo forming method for fine β-grain titanium alloy comprises the following steps:

[0009] S1, adding terbium metal powder or titanium-terbium intermetallic compound to titanium alloy powder to obtain a formed powder;

[0010] S2, preparing fine β-grained titanium alloy by laser stereo forming the forming powder. After forming one layer, if the molten pool temperature is less than 2000°C, stay for 2s-60s to proceed with laser stereo 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 before proceeding with laser stereo forming of the next layer. After the set number of layers are prepared, a sample is obtained; during the laser stereo forming process, the laser energy density is 25 (W·s) / mm-200 (W·s) / mm, and the ambient oxygen content is ≤500ppm;

[0011] S3, after forming is completed, naturally cooling to room temperature to obtain a fine β-crystalline titanium alloy, wherein the grain boundaries of the fine β-crystalline titanium alloy are pinned with α-Tb phase.

[0012] A further improvement of the present invention is:

[0013] Preferably, in S1, the content of terbium in the forming powder is less than 10 wt.%.

[0014] Preferably, in S1, the particle size of the terbium metal powder or titanium-terbium intermetallic compound is 15 μm-200 μm.

[0015] Preferably, in S1, titanium-terbium intermetallic compound is added to titanium alloy powder to obtain a formed powder; the structural formula of the titanium-terbium intermetallic compound is Ti (1-x） -Tb x , where 0<x<1, x is the atomic number of terbium element.

[0016] Preferably, in S1, the titanium-terbium intermetallic compound and the titanium alloy powder are mixed by ball milling, or the terbium metal powder and the titanium alloy powder are mixed by ball milling, and the ball milling jar is sealed during the ball milling process.

[0017] Preferably, during the ball milling process, the rotation speed is 20 Hz-30 Hz and the time is 3 h-6 h.

[0018] Preferably, in S2, during the laser stereo 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 overlap rate is 30%-60%.

[0019] Preferably, before S2, the process of determining the process parameters of the laser stereo forming process is: metallographically observing the sample obtained by laser stereo forming, when the grains are equiaxed crystals and the porosity is ≥99.5%, reducing the laser energy density, repeating the laser stereo forming to obtain the sample, observing the sample and judging whether the grains and porosity meet the preset requirements, if not, reducing the laser energy density again until the grains or porosity of the sample obtained for the nth time meet the preset requirements, then the process parameters of the n-1th laser stereo forming process are the final process parameters; wherein n is the number of cycles, which is a natural number, and the preset requirements are specifically: the grains of the sample are columnar crystals or the porosity is less than 99.5%.

[0020] Preferably, in S2, the molten pool temperature is monitored by an infrared thermometer.

[0021] A fine β-crystalline titanium alloy produced by any one of the above-mentioned laser stereo forming methods, wherein the grain size of the fine β-crystalline titanium alloy is 10 μm-50 μm, and α-Tb phase is pinned at the grain boundaries of the fine β-crystalline titanium alloy.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention discloses a laser stereo forming method for fine β-grain titanium alloy. During the laser stereo forming process, since the molten pool dissipates heat to the formed sample during the forming process, the deposited layer is easily subjected to strong thermal influence, resulting in a titanium alloy with coarse grains. The method of the present invention mainly refines grains through two means. First, terbium (Tb) element is added to the titanium alloy powder. As an extremely strong segregation element in titanium alloy, terbium element can segregate to form α-Tb phase at the grain boundary at the end of solidification of each layer, limit the rapid coarsening of the grains, and play a pinning role. Since terbium element is very active, the oxygen content is strictly controlled during the entire laser stereo forming process to avoid reducing the generation of α-Tb phase at the grain boundary due to the generation of terbium oxide, thereby reducing the pinning effect; second, extremely low laser energy density is used. Lowering the laser energy density can reduce heat input, limit grain growth under thermal action, significantly reduce in-situ thermal effects, and avoid coarsening and growth of β crystals. Therefore, during the laser stereo forming process, the molten pool temperature is observed in situ. Once the temperature is found to be too high, exceeding 2000°C, the corresponding interlayer residence time is increased to reduce the temperature of the sample. Furthermore, by limiting the laser energy density, the heat accumulation of the sample is reduced, thereby increasing the cooling rate during the forming process, causing more α-Tb phase to segregate at the grain boundaries, further pinning the grain boundaries, restricting grain growth, and achieving grain refinement.

[0024] The second aspect of the present invention discloses a fine β-grained titanium alloy prepared by the above method. The grain size of the 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

[0025] Figure 1 The microstructure of the Ti-5Al-5Mo-5V-3Cr-1Zr-4Tb-0.1B alloy prepared in Example 1;

[0026] Figure 2 The microstructure of the Ti-9Mo-6Tb-0.1B alloy prepared in Example 2;

[0027] Figure 3 The microstructure of the Ti-7Mo-3Cr-3Nb-3Al-4.5Tb-0.1B alloy prepared in Example 3;

[0028] Figure 4 The microstructure of the Ti-24Nb-4Zr-8Sn-6Tb-0.1B alloy prepared in Example 4;

[0029] Figure 5 The microstructure of the Ti-12Zr-5Nb-3Ta-6Tb-0.1B alloy prepared in Example 5;

[0030] Figure 6The microstructure of the Ti-24Nb-4Zr-8Sn-4.5Tb-0.1B alloy prepared in Example 6;

[0031] Figure 7 This is the microstructure of the Ti-9Mo-3.8Tb-0.1B alloy prepared in Example 7. DETAILED DESCRIPTION

[0032] The present invention is described in further detail below with reference to the accompanying drawings:

[0033] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0034] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0035] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, 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 fall equally within the scope limited by the appended claims of the application.

[0036] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0037] The metal elements involved in the present invention and their corresponding abbreviations are shown in Table 1 below.

[0038] Table 1 Comparison table of Chinese characters and abbreviations of elements

[0039]

[0040] The first aspect of the present invention discloses a laser stereo forming method for fine β-grained titanium alloy, comprising the following steps:

[0041] S1, adding terbium metal powder or titanium-terbium intermetallic compound to titanium alloy powder to obtain a formed powder;

[0042] S2, preparing fine β-grained titanium alloy by laser stereo forming the forming powder. After forming one layer, if the molten pool temperature is less than 2000°C, stay for 2s-60s to proceed with laser stereo 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 before proceeding with laser stereo forming of the next layer. After the set number of layers are prepared, a sample is obtained; during the laser stereo forming process, the laser energy density is 25 (W·s) / mm-200 (W·s) / mm, and the ambient oxygen content is ≤500ppm;

[0043] S3, after forming is completed, naturally cooling to room temperature to obtain a fine β-crystalline titanium alloy, wherein the grain boundaries of the fine β-crystalline titanium alloy are pinned with α-Tb phase.

[0044] The present invention achieves grain refinement by introducing terbium into titanium alloys and matching laser stereo forming process parameters. Terbium is added during the laser stereo forming process of titanium alloys, and the characteristic of terbium being able to strongly segregate in titanium alloys is utilized. Combined with controlling the laser stereo forming process parameters, more segregated α-Tb phases are generated at the grain boundaries of the titanium alloy, and the growth of β grains is limited during the in-situ thermal cycle process at the end of solidification and after solidification, thereby achieving overall grain refinement and obtaining fine β-grain titanium alloys. In terms of controlling the laser stereo forming process, low laser energy density, high cooling rate, and low molten pool temperature are included; 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, which is above 600 (W·s) / mm. Low laser energy density has two benefits: first, it reduces heat accumulation in the formed specimen, thereby increasing the temperature gradient during rapid solidification, achieving extremely rapid cooling and promoting grain refinement; second, it reduces heat accumulation, minimizing in-situ grain coarsening caused by thermal influences. Regarding specific process control, the present invention pauses after each layer of laser stereo forming to avoid excessive heat accumulation, reduce heat input, and prevent excessive specimen temperatures from causing grain growth.

[0045] It should be noted that the grain size of the β crystals in the fine β crystal titanium alloy defined in the present invention is less than 50 μm.

[0046] In some embodiments of the present invention, in S1, the terbium content in the formed powder obtained is less than 10 wt.%, which allows the terbium element to play its role while preventing excessive terbium content from affecting other properties of the titanium alloy.

[0047] In some embodiments of the present invention, in S1, rather than directly adding terbium metal powder to the titanium alloy powder, it is preferred to add terbium element by adding a titanium-terbium intermetallic compound to the titanium alloy powder; the structural formula of the titanium-terbium intermetallic compound is Ti (1-x） -Tb x , where 0<x<1, x is the number of terbium atoms. Since terbium is an active element and easily oxidized, in order to improve the stability of terbium, terbium is mixed with titanium 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 stereo forming process. The forming powder added with terbium can generate eutectic phases β-Ti and α-Tb in situ during the additive manufacturing process. The α-Tb phase is mainly distributed at the grain boundaries, in the form of spheres or continuous strips at the grain boundaries, pinning the grain boundaries and limiting the growth of grains.

[0048] 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 titanium-terbium intermetallic compound or terbium metal powder to be evenly distributed in the titanium alloy powder when it is subsequently mixed with a titanium alloy powder with a particle size of 45 μm-300 μm, and at the same time can meet the requirements of laser stereo forming for powder particle size.

[0049] Specifically, if titanium-terbium intermetallic compound is added to titanium alloy powder, when selecting the corresponding intermetallic compound powder, titanium-terbium intermetallic compound with different ratios needs to be selected according to the set composition. For example, TiTb can be used, wherein the atomic ratio of Ti to Tb is 1:1.

[0050] In some embodiments of the present invention, in S1, 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 jar is sealed to isolate oxygen and prevent terbium and titanium elements from being oxidized by oxygen, which affects the quality of the powder.

[0051] Furthermore, the parameter ranges during the ball milling process are 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 that the titanium-terbium intermetallic compound and the titanium alloy powder are evenly mixed, or that the terbium metal powder and the titanium alloy powder are evenly mixed.

[0052] Furthermore, after the powders of S1 are mixed, the forming powders are quickly transferred into a vacuum bag, and the vacuum bag is immediately evacuated to avoid oxidation of the forming powders.

[0053] 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.

[0054] In some embodiments of the present invention, in S2, before laser stereo forming, the interior of the cavity of the laser stereo forming device is filled with argon, and the inflation time is at least 20 minutes, so that the oxygen content in the cavity of the laser stereo forming device is less than 500 ppm. Excessive oxygen content will have a great harm to the final mechanical properties of the material.

[0055] In some embodiments of the present invention, in S2, during the laser stereo 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 overlap rate is 30%-60%; this laser power is suitable for most titanium alloys and can obtain good titanium alloy metallurgical quality. It should be understood that for different titanium alloys, the process parameters can be adjusted within the corresponding range.

[0056] In some embodiments of the present invention, although terbium is introduced into titanium alloys with different matrices, due to the differences in their physical and chemical properties, it is difficult to use the same set of process parameters to prepare the finest β crystals. In order to enhance the adaptability of the scheme, the following method for determining the process parameters of the laser stereo forming process is set.

[0057] Specifically, before S2, for various titanium alloys, the process parameters for the laser stereo forming process are determined as follows: metallographic observation of the sample obtained by laser stereo forming is performed. When the grains are equiaxed and the porosity is ≥99.5%, the laser energy density is reduced, and the laser stereo forming process is repeated to obtain a sample. The sample is observed and the grains and porosity are determined to meet the preset requirements. If not, the laser energy density is reduced again until the grains or porosity of the sample obtained for the nth time meet the preset requirements. The process parameters of the laser stereo forming process for the n-1th time are the final process parameters; where n is the number of cycles, which is a natural number. The preset requirements are specifically: the grains of the sample are columnar or the porosity is less than 99.5%. This process hopes to ultimately obtain equiaxed grains with a small porosity. Therefore, this method is used to set the process parameters before the preset requirements are met as the final process parameters.

[0058] In a specific example, the determination process is as follows: the sample is subjected to metallographic SEM (Scanning Electron Microscope) observation to characterize the grain size and porosity. When the observed grains are equiaxed and the porosity is greater than or equal to 99.5%, the laser power or laser scanning speed is adjusted to reduce the laser energy density by 5%, and the laser stereo forming is repeated to form the sample. After n cycles (n ≥ 2), when SEM observation of the sample shows that the grains have transformed into columnar crystals or the porosity is less than 99.5%, the forming experiment is stopped. At this point, the process parameters of the n-1th time are suitable for the titanium alloy of this composition, and the equiaxed crystal structure obtained in the n-1th time is the minimum size microstructure of the titanium alloy of this composition. This method can be used in the subsequent forming process. The cyclic verification method can further highlight this effect and ultimately obtain β crystals with the smallest grain size.

[0059] It should be understood that the value of the laser energy density reduction can be adjusted. The smaller the value of each reduction, the more accurate the final process parameters will be. However, the number of repeated cycles will be too high.

[0060] 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 stereo forming process, the laser energy density is changed by adjusting the laser power or the laser scanning speed so that the laser energy density is finally within the above-mentioned range of 25 (W·s) / mm-200 (W·s) / mm.

[0061] In some embodiments of the present invention, in S2, since heat accumulation in the laser stereo forming process will gradually intensify with the increase of forming height, an infrared thermometer is set up outside the forming chamber, and the infrared thermometer is used to record and monitor the molten pool temperature in situ during the forming process, and the interlayer dwelling process is always protected by high-purity argon gas.

[0062] In some embodiments of the present invention, during the cooling process of S3, argon gas protection is continued until the sample is cooled to room temperature, and finally a fine β-grained titanium alloy is obtained.

[0063] The invention also discloses a fine beta-grain titanium alloy. The final grains formed in the titanium alloy are equiaxed grains, and the grain size is 10 μm-50 μm.

[0064] The following is further described in conjunction with specific embodiments:

[0065] Example 1

[0066] (1) Weigh 4 g of terbium metal powder according to the mass ratio converted from the atomic ratio, where the average particle size of the terbium metal powder is 50 μm.

[0067] (2) The terbium metal powder prepared in step (1) and 996 g of titanium alloy powder Ti-5Al-5Mo-5V-3Cr-1Zr-0.1B were added to a ball mill and mixed at 30 Hz for 6 hours to obtain a uniformly mixed shaped powder. After mixing, the shaped powder was quickly transferred to a vacuum bag, and the vacuum bag was immediately evacuated using a vacuum machine.

[0068] (3) The forming chamber is filled with 99% pure argon for 20 minutes. After the filling is completed, the evenly mixed forming powder is formed using additive manufacturing equipment.

[0069] (4) The specific process parameters are: laser power 420W, laser scanning speed 10mm / s, laser spot diameter 4mm, powder feeding rate 18g / min, lift 0.75mm, overlap rate 50%; the forming path is a single-pass reciprocating type, and the final block is 60mm in length, 45mm in height, and 2mm in width. The forming chamber is filled with 99% pure argon throughout the forming process.

[0070] (5) During the forming process, an infrared thermometer was used to observe the molten pool. The temperatures of the first five layers of the molten pool were all less than 2000°C, and each layer stayed for 2 seconds. The temperatures of the 6th to 10th layers were higher than 2000°C, and stayed for 4 seconds, 8 seconds, 13 seconds, 19 seconds, and 27 seconds, respectively, before the temperatures dropped below 800°C.

[0071] (6) After the forming is completed, continue to fill the forming chamber with 99% pure argon gas, let it stand for 60 minutes before stopping the filling, and take out the block that has cooled to room temperature 30 minutes after the filling is completed.

[0072] (7) According to the microstructure characterization, the grains are equiaxed with an average grain size of about 20 μm and a porosity of 99.6%.

[0073] (8) Adjust the process parameters to: laser power 400W, laser scanning speed 10mm / s, keep other process parameters unchanged, and repeat steps (3) to (6).

[0074] (9) According to the microstructure characterization, the grains are equiaxed with an average grain size of about 10 μm and a porosity of 99.5%.

[0075] (10) Adjust the process parameters to: laser power 380W, laser scanning speed 10mm / s, repeat steps (3) to (6), and keep other process parameters unchanged.

[0076] (11) According to the microstructure characterization, the grains are equiaxed with an average grain size of about 10 μm and a porosity of 99.0%. The cyclic forming process is stopped and the microstructure of step (9) is the optimal microstructure of the alloy grain size. The final titanium alloy is Ti-5Al-5Mo-5V-3Cr-1Zr-4Tb-0.1B, and its finest equiaxed microstructure is as follows: Figure 1 Through the above adjustment process, it can also be found that the method of the present invention can ultimately regulate the grain size and porosity of the formed aluminum alloy by adjusting the laser power and laser scanning speed.

[0077] Example 2

[0078] (1) Weigh 8 g of titanium-terbium intermetallic compound powder TiTb (atomic ratio of 1:1), the average particle size of which is 75 μm.

[0079] (2) The titanium-terbium intermetallic compound powder obtained in step (1) and 992 g of titanium alloy powder Ti-9Mo-0.1B were added to a ball mill and mixed at a speed of 20 Hz for 4 hours to obtain a uniformly mixed shaped powder.

[0080] (3) After mixing, quickly transfer the formed powder into a vacuum bag and immediately evacuate the vacuum bag using a vacuum machine.

[0081] (4) The forming chamber is filled with 99% pure argon for 20 minutes. After the filling is completed, the evenly mixed forming powder is formed using additive manufacturing equipment.

[0082] (5) The specific process parameters are: laser power 600W, laser scanning speed 15mm / s, laser spot diameter 4mm, powder feeding rate 18g / min, lifting amount 0.75mm, overlap rate 50%, forming path is single-pass reciprocating, and the final block is 60mm in length, 45mm in height, and 2mm in width. During the forming process, the forming chamber is filled with 99% pure argon.

[0083] (6) During the forming process, an infrared thermometer was used to observe the molten pool. The temperatures of the first eight layers of the molten pool were all less than 2000°C, and each layer stayed for 30 seconds. The temperatures of the 9th and 10th layers were higher than 2000°C, and they stayed for 8 seconds and 27 seconds respectively before the temperatures dropped below 800°C.

[0084] (7) After the forming is completed, continue to fill the forming chamber with 99% pure argon gas, let it stand for 60 minutes and then stop the filling. 30 minutes after the filling is completed, take out the block that has cooled to room temperature.

[0085] (8) According to the microstructure characterization, the grains at this time are equiaxed grains with an average grain size of about 20 μm and a porosity of 99.9%.

[0086] (9) Adjust the process parameters to: laser power 570W, laser scanning speed 15mm / s, repeat steps (4) to (7), and keep other process parameters unchanged.

[0087] (10) According to the microstructure characterization, the grains are columnar at this time, and the cyclic forming process stops. The microstructure of step (8) is the optimal microstructure of the alloy grain size. The final process parameters adopt the process parameters of step (5), and the final titanium alloy is Ti-9Mo-6Tb-0.1B. Its finest equiaxed microstructure is as follows Figure 2 shown.

[0088] Example 3

[0089] (1) Weigh 6 g of terbium intermetallic compound powder TiTb (atomic ratio of 1:1), the average particle size of the powder is 75 μm.

[0090] (2) The titanium-terbium intermetallic compound powder obtained in step (1) and 994 g of titanium alloy powder Ti-7Mo-3Cr-3Nb-3Al-0.1B were added to a ball mill and mixed at a speed of 20 Hz for 4 hours to obtain a uniformly mixed shaped powder.

[0091] (3) After mixing, quickly transfer the formed powder into a vacuum bag and immediately evacuate the vacuum bag using a vacuum machine.

[0092] (4) The forming chamber is filled with 99% pure argon for 20 minutes. After the filling is completed, the evenly mixed forming powder is formed using additive manufacturing equipment.

[0093] (5) The specific process parameters are: laser power 2000W, laser scanning speed 10mm / s, laser spot diameter 4mm, powder feeding rate 18g / min, lifting amount 0.75mm, overlap rate 50%; the forming path is a single-pass reciprocating type, and the final block is 60mm in length, 60mm in height, and 2mm in width. During the forming process, the forming chamber is filled with 99% pure argon.

[0094] (6) During the forming process, an infrared thermometer was used to observe the molten pool. The temperatures of the first five layers of the molten pool were all less than 2000°C, and each layer stayed for 60 seconds. The temperatures of the 6th to 10th layers were higher than 2000°C, and they stayed for 8 seconds, 27 seconds, 56 seconds, 72 seconds, and 108 seconds, respectively, before the temperatures dropped below 800°C.

[0095] (7) After the forming is completed, continue to fill the forming chamber with 99% pure argon gas, let it stand for 60 minutes and then stop the filling. 30 minutes after the filling is completed, take out the block that has cooled to room temperature.

[0096] (8) The microstructure characterization showed that the grains were equiaxed with an average grain size of about 56 μm and a porosity of 99.8%.

[0097] (9) Adjust the process parameters to: laser power 1800W, laser scanning speed 10mm / s, repeat steps (4) to (7), and keep other process parameters unchanged.

[0098] (10) According to the microstructural characterization, the grains are equiaxed with an average grain size of approximately 21 μm and a porosity of 99.6%.

[0099] (11) Adjust the process parameters to: laser power 1600W, laser scanning speed 10mm / s, repeat steps (4) to (7), and keep other process parameters unchanged.

[0100] (12) According to the microstructure characterization, the porosity is 99.2% at this time, and the cyclic forming process stops. The microstructure of step (10) is the optimal microstructure of the alloy grain size. The final process parameters adopt the process parameters of step (9), and the final titanium alloy obtained is Ti-7Mo-3Cr-3Nb-3Al-4.5Tb-0.1B. Its finest equiaxed grain structure is as follows Figure 3 shown.

[0101] Example 4

[0102] (1) Weigh 8 g of titanium-terbium intermetallic compound powder TiTb (atomic ratio of 1:1), the average particle size of which is 75 μm.

[0103] (2) The titanium-terbium intermetallic compound powder obtained in step (1) and 992 g of titanium alloy powder Ti-24Nb-4Zr-8Sn-0.1B were added to a ball mill and mixed at a speed of 20 Hz for 4 hours to obtain a uniformly mixed shaped powder.

[0104] (3) After mixing, quickly transfer the formed powder into a vacuum bag and immediately evacuate the vacuum bag using a vacuum machine.

[0105] (4) The forming chamber is filled with 99% pure argon for 20 minutes. After the filling is completed, the evenly mixed forming powder is formed using additive manufacturing equipment.

[0106] (5) The specific process parameters are: laser power 1000W, laser scanning speed 10mm / s, laser spot diameter 4mm, powder feeding rate 18g / min, lifting amount 0.75mm, overlap rate 50%; the forming path is a single-pass reciprocating type, and the final block is 60mm in length, 30mm in height, and 2mm in width. During the forming process, the forming chamber is filled with 99% pure argon.

[0107] (6) During the forming process, an infrared thermometer was used to observe the molten pool. The temperatures of the first 11 layers of the molten pool were all less than 2000°C, and each layer stayed for 10 seconds. The temperatures of the 12th to 14th layers were higher than 2000°C, and they stayed for 5 seconds, 17 seconds, and 36 seconds, respectively, before the temperatures dropped below 800°C.

[0108] (7) After the forming is completed, continue to fill the forming chamber with 99% pure argon gas, let it stand for 60 minutes and then stop the filling. 30 minutes after the filling is completed, take out the block that has cooled to room temperature.

[0109] (8) According to the microstructure characterization, the grains are equiaxed with an average grain size of about 28 μm and a porosity of 99.7%.

[0110] (9) Adjust the process parameters to: laser power 950W, laser scanning speed 10mm / s, repeat steps (4) to (7), and keep other process parameters unchanged.

[0111] (10) According to the microstructure characterization, the grains are columnar at this time, and the cyclic forming process stops. The microstructure of step (8) is the optimal microstructure of the alloy grain size. The final process parameters adopt the process parameters of step (5), and the final titanium alloy is Ti-24Nb-4Zr-8Sn-6Tb-0.1B. Its finest equiaxed microstructure is as follows Figure 4 shown.

[0112] Example 5

[0113] (1) Weigh 8 g of titanium-terbium intermetallic compound powder TiTb (atomic ratio of 1:1), the average particle size of which is 75 μm.

[0114] (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 speed of 20 Hz for 4 hours to obtain a uniformly mixed shaped powder.

[0115] (3) After mixing, quickly transfer the formed powder into a vacuum bag and immediately evacuate the vacuum bag using a vacuum machine.

[0116] (4) The forming chamber is filled with 99% pure argon for 20 minutes. After the filling is completed, the evenly mixed forming powder is formed using additive manufacturing equipment.

[0117] (5) The specific process parameters are: laser power 500W, laser scanning speed 15mm / s, laser spot diameter 4mm, powder feeding rate 18g / min, lifting amount 0.75mm, overlap rate 50%; the forming path is a single-pass reciprocating type, and the final block is 60mm in length, 45mm in height, and 2mm in width. During the forming process, the forming chamber is filled with 99% pure argon.

[0118] (6) During the forming process, the molten pool was observed using an infrared thermometer. The temperatures of the first 16 layers of the molten pool were all less than 2000°C, and each layer stayed for 5 seconds. The temperatures of the 17th and 18th layers were higher than 2000°C, and stayed for 4 seconds and 11 seconds, respectively, before the temperatures dropped below 800°C.

[0119] (7) After the forming is completed, continue to fill the forming chamber with 99% pure argon gas, let it stand for 60 minutes and then stop the filling. 30 minutes after the filling is completed, take out the block that has cooled to room temperature.

[0120] (8) According to the microstructure characterization, the grains are equiaxed with an average grain size of about 26 μm and a porosity of 99.9%.

[0121] (9) Adjust the process parameters to: laser power 480W, laser scanning speed 15mm / s, and repeat steps (4) to (7).

[0122] (10) According to the microstructure characterization, the grains are equiaxed with an average grain size of about 17 μm and a porosity of 99.7%.

[0123] (11) Adjust the process parameters to: laser power 460W, laser scanning speed 15mm / s, repeat steps (4) to (7), and keep other process parameters unchanged.

[0124] (12) According to the microstructural characterization, the grains are equiaxed with an average grain size of approximately 15 μm and a porosity of 99.5%.

[0125] (13) Adjust the process parameters to: laser power 440 W, laser scanning speed 15 mm / s, and repeat steps (4) to (7).

[0126] (14) According to the microstructure characterization, the porosity is 99.3% at this time, and the cyclic forming process stops. The microstructure of step (12) is the optimal microstructure of the alloy grain size. The final process parameters adopt the process parameters of step (11), and the final titanium alloy obtained is Ti-12Zr-5Nb-3Ta-6Tb-0.1B. Its finest equiaxed grain structure is as follows Figure 5 shown.

[0127] Example 6

[0128] (1) Weigh 6 g of titanium-terbium intermetallic compound powder TiTb (atomic ratio of 1:1), the average particle size of which is 15 μm.

[0129] (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 speed of 25 Hz for 5 hours to obtain a uniformly mixed shaped powder.

[0130] (3) After mixing, quickly transfer the formed powder into a vacuum bag and immediately evacuate the vacuum bag using a vacuum machine.

[0131] (4) The forming chamber is filled with 99% pure argon for 20 minutes. After the filling is completed, the evenly mixed forming powder is formed using additive manufacturing equipment.

[0132] (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, overlap rate 30%; the forming path is a single-pass reciprocating type, and the final block is 50mm in length, 20mm in height, and 2mm in width. During the forming process, the forming chamber is filled with 99% pure argon.

[0133] (6) During the forming process, an infrared thermometer was used to observe the molten pool. The temperatures of the first 11 layers of the molten pool were all less than 2000°C, and each layer was paused for 30 seconds. The temperatures of the 12th to 14th layers were higher than 2000°C, and they stayed for 5 seconds, 17 seconds, and 36 seconds, respectively, before the temperatures dropped below 800°C.

[0134] (7) After the forming is completed, continue to fill the forming chamber with 99% pure argon gas, let it stand for 60 minutes and then stop the filling. 30 minutes after the filling is completed, take out the block that has cooled to room temperature.

[0135] (8) According to the microstructure characterization, the grains are equiaxed with an average grain size of about 25 μm and a porosity of 99.7%.

[0136] (9) Adjust the process parameters to: laser power 1500W, laser scanning speed 60mm / s, repeat steps (4) to (7), and keep other process parameters unchanged.

[0137] (10) According to the microstructure characterization, the grains are now columnar, and the cyclic forming process stops. The microstructure of step (8) is the optimal microstructure of the alloy grain size. The final process parameters adopt the process parameters of step (5), and the final titanium alloy is Ti-24Nb-4Zr-8Sn-4.5Tb-0.1B. Its finest equiaxed microstructure is as follows: Figure 6 shown.

[0138] Example 7

[0139] (1) Weigh 5 g of titanium-terbium intermetallic compound powder TiTb (atomic ratio of 1:1), the average particle size of which is 200 μm.

[0140] (2) The titanium-terbium intermetallic compound powder obtained in step (1) and 995 g of titanium alloy powder Ti-9Mo-0.1B were added to a ball mill and mixed at a speed of 30 Hz for 6 hours to obtain a uniformly mixed shaped powder.

[0141] (3) After mixing, quickly transfer the formed powder into a vacuum bag and immediately evacuate the vacuum bag using a vacuum machine.

[0142] (4) The forming chamber is filled with 99% pure argon for 20 minutes. After the filling is completed, the evenly mixed forming powder is formed using additive manufacturing equipment.

[0143] (5) The specific process parameters are: laser power 1500W, laser scanning speed 20mm / s, laser spot diameter 5mm, powder feeding rate 20g / min, lifting amount 1mm, overlap rate 60%, forming path is single-pass reciprocating, and the final block is 70mm in length, 30mm in height, and 2mm in width. During the forming process, the forming chamber is filled with 99% pure argon.

[0144] (6) During the forming process, an infrared thermometer was used to observe the molten pool. The temperatures of the first 11 layers of the molten pool were all less than 2000°C, and each layer was paused for 40 seconds. The temperatures of the 12th to 14th layers were higher than 2000°C, and they stayed for 5 seconds, 17 seconds, and 36 seconds, respectively, before the temperatures dropped below 800°C.

[0145] (7) After the forming is completed, continue to fill the forming chamber with 99% pure argon gas, let it stand for 60 minutes and then stop the filling. 30 minutes after the filling is completed, take out the block that has cooled to room temperature.

[0146] (8) According to the microstructure characterization, the grains are equiaxed with an average grain size of about 28 μm and a porosity of 99.7%.

[0147] (9) Adjust the process parameters to: laser power 1200W, laser scanning speed 20mm / s, repeat steps (4) to (7), and keep other process parameters unchanged.

[0148] (10) According to the microstructure characterization, the grains are now columnar, and the cyclic forming process stops. The microstructure of step (8) is the optimal microstructure of the alloy grain size. The final process parameters adopt the process parameters of step (5) to obtain Ti-9Mo-3.8Tb-0.1B, whose smallest equiaxed microstructure is as follows Figure 7 shown.

Claims

1. A laser stereo forming method for fine β-grain titanium alloy, characterized in that: The following steps are involved: S1, adding terbium metal powder or titanium-terbium intermetallic compound to titanium alloy powder to obtain a formed powder; S2, preparing fine β-grained titanium alloy by laser stereo forming the forming powder. After forming one layer, if the molten pool temperature is less than 2000°C, stay for 2s-60s to proceed with laser stereo 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 before proceeding with laser stereo forming of the next layer. After the set number of layers are prepared, a sample is obtained; during the laser stereo forming process, the laser energy density is 25 (W·s) / mm-200 (W·s) / mm, and the ambient oxygen content is ≤500ppm; S3, after forming, naturally cooling to room temperature to obtain a fine β-crystalline titanium alloy, wherein the grain size of the fine β-crystalline titanium alloy is 10 μm-50 μm, and the grain boundaries of the fine β-crystalline titanium alloy are pinned with α-Tb phase; In S1, the content of terbium in the forming powder is less than 10 wt.%; During the laser stereo 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 overlap rate is 30%-60%.

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

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

4. The laser stereo forming method for fine β-grained titanium alloy according to claim 1, characterized in that: In S1, the titanium-terbium intermetallic compound and the titanium alloy powder are mixed by ball milling, or the terbium metal powder and the titanium alloy powder are mixed by ball milling, and the ball milling jar is sealed during the ball milling process.

5. The laser stereo forming method of a fine β-grain titanium alloy according to claim 1, characterized in that: During the ball milling process, the rotation speed is 20Hz-30Hz and the time is 3h-6h.

6. The laser stereo forming method of a fine β-grain titanium alloy according to claim 1, characterized in that: Before S2, the process of determining the process parameters of the laser stereo forming process is: perform metallographic observation on the sample obtained by laser stereo forming, and when the grains are equiaxed crystals and the porosity is ≥99.5%, reduce the laser energy density, repeat the laser stereo forming, obtain the sample, observe the sample 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 sample obtained for the nth time meet the preset requirements, then the process parameters of the n-1th laser stereo forming process are the final process parameters; wherein n is the number of cycles, which is a natural number, and the preset requirements are specifically: the grains of the sample are columnar crystals or the porosity is less than 99.5%.

7. The laser stereo forming method for fine β-grained titanium alloy according to claim 1, characterized in that: In S2, the molten pool temperature is monitored by an infrared thermometer.

8. A fine β-grained titanium alloy produced by the laser stereo forming method according to any one of claims 1 to 7, characterized in that: The grain size of the fine β-crystalline titanium alloy is 10 μm-50 μm, and an α-Tb phase is pinned at the grain boundary of the fine β-crystalline titanium alloy.

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