A method for improving the performance of TC4 alloy by surface modification

Abstract

The application discloses a method for improving the performance of TC4 alloy through surface modification, and comprises the following steps: (1) preparing a mixed slurry; (2) slurry coating; (3) ball milling; (4) diffusion welding; (5) high-temperature solid solution treatment; and (6) low-temperature aging treatment. The TC4 alloy material prepared by the method has a stable twin crystal structure, and the existence of the twin crystal effectively improves the strength, toughness and fatigue resistance of the alloy material, so that the TC4 alloy material has relatively excellent performance, thereby meeting more stringent use requirements.

Description

Technical Field

[0001] This invention belongs to the field of alloy preparation technology and relates to a method for improving the properties of TC4 alloy through surface modification. Background Technology

[0002] TC4 alloy is a titanium alloy material with a composition of Ti-6Al-4V, belonging to the (α+β) type titanium alloy. Due to its excellent specific strength, corrosion resistance, and biocompatibility, TC4 alloy is widely used in aerospace, chemical, and medical device industries. Particularly in the aerospace industry, TC4 alloy is widely used in the manufacture of engine components and fuselage structural parts due to its low density and ability to maintain high strength at high temperatures. Although TC4 alloy already possesses relatively good comprehensive mechanical properties, its plastic deformation process is dominated by traditional slip deformation mechanisms (such as dislocation slip). This deformation mechanism can lead to embrittlement or fatigue crack initiation, thus affecting the plastic deformation capacity and fatigue resistance of TC4 alloy. Therefore, the plastic deformation capacity and fatigue resistance of TC4 alloy can be further improved to meet increasingly stringent application requirements.

[0003] Twinning, as an auxiliary plastic deformation mechanism, can play an important role under high strain rates, low temperatures, or specific stress states. The introduction of twins can effectively improve the ductility and fatigue resistance of materials, while also enhancing their strength to some extent.

[0004] Currently, research on TC4 alloy focuses on controlling grain size, adjusting phase transformation behavior, and improving its strength and corrosion resistance, while neglecting research on its toughness, fatigue resistance, and other properties.

[0005] Therefore, it is necessary to provide a method to improve the properties of TC4 alloy through surface modification, so as to prepare TC4 alloy with excellent strength, toughness and fatigue resistance, so that TC4 alloy can meet more and more stringent application requirements. Summary of the Invention

[0006] To overcome the problems in the prior art, the present invention prepares a TC4 alloy with a twinned structure on its surface and introduces twins into the TC4 alloy to improve the strength, toughness and fatigue resistance of the TC4 alloy.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] The method includes the following steps:

[0009] (1) Mixing powdered zirconium and powdered lanthanum to form a mixed slurry, wherein the mass of the powdered zirconium is 2-5 wt% of the total mass of the mixed slurry, and the mass of the powdered lanthanum is 0.5-2 wt% of the total mass of the mixed slurry.

[0010] (2) The mixed slurry prepared in step (1) is coated on the surface of the TC4 alloy substrate and dried after coating to obtain a TC4 alloy with zirconium powder and lanthanum powder coated on the surface.

[0011] (3) The TC4 alloy obtained in step (2) is ball-milled so that the powdered zirconium and powdered lanthanum coated on the surface are embedded into the surface of the TC4 alloy.

[0012] (4) In an inert gas environment, the alloy obtained in step (3) is subjected to diffusion welding.

[0013] (5) The TC4 alloy after welding in step (4) is subjected to high-temperature solution treatment, and then the TC4 alloy is rapidly cooled by water quenching or oil quenching.

[0014] (6) The TC4 alloy after high-temperature solution treatment in step (5) is subjected to low-temperature aging treatment, and then the TC4 alloy is slowly cooled by air cooling to obtain the modified TC4 alloy.

[0015] Preferably, in step (1), powdered zirconium and powdered lanthanum are added to alcohol to form a mixed slurry.

[0016] Preferably, in step (2), the coating is applied by spraying with a spraying pressure of 0.3-0.5MPa, a nozzle diameter of 1.0-1.5mm, a spraying distance of 200-250mm, a spraying speed of 200-300mm / s, and a coating thickness of 10-50μm.

[0017] Preferably, in step (2), the drying temperature is 80-100℃.

[0018] Preferably, in step (3), the milling medium is tungsten carbide, the milling speed is 50-150 rpm, and the milling time is 1-2 h.

[0019] Preferably, in step (4), the diffusion welding temperature is 700-900℃ and the holding time is 1-4h.

[0020] Preferably, in step (5), the high-temperature solution treatment temperature is 850-950℃, and the temperature is maintained for 1-2 hours.

[0021] Preferably, in step (5), when water quenching is used, the cooling time is 10-30s, and when oil quenching is used, the cooling time is 10-60s.

[0022] Preferably, in step (6), the low-temperature aging treatment temperature is 450-600℃ and the holding time is 3-5h.

[0023] Preferably, the powdered zirconium and powdered lanthanum have a particle size of 10-50 μm.

[0024] The beneficial effects of this invention are:

[0025] 1. This invention adds lanthanum to form fine intermetallic compounds or solid solutions with the titanium matrix, thereby changing the crystal structure of TC4 alloy, increasing the driving force for twin formation, and effectively inducing twin formation.

[0026] 2. By adding zirconium, this invention helps to adjust the phase composition and crystal structure of TC4 alloy, ensuring the formation of twins and keeping the twins in a relatively stable state. At the same time, by forming a stable α phase or changing the phase transformation behavior, it reduces the probability of excessive grain growth during heat treatment, thereby further refining the alloy grains and further improving the toughness and strength of TC4 alloy.

[0027] 3. This invention promotes the full diffusion of lanthanum and zirconium elements in the TC4 alloy matrix by performing solid solution treatment at a higher temperature, thereby eliminating internal stress and improving the uniformity of element distribution. Then, rapid cooling is performed to retain a uniform phase structure and reduce the formation of unfavorable phases during the cooling process.

[0028] 4. The present invention uses aging treatment at a lower temperature to allow lanthanum and zirconium to work together to promote the formation of twins and stabilize their structure. Then, slow cooling is performed to further stabilize the formed twins.

[0029] 5. This invention utilizes diffusion welding to achieve a uniform distribution of lanthanum and zirconium elements embedded on the surface of TC4 alloy, while simultaneously improving the surface properties of TC4 alloy without damaging its matrix structure.

[0030] 6. This invention coats the surface of a TC4 alloy with a mixed slurry of zirconium and lanthanum, and then embeds powdered zirconium and lanthanum into the alloy surface through ball milling. This ensures that the zirconium and lanthanum elements mainly remain on the surface of the TC4 alloy and do not penetrate into the interior of the alloy. Without affecting the internal toughness and strength of the alloy, this invention improves the wear resistance, corrosion resistance, and surface hardness of the alloy surface. At the same time, it inhibits grain boundary slip and grain growth on the alloy surface, which is conducive to the formation of fine grains and twinned structures on the alloy surface. This improves the strength, hardness, fatigue resistance, and other properties of the alloy surface, while effectively hindering the penetration of corrosive media. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments.

[0033] In the embodiments and comparative examples of this invention, the TC4 alloy matrix was made of bar stock, and the composition of the TC4 alloy matrix is ​​shown in Table 1. Unless otherwise specified, all chemical reagents used in the embodiments and comparative examples of this invention were commercially available analytical grade reagents.

[0034] Table 1

[0035] margin 5.5～6.8％ 3.5～4.5％ ≤0.30％ ≤0.10％ ≤0.05％ ≤0.015％ ≤0.20％

[0036] Example 1

[0037] In this embodiment, the TC4 alloy substrate has a length of 2000 mm and a diameter of 20 mm. The TC4 alloy is prepared in this embodiment through the following steps:

[0038] (1) Take 0.5wt% lanthanum powder and 2wt% zirconium powder with a particle size of 20μm, and mix the lanthanum powder and zirconium powder.

[0039] (2) Add the mixed powder from step (1) to alcohol and use alcohol as a binder to make a fluid slurry.

[0040] (3) The mixed slurry prepared in step (2) is coated on the surface of TC4 alloy rod by spraying. The spraying parameters are as follows: spraying pressure is 0.3MPa, nozzle diameter is 1.0mm, spraying distance is 200mm, spraying speed is 200mm / s, coating thickness is 20μm. After coating, it is dried at 90℃ for 1 hour to obtain TC4 alloy rod coated with zirconium powder and lanthanum powder.

[0041] (4) The TC4 alloy rod coated with zirconium powder and lanthanum powder obtained in step (3) is ball-milled using tungsten carbide balls to embed the zirconium powder and lanthanum powder into the surface of the rod. The ball mill speed is 50 rpm and the ball milling time is 2 hours.

[0042] (5) Place the ball-milled rod from step (4) in an argon protective atmosphere for diffusion welding. The welding temperature is 800℃ and the temperature is maintained for 2 hours to ensure that lanthanum and zirconium are evenly distributed on the alloy surface.

[0043] (6) Heat the bar after diffusion welding in step (5) to 900°C, hold for 1.5h, and perform high-temperature solution treatment to promote the full diffusion of lanthanum and zirconium elements in the TC4 alloy matrix and eliminate internal stress. Then, quickly immerse the bar in water for 10s for rapid cooling to retain a uniform phase structure.

[0044] (7) Heat the cooled bar in step (6) to 500°C, keep it at that temperature for 3 hours, and perform low-temperature aging treatment to promote the formation and stabilization of the twin structure. Then place the bar in the air to cool for 3 hours to obtain a TC4 alloy material with a stable twin structure and enhanced mechanical properties.

[0045] In the TC4 alloy prepared in this embodiment, surface twins account for 15%-20% of the entire surface crystal structure.

[0046] Example 2

[0047] In this embodiment, the TC4 alloy substrate has a length of 2500 mm and a diameter of 30 mm. The TC4 alloy is prepared in this embodiment through the following steps:

[0048] (1) Take 1.0 wt% lanthanum powder and 3.0 wt% zirconium powder with a particle size of 20 μm, and mix the lanthanum powder and zirconium powder.

[0049] (2) Add the mixed powder from step (1) to alcohol and use alcohol as a binder to make a fluid slurry.

[0050] (3) The mixed slurry prepared in step (2) is coated on the surface of TC4 alloy rod by spraying. The spraying parameters are as follows: spraying pressure is 0.4MPa, nozzle diameter is 1.2mm, spraying distance is 220mm, spraying speed is 250mm / s, coating thickness is 30μm. After coating, it is dried at 95℃ for 1.5h to obtain TC4 alloy rod coated with zirconium powder and lanthanum powder.

[0051] (4) Use tungsten carbide balls to ball mill the TC4 alloy rod coated with zirconium powder and lanthanum powder obtained in step (3) so that the zirconium powder and lanthanum powder are embedded in the surface of the rod. The ball mill speed is 100 rpm and the ball milling time is 2 hours.

[0052] (5) Place the ball-milled rod from step (4) in an argon protective atmosphere for diffusion welding. The welding temperature is 850℃ and the holding time is 2.5h to ensure that lanthanum and zirconium are evenly distributed on the alloy surface.

[0053] (6) Heat the bar after diffusion welding in step (5) to 925°C and hold for 1.8h for high-temperature solution treatment to promote the full diffusion of lanthanum and zirconium elements in the TC4 alloy matrix and eliminate internal stress. Then, quickly immerse the bar in water for 20s for rapid cooling to retain a uniform phase structure and prevent the formation of unfavorable phases.

[0054] (7) Heat the cooled bar in step (6) to 550°C, keep it at that temperature for 4 hours, and perform low-temperature aging treatment to promote the formation and stabilization of the twin structure. Then place the bar in the air to cool for 4 hours to obtain a TC4 alloy material with a stable twin structure and enhanced mechanical properties.

[0055] In the TC4 alloy prepared in this embodiment, surface twins account for 25%-30% of the entire surface crystal structure.

[0056] Example 3

[0057] In this embodiment, the TC4 alloy substrate is 3000 mm in length and 50 mm in diameter. The TC4 alloy is prepared in this embodiment through the following steps:

[0058] (1) Take 2.0 wt% lanthanum powder and 5.0 wt% zirconium powder with a particle size of 20 μm, and mix the lanthanum powder and zirconium powder.

[0059] (2) Add the mixed powder from step (1) to alcohol and use alcohol as a binder to make a fluid slurry.

[0060] (3) The mixed slurry prepared in step (2) is coated on the surface of TC4 alloy rod by spraying. The spraying parameters are as follows: spraying pressure is 0.5MPa, nozzle diameter is 1.5mm, spraying distance is 250mm, spraying speed is 300mm / s, coating thickness is 40μm. After coating, it is dried at 100℃ for 2 hours to obtain TC4 alloy rod coated with zirconium powder and lanthanum powder.

[0061] (4) The TC4 alloy rod coated with zirconium powder and lanthanum powder obtained in step (3) is ball-milled using tungsten carbide balls to embed the zirconium powder and lanthanum powder into the surface of the rod. The ball mill speed is 150 rpm and the ball milling time is 2 hours.

[0062] (5) Place the ball-milled rod from step (4) in an argon protective atmosphere for diffusion welding. The welding temperature is 900℃ and the temperature is maintained for 3 hours to ensure that lanthanum and zirconium are evenly distributed on the alloy surface.

[0063] (6) Heat the bar after diffusion welding in step (5) to 950°C, hold for 2 hours, and perform high-temperature solution treatment to promote the full diffusion of lanthanum and zirconium elements in the TC4 alloy matrix and eliminate internal stress. Then, quickly immerse the bar in water for 30 seconds for rapid cooling to retain a uniform phase structure and prevent the formation of unfavorable phases.

[0064] (7) Heat the cooled bar in step (6) to 600°C, keep it at that temperature for 5 hours, and perform low-temperature aging treatment to promote the formation and stabilization of the twin structure. Then place the bar in air to cool for 6 hours to obtain a TC4 alloy material with a stable twin structure and enhanced mechanical properties.

[0065] In the TC4 alloy prepared in this embodiment, surface twins account for 35%-40% of the entire surface crystal structure.

[0066] Comparative Example 1

[0067] This comparative example uses the same method as Example 1 to prepare TC4 alloy material, the difference being that: no zirconium or lanthanum elements were added in this comparative example, no coating or ball milling was performed, and the TC4 alloy rod was directly subjected to solution treatment and aging treatment.

[0068] The TC4 alloy material prepared in this comparative example has a surface twin structure accounting for less than 5% of the total surface crystal structure. Because zirconium and lanthanum were not added in this comparative example, the TC4 alloy material could not effectively form a twin structure, resulting in poor performance.

[0069] Comparative Example 2

[0070] This comparative example uses the same method as Example 2 to prepare TC4 alloy material, the difference being that lanthanum was not added in this comparative example.

[0071] The TC4 alloy material prepared in this comparative example has a surface twinning rate of 10-15% of the entire surface crystal structure. Compared with Example 2, the amount of twinning in this comparative example is less, and the effect on improving the performance of the TC4 alloy material is limited. Therefore, it can be seen that zirconium and lanthanum need to be added at the same time to effectively improve the performance of the TC4 alloy material, and the improvement effect is more obvious.

[0072] Comparative Example 3

[0073] This comparative example uses the same method as Example 3 to prepare TC4 alloy material, except that zirconium is not added in this comparative example.

[0074] The TC4 alloy material prepared in this comparative example has a surface twinning rate of 20-25% compared to Example 3. This results in a lower twinning rate and limited improvement in the performance of the TC4 alloy material, primarily manifested as increased strength but insufficient toughness. Therefore, it can be seen that the simultaneous addition of zirconium and lanthanum is necessary to effectively improve the performance of the TC4 alloy material, with a significant improvement effect.

[0075] Comparative Example 4

[0076] The TC4 alloy material in this comparative example was prepared using the same method as in Example 1. The difference is that the solution temperature in this comparative example was 800°C, and after the solution treatment, the TC4 alloy material was placed in the air for cooling.

[0077] In this comparative example, the excessively low solution temperature resulted in a low diffusion rate of lanthanum and zirconium in the alloy matrix, leading to insufficient diffusion and an inability to achieve a sufficiently uniform distribution, negatively impacting the alloy's performance improvement. Furthermore, it caused phase inhomogeneity; the low solution temperature affected the uniformity of the α and β phases, easily resulting in insufficient or uneven distribution of the β phase, affecting the material's mechanical properties and wear resistance. Finally, the excessively low solution temperature led to incomplete stress relief, affecting the alloy's overall mechanical properties. In addition, the excessively slow cooling rate in this comparative example suppressed twin formation, even forming twinned structures, resulting in a significant reduction in the twin content on the alloy surface, thus failing to effectively improve the performance of the TC4 alloy. Moreover, the slow cooling rate easily led to grain growth; coarse grain structures reduced the material's strength and hardness, and worsened its plasticity and toughness. The excessively slow cooling rate also easily caused uneven precipitation of the β phase during cooling, forming a brittle phase structure, leading to reduced toughness and increased brittleness, which is detrimental to the alloy's use.

[0078] Comparative Example 5

[0079] The TC4 alloy material in this comparative example was prepared using the same method as in Example 1. The difference is that the aging temperature in this comparative example was 650°C, and after the aging treatment, the TC4 alloy material was rapidly cooled by water quenching.

[0080] In this comparative example, the excessively high aging temperature exacerbates grain boundary slip, twin disintegration, and grain recrystallization and growth within the alloy. This leads to instability or even disappearance of the twin structure in the TC4 alloy, weakening the strengthening effect of twins or even eliminating their altogether. Consequently, the overall performance of the TC4 alloy significantly declines, increasing the risk of brittle fracture and failure during application. Furthermore, excessively high aging temperatures can cause excessive precipitation of the β phase, reducing the material's toughness and plasticity. While rapid water quenching can preserve some high-temperature phase structures, the destruction of the twin structure after high-temperature aging means that water quenching can actually exacerbate the accumulation of internal stress in the crystal lattice, increasing brittleness and stress corrosion tendency, resulting in the opposite effect. Rapid water quenching also makes it difficult to eliminate residual stress, which may accumulate during service and trigger crack propagation, thus reducing the alloy's fatigue life and impact resistance. Therefore, rapid water quenching should not be performed as the final step.

[0081] In summary, this invention, by adding zirconium and lanthanum elements and combining them with a specific preparation method, can effectively promote the formation and stable existence of twinned structures in TC4 alloys, while reducing excessive grain growth and exhibiting a certain grain refinement and strengthening effect. Through the synergistic effect of twinning strengthening, grain refinement strengthening, and phase structure optimization, the strength, toughness, and fatigue resistance of TC4 alloy materials are effectively improved, making TC4 suitable for high-stress and high-wear environments. This provides a feasible technical solution for the preparation of titanium alloy materials in high-performance equipment manufacturing fields such as aerospace and automotive. Furthermore, the preparation method of this invention has strong controllability and adaptability, making it suitable for industrial-scale application.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for improving the properties of TC4 alloy through surface modification, characterized in that: The method includes the following steps: (1) Mixing powdered zirconium and powdered lanthanum to form a mixed slurry, wherein the mass of the powdered zirconium is 2-5 wt% of the total mass of the mixed slurry, and the mass of the powdered lanthanum is 0.5-2 wt% of the total mass of the mixed slurry; (2) The mixed slurry prepared in step (1) is coated on the surface of the TC4 alloy substrate, and then dried to obtain a TC4 alloy with zirconium powder and lanthanum powder coated on the surface. (3) The TC4 alloy obtained in step (2) is ball-milled so that the powdered zirconium and powdered lanthanum coated on the surface are embedded into the surface of the TC4 alloy. (4) In an inert gas environment, the alloy obtained in step (3) is subjected to diffusion welding; (5) The TC4 alloy after welding in step (4) is subjected to high temperature solution treatment, and then the TC4 alloy is rapidly cooled by water quenching or oil quenching. (6) The TC4 alloy after high-temperature solution treatment in step (5) is subjected to low-temperature aging treatment, and then the TC4 alloy is slowly cooled by air cooling to obtain the modified TC4 alloy.

2. The method for improving the properties of TC4 alloy by surface modification according to claim 1, characterized in that: In step (1), powdered zirconium and powdered lanthanum are added to alcohol to form a mixed slurry.

3. The method for improving the properties of TC4 alloy by surface modification according to claim 1, characterized in that: In step (2), the coating is applied by spraying. The spraying pressure is 0.3-0.5MPa, the nozzle diameter is 1.0-1.5mm, the spraying distance is 200-250mm, the spraying speed is 200-300mm / s, and the coating thickness is 10-50μm.

4. The method for improving the properties of TC4 alloy by surface modification according to claim 1, characterized in that: In step (2), the drying temperature is 80-100℃.

5. A method for improving the properties of TC4 alloy by surface modification according to claim 1, characterized in that: In step (3), the ball milling medium is tungsten carbide, the ball milling speed is 50-150 rpm, and the ball milling time is 1-2 h.

6. A method for improving the properties of TC4 alloy by surface modification according to claim 1, characterized in that: In step (4), the diffusion welding temperature is 700-900℃, and the temperature is maintained for 1-4 hours.

7. A method for improving the properties of TC4 alloy by surface modification according to claim 1, characterized in that: In step (5), the high-temperature solution treatment temperature is 850-950℃, and the temperature is maintained for 1-2 hours.

8. A method for improving the properties of TC4 alloy by surface modification according to claim 7, characterized in that: In step (5), when water quenching is used, the cooling time is 10-30s, and when oil quenching is used, the cooling time is 10-60s.

9. A method for improving the properties of TC4 alloy by surface modification according to claim 1, characterized in that: In step (6), the low-temperature aging treatment temperature is 450-600℃, and the holding time is 3-5h.

10. A method for improving the properties of TC4 alloy by surface modification according to any one of claims 1-9, characterized in that: The powdered zirconium and powdered lanthanum have a particle size of 10-50 μm.

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