A method for preparing titanium with a two-level core-shell structure and high uniform elongation

Abstract

This invention discloses a method for preparing titanium with a two-stage core-shell structure and high uniform elongation. The method includes: 1. Loading titanium powder into a ball mill jar and evacuating the jar, then filling it with argon gas, allowing the titanium powder to undergo ball milling deformation cold welding under an argon atmosphere to obtain ball-milled titanium powder; 2. Pre-compressing and degassing the ball-milled titanium powder at room temperature, followed by spark plasma sintering to obtain titanium with a two-stage core-shell structure. This invention uses a ball milling process to refine the surface grains of the titanium powder, resulting in gradient deformation from the outside to the inside, forming a two-stage core-shell structure powder. Combined with low-temperature, high-pressure sintering to suppress the excessive growth of the fine grain region, the characteristics of the two-stage core-shell structure powder are preserved, thus obtaining titanium with a two-stage core-shell structure. This gives the titanium high strength and high plasticity mechanical properties, expanding the application range of titanium materials. The process is simple and easy to implement, suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of advanced structural materials technology, specifically relating to a method for preparing a two-stage core-shell structure titanium with high uniform elongation. Background Technology

[0002] Pure titanium is a lightweight structural material with comprehensive properties such as low density, good corrosion resistance, and excellent biocompatibility. Compared with titanium alloys, it does not contain toxic alloying elements that can harm the human body, making it a promising candidate for application in the biomedical engineering field. However, commercially available pure titanium has relatively low overall mechanical properties and is prone to fracture and instability in the complex environment inside the human body, thus failing to meet service requirements.

[0003] The most common method currently used is to refine the grains of commercially pure titanium through large plastic deformation treatment, thereby improving the material's strength, but this significantly reduces its plasticity. Therefore, the urgent problem to be solved by those skilled in the art is to propose a method for preparing titanium with a two-level core-shell structure and high uniform elongation, in order to address the technical problem that pure titanium cannot achieve both strength and plasticity in the existing technology. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a method for preparing titanium with a two-level core-shell structure and high uniform elongation, addressing the shortcomings of the prior art. This method employs a ball milling process to refine the surface grains of titanium powder, resulting in gradient deformation from the outside in, forming a two-level core-shell structure powder. Combined with low-temperature, high-pressure sintering to suppress the excessive growth of the fine grain region, the characteristics of the two-level core-shell structure powder are preserved, thereby obtaining titanium with a two-level core-shell structure. This gives the titanium high strength and high plasticity, solving the problem in the prior art that pure titanium cannot achieve both strength and plasticity.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing titanium with a two-level core-shell structure and high uniform elongation, characterized in that the method includes the following steps:

[0006] Step 1: Load titanium powder into a ball mill jar, evacuate the ball mill jar, and then fill it with argon gas, so that the titanium powder is ball-milled and cold-welded under the argon atmosphere to obtain ball-milled titanium powder; The ball milling process parameters are: ball-to-material ratio 10:1, ball milling speed 400 rpm, and effective total ball milling time 4h to 12h.

[0007] Step 2: The ball-milled titanium powder obtained in Step 1 is subjected to room temperature pre-compression crushing and degassing, and then subjected to spark plasma sintering to obtain a two-stage core-shell structure titanium. The process parameters of spark plasma sintering are: sintering pressure 400MPa, sintering temperature 600℃, and holding time 5min.

[0008] This invention first ball-mills titanium powder in an argon atmosphere to obtain ball-milled titanium powder. The ball-milling force refines the surface grains of the titanium powder and induces gradient deformation from the outside to the inside. Then, due to the breaking of the protective film on the surface of the titanium powder by ball milling, the titanium powder is cold-welded and aggregates to form large particles. The surface grains of the large particles are severely refined under continuous ball milling and undergo gradient deformation from the outside to the inside, forming a two-level core-shell structure powder. Then, the ball-milled titanium powder is pre-compressed and degassed at room temperature and then subjected to low-temperature and high-pressure discharge plasma sintering. The low-temperature and high-pressure sintering effect inhibits grain growth while forming a bulk material, and the bulk material retains the grain structure of the powder, thus obtaining a two-level core-shell structure titanium. The fine grains on the "shell" improve the strength of the titanium, while the coarse grains on the "core" improve the plasticity of the titanium, giving the titanium high strength and high plasticity mechanical properties.

[0009] The method for preparing a two-stage core-shell structure titanium with high uniform elongation, as described above, is characterized in that the vacuuming and argon filling process in step one is repeated a total of three times, with argon continuously introduced for 3 minutes during the last step while the inlet and outlet of the ball mill jar are open. This repeated vacuuming and argon filling process minimizes oxygen exposure and prevents oxidation during ball milling.

[0010] The method for preparing a two-stage core-shell structured titanium with high uniform elongation, as described above, is characterized in that, in step one, the argon atmosphere inside the grinding jar after argon filling is positive pressure, and the pressure is 1 MPa. By limiting the atmospheric pressure inside the grinding jar, the grinding process is ensured to be carried out entirely in an argon atmosphere, and excessive pressure is avoided so that the connecting elements and sealing rings on the grinding jar cannot withstand the pressure.

[0011] The method for preparing a two-stage core-shell structured titanium with high uniform elongation, as described above, is characterized in that the titanium powder in step one is spherical with a particle size of 15 μm to 53 μm. This shape and particle size of the titanium powder ensures the performance of the two-stage core-shell structure and avoids the core-shell structure becoming indistinct due to excessively large titanium powder particle size.

[0012] The method for preparing a two-stage core-shell structure titanium with high uniform elongation, as described above, is characterized in that the ball milling process in step one is paused every 30 minutes, with each pause lasting 10 minutes. Continuous ball milling can cause severe overheating of the milling jar, making it easy for titanium powder to cold-weld onto the milling jar and grinding balls; therefore, this invention employs the aforementioned intermittent ball milling process to cool it down and ensure the effective milling. The total effective milling time in this invention is the sum of the milling times excluding the pause times.

[0013] The above-mentioned method for preparing a two-stage core-shell structured titanium with high uniform elongation is characterized in that the room temperature pre-compression pressure in step two is 40 MPa.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. This invention employs a ball milling process to refine the surface grains of titanium powder, resulting in gradient deformation from the outside to the inside, forming a two-level core-shell structure powder. Combined with low-temperature high-pressure sintering to suppress the excessive growth of the fine grain region, the characteristics of the two-level core-shell structure powder are preserved, thereby obtaining titanium with a two-level core-shell structure, which gives the titanium high strength and high plasticity mechanical properties, meeting the service requirements.

[0016] 2. Compared with conventional methods that use large plastic deformation treatment to improve the strength of titanium but lead to a significant decrease in plasticity, this invention changes the grain structure of titanium by controlling the ball milling and sintering processes, thereby improving the comprehensive mechanical properties of titanium materials. The process is simple and easy to implement, and is suitable for large-scale production.

[0017] 3. The preparation method of the present invention focuses on improving the process, without the need to add other elements to improve the performance of titanium materials, effectively avoiding the use of toxic alloying elements and expanding the application range of titanium materials.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a SEM image of the ball-milled titanium powder prepared in Example 2 of the present invention.

[0020] Figure 2 This is a metallographic image of the ball-milled titanium powder prepared in Example 2 of the present invention.

[0021] Figure 3 This is a microstructure diagram of the two-level core-shell structure titanium prepared in Example 2 of the present invention.

[0022] Figure 4 This is an enlarged view of the primary structure of the two-stage core-shell titanium prepared in Example 2 of the present invention.

[0023] Figure 5 This is an enlarged view of the secondary structure in the two-stage core-shell titanium prepared in Example 2 of the present invention.

[0024] Figure 6 This is an engineering stress-strain curve of the two-stage core-shell structure titanium prepared in Example 2 of the present invention. Detailed Implementation

[0025] Example 1

[0026] This embodiment includes the following steps:

[0027] Step 1: Spherical titanium powder with a particle size of 15μm to 53μm is loaded into a ball mill jar, and the jar is evacuated. Then, argon gas is introduced. The evacuation and argon gas introduction process is repeated three times. During the last process, argon gas is continuously introduced for 3 minutes while the inlet and outlet of the ball mill jar are open. The outlet of the ball mill jar is then closed. After the argon atmosphere inside the ball mill jar is positive pressure and the pressure is 1MPa, the inlet of the ball mill jar is closed, so that the titanium powder is ball-milled and cold-welded under an argon atmosphere to obtain ball-milled titanium powder. The ball milling process parameters are: ball-to-powder ratio of 10:1, ball milling speed of 400rpm, and a stop every 30 minutes for 10 minutes during the ball milling process, with a total effective ball milling time of 4 hours.

[0028] Step 2: The ball-milled titanium powder obtained in Step 1 is subjected to room temperature pre-compression crushing and degassing at a pressure of 40 MPa, and then subjected to spark plasma sintering to obtain a two-stage core-shell structure titanium. The process parameters of spark plasma sintering are: sintering pressure 400 MPa, sintering temperature 600℃, and holding time 5 min.

[0029] Testing revealed that the two-stage core-shell structured titanium prepared in this embodiment exhibits excellent strength-ductility matching.

[0030] Example 2

[0031] This embodiment includes the following steps:

[0032] Step 1: Spherical titanium powder with a particle size of 15μm to 53μm is loaded into a ball mill jar, and the jar is evacuated. Then, argon gas is introduced. The evacuation and argon gas introduction process is repeated three times. During the last process, argon gas is continuously introduced for 3 minutes while the inlet and outlet of the ball mill jar are open. The outlet of the ball mill jar is then closed. After the argon atmosphere inside the ball mill jar is positive pressure and the pressure is 1MPa, the inlet of the ball mill jar is closed, so that the titanium powder undergoes ball milling deformation cold welding under an argon atmosphere to obtain ball-milled titanium powder. The ball milling process parameters are: ball-to-powder ratio of 10:1, ball milling speed of 400rpm, and a stop every 30 minutes for 10 minutes during the ball milling process, with a total effective ball milling time of 8 hours.

[0033] Step 2: The ball-milled titanium powder obtained in Step 1 is subjected to room temperature pre-compression crushing and degassing at a pressure of 40 MPa, and then subjected to spark plasma sintering to obtain a two-stage core-shell structure titanium. The process parameters of spark plasma sintering are: sintering pressure 400 MPa, sintering temperature 600℃, and holding time 5 min.

[0034] Figure 1 Here is a SEM image of the ball-milled titanium powder prepared in this embodiment. Figure 1 As can be seen, titanium powder undergoes agglomeration, deformation, and cold welding during ball milling, forming titanium particles with a size of hundreds of micrometers.

[0035] Figure 2 The image shown is a metallographic image of the ball-milled titanium powder prepared in this embodiment. Figure 2 As can be seen, the titanium powder inside the titanium particles remains spherical due to its small deformation, while the titanium powder outside the titanium particles undergoes large plastic deformation and becomes irregular in shape due to mutual compression.

[0036] Figure 3 This is a microstructure image of the two-level core-shell structured titanium prepared in this embodiment, from... Figure 3 As can be seen, the ball-milled titanium powder forms a two-stage core-shell structure after low-temperature and high-pressure sintering, and the thickness of the first-stage "shell" is greater than that of the second-stage "shell".

[0037] Figure 4 This is an enlarged view of the primary structure in the two-stage core-shell titanium prepared in this embodiment. Figure 4 As can be seen, the size of the "shell" grains in the primary structure is significantly smaller than that of the "core" grains.

[0038] Figure 5 This is an enlarged view of the secondary structure in the two-level core-shell titanium prepared in this embodiment. Figure 5 As can be seen, the size of the secondary structure "shell" grains is significantly smaller than that of the "core" grains.

[0039] Figure 6 This is an engineering stress-strain curve of the two-stage core-shell structured titanium prepared in this embodiment. Figure 6 As can be seen, the two-stage core-shell structure titanium has a tensile strength of 665 MPa and a uniform elongation of 15%, exhibiting excellent strength-ductility matching.

[0040] The mechanical properties of the two-stage core-shell structure titanium prepared in this embodiment were tested and compared with those of titanium prepared in the prior art. The results are shown in Table 1 below.

[0041] Table 1

[0042]

[0043]

[0044] Document 1: Ding H, Cui

[0045] Document 2: Sharma B, Miyakoshi M, Vajpai SK, et al.Extra-strengtheningin aharmonic structure designed pure titanium due to preferentialrecrystallization phenomenon through thermomechanicaltreatment.MaterialsScience and Engineering:A,2020,797:140227.

[0046] Document 3: Li D, Fan G, Huang X, et al. Enhanced strength in pure Ti viadesign of alternating coarse-and fine-grain layers. Acta Materialia, 2021, 206: 116627.

[0047] As can be seen from Table 1, the comprehensive mechanical properties of the titanium prepared in this embodiment are significantly better than those in the comparative literature. Compared with Literature 1, the tensile strength of this titanium is slightly higher than that of Literature 1, and the uniform elongation is more than three times that of Literature 1; compared with Literature 2, the tensile strength of this titanium is comparable to that of Literature 2, and the uniform elongation is significantly higher than that of Literature 2; compared with Literature 3, the uniform elongation is the same, but the tensile strength and yield strength are significantly higher than those of Literature 3. By comparing with titanium in the prior art, it can be seen that the preparation method of the present invention introduces a two-level core-shell structure, which effectively improves the comprehensive mechanical properties of titanium and solves the technical problem that titanium in the prior art cannot obtain both strength and plasticity.

[0048] Example 3

[0049] This embodiment includes the following steps:

[0050] Step 1: Spherical titanium powder with a particle size of 15μm to 53μm is loaded into a ball mill jar, and the jar is evacuated. Then, argon gas is introduced. The evacuation and argon gas introduction process is repeated three times. During the last process, argon gas is continuously introduced for 3 minutes while the inlet and outlet of the ball mill jar are open. The outlet of the ball mill jar is then closed. After the argon atmosphere inside the ball mill jar is positive pressure and the pressure is 1MPa, the inlet of the ball mill jar is closed, so that the titanium powder undergoes ball milling deformation cold welding under an argon atmosphere to obtain ball-milled titanium powder. The ball milling process parameters are: ball-to-material ratio 10:1, ball milling speed 400rpm, and a stop every 30 minutes for 10 minutes during the ball milling process, with a total effective ball milling time of 12 hours.

[0051] Step 2: The ball-milled titanium powder obtained in Step 1 is subjected to room temperature pre-compression crushing and degassing at a pressure of 40 MPa, and then subjected to spark plasma sintering to obtain a two-stage core-shell structure titanium. The process parameters of spark plasma sintering are: sintering pressure 400 MPa, sintering temperature 600℃, and holding time 5 min.

[0052] Testing revealed that the two-stage core-shell structured titanium prepared in this embodiment exhibits excellent strength-ductility matching.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing titanium with a two-level core-shell structure and high uniform elongation, characterized in that, The method includes the following steps: Step 1: Load titanium powder into a ball mill jar, evacuate the ball mill jar, and then fill it with argon gas, so that the titanium powder is ball-milled and cold-welded under the argon atmosphere to obtain ball-milled titanium powder; The ball milling process parameters are: ball-to-material ratio 10:1, ball milling speed 400 rpm, and effective total ball milling time 4h to 12h. Step 2: The ball-milled titanium powder obtained in Step 1 is subjected to room temperature pre-compression crushing and degassing, and then subjected to spark plasma sintering to obtain a two-stage core-shell structure titanium. The process parameters of spark plasma sintering are: sintering pressure 400MPa, sintering temperature 600℃, and holding time 5min.

2. The method for preparing a two-stage core-shell structure titanium with high uniform elongation according to claim 1, characterized in that, The process of vacuuming and argon filling described in step one is repeated a total of three times, with argon continuously introduced for 3 minutes during the last time while the inlet and outlet of the ball mill jar are open.

3. The method for preparing a two-stage core-shell structure titanium with high uniform elongation according to claim 1, characterized in that, In step one, after argon gas is introduced, the argon atmosphere inside the ball mill jar is under positive pressure and the pressure is 1 MPa.

4. The method for preparing a two-stage core-shell structure titanium with high uniform elongation according to claim 1, characterized in that, The titanium powder mentioned in step one is spherical with a particle size of 15μm to 53μm.

5. The method for preparing a two-stage core-shell structure titanium with high uniform elongation according to claim 1, characterized in that, During the ball milling process described in step one, the milling is stopped every 30 minutes for a period of 10 minutes.

6. The method for preparing a two-stage core-shell structure titanium with high uniform elongation according to claim 1, characterized in that, The room temperature pre-compression pressure in step two is 40 MPa.

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