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

Abstract

The invention belongs to the technical field of laser additive manufacturing, and discloses a preparation process for additive manufacturing of a pure titanium part, the pure titanium part and application. The preparation process for additive manufacturing of the pure titanium part comprises the steps that a three-dimensional model diagram of the pure titanium part is created, and an STL file is generated; the STL file is imported into data processing software to be subjected to hierarchical slicing processing, and a scanning path is generated; pure titanium powder is adopted as raw material powder, laser powder bed melting additive manufacturing is carried out, and a blank is obtained; the blank is subjected to heat treatment and surface treatment, and the additive manufacturing pure titanium part is obtained; wherein the heat treatment sequentially comprises first-stage heat treatment and second-stage heat treatment; the surface treatment comprises surface polishing. According to the preparation process for additive manufacturing of the pure titanium part, internal defects can be reduced, grains are refined, residual stress is reduced, and the surface quality is improved, so that the plasticity (elongation after fracture) and the fatigue performance of the pure titanium part are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser additive manufacturing, and particularly relates to a preparation process, a pure titanium part and an application of an additively manufactured pure titanium part. Background Art

[0002] Residual stress, pores and cracks are generated in titanium and titanium alloy parts formed by laser powder bed fusion additive manufacturing due to the rapid solidification process. These defects will significantly reduce the plasticity and fatigue performance of the materials. On the one hand, a suitable heat treatment process is usually selected to improve the problems of uneven microstructure and large residual stress in laser additive manufactured titanium and titanium alloy parts to improve the mechanical properties. On the other hand, the heat treatment processes of pure titanium parts and titanium alloys are different. During the heat treatment of titanium alloys, phase transformations between α-phase and β-phase occur, as well as the precipitation and decomposition of metastable phases, forming a complex microstructure. Through solution and aging treatments, the alloy strength can be significantly improved, and a comprehensive performance of high strength and good plasticity can be obtained; while the microstructure changes in the heat treatment of pure titanium parts are relatively simple, mainly the grain growth and recrystallization processes, which can only eliminate stress or improve the processing performance. There are few available processes for improving the performance of pure titanium parts, and the effects are far less than those of titanium alloys. Currently, the generally recognized effective means for improving the plasticity and fatigue performance of additively manufactured pure titanium parts are mainly hot isostatic pressing, but the cost of hot isostatic pressing equipment is relatively high, the cost of a single piece of equipment ranges from millions to tens of millions, and the daily energy consumption usually requires above 1000 °C and high-pressure argon gas conditions. Small and medium-sized additive manufacturing enterprises generally do not have the ability to assemble hot isostatic pressing equipment, and the practicality and popularization are not high.

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

[0004] The present invention aims to solve at least one of the technical problems existing in the above prior art. For this reason, the present invention provides a preparation process, a pure titanium part and an application of an additively manufactured pure titanium part. The preparation process of the additively manufactured pure titanium part of the present invention can reduce internal defects, refine grains, reduce residual stress and improve the surface quality, thereby significantly improving the plasticity (elongation after fracture) and fatigue performance of the pure titanium part.

[0005] In the first aspect of the present invention, a preparation process of an additively manufactured pure titanium part is provided, including the following steps:

[0006] Create a three-dimensional model diagram of the pure titanium part and generate an STL file;

[0007] Import the STL file into data processing software for layer slicing processing to generate a scanning path;

[0008] Use pure titanium powder as the raw material powder and perform laser powder bed fusion additive manufacturing to obtain a blank;

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

[0010] Among them, the heat treatment sequentially includes a first-stage heat treatment and a second-stage heat treatment;

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

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

[0013] The surface treatment includes surface polishing.

[0014] Specifically, the first-stage heat treatment of the present invention is a low-temperature stress relief cycle, and its temperature range is 500-580°C, slightly higher than the lower limit of stress relief annealing, avoiding the risk of over-high temperature oxidation. The purpose is to eliminate residual stress and interlayer defects. Residual stress mainly comes from rapid solidification and thermal gradient during the additive manufacturing process. These stresses may lead to crack initiation and propagation, affecting fatigue performance. The present invention gradually releases these stresses through multiple cycles of heating and slow cooling, reducing the stress concentration of internal defects, thereby improving fatigue life. Through the first-stage heat treatment of the present invention, the residual tensile stress generated by rapid solidification and thermal gradient during the additive manufacturing process is gradually released, reducing the internal stress concentration. At high temperatures, atomic diffusion blunt the sharp edges of microvoids or lack-of-fusion defects, reducing the risk of crack initiation.

[0015] Specifically, the second-stage heat treatment of the present invention is a medium-temperature recrystallization cycle, and its temperature range is 800-850°C, lower than the β transformation temperature (890°C), avoiding phase transformation. The purpose of recrystallization annealing is to refine grains and homogenize, promote the transformation of columnar grains to equiaxed grains, and at the same time close microvoid defects. The equiaxed grain structure usually has better ductility and uniformity, so it can improve the elongation after fracture. In addition, grain refinement also helps to improve the strength and fatigue performance of the material because fine grains can hinder crack propagation. Through the second-stage heat treatment of the present invention, recrystallization of columnar grains is promoted to form fine equiaxed grains (grain size ≤ 20μm), eliminating the anisotropy of additive manufacturing. Through high-temperature diffusion, pores and lack-of-fusion defects are further closed or spheroidized.

[0016] The first-stage heat treatment and the second-stage heat treatment of the present invention act synergistically and are indispensable; among them, the first-stage heat treatment preferentially eliminates stress and passivates defects, provides a low-stress environment for the recrystallization of the second-stage heat treatment, and avoids the interference of residual stress on grain boundary migration; the second-stage heat treatment reconstructs grains through recrystallization, further closes defects and improves uniformity.

[0017] In some embodiments of the present invention, when the pure titanium part is a thin-walled simple structure with a wall thickness ≤ 10 mm, the cycle period of the first-stage heat treatment is 3 times, and the cycle period of the second-stage heat treatment 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 cycle period of the first-stage heat treatment is 4 times, and the cycle period of the second-stage heat treatment is 3 times.

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

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

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

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

[0023] In some embodiments of the present invention, the pure titanium powder is spherical or approximately spherical particles, and the powder particle size is normally distributed.

[0024] In some embodiments of the present invention, before performing laser powder bed fusion additive manufacturing, it further includes pre-treating the pure titanium powder, that is, drying it in a vacuum (vacuum degree ≤ 6.67×10 -3 Pa) for 1 - 2 h to remove moisture and adsorbed gas, and avoid the generation of pores during the forming process; the drying temperature is 135 - 200 °C.

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

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

[0027]

[0028] where E is the laser energy density (J / mm 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 fusion additive manufacturing adopts a rotational scanning strategy (such as rotating 45° - 67° per layer).

[0030] In some embodiments of the present invention, the laser powder bed fusion additive manufacturing is carried out under the protection of an inert gas (such as argon or helium), and the oxygen content is ≤ 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 sequentially includes sandblasting, polishing, and surface polishing.

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

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

[0035] Specifically, the surface roughness of the surface where supports are added on the additively manufactured pure titanium parts is greater than that of other parts, and special treatment should be carried out on this area. Rough materials (such as sandpapers and grinding heads with different grits) are used to manually or automatically grind the support surface. Be careful during grinding to avoid damaging the geometry of the sample.

[0036] Specifically, the fatigue cracks in additively manufactured pure titanium parts mainly come from the surface. To improve the fatigue performance of additively manufactured pure titanium parts, it is necessary to remove the rough outer layer. For additively manufactured pure titanium parts, vibration polishing or tumbling polishing is generally used in combination with polishing abrasives such as corundum, alumina, silicon carbide, and zirconia. For those with professional equipment, laser polishing technology, electrolytic polishing technology, etc. can also be used. Since the surface defects are the most numerous and have the greatest impact on fatigue performance in the range of 50 - 300 μm from the surface, the polishing process needs to achieve a surface polishing depth of 50 - 300 μm without damaging the geometry of the sample, removing the oxide scale and surface defects of the additively manufactured pure titanium parts.

[0037] In some embodiments of the present invention, a machining allowance with a thickness of 0.2 - 1.0 mm is reserved when creating the three-dimensional model diagram of the pure titanium part. The present invention reserves the machining allowance to compensate for subsequent surface treatment requirements. The machining allowance for thin-walled structures is usually 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 cope with interlayer misalignment and internal pores. When creating the three-dimensional model diagram of the pure titanium part, the present invention consciously makes a compensation design in terms of material thickness to ensure that when the grinding and polishing depth of the final surface polishing during the surface treatment of the titanium part reaches 50 - 300 μm, the geometry of the sample can also be not damaged.

[0038] In some embodiments of the present invention, the holding time is obtained through the following formula:

[0039]

[0040] where T is the holding time and D is the maximum cross-sectional thickness of the pure titanium part.

[0041] Specifically, when D ≤ 25 mm, the holding time T directly takes a fixed value according to the thickness interval in the formula, following the piecewise empirical rule (for example, when D ≤ 3 mm, T corresponds to 25 min).

[0042] When D > 25 mm, taking D = 25 mm corresponding to 60 min as the benchmark, for every 5 mm increase in thickness, the holding time increases by at least 10 min.

[0043] Symbol description: represents rounding up, that is, when it is less than 5 mm, it is calculated as 5 mm.

[0044] Example:

[0045] When D = 26 mm,

[0046] When D = 28 mm,

[0047] When D = 31 mm,

[0048] It can be understood that for non-uniform cross-sections (such as structures with holes or rib plates), the effective thickness of the thickest cross-section should be used as the benchmark, and the local soaking time should be superimposed if necessary.

[0049] In the second aspect of the present invention, an additive manufacturing pure titanium part is provided, which is prepared by the preparation process described in the first aspect of the present invention.

[0050] In the third aspect of the present invention, an application of the additive manufacturing pure titanium part described in the second aspect of the present invention in the preparation of aerospace components and medical implants is provided.

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

[0052] (1) The preparation process of the additive manufacturing pure titanium part of the present invention is based on a conventional vacuum furnace design, without the need for high-pressure or cryogenic equipment (such as hot isostatic pressing or liquid nitrogen forging), with lower costs and easy to promote.

[0053] (2) Through the combination of the first-stage heat treatment (low-temperature stress relief cycle, 500 - 580 °C) and the first-stage heat treatment (medium-temperature recrystallization cycle, 800 - 850 °C), combined with dynamic regulation of furnace cooling, the residual stress and grain structure of the additive manufacturing pure titanium part are optimized in stages. Subsequently, the combined process of surface polishing treatment can significantly improve the plasticity (elongation after fracture) and fatigue performance of the additive manufacturing pure titanium part, taking into account the balance between strength and plasticity; among them, the tensile strength ≥ 500 MPa, the elongation after fracture ≥ 25%, and the fatigue strength (N = 10 6 ) is increased by more than 20%, and the density ≥ 99.8%.

[0054] (3) The present invention optimizes the fatigue performance and plasticity of the additive manufacturing pure titanium part, which can not only meet the high-cycle fatigue requirements of aircraft landing gears, engine brackets, etc., but also reduce the risk of fracture during implantation in the field of biomedical implants. Description of the Drawings

[0055] Figure 1 It is a process flow chart of the preparation process of the additive manufacturing pure titanium part of the present invention;

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

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

[0058] Figure 4 It is a microstructural diagram of the blank obtained in Example 1 of the present invention after the first-stage heat treatment;

[0059] Figure 5 The microstructure diagram after the first-stage heat treatment and the second-stage heat treatment of the blank obtained in Embodiment 1 of the present invention;

[0060] Figure 6 The comparison diagram of stress-strain curves of tensile tests of the blank (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) obtained in Embodiment 1 of the present invention. Detailed implementation manners

[0061] The content of the present invention will be further described in detail through specific embodiments below. The raw materials, reagents or devices used in the embodiments can be obtained from conventional commercial channels or can be obtained by existing technical methods without special instructions. Unless otherwise specified, the test or measurement methods are conventional methods in the art.

[0062] The room temperature in the present invention refers to 25 ± 5°C.

[0063] Embodiment 1

[0064] Referring to Figure 1 and Figure 2 A preparation process of an additive manufacturing pure titanium part includes the following steps:

[0065] (1) Data processing

[0066] 1) Model design: Create a three-dimensional model diagram of the pure titanium part with three-dimensional model design software to generate an STL file; among them, the size of the tensile test piece refers to the specimen size specified in the ASTM E8 / E8M Standard Test Methods for Tension Testing of Metallic Materials standard, a small-size specimen with a total length of 100 mm; the size of the fatigue test piece refers to the specimen size specified in the GB / T 3075-2021 "Metallic Materials-Fatigue Testing-Method of Axial Force Control" standard, and a standard fatigue specimen with a working section length of 20 mm is processed; geometric compensation design is performed, and a margin of 0.2 mm is reserved during design.

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

[0068] 3) Layer slicing: Import the STL file into data processing software for layer slicing processing to generate a scanning path.

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

[0070] (2) Laser powder bed fusion additive manufacturing

[0071] 1) Equipment: Use a selective laser melting equipment.

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

[0073] 3) Process parameters: Laser power is 200W, scanning speed is 900mm / s, printing layer thickness is 30μm, scanning spacing is 0.07mm, laser energy density is 105.82J / mm 3 , adopt a rotational scanning strategy with a rotation of 67° per layer, and carry out under the protection of high - purity argon, with oxygen content ≤ 0.1%.

[0074] 4) Conduct laser powder bed fusion additive manufacturing to obtain a blank.

[0075] (3) Cyclic heat treatment

[0076] 1) Equipment: Use a vacuum heat treatment tube furnace, with a working temperature up to 900°C, heating rate ≤ 180°C / min, and ultimate vacuum of 6.67×10 -5 Pa.

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

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

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

[0080] ③ Start from 400°C, heat up to 500°C at a heating rate of 30°C / min, hold for 45 minutes, and then cool down to 400°C with the furnace.

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

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

[0083] ② Start from 100°C, heat up to 800°C at a heating rate of 50°C / min, hold for 45 minutes, and then cool down to 50°C and then air - cool.

[0084] (4) Removal of support: The blank is separated from the support substrate by a wire cutting device for metals, and then the remaining support on the blank is removed by a parallel-jaw vice tool.

[0085] (5) Surface treatment

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

[0087] 2) Grinding the support surface: Sandpapers with 100 mesh, 220 mesh, 400 mesh, and 600 mesh are selected to grind the support surface from coarse to fine.

[0088] 3) Surface polishing: The tumbling polishing method is adopted, with silicon carbide grinding stones as the abrasive, water as the solvent, and a polishing time of 1 h. After polishing, the overall thickness is reduced by an average of 200 μm, and finally a pure titanium part is obtained.

[0089] Example 2

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

[0091] This example is mainly to study whether there are adverse effects on the performance of the pure titanium parts manufactured by laser powder bed fusion additive manufacturing when the holding temperatures of low-temperature stress relief and medium-temperature recrystallization reach the upper limit during cyclic heat treatment.

[0092] Example 3

[0093] The difference from Example 1 is that in the low-temperature stress relief cycle stage of Example 3, the heating rate of 30 °C / min is adjusted to 50 °C / min; in the medium-temperature recrystallization cycle stage, the heating rate of 50 °C / min is adjusted to 150 °C / min, and the remaining process conditions are the same as those in Example 1.

[0094] This example is mainly to study whether there are adverse effects on the performance of the pure titanium parts manufactured by laser powder bed fusion additive manufacturing when the heating rates of low-temperature stress relief and medium-temperature recrystallization reach the upper limit during cyclic heat treatment.

[0095] Comparative Example 1

[0096] The difference from Example 1 is that in Comparative Example 1, no low-temperature stress relief and medium-temperature recrystallization cyclic heat treatment are carried out, and the remaining process conditions are the same as those in Example 1.

[0097] This comparative example is mainly to study the influence of cyclic heat treatment on the performance of the pure titanium parts manufactured by laser powder bed fusion additive manufacturing.

[0098] Comparative Example 2

[0099] The difference from Example 1 is that in Comparative Example 2, no low-temperature stress relief cyclic heat treatment was carried out, and the remaining process conditions were the same as those in Example 1.

[0100] This comparative example is mainly to study the influence of low-temperature stress relief cyclic heat treatment on the properties of laser powder bed fusion additive manufactured pure titanium parts.

[0101] Comparative Example 3

[0102] The difference from Example 1 is that in Comparative Example 3, no medium-temperature recrystallization cyclic heat treatment was carried out, and the remaining process conditions were the same as those in Example 1.

[0103] This comparative example is mainly to study the influence of medium-temperature recrystallization cyclic heat treatment on the properties of laser powder bed fusion additive manufactured pure titanium parts.

[0104] Comparative Example 4

[0105] The difference from Example 1 is that in Comparative Example 4, no surface polishing was carried out.

[0106] This comparative example is mainly to study the influence of not carrying out surface polishing on the properties of laser powder bed fusion additive manufactured pure titanium parts.

[0107] Comparative Example 5

[0108] The difference from Example 1 is that in Comparative Example 5, the order of the two stages of cyclic heat treatment was reversed, that is, medium-temperature recrystallization cyclic heat treatment was carried out first, and then low-temperature stress relief cyclic heat treatment was carried out, and the remaining process conditions were the same as those in Example 1.

[0109] This comparative example is mainly to study the influence of the order of the two stages of cyclic heat treatment on the properties of laser powder bed fusion additive manufactured pure titanium parts.

[0110] Performance test

[0111] (1) For the samples obtained in the preparation process of Example 1, a ZEISS Axio Imager M2m optical microscope (upright type) and a ZEISS Axio Observer 7m optical microscope (inverted type) were used for observation. Among them, the microstructure of the blank obtained by laser powder bed fusion additive manufacturing in step (2) is as Figure 3 shown; the microstructure of the blank after the first-stage heat treatment is as Figure 4 shown; the microstructure of the blank after the first-stage heat treatment and the second-stage heat treatment is as Figure 5 shown.

[0112] From Figure 3It can be seen that: when no heat treatment is performed, the microstructure presents as slender strips and acicular martensite, with a small amount of microvoids.

[0113] From Figure 4 It can be seen that: after low-temperature stress-relieving cyclic heat treatment, the morphology of martensite remains unchanged, there are still a small amount of microvoids in the microstructure, but clear subgrain boundaries also appear.

[0114] From Figure 5 It can be seen that: after medium-temperature recrystallization cyclic heat treatment, the microstructure is transformed into relatively uniform equiaxed grains, with clean and distinct grain boundaries, and the pores are further reduced.

[0115] It can be known from this that: after the first-stage low-temperature stress-relieving cyclic heat treatment, although the temperature is not high enough to trigger recrystallization and the macroscopic morphology of the martensite structure remains unchanged, dislocation rearrangement forms a low-energy subgrain structure, subgrain boundaries appear, and the stress distribution inside the grains is more uniform, indicating that the residual stress is significantly released, the crack propagation tendency is reduced, and the elongation after fracture is increased. After the second-stage medium-temperature recrystallization cyclic heat treatment, the martensite structure is transformed into an equiaxed structure, the grain size is homogenized, the substructure disappears, the grain boundaries are clear, 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, the defects are reduced, and the random orientation of equiaxed grains makes the mechanical properties tend to be isotropic, which is beneficial to improving the fatigue performance.

[0116] (2) Tensile tests were carried out on the specimens obtained during the preparation process of Example 1. The stress-strain curves of the tensile tests of the blank (Line A) obtained by laser powder bed fusion additive manufacturing in step (2), 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) are compared as Figure 6 shown.

[0117] From Figure 6 it can be seen that: the tensile strength (the stress value corresponding to the highest point of the curve): Line A > Line B > Line C, and the 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 < Line B < 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 can be seen from Table 1, the plasticity (elongation after fracture) and fatigue performance of the pure titanium parts prepared in Examples 1-3 of the present invention are significantly better than those of the pure titanium parts prepared in Comparative Examples 1-5; it shows that the first-stage heat treatment and the second-stage heat treatment of the present invention have a synergistic effect and are indispensable. At the same time, combined with surface polishing, the plasticity (elongation after fracture) and fatigue performance of the additively manufactured pure titanium parts can be significantly improved, taking into account the balance between strength and plasticity. In addition, the order of the first-stage heat treatment and the second-stage heat treatment of the present invention cannot be changed. The reversal of the process order will cause the additively manufactured pure titanium material to have insufficient residual stress elimination during the recrystallization heat treatment stage because the stress relief heat treatment is not performed first, resulting in incomplete recrystallization and a decrease in the equiaxed crystal ratio. Finally, the elongation after fracture and the fatigue limit are reduced in terms of the material properties.

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

Claims

1. A preparation process for an additive manufacturing pure titanium part, characterized in that, It includes the following steps: Create a 3D model diagram of the pure titanium part and generate an STL file; Import the STL file into data processing software for layer slicing to generate a scanning path; Use pure titanium powder as the raw material powder and perform laser powder bed fusion additive manufacturing to obtain a blank; Perform heat treatment and surface treatment on the blank to obtain the additive manufactured pure titanium part; Among them, the heat treatment sequentially includes a first-stage heat treatment and a second-stage heat treatment; The first-stage heat treatment includes the steps: 1) Raise the temperature of the blank to 500 - 580°C at a heating rate of 30°C / min to 50°C / min and hold for heat preservation; 2) Cool down to 400°C in the furnace; Steps 1) - 2) are one cycle period, and repeat 3 - 4 cycle periods; The second-stage heat treatment includes the steps: a) Raise the temperature of the blank to 800 - 850°C at a heating rate of 50°C / min to 150°C / min and hold for heat preservation; b) Cool down to 100°C in the furnace; Steps a) - b) are one cycle period, and repeat 2 - 3 cycle periods; 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 ≤ 6.67×10 -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 to 6.67×10 -2 Pa.

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

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

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

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

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

9. An additive manufacturing pure titanium part, characterized in that, Prepared by using the preparation process described in any one of claims 1 - 8.

10. Application of the additive manufactured pure titanium part according to claim 9 in the preparation of aerospace components and medical implants.

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