A method for controlling oxygen element in LPBF additive manufacturing of Ti-O materials

Abstract

This invention relates to a method for controlling oxygen content in Ti-O materials manufactured using powder bed fusion additive manufacturing. Using CP-Ti spherical powder and TiO2 nanopowder as raw materials, and based on a target oxygen content design, the precise mixing ratio of CP-Ti powder and TiO2 nanopowder is calculated, taking into account the oxygen content in both CP-Ti and TiO2 raw materials as well as the oxygen increment during the additive manufacturing process. The calculated ratio of CP-Ti powder and TiO2 nanopowder is then uniformly mixed using a vacuum short-time ball milling method, ensuring that the TiO2 nanopowder adheres uniformly to the surface of the CP-Ti spherical powder without compromising the sphericity of the CP-Ti powder. The Ti-O material manufactured using laser or electron beam powder bed fusion additive manufacturing is then uniformly diffuse-annealed in a vacuum at 300–750°C for 60–720 min, allowing for complete decomposition of TiO2 and uniform solidification of oxygen in the Ti matrix. This invention shows promising application prospects for precisely controlling the oxygen content and distribution in additively manufactured Ti-O materials and for the industrial production of novel Ti-O alloy medical materials.

Description

Technical Field

[0001] This invention belongs to the field of medical titanium alloy preparation, specifically relating to a method for controlling oxygen element in LPBF additive manufacturing Ti-O materials. Background Technology

[0002] Commercial pure titanium (CP-Ti) is currently the most widely used medical implant material, exhibiting excellent biocompatibility. However, its overall mechanical properties are poor, making it prone to catastrophic fracture during use. Ti-O alloys, prepared by introducing interstitial oxygen atoms into the CP-Ti matrix and utilizing the oxygen atom solid solution strengthening mechanism, can effectively improve the strength of titanium-based materials while maintaining their biocompatibility. However, too low an oxygen content in the titanium matrix has limited effect on improving the material's strength, while introducing excessive oxygen leads to a significant decrease in the material's plasticity. Reference 1 reports that introducing low oxygen content (0.082–0.268 wt.%) into CP-Ti materials prepared by suspension melting only increased the yield strength of the prepared Ti-O material from 280 MPa to 400 MPa, but the elongation decreased only slightly. Reference 2 prepared Ti-O materials with oxygen content ranging from 0.21 to 1.23 wt.% using powder metallurgy. The ultimate strength increased from 609 MPa to 1182 MPa with increasing oxygen content, but the elongation decreased from 26.9% to 4.2%. Since medical implants operate under dynamic loads within the human body for extended periods, they require both high strength and resistance to microcrack propagation. Therefore, the preparation of novel Ti-O alloy materials necessitates precise control of the oxygen content and its uniform distribution to ensure good strength and ductility.

[0003] However, existing research on dissolved oxygen-reinforced titanium-based materials mainly relies on vacuum arc melting or powder metallurgy methods, followed by machining for further shaping. For example, Reference 3 proposes a method for preparing oxygen-containing titanium alloys or oxygen-containing zirconium alloys, which involves mixing metal oxides and alloy raw materials, pressing and welding them into electrode blocks, and then preparing the alloy material through arc melting under vacuum or inert gas conditions. Reference 4 proposes a powder metallurgy sintering method for oxygen-containing titanium-based alloys, which involves pre-oxidizing titanium powder in a high-temperature oxygen atmosphere to obtain oxygen-containing titanium-based powder, and then sintering it into a bulk material in a hot-pressing or plasma sintering furnace. However, due to the high work hardening rate and relatively poor thermal conductivity of titanium-based materials, the traditional methods for forming α-Ti-based materials present problems such as difficulties in cutting and plastic processing, severe heat accumulation in localized deformation areas, and easy contamination of the material. Especially for Ti-O materials, the dissolved oxygen atoms significantly increase the strength and work hardening rate, making plastic processing even more difficult, which limits the application of Ti-O materials in the manufacture of medical implants.

[0004] Powder bed fusion (PBF) technology is an additive manufacturing method that uses a high-energy laser beam (LPBF) or electron beam powder bed fusion (EBPBF) as a heat source to scan metal powder within a micro-region on a powder bed according to a set trajectory. This process involves layer-by-layer powder deposition and cumulative melting-solidification to prepare bulk metal materials. Compared to traditional equal-material or subtractive manufacturing methods, the forming process of BPF additive manufacturing is easier to control, and the resulting materials have finer and more uniform microstructures. PBF additive manufacturing can be used to prepare powder-reinforced titanium-based materials. However, due to the high chemical reactivity of Ti, titanium-based powder reacts with residual oxygen in the ambient atmosphere during the PBF additive manufacturing process, leading to an increase in the oxygen content of the material, which is detrimental to the precise control of the oxygen content. Furthermore, PBF additive manufacturing requires high powder sphericity; mixed reinforcing phase powders can affect the flowability of the powder bed during the forming process, thus reducing the quality of the formed material. Furthermore, in the Ti-O alloy system, oxygen needs to be dissolved into the interstitial spaces of the Ti matrix as interstitial atoms to improve the material's strength without significantly reducing its plasticity. Additive manufacturing processes using lasers or electron beams as heat sources are characterized by rapid melting and solidification. However, preparing Ti-O materials using additive manufacturing methods presents challenges such as incomplete decomposition of TiO2 powder and uneven distribution of dissolved oxygen, which negatively impacts the strengthening and toughening effect of dissolved oxygen atoms on the titanium-based material. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the above-mentioned PBF additive manufacturing Ti-O material preparation technology by providing a method for controlling the oxygen element in LPBF additive manufacturing Ti-O materials. Using CP-Ti spherical powder and TiO2 nanopowder as raw materials, based on the oxygen content design target in the Ti-O material, and comprehensively considering the oxygen content in CP-Ti and TiO2 raw materials as well as the oxygen increment during the material forming process, the mixing ratio of CP-Ti powder and TiO2 nanopowder is calculated to achieve precise control of the oxygen content in the Ti-O material. By short-time ball milling of the powders configured according to the calculated ratio under vacuum conditions, while ensuring the sphericity of the CP-Ti powder, the TiO2 nanopowder is uniformly adhered to the surface of the CP-Ti powder, thereby ensuring the flowability of the mixed powder. The PBF additively manufactured Ti-O material is post-treated by vacuum stress relief and homogenization annealing to fully decompose TiO2 and uniformly dissolve oxygen in the Ti matrix, thereby achieving control of the oxygen distribution in the Ti-O material. This invention is of great significance for precisely controlling the oxygen content and distribution in additively manufactured Ti-O materials and improving the mechanical properties of Ti-O materials.

[0006] To achieve the above objectives, the technical solution of this invention is: a method for controlling oxygen element in LPBF additive manufacturing of Ti-O materials. Using CP-Ti spherical powder and TiO2 nanopowder as raw materials, based on the oxygen content design target, and comprehensively considering the oxygen content in CP-Ti and TiO2 raw materials as well as the oxygen increment during the additive manufacturing process, the precise mixing ratio of CP-Ti powder and TiO2 nanopowder is calculated. The CP-Ti powder and TiO2 nanopowder, configured according to the calculated ratio, are uniformly mixed using a vacuum short-time ball milling method, ensuring that the TiO2 nanopowder adheres uniformly to the surface of the CP-Ti spherical powder without damaging the sphericity of the CP-Ti powder. For Ti-O materials prepared by LPBF or EPBF additive manufacturing, stress is further removed from the formed Ti-O material through stress relief and homogenization annealing under vacuum conditions, promoting complete decomposition and uniform solid solution of the TiO2 powder, thereby achieving uniform control of oxygen element distribution in the prepared Ti-O material.

[0007] In one embodiment of the present invention, the CP-Ti spherical powder is a spherical powder prepared by gas atomization method, with a powder particle size of 15~53 μm; the TiO2 nanopowder is a layered nanoscale powder with an average size of 20 nm.

[0008] In one embodiment of the present invention, the formula for calculating the precise ratio of CP-Ti powder and TiO2 nanopowder mixture is as follows:

[0009]

[0010] Where, w(O) Ti-O % represents the target oxygen content in the designed Ti-O material, w(O) CP-Ti The percentage represents the oxygen content in the CP-Ti powder used, w(O). TiO2 % represents the oxygen content in the TiO2 powder used, and Δm(O) is the increase in oxygen content of the material during LPBF additive manufacturing, which is obtained by measuring the increase in oxygen in pure Ti material during additive manufacturing.

[0011] In one embodiment of the present invention, the vacuum short-time ball milling method uniformly mixes CP-Ti powder and TiO2 nanopowder configured according to a calculated ratio, and ensures that TiO2 nanopowder uniformly adheres to the surface of the CP-Ti spherical powder without damaging the sphericity of CP-Ti. Specifically, the method involves uniformly mixing CP-Ti powder and TiO2 powder configured according to the oxygen content design target under vacuum conditions through a short-time ball milling process. To ensure that the morphology of the CP-Ti spherical powder is not damaged during the ball milling process and that the TiO2 powder and CP-Ti powder can be uniformly mixed, the ball-to-powder ratio, the planetary ball mill rotation speed, and the ball milling time in the ball milling process parameters are controlled.

[0012] In one embodiment of the present invention, the ball-to-material ratio is 1:1 to 5:1, the rotation speed of the planetary ball mill is 50 to 400 rpm, the ball milling time is 1 to 5 h, and the vacuum degree inside the tank is maintained at ≤0.1 Pa during the ball milling process.

[0013] In one embodiment of the present invention, the ball-to-material ratio is 3:1, the rotation speed of the planetary ball mill is 120 rpm, and the ball milling time is 3 hours.

[0014] In one embodiment of the present invention, the Ti-O material prepared by LPBF additive manufacturing is obtained by melting CP-Ti / TiO2 mixed powder and obtaining Ti-O material molded parts under vacuum or high-purity argon atmosphere protection conditions.

[0015] In one embodiment of the present invention, the specific process of further removing stress from the formed Ti-O material through stress relief and homogenization annealing under vacuum conditions is as follows:

[0016] First, the Ti-O material formed by LBPF is sealed using a vacuum quartz sealing machine, with a sealing vacuum degree requirement of ≤10. -3 Pa;

[0017] Then, the vacuum-sealed Ti-O material is placed in a box-type heat treatment furnace for stress-relief annealing. The annealing temperature range is 300~650℃, the holding time is 15~240 min, and the cooling method is furnace cooling.

[0018] Finally, the stress-relief annealed Ti-O material was placed in a box-type heat treatment furnace for homogenization annealing. The annealing temperature range was 500~750 ℃, the time was 60~720 min, and the cooling method was water cooling.

[0019] In one embodiment of the present invention, the stress-relief annealing temperature is 400°C and the holding time is 60 min; the homogenization annealing temperature is 600°C and the holding time is 120 min.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) Based on the design target of oxygen content in Ti-O material, this invention patent solution comprehensively considers the oxygen content in CP-Ti and TiO2 raw materials and the oxygen increment in the material forming process, and proposes a calculation method for the configuration ratio of CP-Ti powder and TiO2 powder, thereby realizing the precise control of oxygen content in PBF additive manufacturing Ti-O material.

[0022] (2) The present invention uses CP-Ti spherical powder and lamellar TiO2 nanopowder prepared by gas atomization as raw materials. The CP-Ti / TiO2 mixed powder obtained by short-time ball milling under vacuum conditions can maintain good sphericity, and the TiO2 nanopowder on the surface is uniformly adhered to the surface of the CP-Ti spherical powder, which will not affect the flowability of the powder bed in the PBF additive manufacturing process, and effectively ensures the quality of Ti-O materials manufactured by PBF additive manufacturing.

[0023] (3) In this invention, the patented solution addresses the rapid melting and solidification process characteristics of LPBF additive manufacturing. It employs a post-treatment method of vacuum low-temperature stress-relief annealing followed by high-temperature homogenization annealing. This method eliminates residual stress in the formed Ti-O material, promotes the complete decomposition of TiO2 powder and the solid solution of oxygen, and achieves uniform control of oxygen distribution and improved mechanical strength in LPBF-manufactured Ti-O materials. The heat-treated LBPF-formed Ti-0.2O, Ti-0.4O, and Ti-0.6 exhibit tensile strengths of 801 MPa, 933 MPa, and 958 MPa, respectively, with elongations of 13%, 11%, and 7%, respectively, all demonstrating high mechanical strength and good plasticity. Attached Figure Description

[0024] Figure 1 This is the main technical process for controlling the oxygen content and distribution in the BPF-formed Ti-O material in this invention.

[0025] Figure 2 This is a comparison between the actual oxygen content and the target oxygen content of the Ti-O material obtained by the oxygen element regulation method in this invention.

[0026] Figure 3 The following are the surface morphology and oxygen distribution characteristics of the powder mixed by vacuum ball milling in this invention example: (a) surface morphology of CP-Ti / TiO2 powder after mixing; (b) TiO2 particle distribution on the surface of CP-Ti powder after mixing; (c) oxygen distribution on the surface of CP-Ti powder after mixing.

[0027] Figure 4 This refers to the Ti-O bulk material manufactured using LPBF forming in this embodiment of the invention.

[0028] Figure 5 This is a comparison of the X-ray diffraction characteristic spectra of TiO2 powder and LPBF-formed Ti-O bulk material in the examples of this invention.

[0029] Figure 6 This invention relates to a vacuum heat treatment process for LPBF-formed Ti-O bulk materials.

[0030] Figure 7 The LPBF-formed Ti-0.6O material block in this invention, which is subjected to stress relief and homogenization annealing treatment, shows: (a) metallographic structure; (b) cross-sectional morphology; and (c) oxygen distribution characteristics.

[0031] Figure 8 The tensile properties of LPBF-formed Ti-0.2O, Ti-0.4O, and Ti-0.6O materials subjected to stress relief and homogenization annealing in the examples of this invention are shown. Detailed Implementation

[0032] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0033] The preparation of Ti-O materials using powder bed fusion additive manufacturing (PBF) presents challenges in controlling the oxygen content and achieving uniform oxygen solution. In view of these shortcomings, the technical problem this invention aims to solve is how to adjust the oxygen content and distribution in Ti-O materials manufactured using PBF forming, thereby obtaining high-strength Ti-O alloy materials that meet the design target oxygen content requirements and exhibit uniform oxygen solution distribution.

[0034] like Figure 1 As shown, the key technical feature of this invention for controlling the oxygen content and distribution in Ti-O materials manufactured using PBF lies in:

[0035] (1) Using CP-Ti powder with good sphericity and nano-sized TiO2 powder as raw materials, when configuring the ratio of CP-Ti powder and TiO2 nano powder, the amount of oxygen added to Ti-O material during the additive manufacturing process is considered, so as to achieve accurate control of oxygen content in the formed Ti-O material.

[0036] (2) By performing short-time planetary ball milling on the prepared CP-Ti spherical powder and TiO2 nano powder under vacuum conditions, a CP-Ti / TiO2 mixed powder with TiO2 nano powder uniformly adhered to the surface is obtained without affecting the sphericity of the CP-Ti powder, thereby ensuring the flowability of the powder bed in the process of additive manufacturing Ti-O materials.

[0037] (3) For Ti-O materials prepared by additive manufacturing with LPBF or EPBF, stress in the shaped Ti-O material is further removed by stress relief and homogenization annealing under vacuum conditions, which promotes the complete decomposition and uniform solid solution of TiO2 powder, thereby achieving uniform control of oxygen distribution in the prepared Ti-O material and thus obtaining high-strength Ti-O material.

[0038] In this invention, a certain proportion of CP-Ti powder and TiO2 powder are uniformly mixed using a planetary ball mill. Under vacuum or high-purity argon atmosphere protection, the CP-Ti / TiO2 mixed powder is melted using the LPBF manufacturing method to obtain a Ti-O material molded part. Due to the high chemical reactivity of Ti, the CP-Ti / TiO2 mixed powder reacts with residual oxygen in the ambient atmosphere during the molding process, leading to an increase in the oxygen content of the material. Therefore, when designing the mass percentage of TiO2 powder added to the CP-Ti / TiO2 mixed powder, this invention requires comprehensive consideration of the oxygen content in both the CP-Ti powder and TiO2 powder raw materials, as well as the increase in oxygen in the titanium-based material during the melt molding process. The calculation formula is as follows:

[0039]

[0040] Where, w(O) Ti-O % represents the target oxygen content in the designed Ti-O material, w(O) CP-Ti The percentage represents the oxygen content in the CP-Ti powder used, w(O). TiO2The percentage represents the oxygen content in the TiO2 powder used, and Δm(O) is the increase in oxygen content during the LPBF manufacturing process of the titanium-based material, which can be obtained by measuring the increase in oxygen in the pure Ti material produced by additive manufacturing. Table 1 shows the preparation of Ti-O materials using the LPBF additive manufacturing method. The titanium alloy powder used was CP-Ti powder, with a measured oxygen content of 0.06 wt.%; the TiO2 powder used had a purity of 99.9% and a measured oxygen content of 40.07 wt.%; the oxygen increment during the titanium-based material forming process was (0.14 ± 0.02) wt.%. In a preferred embodiment of the present invention, the designed oxygen content targets for the Ti-O material are 0.20 wt.%, 0.40 wt.%, and 0.60 wt.%, respectively. The calculated required TiO2 proportions are 0%, 0.499%, and 0.998%, respectively. The measured oxygen content in the actual formed Ti-O material is 0.226 wt.%, 0.453 wt.%, and 0.624 wt.%, respectively. Figure 2 As shown, the oxygen element regulation method for preparing Ti-O materials by LPBF proposed in this invention is basically consistent with the design goal, indicating that the oxygen element content in Ti-O materials can be accurately regulated through this method.

[0041] Table 1: Elemental composition (wt. %) of CP-Ti powder, TiO2 nanopowder raw materials, and LPBF-formed Ti-0.2O, Ti-0.4O, and Ti-0.6O material blocks used in the examples of this invention.

[0042]

[0043] To ensure the uniformity and flowability of the CP-Ti and TiO2 mixed powder, the present invention uses spherical CP-Ti powder prepared by gas atomization, with a particle size of 15-53 μm and good sphericity; the TiO2 used is a layered nanoparticle powder with an average size of 20 nm, exhibiting high surface energy and good adhesion. The surface morphology of the spherical CP-Ti powder and TiO2 nanoparticles used in the present invention is as follows: Figure 2 As shown,

[0044] This invention utilizes a vacuum planetary ball milling method to uniformly mix CP-Ti and TiO2 powders, configured according to a target oxygen content, under vacuum conditions for a short time. To ensure the spherical morphology of the CP-Ti powder is not damaged during milling and that the TiO2 powder and CP-Ti powder are mixed uniformly, the ball-to-powder ratio (mass ratio of grinding balls to added powder), the planetary ball mill rotation speed, and the milling time need to be controlled. In this invention, the ball-to-powder ratio is 1:1 to 5:1, the planetary ball mill rotation speed is 50 to 400 rpm, the milling time is 1 to 5 hours, and the vacuum level inside the mill is maintained at ≤0.1 Pa during milling. In a preferred embodiment of this invention, the ball-to-powder ratio is 3:1, the planetary ball mill rotation speed is 120 rpm, and the milling time is 3 hours. Figure 3 As shown, the CP-Ti / TiO2 mixed powder obtained by vacuum ball milling has good sphericity, and TiO2 nanoparticles are uniformly adhered to the surface of the CP-Ti spherical powder, indicating that the mixed powder still has good flowability and will not affect the powder bed quality in the subsequent additive manufacturing process.

[0045] This invention employs an LPBF additive manufacturing method to directly obtain Ti-O materials. For example... Figure 4 As shown, in a preferred embodiment of the present invention, the Ti-O bulk material prepared by the LPBF additive manufacturing method using a laser beam as a heat source achieves a density of over 99% as measured by the Archimedes method, exhibiting excellent density. Figure 5 As shown, by comparing the diffraction patterns of the Ti-O material bulk formed by LPBF and TiO2 powder through X-ray diffraction phase analysis, it was found that the diffraction peaks of TiO2 disappeared in the diffraction pattern, indicating that the TiO2 powder underwent thermal decomposition during the forming process.

[0046] This invention employs a post-treatment method of vacuum stress-relief annealing followed by homogenization annealing to further control the residual stress and oxygen distribution in LPBF-formed Ti-O materials. This ensures uniform microstructure and complete decomposition of TiO2 powder in the rapidly solidified Ti-O materials manufactured via LPBF. The heat treatment process for Ti-O materials described in this invention is as follows: Figure 6 As shown. First, the Ti-O material formed by LBPF is sealed using a vacuum quartz tube sealing machine, with a sealing vacuum degree requirement of ≤10. -3Pa; then, the vacuum-sealed Ti-O material is placed in a box-type heat treatment furnace for stress-relief annealing. The annealing temperature range is 300~650℃, the holding time is 15~240 min, and the cooling method is furnace cooling. Finally, the stress-relief annealed Ti-O material is placed in a box-type heat treatment furnace for homogenization annealing. The annealing temperature range is 500~750℃, the time is 60~720 min, and the cooling method is water cooling. In a preferred embodiment of the first embodiment of this invention, the stress-relief annealing temperature is 400℃, the holding time is 60 min; the homogenization annealing temperature is 600℃, and the holding time is 120 min. Figure 7 As shown, the LPBF-formed Ti-O material after heat treatment exhibits a fine microstructure and uniform oxygen distribution in its cross-sectional morphology, indicating that the TiO2 in the prepared Ti-O material has undergone sufficient decomposition, and the oxygen element can be uniformly dissolved in the titanium matrix. Figure 8 As shown, the tensile strengths of heat-treated LPBF-formed Ti-0.2O, Ti-0.4O and Ti-0.6 reached 801 MPa, 933 MPa and 958 MPa, respectively, and the elongations were 13%, 11% and 7%, respectively, all of which have high mechanical strength and good plasticity.

[0047] The method for controlling oxygen element in LPBF additive manufacturing Ti-O materials involved in this invention is used as follows:

[0048] (1) Calculate the proportion of raw materials

[0049] First, targeting the oxygen content in Ti-O materials, the oxygen content of CP-Ti and TiO2 raw materials was measured using the measured oxygen content in CP-Ti and TiO2 raw materials and the oxygen increment value obtained from LPBF-formed pure titanium samples. This allowed for precise control of the oxygen content in PBF additive manufacturing of Ti-O materials. The proportion of TiO2 raw material added to the CP-Ti powder was determined by the following formula: Calculations were performed. In a preferred embodiment of the first scheme of the present invention, the design targets for the oxygen content of the Ti-O material were 0.20 wt.%, 0.40 wt.%, and 0.60 wt.%, respectively. The calculated required proportions of TiO2 to be added were 0%, 0.499%, and 0.998%, respectively. The measured values ​​of oxygen in the actual formed Ti-O material were 0.226 wt.%, 0.453 wt.%, and 0.624 wt.%, respectively, with an error of (0.035 ± 0.014) wt.% compared to the design oxygen content of the material.

[0050] (2) Short-time ball milling for powder mixing

[0051] Secondly, addressing the powder morphology requirements of the PBF manufacturing method, CP-Ti spherical powder and lamellar TiO2 nanoparticles prepared by gas atomization are used as raw materials. The powders, prepared in a specific ratio, are placed in a vacuum ball mill jar, grinding balls are added, and the air inside the jar is evacuated to ≤0.1 Pa using a vacuum pump. The jar is then placed in a planetary ball mill for short-time vacuum ball milling. This ensures that the CP-Ti spherical powder morphology is not damaged, while allowing the TiO2 nanoparticles to uniformly adhere to the surface of the CP-Ti spherical powder. This guarantees that the mixed powder still has good flowability and does not affect the powder bed quality in subsequent additive manufacturing processes. In a preferred embodiment of this invention, the gas-atomized CP-Ti spherical powder has a particle size of 15~53 μm, and the lamellar TiO2 nanoparticles have an average size of approximately 20 nm. Furthermore, the planetary ball mill rotates at 120 rpm, the mass ratio of grinding balls to added powder (i.e., the ball-to-powder ratio) is 3:1, and the milling time is 3 hours. The CP-Ti / TiO2 mixed powder obtained by vacuum ball milling has good sphericity, and TiO2 nanoparticles are uniformly adhered to the surface of the CP-Ti spherical powder.

[0052] (3) Powder bed melt additive manufacturing

[0053] Next, the proportionally proportioned CP-Ti / TiO2 mixed powder was melt-formed using the LPBF method to prepare Ti-O bulk materials. In a preferred embodiment of the present invention, Ti-0.2O, Ti-0.4O, and Ti-0.6O bulk materials were prepared using the LPBF additive manufacturing method, and the density of the final bulk materials, measured by the Archimedes method, all reached over 99%.

[0054] (4) Heat treatment process scheme for forming materials

[0055] Finally, to address the release of residual stress and the homogenization of oxygen distribution in the Ti-O material, after the formed Ti-O material is removed from the substrate, it is further subjected to post-treatment under vacuum conditions through stress relief and homogenization annealing to remove residual stress and promote complete decomposition and homogenized solid solution of TiO2. In a preferred embodiment of the present invention, the formed Ti-O bulk material is first encapsulated in a high vacuum (≤10) using a vacuum quartz tube sealing machine. -3The Ti-O material was placed in a quartz tube (Pa) and then placed in a box-type heat treatment furnace. The temperature was raised to 400℃ and held for 60 minutes, followed by furnace cooling to eliminate residual stress in the material structure. Finally, the stress-relieved Ti-O material was further heated to 600℃ and held for 120 minutes, then water-cooled to room temperature to promote the decomposition and solid solution of TiO2 particles, resulting in a uniformly structured, fully dissolved and dispersed oxygen-containing LPBF additive manufacturing high-strength Ti-O material. The heat-treated LBPF-formed Ti-0.2O, Ti-0.4O, and Ti-0.6 materials achieved tensile strengths of 801 MPa, 933 MPa, and 958 MPa, respectively, with elongations of 13%, 11%, and 7%, all exhibiting high mechanical strength and good plasticity.

[0056] References:

[0057] [1]KANG DS, LEE KJ, KWON EP, et al. Variation of work hardeningrate by oxygen contents in pure titanium alloy [J]. Materials Science and Engineering: A, 2015, 632:120-126.

[0058] [2] K. Kondoh, Titanium Powder, Titanium Material, and Method for Producing Titanium Powder Containing Solid-Soluted Oxygen, 2016. USPatent20160332233A1

[0059] [3] Liu Riping, Zhang Xing, Zhou Yinian, et al. A method for preparing oxygen-containing titanium alloy or oxygen-containing zirconium alloy [P]. Hebei: CN108265197A, 2018-07-10.

[0060] [4] Xiao Daihong. A powder metallurgy preparation method for oxygen-containing titanium-based alloys [P]. Hunan Province: CN103572084B, 2015-08-12.

[0061] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for controlling oxygen element in LPBF additive manufacturing of Ti-O materials, characterized in that, Using CP-Ti spherical powder and TiO2 nanopowder as raw materials, and based on the oxygen content design target, the precise mixing ratio of CP-Ti spherical powder and TiO2 nanopowder was calculated, taking into account the oxygen content in both CP-Ti and TiO2 raw materials as well as the oxygen increment during the additive manufacturing process. The CP-Ti spherical powder and TiO2 nanopowder, prepared according to the calculated ratio, were uniformly mixed using a vacuum short-time ball milling method, ensuring that the TiO2 nanopowder adhered uniformly to the surface of the CP-Ti spherical powder without compromising the sphericity of the CP-Ti powder. Under vacuum or high-purity argon atmosphere protection, the CP-Ti / TiO2 mixed powder was melted using the LPBF additive manufacturing method to obtain Ti-O material forming parts. Stress relief and homogenization annealing post-treatment under vacuum conditions were used to remove stress from the formed Ti-O material, promoting complete decomposition and uniform solid solution of the TiO2 nanopowder, thus achieving uniform control of the oxygen distribution in the prepared Ti-O material. The formula for calculating the precise mixing ratio of CP-Ti spherical powder and TiO2 nanopowder is as follows: Where, w(O) Ti-O % represents the target oxygen content in the designed Ti-O material, w(O) CP-Ti The percentage represents the oxygen content in the CP-Ti spherical powder used, w(O). TiO2 % represents the oxygen content in the TiO2 nanopowder used, and Δm(O) is the increase in oxygen content of the material during LPBF additive manufacturing, which is obtained by measuring the increase in oxygen element in pure Ti material during additive manufacturing.

2. The method for controlling oxygen element in LPBF additive manufacturing of Ti-O materials according to claim 1, characterized in that, CP-Ti spherical powder is a spherical powder prepared by gas atomization, with a particle size of 15~53 μm; TiO2 nanopowder is a layered nanoscale powder with an average size of 20 nm.

3. The method for controlling oxygen element in LPBF additive manufacturing of Ti-O materials according to claim 1, characterized in that, The vacuum short-time ball milling method uniformly mixes CP-Ti spherical powder and TiO2 nanopowder configured according to a calculated ratio, ensuring that TiO2 nanopowder adheres uniformly to the surface of the CP-Ti spherical powder without damaging the sphericity of the CP-Ti. Specifically, the method involves uniformly mixing CP-Ti spherical powder and TiO2 nanopowder configured according to the oxygen content design target under vacuum conditions for a short time using a vacuum planetary ball milling method. To ensure that the morphology of the CP-Ti spherical powder is not damaged during the ball milling process and that the TiO2 nanopowder and CP-Ti spherical powder are uniformly mixed, the ball-to-powder ratio (i.e., the mass ratio of grinding balls to added powder), the planetary ball mill rotation speed, and the ball milling time are controlled in the ball milling process parameters.

4. The method for controlling oxygen element in LPBF additive manufacturing of Ti-O materials according to claim 3, characterized in that, The ball-to-material ratio is 1:1 to 5:1, the rotation speed of the planetary ball mill is 50 to 400 rpm, the ball milling time is 1 to 5 hours, and the vacuum degree inside the tank is maintained at ≤0.1 Pa during the ball milling process.

5. The method for controlling oxygen element in LPBF additive manufacturing of Ti-O materials according to claim 4, characterized in that, The ball-to-material ratio was 3:1, the planetary ball mill speed was 120 rpm, and the milling time was 3 hours.

6. The method for controlling oxygen element in LPBF additive manufacturing of Ti-O materials according to claim 1, characterized in that, The stress removal process for the formed Ti-O material through stress relief and homogenization annealing under vacuum conditions is as follows: First, the Ti-O material formed by LBPF is sealed using a vacuum quartz sealing machine, with a sealing vacuum degree requirement of ≤10. -3 Pa; Then, the vacuum-sealed Ti-O material is placed in a box-type heat treatment furnace for stress-relief annealing. The annealing temperature range is 300~650℃, the holding time is 15~240 min, and the cooling method is furnace cooling. Finally, the stress-relief annealed Ti-O material was placed in a box-type heat treatment furnace for homogenization annealing. The annealing temperature range was 500~750 ℃, the time was 60~720 min, and the cooling method was water cooling.

7. The method for controlling oxygen element in LPBF additive manufacturing of Ti-O materials according to claim 6, characterized in that, The stress-relief annealing temperature was 400℃ and the holding time was 60 min; the homogenization annealing temperature was 600℃ and the holding time was 120 min.

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