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

Abstract

The invention discloses a heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy. The heat treatment process comprises four stages of preheating treatment, solution treatment, rapid cooling and aging treatment. In the preheating treatment, the temperature is kept at 500-600 DEG C for 60-240 minutes so as to reduce residual stress; carrying out solution treatment and heating to 5-10 DEG C above a beta phase transformation point, carrying out heat preservation, and then carrying out argon rapid cooling (50-80 DEG C / s) to obtain a fine alpha + beta double-phase structure; and the aging treatment is performed at 600-700 DEG C for 240-360 minutes so as to improve the mechanical property. According to the process, the structure uniformity can be improved, the strength, hardness and high-temperature stability of the alloy are remarkably improved, and the process is suitable for performance optimization of complex titanium alloy components in the aerospace field.

Description

TECHNICAL FIELD

[0001] The application relates to a heat treatment process for laser selective additive manufacturing of Ti65 titanium alloy, and belongs to the fields of additive manufacturing and metal heat treatment. BACKGROUND

[0002] High-temperature titanium alloy is a titanium alloy for long-term application in a high-temperature environment. The high-temperature titanium alloy has high instantaneous and persistent strength, good creep resistance and good thermal stability in a working temperature range, has good plasticity, good creep resistance and good thermal stability at room temperature, and has good fatigue resistance at room temperature and high temperature. The high-temperature titanium alloy is mainly used for manufacturing discs, blades, air intake casings in air compressors and aircraft structural parts. According to the organization, the high-temperature titanium alloy is divided into alpha+beta type and near-alpha type titanium alloys.

[0003] Ti65 titanium alloy is a 10-component near-alpha 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 on the basis of Ti60 titanium alloy in China. The Ti65 titanium alloy has excellent high-temperature strength, thermal stability and creep resistance. The maximum temperature for long-term use of the Ti65 titanium alloy is 650 DEG C, and the short-term use temperature is higher than 750 DEG C, so that the Ti65 titanium alloy can maintain good mechanical properties in a high-temperature environment. However, the process performance of the high-temperature titanium alloy in the forming process is poor, and the forging, casting and welding methods are difficult to apply. The Ti65 alloy prepared by using the traditional forming method has complex forming process, low material utilization rate, long production cycle, high cost and low machining efficiency.

[0004] Compared with the traditional manufacturing technology, laser selective additive manufacturing as a rapidly developing near-net-shape fine machining technology adopts the principle of “discrete + accumulation”, which is a bottom-up method. The laser selective additive manufacturing is directly driven by three-dimensional data of a part to manufacture the part, realizes integrated near-net-shape forming of a complex geometric component, reduces time and cost, and the high cooling rate of the additive manufacturing process leads to substantial refinement of the microstructure, and improves the hardness and strength.

[0005] Laser selective additive manufacturing of Ti65 titanium alloy can effectively solve the problems of traditional forming methods in the preparation of Ti65 alloy parts, but the non-steady-state multi-cycle thermal process of additive manufacturing is not conducive to the high-temperature resistance and high-performance microstructure formation of high-temperature titanium alloy. The precipitation, morphology, distribution and size of high-temperature strengthening phase need to be further controlled by post-heat treatment to achieve it. Beijing Institute of Aeronautical Materials carried out the performance optimization research of Ti65 alloy, and controlled the mechanical properties of the alloy by adjusting the aging treatment parameters, but the deficiency is that it only studied the aviation forged Ti65 titanium alloy, and did not carry out test research and analysis on the gradually widely used additive manufacturing Ti65 titanium alloy. A heat treatment process suitable for laser selective additive manufacturing of Ti65 titanium alloy is urgently needed to be developed. SUMMARY

[0006] The technical problem of the present application is to overcome the shortcomings of the prior art, and a heat treatment process for laser selective additive manufacturing of Ti65 titanium alloy to improve the organizational defects and mechanical performance of the existing laser selective additive manufacturing of Ti65 titanium alloy.

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

[0008] S1, the laser selective additive manufacturing Ti65 titanium alloy parts are placed in a vacuum furnace, heated to 500-600 DEG C at a first heating rate, and kept for a certain time;

[0009] S2, measure the beta transition temperature of Ti65 alloy, then heat the laser selective additive manufacturing Ti65 alloy parts to 5-10 DEG C above the beta transition temperature at a second heating rate, and keep for a long time to make the alloy elements in the Ti65 titanium alloy fully dissolved;

[0010] S3, after the heat preservation is over, the Ti65 titanium alloy parts are taken out of the vacuum furnace, and argon is used for rapid cooling to make the alloy quickly pass through the beta phase transition zone to obtain fine and uniform alpha+beta dual-phase structure;

[0011] S4, the cooled Ti65 titanium alloy parts are put back into the vacuum furnace, heated to 600-700 DEG C, and cooled in the furnace after heat preservation to improve the strength and hardness of Ti65 titanium alloy, and the heat treatment is finished.

[0012] Preferably, in S1, the first heating rate is 5-10 DEG C / min; the heat preservation time after heating to 500-600 DEG C is 60-240 min.

[0013] Preferably, in S2, the second heating is heated to 5-10 DEG C above the beta transition temperature at a heating rate of 8-12 DEG C / min;

[0014] S2, the holding time is determined according to the volume of the workpiece, and the holding time is not less than 120 min.

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

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

[0017] Preferably, the beta transformation temperature is determined by differential scanning calorimetry, and the holding time is calculated by increasing 2 minutes per millimeter of the maximum cross-sectional thickness of the workpiece.

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

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

[0020] The holding time after the temperature is raised to 600-700℃ is 240-360 min.

[0021] Preferably, the Ti65 alloy composition 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%, and the balance is Ti and impurities.

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

[0023] (1) The rapid cooling with accurate speed inhibits excessive grain growth, and a bimodal structure with fine grain size and uniformly distributed precipitated phases is obtained.

[0024] (2) The size of alpha phase and the content of beta phase are regulated through stepwise heat treatment, and the strength-plasticity synergistic optimization is realized.

[0025] (3) The Ti3Al phase is uniformly distributed during aging process, and the high-temperature creep resistance is enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The present application is a heat treatment process route map for laser selective additive manufacturing of Ti65 titanium alloy. DETAILED DESCRIPTION

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

[0028] Step 1): pre-heating stage. The laser selective additive manufactured 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 for 60-240min. This stage aims to preliminarily reduce the residual stress of the part, preparing for the subsequent heat treatment;

[0029] Step 2): solution treatment stage. The β-transus temperature of Ti65 alloy is measured, and the laser selective additive manufactured Ti65 alloy part is then heated to 5-10℃ above the β-transus temperature at a heating rate of 8-12℃ / min, and the holding time is determined according to the volume of the part, and the holding time for common part sizes is not less than 120min. In this temperature range, the alloying elements in Ti65 titanium alloy are fully dissolved, promoting homogenization of the microstructure;

[0030] Step 3): cooling treatment stage. After holding, rapid cooling is performed using argon, with a cooling rate controlled at 50-80℃ / s, so that the alloy quickly passes through the β phase transition zone, obtaining fine and uniform α+β dual-phase microstructure.

[0031] Step 4): aging treatment stage. The cooled part is placed back into the vacuum furnace, heated to 600-700℃, and held for 240-360min before furnace cooling. Aging treatment further strengthens the alloy microstructure, improving its strength and hardness.

[0032] The heat treatment process for improving the microstructure of laser selective additive manufactured Ti65 alloy parts includes both solution and aging stages, and the corresponding composition of the Ti65 alloy part is A1: 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 ≤1×10-2Pa, and the temperature fluctuation during the holding stage is ≤±5℃.

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

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

[0036] In step 4), the aging treatment includes two-stage heating, the first stage is heated to 500℃ at a rate of 5℃ / min, and the second stage is heated to the target temperature at a rate of 3℃ / min.

[0037] The technical solutions in the embodiments of the heat treatment process of the laser selective additive manufacturing Ti65 titanium alloy as described in claim 1 will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work are within the protection scope of the present application.

[0038] Embodiment 1

[0039] For the aero-engine blade component (maximum wall thickness 15 mm), the following process is implemented:

[0040] 1. Under vacuum environment, increase the temperature to 580℃ at 8℃ / min and keep for 180 minutes;

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

[0042] 3. Introduce liquid argon, and the cooling rate is controlled to be higher than 65℃ / s;

[0043] 4. Two-stage aging: first increase to 650℃ at 5℃ / min and keep for 300 minutes, and then decrease to 300℃ at 2℃ / min and discharge.

[0044] Microstructure observation is performed on the workpiece, and 10-25% primary α phase and Ti3Al phase dispersedly precipitated in the β phase matrix are formed, the average size of the Ti3Al phase is controlled to be 50-80 nm, and the content of the β phase is 15-20%. It is tested that the tensile strength of the alloy after treatment is 1080MPa at room temperature, the elongation is 12%, and the comprehensive performance is good. Under the condition of 650℃, the deformation amount of the material is 0.15% under the action of 100MPa test stress for 100h, proving that the high-temperature creep performance is good.

[0045] Embodiment 2

[0046] For the aero-engine blade component (maximum wall thickness 15 mm), the following process is implemented:

[0047] 1. Under vacuum environment, increase the temperature to 580℃ at 8℃ / min and keep for 180 minutes;

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

[0049] 3. Introduce liquid argon, and the cooling rate is controlled to be 30℃ / s;

[0050] 4. Two-stage aging: first, increase to 650℃ at 5℃ / min, keep for 300 minutes, then decrease to 300℃ at 2℃ / min and discharge.

[0051] The microstructure of the product is observed, the content of primary α phase is increased to 30-40%, the content of β phase is decreased to 8-12%, and the average size of Ti3Al phase is about 60-90nm. After treatment, the tensile strength of the alloy at room temperature is 1000MPa, the elongation is decreased to 8%, and the comprehensive mechanical properties are decreased. Under the condition of 650℃, the deformation amount of the material is 0.22% under the action of 100MPa test stress for 100h.

[0052] Example 3:

[0053] For the aero-engine blade component (the maximum wall thickness is 15mm), the following process is implemented:

[0054] 1. Increase to 580℃ at 8℃ / min under vacuum environment, keep for 180 minutes;

[0055] 2. Increase to the β phase transition point (measured 1038℃) + 8℃, namely 1046℃, at 10℃ / min, keep for 150 minutes;

[0056] 3. Introduce liquid argon, and the cooling rate is controlled to be more than 65℃ / s;

[0057] 4. Two-stage aging: first, increase to 650℃ at 10℃ / min, keep for 300 minutes, then decrease to 300℃ at 2℃ / min and discharge.

[0058] The microstructure of the product is observed, the content of primary α phase is 15-25%, the content of β phase is increased to 30-35%, the Ti3Al phase precipitated in the β phase matrix is obviously decreased, and the average size is between 20-60nm. After treatment, the tensile strength of the alloy at room temperature is decreased to 950MPa, the elongation is 15%, and the comprehensive mechanical properties are decreased. Under the condition of 650℃, the deformation amount of the material is 0.32% under the action of 100MPa test stress for 100h, and the high-temperature creep performance is deteriorated.

[0059] The content not described in detail in the specification of the present application belongs to the prior art known by the person 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°C 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 alloy. After selective laser additive manufacturing of Ti65 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.

2. The heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy according to claim 1, characterized in that: In S1, the first heating rate is 5-10℃ / min; after heating to 500-600℃, the holding time is 60-240min.

3. The heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy according to claim 1, characterized in that: In S2, the second heating is carried out at a heating rate of 8 to 12 °C / min to 5 to 10 °C above the β transition temperature; 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 minutes.

4. The heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy according to claim 1, characterized in that: In S3, the cooling rate is 50–80 °C / s.

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

6. 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 part.

7. 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℃.

8. 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 used. 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 minutes.

9. The heat treatment process for selective laser additive manufacturing of Ti65 titanium alloy according to claim 1, characterized in that: 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.

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