Heat treatment process for laser selective additive manufacturing of Ti65 titanium alloy

Abstract

This invention discloses a heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy, comprising four stages: preheating, solution treatment, rapid cooling, and aging. The preheating process involves holding at 500–600℃ for 60–240 minutes to reduce residual stress. The solution treatment involves heating to 5–10℃ above the β phase transformation point, holding at this temperature, and then rapidly cooling with argon gas (50–80℃ / s) to obtain a fine α+β dual-phase microstructure. The aging treatment involves holding at 600–700℃ for 240–360 minutes to improve mechanical properties. This process can improve microstructure uniformity, significantly enhance the alloy's strength, hardness, and high-temperature stability, and is suitable for performance optimization of complex titanium alloy components in the aerospace field.

Description

Technical Field

[0001] This invention relates to a heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy, belonging to the fields of additive manufacturing and metal heat treatment. Background Technology

[0002] High-temperature titanium alloys are designed for long-term use in high-temperature environments. They possess high instantaneous and creep strength, good creep resistance, and excellent thermal stability within their operating temperature range. At room temperature, they exhibit good plasticity, creep resistance, and thermal stability. They also demonstrate good fatigue resistance at both room and high temperatures. They are primarily used to manufacture compressor discs, blades, inlet casings, and aircraft structural components. Based on their microstructure, they are classified into α+β type and near-α type titanium alloys.

[0003] Ti65 titanium alloy is a near-alpha type high-temperature titanium alloy with a nominal composition of Ti-5.9Al-4.0Sn-3.5Zr-0.3Mo-0.4Si-0.3Nb-2.0Ta-1.0W-0.05C, developed in my country based on Ti60 titanium alloy. It possesses excellent high-temperature strength, thermal stability, and creep resistance. Ti65 titanium alloy can be used at temperatures up to 650℃ for extended periods and over 750℃ for short periods, allowing it to maintain good mechanical properties in high-temperature environments. However, the forming process of high-temperature titanium alloys is poor; forging, casting, and welding methods are difficult to apply. Traditional forming methods for preparing Ti65 alloy are complex, have low material utilization, long production cycles, high costs, and low machining efficiency.

[0004] Compared to traditional manufacturing technologies, selective laser additive manufacturing (SLM) is a rapidly developing near-net-shape precision machining technology that adopts the "discrete + stacking" principle. This is a bottom-up approach that directly manufactures parts driven by the three-dimensional data of the parts, achieving integrated near-net-shape forming of complex geometric components. While reducing time and costs, the high cooling rate of the additive manufacturing process leads to a significant refinement of the microstructure, improving hardness and strength.

[0005] Laser selective additive manufacturing of Ti65 titanium alloys can effectively solve various problems encountered by traditional forming methods in preparing Ti65 alloy parts. However, the unsteady multi-cycle thermal process of additive manufacturing is also detrimental to the formation of high-temperature resistant and high-performance microstructures in high-temperature titanium alloys. Parameters such as the precipitation, morphology, distribution, and size of high-temperature strengthening phases require further control through post-heat treatment. The Beijing Institute of Aeronautical Materials has conducted performance optimization research on Ti65 alloys, controlling the mechanical properties of the alloy by adjusting aging treatment parameters. However, its research is limited to aerospace forged Ti65 titanium alloy parts, and lacks experimental research and analysis on the increasingly widely used additive manufacturing Ti65 titanium alloys. A suitable heat treatment process for laser selective additive manufacturing of Ti65 titanium alloys urgently needs to be developed. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of the prior art by providing a heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy, thereby improving the problems of microstructural defects and insufficient mechanical properties of existing selective laser additive manufacturing of Ti65 titanium alloy.

[0007] The technical solution of this invention is: a heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy, comprising:

[0008] S1. Place the laser selective additive manufacturing Ti65 titanium alloy part in a vacuum furnace and heat it to 500~600 ℃ at the first heating rate, and hold it at that temperature for a certain period of time.

[0009] S2. Measure the β transformation temperature of Ti65 alloy. After laser selective additive manufacturing of Ti65 alloy parts, heat them to 5-10 °C above the β transformation temperature at the second heating rate and hold them at that temperature for a long time to allow the alloying elements in Ti65 titanium alloy to fully dissolve.

[0010] S3. After the heat preservation is completed, the Ti65 titanium alloy parts are taken out of the vacuum furnace and rapidly cooled with argon gas to allow the alloy to quickly pass through the β phase transformation zone and obtain a fine and uniform α+β dual-phase structure.

[0011] S4. Place the cooled Ti65 titanium alloy parts back into the vacuum furnace, heat to 600~700℃, hold at that temperature, and then cool with the furnace to improve the strength and hardness of the Ti65 titanium alloy. The heat treatment is then complete.

[0012] Preferably, in S1, the first heating rate is 5~10 ℃ / min; and the holding time after heating to 500~600 ℃ is 60~240 min.

[0013] Preferably, in S2, the second heating is performed at a heating rate of 8~12 °C / min to heat to 5~10 °C above the β transition temperature;

[0014] In S2, the heat preservation time is determined according to the volume of the part, and the heat preservation time shall not be less than 120 min.

[0015] Preferably, in S3, the cooling rate is 50~80 ℃ / s.

[0016] Preferably, the vacuum furnace pressure in S1 is ≤1×10 -2 Pa, during the heat preservation stage, the temperature fluctuation is ≤±5℃.

[0017] Preferably, the β transition temperature is determined by differential scanning calorimetry, and the holding time is calculated by increasing the holding time by 2 minutes for every millimeter of the maximum cross-sectional thickness of the part.

[0018] Preferably, the argon purity in S3 is ≥99.999%, and the cooling endpoint temperature is ≤100℃.

[0019] Preferably, when the temperature in S4 is raised to 600~700℃, a two-stage heating method is adopted: the first stage raises the temperature to 500℃ at 5℃ / min, and the second stage raises the temperature to the target temperature at 3℃ / min.

[0020] The holding time after heating to 600~700℃ is 240~360 min.

[0021] Preferably, the Ti65 alloy composition by mass percentage is Al 5.5~6.0%, Sn 3.6~4.5%, Zr 3.0~4.0%, Mo 0.2~0.6%, Si 0.3~0.5%, Nb 0.2~0.4%, Ta 0.8~2.2%, W 0.5~1.6%, C≤0.07%, with the balance being Ti and impurities.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) Precise rapid cooling suppresses excessive grain growth, resulting in a dual-state structure with fine grain size and uniform distribution of precipitates;

[0024] (2) Strength-plasticity synergistic optimization is achieved by controlling the size of the α phase and the content of the β phase through step heat treatment;

[0025] (3) The uniformly distributed Ti3Al phase precipitates during the aging process, which enhances the high-temperature creep resistance. Attached Figure Description

[0026] Figure 1 This is a process flow diagram for the heat treatment of Ti65 titanium alloy in laser selective additive manufacturing according to the present invention. Detailed Implementation

[0027] A heat treatment process for improving the microstructure of Ti65 alloy produced by selective laser additive manufacturing includes the following steps:

[0028] Step 1): Preheating stage. The laser selective additive manufacturing Ti65 titanium alloy part is placed in a vacuum furnace and heated to 500-600 ℃ at a heating rate of 5-10 ℃ / min, and held at that temperature for 60-240 min. This stage aims to initially reduce the residual stress of the part and prepare it for subsequent heat treatment;

[0029] Step 2): Solution treatment stage. The β-transformation temperature of the Ti65 alloy is measured. The Ti65 alloy part manufactured by selective laser additive manufacturing is then heated at a rate of 8–12 °C / min to 5–10 °C above the β-transformation temperature. The holding time is determined based on the part volume; for common part sizes, the holding time should not be less than 120 min. Within this temperature range, the alloying elements in the Ti65 titanium alloy fully dissolve, promoting microstructure homogenization.

[0030] Step 3): Cooling stage. After the heat preservation is completed, rapid cooling with argon gas is used, with the cooling rate controlled at 50~80℃ / s, so that the alloy can quickly pass through the β phase transformation zone and obtain a fine and uniform α+β dual-phase structure.

[0031] Step 4): Aging treatment stage. The cooled components are placed back into the vacuum furnace, heated to 600-700℃, held for 240-360 minutes, and then cooled in the furnace. Aging treatment further strengthens the alloy microstructure and improves its strength and hardness.

[0032] The described method is a heat treatment process for improving the microstructure of Ti65 alloy parts manufactured by selective laser additive manufacturing, comprising two main parts: solution treatment and aging. The corresponding Ti65 alloy parts have the following mass percentage composition: Al: 5.5~6.0%, Sn: 3.6~4.5%, Zr: 3.0~4.0%, Mo: 0.2~0.6%, Si: 0.3~0.5%, Nb: 0.2~0.4%, Ta: 0.8~2.2%, W: 0.5~1.6%, C: 0.0~0.07%, with the balance being Ti and other unavoidable impurities.

[0033] In step 1), the vacuum furnace pressure is ≤1×10⁻⁶. -2 Pa, during the heat preservation stage, the temperature fluctuation is ≤±5℃.

[0034] In step 2), the β transition temperature is determined by differential scanning calorimetry, and the holding time is calculated by increasing the holding time by 2 minutes for every millimeter of the maximum cross-sectional thickness of the part.

[0035] In step 3), the argon purity is ≥99.999%, and the final cooling temperature is ≤100℃.

[0036] Step 4) involves a two-stage heating process: the first stage heats the temperature to 500°C at a rate of 5°C / min, and the second stage heats the temperature to the target temperature at a rate of 3°C / min.

[0037] The technical solution of a laser selective additive manufacturing process for Ti65 titanium alloy heat treatment according to the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0038] Example 1:

[0039] For aero-engine blade components (maximum wall thickness 15 mm), the following processes are implemented:

[0040] 1. Heat to 580℃ at a rate of 8℃ / min and hold for 180 minutes under vacuum;

[0041] 2. Heat at 10 ℃ / min to the β phase transition point (measured 1038 ℃) + 8 ℃, i.e., 1046 ℃, and hold for 150 minutes;

[0042] 3. Introduce liquid argon, and control the cooling rate to above 65 ℃ / s;

[0043] 4. Aging in two stages: First, heat to 650℃ at 5℃ / min and hold for 300 minutes, then cool to 300℃ at 2℃ / min before unloading.

[0044] Microstructural observation of the parts revealed the formation of a primary α-phase comprising 10–25% and a Ti3Al phase dispersed within a β-phase matrix. The average size of the Ti3Al phase was controlled between 50 and 80 nm, and the β-phase content was between 15 and 20%. Testing showed that the treated alloy achieved a room temperature tensile strength of 1080 MPa and an elongation of 12%, demonstrating excellent overall performance. Under a 100 MPa stress at 650 °C for 100 h, the material deformation was 0.15%, proving good high-temperature creep resistance.

[0045] Example 2:

[0046] For aero-engine blade components (maximum wall thickness 15 mm), the following processes are implemented:

[0047] 1. Heat to 580℃ at a rate of 8℃ / min and hold for 180 minutes under vacuum;

[0048] 2. Heat at 10℃ / min to the β phase transition point (measured 1038℃) + 8℃, i.e., 1046℃, and hold for 150 minutes;

[0049] 3. Introduce liquid argon at a cooling rate of 30℃ / s;

[0050] 4. Aging in two stages: First, heat to 650℃ at 5℃ / min and hold for 300 minutes, then cool to 300℃ at 2℃ / min before unloading.

[0051] Microstructural observation of the parts revealed that the proportion of primary α phase increased to 30–40%, while the β phase content decreased to 8–12%, and the average size of the Ti3Al phase was approximately 60–90 nm. Testing showed that the treated alloy had a room temperature tensile strength of 1000 MPa, but the elongation decreased to 8%, indicating a decline in overall mechanical properties. Under a stress of 100 MPa at 650 °C for 100 h, the material deformation was 0.22%.

[0052] Example 3:

[0053] For aero-engine blade components (maximum wall thickness 15 mm), the following processes are implemented:

[0054] 1. Heat to 580℃ at a rate of 8℃ / min and hold for 180 minutes under vacuum;

[0055] 2. Heat at 10 ℃ / min to the β phase transition point (measured 1038 ℃) + 8 ℃, i.e., 1046 ℃, and hold for 150 minutes;

[0056] 3. Introduce liquid argon, and control the cooling rate to above 65 ℃ / s;

[0057] 4. Aging in two stages: First, heat to 650℃ at 10℃ / min and hold for 300 minutes, then cool to 300℃ at 2℃ / min before unloading.

[0058] Microstructural observation of the parts revealed that the primary α-phase content was 15-25%, while the β-phase content increased to 30-35%. The precipitation of Ti3Al phase in the β-phase matrix was significantly reduced, with an average size between 20-60 nm. Testing showed that the treated alloy's room temperature tensile strength decreased to 950 MPa, elongation was 15%, and overall mechanical properties declined. Under 100 MPa stress at 650 °C for 100 h, the material deformation was 0.32%, indicating poor high-temperature creep performance.

[0059] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy, characterized in that... include: S1. Place the laser selective additive manufacturing Ti65 titanium alloy part in a vacuum furnace and heat it to 500~600 ℃ at the first heating rate, and hold it at that temperature for a certain period of time. S2. Measure the β transformation temperature of Ti65 titanium alloy. After selective laser additive manufacturing of Ti65 titanium alloy parts, heat them to 5-10 °C above the β transformation temperature at a second heating rate and hold them at that temperature to allow the alloying elements in the Ti65 titanium alloy to fully dissolve. S3. After the heat preservation is completed, the Ti65 titanium alloy parts are taken out of the vacuum furnace and rapidly cooled with argon gas to allow the Ti65 titanium alloy to quickly pass through the β phase transformation zone and form a fine and uniform α+β dual-phase structure. S4. Place the cooled Ti65 titanium alloy parts back into the vacuum furnace, heat to 600~700℃, hold at that temperature, and then cool with the furnace to improve the strength and hardness of the Ti65 titanium alloy. The heat treatment is then complete. In S1, the first heating rate is 5~10 ℃ / min; After heating to 500~600 ℃, the holding time is 60~240 min; In S2, the second heating is carried out at a heating rate of 8~12 °C / min to 5~10 °C above the β transition temperature; In S2, the heat preservation time is determined according to the component volume, and the heat preservation time shall not be less than 120 min; In S3, the cooling rate is 50~80 ℃ / s.

2. The heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy according to claim 1, characterized in that: The vacuum furnace pressure in S1 is ≤1×10 -2 Pa, during the heat preservation stage, the temperature fluctuation is ≤±5℃.

3. The heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy according to claim 1, characterized in that: The β transition temperature was determined by differential scanning calorimetry, and the holding time was calculated by increasing the holding time by 2 minutes for every millimeter of the maximum cross-sectional thickness of the component.

4. The heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy according to claim 1, characterized in that: The argon purity in S3 is ≥99.999%, and the final cooling temperature is ≤100℃.

5. The heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy according to claim 1, characterized in that: When the temperature in S4 is raised to 600~700℃, a two-stage heating method is adopted. The first stage raises the temperature to 500℃ at a rate of 5℃ / min, and the second stage raises the temperature to the target temperature at a rate of 3℃ / min. The holding time after heating to 600~700℃ is 240~360 min.

6. The heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy according to claim 1, characterized in that: The Ti65 titanium alloy composition by mass percentage is Al 5.5~6.0%, Sn 3.6~4.5%, Zr 3.0~4.0%, Mo 0.2~0.6%, Si 0.3~0.5%, Nb 0.2~0.4%, Ta 0.8~2.2%, W 0.5~1.6%, C≤0.07%, with the balance being Ti and impurities.

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