Processing methods, titanium alloys, and testing methods for improving the service life of titanium alloys

Abstract

This invention relates to a processing method, a titanium alloy, and a testing method for improving the service life of titanium alloys. The processing method further processes TC4 titanium alloy prepared by selective laser melting (SLM). First, the surface of the titanium alloy product to be processed is polished until a mirror finish is achieved, followed by cleaning and drying. Then, a femtosecond laser processing system is used to ablate crisscrossing grid-like grooves on the surface of the titanium alloy product. The femtosecond laser processing system has a laser wavelength of 800 nm, a pulse width of 104 fs, and a frequency of 1 kHz. The titanium alloy product is then left to stand in room temperature air, forming a periodic wavy micro / nano structure on the surface. This processing method significantly improves the non-equilibrium phases that affect service life generated during SLM printing. Furthermore, by leaving the sample to stand in room temperature air, it offers advantages over surface coating and plating methods, including a simpler process, environmental friendliness, lack of impurities, and unattended operation.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy processing technology, and in particular to a processing method for improving the service life of titanium alloys, as well as a titanium alloy processed by the processing method, and a method for testing the corrosion resistance of the titanium alloy. Background Technology

[0002] TC4 titanium alloy (Ti-6Al-4V) possesses a series of advantages such as excellent corrosion resistance, low density, high specific strength, and good toughness and weldability. It has been successfully applied in aerospace, petrochemical, shipbuilding, automotive, and pharmaceutical industries. Currently, selective laser melting (SLM) 3D printing technology is commonly used to obtain TC4 titanium alloy products. SLM is a process in which a laser selectively melts and solidifies powder materials (metals, composite materials, ceramics, etc.) into a three-dimensional solid by stacking discrete points layer by layer. This method can retain the excellent mechanical properties of titanium alloys while offering convenience, no spatial limitations, and high precision.

[0003] Currently, methods such as (1) adjusting laser parameters, (2) surface coating, (3) heating, and (4) using high-energy continuous laser radiation are commonly used to improve the quality of titanium alloys prepared by selective laser melting and extend their service life. However, existing technologies also have the following drawbacks:

[0004] (1) Rapid cooling during the SLM printing process of titanium alloys leads to the formation of non-equilibrium phases, which undermines the excellent service life of the titanium alloys. Adjusting the laser processing parameters cannot fundamentally change the formation of non-equilibrium phases and defects in the alloy microstructure, and has certain limitations in significantly improving its service life.

[0005] (2) While improving service life, the surface coating method introduces new impurities into the original material system, and the stability and service life of the coating itself cannot be guaranteed.

[0006] (3) Although heating can improve the non-equilibrium phase of the sample to a certain extent, it has limited effect on improving the service life of the sample, and an unreasonable heating strategy may degrade the corrosion resistance of the sample.

[0007] (4) High-energy continuous lasers generate a large heat-affected zone when processing sample surfaces, and even under rapid cooling conditions, they can still induce the formation of non-equilibrium phases. Although this can improve surface roughness and mechanical properties, it does not help to extend the service life of metals.

[0008] In summary, current methods for improving the service life of SLM-printed TC4 alloys are prone to introducing impurities and have shortcomings such as low efficiency and lack of convenience. Summary of the Invention

[0009] Therefore, in order to address the technical problems of easily introducing impurities and complex operations when improving the service life of SLM-printed TC4 titanium alloys, this invention provides a processing method, titanium alloy, and testing method for improving the service life of titanium alloys.

[0010] This invention discloses a processing method for improving the service life of titanium alloys, specifically TC4 titanium alloys prepared by selective laser melting. The processing method includes the following steps:

[0011] S1. Provide titanium alloy products, grind and polish the surfaces of the titanium alloy products to be processed until a mirror effect is achieved, and then clean and dry the polished products.

[0012] S2. A femtosecond laser processing system is used to ablate crisscrossing grid-like grooves on the surface of the titanium alloy product. The femtosecond laser processing system has a laser wavelength of 800 nm, a pulse width of 104 fs, and a frequency of 1 kHz.

[0013] S3. The laser-processed titanium alloy product is left to stand in room temperature air to form a periodic wavy micro-nano structure on the surface to be processed.

[0014] As a further improvement to the above scheme, the laser power of the femtosecond laser processing system in S2 is 100mW.

[0015] As a further improvement to the above scheme, in S2, the laser scanning speed of the femtosecond laser processing system is 5 mm / s, and the scanning line spacing is 0.1 mm.

[0016] As a further improvement to the above scheme, in S3, the titanium alloy product is left to stand in air at room temperature for 1-7 days.

[0017] As a further improvement to the above solution, in S1, the specific process of grinding and polishing the surface to be processed is as follows:

[0018] First, use 800, 1200, and 2000 grit sandpaper to grind the surface of the titanium alloy product, and then use a polishing cloth to polish the surface.

[0019] As a further improvement to the above scheme, in S1, the polished titanium alloy product is also immersed in anhydrous ethanol for cleaning and then dried.

[0020] As a further improvement to the above scheme, in S2, after laser ablation of the grid-shaped grooves, the surface to be processed is cleaned with deionized water or anhydrous ethanol to remove the spatter generated by laser ablation adhering to the surface to be processed.

[0021] As a further improvement to the above scheme, in S2, before the femtosecond laser processing system ablates the surface to be processed, the laser focusing of the femtosecond laser processing system is adjusted, and the surface to be processed is leveled.

[0022] This invention also discloses a titanium alloy, which is prepared using any of the above-mentioned processing methods for improving the service life of titanium alloys. The titanium alloy includes a substrate and a corrosion-resistant layer located on the surface of the substrate. The corrosion-resistant layer has crisscrossing square grooves and a periodic corrugated micro / nano structure.

[0023] This invention also discloses a method for testing the corrosion resistance of titanium alloys, the method comprising the following steps:

[0024] We provide titanium alloy products. These products are made from TC4 titanium alloy, prepared through selective laser melting.

[0025] One end of the wire is connected to one side of the titanium alloy product and fixed, and all non-processed surfaces of the titanium alloy product are encapsulated with epoxy resin.

[0026] Using any of the above processing methods to improve the service life of titanium alloys, the surface to be processed of the titanium alloy product is processed to form a corrosion-resistant layer on the surface to be processed, which is then used as the surface to be tested.

[0027] Electrochemical measurements were performed on the test surface of a titanium alloy product using a three-electrode method, resulting in the measurement of the corresponding open-circuit voltage, control potential impedance spectrum, and potentiodynamic polarization curve. A saturated calomel electrode was used as the reference electrode, a platinum electrode as the counter electrode, and the titanium alloy product as the working electrode. The test system was a 3.5 wt% NaCl solution.

[0028] Compared with the prior art, the technical solution disclosed in this invention has the following beneficial effects:

[0029] 1. This invention employs a femtosecond laser ablation combined with air self-oxidation to improve the service life of TC4 titanium alloy and increase its corrosion resistance. Due to the extremely high pulse energy and extremely short pulse width of femtosecond lasers, the substrate material is rapidly removed within a very short time, achieving a "cold processing" characteristic. This cold processing feature significantly improves the non-equilibrium phases that affect service life generated during SLM printing. Furthermore, the post-processing method of allowing the sample to stand in room temperature air offers advantages over surface coating and plating methods, including a simpler process, environmental friendliness, no impurities, and unattended operation. Therefore, it improves the service life of titanium alloys while also offering convenience and high efficiency.

[0030] 2. This test method is used to assess the corrosion resistance of titanium alloys. Due to the excellent properties of titanium alloys, measuring changes in corrosion performance through electrochemical methods can significantly shorten the time required for surface corrosion. It allows for the investigation of the impact of different number of days the processed sample is placed in room temperature air on the corrosion performance of SLM-printed TC4. Furthermore, using a high-resolution field emission electron microscope to observe the microstructure of the titanium alloy surface provides a direct view of the changes in the microstructure before and after processing, facilitating the investigation of the reasons for the improved service life. Attached Figure Description

[0031] Figure 1 This is a flowchart of a processing method for improving the service life of titanium alloys in an embodiment of the present invention;

[0032] Figure 2 This refers to the open-circuit potential of different samples in a 3.5 wt% NaCl solution during performance testing in this embodiment of the invention.

[0033] Figure 3 Impedance spectra of different samples in 3.5 wt% NaCl solution during performance testing in this embodiment of the invention;

[0034] Figure 4 The above are the potentiodynamic polarization curves of different samples in 3.5wt% NaCl solution during performance testing in this embodiment of the invention.

[0035] Figure 5 This is a surface microstructure diagram of a blank titanium alloy sample in an embodiment of the present invention;

[0036] Figure 6 This is a microstructure diagram of the surface of a titanium alloy sample that has been left to stand in room temperature air for one day in an embodiment of the present invention.

[0037] Figure 7 This is a microstructure diagram of the surface of a titanium alloy sample that has been left to stand in room temperature air for 5 days in an embodiment of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] It should be noted that when a component is said to be "installed on" another component, it can be directly on the other component or it may be in a component that is centered on it. When a component is said to be "set on" another component, it can be directly set on the other component or it may also be in a component that is centered on it. When a component is said to be "fixed to" another component, it can be directly fixed to the other component or it may also be in a component that is centered on it.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0041] Please see Figure 1 This embodiment provides a processing method for improving the service life of titanium alloys, specifically TC4 titanium alloys prepared by selective laser melting. The processing method includes the following steps:

[0042] S1. Material surface pretreatment

[0043] A titanium alloy product is provided, and the surface to be processed on the titanium alloy product is ground and polished until a mirror effect is achieved. In this embodiment, the surface to be processed on the titanium alloy product can be ground sequentially using 800, 1200, and 2000 grit sandpaper, and then polished using a polishing cloth. The polished product can then be immersed in anhydrous ethanol for cleaning and drying.

[0044] S2. Femtosecond laser ablation of sample surface

[0045] A femtosecond laser processing system is used to ablate crisscrossing square grooves on the surface of a titanium alloy product. Before ablation, the femtosecond laser processing system is adjusted for laser focusing to prevent the laser spot from going out of focus and to keep the surface horizontal, ensuring that the surface is perpendicular to the direction of laser emission.

[0046] The femtosecond laser processing system has a laser wavelength of 800 nm, a pulse width of 104 fs, and a frequency of 1 kHz. Furthermore, the femtosecond laser processing system can have a laser power of 100 mW, a laser scanning speed of 5 mm / s, and a scanning line spacing of 0.1 mm. Of course, in other embodiments, the scanning spacing, scanning speed, and laser power of the femtosecond laser can be selected to other values, thereby changing the line spacing, groove depth, and width of the grid-like groove structure on the surface to be processed.

[0047] In this embodiment, after laser ablation of the grid-shaped grooves, the surface to be processed can be cleaned with deionized water or anhydrous ethanol to remove the spatter generated by laser ablation adhering to the surface to be processed.

[0048] S3. Room temperature air settling treatment

[0049] The laser-processed titanium alloy products are left to stand in room temperature air for 1 to 7 days, thereby forming a periodic wavy micro-nano structure on the surface to be processed.

[0050] The titanium alloy processed according to the above method has a structure comprising at least a substrate and a corrosion-resistant layer on the surface of the substrate. The corrosion-resistant layer has crisscrossing square grooves and a periodic corrugated micro / nano structure.

[0051] This embodiment also provides a test method for the corrosion resistance of titanium alloys. This method tests the corrosion resistance of titanium alloys processed using the above method. Furthermore, to more clearly characterize performance differences, titanium alloys from different stages are introduced as a control group for comparative testing. The test method generally includes the following steps:

[0052] 1. Sample Pretreatment: The selected material was Ti-6Al-4V (TC4) manufactured by SLM on an MTT SLM 250HL machine. The titanium alloy samples were 10mm × 10mm × 10mm in size, and a total of 6 titanium alloy samples were prepared. First, a wire was provided for each titanium alloy sample, with one end of each wire fixed to the non-processed surface of the corresponding titanium alloy sample and electrically connected. Then, each titanium alloy sample and one end of the corresponding wire were encapsulated in a mold with epoxy resin. After the epoxy resin cured, it was removed from the mold to serve as the electrode for electrochemical testing. Then, step S1 of the above processing method was used to perform a mirror finish treatment on the surface of each titanium alloy sample, followed by cleaning and drying.

[0053] 2. Then, one of the titanium alloy samples was used as a blank sample, without femtosecond laser ablation, and kept for later use. The other titanium alloy samples were subjected to femtosecond laser ablation using the method described in step S2. In this embodiment, a femtosecond laser processing system (the laser generation and amplification system was The Spectra-PhysicsSolstice Ace.) was used to perform femtosecond laser ablation on the samples in the Micro-Nano Fabrication Laboratory of the University of Science and Technology of China. The laser wavelength was 800 nm, the pulse width was 104 fs, the frequency was 1 kHz, and the laser power was 100 mW. When processing the SLM titanium alloy, the processing strategy was horizontal and vertical scanning, with a scanning speed of 5 mm / s, a scanning line spacing of 0.1 mm, and a processing area of ​​9 mm × 9 mm. The final result was a crisscrossing grid-like groove.

[0054] 3. At this point, of the above 6 titanium alloy samples, one of which has not undergone laser processing is used as a blank sample. The remaining five samples that have undergone femtosecond laser processing are placed in room temperature air for different times (0 days, 1 day, 3 days, and 5 days) to allow them to self-oxidize, thereby forming a corrosion-resistant layer on the surface of the sample to be processed, which is then used as the surface to be tested.

[0055] 4. Electrochemical Measurement: Cut electrical tape of appropriate length and width (both larger than the sample side length), and cut 8mm × 8mm square holes in the electrical tape. Prepare 6 such electrical tapes. Then attach these electrical tapes to the test surfaces of the 6 titanium alloy samples respectively, so that the exposed sample surface area is 8mm × 8mm.

[0056] In this embodiment, the electrochemical measurements were performed using the DH7001 electrochemical workstation manufactured by Donghua Instrument Testing Co., Ltd. A three-electrode method was employed: a saturated calomel electrode as the reference electrode (RE), a platinum electrode as the counter electrode (CE), and the encapsulated sample as the working electrode (WE). The test system was a 3.5 wt% NaCl solution.

[0057] (1) Open Circuit Voltage (OCP) Measurement: Six samples (blank sample without laser processing, and samples processed by laser processing and stored for 0, 1, 3, 5, and 7 days) were used as working electrodes and placed in a 3.5 wt% NaCl solution to measure their open circuit voltage sequentially. The test time was 3600 s, with one test per second. The results are as follows: Figure 2 As shown, the open circuit potential of the blank sample after only polishing is only -0.1V. The potential of the processed samples increases after being left to stand, and the open circuit potential of the samples gradually increases with the number of days of standing.

[0058] (2) Controlled potential impedance spectroscopy (EIS) measurement: Controlled potential EIS measurement was selected in the electrochemical workstation software. The start frequency was 10000 Hz, the end frequency was 0.01 Hz, and the amplitude was 10 mV. The impedance spectra of six samples were measured sequentially. The results are as follows: Figure 3 As shown, the capacitive reactance ring of the sample that has only undergone grinding and polishing is the smallest. The capacitive reactance ring of the sample that has undergone femtosecond laser ablation and air self-oxidation treatment is improved. Furthermore, the capacitive reactance ring gradually increases with the increase of self-oxidation time and eventually tends to stabilize.

[0059] (3) Measurement of potentiodynamic polarization curves: The potentiodynamic polarization measurement module was selected in the electrochemical workstation. The starting potential was -0.9V, the ending potential was 2.5V, and the step height was 10mV. The potentiodynamic polarization curves of 6 samples were measured sequentially. The results are as follows: Figure 4As shown, the sample that only underwent grinding and polishing had a higher polarization current and poor passivation stability at high potentials. The sample that underwent femtosecond laser ablation and air self-oxidation showed improved polarization current and passivation stability, with the improvement increasing more significantly with increasing self-oxidation time.

[0060] In some embodiments, a high-resolution scanning electron microscope (SEM, Regulus 8230, Japan) can also be used to observe the microstructure of the sample surface, and the results are as follows: Figures 5 to 7 As shown: The sample surface after only grinding and polishing is relatively smooth, and no obvious micro / nano structures were found. The sample surface after femtosecond laser ablation and air self-oxidation treatment showed a more dense periodic wavy micro / nano structure. It is this induced periodic wavy structure that improves the non-equilibrium phase defects of 3D printed titanium alloys and improves the service life of 3D printed titanium alloys.

[0061] Compared to traditionally cast titanium alloys, 3D-printed titanium alloys retain the excellent mechanical properties of titanium while allowing for the printing of target shapes according to user preferences. They also offer advantages such as convenience, lack of spatial limitations, and high precision. However, the formation of non-equilibrium phases and internal defects during the processing reduces the service life of 3D-printed titanium alloys. Therefore, eliminating non-equilibrium phases and internal defects in SLM (Solid Metal Laminate Printing) is crucial for enhancing the application prospects of 3D-printed titanium alloys.

[0062] Therefore, among the many methods for improving the service performance of 3D-printed titanium alloys, this invention employs a femtosecond laser ablation combined with air self-oxidation. Because femtosecond lasers possess extremely high pulse energy and extremely short pulse widths, the substrate material is rapidly removed within a very short time, achieving the characteristic of "cold processing." This cold processing feature significantly improves the non-equilibrium phases that affect service life generated during SLM printing. Furthermore, this post-processing method, which involves allowing the sample to stand in room temperature air, offers advantages over surface coating and plating methods, including a simpler process, environmental friendliness, lack of impurities, and the ability to operate unattended.

[0063] Furthermore, due to the excellent properties of titanium alloys, measuring changes in corrosion performance through electrochemical methods can significantly shorten the time required for surface corrosion. Moreover, using high-resolution field emission electron microscopy to observe the microstructure of titanium alloy surfaces allows for a direct visualization of changes in the microstructure before and after processing, facilitating the investigation of the reasons for improved service life.

[0064] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0065] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A processing method for improving service life of a titanium alloy, characterized in that, The titanium alloy is a TC4 titanium alloy prepared by selective laser melting; the processing method includes the following steps: S1. Provide a titanium alloy product, grind and polish the surface of the titanium alloy product to be processed until a mirror effect is achieved, and then clean and dry the polished product. S2. Using a femtosecond laser processing system, crisscrossing square grooves are ablated on the surface of the titanium alloy product to be processed; wherein, the laser wavelength of the femtosecond laser processing system is 800nm, the pulse width is 104fs, and the frequency is 1kHz. S3. The laser-processed titanium alloy product is left to stand in room temperature air to form a periodic wavy micro-nano structure on the surface to be processed.

2. The processing method for enhancing service life of titanium alloys according to claim 1, wherein, The laser power of the femtosecond laser processing system described in S2 is 100mW.

3. The processing method for enhancing service life of titanium alloys according to claim 1, wherein, In S2, the laser scanning speed of the femtosecond laser processing system is 5 mm / s, and the scanning line spacing is 0.1 mm.

4. The processing method for enhancing service life of titanium alloys according to claim 1, wherein, In step S3, the titanium alloy product is left to stand in air at room temperature for 1-7 days.

5. The processing method for improving the service life of titanium alloys according to claim 1, characterized in that, In S1, the specific process of grinding and polishing the surface to be processed is as follows: First, use 800, 1200, and 2000 grit sandpaper to grind the surface of the titanium alloy product, and then use a polishing cloth to polish the surface.

6. The processing method for improving the service life of titanium alloys according to claim 5, characterized in that, In S1, the polished titanium alloy products are also immersed in anhydrous ethanol for cleaning and then dried.

7. The processing method for enhancing service life of titanium alloys of claim 1, wherein, In S2, after the square grooves are ablated by laser, the surface to be processed is cleaned with deionized water or anhydrous ethanol to remove the spatter generated by laser ablation that is attached to the surface to be processed.

8. The processing method for enhancing service life of titanium alloys of claim 1, wherein, In S2, before the femtosecond laser processing system ablates the surface to be processed, the femtosecond laser processing system is adjusted for laser focusing, and the surface to be processed is adjusted for horizontality.

9. A titanium alloy characterized by, It is prepared by the processing method for improving the service life of titanium alloy as described in any one of claims 1 to 8; the titanium alloy includes a substrate and a corrosion-resistant layer located on the surface of the substrate; wherein the corrosion-resistant layer is provided with crisscrossing square grooves and has a periodic corrugated micro-nano structure.

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