Preparation process of additive manufacturing pure titanium part, pure titanium part and application

Abstract

The application belongs to the technical field of laser additive manufacturing, and discloses a preparation process of an additive manufacturing pure titanium piece, the pure titanium piece and application. The preparation process of the additive manufacturing pure titanium piece comprises the following steps: creating a three-dimensional model diagram of the pure titanium piece to generate an STL file; importing the STL file into data processing software to perform layering and slicing processing to generate a scanning path; using pure titanium powder as raw material powder to perform laser powder bed fusion additive manufacturing to obtain a blank; performing heat treatment and surface treatment on the blank to obtain the additive manufacturing pure titanium piece; wherein the heat treatment comprises first stage heat treatment and second stage heat treatment in sequence; and the surface treatment comprises surface polishing. The preparation process of the additive manufacturing pure titanium piece can reduce internal defects, refine grains, reduce residual stress and improve surface quality, thereby significantly improving the plasticity (elongation after fracture) and fatigue performance of the pure titanium piece.

Description

Technical Field

[0001] This invention belongs to the field of laser additive manufacturing technology, and specifically relates to a preparation process for additive manufacturing of pure titanium parts, pure titanium parts, and their applications. Background Technology

[0002] Laser-bonded powder bed additive manufacturing (LBD) of titanium and titanium alloy parts generates residual stress, porosity, and cracks due to the rapid solidification process. These defects significantly reduce the material's plasticity and fatigue performance. On the one hand, appropriate heat treatment processes are typically selected to improve the mechanical properties of LBD-manufactured titanium and titanium alloy parts by addressing issues such as uneven microstructure and high residual stress. On the other hand, the heat treatment processes for pure titanium parts and titanium alloys differ. During heat treatment, titanium alloys undergo α- and β-phase transformations, as well as the precipitation and decomposition of metastable phases, resulting in a complex microstructure. Solution treatment and aging can significantly improve the alloy's strength, achieving a combination of high strength and good plasticity. In contrast, the microstructure changes during heat treatment of pure titanium parts are relatively simple, mainly involving grain growth and recrystallization, which can only eliminate stress or improve processing performance. Therefore, there are fewer available processes for improving the performance of pure titanium parts, and their effectiveness is far less than that of titanium alloys. Currently, the most widely recognized effective means to improve the plasticity and fatigue performance of additively manufactured pure titanium parts is hot isostatic pressing (HIP). However, HIP equipment is expensive, with a single unit costing millions to tens of millions of yuan. Daily energy consumption typically requires temperatures above 1000°C and high-pressure argon conditions. Small and medium-sized additive manufacturing companies generally do not have the capability to assemble HIP equipment, resulting in limited practicality and widespread adoption.

[0003] Therefore, how to improve the plasticity and fatigue properties of additively manufactured pure titanium parts remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention provides a process for manufacturing pure titanium parts by additive manufacturing, pure titanium parts, and applications. The process for manufacturing pure titanium parts by additive manufacturing described in the present invention can reduce internal defects, refine grains, reduce residual stress, and improve surface quality, thereby significantly improving the plasticity (elongation after fracture) and fatigue performance of pure titanium parts.

[0005] In a first aspect, the present invention provides a process for additively manufacturing pure titanium parts, comprising the following steps:

[0006] Create a 3D model of the pure titanium part and generate an STL file;

[0007] The STL file is imported into data processing software for layered slicing to generate a scan path.

[0008] Pure titanium powder was used as the raw material powder for laser powder bed fusion additive manufacturing to obtain a blank;

[0009] The blank is subjected to heat treatment and surface treatment to obtain the additively manufactured pure titanium part;

[0010] The heat treatment includes a first stage heat treatment and a second stage heat treatment in sequence.

[0011] The first stage of heat treatment includes the following steps: 1) heating the blank to 500-580°C at a heating rate of 30°C / min to 50°C / min and holding it at that temperature; 2) cooling it to 400°C in the furnace; steps 1) to 2) constitute one cycle, and the cycle is repeated 3 to 4 times.

[0012] The second stage of heat treatment includes the following steps: a) heating the blank to 800-850°C at a heating rate of 50°C / min to 150°C / min and holding it at that temperature; b) cooling it to 100°C in the furnace; steps a) to b) constitute one cycle, and the cycle is repeated 2 to 3 times.

[0013] The surface treatment includes surface polishing.

[0014] Specifically, the first stage of heat treatment in this invention is a low-temperature stress-relief cycle, with a temperature range of 500–580°C, slightly higher than the lower limit of stress-relief annealing, to avoid the risk of oxidation due to excessively high temperatures. The aim is to eliminate residual stress and interlayer defects. Residual stress mainly originates from rapid solidification and thermal gradients during additive manufacturing. These stresses can lead to crack initiation and propagation, affecting fatigue performance. This invention gradually releases these stresses through multiple cycles of heating and slow cooling, reducing stress concentration in internal defects and thus improving fatigue life. The first stage of heat treatment in this invention gradually releases the residual tensile stress generated by rapid solidification and thermal gradients during additive manufacturing, reducing internal stress concentration. At high temperatures, atomic diffusion blunts the sharp edges of micropores or unfused defects, reducing the risk of crack initiation.

[0015] Specifically, the second-stage heat treatment of this invention is a medium-temperature recrystallization cycle with a temperature range of 800–850°C, below the β-transformation temperature (890°C), to avoid phase transformation. The purpose of recrystallization annealing is to refine and homogenize the grains, promote the transformation of columnar crystals to equiaxed crystals, and simultaneously close micro-pore defects. Equiaxed crystal structures generally have better ductility and uniformity, thus improving elongation after fracture. In addition, grain refinement also helps to improve the strength and fatigue performance of the material, as fine grains can hinder crack propagation. This invention, through the second-stage heat treatment, promotes the recrystallization of columnar crystals to form fine equiaxed crystals (grain size ≤20μm), eliminating the anisotropy of additive manufacturing. High-temperature diffusion further closes or spherizes pores and unfused defects.

[0016] The first-stage heat treatment and the second-stage heat treatment of this invention work synergistically and are indispensable. The first-stage heat treatment prioritizes the elimination of stress and passivation defects, providing a low-stress environment for recrystallization in the second-stage heat treatment and avoiding residual stress from interfering with grain boundary migration. The second-stage heat treatment reconstructs grains through recrystallization, further closing defects and improving uniformity.

[0017] In some embodiments of the present invention, when the pure titanium part is a thin-walled simple structure with a wall thickness of ≤10mm, the first stage heat treatment cycle is 3 times, and the second stage heat treatment cycle is 2 times.

[0018] In some embodiments of the present invention, when the pure titanium part is a thick-walled complex structure with a wall thickness > 10 mm, the first stage heat treatment cycle is 4 times, and the second stage heat treatment cycle is 3 times.

[0019] In some embodiments of the present invention, the vacuum degree of the first stage heat treatment is ≤6.67×10⁻⁶. -2 Pa.

[0020] In some embodiments of the present invention, the vacuum degree of the second stage heat treatment is 2 × 10⁻⁶. -3 Pa ~ 6.67 × 10 -2 Pa.

[0021] In some embodiments of the present invention, the particle size of the pure titanium powder is ≤100μm.

[0022] In some embodiments of the present invention, the hollow powder content of the pure titanium powder is ≤5%.

[0023] In some embodiments of the present invention, the pure titanium powder is spherical or nearly spherical particles with a normal particle size distribution.

[0024] In some embodiments of the present invention, prior to laser powder bed fusion additive manufacturing, the pure titanium powder is further pretreated, i.e., under vacuum (vacuum degree ≤ 6.67 × 10⁻⁶). -3 Dry at 135-200℃ for 1-2 hours to remove moisture and adsorbed gas, and avoid the formation of pores during molding; the drying temperature is 135-200℃.

[0025] In some embodiments of the present invention, the process parameters for laser powder bed fused additive manufacturing include at least one of the following: laser power of 180–500 W; scanning speed of 600–1200 mm / s; printing layer thickness of 20–40 μm; scanning spacing of 0.06–0.10 mm; and laser energy density of 50–150 J / mm². 3 The laser energy density is controlled within a suitable range to balance melting and porosity.

[0026] Specifically, the laser energy density is calculated using the following formula:

[0027]

[0028] Where E is the laser energy density (J / mm²) 3 P is the laser power (W), v is the scanning speed (mm / s), h is the printing layer thickness (mm), and d is the scanning spacing (mm).

[0029] In some embodiments of the present invention, the laser powder bed fused additive manufacturing employs a rotational scanning strategy (e.g., rotating 45° to 67° per layer).

[0030] In some embodiments of the present invention, the laser powder bed fused additive manufacturing is carried out under the protection of an inert gas (such as argon or helium) with an oxygen content ≤0.1% to prevent oxidation.

[0031] In some embodiments of the present invention, the surface treatment further includes sandblasting and / or polishing.

[0032] In some embodiments of the present invention, the surface treatment includes sandblasting, grinding and surface polishing in sequence.

[0033] Specifically, a rough surface is detrimental to elongation after fracture and fatigue performance, so surface treatment is required to improve the surface finish of additively manufactured pure titanium parts.

[0034] Specifically, the surface of additively manufactured pure titanium parts usually has unmelted surface spheroids. Generally, zirconium oxide, alumina, hydroxyapatite, quartz sand, glass beads, silicon carbide, garnet sand, etc. with a particle size of 0.07 to 1.68 μm are selected as abrasives for sandblasting, and the working air pressure for sandblasting is 0.3 to 0.66 MPa.

[0035] Specifically, the surface where supports are added to additively manufactured pure titanium parts has a rougher surface compared to other parts, requiring special treatment. Use coarse materials (such as sandpaper of different grits, grinding heads, etc.) manually or with automated grinding tools to specifically grind the support surface. Care must be taken during grinding to avoid damaging the geometry of the part.

[0036] Specifically, fatigue cracks in additively manufactured pure titanium parts primarily originate from the surface. To improve the fatigue performance of these parts, it is necessary to remove the rough outer layer. For additively manufactured pure titanium parts, vibratory polishing or tumbling polishing combined with polishing abrasives such as corundum, alumina, silicon carbide, and zirconium oxide is generally used. With specialized equipment, laser polishing and electrolytic polishing techniques can also be employed. Because surface defects are most abundant and have the greatest impact on fatigue performance within the 50–300 μm range from the surface, the polishing process must achieve a surface polishing depth of 50–300 μm without damaging the geometry of the part, thus removing the oxide scale and surface defects from the additively manufactured pure titanium parts.

[0037] In some embodiments of the present invention, a machining allowance of 0.2–1.0 mm is reserved when creating the three-dimensional model of the pure titanium part. This machining allowance is reserved to compensate for subsequent surface treatment requirements. The machining allowance for thin-walled structures is typically 0.2–0.5 mm to compensate for surface ripples and oxide layers; the machining allowance for complex structures needs to be increased to 0.5–1.0 mm to address interlayer misalignment and internal porosity. In creating the three-dimensional model of the pure titanium part, the present invention intentionally incorporates compensation design in terms of material thickness to ensure that the geometry of the sample is not damaged when the final surface polishing step reaches a depth of 50–300 μm during surface treatment.

[0038] In some embodiments of the present invention, the heat preservation time is obtained by the following formula:

[0039]

[0040] Where T is the heat preservation time and D is the maximum cross-sectional thickness of the pure titanium part.

[0041] Specifically, when D≤25mm, the heat preservation time T is taken as a fixed value directly according to the thickness range in the formula, following the segmented empirical rules (e.g., when D≤3mm, T corresponds to 25min).

[0042] When D>25mm, based on 60min corresponding to D=25mm, the heat preservation time should be increased by at least 10min for every 5mm increase in thickness.

[0043] Symbol explanation: This indicates rounding up, meaning that if the value is less than 5mm, it will be calculated as 5mm.

[0044] Example:

[0045] When D = 26 mm

[0046] When D = 28 mm,

[0047] When D = 31 mm,

[0048] Understandably, for non-uniform cross-sections (such as structures with holes or ribs), the effective thickness of the thickest cross-section should be used as a reference, and local heat equalization time should be added if necessary.

[0049] In a second aspect, the present invention provides an additively manufactured pure titanium part, which is prepared using the preparation process described in the first aspect of the present invention.

[0050] In a third aspect, the present invention provides the application of the additively manufactured pure titanium parts described in the second aspect of the present invention in the preparation of aerospace components and medical implants.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] (1) The additive manufacturing process for pure titanium parts of the present invention is based on conventional vacuum furnace design, which does not require high pressure or cryogenic equipment (such as hot isostatic pressing or liquid nitrogen forging), and is lower in cost and easier to promote.

[0053] (2) This invention optimizes the residual stress and grain structure of additively manufactured pure titanium parts in stages by combining a first-stage heat treatment (low-temperature stress relief cycle, 500-580℃) with a second-stage heat treatment (medium-temperature recrystallization cycle, 800-850℃), along with dynamic control of furnace cooling. This, combined with subsequent surface polishing, significantly improves the plasticity (elongation after fracture) and fatigue performance of additively manufactured pure titanium parts, achieving a balance between strength and plasticity. Specifically, the tensile strength is ≥500MPa, the elongation after fracture is ≥25%, and the fatigue strength (N=10) is ≥25%. 6 The density increased by more than 20%, reaching ≥99.8%.

[0054] (3) This invention optimizes the fatigue performance and plasticity of additively manufactured pure titanium parts, which can meet the high-cycle fatigue requirements of aircraft landing gear, engine brackets, etc., and reduce the risk of intraoperative fracture of implants in the biomedical field. Attached Figure Description

[0055] Figure 1 This is a process flow diagram for the additive manufacturing of pure titanium parts according to the present invention.

[0056] Figure 2 This is a temperature change diagram of the cyclic heat treatment stage in Embodiment 1 of the present invention;

[0057] Figure 3 This is a microstructure diagram of the blank obtained in Example 1 of the present invention;

[0058] Figure 4 This is a microstructure diagram of the blank obtained in Embodiment 1 of the present invention after the first stage of heat treatment;

[0059] Figure 5 The image shows the microstructure of the blank obtained in Embodiment 1 of the present invention after undergoing a first-stage heat treatment and a second-stage heat treatment.

[0060] Figure 6 This is a comparison chart of the stress-strain curves of the blank (line A), the blank after the first stage of heat treatment (line B), and the blank after the first stage of heat treatment and the second stage of heat treatment (line C) obtained in Embodiment 1 of the present invention. Detailed Implementation

[0061] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0062] In this invention, room temperature refers to 25±5℃.

[0063] Example 1

[0064] Reference Figure 1 and Figure 2 As shown, a process for manufacturing pure titanium parts by additive manufacturing includes the following steps:

[0065] (1) Data processing

[0066] 1) Model Design: Create a 3D model of the pure titanium part using 3D model design software and generate an STL file; the tensile test specimen size refers to the specimen size specified in ASTM E8 / E8M Standard Test Methods for Tension Testing of Metallic Materials, with a small specimen having a total length of 100mm; the fatigue test specimen size refers to the specimen size specified in GB / T3075-2021 "Metallic Materials Fatigue Testing Axial Force Control Method", with a standard fatigue specimen having a working section length of 20mm; perform geometric compensation design, reserving a margin of 0.2mm in the design.

[0067] 2) Layout and adding supports: Adjust the product placement and printing direction on the corresponding processing platform, and repair the model; after completing the layout, add supports.

[0068] 3) Layered slicing: Import the STL file into the data processing software for layered slicing to generate scan paths.

[0069] 4) Import data: Import the processed data into the processing equipment and wait for processing.

[0070] (2) Laser Powder Bed Melting Additive Manufacturing

[0071] 1) Equipment: Selective laser melting equipment is used.

[0072] 2) Raw materials: Grade TA1G, particle size 15~53μm, hollow powder rate ≤2%, chemical composition meets the requirements of TA1G materials in GB / T3620.1-2016.

[0073] 3) Process parameters: laser power 200W, scanning speed 900mm / s, printing layer thickness 30μm, scanning spacing 0.07mm, laser energy density 105.82J / mm². 3 The scanning process employs a rotational scanning strategy, rotating each layer by 67°, and is conducted under the protection of high-purity argon gas with an oxygen content ≤0.1%.

[0074] 4) Perform laser powder bed melting additive manufacturing to obtain a blank.

[0075] (3) Cyclic heat treatment

[0076] 1) Equipment: A vacuum heat treatment tube furnace is used, with an operating temperature of up to 900℃, a heating rate of ≤180℃ / min, and an ultimate vacuum of 6.67×10⁻⁶. -5 Pa.

[0077] 2) First stage heat treatment (low-temperature stress-relieving cyclic heat treatment):

[0078] ① Place the blank in a vacuum heat treatment tube furnace, start from room temperature, heat to 500℃ at a heating rate of 30℃ / min, hold for 45min, and then cool with the furnace to 400℃.

[0079] ②Starting from 400℃, heat up to 500℃ at a heating rate of 30℃ / min, hold for 45 minutes, and then cool down to 400℃ in the furnace.

[0080] ③Starting from 400℃, heat up to 500℃ at a rate of 30℃ / min, hold for 45 minutes, and then cool down to 400℃ in the furnace.

[0081] 3) Second stage heat treatment (medium-temperature recrystallization cycle heat treatment):

[0082] ①Starting from 400℃, heat up to 800℃ at a heating rate of 50℃ / min, hold for 45 minutes, and then cool down to 100℃ in the furnace.

[0083] ②Starting from 100℃, heat up to 800℃ at a heating rate of 50℃ / min, hold for 45min, cool down to 50℃ in the furnace, and then air cool.

[0084] (4) Remove support: Separate the blank from the support substrate using a wire cutting machine, and then remove the remaining support from the blank using a flat-nose pliers.

[0085] (5) Surface treatment

[0086] 1) Sandblasting: Select alumina with a particle size of 0.08-0.16μm as the sandblasting abrasive, and the working air pressure for sandblasting is 0.5MPa.

[0087] 2) Grinding the support surface: Select 100 grit, 220 grit, 400 grit, and 600 grit sandpaper and grind the support surface from coarse to fine.

[0088] 3) Surface polishing: Roller polishing is used with silicon carbide grinding stone as abrasive and water as solvent. The polishing time is 1 hour. After polishing, the overall thickness is reduced by an average of 200 μm, and pure titanium parts are finally obtained.

[0089] Example 2

[0090] The difference from Example 1 is that in Example 2, the temperature was adjusted from 500°C to 580°C in the low-temperature stress relief cycle stage; and the temperature was adjusted from 800°C to 850°C in the medium-temperature recrystallization cycle stage. The other process conditions are the same as in Example 1.

[0091] This embodiment is mainly intended to investigate whether the holding temperature for low-temperature stress relief and medium-temperature recrystallization during cyclic heat treatment has any adverse effect on the performance of pure titanium parts manufactured by laser powder bed fusion additive manufacturing when the holding temperature reaches the upper limit.

[0092] Example 3

[0093] The difference from Example 1 is that in Example 3, the heating rate was adjusted from 30℃ / min to 50℃ / min in the low-temperature stress relief cycle stage and from 50℃ / min to 150℃ / min in the medium-temperature recrystallization cycle stage. The other process conditions were the same as in Example 1.

[0094] This embodiment is mainly intended to investigate whether the heating rate at low temperature stress relief and medium temperature recrystallization reaches its upper limit during cyclic heat treatment has any adverse effect on the performance of pure titanium parts manufactured by laser powder bed fusion additive manufacturing.

[0095] Comparative Example 1

[0096] The difference from Example 1 is that Comparative Example 1 did not undergo low-temperature stress relief and medium-temperature recrystallization cycle heat treatment, while the other process conditions were the same as those in Example 1.

[0097] This comparative study is primarily intended to investigate the impact of cyclic heat treatment on the performance of pure titanium parts manufactured using laser powder bed fusion additive manufacturing.

[0098] Comparative Example 2

[0099] The difference from Example 1 is that Comparative Example 2 did not undergo low-temperature stress-relief cyclic heat treatment, while the other process conditions were the same as those in Example 1.

[0100] This comparative study is mainly intended to investigate the effect of low-temperature stress-relief cyclic heat treatment on the performance of pure titanium parts manufactured by laser powder bed fusion additive manufacturing.

[0101] Comparative Example 3

[0102] The difference from Example 1 is that Comparative Example 3 did not undergo medium-temperature recrystallization cycle heat treatment, while the other process conditions were the same as in Example 1.

[0103] This comparative study is mainly intended to investigate the effect of medium recrystallization cyclic heat treatment on the performance of pure titanium parts manufactured by laser powder bed fusion additive manufacturing.

[0104] Comparative Example 4

[0105] The difference from Example 1 is that Comparative Example 4 was not surface polished.

[0106] This comparative study is mainly intended to investigate the impact of not performing surface polishing on the performance of pure titanium parts manufactured by laser powder bed fusion additive manufacturing.

[0107] Comparative Example 5

[0108] The difference from Example 1 is that Comparative Example 5 reverses the order of the two stages of the cyclic heat treatment, that is, it first performs medium-temperature recrystallization cyclic heat treatment and then performs low-temperature stress relief cyclic heat treatment, while the other process conditions are the same as those in Example 1.

[0109] This comparative study is mainly intended to investigate the effect of the order of the two stages of cyclic heat treatment on the performance of pure titanium parts manufactured by laser powder bed fusion additive manufacturing.

[0110] Performance testing

[0111] (1) The samples obtained during the preparation process of Example 1 were observed using a ZEISS Axio Imager M2m optical microscope (upright type) and a ZEISS Axio Observer 7m optical microscope (inverted type). The microstructure of the blank obtained by laser powder bed fusion additive manufacturing in step (2) is as follows: Figure 3 As shown; the microstructure of the blank after the first stage of heat treatment is as follows. Figure 4 As shown; the microstructure of the blank after the first stage heat treatment and the second stage heat treatment is as follows. Figure 5 As shown.

[0112] from Figure 3It can be seen that without heat treatment, the microstructure consists of slender strips and needle-like martensite with a small number of micropores.

[0113] from Figure 4 It can be seen that after low-temperature stress-relief cyclic heat treatment, the martensite morphology remained unchanged, and a small number of micropores still existed in the microstructure, but clear subgrain boundaries also appeared.

[0114] from Figure 5 It can be seen that after medium-temperature recrystallization cycle heat treatment, the microstructure is transformed into relatively uniform equiaxed crystals, clean and clear grain boundaries, and the porosity is further reduced.

[0115] Therefore, it can be seen that after the first stage of low-temperature stress-relief cyclic heat treatment, although the temperature is insufficient to trigger recrystallization and the macroscopic morphology of the martensite structure remains unchanged, dislocation rearrangement forms a low-energy subcrystalline structure, subgrain boundaries appear, and the stress distribution within the grains is more uniform, indicating that residual stress is significantly released, reducing the tendency for crack propagation and increasing the elongation after fracture. After the second stage of medium-temperature recrystallization cyclic heat treatment, the martensite structure transforms into an equiaxed structure, the grain size becomes more uniform, the substructure disappears, the grain boundaries become clearer, the resistance to dislocation movement is reduced, and the plasticity is improved. At the same time, high-temperature diffusion promotes the closure or spheroidization of pores, reduces defects, and the random orientation of equiaxed grains makes the mechanical properties tend to be isotropic, which is beneficial to improving fatigue performance.

[0116] (2) Tensile tests were performed on the samples obtained during the preparation process of Example 1. The tensile stress-strain curves of the blank obtained by laser powder bed fusion additive manufacturing in step (2) (line A), the blank after the first stage heat treatment (line B), and the blank after the first stage heat treatment and the second stage heat treatment (line C) were compared. Figure 6 As shown.

[0117] from Figure 6 It can be seen from the following: tensile strength (stress value corresponding to the highest point of the curve): line A is greater than line B is greater than line C; and elongation after fracture (the strain at the fracture point of the curve corresponds to the ductility of the material, that is, the elongation after fracture): line A is less than line B is less than line C.

[0118] (3) The room temperature tensile properties and fatigue limits of the pure titanium parts prepared in Examples 1-3 and Comparative Examples 1-5 are shown in Table 1.

[0119] Table 1

[0120]

[0121]

[0122] As shown in Table 1, the plasticity (elongation after fracture) and fatigue performance of the pure titanium parts obtained in Examples 1-3 of this invention are significantly better than those obtained in Comparative Examples 1-5. This indicates that the first-stage heat treatment and the second-stage heat treatment of this invention have a synergistic effect and are indispensable. Combined with surface polishing, they can significantly improve the plasticity (elongation after fracture) and fatigue performance of additively manufactured pure titanium parts, achieving a balance between strength and plasticity. In addition, the order of the first-stage heat treatment and the second-stage heat treatment of this invention cannot be changed. Reversing the process order will result in insufficient elimination of residual stress in the recrystallization heat treatment stage of the additively manufactured pure titanium material due to the lack of prior stress relief heat treatment. This leads to incomplete recrystallization, a reduced equiaxed crystal ratio, and ultimately, a decrease in elongation after fracture and fatigue limit in the material properties.

[0123] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A process for preparing additively manufactured pure titanium parts, characterized in that, Includes the following steps: Create a 3D model of the pure titanium part and generate an STL file; The STL file is imported into data processing software for layered slicing to generate a scan path. Pure titanium powder was used as the raw material powder for laser powder bed fusion additive manufacturing to obtain a blank; The blank is subjected to heat treatment and surface treatment to obtain the additively manufactured pure titanium part; The heat treatment includes a first stage heat treatment and a second stage heat treatment in sequence. The first stage of heat treatment includes the following steps: 1) heating the blank to 500-580°C at a heating rate of 30°C / min to 50°C / min and holding it at that temperature; 2) cooling it to 400°C in the furnace; steps 1) to 2) constitute one cycle, and the cycle is repeated 3 to 4 times. The second stage of heat treatment includes the following steps: a) heating the blank to 800-850°C at a heating rate of 50°C / min to 150°C / min and holding it at that temperature; b) cooling it to 100°C in the furnace; steps a) to b) constitute one cycle, and the cycle is repeated 2 to 3 times. The surface treatment includes surface polishing.

2. The preparation process according to claim 1, characterized in that, The vacuum degree of the first stage heat treatment is ≤6.67×10⁻⁶. -2 Pa.

3. The preparation process according to claim 1, characterized in that, The vacuum degree of the second stage heat treatment is 2×10 -3 Pa ~ 6.67 × 10 -2 Pa.

4. The preparation process according to claim 1, characterized in that, The pure titanium powder has a particle size ≤100μm; and / or, the hollow powder content of the pure titanium powder is ≤5%.

5. The preparation process according to claim 1, characterized in that, The process parameters for laser powder bed fused additive manufacturing include at least one of the following: laser power of 180–500 W; scanning speed of 600–1200 mm / s; printing layer thickness of 20–40 μm; scanning spacing of 0.06–0.10 mm; and laser energy density of 50–150 J / mm². 3 .

6. The preparation process according to claim 1, characterized in that, The surface treatment also includes sandblasting and / or polishing.

7. The preparation process according to claim 1, characterized in that, When creating the 3D model of the pure titanium part, a machining allowance of 0.2 to 1.0 mm thickness is reserved.

8. The preparation process according to claim 1, characterized in that, The heat preservation time is obtained using the following formula: Where T is the heat preservation time and D is the maximum cross-sectional thickness of the pure titanium part.

9. An additively manufactured pure titanium part, characterized in that, It is prepared using the preparation process described in any one of claims 1-8.

10. The application of the additively manufactured pure titanium part according to claim 9 in the preparation of aerospace components and medical implants.

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