Hot isostatic pressing forming method for preparing substrate for additive manufacturing by mixing SS-PREP and EIGA Ti6Al4V ELI spherical powder

Abstract

The invention belongs to the field of metal powder hot isostatic pressing and additive manufacturing near-net forming, and discloses a hot isostatic pressing forming method for preparing a substrate for additive manufacturing by mixing SS-PREP and EIGA Ti6Al4V ELI spherical powder, which comprises the following steps of: 1, mixing Ti6Al4V ELI powder prepared by SS-PREP and Ti6Al4V ELI powder prepared by EIGA according to a proportion under atmosphere protection; 2, in vacuum vibration powder loading equipment, the mixed powder is loaded into a steel sheath, and degassing seal welding is carried out; step 3, placing the seal-welded sheath in hot isostatic pressing equipment, carrying out heat preservation and pressure maintaining sintering forming, and then carrying out gradient cooling; and 4, after cooling, the steel sheath is removed through machining, and the large-size substrate for additive manufacturing is obtained. The prepared substrate has excellent comprehensive mechanical properties which are higher than the level of traditional forgings, and the application requirements of additive manufacturing are met.

Description

Technical Field

[0001] The present invention belongs to the fields of hot isostatic pressing of metal powders and near-net shaping by additive manufacturing, and particularly relates to a hot isostatic pressing forming method for preparing a substrate for additive manufacturing by mixing spherical powders of SS-PREP (ultra-high speed plasma rotating electrode) and EIGA (electrode induction gas atomization) Ti6Al4V ELI (a low interstitial element titanium alloy, belonging to the α-β type titanium alloy, widely used in the aerospace, medical device and industrial fields), and is particularly suitable for preparing large-sized Ti6Al4V ELI substrates for industrial-grade metal additive manufacturing. Background Art

[0002] Metal additive manufacturing technology heats metal powders above the melting point, stacks them layer by layer and rapidly solidifies them into parts with complex shapes, mainly including selective laser melting forming, laser powder feeding forming, electron beam selective melting forming, etc. For additive manufacturing of titanium alloy parts, the above three technologies all require a substrate with high flatness, matching thermal expansion coefficient with the forming material and a certain thickness as the base to achieve metallurgical bonding with the part.

[0003] Currently, industrial-grade large-sized titanium alloy substrates are usually prepared by traditional processes such as forging, rolling and casting. Among them, in the forging process, in order to ensure the fatigue resistance and high-temperature stability of the substrate, the substrate needs to withstand high residual stress and repeated thermal cycles (heating - cooling). However, repeated thermal cycles have thermal fatigue, which easily causes the interface stress to exceed the yield strength of the titanium alloy, and there is a tendency to generate microcracks (especially in thin-walled structures), thus shortening the service life of the substrate. Existing industrial-grade substrates usually only support 20 to 50 printing cycles. In the rolling process, the mechanical properties are anisotropic. Specifically, the properties in the rolling direction and the non-rolling direction are significantly different, and it is difficult to process thick plates. Internal stress is likely to occur in hot-rolled thick plates and annealing treatment is required.

[0004] In addition, it is difficult to control the uniform heating and thermal deformation of large-sized substrates prepared by the above traditional methods such as forging and rolling, resulting in a temperature difference between the edge and the center exceeding 100~150°C. The edge of the substrate bends upward due to stress concentration, affecting the accuracy of subsequent printed layers. The typical deformation amount can reach 0.5~2 mm / m. In addition, the difference in internal stress will also cause the fatigue life of the printed part to decrease by 20% to 30%.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The object of the present invention is to overcome the above-mentioned drawbacks of the prior art and propose a hot isostatic pressing forming method for preparing a substrate for additive manufacturing by mixing SS-PREP and EIGA Ti6Al4V ELI spherical powders. Through process optimization, this method achieves multiple objectives of stress control, efficiency improvement, and cost reduction, providing a more economical and reliable technical solution for the industrial production of titanium alloy substrates.

[0007] To achieve the above object, the present invention adopts the following technical solutions: On the one hand, the present invention provides a hot isostatic pressing forming method for preparing a substrate for additive manufacturing by mixing SS-PREP and EIGA Ti6Al4V ELI spherical powders, comprising the following steps: Step 1: Mix the Ti6Al4V ELI powder prepared by SS-PREP and the Ti6Al4V ELI powder prepared by EIGA in a set ratio under atmosphere protection to obtain a mixed powder; Step 2: In a vacuum vibration powder loading device, load the mixed powder into a sleeve adapted to the structure of the to-be-prepared Ti6Al4V ELI substrate, and perform degassing and sealing welding treatments; Step 3: Place the sleeve after the sealing welding treatment in a hot isostatic pressing device, perform heat preservation and pressure holding sintering forming, and then cool down with a gradient; Step 4: After cooling, remove the sleeve by machining to obtain a large-sized Ti6Al4V ELI substrate.

[0008] Further, in Step 1, the Ti6Al4V ELI powder prepared by SS-PREP has a particle size of 53 - 250 μm, a sphericity > 95%, a fluidity < 25 s / 50 g, a hollow powder ratio < 0.5%, a tapped density > 2.9 g / cm 3 , and an oxygen content of 600 - 800 ppm; the Ti6Al4V ELI powder prepared by EIGA has a particle size of 53 - 250 μm, a sphericity > 85%, a fluidity < 35 s / 50 g, a hollow powder ratio < 1%, a tapped density > 2.8 g / cm 3 , and an oxygen content of 800 - 1300 ppm.

[0009] Further, in Step 1, the atmosphere is 99.999% argon.

[0010] Further, in Step 1, the set ratio is a mass ratio of 1:1; during the mixing process, the single mixing weight is 100 - 1000 kg, the rotation speed is 15 - 20 r / min, and the time is 2 - 4 h.

[0011] Further, in step 1, the sphericity of the mixed powder > 90%, the fluidity < 30 s / 50 g, the hollow powder rate ranges from 0.25% to 0.75%, and the tapped density > 2.8 g / cm 3 , and the oxygen content ranges from 700 to 1050 ppm.

[0012] Further, in step 2, the powder loading vacuum < 10 -3 Pa, the powder loading temperature is 400 - 450 °C, and degassing treatment is carried out after heat preservation for 2 - 3 h.

[0013] Further, in step 3, during the isothermal and isostatic pressure sintering and forming process, the heating rate is 10 °C / min, the isothermal temperature is 920 - 950 °C, the isostatic pressure is 150 MPa, and the isothermal and isostatic pressure time is 2 - 4 h.

[0014] Further, in step 3, during the gradient cooling process, in the first stage of gradient cooling, the cooling rate is 8 - 10 °C / min to reduce the temperature from the HIP (hot isostatic pressing) temperature to 900 °C; in the second stage of gradient cooling, the cooling rate is 5 - 8 °C / min to reduce the temperature from 900 °C to 800 °C; in the third stage of gradient cooling, the cooling rate is 3 - 5 °C / min to reduce the temperature from 800 °C to 600 °C; in the fourth stage of gradient cooling, the cooling rate is 1 - 3 °C / min to reduce the temperature from 600 °C to 300 °C; in the fifth stage of gradient cooling, natural cooling is used to reduce the temperature from 300 °C to room temperature.

[0015] Further, for the Ti6Al4V ELI substrate obtained in step 4, its oxygen content is 800 - 1300 ppm, the tensile strength > 920 MPa, the yield strength > 850 MPa, the elongation > 12%, the reduction of area > 40%, the fracture toughness > 100 MPa·mˆ1 / 2, the hardness > 35 HRC, and the relative density > 99.99%.

[0016] On the other hand, the present invention provides an application of a Ti6Al4V ELI substrate prepared by a hot isostatic pressing forming method for preparing a substrate for additive manufacturing as described above in additive manufacturing of titanium alloy parts.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1) Through innovative raw material systems and forming processes, the present invention mixes the Ti6Al4VELI spherical powders prepared by the SS-PREP and EIGA processes in a specific ratio to form a composite raw material system with complementary properties. Through the hot isostatic pressing near-net-shape forming process, relying on the combined action of particle approaching and rearrangement mechanisms, plastic deformation mechanisms, and diffusion creep mechanisms, it is finally formed into a large-sized Ti6Al4V ELI substrate. This solves the problems that repeated thermal cycles in traditional processes tend to cause microcracks in the substrate, thereby shortening the service life of the substrate, and that it is difficult to control uniform heating and thermal deformation when preparing large-sized substrates by traditional processes, resulting in warping deformation due to stress concentration at the edges. The method of the present invention can effectively improve material utilization rate, save the R & D and production cycle, enhance tissue uniformity, and at the same time eliminate the differences in mechanical properties in different directions of the substrate, providing a new technical path with both reliability and economy for the industrial preparation of high-performance large-sized titanium alloy substrates.

[0018] 2) The present invention mixes the spherical powders prepared by the SS-PREP and EIGA processes in proportion, realizing precise control of the powder properties. The hollow powder rate of the powder is adjusted to 0.25% - 0.75%, and the oxygen content is adjusted to 700 - 1050 ppm, thereby giving play to the excellent fracture toughness and plasticity of the SS-PREP Ti6Al4V ELI powder parts and the excellent strength and hardness of the EIGA Ti6Al4V ELI powder parts; it breaks through the bottlenecks such as insufficient comprehensive performance, low utilization rate, and limited application scenarios existing in the preparation of 53 - 250μm coarse-grained Ti6Al4V ELI titanium alloy powders by traditional atomization processes. Further, through the hot isostatic pressing forming process of the mixed powder, it is applied to the preparation of large-sized substrates in the field of additive manufacturing, significantly improving the comprehensive mechanical properties of the substrates, and providing a new path for the low-cost and high-efficiency production of high-performance large-sized titanium alloy substrates.

[0019] 3) The present invention uses powders in the 53 - 250μm particle size range to replace powders in the 15 - 53μm particle size range as raw materials. Through the dual paths of raw material cost optimization and process technology innovation, while ensuring the high performance of the substrate, it significantly reduces the raw material consumption cost and maximizes economic benefits. Specifically, the selection of larger particle size powders can directly reduce the raw material cost. At the same time, combined with targeted process optimization, it avoids performance losses caused by particle size differences, and finally achieves the efficient coordination of low-cost raw materials and high-performance substrate preparation.

[0020] 4) The present invention innovatively adopts a gradient cooling method after the hot isostatic pressing process, which can reduce the residual stress of the Ti6Al4V ELI substrate by 40% - 60%. Compared with traditional forgings, it eliminates the stress relief annealing process, reduces manufacturing costs and shortens the production cycle. At the same time, the prepared substrate has excellent comprehensive mechanical properties, higher than the forging level, meeting the application requirements of additive manufacturing. Brief Description of the Drawings

[0021] The drawings herein are incorporated into and form a part of this specification, and are used together with the specification to explain the principles of the present invention.

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 Schematic flow chart of the hot isostatic pressing forming method for preparing the substrate for additive manufacturing of the present invention; Figure 2 Scanning photo of the ultra-high speed plasma rotating electrode SS-PREP Ti6Al4V ELI powder of the present invention; Figure 3 Scanning photo of the electrode induction gas atomization EIGA Ti6Al4V ELI powder of the present invention; Figure 4 Scanning photo after mixing the ultra-high speed plasma rotating electrode SS-PREP and the electrode induction gas atomization EIGA Ti6Al4VELI powder of the present invention; Figure 5 Metallographic structure photo of the hot isostatic pressing substrate of the Ti6Al4V ELI mixed powder in Example 1; Figure 6 Physical photo of the hot isostatic pressing substrate of the 1Ti6Al4V ELI mixed powder of the present invention; Figure 7 Metallographic structure photo of the hot isostatic pressing substrate of the Ti6Al4V ELI mixed powder in Example 2; Figure 8 Metallographic structure photo of the hot isostatic pressing substrate of the Ti6Al4V ELI mixed powder in Example 3. Detailed Description of the Embodiments

[0024] Here, the exemplary embodiments will be described in detail. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. On the contrary, they are only examples consistent with some aspects of the present invention detailed in the appended claims.

[0025] On the one hand, please refer to Figure 1 , the present invention provides a hot isostatic pressing forming method for preparing a substrate for additive manufacturing by mixing SS-PREP and EIGA Ti6Al4V ELI spherical powders, including the following steps: Step 1: Mix the Ti6Al4V ELI spherical powder prepared by SS-PREP and the Ti6Al4V ELI spherical powder prepared by EIGA in a mass ratio of 1:1 under the protection of 99.999% argon using a double-cone mixer to obtain a mixed powder. Specifically, as Figure 2 shown, the particle size of the Ti6Al4V ELI spherical powder prepared by the SS-PREP process is 53 - 250 μm, the sphericity > 95%, the fluidity < 25 s / 50 g, the hollow powder rate < 0.5%, and the tapped density > 2.9 g / cm 3 , and the oxygen content is 600 - 800 ppm; as Figure 3 shown, the particle size of the Ti6Al4V ELI spherical powder prepared by EIGA is 53 - 250 μm, the sphericity > 85%, the fluidity < 35 s / 50 g, the hollow powder rate < 1%, and the tapped density > 2.8 g / cm 3 , and the oxygen content is 800 - 1300 ppm.

[0026] Mix the two powders. The single mixing weight is 100 - 1000 kg, the rotation speed is 15 - 20 r / min, and the time is 2 - 4 h.

[0027] It should be noted that although metal spherical powders have good fluidity, they are prone to segregation. Therefore, it is particularly crucial to select a suitable mixing equipment and optimize the mixing parameters (to avoid overmixing). The double-cone mixer selected in the present invention, combined with the above mixing method, can ensure the uniformity of the final powder, and thus ensure the composition consistency, microstructure uniformity, and reliability of the mechanical properties, physical properties, and overall quality of the final product.

[0028] As Figure 4 shown, after uniform mixing, the sphericity of the mixed powder > 90%, the fluidity < 30 s / 50 g, the hollow powder rate is between 0.25% - 0.75%, the tapped density > 2.8 g / cm 3 , and the oxygen content is between 700 - 1050 ppm.

[0029] It should be noted that when preparing large-sized Ti6Al4V ELI substrates using the HIP process, the optimized parameters after the Ti6Al4V ELI powder is evenly mixed can significantly improve the process efficiency and product performance. Specifically, appropriate sphericity and reasonable fluidity ensure that the powder is tightly filled and evenly distributed in the cladding, avoiding stress concentration or deformation during the HIP process caused by local packing differences. At the same time, it supports near-net shaping of complex shapes and reduces subsequent machining costs. In addition, a lower hollow powder rate can eliminate potential internal pore hazards from the source. Combining with the high tapped density characteristics, it significantly reduces the pressure and holding time required for HIP densification (the cycle can be shortened by 15% - 20%), enabling the relative density of the substrate to exceed 99.9%, with almost no residual pores, thereby improving the ultrasonic inspection qualification rate to the ASTM B311 Class A standard (defects < 200μm), and having relatively low costs at the same time. Strictly controlled oxygen content (700 - 1050ppm) inhibits the coarsening of the α phase under the high-temperature and high-pressure (920 - 950°C / 150MPa) process window, ensuring that the substrate meets aerospace-grade mechanical properties: tensile strength ≥ 920MPa, elongation ≥ 12% (meeting the AMS 4928 standard), and the fatigue life is improved compared to conventional powders. As can be seen from the above, the synergistic effect of the parameters of the mixed powder in the present invention not only optimizes the economic efficiency of the HIP process (yield > 98%, material utilization rate increased by 30%), but also endows the Ti6Al4V ELI substrate with excellent reliability.

[0030] Step 2: In a vacuum vibration powder loading device, load the mixed powder into a steel cladding adapted to the structure of the substrate to be prepared, and perform degassing and sealing welding treatments; Specifically, the powder loading vacuum degree < 10 -3 Pa, the powder loading temperature is 400 - 450°C, and after holding for 2 - 3h, degassing treatment is carried out.

[0031] The vacuum vibration powder loading device is a powder loading device that can continuously load powder into a vibrating cladding in a high-vacuum environment, which belongs to the prior art and will not be elaborated here.

[0032] It should be noted that the core reason for choosing a steel cladding in the HIP process is that its comprehensive performance perfectly matches the strict requirements of this technology for high-temperature and high-pressure environments, while taking into account process reliability and economy. Steel (especially stainless steel) maintains excellent high-temperature strength and creep resistance under the HIP process, effectively resisting plastic deformation or rupture caused by high-pressure gas, while light metals (such as titanium and aluminum) or ceramics are prone to softening collapse or brittle cracking under such conditions. The ductility of steel enables it to achieve high airtightness sealing through welding, completely isolating the contact between the pressure medium (argon gas) and the powder, avoiding contamination of the workpiece. At the same time, its thermal expansion coefficient (about 12 - 18×10 -6 / °C) is relatively close to that of common metal powders (such as TC4 titanium alloy: 8.6 - 9.5×10 -6 / °C), significantly reducing the residual stress caused by shrinkage differences during the cooling stage and ensuring the geometric accuracy and internal integrity of the workpiece. In addition, the steel can be made into complex-shaped jackets through mature processing technologies (welding, spinning), supporting near-net forming, and the cost is much lower than that of refractory metals such as tantalum and molybdenum. After HIP, it can be efficiently removed by mechanical peeling combined with conventional pickling, avoiding damage to the surface of the workpiece.

[0033] Step 3: Place the jacket after seal welding in a hot isostatic pressing device, perform sintering and forming under constant temperature and pressure, and then cool down with a gradient. Specifically, during the sintering and forming process under constant temperature and pressure, the heating rate is 10°C / min, the holding temperature is 920 - 950°C, the holding pressure is 150 MPa, and the holding time under constant temperature and pressure is 2 - 4 h.

[0034] It should be noted that the heating rate of 10°C / min is adopted in the present invention to avoid premature sintering of the surface layer of the mixed powder particles to form closed pores due to rapid thermal shock in the HIP process, and at the same time reduce the temperature gradient caused by the low thermal conductivity of the titanium alloy (about 7 W / m·K), providing a uniform thermal field for subsequent densification. The holding temperature is set in the α+β two-phase region of 920 - 950°C, which not only utilizes the high diffusion rate of the β phase (body-centered cubic) to accelerate atomic migration, but also inhibits grain coarsening by pinning the grain boundaries with the α phase (hexagonal close-packed), obtaining a fine-grained equiaxed structure (grain < 20 μm) while achieving pore closure. Applying a high pressure of 150 MPa far exceeds the yield strength of TC4 at 900°C (≈20 MPa), crushing the particle gaps and potential hollow powders through forced plastic flow, and increasing the chemical potential of vacancies to make the diffusion densification rate increase by more than 10 times. Setting the holding time under constant temperature and pressure for 2 - 4 h covers three stages of densification: in the initial stage, particle rearrangement eliminates large pores; in the middle stage, volume diffusion closes sub-micron pores; in the final stage, vacancy diffusion eliminates isolated closed pores, and at the same time promotes the uniform distribution of β-stabilizing elements (V, Fe). This parameter set achieves a comprehensive performance with a residual porosity < 0.05% and a tensile strength ≥920 MPa through a thermal activation (diffusion)-force-driven (plastic)-time synergistic mechanism, providing a high-reliability substrate for aerospace components.

[0035] Further, during the gradient cooling process, in the first stage of gradient cooling, the temperature is reduced from the HIP temperature to 900 °C at a cooling rate of 8 - 10 °C / min. The rapid cooling to 900 °C is to reduce the high-temperature residence time, inhibit the coarsening of β grains, and at the same time avoid the thickening of the oxide layer caused by slow cooling; in the second stage of gradient cooling, the temperature is reduced from 900 °C to 800 °C at a cooling rate of 5 - 8 °C / min. Slowing down the cooling rate can reduce the phase transformation driving force, make the precipitation of α phase more uniform, and reduce the stress concentration caused by local volume change; in the third stage of gradient cooling, the temperature is reduced from 800 °C to 600 °C at a cooling rate of 3 - 5 °C / min. Slowly cooling in the α + β two-phase region promotes the uniformity of phase transformation and reduces the microstructure stress; in the fourth stage of gradient cooling, the temperature is reduced from 600 °C to 300 °C at a cooling rate of 1 - 3 °C / min. Further reducing the cooling rate in the low-temperature region allows the residual stress to be released through plastic deformation and diffusion mechanisms; in the fifth stage of gradient cooling, natural cooling is carried out from 300 °C to room temperature, relying on natural heat dissipation of the environment to ensure the overall temperature uniformity and prevent the residual tensile stress caused by sudden surface cooling.

[0036] Step 4: After cooling, the jacket is removed by machining to obtain a large-sized Ti6Al4V ELI substrate. Among them, for the Ti6Al4V ELI substrate obtained in Step 4, its oxygen content is 800 - 1300 ppm, the tensile strength > 920 MPa, the yield strength > 850 MPa, the elongation > 12%, the reduction of area > 40%, the fracture toughness > 100 MPa·mˆ1 / 2, the hardness > 35 HRC, and the relative density > 99.99%.

[0037] It should be added that the length of the industrial-grade large-sized Ti6Al4V ELI substrate is not less than 1000 mm, the width is not less than 800 mm, and the thickness is not less than 80 mm.

[0038] On the other hand, the present invention provides an application of a large-sized Ti6Al4V ELI substrate prepared by a hot isostatic pressing forming method for preparing a substrate for additive manufacturing as described above in additive manufacturing of titanium alloy parts, such as in the manufacturing of titanium alloy parts by selective laser melting forming, laser powder feeding forming, electron beam selective melting forming, etc.

[0039] In order to further verify the efficacy of the present invention, the inventor conducted the following specific experiments:

[0040] Example 1 This example provides a hot isostatic pressing forming method for preparing a substrate for additive manufacturing by mixing SS-PREP and EIGA Ti6Al4V ELI spherical powders, including the following steps: Step 1: Mix the Ti6Al4V ELI powder prepared by SS-PREP and the Ti6Al4V ELI powder prepared by EIGA in a mass ratio of 1:1 under the protection of 99.999% argon using a double-cone mixer to obtain a mixed powder; Specifically, the Ti6Al4V ELI powder prepared by the SS-PREP process has a particle size of 53 - 250 μm, a sphericity of 96%, a flowability of 24 s / 50 g, a hollow powder ratio of 0.48%, and a tapped density of 2.91 g / cm 3 , and an oxygen content of 600 ppm; The Ti6Al4V ELI powder prepared by the EIGA process has a particle size of 53 - 250 μm, a sphericity of 86%, a flowability of 34 s / 50 g, a hollow powder ratio of 0.98%, and a tapped density of 2.81 g / cm 3 , and an oxygen content of 1300 ppm; Mix the two powders. The single mixing weight is 1000 kg, the time is 4 h, and the rotation speed is 20 r / min; After mixing evenly, the sphericity of the mixed powder is 91%, the flowability is 29 s / 50 g, the hollow powder ratio is 0.73%, the tapped density is 2.86 g / cm 3 , and the oxygen content is 950 ppm.

[0041] Step 2: Load the mixed powder into a rectangular steel jacket in a vacuum vibration powder loading device, and perform degassing and sealing welding treatments; Specifically, the powder loading vacuum is 9×10 -4 Pa, the powder loading temperature is 450 °C, and degassing is performed under the condition of holding for 3 h.

[0042] Step 3: Place the jacket after sealing welding in a hot isostatic pressing device, perform sintering and forming under temperature and pressure holding, and then cool down with a gradient temperature reduction; Specifically, during the sintering and forming process under temperature and pressure holding, the heating rate is 10 °C / min, the holding temperature is 950 °C, the holding pressure is 150 MPa, and the holding time is 4 h; In the first stage of gradient temperature reduction, cool from 950 °C to 900 °C at a cooling rate of 10 °C / min; in the second stage of gradient temperature reduction, cool from 900 °C to 800 °C at a cooling rate of 8 °C / min; in the third stage of gradient temperature reduction, cool from 800 °C to 600 °C at a cooling rate of 5 °C / min; in the fourth stage of gradient temperature reduction, cool from 600 °C to 300 °C at a cooling rate of 3 °C / min; in the fifth stage of gradient temperature reduction, cool naturally from 300 °C to room temperature.

[0043] Step 4: After cooling, machine-process to remove the jacket to obtain a large-sized Ti6Al4V ELI substrate, as shown in Figure 5 and Figure 6 shown; The Ti6Al4V ELI substrate prepared by the method of this embodiment has a length of 1000 mm, a width of 800 mm, and a thickness of 80 mm; the oxygen content is 1100 ppm, the tensile strength is 938 MPa, the yield strength is 876 MPa, the elongation is 14%, the reduction of area is 44%, the fracture toughness is 108 MPa·mˆ1 / 2, the hardness is 35.3 HRC, and the relative density is 99.997%.

[0044] In this embodiment, the life of the Ti6Al4V ELI substrate is 55 printing cycles.

[0045] Example 2

[0046] This embodiment provides a hot isostatic pressing forming method for preparing a substrate for additive manufacturing by mixing SS-PREP and EIGA Ti6Al4V ELI spherical powders, including the following steps: Step 1: Mix the Ti6Al4V ELI powder prepared by SS-PREP and the Ti6Al4V ELI powder prepared by EIGA in a mass ratio of 1:1 under the protection of 99.999% argon gas, and select a double-cone mixer for mixing to obtain mixed powder; Specifically, the particle size of the Ti6Al4V ELI powder prepared by the SS-PREP process is 53~250 μm, the sphericity is 97%, the fluidity is 23 s / 50 g, the hollow powder rate is 0.25%, and the tapped density is 2.92 g / cm 3 , and the oxygen content is 600 ppm; The particle size of the Ti6Al4V ELI powder prepared by the EIGA process is 53~250 μm, the powder sphericity is 87%, the fluidity is 33 s / 50 g, the hollow powder rate is 0.75%, and the tapped density is 2.82 g / cm 3 , and the oxygen content is 800 ppm; Mix the two powders, the single mixing weight is 100 kg, the time is 2 h, and the rotation speed is 15 r / min; After mixing evenly, the sphericity of the mixed powder is 92%, the fluidity is 28 s / 50 g, the hollow powder rate is 0.50%, the tapped density is 2.87 g / cm 3 , and the oxygen content is 700 ppm.

[0047] Step 2: In a vacuum vibration powder loading device, load the mixed powder into a rectangular steel jacket, and perform degassing and sealing welding treatments; Specifically, the powder loading vacuum is 8×10 -4 Pa, the powder loading temperature is 400 °C, and degassing is carried out under the condition of heat preservation for 2 h.

[0048] Step 3: Place the encapsulated sleeve after seal welding in a hot isostatic pressing device, sinter and form it under heat preservation and pressure, and then cool it down with a gradient temperature reduction. Specifically, during the sintering and forming process under heat preservation and pressure, the heating rate is 10 °C / min, the heat preservation temperature is 920 °C, the pressure holding pressure is 150 MPa, and the heat preservation and pressure holding time is 2 h. In the first stage of gradient temperature reduction, cool from 920 °C to 900 °C at a cooling rate of 8 °C / min; in the second stage of gradient temperature reduction, cool from 900 °C to 800 °C at a cooling rate of 5 °C / min; in the third stage of gradient temperature reduction, cool from 800 °C to 600 °C at a cooling rate of 3 °C / min; in the fourth stage of gradient temperature reduction, cool from 600 °C to 300 °C at a cooling rate of 1 °C / min; in the fifth stage of gradient temperature reduction, cool naturally from 300 °C to room temperature.

[0049] Step 4: After cooling, remove the encapsulated sleeve by machining to obtain a large-sized Ti6Al4V ELI substrate, as Figure 7 shown; Specifically, for the Ti6Al4V ELI substrate prepared in this example, its length is 1000 mm, width is 850 mm, and thickness is 100 mm. The oxygen content is 800 ppm, the tensile strength is 930 MPa, the yield strength is 865 MPa, the elongation is 15%, the reduction of area is 46%, the fracture toughness is 110 MPa·mˆ1 / 2, the hardness is 36.6 HRC, and the relative density is 99.998%.

[0050] In this example, the Ti6Al4V ELI substrate has a lifespan of 60 printing cycles.

[0051] Example 3

[0052] This example provides a hot isostatic pressing forming method for preparing a substrate for additive manufacturing by mixing SS-PREP and EIGA Ti6Al4V ELI spherical powders, including the following steps: Step 1: Mix the Ti6Al4V ELI powder prepared by SS-PREP and the Ti6Al4V ELI powder prepared by EIGA in a mass ratio of 1:1 under the protection of 99.999% argon, and use a double-cone mixer to obtain a mixed powder. Specifically, the particle size of the Ti6Al4V ELI powder prepared by the SS-PREP process is 53~250 μm, the sphericity is 98%, the fluidity is 22 s / 50 g, the hollow powder rate is 0.02%, and the tapped density is 2.93 g / cm 3 , and the oxygen content is 800 ppm; The Ti6Al4V ELI powder prepared by the EIGA process has a particle size of 53 - 250 μm, a sphericity of 88%, a flowability of 32 s / 50 g, a hollow powder ratio of 0.52%, and a tapped density of 2.82 g / cm 3 , and the oxygen content is 1300 ppm; Mix the two powders. The single - time mixing weight is 500 kg, the time is 3 h, and the rotation speed is 18 r / min; After uniform mixing, the sphericity of the mixed powder is 93%, the flowability is 27 s / 50 g, the hollow powder ratio is 0.27%, the tapped density is 2.88 g / cm 3 , and the oxygen content is 1050 ppm.

[0053] Step 2: In a vacuum vibration powder - filling device, fill the mixed powder into a rectangular steel - made jacket, and perform degassing and sealing - welding treatments; Specifically, the powder - filling vacuum degree is 7×10 -4 Pa, the powder - filling temperature is 425 °C, and degassing is performed under the condition of keeping warm for 2.5 h.

[0054] Step 3: Place the jacket after sealing - welding treatment in a hot isostatic pressing device, perform sintering and forming under heat preservation and pressure, and then cool down with a gradient temperature drop; Specifically, during the sintering and forming process under heat preservation and pressure, the heating rate is 10 °C / min, the heat - preservation temperature is 935 °C, the pressure - holding pressure is 150 MPa, and the heat - preservation and pressure - holding time is 3 h; In the first stage of gradient temperature drop, cool from 935 °C to 900 °C at a cooling rate of 9 °C / min; in the second stage of gradient temperature drop, cool from 900 °C to 800 °C at a cooling rate of 6.5 °C / min; in the third stage of gradient temperature drop, cool from 800 °C to 600 °C at a cooling rate of 4 °C / min; in the fourth stage of gradient temperature drop, cool from 600 °C to 300 °C at a cooling rate of 2 °C / min; in the fifth stage of gradient temperature drop, cool naturally from 300 °C to room temperature.

[0055] Step 4: After cooling, remove the jacket by machining to obtain a large - size Ti6Al4V ELI substrate, as Figure 8 shown; Specifically, for the Ti6Al4V ELI substrate prepared in this embodiment, its length is 1250 mm, width is 1250 mm, and thickness is 120 mm. The oxygen content is 1300 ppm, the tensile strength is 946 MPa, the yield strength is 887 MPa, the elongation is 14%, the reduction of area is 45%, the fracture toughness is 108 MPa·mˆ1 / 2, the hardness is 36.0 HRC, and the relative density is 99.999%.

[0056] In this embodiment, the life of the Ti6Al4V ELI substrate is 52 printing cycles.

[0057] Comparative Example 1 The preparation process is as follows: Step 1: Select Ti6Al4V ELI powder in the particle size range of 53 - 250 μm prepared by ultra-high speed plasma rotating electrode atomization SS-PREP; Specifically, for the Ti6Al4V ELI powder in the particle size range of 53 - 250 μm prepared by SS-PREP, its sphericity is 96%, fluidity is 21 s / 50 g, the hollow powder ratio is 0.45%, the tapped density is 2.91 g / cm 3 , and the oxygen content is 500 ppm; Step 2: In a vacuum vibration powder loading device, load the SS-PREP powder into a rectangular steel jacket, and perform degassing and sealing welding treatments; The powder loading vacuum degree is 2×10 -2 Pa, the powder loading temperature is 350 °C, and degassing is performed under the condition of keeping warm for 1 h; Step 3: Place the sealed jacket in a hot isostatic pressing device, perform sintering and forming under heat preservation and pressure holding, and then cool with the furnace; Specifically, during the sintering and forming process under heat preservation and pressure holding, the heating rate is 10 °C / min, the heat preservation temperature is 960 °C, the pressure holding pressure is 120 MPa, and the heat preservation time is 1 h; Cool with the furnace to 100 °C, and then air cool from 100 °C to room temperature.

[0058] After cooling, machine-process to remove the steel jacket to obtain a large-sized Ti6Al4V ELI substrate; For the Ti6Al4V ELI substrate prepared by the method of this comparative example, its length is 1000 mm, width is 800 mm, thickness is 80 mm; the oxygen content is 700 ppm, the tensile strength is 873 MPa, the yield strength is 796 MPa, the elongation is 15%, the reduction of area is 50%, the fracture toughness is 113 MPa·mˆ1 / 2, the hardness is 30.0 HRC, and the relative density is 99.997%.

[0059] In this comparative example, the life of the Ti6Al4V ELI substrate is 36 printing cycles.

[0060] Comparative Example 2 The preparation process is as follows: Step 1: Select Ti6Al4V ELI powder in the particle size range of 53 - 250 μm prepared by electrode induction gas atomization EIGA; Specifically, for the Ti6Al4V ELI powder in the particle size range of 53 - 250 μm prepared by EIGA, its sphericity is 87%, fluidity is 33 s / 50 g, the hollow powder ratio is 0.95%, the tapped density is 2.82 g / cm 3 , and the oxygen content is 1200 ppm; Step 2: In a vacuum vibration powder loading device, load the EIGA powder into a rectangular steel jacket, and perform degassing and sealing welding treatments; The powder loading vacuum degree is 3×10 -2 Pa, the powder loading temperature is 500 °C, and degassing is performed under the condition of keeping the temperature for 1 h; Step 3: Place the sealed jacket in a hot isostatic pressing device, perform sintering and forming under temperature and pressure holding, and then cool with the furnace; Specifically, during the sintering and forming process under temperature and pressure holding, the heating rate is 10 °C / min, the temperature holding is 880 °C, the pressure holding is 120 MPa, and the temperature holding time is 1 h; Cool with the furnace to 100 °C, and then air-cool from 100 °C to room temperature.

[0061] After cooling, machine-process to remove the steel jacket to obtain a large-sized Ti6Al4V ELI substrate; The Ti6Al4V ELI substrate prepared by the method of this comparative example has a length of 1000 mm, a width of 1000 mm, and a thickness of 100 mm; the oxygen content is 1450 ppm, the tensile strength is 957 MPa, the yield strength is 889 MPa, the elongation is 8.2%, the reduction of area is 32%, the fracture toughness is 86 MPa·mˆ1 / 2, the hardness is 37.0 HRC, and the relative density is 99.981%.

[0062] In this comparative example, the life of the Ti6Al4V ELI substrate is 31 printing cycles.

[0063] In order to verify the performance of the Ti6Al4V ELI substrates prepared in Examples 1 to 3 and Comparative Examples 1 to 2, refer to the oxygen content "Determination of Oxygen, Nitrogen, and Hydrogen Contents in Titanium and Titanium Alloys" GB / T 4698.7-2019; tensile strength / yield strength / elongation after fracture / reduction of area "Metallic Materials - Tensile Testing at Room Temperature" GB / T 228.1-2021; fracture toughness "Metallic Materials - Plane-Strain Fracture Toughness Testing" GB / T 4161-2022; hardness "Brinell Hardness: Brinell Hardness Testing of Metallic Materials" GB / T 230.1-2018; relative density "Metallographic Method: Quantitative Analysis of Porosity" ASTM E2109-23 standards, and test the above-mentioned examples and comparative examples. The test results are shown in Table 1.

[0064] Table 1 Performance test results of Ti6Al4V ELI substrates prepared in each example and comparative example

[0065] As can be seen from the data in Table 1, the Ti6Al4V ELI substrate prepared by the method of the present invention has excellent comprehensive performance, giving full play to the characteristics of excellent fracture toughness and plasticity of the SS-PREP Ti6Al4V ELI powder parts and excellent strength and hardness of the EIGA Ti6Al4V ELI powder parts.

[0066] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0067] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A hot isostatic pressing forming method for preparing a substrate for additive manufacturing by mixing SS-PREP and EIGA Ti6Al4V ELI spherical powder, characterized in that, It includes the following steps: Step 1: Mix the Ti6Al4V ELI powder prepared by SS-PREP and the Ti6Al4V ELI powder prepared by EIGA in a certain proportion under atmosphere protection to obtain a mixed powder; Step 2: In a vacuum vibration powder loading device, load the mixed powder into a sleeve adapted to the structure of the Ti6Al4V ELI substrate to be prepared, and perform degassing and sealing welding treatments; Step 3: Place the sleeve after sealing welding treatment in a hot isostatic pressing device, carry out sintering and forming under constant temperature and pressure, and then cool down with a gradient temperature reduction; Step 4: After cooling, machine-process to remove the sleeve to obtain a large-sized Ti6Al4V ELI substrate.

2. The hot isostatic pressing forming method according to claim 1, characterized in that, In Step 1, the particle size of the Ti6Al4V ELI powder prepared by SS-PREP is 53 - 250 μm, the sphericity > 95%, the flowability < 25 s / 50 g, the hollow powder rate < 0.5%, the tapped density > 2.9 g / cm 3 , and the oxygen content is 600 - 800 ppm; the particle size of the Ti6Al4V ELI powder prepared by EIGA is 53 - 250 μm, the sphericity > 85%, the flowability < 35 s / 50 g, the hollow powder rate < 1%, the tapped density > 2.8 g / cm 3 , and the oxygen content is 800 - 1300 ppm.

3. The hot isostatic pressing forming method according to claim 1, characterized in that In Step 1, the atmosphere is 99.999% argon.

4. The hot isostatic pressing forming method according to claim 1, characterized in that In Step 1, the set proportion is a mass ratio of 1:1; during the mixing process, the single mixing weight is 100 - 1000 kg, the rotation speed is 15 - 20 r / min, and the time is 2 - 4 h.

5. The hot isostatic pressing forming method according to claim 1, characterized in that, In Step 1, the sphericity of the mixed powder > 90%, the fluidity < 30 s / 50 g, the hollow powder rate ranges from 0.25% to 0.75%, the tapped density > 2.8 g / cm 3 , and the oxygen content ranges from 700 to 1050 ppm.

6. The hot isostatic pressing forming method according to claim 1, wherein In Step 2, the powder loading vacuum degree < 10 - 3 Pa, the powder loading temperature is 400 - 450 °C, and after heat preservation for 2 - 3 h, degassing treatment is carried out.

7. The hot isostatic pressing forming method according to claim 1, wherein, In Step 3, during the sintering and forming process under constant temperature and pressure, the heating rate is 10 °C / min, the holding temperature is 920 - 950 °C, the holding pressure is 150 MPa, and the holding time under constant temperature and pressure is 2 - 4 h.

8. The hot isostatic pressing forming method according to claim 1, characterized in that, In Step 3, during the gradient temperature reduction cooling process, in the first stage of gradient temperature reduction, the cooling rate is 8 - 10 °C / min to reduce the temperature from the HIP temperature to 900 °C; in the second stage of gradient temperature reduction, the cooling rate is 5 - 8 °C / min to reduce the temperature from 900 °C to 800 °C; in the third stage of gradient temperature reduction, the cooling rate is 3 - 5 °C / min to reduce the temperature from 800 °C to 600 °C; in the fourth stage of gradient temperature reduction, the cooling rate is 1 - 3 °C / min to reduce the temperature from 600 °C to 300 °C; in the fifth stage of gradient temperature reduction, it is naturally cooled from 300 °C to room temperature.

9. The hot isostatic pressing forming method according to claim 1, characterized in that, For the Ti6Al4V ELI substrate obtained in Step 4, its oxygen content is 800 - 1300 ppm, the tensile strength > 920 MPa, the yield strength > 850 MPa, the elongation > 12%, the reduction of area > 40%, the fracture toughness > 100 MPa·mˆ1 / 2, the hardness > 35 HRC, and the relative density > 99.99%.

10. Application of a Ti6Al4V ELI substrate prepared by the hot isostatic pressing forming method according to any one of claims 1 - 9 in additive manufacturing of titanium alloy parts.

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