A method for determining optimal time of thermal oxidation of titanium alloy based on oxidation kinetics

Abstract

The application belongs to the technical field of surface treatment, and particularly relates to a method for determining optimal time of thermal oxidation of titanium alloy based on oxidation kinetics. The application establishes a determination method of "establishing a normal oxidation growth standard curve, comparing measured data of a small number of time points, identifying a peeling critical point lower than the standard curve, and taking the last normal growth point before peeling as the best". Whether the oxidation film is converted from normal growth to cracking and peeling stage can be judged through oxidation weight gain data of a small number of time points. Compared with a traditional full-time scanning and a large number of performance test screening method, the method can significantly reduce the sample quantity, experimental period and process screening cost, and improve the scientificity of the determination of the optimal thermal oxidation time. The method provided by the application is simple in process and beneficial to industrialization promotion.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment technology, specifically relating to a method for determining the optimal time for thermal oxidation of titanium alloys based on oxidation kinetics. Background Technology

[0002] With the rapid development of biomedical devices, especially the increasing demands on material performance for long-term implantable devices such as artificial joints and dental implants, traditional titanium alloys are gradually becoming insufficient to meet the application requirements of synergistic low modulus and high wear resistance. Titanium-niobium (Ti–Nb) near-β-type titanium alloys, due to their low elastic modulus, excellent biocompatibility, and good corrosion resistance, have become an important development direction for next-generation medical titanium alloys. Compared to traditional α+β-type titanium alloys such as Ti-6Al-4V, these materials do not contain potentially harmful elements such as Al and V, and their elastic modulus is closer to that of human bone tissue, which helps reduce the "stress shielding effect," showing promising application prospects in the field of orthopedic implants.

[0003] However, existing Ti-Nb alloys still have significant shortcomings in actual service, especially their poor surface wear resistance, making it difficult to meet the requirements of high load and long service life. These alloys have low hardness, making them prone to wear failure during frictional contact, leading to surface damage and performance degradation. In applications such as artificial joints, wear particles can also trigger adverse biological reactions, further affecting the stability and lifespan of the implant. Therefore, improving the surface wear resistance of Ti-Nb alloys while maintaining their low elastic modulus advantage has become a key issue restricting their engineering applications.

[0004] To address the aforementioned issues, existing technologies typically employ surface modification methods such as physical vapor deposition, plasma spraying, micro-arc oxidation, and laser cladding to improve wear resistance. However, these methods generally suffer from high equipment requirements, complex processes, high costs, or insufficient coating stability. Furthermore, under long-term service conditions, coating cracking and peeling are prone to failure, making it difficult to meet the needs of practical engineering applications. Therefore, developing a surface strengthening method that is simple in process, cost-effective, requires no complex equipment, and is suitable for large-scale production is of great significance for improving the wear resistance and service reliability of Ti-Nb alloys. In contrast, thermal oxidation treatment in an air atmosphere can achieve surface strengthening by generating an oxide film in situ on the alloy surface. It features simple process, low equipment requirements, and good engineering applicability, making it a low-cost surface modification method with application potential. The key challenge of thermal oxidation treatment lies in controlling the oxidation time. Appropriately extending the thermal oxidation time is beneficial for promoting oxide film growth, thereby improving the surface hardness, wear resistance, and corrosion resistance of the alloy. However, when the oxidation time is too long, the oxide film thickness continuously increases, and the internal thermal stress and growth stress of the film layer accumulate continuously. At the same time, there is a difference in the coefficient of thermal expansion and structural matching between the oxide film and the titanium alloy substrate, which can easily induce oxide film cracking, local breakage, or even peeling. The decline in oxide film integrity weakens the surface strengthening effect. Therefore, thermal oxidation treatment presents a technical contradiction: "the oxide film needs to be thick enough to exert a strengthening effect, but if it is too thick, it is prone to cracking and peeling."

[0005] Current thermal oxidation process optimization typically relies on preparing a large number of samples at different times and subsequent testing of hardness, tribology, and corrosion performance. The optimal treatment time is then empirically determined by comparing experimental results. This approach is time-consuming, consumes many samples, and often only passively confirms over-oxidation after failure occurs, making it difficult to identify the critical time point at which the oxide film transitions from stable growth to cracking and peeling. Therefore, there is an urgent need to establish a method that can rapidly identify the peeling critical point and determine the optimal thermal oxidation treatment time based on small-sized samples and a limited number of experiments. This would reduce process screening costs and improve the reliability of thermal oxidation process determination. Summary of the Invention

[0006] The purpose of this invention is to provide a method for determining the optimal time for thermal oxidation of titanium alloys based on oxidation kinetics.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for determining the optimal time for thermal oxidation of titanium alloys based on oxidation kinetics, comprising the following steps: Using the oxidation kinetic equation (Δm / S) n =kt establishes a standard parabolic curve for normal oxidative growth, where n=2; the abscissa of the standard parabolic curve is time t, and the ordinate is Δm / S; At a set temperature, the titanium alloy sample to be tested is subjected to thermal oxidation treatment for different test times, the oxidation weight gain at different times is measured, and the Δm / S value is calculated; the number of test times is not less than 4, the difference between adjacent test times is not less than 30 min, and the maximum value of the test time does not exceed the abscissa value corresponding to the vertex of the standard parabola; Substitute (x, y) into the standard parabolic curve, and take the x-coordinate value corresponding to the last point that falls on the standard parabolic curve as the optimal time for thermal oxidation, where x is the thermal oxidation test time and y is the calculated value of Δm / S.

[0008] Preferably, the titanium alloy sample to be tested includes 25-27% Nb, 3.5-4.5% Zr, 3.5-4.5% Sn, 0.8-1.2% Mo, 0.8-1.2% Ta, and the balance Ti.

[0009] Preferably, the method for preparing the titanium alloy test sample includes the following steps: According to the composition of the titanium alloy sample to be tested, the raw materials were melted to obtain an alloy ingot; The alloy ingot was subjected to annealing and deformation treatments in sequence to obtain the titanium alloy sample to be tested.

[0010] Preferably, the melting method is vacuum non-consumable arc melting; the melting conditions include: temperature of 2500~3000℃, time of 60~120min, and vacuum degree ≤0.01Pa.

[0011] Preferably, the annealing conditions include: a temperature of 1050~1150℃, a time of 24~48h, and the annealing is carried out under vacuum conditions.

[0012] Preferably, the deformation treatment includes hot rolling deformation or cold rolling deformation; the deformation amount of hot rolling deformation is ≥80%; and the deformation amount of cold rolling deformation is ≤30%.

[0013] Preferably, after the deformation process, the steps further include cutting, grinding, polishing, cleaning, and drying in sequence; The polishing is performed using 2000-grit sandpaper; the surface roughness Ra after polishing is ≤0.5μm. The cleaning process involves ultrasonic cleaning in acetone and anhydrous ethanol, with each solvent requiring 10-15 minutes of ultrasonic cleaning.

[0014] Preferably, the number of test times is 4, and the difference between adjacent test times is 2 hours.

[0015] Preferably, the thermal oxidation treatment is carried out in an air atmosphere; the set temperature is 873k~1073k.

[0016] Preferably, after obtaining the optimal thermal oxidation time, the method further includes testing the surface morphology, surface hardness, tribological wear performance, and electrochemical corrosion performance of samples obtained at different test times to verify the determined optimal thermal oxidation time.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The optimal thermal oxidation process can be quickly determined using a small number of small-sized samples and a small number of thermal oxidation time points: This invention establishes a method for determining the optimal process by “establishing a standard curve for normal oxidation growth → comparing measured data at a small number of time points → identifying the peeling critical point below the standard curve → identifying the last normal growth point before peeling as the optimal point”. By using oxidation weight gain data at a small number of time points, it is possible to determine whether the oxide film has transitioned from normal growth to the cracking and peeling stage. Compared with traditional full-time scanning and large-scale performance testing screening methods, this method can significantly reduce the number of samples, experimental cycle and process screening costs, and improve the scientific validity of determining the optimal thermal oxidation time.

[0018] (2) The thermal oxidation process is simple and conducive to industrial promotion: The thermal oxidation process of the present invention can be completed under normal conditions. It does not require vacuum equipment, external coating device, or complex post-processing. The equipment investment is low, the operation is simple, and it is easy to realize large-scale industrial production.

[0019] (3) The optimal comprehensive performance is achieved at the determined 6h time point: Through the optimal time (1073K, 6h) determined by the present invention, the nano hardness of the alloy surface is increased from 4.76GPa to about 14.86GPa, the specific wear rate is reduced by two orders of magnitude, the self-corrosion potential is positively shifted by about 150mV, and the corrosion resistance is significantly improved.

[0020] (4) Low modulus characteristics are maintained: thermal oxidation only changes the surface microstructure, while the β phase and α″ phase structure inside the matrix remain stable. The overall low elastic modulus characteristics of the alloy are not affected, and the stress shielding effect can still be effectively reduced.

[0021] (5) It has universality and can be extended to other titanium alloy systems: The method of “identifying the optimal time based on the deviation of oxidation weight gain from the normal growth curve” proposed in this invention is not only applicable to Ti-26Nb-4Zr-4Sn-1Mo-1Ta alloy, but can also be extended to other multi-element titanium alloy thermal oxidation systems, providing a general idea for the rapid optimization of titanium alloy surface strengthening process. Attached Figure Description

[0022] Figure 1 The oxidation kinetic curves of the samples oxidized at 1073K for 2h, 4h, 6h and 8h in the examples are compared with the standard curve of normal oxidation growth. Figure 2Here is a scanning electron microscope image of the surface morphology of the sample thermally oxidized at 1073K for 2 hours in the example; Figure 3 Here is a scanning electron microscope image of the surface morphology of the sample thermally oxidized at 1073K for 4 hours in the example; Figure 4 Here is a scanning electron microscope image of the surface morphology of the sample thermally oxidized at 1073K for 6 hours in the example; Figure 5 Here is a scanning electron microscope image of the surface morphology of the sample thermally oxidized at 1073K for 8 hours in the example; Figure 6 The X-ray photoelectron spectra (XPS) of the samples thermally oxidized at 1073K for 2h, 4h, 6h and 8h in the examples are shown. Figure 7 The X-ray photoelectron fine spectra (XPS) of the samples thermally oxidized at 1073 K for 2 h, 4 h, 6 h and 8 h in the examples are shown. Figure 8 The Vickers hardness test results are for untreated alloy samples and samples hot-oxidized at 1073K for 2h, 4h, 6h and 8h. Figure 9 The wear track profiles of untreated alloy samples and samples subjected to thermal oxidation at 1073K for 2h, 4h, 6h and 8h are shown. Figure 10 The results show the specific wear rate of untreated alloy samples and samples oxidized at 1073K for 2h, 4h, 6h and 8h. Figure 11 The potentiodynamic polarization curves are for untreated alloys and samples thermally oxidized at 1073 K for 2 h, 4 h, 6 h and 8 h. Figure 12 Tensile mechanical properties curves for the untreated alloy and the sample oxidized at 1073 K for 2 hours; Figure 13 Tensile mechanical properties curves of samples thermally oxidized at 1073 K for 4 h and 6 h; Figure 14 The tensile mechanical properties curve of the sample after thermal oxidation at 1073 K for 8 hours. Detailed Implementation

[0023] This invention provides a method for determining the optimal time for thermal oxidation of titanium alloys based on oxidation kinetics, comprising the following steps: Using the oxidation kinetic equation (Δm / S) n =kt establishes a standard parabolic curve for normal oxidative growth, where n=2; the abscissa of the standard parabolic curve is time t, and the ordinate is Δm / S; At a set temperature, the titanium alloy sample to be tested is subjected to thermal oxidation treatment for different test times, the oxidation weight gain at different times is measured, and the Δm / S value is calculated; the number of test times is not less than 4, the difference between adjacent test times is not less than 30 min, and the maximum value of the test time does not exceed the abscissa value corresponding to the vertex of the standard parabola; Substitute (x, y) into the standard parabolic curve, and take the x-coordinate value corresponding to the last point that falls on the standard parabolic curve as the optimal time for thermal oxidation, where x is the thermal oxidation test time and y is the calculated value of Δm / S.

[0024] This invention utilizes the oxidation kinetic equation (Δm / S) n =kt establishes a standard parabolic curve for normal oxidative growth.

[0025] In this invention, n (oxidation kinetic index) = 2; where k is the oxidation rate constant, with a value of 2.59 × 10⁻⁶. -1 mg·cm -2 Δm / S represents the weight gain due to oxidation per unit area S; t represents the thermal oxidation time.

[0026] This invention involves subjecting a titanium alloy sample to thermal oxidation treatment at a set temperature for different test times, measuring the weight gain due to oxidation at different times, and obtaining the calculated value of Δm / S.

[0027] In this invention, the titanium alloy test sample preferably comprises, by mass percentage, 25-27% Nb, 3.5-4.5% Zr, 3.5-4.5% Sn, 0.8-1.2% Mo, 0.8-1.2% Ta, and the balance Ti. In a specific embodiment of this invention, the titanium alloy test sample preferably comprises 26% Nb, 4% Zr, 4% Sn, 1% Mo, 1% Ta, and the balance Ti. In this invention, the titanium alloy test sample is preferably a near-β type titanium alloy.

[0028] In this invention, the method for preparing the titanium alloy test sample preferably includes the following steps: According to the composition of the titanium alloy sample to be tested, the raw materials were melted to obtain an alloy ingot; The alloy ingot was subjected to annealing and deformation treatments in sequence to obtain the titanium alloy sample to be tested. In this invention, the preferred melting method is vacuum non-consumable arc melting; the preferred melting conditions include: a temperature of 2500~3000℃, specifically 2500℃, 2600℃, 2700℃, 2800℃, 2900℃, or 3000℃; a time of 60~120min, specifically 60min, 70min, 80min, 90min, 100min, 110min, or 120min; a vacuum degree ≤0.01Pa; and the preferred number of melting cycles is no less than 6. In this invention, the preferred annealing conditions include: a temperature of 1050~1150℃, specifically 1050℃, 1100℃, or 1150℃; a time of 24~48h, specifically 24h, 30h, 36h, 42h, or 48h; the annealing is preferably performed under vacuum conditions; and after annealing, air cooling to room temperature is also preferred.

[0029] In this invention, the deformation treatment method preferably includes hot rolling deformation or cold rolling deformation; the deformation amount of hot rolling deformation is preferably ≥80%; the deformation amount of cold rolling deformation is preferably ≤30%.

[0030] In this invention, after the deformation treatment, the process preferably includes cutting, grinding, polishing, cleaning, and drying in sequence; the cutting method is preferably wire cutting; the size of the cut sample is preferably 10mm×10mm×3mm; the grinding is preferably performed using 2000-grit sandpaper; the surface roughness Ra of the polished surface is preferably ≤0.5μm; the cleaning is preferably performed by ultrasonic cleaning in acetone and anhydrous ethanol respectively, and the ultrasonic cleaning time in each solvent is preferably 10~15min.

[0031] In this invention, the thermal oxidation treatment is preferably carried out in an air atmosphere; the set temperature is preferably 873K~1073K, specifically 873K, 973K, or 1073K; after the thermal oxidation treatment, it is also preferable to air cool to room temperature.

[0032] In this invention, the number of test times is no less than four, the difference between adjacent test times is no less than 30 minutes, and the maximum value of the test time does not exceed the abscissa value corresponding to the vertex of the standard parabolic curve. In a specific embodiment of this invention, the number of test times is preferably four, and the difference between adjacent test times is preferably 2 hours.

[0033] In this invention, after obtaining the optimal thermal oxidation time, it is also preferable to test the surface morphology, surface hardness, tribological wear performance and electrochemical corrosion performance of the samples obtained at different test times, and to verify the determined optimal thermal oxidation time.

[0034] The present invention does not impose any special limitations on the testing methods for the surface morphology, surface hardness, tribological wear performance and electrochemical corrosion performance, and any methods well known to those skilled in the art can be used.

[0035] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0036] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0037] Example 1 This embodiment provides a near-β type titanium alloy sample with the composition Ti-26Nb-4Zr-4Sn-1Mo-1Ta, that is, the Nb content is 26wt.%, the Zr content is 4wt.%, the Sn content is 4wt.%, the Mo content is 1wt.%, the Ta content is 1wt.%, and the balance is Ti and unavoidable impurities; According to the above composition, high-purity Ti, Nb, Zr, Sn, Mo and Ta raw materials were weighed and alloy ingots were prepared by vacuum non-consumable arc melting method. During the melting process, the alloy ingot was melted for 120 min at a temperature of 3000℃ and a vacuum degree of less than 0.01 Pa, and the alloy ingot was turned over and remelted at least 6 times. After the melting was completed, the obtained ingot was placed in a vacuum environment and homogenized and annealed at 1100℃ for 24 h, and then air-cooled to room temperature. The homogenized annealed alloy was hot-rolled and deformed by 80%, and then processed into sheet-shaped samples of 10mm×10mm×3mm by wire cutting. The surface of the sample was sanded with sandpaper to 2000#, and then polished with diamond polishing paste to a mirror finish, so that the surface roughness Ra≤0.5μm. The polished sample was then ultrasonically cleaned in acetone and anhydrous ethanol for 15min each, and then dried with cold air for later use.

[0038] Example 2 Verify the optimal thermal oxidation time of the titanium alloy sample obtained in Example 1 at 1073 K; The titanium alloy obtained in Example 1 was placed in a muffle furnace and subjected to thermal oxidation treatment in an air atmosphere. The thermal oxidation temperature was fixed at 1073K, and the thermal oxidation test times were set to 2h, 4h, 6h and 8h respectively. After the muffle furnace was heated to 1073K and stabilized, the sample was quickly placed into the constant temperature zone of the furnace and held at that temperature for the corresponding time. Then it was taken out and air-cooled to room temperature. The mass of each sample before and after thermal oxidation was measured using a precision electronic balance. Each sample was weighed at least three times and the average value was taken. Based on the mass difference of the sample before and after thermal oxidation and the exposed surface area, the weight gain per unit area was calculated, which yielded the calculated value of Δm / S. A standard parabolic curve for normal oxidative growth was established using an oxidation kinetic equation, which is (Δm / S)^n = kt; where Δm / S is the weight gain per unit area due to oxidation, t is the thermal oxidation time, and k is the oxidation rate constant (2.59 × 10^6). -1 mg·cm -2 ), where n is the oxidation kinetic index, n=2; Substituting the above test times and the calculated Δm / S values ​​corresponding to different test times into the standard parabolic curve, as follows: Figure 1 As shown, the data points of the samples corresponding to thermal oxidation times of 2h, 4h and 6h are basically located on the standard parabolic curve, indicating that the oxide film at the above three time points is still in a normal and continuous growth stage, and has not yet experienced obvious cracking or local peeling.

[0039] In contrast, the calculated Δm / S value for the sample at 8 hours was significantly lower than the value corresponding to the standard parabolic curve, indicating that the apparent oxidation weight gain at this time point had deviated from the normal growth pattern. This deviation suggests that as the thermal oxidation time increases, the oxide film thickness increases, and the internal thermal stress and growth stress of the film gradually accumulate. When the stress exceeds the strength of the oxide film itself or the film's stable bearing capacity, microcracks propagate and localized peeling occurs, resulting in the actual measured oxidation weight gain per unit area being far lower than the value corresponding to the normal growth standard curve.

[0040] Therefore, 8 hours was determined to be the critical time point for oxide film peeling. The last point falling on the standard parabolic curve, i.e., 6 hours, was taken as the optimal thermal oxidation time for sufficient oxide film growth and good surface integrity. Thus, the optimal thermal oxidation time for the Ti-26Nb-4Zr-4Sn-1Mo-1Ta alloy in an air atmosphere at 1073K was determined to be 6 hours.

[0041] The surface morphology, composition, surface hardness, tribological wear properties and electrochemical corrosion properties of the samples obtained under the above different test times were tested, and the determined optimal thermal oxidation time was verified. (1) Characterization of surface morphology of thermally oxidized samples It is used to observe the changes in surface morphology of untreated substrates and samples with different thermal oxidation times, and to verify the rationality of the determined optimal thermal oxidation time; The surface morphology of samples oxidized at 1073K for 2h, 4h, 6h and 8h was observed using scanning electron microscopy. Figure 2As shown, after thermal oxidation at 1073K for 2 hours, oxide nucleation and initial growth characteristics began to appear on the sample surface. The oxide distribution was insufficient, and the surface coverage was weak. When the thermal oxidation time was extended to 4 hours (…),… Figure 3 The oxides on the sample surface further grew and gradually connected, increasing the oxide film coverage and resulting in a more continuous surface morphology compared to the 1-hour sample. Further extending the thermal oxidation time to 6 hours... Figure 4 A relatively continuous and dense oxide film formed on the sample surface, and no obvious through cracks or large-area peeling areas were observed, indicating that the oxide film had good surface integrity at this time. When the thermal oxidation time was further extended to 8 hours ( Figure 5 The presence of obvious cracks, localized breakage, or peeling on the sample surface indicates that prolonged oxidation leads to stress accumulation within the oxide film, which in turn causes the oxide film to crack and become locally unstable.

[0042] The surface morphology results above indicate that samples oxidized at 1073K for 6 hours can form a relatively continuous, dense oxide film with good surface integrity; while samples oxidized at 1073K for 8 hours show oxide film cracking or localized peeling. This result is consistent with the results of the oxidation weight gain kinetic analysis, in which the measured oxidation weight gain of the 8-hour sample was significantly lower than that of the normal oxidation growth standard curve, further verifying the rationality of determining 8 hours as the critical time point for peeling and 6 hours as the optimal thermal oxidation time.

[0043] (2) Chemical composition analysis of oxide film Used to analyze the chemical composition of the oxide film on the surface of samples after thermal oxidation; X-ray photoelectron spectroscopy is used to analyze the surfaces of different samples. For example... Figure 6 and Figure 7 As shown, Ti is present on the surface of all samples. 4+ and Nb 5+ Oxidation state, where Ti 2p 3 / 2 The peak corresponds to Ti in TiO2 4+ Nb3d 5 / 2 The peak corresponds to Nb in Nb2O5 5+ This indicates that the surface layer of the sample after thermal oxidation is mainly composed of stable oxides such as TiO2 and a small amount of Nb2O5.

[0044] Further verification of the oxidation products and elemental distribution can be achieved using X-ray diffraction or energy dispersive spectroscopy. Since X-ray photoelectron spectroscopy mainly reflects the chemical state of the sample surface, the conclusions regarding the composition of the oxide film in this detection example are primarily used to describe the chemical state of the outermost oxide layer, without limiting the phase composition to be completely consistent throughout the thickness of the entire oxide layer.

[0045] (3) Oxide film surface hardness test This study evaluated the effect of thermal oxidation treatment on the surface hardness of Ti-26Nb-4Zr-4Sn-1Mo-1Ta alloy. Nanoindentation tests were performed on untreated samples and samples after 2 hours, 4 hours, 6 hours, and 8 hours of oxidation. At least five test points were selected on the surface of each sample, and the average value was taken as the hardness value of that sample. Figure 8 The test results show that the surface nanohardness of the untreated titanium alloy is approximately 4.76 GPa. After thermal oxidation treatment at 1073 K, the surface hardness of the samples significantly increased, gradually increasing with the oxidation time from 2 h to 6 h. Specifically, the nanohardness of the 2-h sample was approximately 8.95 GPa, the 4-h sample was approximately 12.81 GPa, and the 6-h sample reached approximately 14.86 GPa. When the thermal oxidation time was further extended to 8 h, the stability of the surface hardness test decreased due to cracking and local peeling of the oxide film, and the hardness fluctuation in local areas increased. Therefore, the 6-h sample exhibited a better and more stable surface hardening effect.

[0046] (4) Tribological and wear performance test This study evaluated the tribological properties of samples after different thermal oxidation times. Ball-disc tribological tests were conducted on untreated samples and samples after 2 hours, 4 hours, 6 hours, and 8 hours of oxidation. The test medium was Hank's equilibrium salt solution, the test temperature was 37℃, the paired balls were Si3N4 ceramic balls, the load was 5N, and the sliding speed was 0.1m / s. Figure 9 As shown.

[0047] Figure 10 The test results show that the specific wear rate of the untreated alloy is approximately 21.8 × 10⁻⁶. -4 mm 3 / (N·m). The wear rate of the 2h, 4h and 6h samples decreased by about two orders of magnitude, with the 6h sample showing the lowest wear rate.

[0048] (5) Electrochemical corrosion performance test This study evaluated the corrosion resistance of samples with different thermal oxidation times in a simulated body fluid environment. Potentiodynamic polarization tests were performed on untreated samples and samples after 2 hours, 4 hours, 6 hours, and 8 hours of oxidation. The test medium was Hank's equilibrium salt solution, and the test temperature was 37℃. A standard three-electrode system was used, with the test sample as the working electrode and an exposure area of ​​1 cm². 2 A saturated calomel electrode is used as the reference electrode, and a platinum sheet is used as the counter electrode.

[0049] Figure 11 The test results show that the self-corrosion potential of the untreated alloy is approximately -450mV, and the self-corrosion current density is approximately 2.5×10⁻⁶. -6 A / cm 2After thermal oxidation treatment, the self-corrosion potential of the samples shifted positively, and the self-corrosion current density decreased significantly. Specifically, the self-corrosion potential of the sample after 2 hours was approximately -380 mV, and the self-corrosion current density was approximately 8.0 × 10⁻⁶ mV. -7 A / cm 2 The self-corrosion potential of the sample after 4 hours is approximately -320mV, and the self-corrosion current density is approximately 5.0×10⁻⁶. -7 A / cm 2 After 6 hours, the self-corrosion potential of the sample shifted further to approximately -300 mV, and the self-corrosion current density decreased to approximately 3.0 × 10⁻⁶ mV. -7 A / cm 2 .

[0050] The 6-hour sample exhibited the best corrosion resistance, indicating that the continuous and dense oxide film formed at this time effectively prevents corrosive media from penetrating into the substrate. The 8-hour sample, due to cracks and localized peeling of the oxide film, allowed corrosive media to potentially enter the oxide film along these defects, preventing further improvement in its corrosion resistance.

[0051] (6) Elastic modulus test Tensile properties of the samples were tested according to GB4338-1995 standard for high-temperature tensile testing of metallic materials. To obtain accurate strain, an extensometer was used. The equipment was an INSTRON 3369 electronic universal testing machine. Three sets of tests were performed for each item, and the average value was taken. The tensile rate was 2.0 mm / min. The resulting true stress-strain curves are shown below. Figures 12-14 As shown, by fitting the linear portion at the front end, the elastic modulus of the untreated alloy was measured to be 45±3.3 GPa, the elastic modulus of the 2h sample was 42.3±2.8 GPa, the elastic modulus of the 4h sample was 39.8±3.4 GPa, the elastic modulus of the 6h sample was the lowest at 33.5±3.3 GPa, and the elastic modulus of the 8h sample was 43.7±4.1 GPa.

[0052] As shown in the above examples and test cases, when comparing the measured oxidation weight gain data of Ti-26Nb-4Zr-4Sn-1Mo-1Ta alloy samples at 2h, 4h, 6h, and 8h in an air atmosphere with the standard curve of normal growth of parabolic oxidation (n=2), the data points of the 2h, 4h, and 6h samples are basically located on the standard curve, indicating that the oxide film is in a normal and continuous diffusion-controlled growth state at this stage. When the oxidation time is extended to 8h, the measured oxidation weight gain is significantly lower than the corresponding value of the standard curve, and cracks and local peeling appear on the oxide film surface, indicating that 8h is the critical time point for oxide film peeling. Therefore, the last normal growth time point before the peeling critical point, 6h, is determined as the optimal thermal oxidation time. After 6h of thermal oxidation at 1073K, a relatively continuous and dense TiO2 / Nb2O5 composite oxide film is formed on the alloy surface, and the surface hardness, wear resistance, and corrosion resistance are significantly improved.

[0053] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for determining the optimal thermal oxidation time of titanium alloys based on oxidation kinetics, characterized in that, Includes the following steps: Using the oxidation kinetic equation (Δm / S) n =kt establishes a standard parabolic curve for normal oxidative growth, where n=2; the abscissa of the standard parabolic curve is time t, and the ordinate is Δm / S; At a set temperature, the titanium alloy sample to be tested is subjected to thermal oxidation treatment for different test times, the oxidation weight gain at different times is measured, and the Δm / S value is calculated; the number of test times is not less than 4, the difference between adjacent test times is not less than 30 min, and the maximum value of the test time does not exceed the abscissa value corresponding to the vertex of the standard parabola; Substitute (x, y) into the standard parabolic curve, and take the x-coordinate value corresponding to the last point that falls on the standard parabolic curve as the optimal time for thermal oxidation, where x is the thermal oxidation test time and y is the calculated value of Δm / S.

2. The method according to claim 1, characterized in that, The titanium alloy sample to be tested, by mass percentage, comprises 25-27% Nb, 3.5-4.5% Zr, 3.5-4.5% Sn, 0.8-1.2% Mo, 0.8-1.2% Ta, and the balance Ti.

3. The method according to claim 1, characterized in that, The preparation method of the titanium alloy sample to be tested includes the following steps: According to the composition of the titanium alloy sample to be tested, the raw materials were melted to obtain an alloy ingot; The alloy ingot was subjected to annealing and deformation treatments in sequence to obtain the titanium alloy sample to be tested.

4. The method according to claim 3, characterized in that, The melting method is vacuum non-consumable arc melting; the melting conditions include: temperature of 2500~3000℃, time of 60~120min, and vacuum degree ≤0.01Pa.

5. The method according to claim 3, characterized in that, The annealing conditions include: a temperature of 1050~1150℃ and a time of 24~48h, and the annealing is carried out under vacuum conditions.

6. The method according to claim 3, characterized in that, The deformation treatment methods include hot rolling deformation or cold rolling deformation; the deformation amount of hot rolling deformation is ≥80%; the deformation amount of cold rolling deformation is ≤30%.

7. The method according to claim 3 or 6, characterized in that, After the deformation process, the process also includes cutting, grinding, polishing, cleaning, and drying in sequence. The polishing is performed using 2000-grit sandpaper; the surface roughness Ra after polishing is ≤0.5μm. The cleaning process involves ultrasonic cleaning in acetone and anhydrous ethanol, with each solvent requiring 10-15 minutes of ultrasonic cleaning.

8. The method according to claim 1, characterized in that, The test time is 4 times, and the difference between adjacent test times is 2 hours.

9. The method according to claim 1, characterized in that, The thermal oxidation treatment is carried out in an air atmosphere; the set temperature is 873k~1073k.

10. The method according to claim 1, characterized in that, After obtaining the optimal thermal oxidation time, the method further includes testing the surface morphology, surface hardness, tribological wear performance, and electrochemical corrosion performance of samples obtained at different test times to verify the determined optimal thermal oxidation time.

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