Method for realizing additive manufacturing high-temperature alloy grain supernormal coarsening based on seed crystal guided directional recrystallization heat treatment

Abstract

The invention discloses a method for achieving additive manufacturing high-temperature alloy grain supernormal coarsening based on seed crystal guided directional recrystallization heat treatment, and relates to a coarsening method for additive manufacturing high-temperature alloy grains. The invention aims to solve the technical problem of insufficient high-temperature creep property caused by small grain size of the existing additive manufacturing nickel-based high-temperature alloy. According to the method, the single crystal layer with target orientation, namely the seed crystal, is prepared in the additive manufacturing stage, then the grain boundary of the seed crystal is continuously heated through the electromagnetic induction coil in the subsequent heat treatment, forced recrystallization is carried out by taking the seed crystal as a unique or absolute dominant growth source, namely oriented recrystallization is carried out, so that the growth of other crystal grains is inhibited, and the yield of the product is improved. And finally, an ultra-large grain structure with the seed crystal as the main source is obtained in the additive component, the average grain length of the ultra-large grain structure can be increased by two or more orders of magnitude compared with the original additive state and reaches the millimeter level or even the centimeter level, and the crystal orientation is highly consistent with the preset seed crystal orientation.

Description

Technical Field

[0001] This invention relates to a method for coarsening grains in additive manufacturing of high-temperature alloys. Background Technology

[0002] Nickel-based superalloys are key materials for manufacturing hot-end components of aero-engines and gas turbines, such as turbine blades. Additive manufacturing technologies, such as laser powder bed melting, have provided a revolutionary approach to manufacturing these components with complex cooling channels. However, the inherent rapid solidification characteristics of additive manufacturing result in components typically forming fine grains (average grain size below 100 μm). While this fine-grained structure exhibits high strength at room temperature, its creep resistance under long-term high-temperature loads is significantly inferior to the coarse-grained structures obtained through traditional polycrystalline casting, directional solidification casting, or single-crystal casting. This is the core bottleneck limiting the application of additively manufactured superalloys in high-end load-bearing hot-end components.

[0003] High-temperature solution heat treatment is commonly used to coarsen the grains of additively manufactured superalloys. However, conventional heat treatment, which involves placing the entire component in a heat treatment furnace, often only increases the grain size to the hundred-micrometer range (e.g., ~200 μm), failing to achieve a breakthrough in size and offering limited improvement in creep properties. In recent years, directional recrystallization technology has been explored for use in additive manufacturing materials. This technology uses a directionally moving high-temperature hot zone to sweep across the entire component, enabling recrystallized grains to grow along the direction of the hot zone's movement, thus coarsening the grains.

[0004] However, existing methods for directional recrystallization of additive manufacturing materials have fundamental limitations: (1) Significant grain anisotropy: Grain growth is strongly direction-dependent, and lateral dimensions are difficult to increase synchronously; (2) Low upper limit of grain size: During directional recrystallization, multiple grains participate in nucleation and compete for growth, making it difficult to stably control the grain boundary migration direction, thus restricting further directional grain growth. The grain size in the drawing direction can only reach ~650μm; (3) Passive orientation control: The random competitive growth of polycrystalline materials makes it impossible to actively control the crystal orientation. Therefore, it is urgent to develop a heat treatment method that can suppress the competitive growth of polycrystalline materials during directional recrystallization, realize grain size from micrometer to millimeter / centimeter level, and controllable grain orientation. Summary of the Invention

[0005] The present invention aims to address the technical problems of existing additive manufacturing materials having small grain size, significant grain anisotropy and low upper limit of size during directional recrystallization, making it difficult to break through the millimeter-level threshold and passive orientation control. The invention provides a method for achieving extraordinary grain coarsening of high-temperature alloys in additive manufacturing based on seed-guided directional recrystallization heat treatment.

[0006] The method for achieving ultra-coarsening of grains in additive manufacturing high-temperature alloys based on seed-guided directional recrystallization heat treatment of the present invention is carried out according to the following steps:

[0007] S1. Seed crystal preparation in the additive manufacturing process: Using a single-crystal substrate with a preset crystal orientation as an epitaxial template, a single-crystal region with the same orientation as the single-crystal substrate is epitaxially grown on the single-crystal substrate through laser additive manufacturing or electron beam additive manufacturing processes. This region serves as the "seed" for the entire subsequent recrystallization process. Then, the parameters of the additive manufacturing process are adjusted to continue growing a polycrystalline region with a typical fine-grained structure. The boundary between the polycrystalline region and the seed crystal region is the grain boundary region.

[0008] S2. Additive Component Assembly: The component manufactured in S1 is placed vertically with the polycrystalline region at the bottom, and most of the polycrystalline region is placed in cooling water. The grain boundary region is 2mm~3mm above the water surface, while the seed crystal region is completely above the cooling water surface. An induction heating coil is installed outside the seed crystal region. The height of the induction heating coil is less than 10mm, and the distance between the lower surface of the induction heating coil and the cooling water surface below is 2mm~10mm. This aims to create an extremely steep axial temperature gradient (≥1×10⁻⁶) below the hot zone. 5 (℃ / m) This "thermal confinement" design aims not only to create a temperature field that drives recrystallization, but more importantly, to rapidly "freeze" the unrecrystallized material at the front of the hot zone, preventing it from having sufficient thermal activation energy for independent nucleation, thereby clearing obstacles for grain boundary migration in the seed crystal region;

[0009] S3. Seed-guided directional recrystallization: Under a protective atmosphere, an induction coil is activated to heat and form a narrow and strong moving hot zone. By moving the component upward at a uniform speed, the hot zone scans the entire component from the seed crystal area downward. Driven by the moving hot zone, the seed crystal grain boundary continues to migrate downward to the additive polycrystalline region and engulfs the polycrystalline grains formed during the original additive solidification process, transforming them into coarse grains with the same orientation. The entire process is dominated by seed crystal growth, inhibiting the growth of other grains.

[0010] The core of this invention lies in preparing a "seed crystal" with a target orientation during the additive manufacturing stage, and then constraining the recrystallization process through a localized severe temperature gradient in the subsequent heat treatment, forcing recrystallization to take the seed crystal as the sole or absolutely dominant growth source, thereby suppressing random nucleation and achieving extreme grain coarsening.

[0011] This invention first uses a single-crystal substrate as a template to prepare a seed crystal region with a predetermined orientation through additive epitaxy. Then, under the synergistic effect of localized induction heating and forced water cooling, the high-temperature hot zone is directionally moved from the seed crystal region for heat treatment. By using the seed crystal as the dominant growth source to suppress the growth of other grains, the grain size of the additively manufactured component is increased from the traditional micrometer level to the millimeter or even centimeter level, resulting in an ultra-large columnar crystal structure with a specific orientation. Compared with traditional heat treatment processes, this invention not only achieves a breakthrough in grain size by orders of magnitude but also actively controls crystal orientation, thereby significantly improving the high-temperature creep performance of the component, making it particularly suitable for manufacturing key components such as turbine blades for aero-engines.

[0012] Through the above-described method, the present invention ultimately obtains an ultra-large columnar crystal structure in the main body of the component, with the seed crystal as the main origin. The average grain length can be increased by more than two orders of magnitude compared with the original additive state (~20μm), reaching the millimeter level (≥1mm) or even the centimeter level, and the crystal orientation is highly consistent with the preset seed crystal orientation.

[0013] The beneficial effects of this invention are:

[0014] 1. The method of this invention achieves a breakthrough in grain size by orders of magnitude: it increases the typical grain size of additively manufactured high-temperature alloys from the micrometer level to the millimeter level, and some grains can even reach the centimeter level, which is unattainable by traditional heat treatment;

[0015] 2. This invention achieves active control of crystal orientation: the macroscopic texture of the final structure is determined by the orientation of the seed crystals in the initial preparation, and can be customized according to the load-bearing requirements of different directions of the component to maximize the material potential;

[0016] 3. High process stability and wider window: "Water-cooled constraint" physically suppresses random nucleation and reduces dependence on extreme sensitivity to migration rate, enabling the acquisition of ultra-large grains over a wider parameter range, thus improving process robustness and repeatability.

[0017] 4. Brought about a leap in performance: The combination of millimeter-level coarse columnar crystal structure and strong texture fundamentally improves the high-temperature creep resistance of components, clearing the most important material structure obstacle for additive manufacturing of key components such as high-performance turbine blades. Attached Figure Description

[0018] Figure 1 The diagram below illustrates the principle of the method in Experiment 1. The left diagram represents S1, and the right diagram represents S3.

[0019] Figure 2 This is a schematic diagram comparing the microstructure of existing technologies with the expected effects of this invention. Detailed Implementation

[0020] Specific Implementation Method 1: This implementation method is a method for achieving extraordinary grain coarsening of high-temperature alloys in additive manufacturing based on seed-guided directional recrystallization heat treatment, specifically carried out according to the following steps:

[0021] S1. Seed crystal preparation in the additive manufacturing process: Using a single-crystal substrate with a preset crystal orientation as an epitaxial template, a single-crystal region with the same orientation as the single-crystal substrate is epitaxially grown on the single-crystal substrate through laser additive manufacturing or electron beam additive manufacturing processes. This region serves as the "seed" for the entire subsequent recrystallization process. Then, the parameters of the additive manufacturing process are adjusted to continue growing a polycrystalline region with a typical fine-grained structure. The boundary between the polycrystalline region and the seed crystal region is the grain boundary region.

[0022] S2. Additive Component Assembly: The component manufactured in S1 is placed vertically with the polycrystalline region at the bottom, and most of the polycrystalline region is placed in cooling water. The grain boundary region is 2mm~3mm above the water surface, while the seed crystal region is completely above the cooling water surface. An induction heating coil is installed outside the seed crystal region. The height of the induction heating coil is less than 10mm, and the distance between the lower surface of the induction heating coil and the cooling water surface below is 2mm~10mm. This aims to create an extremely steep axial temperature gradient (≥1×10⁻⁶) below the hot zone. 5 (℃ / m) This "thermal constraint" design aims not only to create a temperature field that drives recrystallization, but more importantly, to "freeze" the recrystallization zone at the front of the hot zone, so that it does not have enough thermal activation energy to carry out independent nucleation, thereby clearing obstacles for seed crystal boundary migration;

[0023] S3. Seed-guided directional recrystallization: Under a protective atmosphere, an induction coil is activated to heat and form a narrow and strong moving hot zone. By moving the component upward at a uniform speed, the hot zone scans the entire component from the seed crystal area downward. Driven by the moving hot zone, the seed crystal grain boundary continues to migrate downward to the additive polycrystalline region and engulfs the polycrystalline grains formed during the original additive solidification process, transforming them into coarse grains with the same orientation. The entire process is dominated by seed crystal growth, inhibiting the growth of other grains.

[0024] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the preset crystallographic direction of the single-crystal substrate with a preset crystal orientation described in S1 is <001>, <100>, <110>, or <111>. Everything else is the same as in Specific Implementation Method One.

[0025] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the component manufactured in S1 is a nickel-based high-temperature alloy. Everything else is the same as in Specific Implementation Method One or Two.

[0026] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the component manufactured by S1 is made of IN738LC alloy. Everything else is the same as in Specific Implementation Methods One to Three.

[0027] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the additive manufacturing process parameters for the seed crystal region in S1 are: scanning speed of 1000 mm / s, scanning spacing of 0.08 mm, layer thickness of 0.04 mm, laser power of 330 W, and a scanning strategy of continuous interlayer rotation of 90°. Everything else is the same as in Specific Implementation Method Four.

[0028] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the additive manufacturing process parameters for the polycrystalline region in S1 are: scanning speed 1400 mm / s, scanning spacing 0.09 mm, layer thickness 0.04 mm, laser power 270 W, and a scanning strategy of continuous interlayer rotation of 67°. Everything else is the same as in Specific Implementation Method Five.

[0029] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that: in S3, the induction coil is activated to heat and form a narrow and strong moving hot zone, with a peak temperature of 1210℃~1260℃. Everything else is the same as in Specific Implementation Method Six.

[0030] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the upward uniformly moving member described in S3 has a speed of 0.5 mm / h to 50 mm / h. Everything else is the same as in Specific Implementation Method Seven.

[0031] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the protective atmosphere described in S3 is argon. Everything else is the same as in Specific Implementation Method Eight.

[0032] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the protective atmosphere described in S3 is nitrogen. Everything else is the same as in Specific Implementation Method Nine.

[0033] The invention was verified using the following experiments:

[0034] Experiment 1: This experiment demonstrates a method for achieving exceptional grain coarsening in additive manufacturing high-temperature alloys through seed-guided directional recrystallization heat treatment. The specific steps are as follows:

[0035] S1. Seed crystal preparation in the additive manufacturing process: Using a single-crystal substrate with a preset crystal orientation as an epitaxial template, a single-crystal region with the same orientation as the single-crystal substrate is epitaxially grown on the single-crystal substrate through laser additive manufacturing or electron beam additive manufacturing processes. This region serves as the seed crystal region with a height of 4 mm, and it acts as the "seed" for the entire subsequent recrystallization process. Then, the parameters of the additive manufacturing process are adjusted to continue growing a 60 mm polycrystalline region with a typical fine-grained structure (grain size ~20 μm). The boundary between the polycrystalline region and the seed crystal region is the grain boundary region.

[0036] The preset crystallographic direction of the single crystal substrate with a preset crystal orientation described in S1 is <001>.

[0037] The components manufactured by S1 are made of IN738LC alloy;

[0038] The single-crystal substrate manufactured by S1 is made of IN738LC alloy;

[0039] The additive manufacturing process parameters for the seed crystal region in S1 are: scanning speed of 1000 mm / s, scanning spacing of 0.08 mm, layer thickness of 0.04 mm, laser power of 330 W, and scanning strategy of continuous interlayer rotation of 90°.

[0040] The additive manufacturing process parameters for the polycrystalline region in S1 are: scanning speed 1400mm / s, scanning spacing 0.09mm, layer thickness 0.04mm, laser power 270W, and scanning strategy of continuous interlayer rotation 67°.

[0041] S2. Additive Component Assembly: The component manufactured in S1 is placed vertically with the polycrystalline region at the bottom, and most of the polycrystalline region is placed in cooling water. The grain boundary region is 3mm above the water surface, while the seed crystal region is completely above the cooling water surface. An induction heating coil is installed outside the seed crystal region. The height of the induction heating coil is less than 10mm, and the distance between the lower surface of the induction heating coil and the cooling water surface below is 5mm. This aims to create an extremely steep axial temperature gradient (≥1×10⁻⁶) below the hot zone. 5 (℃ / m) This "thermal constraint" design aims not only to create a temperature field that drives recrystallization, but more importantly, to "freeze" the recrystallization zone at the front of the hot zone, so that it does not have enough thermal activation energy to carry out independent nucleation, thereby clearing obstacles for seed crystal boundary migration;

[0042] S3. Seed-guided directional recrystallization: Under an argon atmosphere, an induction coil is activated to heat and form a narrow and strong moving hot zone with a peak temperature of 1240℃. The hot zone is then moved upward at a uniform speed of 2mm / h to scan the entire component from the seed crystal area downward. Driven by the moving hot zone, the grain boundaries of the seed crystal area continue to migrate downward to the additive polycrystalline area and engulf the polycrystalline grains formed during the original additive solidification process, transforming them into coarse grains with the same orientation. The entire process is dominated by seed crystal growth, which inhibits the growth of other grains.

[0043] Figure 2 Figure 1 is a schematic diagram comparing the microstructure of the prior art and the expected effect of the present invention. Figure 2 shows the equiaxed crystal structure of traditional static recrystallization; Figure 3 shows the competitive growth columnar crystal structure of seedless directional recrystallization; and Figure 4 shows the ultra-large single columnar crystal structure expected by the method of the present invention.

[0044] Organizational evolution: This invention enables the transformation from... Figure 2 (b) to Figure 2 (c) Crossing. Without a seed crystal, polycrystalline growth competes within the hot zone, forming... Figure 2 (b) shows a polycrystalline columnar structure. In this invention, the seed crystal, as the absolute growth advantage during directional recrystallization, is expected to achieve, as shown in [example missing]. Figure 2 (c) shows a single super-large columnar crystal that runs through the entire recrystallization zone, with a grain length of up to tens of millimeters (≥10mm).

[0045] Orientation control: This super-large columnar crystal will inherit the <001> orientation of the seed crystal, thus achieving active control of the texture.

[0046] Performance Expectations: Based on the classic creep mechanism, the order-of-magnitude increase in grain size (from hundreds of micrometers to centimeters) will significantly suppress grain boundary slip during creep, thereby improving creep life. Therefore, components treated with this method will exhibit a longer high-temperature creep life. Figure 2 (a) shows the traditional equiaxed crystal structure (static recrystallization) and Figure 2 (b) shows a significant improvement in the conventional columnar crystal structure (directional recrystallization without seed crystal guidance), potentially reaching orders of magnitude improvement.

[0047] The seed crystal orientation in the method of this invention can be based on Figure 1 The "single-crystal substrate" can be designed arbitrarily, not limited to <001>. By controlling the heat treatment parameters in segments, it is also expected to achieve gradient microstructure preparation on a single component.

[0048] Figure 1 and Figure 2Together, they elucidated the core concept, implementation device, and organizational effect of the synergistic effect of "seed crystal guidance" and "local thermal confinement" in this invention. This method provides a clear path in principle to push the grain size of additively manufactured high-temperature alloys from the micrometer level to the millimeter level and even the centimeter level, which can fundamentally solve the bottleneck problem of insufficient high-temperature creep performance and has significant industrial application prospects.

Claims

1. A method for achieving ultra-coarsening of grains in additive manufacturing high-temperature alloys based on seed-guided directional recrystallization heat treatment, characterized in that... The method is performed according to the following steps: S1. Seed crystal preparation in the additive manufacturing process: Using a single-crystal substrate with a preset crystal orientation as an epitaxial template, a single-crystal domain with the same orientation as the single-crystal substrate is epitaxially grown on the single-crystal substrate through laser additive manufacturing or electron beam additive manufacturing processes. This region serves as the seed crystal region, and it acts as the seed for the entire subsequent recrystallization process. Then, the parameters of the additive manufacturing process are adjusted to continue growing a polycrystalline region with a typical fine-grained structure. The boundary between the polycrystalline region and the seed crystal region is the grain boundary region. S2. Additive component assembly: The component manufactured in S1 is placed vertically with the polycrystalline region at the bottom and most of the polycrystalline region placed in the cooling water. The grain boundary region is 2mm to 3mm above the water surface, while the seed crystal region is completely above the cooling water surface. An induction heating coil is set outside the seed crystal region. The height of the induction heating coil is less than 10mm, and the distance between the lower surface of the induction heating coil and the lower cooling water surface is 2mm to 10mm. S3. Seed-guided directional recrystallization: Under a protective atmosphere, an induction coil is activated to heat and form a narrow and strong moving hot zone. By moving the component upward at a uniform speed, the hot zone scans the entire component from the seed crystal area downward. Driven by the moving hot zone, the seed crystal grain boundary continues to migrate downward to the additive polycrystalline region and engulfs the polycrystalline grains formed during the original additive solidification process, transforming them into coarse grains with the same orientation. The entire process is dominated by seed crystal growth, inhibiting the growth of other grains.

2. The method for achieving ultra-coarsening of grains in additive manufacturing high-temperature alloys based on seed-guided directional recrystallization heat treatment according to claim 1, characterized in that... The preset crystallographic orientation of the single-crystal substrate with preset crystal orientation described in S1 is <001>, <100>, <110> or <111>.

3. The method for achieving ultra-coarsening of grains in additive manufacturing high-temperature alloys based on seed-guided directional recrystallization heat treatment according to claim 1, characterized in that... The components manufactured by S1 are made of nickel-based high-temperature alloys.

4. The method for achieving extraordinary grain coarsening of high-temperature alloys in additive manufacturing based on seed-guided directional recrystallization heat treatment according to claim 1, characterized in that... The components manufactured by S1 are made of IN738LC alloy.

5. The method for achieving extraordinary grain coarsening of high-temperature alloys in additive manufacturing based on seed-guided directional recrystallization heat treatment according to claim 1, characterized in that... The additive manufacturing process parameters for the seed crystal region in S1 are: scanning speed of 1000 mm / s, scanning spacing of 0.08 mm, layer thickness of 0.04 mm, laser power of 330 W, and a scanning strategy of continuous interlayer rotation of 90°.

6. The method for achieving extraordinary grain coarsening of high-temperature alloys in additive manufacturing based on seed-guided directional recrystallization heat treatment according to claim 5, characterized in that... The additive manufacturing process parameters for the polycrystalline region in S1 are: scanning speed 1400 mm / s, scanning spacing 0.09 mm, layer thickness 0.04 mm, laser power 270 W, and a scanning strategy of continuous interlayer rotation of 67°.

7. The method for achieving extraordinary grain coarsening of high-temperature alloys in additive manufacturing based on seed-guided directional recrystallization heat treatment according to claim 1, characterized in that... In S3, the induction coil is activated to heat up and form a narrow and strong moving hot zone with a peak temperature of 1210℃~1260℃.

8. The method for achieving ultra-coarsening of grains in additive manufacturing high-temperature alloys based on seed-guided directional recrystallization heat treatment according to claim 1, characterized in that... The upward uniformly moving component described in S3 has a speed of 0.5 mm / h to 50 mm / h.

9. The method for achieving ultra-coarsening of grains in additive manufacturing high-temperature alloys based on seed-guided directional recrystallization heat treatment according to claim 1, characterized in that... The protective atmosphere described in S3 is argon.

10. The method for achieving ultra-coarsening of grains in additive manufacturing high-temperature alloys based on seed-guided directional recrystallization heat treatment according to claim 1, characterized in that... The protective atmosphere described in S3 is nitrogen.

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