Titanium alloy bar with high fatigue performance and method for manufacturing the same

Abstract

The application discloses a titanium alloy rod with high fatigue performance and a preparation method thereof, and relates to the technical field of titanium alloy surface treatment. The titanium alloy rod with high fatigue performance is prepared by the following process: taking a titanium alloy rod as a substrate, depositing a TiAl alloy coating on the surface of the titanium alloy rod, and then performing low-temperature ion nitriding to form a nitriding layer, thereby obtaining the titanium alloy rod with high fatigue performance. The application forms a composite surface modification layer on the surface of the titanium alloy substrate through surface TiAl alloying and low-temperature ion nitriding. Cu, Ni and Al are helpful to refining nitride grains and provide sufficient Ti elements for subsequent nitriding, thereby forming a nitriding layer with firm combination with the substrate, high hardness and high wear resistance, and introducing residual compressive stress on the surface, so that the fatigue resistance of the titanium alloy rod is significantly improved, and the microstructure and performance characteristics of the titanium alloy substrate are maintained.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy surface treatment technology, specifically to a high-fatigue-performance titanium alloy bar and its preparation method. Background Technology

[0002] In applications with extreme performance requirements, surface-coated titanium alloy bars are irreplaceable. Coating types include wear-resistant coatings, fretting fatigue-resistant coatings, oxidation-resistant coatings, corrosion-resistant coatings, and dry film lubrication coatings. Some titanium alloy components often bear both frictional contact and alternating fatigue loads during their service life. However, titanium alloys have low hardness and poor wear resistance, making them prone to wear when in frictional contact with other titanium alloys or materials, which greatly limits their engineering applications. Conventional surface treatments such as electroplating, thermal spraying, and vapor deposition, while improving the wear resistance of titanium alloys, often cause serious damage to their fatigue performance. Therefore, we propose a high-fatigue-performance titanium alloy bar and its preparation method. Summary of the Invention

[0003] The purpose of this invention is to provide a high-fatigue-performance titanium alloy bar and its preparation method, so as to solve the problems mentioned in the background art.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing high fatigue performance titanium alloy bars, comprising the following processes:

[0005] A titanium alloy rod is used as the substrate, and a TiAl alloy coating is deposited on its surface. Then, low-temperature ion nitriding is performed to form a nitriding layer, resulting in a titanium alloy rod with high fatigue performance.

[0006] Furthermore, the titanium alloy matrix comprises the following components by mass percentage: iron: ≤0.30%, carbon: ≤0.08%, nitrogen: ≤0.03%, oxygen: ≤0.25%, hydrogen: <0.005%, with the balance being titanium and other alloying elements.

[0007] Furthermore, the titanium alloy matrix is ​​one of TA2, TC4, Ti-6Al-4V, GR2, GR4, and TA15.

[0008] Furthermore, the titanium alloy matrix comprises the following components by mass percentage: aluminum (Al): 4.5–5.5%, molybdenum (Mo): 4.0–5.0%, vanadium (V): 4.5–5.5%, chromium (Cr): 3.0–4.0%, zirconium (Zr): 3.5–4.5%, tantalum (Ta) or palladium (Pd): 0.5–1.0%, iron (Fe): ≤0.25%, carbon (C): ≤0.08%, nitrogen (N): ≤0.03%, oxygen (O): ≤0.10%, hydrogen (H): <0.005%; the balance being titanium (Ti).

[0009] The substrate is cleaned and surface activated to remove oxide layers and contaminants.

[0010] In the above technical solution, the titanium alloy matrix includes a basic high-strength and high-toughness component: the Ti-Al-Mo-V-Cr-Zr system, which achieves its performance through the composite addition of multi-component β-stabilizing elements and aging strengthening; and contains components with high fatigue resistance: on the basis of reducing the content of impurities such as Fe and O, and preferentially selecting beneficial elements such as Mo and Zr to ensure the purity of the alloy and reduce fatigue crack initiation points from the source.

[0011] Aluminum (Al) is a major α-phase stabilizing element and solid solution strengthening element. It improves the strength, elastic modulus, and hot strength of alloys, but excessive amounts can form brittle phases, reducing toughness and thermal stability. Molybdenum (Mo), vanadium (V), and chromium (Cr) are all β-phase stabilizing elements. As core elements, they significantly improve hardenability, ensuring a uniform β-phase microstructure across the entire cross-section of large-section materials during heat treatment; they also exert solid solution strengthening effects, reinforcing the β-phase matrix; and during subsequent aging treatment, they precipitate fine α-phase from the metastable β-phase, achieving high alloy strength. Zirconium (Zr) is a neutral element with high solid solubility in both α-Ti and β-Ti, significantly enhancing solid solution strengthening without significantly altering the phase ratio; it also improves strength and toughness, and enhances hot working properties. Palladium (Pd) or tantalum (Ta) are noble metal elements that greatly improve the corrosion resistance of alloys, exhibiting excellent resistance to crevice corrosion in non-oxidizing reducing acids and chloride environments. Iron (Fe), oxygen (O), and hydrogen (H) are impurity elements and need to be strictly controlled at low levels to prevent their negative impact on plasticity, toughness, and thermal stability.

[0012] Furthermore, the titanium alloy matrix is ​​prepared by the following process:

[0013] Sponge titanium is mixed with alloying elements, smelted, and cast into ingots; then it undergoes forging, rolling, heat treatment, machining, surface treatment, non-destructive testing and physical and chemical inspection, labeling, packaging, and warehousing in sequence.

[0014] Furthermore, the sponge titanium is grade 0 sponge titanium, with alloying elements added in the form of aluminum granules, Al-Mo master alloy, Al-V master alloy, Al-Cr master alloy, pure Zr, and pure Ta / Pd particles.

[0015] Furthermore, the smelting process employs vacuum consumable arc melting (VAR), with low-current arc initiation. The initial smelting is performed at 8000–10000A, followed by a second VAR smelting at 10000–12000A, and a third smelting at 12000–15000A. The vacuum level is <5×10⁻⁶. - 2 Pa.

[0016] Furthermore, forging includes the following processes:

[0017] Forging of billets: temperature 1050~1150℃, deformation per forging 20~40%, total deformation >60%, final forging temperature ≥950℃;

[0018] Intermediate forging: temperature 900~950℃, deformation per forging 30~50%, total deformation 50~70%, final forging temperature ≥850℃;

[0019] Final forging: Temperature 800~820℃, deformation per forging pass 15~30%, total deformation 40~60%, final forging temperature ≥780℃, air cooling or wind cooling.

[0020] Furthermore, in the rolling process, the heating temperature is 800-850℃, the final rolling temperature is >800℃, the deformation per pass is 10-20%, the total deformation is 70-90%, and the final rolling temperature is ≥780℃; air cooling is used.

[0021] Furthermore, heat treatment is performed using annealing or solution treatment followed by aging.

[0022] Solution treatment: Temperature 870~890℃, holding time 1 hour + 1 hour for every 25mm section, water quenching;

[0023] Aging treatment: Temperature 500~580℃, holding time 4~8 hours, air cooling;

[0024] Annealing: Temperature 800~820℃, holding time 1~2 hours, air cooling.

[0025] Further surface treatments include pickling and shot peening / blasting. Pickling uses a mixed acid solution of HF-HNO3 to remove the surface oxide layer (alpha contaminant layer) and embedded iron contaminants. Shot peening / blasting is used to improve surface condition or introduce beneficial residual compressive stress, thereby increasing fatigue strength.

[0026] In a mixed acid solution of HF-HNO3, the ratio of HF:HNO3:H2O is 1:3:(6-10), the pickling temperature is 40-50℃, and the pickling time is 5-15 min.

[0027] Sandblasting uses 100-150 mesh alumina sand or glass beads at a pressure of 0.3-0.5 MPa;

[0028] In the shot peening process, the strength is 0.15~0.25mmA, the coverage is ≥100%, and the shot is cast steel shot, ceramic shot or glass shot.

[0029] Furthermore, the TiAl alloy coating was obtained by DC magnetron sputtering deposition.

[0030] The process parameters for magnetron sputtering are: power 80-120W, working gas pressure 0.4-0.8Pa (3-6mTorr), target-substrate distance 100-120mm, and stage rotation speed 10-20rpm.

[0031] Furthermore, the target material used in the preparation of the TiAl alloy coating is a TiAl alloy target, a TiCuAl alloy target, or a TiNiAl alloy target.

[0032] Furthermore, the TiCuAl alloy target material comprises the following components by mass percentage: Ti: 60-70%, Cu: 20-30%, Al: 5-10%, deposited to form a TiCuAl alloy coating.

[0033] Furthermore, the TiNiAl alloy target material comprises the following components by mass percentage: Ti: 60-70%, Ni: 20-30%, Al: 5-10%, deposited to form a TiNiAl alloy coating.

[0034] Furthermore, the thickness of the TiAl alloy coating is 1–3 μm.

[0035] Furthermore, the low-temperature ion nitriding process is as follows:

[0036] Titanium alloys with a TiAl alloy coating are placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen (N2) and argon (Ar) is introduced. The pressure in the vacuum chamber is adjusted to 30–50 Pa. A DC pulse power supply is applied to the workpiece electrode and the auxiliary electrode to perform glow discharge nitriding treatment. The treatment temperature is 450–500 °C and the time is 4–24 h. The furnace is then cooled after treatment.

[0037] Furthermore, the flow ratio of N2 to Ar is 1:4 to 1:3.

[0038] The nitrided workpiece is polished to remove the loose surface layer, reduce surface roughness, and obtain the final high-fatigue-performance titanium alloy bar.

[0039] In the above technical solution, (1) a composite surface modification layer is formed on the surface of the titanium alloy substrate by surface alloying (TiCuAl coating) and low temperature ion nitriding process. The TiCuAl coating is an intermediate layer. Nitrogen atoms will preferentially react with Ti. A large number of Cu phases will exist in the form of soft islands, which can absorb stress, inhibit crack propagation, and form short-circuit diffusion paths inside the coating. The diffusion rate of nitrogen atoms along these paths is much higher than the diffusion rate in the titanium alloy substrate, which reduces the energy barrier required for the formation of Ti-N bonds. This allows nitrogen atoms to be absorbed in large quantities and quickly and combined with Ti at a low temperature of 400-500℃ to form high-density fine nitride (such as TiN, Ti2N) particles. Al exhibits higher reactivity than Ti and a stronger affinity for N, preferentially reacting with N to form fine AlN particles. These particles act as heterogeneous nucleation sites, refining TiN grains and creating more grain boundaries and defects, providing short-circuit paths for further nitrogen diffusion and acting as a catalyst. Simultaneously, these AlN particles play a strong role in dispersion strengthening and grain refinement within the diffusion layer. The plastic deformation capability of the Cu phase can coordinate and release the internal stress generated by nitride formation, as well as the thermal stress between the coating and the substrate, effectively suppressing the formation of microcracks. This is crucial for achieving high bonding strength and high fatigue performance.

[0040] Ultimately, a composite reinforcing layer is formed with hard TiN, Ti2N and AlN as the skeleton to bear the load, and soft Cu phase as the filler to wrap these particles. It has high surface hardness, which greatly improves the wear resistance of the material. It absorbs energy through plastic deformation, blunts crack tips, and improves toughness.

[0041] (2) Ti and Al have good compatibility with the titanium alloy matrix. At the nitriding temperature, a more gentle interdiffusion occurs at the interface between the coating and the matrix, forming a strong metallurgical bond. Furthermore, the volume expansion caused by nitriding generates compressive stress at the interface, which helps to improve the bonding strength, which is the basis for ensuring improved fatigue performance.

[0042] (3) The infiltration of nitrogen atoms and the formation of new phases (TiN, AlN) during the nitriding process will cause volume expansion. This expansion is constrained by the matrix, thus forming a residual compressive stress layer on the material surface. This compressive stress layer can effectively offset the tensile stress generated by external loads, greatly suppress the initiation of fatigue cracks, and thus improve the fatigue resistance of titanium alloy bars.

[0043] The low-temperature nitriding process (<500℃) ensures that the microstructure of the titanium alloy matrix remains unchanged, avoiding grain coarsening and phase transformation embrittlement caused by overheating, thus preserving the core's strength and toughness balance. The resulting bars not only exhibit outstanding fatigue performance, but also show simultaneous enhancements in surface hardness, wear resistance, and corrosion resistance. This fully leverages the advantages of surface modification technology, stably producing titanium alloy bars with high fatigue performance, capable of meeting the stringent requirements for comprehensive material performance in key components of high-end equipment.

[0044] The Ni element in the TiNiAl coating creates numerous rapid diffusion channels for nitrogen atoms and catalyzes the nitriding reaction at low temperatures, achieving deep nitriding at low temperatures. After prolonged nitriding, a nitrided diffusion layer of considerable thickness and a smooth transition in hardness is formed. This layer bonds firmly to the substrate, preventing abrupt changes in performance. The high-hardness nitride layer on the surface and the diffusion layer beneath it effectively suppress the initiation of fatigue cracks. More importantly, the nitriding process and subsequent polishing introduce significant residual compressive stress on the surface, which greatly offsets the tensile stress generated by external alternating loads, thereby significantly improving the fatigue limit and fatigue life. The low-temperature nitriding process ensures that the microstructure and strength-toughness balance of the titanium alloy substrate itself do not deteriorate. Replacing Cu with Ni optimizes the rapid diffusion channels for nitrogen atoms, catalyzes the low-temperature nitriding process, increases the thickness of the nitrided layer, and improves layer toughness and adhesion.

[0045] Furthermore, the alloy target material also contains 0.5% to 2% rare earth elements, specifically yttrium (Y) and cerium (Ce). Introducing rare earth elements can refine the grains of the coating and nitriding layer, promote nitrogen diffusion, increase the nitriding rate and layer depth, and enhance the coating's toughness and adhesion.

[0046] Furthermore, in the alloy target material, silicon (Si) is used to partially replace Ni or Cu;

[0047] Replacement amount: 1-5% Ni or Cu. Introducing silicon can significantly improve the high-temperature oxidation resistance and hardness of the bar, and at higher temperatures (such as 500-600℃), it has better oxidation resistance, temper softening resistance and thermal fatigue performance.

[0048] Furthermore, in the low-temperature ion nitriding process, methane is also introduced, with a flow ratio of 1:10 to 1:5 with N2.

[0049] In low-temperature ion nitriding, methane, along with active nitrogen atoms, diffuses into the coating and substrate surface to form carbonitriding compounds such as Ti(CN). Compared to pure TiN or Ti₂N, this phase has a lower coefficient of friction and better toughness, effectively suppressing the initiation of fatigue cracks. The co-diffusion of C and N can produce more significant solid solution strengthening and precipitation strengthening effects, resulting in a gentler hardness gradient in the diffused layer, reducing stress concentration, and improving fatigue performance. The introduction of carbon can refine the nitride grains, making the diffused layer more dense and uniform.

[0050] Furthermore, the alloy target material undergoes surface treatment, specifically the following process: the alloy target material is placed in a boronizing agent and kept at 950–1050°C for 10–30 hours; then it is alkali washed, ground, and polished.

[0051] Furthermore, the boronizing agent comprises the following components by weight: 50-70 parts borax, 15-25 parts aluminum powder, 10-20 parts boron powder, and 3-8 parts cerium dioxide.

[0052] A highly hard TiB2 diffusion layer is formed on the target surface, significantly improving the surface hardness, wear resistance, and arc erosion resistance, while reducing the generation of microparticles during sputtering, resulting in a denser coating with fewer defects. Trace amounts of boron (B) are sputtered and incorporated into the coating. B is a strong grain boundary strengthener, which can further refine the coating grains and may form a highly hard BN phase during subsequent nitriding, thus playing a positive role in improving surface hardness and wear resistance.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] This invention forms a composite surface modification layer on the surface of a titanium alloy substrate through surface TiAl alloying and low-temperature ion nitriding. Cu, Ni, and Al help refine the nitride grains and provide sufficient Ti elements for subsequent nitriding, forming a nitriding layer that is firmly bonded to the substrate, with high hardness and high wear resistance. At the same time, residual compressive stress is introduced on the surface, thereby significantly improving the fatigue resistance of the titanium alloy bar and maintaining the microstructure and performance characteristics of the titanium alloy substrate. Detailed Implementation

[0055] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0056] In the following specific embodiments, the number of "parts" and "%" are both parts by mass or mass percentage, unless otherwise specified;

[0057] In Examples 1-7 and Comparative Examples 1-3, the titanium alloy matrix was obtained by mixing sponge titanium and alloying elements, melting, and casting into ingots; then, it was sequentially forged, rolled, heat-treated, machined, surface-treated, non-destructive tested, and subjected to physical and chemical tests. The melting process employed vacuum consumable arc melting, with low-current arc initiation. The initial melting was performed at 9000A, followed by a second VAR melting at 11000A, and a third melting at 13500A, with a vacuum degree <5×10⁻⁶. -2 Pa; Forging: Open forging: temperature 1100℃, deformation per pass 30%, total deformation 66%, final forging temperature 955℃; Intermediate forging: temperature 920℃, deformation per pass 40%, total deformation 64%, final forging temperature 855℃; Final forging: temperature 810℃, deformation per pass 22%, total deformation 53%, final forging temperature 785℃, air cooling; In the rolling process, heating temperature 820℃, final rolling temperature 810℃, deformation per pass 15%, total deformation 80%, final rolling temperature 785℃, air cooling; Heat treatment adopts solution treatment + aging treatment, solution treatment temperature 880℃, holding time 1h, water quenching; aging treatment temperature 540℃, holding time 6h, air cooling; Surface treatment includes pickling and spraying. Shot peening / acid pickling was performed using a 45℃ HF-HNO3 mixed acid solution (HF:HNO3:H2O volume ratio 1:3:8) for 10 min; sand peening used 100-150 mesh glass beads at a pressure of 0.4 MPa; shot peening intensity was 0.20 mmA, coverage was 120%, and the shot was cast glass pellets; the titanium alloy matrix consisted of the following components by mass percentage: aluminum: 4.7%, molybdenum: 4.3%, vanadium: 5.1%, chromium: 3.5%, zirconium: 4.0%, palladium: 0.7%, iron: 0.05%, carbon: 0.013%, nitrogen: 0.010%, oxygen: 0.020%, hydrogen: 0.0012%; the balance was titanium; it was then cleaned and surface activated to remove the oxide layer and contaminants;

[0058] Borax (Na2B4O7): Purity > 99%; Aluminum powder: Al ≥ 99.9%; Boron powder: Amorphous boron powder, B > 95%; Cerium dioxide: CeO2 > 99%;

[0059] Target dimensions: Φ50mm×3mm.

[0060] Example 1: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0061] Step 1: Deposit TiCuAl alloy coating:

[0062] A titanium alloy rod was used as the substrate, and a TiCuAl alloy coating with a thickness of 1 μm was deposited on its surface. The TiCuAl alloy coating was obtained by DC magnetron sputtering. The magnetron sputtering process parameters were: power 80W, working pressure 0.4Pa, target-substrate distance 120mm, and stage rotation speed 20rpm. The TiCuAl alloy target material included the following composition by mass percentage: Ti: 60%, Cu: 30%, Al: 10%.

[0063] Step 2, Low-temperature ion nitriding:

[0064] Titanium alloy with a TiCuAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen and argon was introduced with a flow ratio of N2 to Ar of 1:4. The pressure in the vacuum chamber was adjusted to 30 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment at a temperature of 450 °C for 24 h. After treatment, the material was cooled in the furnace and polished to form a nitrided layer, resulting in high fatigue performance titanium alloy bars.

[0065] Example 2: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0066] Step 1: Deposit TiCuAl alloy coating:

[0067] A titanium alloy rod was used as the substrate, and a TiCuAl alloy coating with a thickness of 2 μm was deposited on its surface. The TiCuAl alloy coating was obtained by DC magnetron sputtering. The magnetron sputtering process parameters were: power 100W, working pressure 0.6Pa, target-substrate distance 110mm, and stage rotation speed 15rpm. The TiCuAl alloy target material included the following composition by mass percentage: Ti: 65%, Cu: 22%, Al: 10%, Si: 2%, Y: 1%.

[0068] Step 2, Low-temperature ion nitriding:

[0069] Titanium alloy with a TiCuAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen and argon was introduced with a flow ratio of N2 to Ar of 1:3.5. The pressure in the vacuum chamber was adjusted to 40 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment at a temperature of 480℃ for 18 hours. After treatment, the material was cooled in the furnace and polished to form a nitrided layer, resulting in high-fatigue-performance titanium alloy bars.

[0070] Example 3: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0071] Step 1: Deposit TiCuAl alloy coating:

[0072] A titanium alloy rod was used as the substrate, and a TiCuAl alloy coating with a thickness of 3 μm was deposited on its surface.

[0073] The TiCuAl alloy coating was obtained by DC magnetron sputtering deposition. The magnetron sputtering process parameters were: power 120W, working gas pressure 0.8Pa, target-substrate distance 100mm, and stage rotation speed 10rpm. The TiCuAl alloy target material consisted of the following components by mass percentage: Ti: 70%, Cu: 20%, Al: 8%, Y: 2%.

[0074] Step 2, Low-temperature ion nitriding:

[0075] Titanium alloy with a TiCuAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen and argon was introduced with a flow ratio of N2 to Ar of 1:3. The pressure in the vacuum chamber was adjusted to 50 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment at a temperature of 500℃ for 12 hours. After treatment, the material was cooled in the furnace and polished to form a nitrided layer, resulting in high fatigue performance titanium alloy bars.

[0076] Example 4: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0077] Step 1: Deposit TiNiAl alloy coating:

[0078] A titanium alloy rod was used as the substrate, and a TiNiAl alloy coating with a thickness of 3 μm was deposited on its surface. The TiNiAl alloy coating was obtained by DC magnetron sputtering. The magnetron sputtering process parameters were: power 120W, working pressure 0.8Pa, target-substrate distance 100mm, and stage rotation speed 10rpm. The TiNiAl alloy target material included the following composition by mass percentage: Ti: 70%, Ni: 20%, Al: 8%, Y: 2%.

[0079] Step 2, Low-temperature ion nitriding:

[0080] Titanium alloy with a TiNiAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen and argon was introduced with a flow ratio of N2 to Ar of 1:4. The pressure in the vacuum chamber was adjusted to 30 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment at a temperature of 450 °C for 24 h. After treatment, the material was cooled in the furnace and polished to form a nitrided layer, resulting in a high-fatigue-performance titanium alloy bar.

[0081] Example 5: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0082] Step 1: Deposit TiNiAl alloy coating:

[0083] The TiNiAl alloy target was placed in a boronizing agent and kept at 950℃ for 30 hours; then it was alkali washed, ground, and polished. The TiNiAl alloy target included the following components by mass percentage: Ti: 70%, Ni: 20%, Al: 8%, Y: 2%; the boronizing agent included the following components by mass: 50 parts borax, 15 parts aluminum powder, 10 parts boron powder, and 3 parts cerium dioxide.

[0084] A titanium alloy rod was used as the substrate, and a TiNiAl alloy coating with a thickness of 3 μm was deposited on its surface. The TiNiAl alloy coating was obtained by DC magnetron sputtering deposition with a power of 120 W, a working gas pressure of 0.8 Pa, a target-substrate distance of 100 mm, and a stage rotation speed of 10 rpm.

[0085] Step 2, Low-temperature ion nitriding:

[0086] Titanium alloy with a TiNiAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen and argon was introduced with a flow ratio of N2 to Ar of 1:4. The pressure in the vacuum chamber was adjusted to 30 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment at a temperature of 450 °C for 24 h. After treatment, the material was cooled in the furnace and polished to form a nitrided layer, resulting in a high-fatigue-performance titanium alloy bar.

[0087] Example 6: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0088] Step 1: Deposit TiNiAl alloy coating:

[0089] The TiNiAl alloy target was placed in a boronizing agent and kept at 1000℃ for 20 hours; then it was alkali washed, ground, and polished. The TiNiAl alloy target included the following components by mass percentage: Ti: 70%, Ni: 20%, Al: 8%, Y: 2%; the boronizing agent included the following components by mass: 60 parts borax, 20 parts aluminum powder, 15 parts boron powder, and 5 parts cerium dioxide.

[0090] A titanium alloy rod was used as the substrate, and a TiNiAl alloy coating with a thickness of 3 μm was deposited on its surface. The TiNiAl alloy coating was obtained by DC magnetron sputtering. The magnetron sputtering process parameters were: power 120W, working gas pressure 0.8Pa, target-substrate distance 100mm, and stage rotation speed 10rpm.

[0091] Step 2, Low-temperature ion nitriding:

[0092] Titanium alloy with a TiNiAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen, methane, and argon was introduced. The flow ratio of N2 to Ar was 1:4, and the flow ratio of methane to N2 was 1:10. The pressure in the vacuum chamber was adjusted to 30 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment. The treatment temperature was 450℃ and the time was 24 h. After treatment, the alloy was cooled in the furnace and polished to form a nitrided layer, resulting in a high-fatigue-performance titanium alloy bar.

[0093] Example 7: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0094] Step 1: Deposit TiNiAl alloy coating:

[0095] The TiNiAl alloy target was placed in a boronizing agent and kept at 1050℃ for 10 hours; then it was alkali washed, ground, and polished. The TiNiAl alloy target included the following components by mass percentage: Ti: 70%, Ni: 20%, Al: 8%, Y: 2%; the boronizing agent included the following components by mass: 70 parts borax, 25 parts aluminum powder, 20 parts boron powder, and 8 parts cerium dioxide.

[0096] A titanium alloy rod was used as the substrate, and a TiNiAl alloy coating with a thickness of 3 μm was deposited on its surface. The TiNiAl alloy coating was obtained by DC magnetron sputtering. The magnetron sputtering process parameters were: power 120W, working gas pressure 0.8Pa, target-substrate distance 100mm, and stage rotation speed 10rpm.

[0097] Step 2, Low-temperature ion nitriding:

[0098] Titanium alloy with a TiNiAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen, methane, and argon was introduced. The flow ratio of N2 to Ar was 1:4, and the flow ratio of methane to N2 was 1:5. The pressure in the vacuum chamber was adjusted to 30 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment. The treatment temperature was 450℃ and the treatment time was 24 h. After treatment, the alloy was cooled in the furnace and polished to form a nitrided layer, resulting in a high-fatigue-performance titanium alloy bar.

[0099] Comparative Example 1: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0100] Step 1: Deposit TiAl alloy coating:

[0101] A titanium alloy rod was used as the substrate, and a TiAl alloy coating with a thickness of 1 μm was deposited on its surface. The TiAl alloy coating was obtained by DC magnetron sputtering. The magnetron sputtering process parameters were: power 80W, working pressure 0.4Pa, target-substrate distance 120mm, and stage rotation speed 20rpm. The TiAl alloy target material included the following composition: by mass percentage, Ti: 85%, Al: 15%.

[0102] Step 2, Low-temperature ion nitriding:

[0103] Titanium alloy with a TiAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen and argon was introduced with a flow ratio of N2 to Ar of 1:4. The pressure in the vacuum chamber was adjusted to 30 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment at a temperature of 450℃ for 24 hours. After treatment, the material was cooled in the furnace and polished to form a nitrided layer, resulting in high fatigue performance titanium alloy bars.

[0104] Comparative Example 2: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0105] Titanium alloy with a TiAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen and argon was introduced with a flow ratio of N2 to Ar of 1:4. The pressure in the vacuum chamber was adjusted to 30 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment at a temperature of 450℃ for 24 hours. After treatment, the material was cooled in the furnace and polished to form a nitrided layer, resulting in high fatigue performance titanium alloy bars.

[0106] Comparative Example 3: A method for preparing a high-fatigue-performance titanium alloy bar, comprising the following processes:

[0107] Titanium alloy with a TiAl alloy coating was placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen and argon was introduced with a flow ratio of N2 to Ar of 1:4. The pressure in the vacuum chamber was adjusted to 30 Pa. A DC pulse power supply was applied to the workpiece electrode and the auxiliary electrode for glow discharge nitriding treatment at a temperature of 650 °C for 24 h. After treatment, the material was cooled in the furnace and polished to form a nitrided layer, resulting in high fatigue performance titanium alloy bars.

[0108] Comparative Example 4: The titanium alloy matrix comprises the following components by mass percentage: iron: 0.040%, carbon: 0.021%, nitrogen: 0.023%, oxygen: 0.104%, hydrogen: 0.0014%, with the balance being titanium.

[0109] Experiment: Titanium alloy matrices and titanium alloy rods obtained in Examples 1-7 and Comparative Examples 1-4 were used to prepare samples. Their properties were tested and the test results were recorded.

[0110] The room temperature tensile properties of titanium alloy matrix specimens were tested with reference to GB / T228.1-2010.

[0111] Fatigue performance test: Using ASTM E466 / ISO 1099 as the reference standard, a servo hydraulic fatigue testing machine was used to test the high-cycle fatigue performance of the specimens and record the fatigue limit at 10^7 cycles.

[0112] Surface micro Vickers hardness test: Using ASTM E384 / ISO 6507 as the reference standard, a micro Vickers hardness tester was used to test the surface hardness (HV0.05) of the sample.

[0113] Wear resistance test: Using ASTM G99 as the reference standard, a ball-disc friction and wear tester was used with Si3N4 grinding balls to detect the wear volume of the sample in order to characterize the wear resistance.

[0114] Corrosion resistance test: Using ASTM G61 as the reference standard, an electrochemical test was conducted in a 3.5 wt% NaCl solution to detect the self-corrosion potential of the sample in order to characterize its corrosion resistance.

[0115] Surface layer bonding strength test: Using ASTM C1624 as the reference standard, a scratch tester with a diamond indenter was used to test the critical load at which the sample completely peels off.

[0116] Table 1. Experimental data on the properties of titanium alloy matrix

[0117]

[0118] Table 2. Performance test data of titanium alloy bars

[0119]

[0120] Based on the data in the table above, the following conclusions can be clearly drawn:

[0121] The titanium alloy bars obtained in Examples 1-7 are compared with those obtained in Comparative Examples 1-3. The test results show that...

[0122] Compared with the comparative examples and the titanium alloy matrix, the titanium alloy bars obtained in Examples 1-7 exhibit higher fatigue limit, surface hardness, critical load, self-corrosion potential, and lower wear volume. This fully demonstrates that the present invention improves the fatigue resistance of the prepared titanium alloy bars, while synergistically improving hardness, wear resistance, and corrosion resistance, and the surface layer formed by alloying and nitriding has good bonding strength.

[0123] Compared to Example 1, the alloy targets of Examples 2 and 3 have added silicon and yttrium, which improves their hardness, wear resistance, corrosion resistance, and bonding strength.

[0124] Compared to Example 4, the alloy target in Example 5 is a boron-diffused target. After magnetron sputtering, the resulting alloy coating has higher quality, and the surface layer is more dense after nitriding, with improved hardness, wear resistance, and corrosion resistance.

[0125] In Examples 6 and 7, CH4 was introduced into the ion nitriding process, and the carbonitriding formed the TiCN phase, which has higher hardness and wear resistance. At the same time, the introduction of carbon improved the toughness of the nitrided layer and increased the critical load (bonding force).

[0126] The alloy coating in Comparative Example 1 is a TiAl coating, without the elements Cu and Ni. Its performance is inferior to the TiCuAl and TiNiAl series, and the performance of various data is reduced.

[0127] Comparative Example 2 directly nitrided the titanium alloy bar without any coating assistance. The nitrided layer was thin and had limited performance, resulting in only a small improvement in wear resistance and corrosion resistance.

[0128] In Comparative Example 3, the surface treatment process for the titanium alloy was high-temperature nitriding. The high temperature severely damaged the titanium alloy matrix, reduced the core hardness, and led to the deterioration of the overall fatigue performance. Although the diffusion layer was deep, it was loose, and the wear resistance and corrosion resistance decreased significantly due to the deterioration of the surface condition.

[0129] Comparative Example 4, consisting of a titanium alloy matrix without alloying elements, showed that its mechanical properties, corrosion resistance, fatigue resistance, surface hardness, and wear resistance were all inferior to those of the titanium alloy matrix in Example 1. This indicates that alloying the titanium alloy matrix helps improve its various properties.

[0130] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing high-fatigue-performance titanium alloy bars, characterized in that: Including the following processes: A titanium alloy rod is used as the substrate, and a TiAl alloy coating is deposited on its surface. Then, low-temperature ion nitriding is performed to form a nitrided layer, resulting in high-fatigue-performance titanium alloy bars. The alloy target used in the preparation of TiAl alloy coating is a TiAl alloy target, a TiCuAl alloy target, or a TiNiAl alloy target; The alloy target material undergoes boronizing surface treatment.

2. The method for preparing a high-fatigue-performance titanium alloy bar according to claim 1, characterized in that: The TiAl alloy coating is obtained by deposition of an alloy target using DC magnetron sputtering.

3. The method for preparing a high-fatigue-performance titanium alloy bar according to claim 1, characterized in that: The low-temperature ion nitriding process is as follows: Titanium alloys with TiAl alloy coatings are placed in the vacuum chamber of an ion nitriding furnace. After evacuation, a mixture of nitrogen and argon is introduced. The pressure in the vacuum chamber is adjusted to 30–50 Pa. A DC pulse power supply is applied to the workpiece electrode and the auxiliary electrode to perform glow discharge nitriding treatment. The treatment temperature is 450–500 °C and the time is 4–24 h. The furnace is then cooled after treatment.

4. The method for preparing a high-fatigue-performance titanium alloy bar according to claim 2, characterized in that: The alloy target material also contains 0.5wt% to 2wt% of rare earth elements, one of which is yttrium or cerium.

5. The method for preparing a high-fatigue-performance titanium alloy bar according to claim 1, characterized in that: The boronizing surface treatment process of the alloy target is as follows: the alloy target is placed in a boronizing agent and kept at 950-1050℃ for 10-30 hours.

6. The method for preparing a high-fatigue-performance titanium alloy bar according to claim 5, characterized in that: The boronizing agent comprises the following components by weight: 50-70 parts borax, 15-25 parts aluminum powder, 10-20 parts boron powder, and 3-8 parts cerium dioxide.

7. The method for preparing a high-fatigue-performance titanium alloy bar according to claim 1, characterized in that: The titanium alloy matrix comprises the following components by mass percentage: aluminum: 4.5–5.5%, molybdenum: 4.0–5.0%, vanadium: 4.5–5.5%, chromium: 3.0–4.0%, zirconium: 3.5–4.5%, iron: ≤0.25%, oxygen: ≤0.10%, tantalum or palladium: 0.5–1.0%, hydrogen: <50 ppm; the balance being titanium.

8. The method for preparing a high-fatigue-performance titanium alloy bar according to claim 2, characterized in that: In the alloy target material, silicon is used to replace 1wt% to 5wt% of Ni or Cu.

9. The method for preparing a high-fatigue-performance titanium alloy bar according to claim 3, characterized in that: The flow rate ratio of nitrogen to argon is 1:4 to 1:

3.

10. A high-fatigue-performance titanium alloy bar prepared by the preparation method according to any one of claims 1-9.

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