Additively manufactured high fatigue strength titanium alloy and method of making

Abstract

The application provides additive manufacturing high fatigue strength titanium alloy and a preparation method thereof. The additive manufacturing high fatigue strength titanium alloy is Ti6Al5Cu4V2Mo1Ni0.4Si; the chemical composition of the titanium alloy is as follows in percentage by weight: Al: 5.2-6.8; Cu: 1.0-9.0; V: 3.2-4.8; Mo: 0.01-4.0; Ni: 0.01-2.0; Si: 0.01-0.80; and the balance is Ti. The preparation method of the additive manufacturing high fatigue strength titanium alloy is as follows: the titanium alloy is prepared by a coaxial powder feeding laser additive manufacturing technology, the laser power is between 1500-3100 W, the scanning speed is between 700-1500 mm / min, and the layer spacing is 0.4-1.2 mm. The titanium alloy prepared by the application has excellent comprehensive mechanical properties and can be widely applied to many important fields such as aerospace, biological medicine, petroleum chemical industry, automobile industry and marine engineering.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy material design and preparation technology, specifically to an additive manufacturing method for high fatigue strength titanium alloys and its preparation method. Background Technology

[0002] In the aerospace field, advanced equipment such as new fighter jets and hypersonic vehicles are rapidly developing towards higher speeds, larger sizes, and more integrated and complex structures, requiring the use of lightweight, high-strength structural materials with higher overall performance in structural design. For the manufacturing of large and 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 and severe alloy segregation in large ingots, high requirements for large forging equipment and molds, difficulties in deformation, and high costs. Therefore, the fabrication of such large and complex structural components is extremely difficult. In contrast, large and complex high-strength / ultra-high-strength titanium alloy components fabricated using near-net-shape additive manufacturing technology have many advantages, such as 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 restricting 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.

[0004] There is an urgent need to obtain a high-fatigue-strength titanium alloy for additive manufacturing with excellent technical performance and its preparation method. Summary of the Invention

[0005] This invention provides a high-fatigue-strength Ti6Al5Cu4V2Mo1Ni0.4Si alloy for additive manufacturing. Through unique alloy composition design and optimized additive manufacturing process, this invention enables Cu, Mo, Ni, and Si elements to be distributed from martensite to the β phase during deposition, significantly increasing the proportion of metastable β phase within the material. Furthermore, the metastable β phase is used to passivate microcracks within the additively manufactured metal, greatly improving the material's fatigue resistance and providing a new foundation and opportunity for the development of additive-manufactured titanium alloys. The technical solution of this invention is as follows:

[0006] The key technology for additive manufacturing of high fatigue strength titanium alloys is:

[0007] The titanium alloy is Ti6Al5Cu4V2Mo1Ni0.4Si, and its chemical composition by weight percentage is: Al: 5.2–6.8; Cu: 1.0–9.0; V: 3.2–4.8; Mo: 0.01–4.0; Ni: 0.01–2.0; Si: 0.01–0.80; with the balance being Ti. The content of impurity elements in the alloy should meet the corresponding requirements in the national standard "Table of Titanium and Titanium Alloy Grades and Chemical Compositions". The additive manufacturing high-fatigue-performance titanium alloy, when quenched from the single β-phase region, can achieve a critical cooling rate of less than 30℃ / s to obtain a fully martensitic structure, and the martensitic transformation termination temperature (Mf point) is between 250 and 500℃.

[0008] 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:

[0009] The titanium alloy was prepared by coaxial powder feeding laser additive manufacturing technology, with laser power between 1500 and 3100 W, scanning speed between 700 and 1500 mm / min, and interlayer spacing between 0.4 and 1.2 mm.

[0010] The preferred technical requirements of the additive manufacturing method for high fatigue strength titanium alloys described in this invention are:

[0011] During the preparation of this titanium alloy, the cooling rate of each thermal cycle is required to be higher than 30°C / s during the deposition process, so that a large amount of martensite structure is formed in the material.

[0012] The preferred requirement is that the titanium alloy is deposited on a substrate at 250–500°C.

[0013] During preparation, the abutment temperature needs to be maintained below the Ms point and above the Mf point of the alloy to ensure that the martensitic transformation is incomplete and that a certain proportion of untransformed β phase is retained in the microstructure.

[0014] After deposition is complete, the abutment temperature is raised to 700–860°C and held for 1–9 hours to allow Cu, Mo, Ni, and Si elements to be distributed from martensite into the untransformed β phase, thereby improving the stability of the β phase through Cu, Mo, Ni, and Si.

[0015] After deposition was completed and the substrate temperature was raised to 700–860°C, the holding time was greater than t = 2.5D min, where D is the effective thickness of the sample in millimeters (mm). After the holding time was completed, the sample was quenched to room temperature using a 10 wt.% NaCl aqueous solution to retain a large amount of metastable β phase in the material.

[0016] When depositing this titanium alloy on a substrate at 320–380℃, the deposition laser power is 2300–2700W, the scanning rate is 1100–1300mm / min, and the interlayer spacing is 0.8–1.0mm.

[0017] After deposition, the abutment temperature is raised to 740–780°C and held for 5–7 hours before being quenched to room temperature with a 10 wt.% NaCl aqueous solution.

[0018] The microstructure is a mixture of martensite and metastable β phase. Its room temperature tensile strength is 1140–1580 MPa, yield strength is 870–1120 MPa, elongation is 6–24%, and reduction of area is 10–36%.

[0019] The obtained titanium alloy has a fatigue limit of 820–1120 MPa under the conditions of a stress ratio of 0.1 and a cycle count of 107.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. Unlike existing technologies, the titanium alloy provided by this invention uses a base heating technology in the additive manufacturing process to distribute Cu, Mo, Ni, and Si from martensite into the β phase, thereby increasing the proportion of metastable β phase in the material.

[0022] 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 820–1120 MPa.

[0023] 3. The titanium alloy provided by the present invention has good room temperature tensile properties, with a room temperature tensile strength of 1140-1580 MPa, a yield strength of 870-1120 MPa, an elongation of 6-24%, and a reduction of area of ​​10-36%. Attached Figure Description

[0024] Figure 1 One of the microstructures for additive manufacturing of high fatigue strength titanium alloys;

[0025] Figure 2 The second microstructure for additive manufacturing of high fatigue strength titanium alloys;

[0026] Figure 3 The third microstructure for additive manufacturing of high fatigue strength titanium alloys;

[0027] Figure 4 The fourth microstructure for additive manufacturing of high fatigue strength titanium alloys;

[0028] Figure 5 Fatigue SN curves for additive manufacturing of high fatigue strength titanium alloys. Detailed Implementation

[0029] To make the purpose, technical solution and effects of this application clearer and more explicit, the following describes this application in further detail with reference to the accompanying drawings and embodiments.

[0030] This invention provides a novel titanium alloy with the following composition: Al: 5.2–6.8; Cu: 1.0–9.0; V: 3.2–4.8; Mo: 0.01–4.0; Ni: 0.01–2.0; Si: 0.01–0.80; and 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".

[0031] Please see Figures 1-2 . Figures 1-4 This is the TEM microstructure of the high fatigue strength Ti6Al5Cu4V2Mo1Ni0.4Si alloy in Embodiment 5 of this invention. The TEM image shows that the microstructure of the material consists of martensite and a metastable β phase.

[0032] Figure 5 The SN curve of Example 6 of the present invention under the condition of stress ratio of 0.1 is compared with the SN curve of the additively manufactured Ti6Al4V alloy of Comparative Example 10. It can be seen that the material provided by the present invention has better fatigue performance.

[0033] The present application will be described and explained below through several specific embodiments and comparative examples, but these should not be used to limit the scope of the present application.

[0034] Examples 1-9: These are high fatigue strength Ti6Al5Cu4V2Mo1Ni0.4Si alloys manufactured using additive manufacturing within the chemical composition range provided by this invention. The contents of Cu, Mo, Ni, Si, Al, and V 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.

[0035] 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, and 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 Cu, Mo, Ni, Si, Al, and V content on additive manufacturing of high fatigue strength Ti6Al5Cu4V2Mo1Ni0.4Si alloy are explained.

[0036] The laser deposition parameters of Comparative Example 3 are lower than the lower limit of the parameters provided by the present invention, and 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 Ti6Al5Cu4V2Mo1Ni0.4Si alloy is explained.

[0037] 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 it with Example 5, the effect of the cooling rate of each thermal cycle during deposition on the additive manufacturing of high fatigue strength Ti6Al5Cu4V2Mo1Ni0.4Si alloy was demonstrated.

[0038] 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 Ti6Al5Cu4V2Mo1Ni0.4Si alloy is illustrated.

[0039] Comparative Example 8 raises the stage temperature to above the upper temperature limit specified in this invention after laser deposition, and Comparative Example 9 raises the stage temperature to below the lower temperature limit 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 Ti6Al5Cu4V2Mo1Ni0.4Si alloy is explained.

[0040] 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.

[0041] Table 1. Chemical composition and additive manufacturing process of the materials used in the examples and comparative examples.

[0042]

[0043] 1. Microstructure Characterization: The microstructure of the material was characterized using a Talos F200x transmission electron microscope (TEM). After manual thinning to 50 nm, the TEM-tested samples underwent 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 .

[0044] 2. Tensile Properties Testing: The room temperature tensile mechanical properties of the materials in the comparative example and the embodiment 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.

[0045] 3. Fatigue Performance Testing: 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 "Metallic Materials Fatigue Testing - Axial Force Control Method". 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.

[0046] Table 2. Room temperature tensile properties and fatigue limits of the materials in the examples and comparative examples.

[0047]

[0048] 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 Cu, Mo, Ni, Si, Al, and V element contents specified in this invention, as the contents of Cu, Mo, Ni, Si, Al, and V increase, the yield strength, tensile strength, and fatigue limit of the material gradually increase, while the elongation and reduction of area gradually decrease.

[0049] The low content of Cu, Mo, Ni, Si, Al, and V 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 Cu, Mo, Ni, Si, Al, and V in Comparative Example 2 exceeded the upper limit specified in the present 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.

[0050] 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.

[0051] 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.

[0052] 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 Cu, Mo, Ni, and Si 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.

[0053] 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 Cu, Mo, Ni, and Si elements to be unable to distribute from martensite into 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.

[0054] 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.

[0055] 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. Additively manufactured high fatigue strength titanium alloy, characterized in that: The chemical composition of the titanium alloy is, in percentage by weight: Al: 6.0-6.5; Cu: 5.1-7.0; Mo: 2.0-3.0; Ni: 1.0-1.5; Si: 0.40-0.65; and the balance being Ti. V：4.0~4.5； The preparation method of the additive manufacturing high fatigue strength titanium alloy is: the titanium alloy is prepared by a coaxial powder feeding laser additive manufacturing technology, the laser power is between 1500-3100 W, the scanning rate is between 700-1500 mm / min, and the layer spacing is 0.4-1.2 mm. During the deposition process, the cooling rate of each thermal cycle is required to be higher than 30℃ / s, so that a large amount of martensite organization is formed in the material. The titanium alloy is deposited on a base platform at 250-500℃. During the preparation, the temperature of the base platform needs to be kept below the Ms point and above the Mf point of the alloy, so that the martensite phase change is not completely performed, and a certain proportion of untransformed beta phase is retained in the organization. After the deposition is completed, the temperature of the base platform is increased to 700-860℃ for 1-9 hours, so that the Cu, Mo, Ni and Si elements are partitioned from the martensite to the untransformed beta phase, and the stability of the beta phase is improved through Cu, Mo, Ni and Si. The titanium alloy is prepared by a coaxial powder feeding laser additive manufacturing technology, the laser power is between 1500-3100 W, the scanning rate is between 700-1500 mm / min, and the layer spacing is 0.4-1.2 mm.

2. The method of claim 1, wherein the method of additive manufacturing of high fatigue strength titanium alloys is characterized by: During the deposition process, the cooling rate of each thermal cycle is required to be higher than 30℃ / s, so that a large amount of martensite organization is formed in the material. The titanium alloy is deposited on a base platform at 250-500℃. During the preparation, the temperature of the base platform needs to be kept below the Ms point and above the Mf point of the alloy, so that the martensite phase change is not completely performed, and a certain proportion of untransformed beta phase is retained in the organization. After the deposition is completed, the temperature of the base platform is increased to 700-860℃ for 1-9 hours, so that the Cu, Mo, Ni and Si elements are partitioned from the martensite to the untransformed beta phase, and the stability of the beta phase is improved through Cu, Mo, Ni and Si. After the deposition is completed and the temperature of the base platform is increased to 700-860℃, the holding time is greater than 2.5D min, wherein D is the effective thickness of the sample; unit: millimeter mm; after the holding is completed, quenching to room temperature is performed by using a 10wt.% NaCl aqueous solution, so that a large amount of metastable beta phase is retained in the material.

3. The method of claim 2, wherein the method of additive manufacturing of high fatigue strength titanium alloys is characterized by: When the titanium alloy is deposited on a base platform at 320-380℃, the deposition laser power is 2300-2700 W, the scanning rate is 1100-1300 mm / min, and the layer spacing is 0.8-1.0 mm.

4. The method of claim 2, wherein the method of additive manufacturing of high fatigue strength titanium alloys is characterized by: After the deposition is completed, the temperature of the base platform is increased to 740-780℃, and after being kept for 5-7 hours, quenching to room temperature is performed by using a 10wt.% NaCl aqueous solution. The microstructure is a mixed structure of martensite and metastable beta phase, the room temperature tensile strength is 1140-1580 MPa, the yield strength is 870-1120 MPa, the elongation is 6-24%, and the reduction of area is 10-36%.

5. The additively manufactured high fatigue strength titanium alloy of claim 1, wherein: ​ The obtained titanium alloy has a fatigue limit of 820~1120 MPa under the conditions of stress ratio of 0.1 and 107 cycles.

Images