A grain boundary optimization method for additive manufacturing of high-temperature alloy based on deep cooling-current synergistic regulation

Abstract

A grain boundary optimization method for additive manufacturing of high-temperature alloy based on deep cooling-current synergistic regulation, which relates to the field of metal additive manufacturing post-processing technology. The purpose of the present application is to solve the problem of optimizing the distribution of grain characteristics of GH4099 nickel-based high-temperature alloy manufactured by the existing method due to the lack of recrystallization driving force and the grain boundary pinning effect. Method: 1. Powder pretreatment; 2. Laser additive manufacturing; 3. Cryogenic treatment; 4. Pulse current annealing. The present application proposes a composite process based on "deep cooling treatment-current rapid annealing", which introduces uniform internal stress energy through non-destructive deep cooling treatment, and reduces the recrystallization energy barrier by combining pulse current annealing, thereby realizing high-proportion low-ΣCSL grain boundary construction (target proportion > 50%) while maintaining the advantages of near-net-shape additive manufacturing, thereby significantly improving the material's resistance to grain boundary failure and high-temperature service performance.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing post-processing technology, specifically to a grain boundary optimization method for additive manufacturing of high-temperature alloys based on cryogenic-current synergistic regulation. Background Technology

[0002] GH4099 nickel-based superalloy is widely used in hot-end components such as aero-engine combustion chamber parts and turbine guide vanes due to its excellent high-temperature mechanical properties, creep resistance, and corrosion resistance. In its solution-treated and aged state, this alloy can operate continuously at 900°C, with instantaneous temperature resistance reaching 1000°C. However, under the coupled effects of high-temperature corrosion and complex stress, grain boundaries become failure-sensitive areas, with over 80% of high-temperature failures originating from early cracking caused by grain boundary oxidation.

[0003] Studies have shown that low-Σ coincidence site lattice (CSL, Σ≤29) grain boundaries exhibit 3-5 times higher corrosion resistance than ordinary large-angle grain boundaries due to their low interfacial energy (<0.5 J / m²) and high structural order. Improving the proportion of low-Σ CSL grain boundaries (target >60%) by optimizing the grain boundary characteristic distribution (GBCD) has become a key approach to enhancing the service reliability of high-temperature alloys. Traditional GBCD optimization relies on deformation heat treatment (such as rolling + annealing), requiring the introduction of stored energy through ≥30% plastic deformation. However, this method leads to geometric deformation, which severely conflicts with the near-net-shape characteristics of additive manufacturing (AM). The AM process for preparing GH4099 alloy faces a dual bottleneck: 1) Insufficient recrystallization driving force: The inherent rapid solidification characteristics of the AM process result in a low and uneven initial storage energy level (affected by repeated thermal cycling, interlayer dwell, and residual stress), making it difficult to drive complete recrystallization in subsequent heat treatment, thus hindering the formation of the ideal GBCD; 2) Impeded grain boundary migration: Subgrain boundary segregation elements (Cr, Mo) create a pinning effect, increasing the grain boundary migration activation energy by 40% (up to 280 kJ / mol), usually requiring higher annealing temperatures or longer holding times, which easily induces inhomogeneous recrystallization and grain coarsening. Therefore, it is urgent to develop a new GBCD control method that is geometrically compatible (non-deformation), low-temperature, short-time, and can effectively drive recrystallization, in order to solve the GBCD optimization problem caused by insufficient / inhomogeneous storage energy and difficulty in recrystallization control in additive manufacturing of GH4099 alloy. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of difficulty in optimizing the grain boundary feature distribution of GH4099 nickel-based superalloys manufactured by existing additive manufacturing methods due to insufficient recrystallization driving force and grain boundary pinning effect, and to provide a grain boundary optimization method for additive manufacturing superalloys based on cryogenic-current synergistic regulation.

[0005] This invention proposes a composite process based on "deep cryogenic treatment-current rapid annealing" (DCT-EPT). This method introduces uniform internal stress energy storage through non-destructive deep cryogenic treatment, and reduces the recrystallization energy barrier by combining pulsed current annealing. While maintaining the near-net-shape advantages of additive manufacturing, it achieves a high proportion of low ΣCSL grain boundary construction (target proportion >50%), thereby significantly improving the material's resistance to grain boundary failure and high-temperature service performance.

[0006] This invention proposes a novel method for optimizing the grain boundary characteristic distribution of additive manufacturing GH4099 nickel-based superalloy using a composite process of "deep cryogenic treatment-electropulsing treatment (EPT)". The method aims to: (1) introduce uniform, high-density internal stress (stored energy) into the AM alloy in a non-deformable manner through deep cryogenic treatment (DCT), providing sufficient driving force for recrystallization; and (2) combine this with electropulsing treatment (EPT) to significantly reduce the recrystallization activation energy and initiation temperature of the alloy using its electro-induced effect. Through the synergistic effect of both methods, while optimizing the grain boundary characteristic distribution (GBCD) (increasing the proportion of low ΣCSL grain boundaries), grain coarsening is effectively suppressed, resulting in a uniform and fine recrystallized structure.

[0007] A method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation is specifically accomplished through the following steps:

[0008] I. Powder Pretreatment:

[0009] The nickel-based superalloy powder was vacuum dried to obtain pretreated nickel-based superalloy powder.

[0010] II. Laser Additive Manufacturing:

[0011] Laser additive manufacturing process is used to print pretreated nickel-based superalloy powder into shaped parts layer by layer according to preset three-dimensional model data;

[0012] III. Cryogenic Treatment:

[0013] The formed part is cryogenically treated at -196℃ to -100℃ for a period of time, and then cooled to room temperature to obtain the cryogenically treated formed part;

[0014] IV. Pulse Current Annealing:

[0015] After cryogenic treatment, the molded part is annealed with pulsed current for a period of time and then cooled to room temperature to obtain a molded part with optimized grain boundaries.

[0016] The principle and beneficial effects of this invention are as follows:

[0017] I. Principle of this invention: DCT introduces uniform stored energy (increasing KAM value by 15-20%) under deformation-free conditions through deep cooling with liquid nitrogen. EPT utilizes the electron wind effect to reduce the atomic diffusion activation energy by 45±5%, lowering the recrystallization temperature window to 950-1100℃ (150-200℃ lower than conventional processes). Together, these two technologies overcome substructure segregation pinning and promote Σ3 twin boundary proliferation.

[0018] II. Beneficial effects of the present invention: ① Zero geometric deformation throughout the process, suitable for complex components with topology optimization; ② Significant GBCD optimization, with a low ΣCSL grain boundary ratio of 65-75% (Σ3 grain boundaries 55-65%); ③ Grain refinement to below 20μm, with no abnormal grain growth; ④ Simple operation, no oxidation pollution, and low cost. Attached Figure Description

[0019] Figure 1 This invention presents an optimized process route for the distribution of grain boundary features in additive manufacturing of high-temperature alloys.

[0020] Figure 2 This is a diagram showing the average orientation difference of the crystal nuclei. Figure 2 (a) is the molded part printed in step two of Example 1, and (b) is the molded part after cryogenic treatment obtained in step three of Example 1.

[0021] Figure 3 This is a grain boundary feature distribution diagram of the formed part obtained in step two of Example 1;

[0022] Figure 4 This is a grain boundary feature distribution diagram of the shaped part after grain boundary optimization obtained in step four of Example 1;

[0023] Figure 5 This is a grain boundary feature distribution diagram of the shaped part after grain boundary optimization obtained in step four of Example 2;

[0024] Figure 6 This is a grain boundary feature distribution diagram of the shaped part after grain boundary optimization obtained in step four of Example 3;

[0025] Figure 7 This is a grain boundary feature distribution diagram of the nickel-based superalloy obtained after conventional heat treatment in step three of Comparative Example 1. Detailed Implementation

[0026] Specific Implementation Method 1: This implementation method is a grain boundary optimization method for additive manufacturing of high-temperature alloys based on cryogenic-current synergistic regulation, which is specifically completed according to the following steps:

[0027] I. Powder Pretreatment:

[0028] The nickel-based superalloy powder was vacuum dried to obtain pretreated nickel-based superalloy powder.

[0029] II. Laser Additive Manufacturing:

[0030] Laser additive manufacturing process is used to print pretreated nickel-based superalloy powder into shaped parts layer by layer according to preset three-dimensional model data;

[0031] III. Cryogenic Treatment:

[0032] The formed part is cryogenically treated at -196℃ to -100℃ for a period of time, and then cooled to room temperature to obtain the cryogenically treated formed part;

[0033] IV. Pulse Current Annealing:

[0034] After cryogenic treatment, the molded part is annealed with pulsed current for a period of time and then cooled to room temperature to obtain a molded part with optimized grain boundaries.

[0035] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the nickel-based high-temperature alloy powder mentioned in step one is GH4099 alloy, GH4169 alloy, or GH3536 alloy. The other steps are the same as in Specific Implementation Method One.

[0036] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the vacuum drying temperature in step one is 120℃~150℃, and the vacuum drying time is 2h~5h. Other steps are the same as in Specific Implementation Method One or Two.

[0037] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the oxygen content of the pretreated nickel-based superalloy powder described in Step One is ≤0.03wt%, and the moisture content is ≤0.02wt%. The other steps are the same as in Specific Implementation Methods One to Three.

[0038] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the parameters of the laser additive manufacturing process described in step two are: laser power 250W~350W, scanning speed 1000mm / s~1200mm / s, scanning spacing 0.07mm~0.11mm, and layer thickness 0.03mm~0.05mm. The other steps are the same as in Specific Implementation Methods One to Four.

[0039] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the cryogenic treatment time described in step three is 5 to 60 hours. The other steps are the same as in Specific Implementation Methods One to Five.

[0040] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that the cryogenic treatment described in step three is performed in a liquid nitrogen environment; and the cooling method described in step three is water cooling. The other steps are the same as in Specific Implementation Methods One through Six.

[0041] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the process parameters for pulse current annealing in step four are: frequency 80Hz~120Hz, duty cycle 45%~55%, and current density 120A / mm². 2 ~130A / mm 2 Processing time is 3 to 10 minutes. Other steps are the same as in specific implementation methods one to seven.

[0042] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the cooling method described in step four is water cooling, with a cooling rate ≥ 50℃ / s; the pulse current annealing described in step four uses square wave or sawtooth wave pulses with a duty cycle of 45%~55%. Other steps are the same as in Specific Implementation Methods One to Eight.

[0043] Specific Implementation Method 10: The difference between this implementation method and Specific Implementation Methods 1 to 9 is that the proportion of Σ3 grain boundaries in the grain boundary optimized forming part obtained in step 4 is ≥45%; and the proportion of low ΣCSL grain boundaries is ≥50%. The other steps are the same as those in Specific Implementation Methods 1 to 9.

[0044] The beneficial effects of the present invention are verified using the following embodiments:

[0045] Example 1: A method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation, specifically completed according to the following steps:

[0046] I. Powder Pretreatment:

[0047] The nickel-based superalloy powder was vacuum dried to obtain pretreated nickel-based superalloy powder.

[0048] The nickel-based superalloy powder mentioned in step one is GH4099 alloy;

[0049] The vacuum drying temperature described in step one is 120℃, and the vacuum drying time is 2 hours;

[0050] The oxygen content and moisture content of the pretreated nickel-based superalloy powder described in step one are ≤0.03wt% and ≤0.02wt%, respectively.

[0051] II. Laser Additive Manufacturing:

[0052] Laser additive manufacturing process is used to print pretreated nickel-based superalloy powder into shaped parts layer by layer according to preset three-dimensional model data;

[0053] The parameters of the laser additive manufacturing process described in step two are: laser power 300W, scanning speed 1100mm / s, scanning spacing 0.09mm, and layer thickness 0.04mm.

[0054] III. Cryogenic Treatment:

[0055] The molded part is placed in a cryogenic treatment equipment (liquid nitrogen cryogenic chamber) for cryogenic treatment at -196℃ for 12 hours, and then taken out and cooled to room temperature with water to obtain the cryogenically treated molded part.

[0056] IV. Pulse Current Annealing:

[0057] After cryogenic treatment, the formed part is annealed with pulsed current for a period of time, and then cooled to room temperature to obtain a formed part with optimized grain boundaries.

[0058] The process parameters for pulsed current annealing described in step four are: frequency 100Hz, duty cycle 50%, and current density 120A / mm². 2 (Heating temperature is approximately 950℃), processing time is 5 minutes;

[0059] The cooling method described in step four is water cooling, and the cooling rate is 100℃ / s;

[0060] The pulsed current annealing described in step four uses a square wave pulse with a duty cycle of 50%.

[0061] Figure 2 This is a diagram showing the average orientation difference of the crystal nuclei. Figure 2 (a) is the molded part printed in step two of Example 1, and (b) is the molded part after cryogenic treatment obtained in step three of Example 1.

[0062] Figure 2 It can reflect the local stress distribution of the material and is directly proportional to the geometrically required dislocation density. As can be seen from the figure, the average orientation difference (KAM) of the crystal nuclei increased from 1.21° to 1.39° after 12 hours of cryogenic treatment. At the same time, the stress distribution inside the alloy is more uniform, indicating that the dislocation density of the alloy increases after cryogenic treatment and the local stress distribution is more uniform.

[0063] Figure 3 This is a grain boundary feature distribution diagram of the formed part obtained in step two of Example 1;

[0064] Figure 4 This is a grain boundary feature distribution diagram of the shaped part after grain boundary optimization obtained in step four of Example 1;

[0065] from Figure 3 and Figure 4 As can be seen, the proportion of Σ3 grain boundaries in the original additive-manufactured GH4099 alloy is only 2.13%, while the proportion of Σ3 grain boundaries in the treated alloy rapidly increases to 45.80%, and the proportion of low Σ-CSL grain boundaries is 52.76%, showing a significant GBCD optimization effect.

[0066] Example 2: A method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation, specifically completed according to the following steps:

[0067] I. Powder Pretreatment:

[0068] The nickel-based superalloy powder was vacuum dried to obtain pretreated nickel-based superalloy powder.

[0069] The nickel-based superalloy powder mentioned in step one is GH4099 alloy;

[0070] The vacuum drying temperature described in step one is 120℃, and the vacuum drying time is 2 hours;

[0071] The oxygen content and moisture content of the pretreated nickel-based superalloy powder described in step one are ≤0.03wt% and ≤0.02wt%, respectively.

[0072] II. Laser Additive Manufacturing:

[0073] Laser additive manufacturing process is used to print pretreated nickel-based superalloy powder into shaped parts layer by layer according to preset three-dimensional model data;

[0074] The parameters of the laser additive manufacturing process described in step two are: laser power 300W, scanning speed 1100mm / s, scanning spacing 0.09mm, and layer thickness 0.04mm.

[0075] III. Cryogenic Treatment:

[0076] The molded part is placed in a cryogenic treatment equipment (liquid nitrogen cryogenic chamber) for cryogenic treatment at -196℃ for 12 hours, and then taken out and cooled to room temperature with water to obtain the cryogenically treated molded part.

[0077] IV. Pulse Current Annealing:

[0078] After cryogenic treatment, the formed part is annealed with pulsed current for a period of time, and then cooled to room temperature to obtain a formed part with optimized grain boundaries.

[0079] The process parameters for pulsed current annealing described in step four are: frequency 100Hz, duty cycle 50%, and current density 125A / mm². 2 (Heating temperature is approximately 1000℃), processing time is 5 minutes;

[0080] The cooling method described in step four is water cooling, and the cooling rate is 100℃ / s;

[0081] The pulsed current annealing described in step four uses a square wave pulse with a duty cycle of 50%.

[0082] Figure 5 This is a grain boundary feature distribution diagram of the shaped part after grain boundary optimization obtained in step four of Example 2;

[0083] from Figure 5 It can be seen that the proportion of Σ3 grain boundaries in the shaped part after grain boundary optimization obtained in step four of Example 2 is increased to 58.9%, and the proportion of low Σ-CSL grain boundaries is increased to 66.82%, further improving its GBCD optimization effect.

[0084] Example 3: A method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation, specifically completed according to the following steps:

[0085] I. Powder Pretreatment:

[0086] The nickel-based superalloy powder was vacuum dried to obtain pretreated nickel-based superalloy powder.

[0087] The nickel-based superalloy powder mentioned in step one is GH4099 alloy;

[0088] The vacuum drying temperature described in step one is 120℃, and the vacuum drying time is 2 hours;

[0089] The oxygen content and moisture content of the pretreated nickel-based superalloy powder described in step one are ≤0.03wt% and ≤0.02wt%, respectively.

[0090] II. Laser Additive Manufacturing:

[0091] Laser additive manufacturing process is used to print pretreated nickel-based superalloy powder into shaped parts layer by layer according to preset three-dimensional model data;

[0092] The parameters of the laser additive manufacturing process described in step two are: laser power 300W, scanning speed 1100mm / s, scanning spacing 0.09mm, and layer thickness 0.04mm.

[0093] III. Cryogenic Treatment:

[0094] The molded part is placed in a cryogenic treatment equipment (liquid nitrogen cryogenic chamber) for cryogenic treatment at -196℃ for 12 hours, and then taken out and cooled to room temperature with water to obtain the cryogenically treated molded part.

[0095] IV. Pulse Current Annealing:

[0096] After cryogenic treatment, the formed part is annealed with pulsed current for a period of time, and then cooled to room temperature to obtain a formed part with optimized grain boundaries.

[0097] The process parameters for pulsed current annealing described in step four are: frequency 100Hz, duty cycle 50%, and current density 130A / mm². 2 (Heating temperature is approximately 1080℃), processing time is 5 minutes;

[0098] The cooling method described in step four is water cooling, and the cooling rate is 100℃ / s;

[0099] The pulsed current annealing described in step four uses a square wave pulse with a duty cycle of 50%.

[0100] Figure 6 This is a grain boundary feature distribution diagram of the shaped part after grain boundary optimization obtained in step four of Example 3;

[0101] from Figure 6 It can be seen that the proportion of Σ3 grain boundaries in the shaped part after grain boundary optimization obtained in step four of Example 3 is further increased to 65.3%, and the proportion of low Σ-CSL grain boundaries is as high as 75.28%, which shows that the GBCD optimization effect is obvious.

[0102] Comparative Example 1: A method for grain boundary optimization of additive manufacturing high-temperature alloys based on conventional heat treatment, characterized in that the method is specifically carried out according to the following steps:

[0103] I. Powder Pretreatment:

[0104] The nickel-based superalloy powder was vacuum dried to obtain pretreated nickel-based superalloy powder.

[0105] The nickel-based superalloy powder mentioned in step one is GH4099 alloy;

[0106] The vacuum drying temperature described in step one is 120℃, and the vacuum drying time is 2 hours;

[0107] The oxygen content and moisture content of the pretreated nickel-based superalloy powder described in step one are ≤0.03wt% and ≤0.02wt%, respectively.

[0108] II. Laser Additive Manufacturing:

[0109] Laser additive manufacturing process is used to print pretreated nickel-based superalloy powder into shaped parts layer by layer according to preset three-dimensional model data;

[0110] The parameters of the laser additive manufacturing process described in step two are: laser power 300W, scanning speed 1100mm / s, scanning spacing 0.09mm, and layer thickness 0.04mm.

[0111] III. Conventional heat treatment:

[0112] The formed part was subjected to conventional heat treatment at a temperature of 1100℃ for 60 minutes to obtain a nickel-based superalloy after conventional heat treatment.

[0113] Figure 7 This is a grain boundary feature distribution diagram of the nickel-based superalloy obtained after conventional heat treatment in step three of Comparative Example 1.

[0114] from Figure 7 It can be seen that the Σ3 grain boundaries of the nickel-based superalloy obtained after conventional heat treatment in Step 3 of Comparative Example 1 are only 10.9%, while the proportion of low Σ-CSL grain boundaries is as high as 12.93%. Therefore, conventional heat treatment cannot effectively improve the low Σ-CSL grain boundaries in the laser additive manufacturing GH4099 alloy, making it difficult to achieve GBCD in the additive manufacturing alloy.

[0115] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for grain boundary optimization of additively manufactured high temperature alloys based on cryogenic-current synergistic regulation, characterized by This method is specifically completed in the following steps: I. Powder Pretreatment: The nickel-based superalloy powder was vacuum dried to obtain pretreated nickel-based superalloy powder. The nickel-based superalloy powder mentioned in step one is GH4099 alloy, GH4169 alloy or GH3536 alloy; The vacuum drying temperature in step one is 120℃~150℃, and the vacuum drying time is 2h~5h; The oxygen content and moisture content of the pretreated nickel-based superalloy powder described in step one are ≤0.03wt% and ≤0.02wt%, respectively. II. Laser Additive Manufacturing: Laser additive manufacturing process is used to print pretreated nickel-based superalloy powder into shaped parts layer by layer according to preset three-dimensional model data; III. Cryogenic Treatment: The formed part is cryogenically treated at -196℃ to -100℃ for a period of time, and then warmed back to room temperature to obtain the cryogenically treated formed part. IV. Pulse Current Annealing: After cryogenic treatment, the molded part is annealed with pulsed current for a period of time and then cooled to room temperature to obtain a molded part with optimized grain boundaries.

2. The method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation according to claim 1, characterized in that... The parameters of the laser additive manufacturing process described in step two are: laser power 250W~350W, scanning speed 1000mm / s~1200mm / s, scanning spacing 0.07mm~0.11mm, and layer thickness 0.03mm~0.05mm.

3. The method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation according to claim 1, characterized in that... The cryogenic treatment described in step three takes 5 to 60 hours.

4. The method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation according to claim 1, characterized in that... The cryogenic treatment described in step three is carried out in a liquid nitrogen environment; the warming method described in step three is water cooling.

5. The method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation according to claim 1, characterized in that... The process parameters of the pulse current annealing in step four are: frequency 80 Hz~120 Hz, duty cycle 45%~55%, current density 120 A / mm 2 ~130 A / mm 2 , processing time 3 min~10 min.

6. The method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation according to claim 1, characterized in that... The cooling method described in step four is water cooling, with a cooling rate ≥ 50℃ / s; the pulse current annealing described in step four uses square wave or sawtooth wave pulses with a duty cycle of 45%~55%.

7. The method for grain boundary optimization of additive manufacturing high-temperature alloys based on cryogenic-current synergistic regulation according to claim 1, characterized in that... The proportion of Σ3 grain boundaries in the grain boundary optimized part obtained in step four is ≥45%; the proportion of low ΣCSL grain boundaries is ≥50%.

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