Additive manufacturing of high fatigue strength titanium alloys and methods of making the same

Abstract

This invention relates to the field of titanium alloy materials, specifically to an additive manufacturing method for a high fatigue strength Ti4Mo6Zr2Fe5Cu0.25O alloy and its preparation method. The chemical composition of this titanium alloy, by weight percentage, is: Mo: 3.0–5.0; Zr: 4.0–8.0; Fe: 1.0–3.0; Cu: 3.0–7.0; O: 0.10–0.40; with the balance being Ti. The preparation method of this titanium alloy is as follows: the titanium alloy is prepared using coaxial powder-feed laser additive manufacturing technology, with a laser power between 1500 and 3100 W, a scanning rate between 700 and 1500 mm / min, and an interlayer spacing of 0.4–1.2 mm. The titanium alloy prepared by this invention possesses excellent comprehensive mechanical properties and can be widely used in many important fields such as aerospace, biomedicine, petrochemicals, automotive industry, and marine engineering.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy materials, specifically to an additive manufacturing method for a high fatigue strength Ti4Mo6Zr2Fe5Cu0.25O alloy and its preparation method. Background Technology

[0002] As advanced equipment in the aerospace field, such as new fighter jets and hypersonic vehicles, rapidly advances towards higher speeds, larger sizes, and more integrated and complex structures, there is a growing demand for lightweight, high-strength structural materials with superior overall performance in structural design. For the manufacturing of large, complex high-strength / ultra-high-strength titanium alloy structural components, traditional smelting-forging processes often face numerous challenges, including complex alloy smelting and forming processes, coarse solidification structures in large ingots with severe alloy segregation, high requirements for large forging equipment and molds, difficulties in deformation, and high costs. Therefore, the fabrication of such large, complex structural components is extremely difficult. In contrast, large, complex high-strength / ultra-high-strength titanium alloy components fabricated using near-net-shape additive manufacturing technology offer numerous advantages, including less alloy segregation, higher material utilization, shorter manufacturing cycles, and lower costs. However, the microstructure of additively manufactured titanium alloys inevitably contains defects such as micropores, which significantly reduce the material's fatigue performance, thus hindering its development and application.

[0003] During fatigue, large defects in additively manufactured titanium alloys are equivalent to fatigue crack initiations. The larger the area of ​​the plastic zone at the crack tip, the slower the fatigue crack propagation rate. When the size of the plastic zone at the crack tip exceeds a certain critical size, the fatigue initiation in the additively manufactured titanium alloy can be completely passivated, thereby significantly improving the fatigue strength of the additively manufactured metal. To this end, this invention, through unique alloy composition design and optimization of the additive manufacturing process, enables Fe and Cu elements to be distributed from martensite to the β phase during deposition, significantly increasing the proportion of metastable β phase in the material. The metastable β phase is then used to passivate microcracks in the additively manufactured metal, greatly improving the material's fatigue resistance and bringing new foundations and opportunities for the development of additively manufactured titanium alloys. Summary of the Invention

[0004] This invention provides an additive manufacturing method for a high fatigue strength Ti4Mo6Zr2Fe5Cu0.25O alloy and its preparation method.

[0005] The technical solution of this invention is as follows:

[0006] The key technology of additive manufacturing of high fatigue strength titanium alloy is that the titanium alloy is Ti4Mo6Zr2Fe5Cu0.25O, and the chemical composition of the titanium alloy by weight percentage is: Mo: 3.0~5.0; Zr: 4.0~8.0; Fe: 1.0~3.0; Cu: 3.0~7.0; O: 0.10~0.40; balance Ti.

[0007] A further preferred technical requirement is that, by weight percentage, the chemical composition of the titanium alloy is: Mo: 4.0–4.5; Zr: 6.0–7.0; Fe: 2.0–2.5; Cu: 5.0–6.0; O: 0.25–0.32; with the balance being Ti.

[0008] As can be seen from Table 2, corresponding to the chemical compositions of Examples 5, 6, and 7 in Table 1, Examples 5, 6, and 7 have high mechanical and fatigue properties.

[0009] When quenching from the single β phase region, the critical cooling rate to obtain a fully martensitic structure is less than 30℃ / s, and the temperature M at which the martensitic transformation ends is [missing information]. f The temperature range is 250–500℃. The microstructure is a mixture of martensite and metastable β phase, with a room temperature tensile strength of 1150–1380 MPa, a yield strength of 860–940 MPa, an elongation of 10–20%, and a reduction of area of ​​26–34%. Under a stress ratio of 0.1 and a cycle count of 10... 7 The fatigue limit under these conditions is 850–1100 MPa.

[0010] This invention also relates to a method for preparing high fatigue strength titanium alloys by additive manufacturing as described above, the key technology of which is:

[0011] The high fatigue strength titanium alloy produced by additive manufacturing is Ti4Mo6Zr2Fe5Cu0.25O, and its preparation method meets the requirements: the titanium alloy is prepared by coaxial powder feeding laser additive manufacturing technology, with laser power between 1500 and 3100W, scanning rate between 700 and 1500mm / min, and interlayer spacing between 0.4 and 1.2mm.

[0012] Because the range of compositions to be protected is very large, and different compositions require different additive manufacturing parameters, the aforementioned range varies considerably. Furthermore, due to the different Ms and Mf points of titanium alloys with different compositions, the details of the "quenching and partitioning process" in the subsequent claims also vary significantly, further increasing the range of material properties. These changes are all reflected in the examples and comparative examples in Tables 1 and 2.

[0013] Other preparation details are crucial; claim 2 merely provides an additive manufacturing parameter. The main purpose of this invention is to achieve the quenching and partitioning process of Fe and Cu elements through the subsequent claims, obtaining a "martensite + metastable β-phase structure" with good fatigue performance.

[0014] The preferred technical content of the additive manufacturing method for producing high fatigue strength titanium alloys is as follows:

[0015] When this titanium alloy was prepared using coaxial powder-feed laser additive manufacturing technology, the cooling rate of each thermal cycle during the deposition process was higher than 30°C / s, which caused the formation of martensitic structure in the material.

[0016] When materials are rapidly cooled from the β-phase region to below the Ms point, a martensitic transformation occurs, resulting in the formation of a martensitic microstructure. See [link to specific evidence]. Figure 1 It exhibits typical lath martensite morphology; the final microstructure is martensite + metastable β phase.

[0017] The titanium alloy was deposited on a substrate at 250–500°C using coaxial powder-feed laser additive manufacturing technology.

[0018] When depositing this titanium alloy on a substrate at 250–500°C, the substrate temperature is maintained at the M value of the alloy. s Click below and M f Above a certain point, the martensitic phase transformation is incomplete, and a certain proportion of untransformed β phase is retained in the microstructure.

[0019] The core idea is to draw on the quenching and partitioning concept of steel materials. After holding the steel material in the γ phase region, it is rapidly cooled to between the Ms and Mf points, and then heated again to allow the C element to partition from martensite to austenite, forming martensite + metastable γ phase.

[0020] This invention involves holding the material at a temperature in the β-phase region, then rapidly cooling it to between the Ms and Mf points, followed by reheating. This causes Fe and Cu elements to distribute from martensite to the β-phase, forming a martensite + metastable β-phase microstructure. The advantages of this microstructure are: the martensite ensures high strength, while the metastable β-phase can transform into the α′ phase under strain, exhibiting a TRIP effect that improves the material's ductility and toughness.

[0021] After deposition is complete, the abutment temperature is raised to 700–860℃ and held for 1–9 hours to allow Fe and Cu elements to be distributed from martensite to the untransformed β phase. The stability of the β phase is improved by the eutectoid β-stabilizing elements Fe and Cu.

[0022] Provide attached Figure 1 The purpose is to prove that Cu and Fe undergo partitioning during the deposition process, with Cu and Fe partitioning from martensite into the β phase. Since Cu and Fe are β-stable elements, their partitioning into the β phase will enhance the stability of the β phase.

[0023] After deposition, the substrate temperature is raised to 700-860℃ and held for 1-9 hours, with a holding time greater than t = 2.5Dmin, where D is the effective thickness of the sample in millimeters (mm). After holding, the sample is quenched to room temperature using a 10wt.% NaCl aqueous solution to retain a large amount of metastable β phase in the material.

[0024] The titanium alloy was deposited on a substrate at 320–380°C using coaxial powder-feeding laser additive manufacturing technology.

[0025] The deposition laser power was 2300–2700 W, the scanning rate was 1100–1300 mm / min, and the interlayer spacing was 0.8–1.0 mm. After deposition, the stage temperature was raised to 740–780 °C, held at that temperature for 5–7 hours, and then quenched to room temperature with a 10 wt.% NaCl aqueous solution.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. Unlike existing technologies, the titanium alloy provided by this invention uses a base heating technology in the additive manufacturing process to distribute Fe and Cu elements from martensite to the β phase, thereby increasing the proportion of metastable β phase in the material.

[0028] 2. The method described in this invention can significantly improve the fatigue performance of additively manufactured titanium alloys, at a stress ratio of 0.1 and a cycle count of 10. 7 The fatigue limit under these conditions is 850–1100 MPa.

[0029] 3. The titanium alloy provided by the present invention has good room temperature tensile properties, with a room temperature tensile strength of 1150-1380 MPa and an elongation of 10-20%. Attached Figure Description

[0030] Figure 1 This is one of the microstructures of the additively manufactured high fatigue strength titanium alloy Ti4Mo6Zr2Fe5Cu0.25O described in Example 1;

[0031] Figure 2 This is the second microstructure of the additively manufactured high fatigue strength titanium alloy Ti4Mo6Zr2Fe5Cu0.25O described in Example 1;

[0032] Figure 3 This is the third microstructure of the additively manufactured high fatigue strength titanium alloy Ti4Mo6Zr2Fe5Cu0.25O described in Example 1;

[0033] Figure 4 This is the fourth microstructure of the additively manufactured high fatigue strength titanium alloy Ti4Mo6Zr2Fe5Cu0.25O described in Example 1;

[0034] Figure 5 The fatigue SN curves of the Ti4Mo6Zr2Fe5Cu0.25O alloy with high fatigue performance are shown. Detailed Implementation

[0035] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0036] The chemical composition of the materials involved in each embodiment (1-9) and comparative example (1-10) and the additive manufacturing process are shown in Table 1.

[0037] A novel titanium alloy, Ti4Mo6Zr2Fe5Cu0.25O, has the following composition: Mo: 3.0–5.0; Zr: 4.0–8.0; Fe: 1.0–3.0; Cu: 3.0–7.0; O: 0.10–0.40; with the balance being Ti. The content of impurity elements in the alloy should meet the corresponding requirements in the national standard "Table of Grades and Chemical Compositions of Titanium and Titanium Alloys".

[0038] Please see Figures 1-2 . Figure 1 The TEM microstructure of Ti4Mo6Zr2Fe5Cu0.25O alloy exhibiting high fatigue strength is shown in Figure 5. The TEM image reveals that the microstructure consists of martensite and a metastable β phase.

[0039] Figure 2 The SN curve of Example 6 under a stress ratio of 0.1 is compared with the SN curve of the additively manufactured Ti6Al4V alloy in Comparative Example 10. It can be seen that the titanium alloy material provided by the present invention has superior fatigue performance.

[0040] The present invention will be described and explained below through several specific embodiments and comparative examples, but these should not be used to limit the scope of this application.

[0041] Examples 1-9: These are high fatigue strength Ti4Mo6Zr2Fe5Cu0.25O alloys manufactured using additive manufacturing within the chemical composition range provided by this invention. The contents of Mo, Zr, Fe, Cu, and O elements are progressively increased, and the corresponding preparation process is also appropriately adjusted within the technical parameter range specified in this invention. The dimensions of the prepared bulk nanocrystalline metal material are 120×120×60mm.

[0042] Comparative Examples 1-10: The chemical composition of Comparative Example 1 is lower than the lower limit of the chemical composition range provided by the present invention; the chemical composition of Comparative Example 2 is higher than the upper limit of the chemical composition range provided by the present invention; by comparing with Examples 1 and 9 respectively, the effects of Mo, Zr, Fe, Cu and O content on additive manufacturing of high fatigue strength Ti4Mo6Zr2Fe5Cu0.25O alloy are explained.

[0043] The laser deposition parameters of Comparative Example 3 are lower than the lower limit of the parameters provided by the present invention; the laser deposition parameters of Comparative Example 4 are higher than the upper limit of the parameters provided by the present invention. By comparing with Examples 3 and 4 respectively, the influence of laser deposition parameters on additive manufacturing of high fatigue strength Ti4Mo6Zr2Fe5Cu0.25O alloy is explained.

[0044] Comparative Example 5 showed that the cooling rate of each thermal cycle during laser deposition was lower than the lower limit specified in this invention; by comparing with Example 5, the effect of the cooling rate of each thermal cycle during deposition on the additive manufacturing of high fatigue strength Ti4Mo6Zr2Fe5Cu0.25O alloy was illustrated.

[0045] Comparative Example 6 shows that the temperature of the substrate during laser deposition is lower than the lower limit of the substrate temperature specified in this invention, while Comparative Example 7 shows that the temperature of the substrate during laser deposition is higher than the upper limit of the substrate temperature specified in this invention. By comparing with Examples 6 and 7 respectively, the effect of the substrate temperature during laser deposition on the additive manufacturing of high fatigue strength Ti4Mo6Zr2Fe5Cu0.25O alloy is explained.

[0046] Comparative Example 8 raises the stage temperature to above the upper limit of the temperature specified in this invention after laser deposition, and Comparative Example 9 raises the stage temperature to below the lower limit of the temperature specified in this invention after laser deposition. By comparing with Examples 8 and 9 respectively, the effect of the stage holding temperature after laser deposition on the additive manufacturing of high fatigue strength Ti4Mo6Zr2Fe5Cu0.25O alloy is explained.

[0047] Comparative Example 10 is the Ti6Al4V alloy, which is currently the most widely used in the field of titanium alloy additive manufacturing. By comparing it with Examples 1 to 9 of the present invention, the advantages of the room temperature tensile and fatigue properties of the material provided by the present invention are illustrated.

[0048] Table 1. Chemical composition and additive manufacturing process of the materials used in the examples and comparative examples.

[0049]

[0050]

[0051] 1. Microscopic tissue characterization

[0052] The microstructure of the material was characterized using a Talos F200x transmission electron microscope (TEM). The TEM-tested samples were manually thinned to 50 nm, followed by chemical double-spray thinning in a 10 vol.% HClO4 + 90 vol.% C2H5OH solution. The voltage during thinning was set to 25 V, and the temperature was -25 °C. The experimental results are shown in [Figure number missing]. Figures 1-4 .

[0053] 2. Tensile property test

[0054] The room temperature tensile mechanical properties of the materials in the comparative and example cases were tested using an Instron 8872 tensile testing machine at a tensile rate of 0.5 mm / min. Before testing, the materials were machined into standard tensile specimens with a thread diameter of 10 mm, a gauge length of 5 mm, and a gauge length of 25 mm using a lathe. Three parallel specimens were taken from each group of heat-treated specimens. The mechanical properties obtained from the experiment included tensile strength, yield strength, elongation, and reduction of area. The results are shown in Table 2.

[0055] 3. Fatigue performance test

[0056] The fatigue performance of the embodiments and comparative examples of this invention was tested using an INSTRON 8801 (MTB15816) fatigue testing machine. The test temperature was 23℃, the loading waveform was a sine wave, the loading frequency was 30Hz, and the stress ratio R was 0.1. The specimens were processed according to the dimensions specified in GB / T 3075-2021 "Methods for Controlling Axial Force in Fatigue Testing of Metallic Materials". Standard fatigue specimens with a working section length of 20 mm were tested, and the fatigue limit of the embodiment and comparative materials was tested using the lifting method. The results are shown in […]. Figure 5 Table 2.

[0057] Table 2. Room temperature tensile properties and fatigue limits of the materials in the examples and comparative examples.

[0058]

[0059] As can be seen from the results in Table 2, Examples 1-9 exhibit good room temperature tensile properties and high fatigue limits. Within the range of Mo, Zr, Fe, Cu, and O element contents specified in this invention, as the contents of Mo, Zr, Fe, Cu, and O elements increase, the yield strength, tensile strength, and fatigue limit of the material gradually increase, while the elongation and reduction of area gradually decrease.

[0060] The low content of Mo, Zr, Fe, Cu, and O in Comparative Example 1 resulted in yield strength, tensile strength, and fatigue limit that were significantly lower than those of the embodiments of the present invention. The higher content of Mo, Zr, Fe, Cu, and O in Comparative Example 2 exceeded the upper limit specified in this invention, resulting in higher tensile strength and yield strength, but an elongation of only 2% and a fatigue limit that was also lower than those of the embodiments of the present invention.

[0061] Comparative Example 3 had laser deposition parameters lower than the lower limit specified in this invention, resulting in a less dense deposited sample block with more internal defects. Its room temperature tensile properties and fatigue limit were both lower than those of the embodiments of this invention. Comparative Example 4 had laser deposition parameters higher than the upper limit specified in this invention, resulting in a coarse microstructure in the deposited sample. Its room temperature tensile elongation, reduction of area, and fatigue limit were all lower than those of the embodiments of this invention.

[0062] In Comparative Example 5, the cooling rate of each thermal cycle during laser deposition was lower than the lower limit specified in this invention, which resulted in the absence of martensite in the deposited material, and its tensile strength and fatigue limit were lower than those of the embodiments of this invention.

[0063] In Comparative Example 6, the stage temperature during laser deposition was lower than the lower limit of the stage temperature specified in this invention, while in Comparative Example 7, the stage temperature during laser deposition was higher than the upper limit of the stage temperature specified in this invention. This resulted in Fe and Cu elements being unable to partition from martensite into the untransformed β phase, reducing the proportion of metastable β phase in the deposited material and causing the fatigue limit of the material to be lower than that of the embodiments of this invention.

[0064] In Comparative Example 8, after laser deposition, the abutment temperature was raised to above the upper limit of the temperature specified in this invention, causing the material to transform into a fully martensitic structure. Although its strength was high, its ductility, toughness, and fatigue limit were low. In Comparative Example 9, after laser deposition, the abutment temperature was raised to below the lower limit of the temperature specified in this invention, causing Fe and Cu elements to be unable to distribute from martensite to the untransformed β phase. This reduced the proportion of metastable β phase in the deposited material, resulting in a fatigue limit lower than that of the embodiments of this invention.

[0065] Comparative Example 10 is a widely used additively manufactured Ti6Al4V alloy, whose room temperature tensile properties and fatigue limit are significantly lower than those of the embodiments of the present invention.

[0066] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. An additively manufactured high fatigue strength titanium alloy, characterized in that: The chemical composition of this titanium alloy, by weight percentage, is: Mo: 4.0~4.5; Zr：6.0~7.0； Fe: 2.0~2.5; Cu: 5.0~6.0; O: 0.25~0.32; balance is Ti; The method for preparing the high fatigue strength titanium alloy by additive manufacturing meets the following requirements: the titanium alloy is prepared by coaxial powder feeding laser additive manufacturing technology, with laser power between 1500 and 3100 W, scanning rate between 700 and 1500 mm / min, and interlayer spacing between 0.4 and 1.2 mm. During the preparation of this titanium alloy, the cooling rate of each thermal cycle during the deposition process is higher than 30°C / s, which causes the formation of martensitic structure in the material. The titanium alloy was deposited on a substrate at 250~500℃; The abutment temperature is maintained at M for the alloy s Click below and M f Above a certain point, the martensitic phase transformation is incomplete, and a certain proportion of untransformed β phase is retained in the microstructure. After deposition is complete, the abutment temperature is raised to 700~860℃ and held for 1~9 hours to allow Fe and Cu elements to be distributed from martensite to the untransformed β phase. The stability of the β phase is improved by the eutectoid β-stabilizing elements Fe and Cu.

2. A method for preparing a high fatigue strength titanium alloy by additive manufacturing as described in claim 1, characterized in that: The method for preparing the high fatigue strength titanium alloy by additive manufacturing meets the following requirements: the titanium alloy is prepared by coaxial powder feeding laser additive manufacturing technology, with laser power between 1500 and 3100 W, scanning rate between 700 and 1500 mm / min, and interlayer spacing between 0.4 and 1.2 mm. During the preparation of this titanium alloy, the cooling rate of each thermal cycle during the deposition process is higher than 30°C / s, which causes the formation of martensitic structure in the material. The titanium alloy was deposited on a substrate at 250~500℃; The abutment temperature is maintained at M for the alloy s Click below and M f Above a certain point, the martensitic phase transformation is incomplete, and a certain proportion of untransformed β phase is retained in the microstructure. After deposition is complete, the abutment temperature is raised to 700~860℃ and held for 1~9 hours to allow Fe and Cu elements to be distributed from martensite to the untransformed β phase. The stability of the β phase is improved by the eutectoid β-stabilizing elements Fe and Cu.

3. The method for preparing high fatigue strength titanium alloy by additive manufacturing according to claim 2, characterized in that: After deposition, the stage temperature is raised to 700-860℃ and held for 1-9 hours, meeting the requirement that the holding time is greater than 2.5 hours. D min, where D The effective thickness of the sample is measured in millimeters (mm). After heat preservation, the sample was quenched to room temperature using a 10 wt.% NaCl aqueous solution to retain a large amount of metastable β phase within the material.

4. The method for preparing high fatigue strength titanium alloy by additive manufacturing according to claim 2, characterized in that: The titanium alloy was deposited on a substrate at 320~380℃ using coaxial powder feeding laser additive manufacturing technology. The deposition laser power is 2300~2700 W, the scanning rate is 1100~1300 mm / min, and the interlayer spacing is 0.8~1.0 mm; After deposition, the substrate temperature is raised to 740~780℃ and held for 5~7 hours before being quenched to room temperature with a 10wt.% NaCl aqueous solution.

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