Method for processing zrnb alloy by femtosecond laser combined with thermal oxidation

Abstract

The application discloses a method for processing ZrNb alloy by combining femtosecond laser with thermal oxidation, and comprises the following steps: fixing a workpiece subjected to wire cutting and processing on an electric displacement platform, making a laser beam act on the surface of the workpiece through a focusing mirror, and adjusting femtosecond laser parameters by changing a scanning speed, a laser frequency and a laser power, so as to obtain LIPSS structure, Groove structure or Bulge structure; placing the sample processed by the femtosecond laser in a muffle furnace, heating the sample to 500-800 DEG C for 1.5-2.5 hours, with a heating rate of 3-6 DEG / min, an oxidation atmosphere being air, and cooling the sample to room temperature after heating is completed. The application makes up for the shortcomings of a single surface treatment method, and the wear resistance of the Zr-2.5Nb alloy subjected to the composite treatment is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of zirconium alloys, and in particular to a method for improving the corrosion resistance, wear resistance and biocompatibility of Zr-2.5Nb alloys through a combination of femtosecond laser and thermal oxidation composite surface treatment. Background Technology

[0002] In recent years, the prevalence of osteoarthritis has been increasing, making artificial joint replacement surgery a widely recognized treatment option. Improving joint wear resistance and biocompatibility is therefore crucial. Titanium alloys have become a relatively ideal implant material in recent years, but their elastic modulus is also quite high (approximately 60-120 GPa), about five times that of human bone. This can lead to stress shielding and muscle atrophy after implantation. As artificial joint implants, they suffer from short lifespan and poor biocompatibility. Biomedical Zr alloys, specifically the Zr-Nb system, typically have a lower elastic modulus (50-100 GPa) compared to titanium alloys. Furthermore, niobium (Nb) is a non-toxic element with good biocompatibility. Therefore, improving the wear resistance of Zr alloys and using them as orthopedic implants is a good option. Surface treatment techniques are commonly used to improve the material's wear resistance and other properties.

[0003] Thermal oxidation (TO) technology utilizes the high-temperature oxygen diffusion phenomenon to form a thicker ZrO2 film in the oxygen diffusion zone of Zr alloys, which is beneficial for improving their wear resistance and other properties. TO technology has advantages such as not being limited by sample shape, simple operation, and economy. Furthermore, under suitable conditions, the oxide film formed is denser and non-porous, making it more suitable as an implant material. Therefore, using thermal oxidation to prepare the oxide ceramics required for implants is a suitable solution. However, simple thermal oxidation technology has some drawbacks. Only a ceramic thin film layer of a few micrometers can be formed on the surface, and the already formed ceramic layer can block further oxygen diffusion, making it impossible to form a dense oxide ceramic layer.

[0004] In recent years, laser surface processing technology has been increasingly explored as a promising method to overcome most of its tribological limitations. Among these, femtosecond (fs) laser surface modification technology has attracted widespread attention due to its extremely high precision, the extreme processing conditions of laser excitation, and the limited thermal effects on the substrate. Many researchers have been dedicated to this field, attempting to develop novel materials based on ultrashort lasers and achieve better modulation process performance. Femtosecond laser processing technology is widely used in surface textures due to its small thermal effect, non-contact nature, and high processing efficiency. Numerous studies have shown that surface texture is a crucial factor affecting surface wear resistance during friction. By designing appropriate texture morphologies, surface tribological properties can be significantly improved.

[0005] However, single surface treatments have certain limitations. For example, laser treatment results in severe texture wear and high edge stress, while thermal oxidation results in a thin oxide film with a thickness of only about 1-3 μm, leading to a short implant lifespan. Summary of the Invention

[0006] The purpose of this invention is to address the limitations of current technologies by providing a method for composite treatment of ZrNb alloys using femtosecond laser combined with thermal oxidation. This method first uses femtosecond laser technology to construct three different micro / nano textures, then thermally oxidizes the laser-treated sample to construct a novel medical-grade ZrNb alloy with integrated structure and function. This invention overcomes the shortcomings of single surface treatment methods, and the wear resistance of the composite-treated Zr-2.5Nb alloy is significantly improved.

[0007] The technical solution of this invention is as follows:

[0008] A method for femtosecond laser combined with thermal oxidation composite treatment of ZrNb alloy, the method comprising the following steps:

[0009] Step 1: Wire EDM processing;

[0010] ZrNb alloy is processed into sheets using a wire EDM machine;

[0011] The thickness of the sheet is 1.0 to 5.0 mm.

[0012] The ZrNb alloy mentioned is specifically a Zr-2.5Nb alloy.

[0013] Step 2: Grinding and polishing;

[0014] The grinding and polishing process is as follows: the cut ZrNb alloy is ground sequentially with SiC sandpaper of grades 60#, 240#, 600#, 800#, 1000#, 2000#, 3000#, and 5000# until there are no obvious scratches on the sample surface. Then, it is polished with polishing liquid, cleaned with deionized water, immersed in alcohol for ultrasonic cleaning for 10-20 minutes, and dried for later use.

[0015] Step 3: Femtosecond laser pre-parameter adjustment;

[0016] The workpiece obtained in the previous step is fixed on an electric displacement platform. The laser beam acts on the surface of the workpiece through a focusing lens. By changing the scanning speed, laser frequency, and laser power, the femtosecond laser parameters are controlled to obtain one of the following three structures.

[0017] Structure 1: Frequency 310KHz, defocusing amount 1mm, line spacing 0.07mm, scanning speed 150mm / s, laser power 2.8W, constructing a LIPSS structure;

[0018] Alternatively, structure two: frequency 310KHz, defocus amount 1mm, line spacing 0.07mm, scanning speed 150mm / s, laser power 10W, to construct the Groove structure;

[0019] The latter, structure three: frequency 40KHz, line spacing 0.07mm, defocus amount 1mm, scanning speed 2mm / s, laser power 0.6W, constructing a Bulge structure;

[0020] Step 4: Thermal oxidation treatment

[0021] The femtosecond laser-treated sample was placed in a muffle furnace and heated to 500–800°C for 1.5–2.5 hours at a heating rate of 3–6°C / min. The oxidizing atmosphere was air. After heating, the sample was cooled to room temperature with the furnace.

[0022] The essential features of this invention are:

[0023] Because thermal oxidation of ZrNb alloys results in a thin and poorly dense oxide film, it leads to insufficient wear resistance and a short lifespan when implanted in joints, failing to meet practical requirements. Femtosecond laser technology, as a novel surface processing technique, has attracted widespread attention for its ability to create micro-nano textures with excellent friction-reducing effects.

[0024] This invention employs a composite surface treatment method combining femtosecond laser and thermal oxidation. Three different micro / nano textures are constructed using femtosecond lasers, followed by thermal oxidation treatment on the texture surfaces. The changes in wear resistance, corrosion resistance, and other properties after thermal oxidation of the different structures are investigated. This not only overcomes the shortcomings of single treatment methods but also strengthens the bond between the structure and the oxide film, resulting in a significant improvement in wear resistance.

[0025] The beneficial effects of this invention are as follows:

[0026] (1) The method of the present invention increases the penetration depth of the oxide film of Zr-2.5Nb alloy, wherein the depth of the oxide film of simple thermal oxidation is 2.606μm, the depth of LIPSS structure is 4.661μm, the depth of Groove structure is 10.500μm, and the depth of Bulge structure is 15.48μm.

[0027] (2) The method of the present invention greatly improves the wear resistance of Zr-2.5Nb alloy. The wear amount of all composite-treated samples is reduced. Among them, the wear amount of LIPSS structure is reduced by about 35% relative to the matrix, and the wear amount of Groove structure is reduced by about 11%.

[0028] (3) The method of the present invention enables Zr-2.5Nb alloy to have good biocompatibility, with a hemolysis rate of less than 5%, which meets the standards for biomedical materials. It also has excellent hydrophilicity and is non-toxic to cells, which meets the biological requirements of implant materials.

[0029] (4) The femtosecond laser combined with thermal oxidation process is simple and has a low production cost. Attached Figure Description

[0030] Figure 1 These are scanning electron microscope (SEM) images of the surface morphology after laser treatment in Examples 1-3; wherein, Figure 1 (a) is a surface morphology diagram of the LIPSS structure in Example 1. Figure 1 (b) is a surface morphology diagram of the Groove structure in Example 2. Figure 1 (c) is a surface morphology diagram of the Bulge structure in Example 3;

[0031] Figure 2 The image is a scanning electron microscope image of Comparative Example 1, which only underwent thermal oxidation.

[0032] Figure 3 The image shows a scanning electron microscope (SEM) image of the LIPSS structure obtained in Example 1 combined with thermal oxidation.

[0033] Figure 4 This is a scanning electron microscope image of the Groove structure obtained in Example 2 combined with thermal oxidation;

[0034] Figure 5 The image shows a scanning electron microscope (SEM) image of the Bulge structure obtained in Example 3, combined with thermal oxidation.

[0035] Figure 6 This is a comparison of XRD patterns between Comparative Example 1 and Examples 1-3;

[0036] Figure 7 This is a comparison chart of wear amount between Comparative Example 1 and Examples 1-3;

[0037] Figure 8 This is a comparison chart of the hemolysis rates between Comparative Example 1 and Examples 1-3. Detailed Implementation

[0038] The embodiments of the present invention will be described in further detail below to make the technology, objectives and advantages of the present invention clearer.

[0039] (1) The surface morphology of the alloy after femtosecond laser treatment was tested by scanning electron microscopy.

[0040] (2) The interface of the sample after femtosecond laser combined with thermal oxidation treatment was tested by scanning electron microscopy.

[0041] (3) XRD tests were performed on the samples after femtosecond laser combined with thermal oxidation treatment. The XRD pattern was measured using a Bruker D8 Discover instrument from Germany. The target material was CuKα, the operating voltage was 40KV, the scanning speed was 6° / min, and the 2θ range was from 10° to 90°. The experimental data were saved after the test was completed.

[0042] (4) The friction and wear coefficient of the samples was measured using a room temperature reciprocating friction and wear tester (CFT-Ⅰ). The applied load was 30 N, the number of reciprocations was 150 t / m, the reciprocating length was 5 mm, and the grinding balls were ZrO2 ceramic balls with a diameter of 5 mm. Then, the wear tracks of the samples after friction and wear were tested. The wear track depth was measured using a surface profilometer (ContourGT-K, Bruker, Germany), and the wear amount was calculated.

[0043] (5) Hemolysis test using fresh rabbit blood: 8 mL (±0.1 mL) of fresh rabbit blood was mixed with 10 mL (±0.1 mL) of physiological saline and placed in a centrifuge tube. The mixture was heated in a 37°C water bath for 30 min. Then, the sample was placed in 10 mL (±0.1 mL) of physiological saline and diluted blood and heated in a water bath for 30 min. After heating, 0.2 mL (±0.01 mL) of diluted blood was added to the centrifuge tube containing the sample and the mixture was heated in a water bath for another 1 h. Finally, the mixture was centrifuged at 2500 r / min for 5 min. The absorbance of the supernatant was measured at 545 nm using a 721 spectrophotometer. Positive control group: 0.2 ± 0.01 mL diluted blood, 10 ± 0.1 mL distilled water; Negative control group: 0.2 ± 0.01 mL diluted blood, 10 ± 0.1 mL physiological saline.

[0044] Comparative Example 1

[0045] Zr-2.5Nb was processed into 10mm×10mm×2mm thin sheets using a wire EDM machine. The cut ZrNb alloy was then polished with SiC sandpaper of various grades (60#, 240#, 600#, 800#, 1000#, 2000#, 3000#, and 5000#) until there were no obvious scratches on the sample surface. After polishing with polishing liquid, the sample was cleaned with deionized water, immersed in alcohol for ultrasonic cleaning for 10-20 minutes, and then dried for later use.

[0046] The processed sample was placed in a muffle furnace for oxidation at a heating rate of 6° / min and an oxidizing atmosphere of air. The oxidation was carried out at 600°C for 2 hours. After the oxidation was completed, the furnace was cooled to room temperature. The sample was then removed and stored in a drying oven.

[0047] Example 1

[0048] Zr-2.5Nb was processed into 10mm×10mm×2mm thin sheets using a wire EDM machine. The cut ZrNb alloy was then polished with SiC sandpaper of various grades (60#, 240#, 600#, 800#, 1000#, 2000#, 3000#, and 5000#) until there were no obvious scratches on the sample surface. After polishing with polishing liquid, the sample was cleaned with deionized water, immersed in alcohol for ultrasonic cleaning for 10-20 minutes, and then dried for later use.

[0049] A femtosecond laser, model SY-5549 (Amplitude), with a wavelength of 1035 nm, a pulse width of 350 fs, a repetition rate of 1 kHz to 1240 kHz, and a spot diameter of 2 nm to 3 nm, was used to treat the polished substrate surface. The laser scanning path was guided by a galvanometer scanner, and the sample was placed on an XYZ stage, using a parallel scanning path in air. The cleaned sample was fixed on a programmable electrically controlled displacement platform, and the laser beam was focused onto the sample on a computer-controlled electrically controlled translation stage through a lens. A one-dimensional parallel microchannel array was woven into the sample surface by grating scanning with the laser beam, fabricating a periodic striped LIPSS structure. The selected equipment was a Satsuma Amplitude laser with femtosecond laser parameters of 310 kHz frequency, 1 mm defocusing amount, 0.07 mm line spacing, 150 mm / s scanning speed, and 2.8 W laser power.

[0050] The processed sample was placed in a muffle furnace for oxidation at a heating rate of 6° / min and an oxidizing atmosphere of air. The oxidation was carried out at 600°C for 2 hours. After the oxidation was completed, the furnace was cooled to room temperature. The sample was then removed and stored in a drying oven.

[0051] Example 2

[0052] Zr-2.5Nb was processed into 10mm×10mm×2mm thin sheets using a wire EDM machine. The cut ZrNb alloy was then polished with SiC sandpaper of various grades (60#, 240#, 600#, 800#, 1000#, 2000#, 3000#, and 5000#) until there were no obvious scratches on the sample surface. After polishing with polishing liquid, the sample was cleaned with deionized water, immersed in alcohol for ultrasonic cleaning for 10-20 minutes, and then dried for later use.

[0053] A femtosecond laser, model SY-5549 (Amplitude), with a wavelength of 1035 nm, a pulse width of 350 fs, a repetition rate of 1 kHz to 1240 kHz, and a spot diameter of 2 nm to 3 nm, was used to treat the polished substrate surface. The laser scanning path was guided by a galvanometer scanner, and the sample was placed on an XYZ stage, using a parallel scanning path in air. The cleaned sample was fixed on a programmable electrically controlled displacement platform, and the laser beam was focused onto the sample on a computer-controlled electrically controlled translation stage through a lens. A grating scan of the sample was performed using the laser beam to weave a one-dimensional parallel microchannel array on the sample surface, creating a small island-like groove structure (Groove). The selected equipment was a Satsuma Amplitude laser with femtosecond laser parameters of 310 kHz frequency, 1 mm defocusing amount, 0.07 mm line spacing, 150 mm / s scanning speed, and 10 W laser power.

[0054] The processed sample was placed in a muffle furnace for oxidation at a heating rate of 6° / min and an oxidizing atmosphere of air. The oxidation was carried out at 600°C for 2 hours. After the oxidation was completed, the furnace was cooled to room temperature. The sample was then removed and stored in a drying oven.

[0055] Example 3

[0056] Zr-2.5Nb was processed into 10mm×10mm×2mm thin sheets using a wire EDM machine. The cut ZrNb alloy was then polished with SiC sandpaper of various grades (60#, 240#, 600#, 800#, 1000#, 2000#, 3000#, and 5000#) until there were no obvious scratches on the sample surface. After polishing with polishing liquid, the sample was cleaned with deionized water, immersed in alcohol for ultrasonic cleaning for 10-20 minutes, and then dried for later use.

[0057] A femtosecond laser, model SY-5549 (Amplitude), with a wavelength of 1035 nm, a pulse width of 350 fs, a repetition rate of 1 kHz to 1240 kHz, and a spot diameter of 2 nm to 3 nm, was used to treat the polished substrate surface. The laser scanning path was guided by a galvanometer scanner, and the sample was placed on an XYZ stage, using a parallel scanning path in air. The cleaned sample was fixed on a programmable electrically controlled displacement platform, and the laser beam was focused onto the sample on a computer-controlled electrically controlled translation stage through a lens. A grating scan of the sample was performed using the laser beam to weave a one-dimensional parallel microchannel array on the sample surface, fabricating a bulge structure. The selected equipment was a Satsuma Amplitude laser with femtosecond laser parameters of 40 kHz frequency, 0.07 mm line spacing, 1 mm defocusing amount, 2 mm / s scanning speed, and 0.6 W laser power.

[0058] The processed sample was placed in a muffle furnace for oxidation at a heating rate of 6° / min and an oxidizing atmosphere of air. The oxidation was carried out at 600°C for 2 hours. After the oxidation was completed, the furnace was cooled to room temperature. The sample was then removed and stored in a drying oven.

[0059] The alloys of Examples 1, 2, and 3 that underwent femtosecond laser treatment were observed using a scanning electron microscope. Figure 1 (a) is a striped periodic structure LIPSS after laser treatment. It can be seen that the surface stripes are evenly distributed and the stripe period is about 240nm. Figure 1 (b) is a Groove structure that has been laser-processed to resemble a small island. This structure is formed on the basis of the LIPSS structure, similar to the stripes being broken. Its period is about 580 nm. Figure 1 (c) is a raised structure formed after laser processing. This structure has a relatively large period, approximately 10.03 μm.

[0060] The alloys of Comparative Example 1, Examples 1, 2, and 3 were observed using scanning electron microscopy. Figure 2 The interface after thermal oxidation of the substrate shows an oxide film of 2.606 μm. Figure 3 The depth of the LIPSS structure after laser-assisted thermal oxidation treatment is 4.661 μm. Figure 4 The oxide film depth of the Groove structure after laser combined with thermal oxidation treatment is 10.500 μm. Figure 5 The oxide film depth of the Bulge structure after laser-assisted thermal oxidation is 15.48 μm. The elemental distribution at the interfaces of different structures is the same as that of the substrate sample. The oxide ceramic layer covers the structure according to the laser beam path, and the oxide layer depth increases with structural evolution. The LIPSS structure has the smallest depth at 4.661 μm, the Groove structure at 10.500 μm, and the Bulge structure at 15.48 μm.

[0061] The alloys of Comparative Example 1, Examples 1, 2, and 3 were subjected to XRD tests, and the results are as follows: Figure 6 As shown, matrix peaks α-Zr and β-Zr are still present in the matrix that has only undergone thermal oxidation treatment. This is because Zr and O have not reacted completely, resulting in a thin oxide film that cannot completely absorb X-rays. At the same time, a small amount of room temperature stable phase m-ZrO2 (monoclinic zirconia) appears. The appearance of this phase is due to the transformation of martensite into m-ZrO2 at room temperature.

[0062] Friction and wear tests were conducted on the alloys of Comparative Example 1, Examples 1, 2, and 3. After the tests, the surface wear depth was measured using a surface profilometer, and the wear amount was calculated. The wear amount results are as follows: Figure 7 As shown, from Figure 7As can be seen from the data, the LIPSS structure exhibits the most significant wear, with a reduction of nearly 35% compared to the matrix sample. This indicates that the structure bonds most firmly to the matrix after thermal oxidation and possesses the best wear resistance.

[0063] Hemolysis experiments were conducted on the alloys of Comparative Example 1, Examples 1, 2, and 3, and the experimental data are as follows: Figure 8 As shown in the figure, the hemolysis rate of all samples was less than 5%, indicating that the samples have good biocompatibility and are suitable as materials for human implants.

[0064] In summary, samples treated with femtosecond laser combined with thermal oxidation exhibit excellent wear resistance, providing theoretical guidance for artificial joint prosthesis implantation technology.

[0065] This invention is illustrated by way of examples, but does not constitute a limitation thereof. Referring to the description of this invention, other variations in the disclosed examples are readily conceived by researchers in the field of zirconium alloys, and such variations should fall within the scope defined by the claims of this patent.

[0066] Matters not covered in this invention are common knowledge.

Claims

1. A method for femtosecond laser combined with thermal oxidation composite treatment of ZrNb alloy, characterized in that the method includes the following steps: Step 1: Wire EDM processing; ZrNb alloy is processed into sheets using a wire EDM machine; Step 2: Grinding and polishing; Step 3: Femtosecond laser pre-parameter adjustment; The workpiece obtained in the previous step is fixed on an electric displacement platform. The laser beam acts on the surface of the workpiece through a focusing lens. By changing the scanning speed, laser frequency, and laser power, the femtosecond laser parameters are controlled to obtain one of the following three structures. Structure 1: Frequency 310KHz, defocusing amount 1mm, line spacing 0.07mm, scanning speed 150mm / s, laser power 2.8W, constructing a LIPSS structure; Alternatively, structure two: frequency 310KHz, defocus amount 1mm, line spacing 0.07mm, scanning speed 150mm / s, laser power 10W, to construct the Groove structure; Alternatively, structure three: frequency 40KHz, line spacing 0.07mm, defocusing amount 1mm, scanning speed 2mm / s, laser power 0.6W, to construct the Bulge structure; Step 4: Thermal oxidation treatment The femtosecond laser-treated sample was placed in a muffle furnace and heated to 500-800℃ for 1.5-2.5 hours in an oxidizing atmosphere of air. After heating, the sample was cooled to room temperature with the furnace. The thickness of the sheet material mentioned in the first step is 1.0~5.0mm; The ZrNb alloy mentioned in the first step is specifically a Zr-2.5Nb alloy; The grinding and polishing process described in the second step is as follows: The cut ZrNb alloy is ground in sequence with SiC sandpaper of grades 60#, 240#, 600#, 800#, 1000#, 2000#, 3000#, and 5000# until there are no obvious scratches on the sample surface. Then, it is polished with polishing liquid, cleaned with deionized water, immersed in alcohol for ultrasonic cleaning for 10-20 minutes, and dried for later use. In the fourth step, the heating rate is 3~6℃ / min.

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