Heat treatment method for realizing high strength and high plasticity of forged two-phase titanium alloy

Abstract

The invention relates to a heat treatment method for realizing high strength and high plasticity of a forged two-phase titanium alloy, and the preparation method comprises the following steps: (1) preheating the forged two-phase titanium alloy in advance to a heating furnace which is slightly lower than beta transformation temperature, preserving heat for a short time, and then immediately performing water quenching to room temperature; and (2) preserving heat of a sample obtained after water quenching at 450-550 DEG C for 2 hours, taking out the sample, and performing air cooling to room temperature. By means of the method, the strength of the forged two-phase titanium alloy can be greatly improved, and meanwhile good plasticity is kept.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy materials and relates to a heat treatment method for achieving high strength and high plasticity of a forged two-phase titanium alloy. Background Art

[0002] Dual-phase titanium alloys, with their high specific strength, excellent tensile properties, corrosion resistance, and thermal stability, are widely used in aerospace applications. Cast titanium alloys contain numerous casting defects, resulting in low strength that fails to meet service standards. Therefore, forging techniques are often used to manipulate the alloy's microstructure and improve its strength. With the rapid development of aerospace, the harsh service environments have placed even higher demands on the strength of dual-phase titanium alloys. Consequently, many researchers have focused on further improving the strength of forged titanium alloys through simple heat treatments. Studies have shown that martensite, obtained through solution-annealing combined with quenching, can significantly strengthen titanium alloys, with the finer the martensite, the greater the strengthening effect. However, rapid cooling rates lead to a high density of defects within the martensite, which severely hinders dislocation motion and results in extremely low ductility. In contrast, most researchers prefer to use solution-annealing treatments to decompose the martensite into fine (α+β) lamellae, thereby achieving high-strength and high-ductility titanium alloys. The characteristic of this treatment method is to carry out long-term solid solution at 30-50 ℃ below the β transformation temperature, so that the primary α phase in the structure reaches dissolution equilibrium while retaining a specific volume fraction of the primary α phase's coordinated deformation ability and maintaining plasticity; then water quenching to room temperature obtains martensitic structure; the main purpose of the subsequent aging process is to completely decompose the martensitic structure into fine (α+β) sheets, thereby obtaining a high-strength titanium alloy. TC4 titanium alloy is a typical two-phase titanium alloy. Chinese invention patent CN201210187576.4 improves the strength of TC4 titanium alloy by holding it at 950-970°C for 1-1.5 hours and then aging it at 530-550°C for 3-4 hours. Chinese invention patent CN201310093912.3 applies solution treatment at 950-980°C after forging TC4 titanium alloy, followed by high-temperature aging at 650-700°C. The resulting titanium alloy has a strength of no less than 1000 MPa and an elongation of no less than 10%. However, the lamellar structure produced by the decomposition of martensite does not actually strengthen the titanium alloy as much as martensite does, and current conventional treatment methods do not fully utilize the excellent strengthening capabilities of martensite. Therefore, the present invention proposes a brief holding temperature slightly below the β-transus temperature to dissolve the primary α phase and transform it into the high-temperature β phase as much as possible in a short period of time while hindering the growth of the β grains; during the quenching process, the β phase transforms into a martensite structure; and finally, aging is performed at a lower aging temperature (450-550°C) for 2 hours. The main purpose is to retain most of the martensite while reducing defects in the martensite, thereby significantly improving the strength of the forged two-phase titanium alloy while maintaining good plasticity. Summary of the Invention

[0003] A heat treatment method for achieving high strength and high plasticity of a forged two-phase titanium alloy is provided. By increasing the solution temperature, shortening the solution time, and reducing the aging temperature, the strength of the two-phase titanium alloy after forging is improved while maintaining good plasticity.

[0004] The present invention relates to a heat treatment method for achieving high strength and high plasticity of a forged two-phase titanium alloy, comprising the following steps:

[0005] Step 1: The forged two-phase titanium alloy is briefly kept warm in a heating furnace preheated to a temperature slightly below the β-transus temperature, and then immediately water quenched;

[0006] Step 2: Place the water-quenched sample obtained in step 1 into a heating furnace that has been preheated to a certain temperature, continue to keep the temperature for 2 hours, then take out the sample and air-cool it to room temperature.

[0007] The slightly lower than β transition temperature in step (1) refers to 5-10°C below the β transition temperature, and the short-term holding time is 5-10 min. The certain temperature in step (2) refers to a certain temperature between 450-550°C.

[0008] Compared with the prior art, the present invention has the following significant features:

[0009] (1) By using a simple solution aging treatment, the decomposition behavior of martensite is regulated, the defect density is reduced, and the relative content of martensite and (α+β) lamellae is controlled, significantly improving the strength of the wrought two-phase titanium alloy while maintaining good plasticity. The tensile strength of the two-phase titanium alloy treated by this method can reach about 1250 MPa, the yield strength can reach about 1150 MPa, and its elongation can be maintained at about 13%.

[0010] (2) A two-phase titanium alloy with ultra-high strength is obtained by heat treatment, which is easy to operate and low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Comparison of the mechanical properties of TC4 titanium alloy before and after heat treatment in Example 1: (a) tensile strength and (b) elongation at break. DETAILED DESCRIPTION

[0012] Example 1

[0013] (1) TC4 titanium alloy is a typical two-phase titanium alloy. Three TC4 titanium alloy round bars with a size of φ12×75 mm were quickly placed in a heating furnace that had been preheated to 990 ℃. The timer started after the furnace temperature rose to the predetermined 990 ℃ again. After the temperature was kept at 990 ℃ for 10 min, the sample was quickly taken out and immediately water quenched.

[0014] (2) The water-quenched sample obtained in step (1) was quickly placed back into the heating furnace that had been preheated to 550 °C. The timing was started after the furnace temperature rose to the predetermined 550 °C. After the temperature was kept at this temperature for 2 h, the sample was quickly taken out and air-cooled to room temperature.

[0015] The sample obtained in Example 1 was processed into a tensile specimen and tested using the ASTM / E8 standard. The tensile strength (average value) was 1248 MPa, the yield strength (average value) was 1153 MPa, and the elongation after fracture (average value) was 13%.

Claims

1. A heat treatment method for achieving high strength and high plasticity of a forged two-phase titanium alloy, characterized in that: The method comprises the following steps: (1) briefly keeping the forged two-phase titanium alloy in a heating furnace preheated to a temperature slightly below the β-transus temperature, and then immediately water quenching it; (2) keeping the sample obtained after water quenching at a certain temperature for 2 h, and air-cooling it to room temperature.

2. The preparation method according to claim 1, wherein: The temperature slightly below the β-transus temperature in step (1) refers to 5-10°C below the β-transus temperature, and the short-term holding time is 5-10 min. The certain temperature in step (2) refers to a temperature between 450-550°C.

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