Heat treatment method for improving room-temperature plasticity of additive manufacturing IN738LC alloy

Abstract

The invention discloses a heat treatment method for improving the room-temperature plasticity of an additive manufacturing IN738LC alloy, and relates to a heat treatment method for improving the room-temperature plasticity of an additive manufacturing alloy. The invention aims to solve the technical problem that the IN738LC alloy subjected to additive manufacturing at present cannot have both strength and plasticity after being subjected to heat treatment. Composite heat treatment is carried out on the IN738LC alloy subjected to additive manufacturing, specifically, recrystallization annealing treatment is carried out firstly, solid solution treatment is carried out after air cooling, aging treatment is carried out after air cooling, and air cooling is carried out. According to the heat treatment method for improving the room-temperature mechanical property of the IN738LC alloy by optimizing the size and distribution of the gamma'phase, a composite heat treatment scheme of recrystallization annealing treatment, solution treatment and aging treatment is designed, gamma 'in the alloy subjected to heat treatment is evenly distributed, the tensile strength of the alloy is 1292.66 MPa, the ductility of the alloy is 15.91%, and the mechanical property of the alloy is improved. And the obtained IN738LC alloy has both excellent strength and plasticity.

Description

Technical Field

[0001] This invention relates to a heat treatment method for room temperature plasticity of additive manufacturing alloys. Background Technology

[0002] Selective laser melting (SLM) additive manufacturing technology offers significant advantages in the preparation of IN738LC alloys, enabling rapid prototyping of complex parts. It is particularly suitable for critical components with complex structures, such as turbine blades and combustion chambers for aero-engines, significantly shortening manufacturing cycles and reducing mold costs and processing difficulty, making it widely used in high-end aerospace equipment. However, the SLM layer-by-layer melting and solidification process has inherent microstructural defects: extremely high cooling rates and temperature gradients cause the alloy to form coarse columnar crystal textures along the construction direction, accompanied by submicron-level cellular structures and high-density dislocations, resulting in microstructural anisotropy; rapid solidification induces elemental microsegregation, causing extremely uneven precipitation of the strengthening γ' phase, with some areas forming coarse blocky γ' phases and others having insufficient quantity and low dispersion of γ' phase. Simultaneously, the high residual stress formed by the accumulation of interlayer thermal stress exacerbates brittleness, and the room-temperature elongation of the deposited alloy is typically low, failing to meet engineering application requirements. Subsequent heat treatment is necessary to optimize the microstructure and properties. Currently, there are technical shortcomings in the heat treatment of IN738LC alloys for additive manufacturing: traditional solution aging cannot reconstruct coarse columnar crystals due to insufficient temperature, resulting in incomplete dissolution of the γ' phase, significant size differences after aging, and large performance fluctuations; single high-temperature recrystallization lacks precise solution control, elemental segregation is not resolved, and the γ' phase easily coarsens at grain boundaries to form a continuous network structure, reducing toughness; when directly using 850℃ / 24h aging, the columnar crystal texture and elemental segregation are not improved, the γ' phase only precipitates in the segregation zone, with uneven size distribution, residual stress not released, and limited improvement in room temperature plasticity, which is difficult to meet engineering requirements. Summary of the Invention

[0003] The present invention aims to solve the technical problem that the IN738LC alloy produced by additive manufacturing cannot simultaneously possess both strength and plasticity after heat treatment, and provides a heat treatment method to improve the room temperature plasticity of the IN738LC alloy produced by additive manufacturing.

[0004] The heat treatment method of the present invention for improving the room temperature plasticity of IN738LC alloy in additive manufacturing is carried out according to the following steps:

[0005] The additively manufactured IN738LC alloy undergoes a composite heat treatment process, specifically recrystallization annealing followed by air cooling, solution treatment, air cooling, aging treatment, and air cooling.

[0006] This invention proposes a composite heat treatment process of "1250℃ / 2h recrystallization + 1120℃ / 4h solution treatment + 850℃ / 24h aging". The high temperature of 1250℃ provides the conditions for the transformation of columnar crystals to equiaxed crystals. The 2h holding time ensures the complete elimination of columnar crystals and the uniform refinement of equiaxed crystals, while fully dissolving the coarse γ' phase and releasing residual stress. The medium temperature of 1120℃ can inhibit the premature precipitation of the γ' phase. The 4h holding time allows the alloying elements to diffuse fully, which not only solves the problem of uneven element distribution in a short time, but also prevents abnormal precipitation of the γ' phase caused by excessive time. The 24h heat treatment at 850℃ can induce the full precipitation of the γ' phase, forming a cubic γ' phase with uniform size and diffuse distribution. The grain boundaries are discontinuous and granular, avoiding insufficient precipitation due to too short a time or coarsening of the γ' phase and formation of grain boundary films due to too long a time. The present invention ensures a sufficient volume fraction of the γ' phase through the above-mentioned composite heat treatment, improves the size uniformity and distribution, effectively enhances room temperature plasticity and maintains strength.

[0007] This invention proposes a heat treatment method to improve the room temperature mechanical properties of IN738LC alloy by optimizing the size and distribution of the γ' phase. A composite heat treatment scheme of "recrystallization annealing + solution treatment + aging treatment" is designed to optimize the size and distribution of the γ' phase while releasing the internal stress of the alloy, thereby obtaining an IN738LC alloy with both strength and plasticity.

[0008] This invention uses IN738LC alloy powder as raw material and employs an additive manufacturing method with laser powder bed melting to prepare IN738LC alloy. For directly aged IN738LC alloy, local enrichment of the γ' phase occurs. The alloy exhibits a high tensile strength (1428.81 MPa) and elongation (4.62%), but poor room temperature plasticity. The IN738LC alloy is then subjected to a composite heat treatment method according to this invention. This method is simple, has a short cycle time, and low cost. After heat treatment, the γ' phase distribution in the alloy is more uniform, with a tensile strength of 1292.66 MPa and an elongation of 15.91%. The resulting IN738LC alloy possesses both excellent strength and plasticity. Compared to the directly aged IN738LC alloy, the room temperature tensile strength decreases by only 9.5%, while the elongation increases by 244.4%. Attached Figure Description

[0009] Figure 1 This is a microstructure diagram of the IN738LC alloy with γ' phase obtained from comparative experiments;

[0010] Figure 2 This is a microstructure diagram of the IN738LC alloy with a uniformly distributed γ' phase obtained in Experiment 1.

[0011] Figure 3This is a flowchart of the composite heat treatment process in Experiment 1;

[0012] Figure 4 The image shows the room temperature tensile stress-strain curves of the IN738LC alloy after direct aging treatment, as compared in the comparative experiment.

[0013] Figure 5 This is the room temperature tensile stress-strain curve of the IN738LC alloy after composite heat treatment in Experiment 1. Detailed Implementation

[0014] Specific Implementation Method 1: This implementation method is a heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing, specifically carried out according to the following steps:

[0015] The additively manufactured IN738LC alloy undergoes a composite heat treatment process, specifically recrystallization annealing followed by air cooling, solution treatment, air cooling, aging treatment, and air cooling.

[0016] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the additive manufacturing technology used for the IN738LC alloy is laser powder bed melting technology. Everything else is the same as in Specific Implementation Method One.

[0017] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 2 in that the preparation method of the IN738LC alloy by additive manufacturing is as follows: IN738LC alloy powder is placed in an additive manufacturing device, argon gas is introduced into the device to remove air, the laser power is 270W, the layer thickness is 40μm, the scanning speed is 1m / s, the scanning interval is 90μm, the rotation between each layer is 67°, and the spot size is 100μm, thus obtaining the IN738LC alloy. Everything else is the same as in Specific Implementation Method 2.

[0018] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Three in that the elemental composition of the IN738LC alloy by weight percentage is as follows: Cr 15.7%~16.3%, Co 8%~9%, Mo 1.5%~2%, W 2.4%~2.8%, Ta 1.5%~2%, Al 3.2%~3.7%, Ti 3.2%~3.7%, Nb 0.6%~1.1%, C 0.09%~0.13%, B 0.07%~0.12%, Zr 0.02%~0.08%, with the balance being Ni. Everything else is the same as in Specific Implementation Method Three.

[0019] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Three in that the particle size of the IN738LC alloy powder is 15μm~45μm. Everything else is the same as in Specific Implementation Method Three.

[0020] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the recrystallization annealing process is as follows: the IN738LC alloy is recrystallized and annealed at 1250°C for 2 hours. Everything else is the same as in Specific Implementation Method Five.

[0021] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that the solution treatment process is performed at 1120°C for 4 hours. Everything else is the same as in Specific Implementation Method Six.

[0022] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the aging process involves aging at 850°C for 24 hours. Everything else is the same as in Specific Implementation Method Seven.

[0023] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Four in that the elemental composition of the IN738LC alloy by weight percentage is: Cr 16.1%, Co 8.6%, Mo 1.8%, W 2.8%, Ta 1.7%, Al 3.5%, Ti 3.4%, Nb 0.9%, C 0.1%, B 0.09%, Zr 0.07%, with the balance being Ni. Everything else is the same as in Specific Implementation Method Four.

[0024] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the room temperature tensile strength of the IN738LC alloy after composite heat treatment is 1292.66 MPa, and the elongation is 15.91%. Everything else is the same as in Specific Implementation Method Nine.

[0025] The invention was verified using the following experiments:

[0026] Experiment 1: This experiment presents a heat treatment method to improve the room temperature plasticity of IN738LC alloy in additive manufacturing. The specific steps are as follows:

[0027] 1. IN738LC alloy powder is placed in an additive manufacturing equipment. Argon gas is introduced into the equipment to remove air. The laser power is 270W, the layer thickness is 40μm, the scanning speed is 1m / s, the scanning interval is 90μm, the rotation between each layer is 67°, and the spot size is 100μm to obtain IN738LC alloy. The particle size of the IN738LC alloy powder is 15μm~45μm. The elemental composition of the IN738LC alloy by weight percentage is: Cr 16.1%, Co 8.6%, Mo 1.8%, W 2.8%, Ta 1.7%, Al 3.5%, Ti 3.4%, Nb 0.9%, C 0.1%, B 0.09%, Zr 0.07%, with the balance being Ni.

[0028] 2. The additively manufactured IN738LC alloy is subjected to composite heat treatment, specifically recrystallization annealing, air cooling, solution treatment, air cooling, aging treatment, and air cooling.

[0029] The recrystallization annealing process is as follows: the IN738LC alloy is recrystallized and annealed at 1250℃ for 2 hours;

[0030] The solution treatment process is as follows: solution treatment at 1120℃ for 4 hours;

[0031] The aging process is as follows: aging at 850℃ for 24 hours.

[0032] The room temperature tensile strength and elongation of the IN738LC alloy after composite heat treatment in Experiment 1 were 1292.66 MPa and 15.91%, respectively.

[0033] Comparative Experiment: This experiment demonstrates a direct aging treatment method for additively manufactured IN738LC alloy. Unlike Experiment 1, in step two, the additively manufactured IN738LC alloy undergoes only aging treatment followed by air cooling. The aging process involves aging at 850℃ for 24 hours. All other steps are the same as in Experiment 1. The tensile strength and elongation of the IN738LC alloy using the direct aging treatment in the comparative experiment were 1428.81 MPa and 4.62%, respectively. Compared to Experiment 1, although the tensile strength decreased by 9.5%, the elongation increased by 244.4%.

[0034] Figure 1 The image shows the microstructure of the IN738LC alloy with γ' phase obtained from the comparative experiment. It can be seen that the γ' phase exhibits local enrichment at the dendrite boundaries.

[0035] Figure 2 This is a microstructure diagram of the IN738LC alloy with a uniformly distributed γ' phase obtained from Experiment 1. It can be seen that the γ' phase is blocky and uniformly distributed.

[0036] Figure 3 This is a flowchart of the composite heat treatment process in Experiment 1. It can be seen that this process is simple and has a short cycle.

[0037] Figure 4 The figure shows the room temperature tensile stress-strain curve of the IN738LC alloy after direct aging treatment in the comparative test. It can be seen that the alloy has high room temperature tensile strength but poor room temperature plasticity.

[0038] Figure 5The figure shows the room temperature tensile stress-strain curve of the IN738LC alloy after composite heat treatment in Experiment 1. It can be seen that compared with the alloy directly aged in the comparative experiment, although the tensile strength of the IN738LC alloy decreased slightly after composite heat treatment, the alloy plasticity was greatly improved.

Claims

1. A heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing, characterized in that... The method is performed according to the following steps: The additively manufactured IN738LC alloy undergoes a composite heat treatment process, specifically recrystallization annealing followed by air cooling, solution treatment, air cooling, aging treatment, and air cooling.

2. The heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing according to claim 1, characterized in that... The additive manufacturing technology for the IN738LC alloy is laser powder bed melting technology.

3. The heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing according to claim 2, characterized in that... The method for preparing the IN738LC alloy by additive manufacturing is as follows: IN738LC alloy powder is placed in an additive manufacturing equipment, argon gas is introduced into the equipment to remove air, the laser power is 270W, the layer thickness is 40μm, the scanning speed is 1m / s, the scanning interval is 90μm, the rotation between each layer is 67°, and the spot size is 100μm to obtain the IN738LC alloy.

4. The heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing according to claim 1, characterized in that... The raw material alloy powder used in the additive manufacturing of the IN738LC alloy has the following elemental composition by weight percentage: Cr 15.7%~16.3%, Co 8%~9%, Mo 1.5%~2%, W 2.4%~2.8%, Ta 1.5%~2%, Al 3.2%~3.7%, Ti 3.2%~3.7%, Nb 0.6%~1.1%, C 0.09%~0.13%, B 0.07%~0.12%, Zr 0.02%~0.08%, with the balance being Ni.

5. A heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing according to claim 3, characterized in that... The particle size of the IN738LC alloy powder is 15μm~45μm.

6. The heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing according to claim 1, characterized in that... The recrystallization annealing process is as follows: IN738LC alloy is recrystallized and annealed at 1250℃ for 2 hours.

7. A heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing according to claim 6, characterized in that... The solution treatment process is as follows: solution treatment at 1120℃ for 4 hours.

8. A heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing according to claim 7, characterized in that... The aging process is as follows: aging at 850℃ for 24 hours.

9. A heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing according to claim 4, characterized in that... The raw material alloy powder used in the additive manufacturing of the IN738LC alloy has the following elemental composition by weight percentage: Cr 16.1%, Co 8.6%, Mo 1.8%, W 2.8%, Ta 1.7%, Al 3.5%, Ti 3.4%, Nb 0.9%, C 0.1%, B 0.09%, Zr 0.07%, with the balance being Ni.

10. A heat treatment method for improving the room temperature plasticity of IN738LC alloy in additive manufacturing according to claim 9, characterized in that... The room temperature tensile strength of the IN738LC alloy after composite heat treatment is 1292.66 MPa, and the elongation is 15.91%.

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