Cryogenic-current collaborative regulation-based grain boundary optimization method for additive manufacturing high-temperature alloy

Abstract

The invention discloses a grain boundary optimization method of an additive manufacturing high-temperature alloy based on cryogenic-current cooperative regulation and control, and relates to the technical field of metal additive manufacturing post-treatment. The invention aims to solve the problem that the grain boundary characteristic distribution is difficult to optimize due to insufficient recrystallization driving force and grain boundary pinning effect of the GH4099 nickel-based superalloy manufactured by using the existing method. The method comprises the following steps: 1, powder pretreatment; 2, laser additive manufacturing; 3, subzero treatment; and 4, pulse current annealing. According to the composite technology based on'cryogenic treatment-current rapid annealing ', uniform internal stress energy storage is introduced through non-destructive cryogenic treatment, recrystallization energy barriers are reduced in combination with pulse current annealing, and on the premise that the advantages of additive manufacturing near-net forming are kept, high-proportion low-sigma CSL grain boundary construction (the target proportion gt; therefore, the grain boundary failure resistance and the high-temperature service performance of the material are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal additive manufacturing post-processing, in particular to a grain boundary optimization method for additive manufacturing of high-temperature alloy based on deep cooling-current synergistic regulation. BACKGROUND

[0002] GH4099 nickel-based superalloy is widely used in hot end components such as aero-engine combustion chamber components and turbine guide vanes due to its excellent high-temperature mechanical properties, creep resistance and corrosion resistance. The solid solution aging state of the alloy can serve for a long time at 900°C, and the instantaneous temperature resistance capacity can reach 1000°C. However, under the coupling effect of high temperature corrosion and complex stress, the grain boundary becomes a failure sensitive area, and more than 80% of high-temperature failures are caused by early cracking induced by grain boundary oxidation.

[0003] Studies have shown that low Σ Coin site lattice (CSL, Σ≤29) grain boundaries have 3-5 times higher corrosion resistance than ordinary high-angle grain boundaries due to their low interfacial energy (<0.5 J / m²) and high structural order. Optimizing grain boundary characteristic distribution (GBCD) to increase the proportion of low Σ CSL grain boundaries (target >60%) has become a key way to enhance the service reliability of high-temperature alloys. Traditional GBCD optimization relies on deformation heat treatment (such as rolling + annealing), which requires the introduction of stored energy through ≥30% plastic deformation. However, this method causes geometric deformation, which seriously conflicts with the near-net shaping characteristics of additive manufacturing (AM). AM preparation of GH4099 alloy faces double bottlenecks: 1) insufficient recrystallization driving force: the inherent rapid solidification characteristics of the AM process result in low and uneven initial stored energy levels (affected by repeated thermal cycling, interlayer residence and residual stress), making it difficult to drive complete recrystallization during subsequent heat treatment and hindering the formation of ideal GBCD; 2) grain boundary migration is blocked: the pinning effect of subgrain boundary segregation elements (Cr, Mo) increases the activation energy of grain boundary migration by 40% (up to 280 kJ / mol), which usually requires higher annealing temperature or longer holding time, but this easily induces inhomogeneous recrystallization and grain coarsening. Therefore, it is urgent to develop a new GBCD regulation method that is geometrically compatible (non-deformation), low temperature and short time, and can effectively drive recrystallization, to solve the GBCD optimization problem of additive manufacturing GH4099 alloy caused by insufficient / uneven stored energy and difficulty in controlling recrystallization. SUMMARY

[0004] The purpose of the present application is to solve the problem of optimizing the grain boundary characteristic distribution of GH4099 nickel-based high-temperature alloy prepared by additive manufacturing using existing methods due to insufficient recrystallization driving force and grain boundary pinning effect, and to provide a grain boundary optimization method for additive manufacturing of high-temperature alloy based on deep cooling-current synergistic regulation.

[0005] The application provides a composite process based on "deep cryogenic treatment-electric current rapid annealing" (DCT-EPT), which introduces uniform internal stress energy by non-destructive deep cryogenic treatment, and reduces the recrystallization energy barrier by combining pulse current annealing, realizes high proportion of low Sigma CSL grain boundary construction (target proportion > 50%) under the premise of maintaining the advantages of additive manufacturing near net shape, and significantly improves the material anti-grain boundary failure ability and high temperature service performance.

[0006] The application provides a new method for optimizing the grain boundary characteristic distribution of GH4099 nickel-based superalloy by using a "deep cryogenic treatment-electric current rapid annealing" composite process. The method aims to: (1) introduce uniform and high-density internal stress (stored energy) in the AM alloy by deep cryogenic treatment (DCT) in a non-deformation manner, providing sufficient driving force for recrystallization; (2) combined with electropulsing treatment (EPT), the recrystallization activation energy and the starting temperature of the alloy are significantly reduced by using its electro-effect. Through the synergistic effect of the two, the grain boundary characteristic distribution (GBCD) is optimized (the proportion of low Sigma CSL grain boundaries is improved), and the grain coarsening is effectively inhibited, and a uniform and fine recrystallized structure is obtained.

[0007] A grain boundary optimization method for additive manufacturing of high-temperature alloy based on deep cryogenic-electricity synergistic regulation, specifically completed by the following steps:

[0008] I. Powder pretreatment:

[0009] The nickel-based superalloy powder is vacuum dried to obtain pretreated nickel-based superalloy powder;

[0010] II. Laser additive manufacturing:

[0011] The pretreated nickel-based superalloy powder is printed into a shaped part layer by layer according to the preset three-dimensional model data by using the laser additive manufacturing process;

[0012] III. Deep cryogenic treatment:

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

[0014] IV. Pulse current annealing:

[0015] The deep cryogenically treated shaped part is subjected to pulse current annealing for a period of time, and then cooled to room temperature to obtain a grain boundary optimized shaped part.

[0016] The principles and beneficial effects of the application are:

[0017] Principle of the Invention: DCT uses liquid nitrogen cryogenic cooling to introduce uniform storage energy (KAM) without deformation (increasing the KAM value by 15-20%). EPT utilizes the electron wind effect to reduce the atomic diffusion activation energy by 45±5%, lowering the recrystallization temperature window to 950-1100°C (150-200°C lower than conventional processes). These two processes work together to overcome substructural segregation pinning and promote the proliferation of Σ3 twin boundaries.

[0018] 2. Beneficial effects of the present invention: ① Zero geometric deformation throughout the entire process, suitable for topological optimization of complex components; ② Significant GBCD optimization, with the proportion of low ΣCSL grain boundaries reaching 65-75% (Σ3 grain boundaries 55-65%); ③ Grains are refined to below 20μm without abnormal grain growth; ④ Simple operation, no oxidation pollution, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The optimized process route for the grain boundary characteristic distribution of high-temperature alloys in additive manufacturing proposed by the present invention;

[0020] Figure 2 is the average orientation difference diagram of the crystal core, Figure 2 (a) is the molded part printed in step 2 of Example 1, and (b) is the molded part after cryogenic treatment obtained in step 3 of Example 1;

[0021] Figure 3 This is the grain boundary characteristic distribution diagram of the formed part obtained in step 2 of Example 1;

[0022] Figure 4 This is the grain boundary characteristic distribution diagram of the formed part after grain boundary optimization obtained in step 4 of Example 1;

[0023] Figure 5 This is the grain boundary characteristic distribution diagram of the formed part after grain boundary optimization obtained in step 4 of Example 2;

[0024] Figure 6 This is the grain boundary characteristic distribution diagram of the formed part after grain boundary optimization obtained in step 4 of Example 3;

[0025] Figure 7 This is the grain boundary characteristic distribution diagram of the nickel-based high-temperature alloy after conventional heat treatment obtained in step 3 of comparative example 1. DETAILED DESCRIPTION

[0026] Specific embodiment 1: This embodiment is a method for optimizing grain boundaries of high-temperature alloys in additive manufacturing based on cryogenic-current coordinated control, which is specifically completed in the following steps:

[0027] 1. Powder pretreatment:

[0028] vacuum drying the nickel-based high-temperature alloy powder to obtain pretreated nickel-based high-temperature alloy powder;

[0029] II. Laser additive manufacturing:

[0030] The pretreated nickel-based superalloy powder is printed into a shaped part according to a preset three-dimensional model data layer by layer by using a laser additive manufacturing process;

[0031] III. Cryogenic treatment:

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

[0033] IV. Pulse current annealing:

[0034] The cryogenically treated shaped part is subjected to pulse current annealing for a period of time, and then cooled to room temperature to obtain a grain boundary optimized shaped part.

[0035] Specific embodiment two: The difference between this embodiment and specific embodiment one is that the nickel-based superalloy powder in step one is GH4099 alloy, GH4169 alloy or GH3536 alloy. The other steps are the same as specific embodiment one.

[0036] Specific embodiment three: The difference between this embodiment and one of specific embodiments one or two is that the temperature of vacuum drying in step one is 120℃-150℃, and the time of vacuum drying is 2h-5h. The other steps are the same as specific embodiments one or two.

[0037] Specific embodiment four: The difference between this embodiment and one of specific embodiments one to three is that the oxygen content of the pretreated nickel-based superalloy powder in step one is ≤0.03wt%, and the moisture content is ≤0.02wt%. The other steps are the same as specific embodiments one to three.

[0038] Specific embodiment five: The difference between this embodiment and one of specific embodiments one to four is that the parameters of the laser additive manufacturing process in step two are: laser power 250W-350W, scanning speed 1000mm / s-1200mm / s, scanning interval 0.07mm-0.11mm, and layer thickness 0.03mm-0.05mm. The other steps are the same as specific embodiments one to four.

[0039] Specific embodiment six: The difference between this embodiment and one of specific embodiments one to five is that the time of cryogenic treatment in step three is 5h-60h. The other steps are the same as specific embodiments one to five.

[0040] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that the cryogenic treatment in step three is completed in a liquid nitrogen environment; the cooling method in step three is water cooling. The other steps are the same as specific embodiments one to six.

[0041] Specific embodiment eight: the difference between this embodiment and one of the specific embodiments one to seven is that the process parameters of the pulse current annealing in step four are: frequency 80Hz~120Hz, duty cycle 45%~55%, current density 120A / mm 2 ~130A / mm 2 , treatment time 3min~10min. The other steps are the same as specific embodiments one to seven.

[0042] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the cooling method in step four is water cooling, and the cooling rate is ≥50℃ / s; the pulse current annealing in step four adopts square wave or sawtooth wave pulse, and the duty cycle is 45%~55%. The other steps are the same as specific embodiments one to eight.

[0043] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that the proportion of Σ3 grain boundaries of the grain-optimized shaped part obtained in step four is ≥45%; the low-Σ CSL grain boundaries are ≥50%. The other steps are the same as specific embodiments one to nine.

[0044] The beneficial effects of the present application are verified by the following examples:

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

[0046] I. Powder pretreatment:

[0047] The nickel-based high-temperature alloy powder is vacuum dried to obtain pretreated nickel-based high-temperature alloy powder;

[0048] The nickel-based high-temperature alloy powder in step one is GH4099 alloy;

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

[0050] The oxygen content of the pretreated nickel-based high-temperature alloy powder in step one is ≤0.03wt%, and the water content is ≤0.02wt%;

[0051] II. Laser additive manufacturing:

[0052] The pretreated nickel-based superalloy powder is printed into a shaped part according to preset three-dimensional model data layer by layer by using a laser additive manufacturing process;

[0053] The parameter of the laser additive manufacturing process in step two is as follows: laser power 300 W, scanning speed 1100 mm / s, scanning interval 0.09 mm, and layer thickness 0.04 mm;

[0054] III. Deep cryogenic treatment:

[0055] The shaped part is placed into a deep cryogenic treatment device (a liquid nitrogen deep cryogenic tank) for deep cryogenic treatment, and is deep cryogenically treated at-196 ℃ for 12 h, and then is taken out and cooled to room temperature to obtain a deep cryogenically treated shaped part;

[0056] IV. Pulse current annealing:

[0057] The deep cryogenically treated shaped part is subjected to pulse current annealing for a period of time, and then is cooled to room temperature to obtain a grain boundary optimized shaped part;

[0058] The process parameter of the pulse current annealing in step four is as follows: frequency 100 Hz, duty cycle 50%, current density 120 A / mm 2 (heating temperature is about 950 ℃), and treatment time 5 min;

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

[0060] The pulse current annealing in step four adopts a square wave pulse, and the duty cycle is 50%.

[0061] Figure 2 is a grain boundary characteristic distribution diagram of the shaped part obtained in step two of Example 1, Figure 2 (a) is the shaped part printed in step two of Example 1, and (b) is the deep cryogenically treated shaped part obtained in step three of Example 1;

[0062] Figure 2 The KAM value of the grain boundary increases from 1.21° to 1.39° after 12 h of deep cryogenic treatment, and the stress value distribution in the alloy is more uniform, indicating that the dislocation density value of the deep cryogenically treated alloy increases, and the local stress distribution is more uniform.

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

[0064] Figure 4 is a grain boundary characteristic distribution diagram of the grain boundary optimized shaped part obtained in step four of Example 1;

[0065] FromFigure 3 and Figure 4 It can be seen that the proportion of Σ3 grain boundaries of the original additive manufacturing GH4099 alloy is only 2.13%, and the proportion of Σ3 grain boundaries of the treated alloy is rapidly increased to 45.80%, and the proportion of low-Σ-CSL grain boundaries is 52.76%, and the GBCD optimization effect is obvious.

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

[0067] I. Powder pretreatment:

[0068] The nickel-based high-temperature alloy powder is vacuum dried to obtain a pretreated nickel-based high-temperature alloy powder;

[0069] The nickel-based high-temperature alloy powder in step one is GH4099 alloy;

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

[0071] The oxygen content of the pretreated nickel-based high-temperature alloy powder in step one is ≤0.03wt%, and the moisture content is ≤0.02wt%;

[0072] II. Laser additive manufacturing:

[0073] The pretreated nickel-based high-temperature alloy powder is printed into a shaped part according to the preset three-dimensional model data layer by layer by using a laser additive manufacturing process;

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

[0075] III. Deep cooling treatment:

[0076] The shaped part is placed into a deep cooling treatment device (liquid nitrogen deep cooling tank) for deep cooling treatment, and is deep cooled at-196℃ for 12h, and then taken out and water cooled to room temperature to obtain a deep cooling treated shaped part;

[0077] IV. Pulse current annealing:

[0078] The deep cooling treated shaped part is subjected to pulse current annealing for a period of time, and then cooled to room temperature to obtain a grain boundary optimized shaped part;

[0079] The process parameters of the pulse current annealing in step four are: frequency 100Hz, duty cycle 50%, current density 125A / mm 2 (heating temperature is about 1000℃), and treatment time 5min;

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

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

[0082] Figure 5 The grain boundary characteristic distribution map of the grain boundary optimized forming part obtained in step four of Example 2;

[0083] From Figure 5 It can be seen that the proportion of Σ3 grain boundaries of the grain boundary optimized forming part 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%, and the GBCD optimization effect is further improved.

[0084] Example 3: A grain boundary optimization method for additive manufacturing of high-temperature alloy based on deep cooling-current synergistic regulation, which is completed according to the following steps:

[0085] I. Powder pretreatment:

[0086] The nickel-based high-temperature alloy powder is vacuum dried to obtain a pretreated nickel-based high-temperature alloy powder;

[0087] The nickel-based high-temperature alloy powder in step one is GH4099 alloy;

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

[0089] The oxygen content of the pretreated nickel-based high-temperature alloy powder in step one is ≤0.03wt%, and the water content is ≤0.02wt%;

[0090] II. Laser additive manufacturing:

[0091] The pretreated nickel-based high-temperature alloy powder is printed into a forming part layer by layer according to the preset three-dimensional model data by using a laser additive manufacturing process;

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

[0093] III. Deep cooling treatment:

[0094] The forming part is placed into a deep cooling treatment device (liquid nitrogen deep cooling tank) for deep cooling treatment, and is deep cooled at-196℃ for 12h, and then taken out and water cooled to room temperature to obtain a deep cooling treated forming part;

[0095] IV. Pulse current annealing:

[0096] Apply pulse current to the formed part after cryogenic treatment for a period of time, and then cool it to room temperature to obtain a formed part with optimized grain boundaries;

[0097] The process parameters of the pulse current annealing described in step 4 are: frequency 100 Hz, duty cycle 50%, current density 130 A / mm 2 (heating temperature is about 1080℃), processing time is 5min;

[0098] The cooling method described in step 4 is water cooling, and the cooling rate is 100°C / s;

[0099] The pulse current annealing described in step 4 uses square wave pulses with a duty cycle of 50%.

[0100] Figure 6 This is the grain boundary characteristic distribution diagram of the formed part after grain boundary optimization obtained in step 4 of Example 3;

[0101] from Figure 6 It can be seen that the proportion of Σ3 grain boundaries in the formed part after grain boundary optimization obtained in step 4 of Example 3 is further increased to 65.3%, and the proportion of low Σ-CSL grain boundaries is as high as 75.28%, and its GBCD optimization effect is obvious.

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

[0103] 1. Powder pretreatment:

[0104] vacuum drying the nickel-based high-temperature alloy powder to obtain pretreated nickel-based high-temperature alloy powder;

[0105] The nickel-based high-temperature alloy powder described in step 1 is GH4099 alloy;

[0106] The vacuum drying temperature in step 1 is 120° C. and the vacuum drying time is 2 h;

[0107] The oxygen content of the nickel-based high-temperature alloy powder after the pretreatment described in step 1 is ≤0.03wt%, and the moisture content is ≤0.02wt%;

[0108] 2. Laser Additive Manufacturing:

[0109] The laser additive manufacturing process is used to print the pre-treated nickel-based high-temperature alloy powder layer by layer into a formed part according to the preset three-dimensional model data;

[0110] The parameters of the laser additive manufacturing process described in step 2 are: laser power 300 W, scanning speed 1100 mm / s, scanning spacing 0.09 mm, and layer thickness 0.04 mm;

[0111] III. Conventional heat treatment:

[0112] The shaped part was subjected to conventional heat treatment, the temperature of the heat treatment was 1100℃, and the time was 60min, to obtain the nickel-based superalloy after conventional heat treatment.

[0113] Figure 7 The grain boundary characteristic distribution diagram of the nickel-based superalloy after conventional heat treatment obtained in step three of Comparative Example 1;

[0114] From Figure 7 It can be seen that the Σ3 grain boundary of the nickel-based superalloy after conventional heat treatment obtained in step three of Comparative Example 1 is only 10.9%, and the high-Σ CSL grain boundary accounts for as high as 12.93%. It can be seen that the conventional heat treatment cannot effectively improve the low-Σ CSL grain boundary in the laser additive manufacturing GH4099 alloy, and it is difficult to realize the GBCD of the additive manufacturing alloy.

[0115] Of course, the above description is not a limitation on the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the spirit and scope of the present application should also be within the protection scope of the present application.

Claims

1. A grain boundary optimization method for additive manufacturing of high-temperature alloys based on deep cooling and electric current coordinated control, characterized in that The method is specifically completed in the following steps:

1. Powder pretreatment: vacuum drying the nickel-based high-temperature alloy powder to obtain pretreated nickel-based high-temperature alloy powder; 2. Laser Additive Manufacturing: The laser additive manufacturing process is used to print the pre-treated nickel-based high-temperature alloy powder layer by layer into a formed part according to the preset three-dimensional model data; 3. Cryogenic treatment: The formed part is cryogenically treated at -196°C to -100°C for a period of time, and then cooled to room temperature to obtain a cryogenically treated formed part; 4. Pulse current annealing: The formed part after cryogenic treatment is subjected to pulse current annealing for a period of time, and then cooled to room temperature to obtain a formed part with optimized grain boundaries.

2. The grain boundary optimization method for additive manufacturing of high-temperature alloys based on deep cooling and electric current coordinated control according to claim 1 is characterized in that The nickel-based high-temperature alloy powder described in step 1 is GH4099 alloy, GH4169 alloy or GH3536 alloy.

3. The grain boundary optimization method for additive manufacturing of high-temperature alloys based on deep cooling and electric current coordinated control according to claim 1 is characterized in that The vacuum drying temperature in step 1 is 120° C. to 150° C., and the vacuum drying time is 2 h to 5 h.

4. The grain boundary optimization method for additive manufacturing of high-temperature alloys based on deep cooling and electric current coordinated control according to claim 1 is characterized in that The oxygen content of the nickel-based high-temperature alloy powder after the pretreatment described in step 1 is ≤0.03wt%, and the moisture content is ≤0.02wt%.

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

6. The grain boundary optimization method for additive manufacturing of high-temperature alloys based on deep cooling and electric current coordinated control according to claim 1, characterized in that The cryogenic treatment time in step 3 is 5 to 60 hours.

7. The grain boundary optimization method for additive manufacturing of high-temperature alloys based on deep cooling and electric current coordinated control according to claim 1, characterized in that The cryogenic treatment described in step 3 is completed in a liquid nitrogen environment; the cooling method described in step 3 is water cooling.

8. The grain boundary optimization method for additive manufacturing of high-temperature alloys based on deep cooling and electric current coordinated control according to claim 1, characterized in that The process parameters of the pulse current annealing described in step 4 are: frequency 80Hz~120Hz, duty cycle 45%~55%, current density 120A / mm 2 ~130A / mm 2 , processing time 3min~10min.

9. The grain boundary optimization method for additive manufacturing of high-temperature alloys based on deep cooling and electric current coordinated control according to claim 1, characterized in that The cooling method in step 4 is water cooling, and the cooling rate is ≥50°C / s; the pulse current annealing in step 4 adopts square wave or sawtooth wave pulse with a duty cycle of 45%~55%.

10. The grain boundary optimization method for additive manufacturing of high-temperature alloys based on deep cooling and electric current coordinated control according to claim 1, characterized in that The proportion of Σ3 grain boundaries of the formed part after grain boundary optimization obtained in step 4 is ≥45%; the proportion of low ΣCSL grain boundaries is ≥50%.

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