A surface treatment method for a titanium alloy

Abstract

This invention discloses a surface treatment method for titanium alloys. The specific steps are as follows: placing the titanium alloy structural component or thin-walled component in an oxygen atmosphere at 0.5 to 3 times the standard atmospheric pressure, or a mixed atmosphere with an equivalent oxygen concentration, and holding it at 400℃ to 420℃ for 50 to 200 hours, results in an oxide layer with a thickness less than 3 μm and greater than 1 μm on the surface of the titanium alloy sample, and a gradient oxygen-permeable structure forming on the subsurface. The surface treatment process of this invention is simple to operate, highly adaptable, and effective, and can be applied to various complex titanium alloy structural components or thin-walled components.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy surface treatment technology, specifically relating to a surface treatment method for titanium alloy structural parts and thin-walled parts. Background Technology

[0002] Titanium alloys have high specific strength and a density typically around 4.51 g / cm³. 3 With its relatively low wall thickness, titanium alloy possesses both good thermal stability and high-temperature strength, making thin-walled components made from it highly promising for applications in aerospace and other fields. However, due to the low wall thickness after forming, fatigue failure is currently the main cause of damage to thin-walled titanium alloy components, posing a critical threat, especially for military products. Therefore, finding a simple and effective way to improve the fatigue strength of the alloy has been a hot topic of research.

[0003] To meet the design requirements of aerospace and other fields for long service life, high reliability, and high safety of thin-walled titanium alloy components, various surface strengthening processes (such as shot peening and rolling) are used in engineering to treat the components and improve their surface integrity. However, for some structurally complex thin-walled components, conventional surface strengthening processes are difficult to implement and are prone to surface defects, leading to a decrease in material surface integrity and hindering the improvement of material fatigue performance. Therefore, this invention provides an economical, convenient, reliable, and adaptable surface treatment method to further improve the fatigue performance of complex thin-walled titanium alloy components. Summary of the Invention

[0004] The purpose of this invention is to provide a surface treatment method for titanium alloys. This process is simple to implement and can significantly improve the fatigue performance of titanium alloy structural parts or thin-walled parts. In particular, it can be used for complex titanium alloy structural parts or thin-walled parts that cannot be treated by conventional surface strengthening processes such as shot peening and rolling.

[0005] This invention is achieved using the following specific technical solutions:

[0006] The first aspect of the present invention provides a surface treatment method for titanium alloys, the specific steps of which are: placing the titanium alloy structural parts in an oxygen atmosphere of 0.5 to 3 times the standard atmospheric pressure or a mixed atmosphere with an equivalent oxygen concentration, and holding them at 400℃ to 420℃ for 50h to 200h, an oxide layer of less than 3μm and greater than 1μm is formed on the surface of the titanium alloy sample, and a gradient oxygen-permeable structure is formed on the subsurface.

[0007] Preferably, before the titanium alloy structural component is placed in an oxygen atmosphere, the sample surface is cleaned and polished to ensure that the surface is clean and the roughness Ra≤0.2.

[0008] Preferably, after the titanium alloy structural component undergoes surface treatment in an oxygen atmosphere, the sample surface is polished to a depth of 1μm to 3μm to remove the oxide layer and retain the oxygen-permeable layer.

[0009] Preferably, the polishing process involves using a SiO2 polishing solution to remove the oxide layer from the surface of the component.

[0010] Preferably, the titanium alloy is an α+β type titanium alloy or a near-α type titanium alloy. Further, the titanium alloy includes titanium alloys with grades such as TC4, TA15, TC11, Ti-55, Ti60, or Ti65, or similar or closely related grades.

[0011] The second aspect of the present invention provides a surface treatment method for thin-walled titanium alloy parts, wherein the thin-walled parts are placed in an oxygen atmosphere of 0.5 to 3 times the standard atmospheric pressure or a mixed atmosphere with an equivalent oxygen concentration, and after being kept at 400°C to 420°C for 50 to 200 hours, an oxide layer of less than 3 μm and greater than 1 μm is formed on the surface, and a gradient oxygen-permeable structure is formed on the subsurface.

[0012] The preferred embodiment of the surface treatment method for the titanium alloy thin-walled part is that, before the titanium alloy thin-walled part is placed in an oxygen atmosphere, the sample surface is cleaned and polished to ensure that the sample surface is clean and the roughness Ra≤0.2.

[0013] The preferred embodiment of the surface treatment method for the titanium alloy thin-walled part is that after the titanium alloy thin-walled part is surface treated in an oxygen atmosphere, the surface of the part is polished to a depth of 1μm to 3μm to remove the oxide layer and retain the oxygen-permeable layer.

[0014] Preferably, the polishing process involves using a SiO2 polishing solution to remove the oxide layer from the surface of the component.

[0015] According to a further description of the present invention: the titanium alloy is an α+β type titanium alloy or a near-α type titanium alloy. Further, the titanium alloy is TC4 alloy or TA15 alloy.

[0016] A third aspect of the present invention provides an application of the aforementioned surface treatment method in the surface treatment of titanium alloy structural parts or thin-walled titanium alloy parts.

[0017] Titanium alloys can be classified into structural titanium alloys and heat-resistant titanium alloys, or α-type titanium alloys, β-type titanium alloys, and α+β-type titanium alloys. Titanium alloys containing α-stabilizing elements and having an α-phase matrix at room temperature are called α-type titanium alloys. Titanium alloys with an α-phase matrix and only a small amount of β-phase are called near-α-type titanium alloys. Titanium alloys composed of both α-phase and β-phase at room temperature are called α+β-type titanium alloys. Because near-α-type and α+β-type titanium alloys possess both corrosion resistance and excellent mechanical properties, they are widely used in various industries. Near-α-type titanium alloys are based on α-solid solutions and contain 2%–8% β-phase in the stable state, and 8%–15% β-phase after rapid cooling from the β region. α+β-type titanium alloys incorporate both α-stabilizing and β-stabilizing elements, strengthening both the α-phase and β-phase simultaneously. The addition of β-stabilizing elements is 4%–6%, primarily to obtain a sufficient quantity of β phase, thereby improving the alloy's plasticity and formability and imparting heat-treatable strengthening capabilities. Therefore, the properties of α+β type titanium alloys are mainly determined by the β-phase stabilizing elements. The greater the element's solid solution strengthening and stabilizing ability on the β phase, the more significant its performance improvement effect. The α-phase stabilizing element in α+β type titanium alloys is mainly aluminum. Aluminum is almost indispensable in this type of alloy, but its addition should be controlled below 6%–7% to avoid ordered reactions that generate the α2 phase, impairing the alloy's toughness. To further strengthen the α phase, only small amounts of neutral elements such as tin and zirconium are added. α+β type titanium alloys are widely used in aerospace, automotive, golf club heads, bicycles, and other fields. A typical example is the Ti-6Al-4V alloy, developed in the United States in 1954. The Ti-6Al-4V alloy possesses excellent comprehensive properties. Currently, Ti-6Al-4V alloy accounts for more than half of all titanium alloys used, but because Ti-6Al-4V alloy contains the precious metal vanadium, its price is also quite expensive.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1) This process is simple and easy to operate, highly adaptable, and has significant effects. Oxygen atmosphere treatment can surround the entire titanium alloy structural component or thin-walled component, thus it can be widely applied to various types and shapes of titanium alloy structural components or thin-walled components. In particular, it can be applied to complex thin-walled titanium alloy components with various complex structures and complex thin-walled titanium alloy components that cannot be treated or are difficult to fully cover using conventional surface strengthening processes such as shot peening and rolling, such as U-shaped tubes, where shot peening processes will have dead corners. This invention can also be used for surface strengthening treatment of thin-walled components with rotating structures or large curved thin-walled components.

[0020] 2) After being exposed to an oxygen atmosphere at atmospheric pressure, the sample surface of this invention forms an oxide layer of approximately 3 μm to 1 μm, and a gradient oxygen-permeable structure is formed on the subsurface, which allows for a slow transition in strength from the surface of the thin-walled part to the substrate. This can simultaneously improve the room temperature and high temperature fatigue properties of the alloy. The room temperature and 400°C high temperature fatigue limits of complex thin-walled titanium alloy parts treated in the above manner are increased by more than 15%; the fatigue limit of titanium alloy structural parts treated in the above manner is increased by at least 10%. Attached Figure Description

[0021] Figure 1 The image shows the microstructure of the complex thin-walled TC4 alloy part in Example 2 of this invention after surface treatment (oxidation + polishing) according to this invention.

[0022] Figure 2 This is a microstructure photograph of the complex thin-walled TA15 alloy part in Example 4 of the present invention after surface treatment (oxidation + polishing) according to the present invention. Detailed Implementation

[0023] The present invention will be further illustrated below using TC4 alloy and TA15 alloy irregular thin-walled parts as examples, in conjunction with embodiments. TC4 alloy is a medium-strength α+β type two-phase titanium alloy. This alloy has excellent comprehensive properties and is the most widely used in the aerospace industry. The composition of TC4 titanium alloy is Ti-6Al-4V, belonging to the (α+β) type titanium alloy. The nominal composition of TA15 titanium alloy is Ti-6.5Al-2Zr-1Mo-1V, belonging to the high Al equivalent near-α type titanium alloy.

[0024] Example 1, Example 2:

[0025] The raw material used in Examples 1 and 2, and Comparative Example 1, was a TC4 alloy with an alloy composition of Ti-6.02Al-4.15V. The phase transformation point of the alloy was 990℃, and the volume fraction of the primary α phase was ~30%. The microstructure of the alloy after surface treatment and polishing according to the present invention is as follows: Figure 1 As shown. After being integrally extruded, the thin-walled parts are ground and polished to achieve a surface finish of R=0.1. Before the polishing process, the thin-walled parts are cleaned with petroleum ether.

[0026] Example 1: The thin-walled component was placed in an oxygen atmosphere at 1 standard atmosphere and kept at 400℃ for 150 hours. After being removed and air-cooled, a fatigue limit test was performed directly. Example 2: After treatment according to Example 1, the oxide layer on the surface of the component was removed using SiO2 polishing slurry, with a polishing thickness of 1μm to 2μm. After polishing, a fatigue limit test was performed. Comparative Example 1 is a thin-walled component that has not undergone oxygen atmosphere oxidation treatment. The fatigue limits of Examples 1-2 and Comparative Example 1 are shown in Table 1.

[0027] Table 1. Fatigue limits of thin-walled specimens from Examples 1 and 2 compared to untreated specimens from Comparative Example 1.

[0028]

[0029] Test Results: Comparing the thin-walled parts of Examples 1 and 2 with the untreated parts at room temperature and high temperature fatigue limits, Examples 1 and 2 showed significantly improved fatigue performance, and the fatigue limit of the polished Example 2 was approximately 20-40 MPa higher than that of the unpolished Example 1. This demonstrates that the titanium alloy thin-walled parts treated with oxidation and polishing according to this invention exhibit better fatigue performance. Figure 1 As shown, Figure 1 The image shows the microstructure of the complex thin-walled TC4 alloy part in Example 2 after surface treatment (oxidation + polishing) according to the present invention.

[0030] Example 3, Example 4:

[0031] The raw materials used in Examples 3-4 and Comparative Example 2 were TA15 alloys with an alloy composition of Ti-6.6Al-1.95Zr-1.00Mo-1.03V. The phase transformation point of the alloy was 1005℃, and the volume fraction of the primary α phase was ~15%. The microstructure of the alloy after surface treatment and polishing according to the present invention is as follows: Figure 2 As shown. After being integrally extruded, the thin-walled parts are ground and polished to achieve a surface finish of R=0.1. Before the polishing process, the thin-walled parts are cleaned with petroleum ether.

[0032] Example 3: The thin-walled component was placed in an atmosphere with 3 atmospheres of pressure and kept at 420℃ for 100 hours. After being removed and air-cooled, it was directly subjected to fatigue limit testing. Example 4: After being treated as in Example 1, the oxide layer on the surface of the component was removed using SiO2 polishing slurry, with a polishing thickness of 1μm to 2μm. After polishing, fatigue limit testing was performed. Comparative Example 2: A thin-walled component that has not undergone oxygen atmosphere oxidation treatment. The fatigue limits of Examples 3-4 and Comparative Example 2 are shown in Table 2.

[0033] Table 2 shows the fatigue limits of the thin-walled specimens in Examples 3 and 4 compared to those in Comparative Example 2 (without treatment).

[0034]

[0035]

[0036] Test results: At room temperature and high temperature fatigue limits, Examples 3 and 4, compared with the untreated thin-walled part in Comparative Example 2, showed significantly improved fatigue performance. Furthermore, the fatigue limit of the polished Example 4 was approximately 20-40 MPa higher than that of the unpolished Example 3. This demonstrates that the titanium alloy thin-walled part treated and polished according to this invention exhibits better fatigue performance. Figure 2 As shown, Figure 2This is a microstructure photograph of the complex thin-walled TA15 alloy part in Example 4 of the present invention after surface treatment (oxidation + polishing) according to the present invention.

[0037] Example 5 and Example 6:

[0038] The raw materials used in Examples 5-6 and Comparative Example 3 were TC4 alloys with an alloy composition of Ti-5.98Al-4.02V, a phase transformation point of 985℃, and a volume fraction of primary α phase of ~20%. The thin-walled parts were integrally extruded and then polished to achieve a surface finish of R=0.1. Before the polishing process, the thin-walled parts were cleaned with petroleum ether.

[0039] Example 5: The thin-walled component was placed in an atmosphere at twice atmospheric pressure and kept at 420°C for 50 hours. After being removed and air-cooled, it was directly subjected to fatigue limit testing. Example 6: After being treated as in Example 1, the oxide layer on the surface of the component was removed using SiO2 polishing slurry, with a polishing thickness of 1μm to 2μm. After polishing, fatigue limit testing was performed. Comparative Example 3: A thin-walled component that has not undergone oxygen atmosphere oxidation treatment. The fatigue limits of Examples 5-6 and Comparative Example 2 are shown in Table 3.

[0040] Table 3. Fatigue limits of thin-walled specimens from Examples 3 and 4 and the untreated Comparative Example 2.

[0041]

[0042] Test results: Compared with the untreated thin-walled part of Example 3, Examples 5-6 showed significantly improved fatigue performance at room temperature and high temperature fatigue limits. Furthermore, the fatigue limit of the polished Example 6 was approximately 20-40 MPa higher than that of the unpolished Example 5. Therefore, the titanium alloy thin-walled part treated and polished according to this invention exhibits better fatigue performance.

[0043] Examples 7 and 8:

[0044] In Examples 7-8 and Comparative Example 4, the raw material used was a Ti-6.2Al-2.01Zr-0.98Mo-1.02V TA15 alloy with a phase transformation point of 995℃ and a primary α phase volume fraction of ~20%. The thin-walled parts were integrally extruded and then polished to a surface finish of R=0.1. Before processing, the thin-walled parts were cleaned with petroleum ether.

[0045] Example 7: The thin-walled component was placed in an atmosphere at twice atmospheric pressure and kept at 400°C for 200 hours. After being removed and air-cooled, a fatigue limit test was performed directly. Example 8: After treatment according to Example 1, the oxide layer on the surface of the component was removed using SiO2 polishing slurry, with a polishing thickness of 1μm to 2μm. After polishing, a fatigue limit test was performed. Comparative Example 3: A thin-walled component that has not undergone oxygen atmosphere oxidation treatment. The fatigue limits of Examples 7-8 and Comparative Example 4 are shown in Table 4.

[0046] Table 4. Fatigue limits of thin-walled specimens from Examples 7 and 8 and the untreated Comparative Example 4 (thin-walled specimens).

[0047]

[0048] Test results: Compared with the untreated thin-walled part in Example 4, Examples 7-8 showed significantly improved fatigue performance at room temperature and high temperature fatigue limits. Furthermore, the fatigue limit of the polished Example 8 was approximately 20-40 MPa higher than that of the unpolished Example 7. Therefore, the titanium alloy thin-walled part treated and polished according to this invention exhibits better fatigue performance.

[0049] Extensive experiments have shown that when titanium alloys of the α+β type or near-α type, such as TC4, TA15, TC11, Ti-55, Ti60, or Ti65, are used to manufacture other titanium alloy structural parts, the same experimental results can be obtained. In other words, the titanium alloy structural parts of this invention, which are subjected to oxidation treatment and polishing, have better fatigue performance, with fatigue limits improved by at least 10% at both room temperature and high temperature.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A surface treatment method for titanium alloys, characterized in that, The specific process is as follows: The titanium alloy structural component is placed in an oxygen atmosphere at 0.5 to 3 times the standard atmospheric pressure, or a mixed atmosphere with an oxygen concentration equivalent to 0.5 to 3 times the standard atmospheric pressure. After being held at 400℃ to 420℃ for 50 to 200 hours, a surface layer of the titanium alloy sample forms below... And higher than An oxide layer forms a gradient oxygen-permeable structure on the subsurface; then the sample surface is polished to a depth of... ~ The oxide layer is removed while retaining the gradient oxygen-permeable structure; the titanium alloy structural component is a thin-walled titanium alloy component.

2. The surface treatment method for titanium alloys according to claim 1, characterized in that: Before being placed in an oxygen atmosphere, the surface of the titanium alloy structural component is cleaned and polished to ensure that the surface is clean and the roughness Ra≤0.

2.

3. The surface treatment method for titanium alloys according to claim 1, characterized in that: The polishing process involves using SiO2 polishing fluid to remove the oxide layer from the surface of the component.

4. The surface treatment method for titanium alloys according to claim 1, characterized in that: The titanium alloy is an α+β type titanium alloy or a near-α type titanium alloy.

5. The surface treatment method for titanium alloys according to claim 4, characterized in that: The titanium alloy is either TC4 alloy or TA15 alloy.

6. The application of the surface treatment method according to any one of claims 1-5 in the surface treatment of thin-walled titanium alloy parts.

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