Titanium alloy surface strengthening method

Abstract

The invention provides a titanium alloy surface strengthening method. The titanium alloy surface strengthening method comprises the following steps that S1, the surface of a titanium alloy test piece is cleaned; s2, forming a urea medium layer on the surface of the titanium alloy test piece; and S3, the surface of the titanium alloy test piece is subjected to laser shock strengthening, and a titanium nitride hard layer is generated. Urea serves as a dielectric layer material, the urea is decomposed into ammonia gas through the heat effect of laser, the ammonia gas chemically reacts with titanium atoms on the surface of the titanium alloy in the high-temperature environment generated by laser shock waves to generate titanium nitride, and then the defects such as gaps and bubbles generated in the titanium nitride generation process are eliminated through the force effect of the laser shock waves. Therefore, a uniform, continuous and defect-free titanium nitride hard layer is generated on the surface of the titanium alloy in situ, and the surface hardness, wear resistance and corrosion resistance of the titanium alloy are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy material processing, in particular to a titanium alloy surface strengthening method. Background Art

[0002] Titanium alloys are widely used in aviation, aerospace, medicine, and other fields due to their low density and high specific strength. However, disadvantages such as poor wear resistance and low surface hardness significantly limit their application. Existing technologies utilize surface strengthening treatments to meet the demands of industrial and medical applications.

[0003] At present, titanium alloy surface strengthening treatment technologies include laser cladding, electric spark strengthening, plasma spraying and other methods. For example, patent document CN114196951A discloses a titanium alloy surface strengthening method, which adopts laser cladding technology to first clad a mixed powder of self-fluxing alloy and ceramic on the surface of the titanium alloy as a transition layer, and then clad a mixed powder of titanium alloy and ceramic as a wear-resistant layer to improve the wear resistance of the titanium alloy surface. However, the thickness of the laser cladding layer is large, which is prone to produce defects such as pores. The transition layer and the wear-resistant layer are a laminated structure, which is prone to excessive local stress, thereby generating cracks. Patent document CN116197492A discloses a titanium alloy surface strengthening layer preparation method, which adopts electric spark strengthening technology, using a mist generator to spray a strengthening medium on the surface of the specimen, and then using electric spark machining technology to prepare a strengthening layer on the surface of the specimen. The surface quality of the electric spark machining is poor, the roughness is high, the surface strengthening layer is prone to defects, and the uniformity is poor. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a new titanium alloy surface strengthening technology to form a uniform, continuous, defect-free strengthening layer on the surface of the titanium alloy, thereby improving the surface hardness, wear resistance, corrosion resistance and other properties of the titanium alloy.

[0005] To achieve the above object, the present invention provides a titanium alloy surface strengthening method, comprising the following steps:

[0006] S1. Clean the surface of the titanium alloy specimen;

[0007] S2, forming a urea dielectric layer on the surface of the titanium alloy specimen;

[0008] S3. Perform laser shock peening on the surface of the titanium alloy specimen to generate a titanium nitride hard layer.

[0009] The present invention uses urea (NH2CONH2) as the dielectric layer material and utilizes the thermal effect of laser to decompose urea to generate ammonia. The ammonia chemically reacts with titanium atoms on the surface of the titanium alloy under the high temperature environment generated by the laser shock wave to generate titanium nitride. The force effect of the laser shock wave is then utilized to eliminate defects such as voids and bubbles generated during the titanium nitride generation process, thereby generating a uniform, continuous, defect-free titanium nitride hard layer in situ on the titanium alloy surface. There is no problem of bonding strength between the hard layer and the substrate, thereby effectively improving the surface hardness, wear resistance, and corrosion resistance of the titanium alloy.

[0010] Furthermore, the step S2 specifically includes placing the titanium alloy specimen in a urea solution or spraying flowing urea solution onto the surface of the titanium alloy specimen.

[0011] Furthermore, in step S2, the urea solution is 1-2 mm higher than the surface of the titanium alloy test piece.

[0012] Furthermore, in step S3, a high-energy pulsed laser beam is emitted to the surface of the titanium alloy specimen to achieve laser shock strengthening.

[0013] In some embodiments of the present invention, a urea solution is used as a reaction medium, and the urea solution also plays a role in laser shock confinement.

[0014] Furthermore, the titanium alloy surface strengthening method further includes step S4, polishing the surface of the titanium alloy specimen. The laser shock process will cause ablation on the surface of the specimen, and polishing can remove the ablation layer on the surface.

[0015] Furthermore, the step S2 specifically includes evenly spreading urea powder on the surface of the specimen and covering the absorption layer on the urea powder.

[0016] Furthermore, in step S3, the surface of the titanium alloy specimen is first scanned using a low-energy continuous laser, and then a high-energy pulsed laser beam is emitted to achieve laser shock peening.

[0017] In some embodiments of the present invention, urea powder is used as the reaction medium. The thermal effect of a low-energy continuous laser is first used to melt and decompose the urea powder, and a chemical reaction occurs with Ti to form TiN. A high-energy pulsed laser beam is then used to perform laser shock strengthening on the surface to remove defects such as voids and bubbles generated during the TiN formation process.

[0018] Furthermore, in step S3, the laser energy of the high-energy pulse laser beam is 10 mJ-30 J, the repetition rate is 10 Hz-1 kHz, the spot diameter is 0.1 mm-5 mm, and the spot overlap rate is 10%-90%.

[0019] Furthermore, the material of the absorption layer is selected from one of black paint, black tape, and aluminum foil.

[0020] Urea solution or an independently set absorption layer can quickly absorb laser energy and instantly vaporize to produce dense, high-temperature and high-pressure plasma. The plasma continues to absorb laser energy to form a high-pressure plasma shock wave. The plasma shock wave propagates into the interior of the material, causing the material to show grain refinement and increased dislocation density at the microscopic level, and at the macroscopic level, the hardness and mechanical properties are improved.

[0021] Furthermore, in step S3, laser shock peening is performed under a nitrogen protective atmosphere. Using nitrogen as the protective gas can provide sufficient nitrogen atoms for the chemical reaction, avoiding the phenomenon of uneven distribution of generated titanium nitride due to insufficient nitrogen atoms caused by low urea solution concentration or insufficient decomposition, thereby ensuring the uniformity of the titanium nitride hard layer.

[0022] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention adopts laser shock peening technology to treat the surface of titanium alloy, and utilizes the high temperature effect and mechanical effect of laser to generate a titanium nitride hard layer in situ on the surface of titanium alloy, effectively improving the hardness, wear resistance, corrosion resistance and other properties of titanium alloy specimens.

[0024] 2. The present invention performs laser shock strengthening on the surface of titanium alloy under nitrogen protection. Nitrogen itself can also chemically react with titanium to generate titanium nitride. At the same time, the force effect of the laser shock wave can eliminate defects such as voids and bubbles generated during the titanium nitride generation process, thereby generating a uniform, continuous, defect-free titanium nitride hard layer.

[0025] 3. The process of the present invention is simple, the raw material composition is low, and it has a significant effect on improving the surface properties of titanium alloys. It does not involve the problem of the bonding strength between the hard layer and the substrate, and has good application prospects in the fields of industry, medicine, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the state of strengthening the surface of a titanium alloy specimen in Example 1 of the present invention.

[0027] Figure 2 This is a schematic diagram of the state of strengthening the surface of a titanium alloy specimen in Example 2 of the present invention.

[0028] Figure 3 This is a schematic diagram of the state of strengthening the surface of a titanium alloy specimen in Example 3 of the present invention.

[0029] Figure 4 This is a comparison chart of the cross-sectional hardness of the titanium alloy specimens of Example 1 of the present invention and Comparative Examples 1 and 2.

[0030] Figure 5This is a comparison chart of the cross-sectional hardness of the titanium alloy specimens of Example 1 of the present invention and Comparative Examples 1 and 2.

[0031] Figure 6 2 is a comparison diagram of the wear scar profiles of the titanium alloy specimens of Example 1 of the present invention and Comparative Examples 1 and 2.

[0032] Description of reference numerals:

[0033] 1- high-energy pulsed laser beam, 2- gas nozzle, 3- titanium alloy specimen, 4- bracket, 5- urea solution, 6- absorption layer, 7- urea nozzle, 8- urea powder. DETAILED DESCRIPTION

[0034] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be noted that the following embodiments are only intended to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter ranges described in the present invention. Reasonable variations derived therefrom are still within the scope of protection of the claims of the present invention.

[0035] It should be noted that the endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0036] A specific embodiment of the present invention provides a titanium alloy surface strengthening method, comprising the following steps:

[0037] (1) The titanium alloy specimens were surface treated to remove surface oil and impurities, ultrasonically cleaned with anhydrous ethanol and air-dried.

[0038] (2) Forming a urea dielectric layer on the surface of the titanium alloy specimen. There are many ways to form a urea dielectric layer. In some embodiments, the titanium alloy specimen is placed in a urea solution, and the urea solution is 1-2 mm higher than the surface of the titanium alloy specimen; in other embodiments, a flowing urea solution is sprayed onto the surface of the titanium alloy specimen. In the embodiment using urea solution as the dielectric material, the urea solution serves as both a reaction medium and a constraint layer during the laser shock process. The concentration of the urea solution is 10% to 50%; preferably, the urea solution is heated to promote the decomposition of the urea solution. In other embodiments, urea powder is evenly spread on the surface of the specimen, and an absorption layer is applied to the urea powder. The material of the absorption layer can be selected from black paint, black tape, aluminum foil, etc.

[0039] (3) Blow nitrogen as a protective gas on the surface of the specimen to prevent the ammonia generated by the reaction of urea solution and titanium alloy from overflowing, while providing sufficient nitrogen atoms for the chemical reaction.

[0040] (4) Laser shock peening is performed on the surface of the titanium alloy specimen to generate a titanium nitride hard layer. In some embodiments, a high-energy pulsed laser beam is emitted to achieve laser shock peening, wherein the laser energy of the high-energy pulsed laser beam is 10mJ-30J, the repetition rate is 10Hz-1KHz, the spot diameter is 0.1mm-5mm, and the spot overlap rate is 10%-90%. In other embodiments, a low-energy continuous laser is first used to scan the surface of the titanium alloy specimen, and the thermal effect of the continuous laser is used to melt and decompose urea, and chemically react with Ti to generate TiN. The surface is then laser shock peened with a high-energy pulsed laser beam to remove defects such as voids and bubbles generated during the TiN generation process.

[0041] (5) Polishing the surface of the titanium alloy specimen to remove the ablation layer on the surface. In some embodiments, step (2) of applying an absorption layer to the surface of the specimen does not cause ablation, and this step can be omitted.

[0042] The above method uses laser shock peening technology to treat the surface of titanium alloy, and at the same time utilizes the high temperature effect and mechanical effect of laser to generate a uniform, continuous, defect-free titanium nitride hard layer in situ on the surface of titanium alloy, effectively improving the hardness, wear resistance, corrosion resistance and other properties of titanium alloy specimens.

[0043] The technical solutions and effects of the present invention are further described below in conjunction with specific embodiments.

[0044] Example 1

[0045] The surface of the titanium alloy specimen is strengthened. The state of the titanium alloy specimen during the working process is as follows: Figure 1 As shown, the specific steps include:

[0046] (1) The titanium alloy specimen 3 was surface treated to remove surface oil and impurities, ultrasonically cleaned with anhydrous ethanol and air-dried.

[0047] (2) The titanium alloy specimen 3 is fixed on the bracket 4, and the surface is immersed in the urea solution 5. The surface of the urea solution 5 is 1 mm higher than the surface of the titanium alloy specimen.

[0048] (3) Nitrogen was blown onto the surface of the specimen through a gas nozzle 2, and a high-energy pulsed laser beam 1 was emitted for laser shock peening. The laser energy was 10 mJ, the wavelength was 532 nm, the spot diameter was 0.1 mm, the repetition rate was 500 Hz, and the spot overlap rate was 50%.

[0049] (4) Polish the surface of the specimen.

[0050] Example 2

[0051] The surface of the titanium alloy specimen is strengthened. The state of the titanium alloy specimen during the working process is as follows: Figure 2 As shown, the specific steps include:

[0052] (1) The titanium alloy specimen 3 was surface treated to remove surface oil and impurities, ultrasonically cleaned with anhydrous ethanol and air-dried.

[0053] (2) The absorption layer 6 is attached to the surface of the titanium alloy specimen 3 , the urea solution is heated, and the flowing urea solution is sprayed onto the surface of the titanium alloy specimen 3 through the urea nozzle 7 .

[0054] (3) The surface of the specimen was subjected to laser shock peening by emitting a high-energy pulsed laser beam 1, with a laser energy of 3 J, a wavelength of 1064 nm, a spot diameter of 2 mm, a repetition rate of 10 Hz, and a spot overlap rate of 30%.

[0055] Example 3

[0056] The surface of the titanium alloy specimen is strengthened. The state of the titanium alloy specimen during the working process is as follows: Figure 3 As shown, the specific steps include:

[0057] (1) The titanium alloy specimen 3 was surface treated to remove surface oil and impurities, ultrasonically cleaned with anhydrous ethanol and air-dried.

[0058] (2) Urea powder 8 is evenly spread on the surface of the titanium alloy specimen 3 , and then the absorption layer 6 is attached to the urea powder 8 .

[0059] (3) The surface of the specimen was subjected to laser shock peening by emitting a high-energy pulsed laser beam 1, with a laser energy of 30 mJ, a wavelength of 532 nm, a spot diameter of 0.5 mm, a repetition rate of 200 Hz, and a spot overlap rate of 75%.

[0060] Example 4

[0061] Strengthening the surface of the titanium alloy specimen includes the following steps:

[0062] (1) The titanium alloy specimens were surface treated to remove surface oil and impurities, ultrasonically cleaned with anhydrous ethanol and air-dried.

[0063] (2) Urea powder is evenly spread on the surface of the titanium alloy specimen, and then an absorption layer is applied on the urea powder.

[0064] (3) Use low-energy continuous laser to scan the surface of the titanium alloy specimen covered with urea powder.

[0065] (4) Laser shock strengthening of the surface using a high-energy pulsed laser beam.

[0066] Comparative Example 1

[0067] Titanium alloy specimens without surface strengthening.

[0068] Comparative Example 2

[0069] Strengthening the surface of the titanium alloy specimen includes the following steps:

[0070] (1) The titanium alloy specimens were surface treated to remove surface oil and impurities, ultrasonically cleaned with anhydrous ethanol and air-dried.

[0071] (2) The titanium alloy specimen was fixed on a bracket and its surface was immersed in ultrapure water, with the water surface 1 mm higher than the surface of the titanium alloy specimen.

[0072] (3) The surface of the specimen was subjected to laser shock peening by emitting a high-energy pulsed laser beam with a laser energy of 10 mJ, a wavelength of 532 nm, a spot diameter of 0.1 mm, a repetition rate of 500 Hz, and a spot overlap rate of 50%.

[0073] (4) Polish the surface of the specimen.

[0074] The microhardness test was carried out on the titanium alloy specimens of Example 1, Comparative Example 1 and Comparative Example 2. The results are as follows: Figure 4 Compared to Comparative Example 1, which did not undergo surface strengthening, Comparative Example 2, which used water as a constraining layer to strengthen the specimen, showed a 4% increase in microhardness. In contrast, Example 1, which used urea solution as both a constraining layer and a reaction medium to strengthen the specimen, showed a 12% increase in microhardness. This demonstrates that the process of the present invention significantly improves the surface hardness of the titanium alloy.

[0075] The friction and wear performance of the titanium alloy specimens of Example 1, Comparative Example 1 and Comparative Example 2 were tested. The friction coefficient was as follows: Figure 5 As shown, the wear scar profile is Figure 6 Compared with Comparative Example 1, which did not undergo surface strengthening, the friction coefficient of the specimen in Comparative Example 2, which was strengthened using water as a constraining layer, was slightly reduced, and the wear scar profile was similar to that of the untreated specimen. Strengthening the specimen using urea solution as both a constraining layer and a reaction medium significantly reduced the friction coefficient, with the wear scar width reduced by 25.8% and the wear scar depth by 46.4%. This indicates that the wear resistance of the titanium alloy surface is significantly improved after treatment using the process of the present invention.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A titanium alloy surface strengthening method, characterized in that: The following steps are involved: S1. Clean the surface of the titanium alloy specimen; S2, forming a urea dielectric layer on the surface of the titanium alloy specimen; S3. Perform laser shock peening on the surface of the titanium alloy specimen to generate a titanium nitride hard layer.

2. The titanium alloy surface strengthening method according to claim 1, characterized in that: The step S2 specifically includes placing the titanium alloy specimen in a urea solution, or spraying flowing urea solution onto the surface of the titanium alloy specimen.

3. The titanium alloy surface strengthening method according to claim 2, characterized in that: In step S2, the urea solution is 1-2 mm higher than the surface of the titanium alloy test piece.

4. The titanium alloy surface strengthening method according to claim 2, characterized in that: In step S3, a high-energy pulsed laser beam is emitted to the surface of the titanium alloy specimen to achieve laser shock peening.

5. The titanium alloy surface strengthening method according to claim 2, characterized in that: The method further includes step S4 of polishing the surface of the titanium alloy specimen.

6. The titanium alloy surface strengthening method according to claim 1, characterized in that: The step S2 specifically comprises evenly spreading urea powder on the surface of the test piece and covering the urea powder with an absorption layer.

7. The titanium alloy surface strengthening method according to claim 6, characterized in that: In step S3, the surface of the titanium alloy specimen is first scanned using a low-energy continuous laser, and then a high-energy pulsed laser beam is emitted to achieve laser shock peening.

8. The titanium alloy surface strengthening method according to claim 4 or 7, characterized in that: In step S3, the laser energy of the high-energy pulse laser beam is 10 mJ-30 J, the repetition rate is 10 Hz-1 kHz, the spot diameter is 0.1 mm-5 mm, and the spot overlap rate is 10%-90%.

9. The titanium alloy surface strengthening method according to claim 6, characterized in that: The material of the absorption layer is selected from one of black paint, black tape and aluminum foil.

10. The titanium alloy surface strengthening method according to claim 1, characterized in that: In step S3, laser shock peening is performed under a nitrogen protective atmosphere.

Images